Winter, Spring, and Summer – All at the Same Time

The current weather pattern across the country is one that is fairly typical of Spring. However, the results of that pattern are wintry weather in the Rockies and summer-like weather in the East. In the battlezone between the two there is plenty of severe weather, which is fairly typical of Spring.

500mb analysis map from 8am EDT May 17, shows a ridge of hgh pressure in the East and a trough of low pressure in the West. Image provided by College of DuPage.
500mb analysis map from 8am EDT May 17, shows a ridge of hgh pressure in the East and a trough of low pressure in the West. Image provided by College of DuPage.

An upper-level low pressure area will move out of the Pacific Northwest and into the nation’s midsection over the next few days. While one surface low pressure area moves into the Upper Midwest today, a second one will develop east of the Rockies and move into the Plains states on Thursday. With cold air moving in behind the system, and warm, moist air flowing northward from the Gulf of Mexico ahead of it, strong to severe thunderstorms are likely again today, Thursday, and Friday across the Plains states.

Severe weather has plagued the nation’s midsection for the past few days, with over 500 reports of severe weather between Monday and Tuesday. Nearly 30 tornadoes were reported, along with hail as large as softballs, and hundreds of reports of wind damage from gusts as high as 85 mph.

GFS model snowfall forecast through Saturday morning for the Rockies. Image provided by WeatherBell.
GFS model snowfall forecast through Saturday morning for the Rockies. Image provided by WeatherBell.

Behind the low pressure area, a late-season snowstorm is expected across the Rocky Mountains. Heavy snow will continue across portions of Montana and Idaho today, spreading into Wyoming and Colorado for Thursday into Friday. Across the higher elevations, totals of 1-3 feet are expected, which will keep the ski season going for a while longer. Snow may also spread into the High Plains of eastern Colorado and western Nebraska, with some minor accumulations possible. In Denver, it looks a couple of slushy inches may fall, though at least 1 model is forecasting much heavier amounts. In a normal year, Denver averages 1.7″ of snow, and the city has seen measurable snow during the month of May in 11 out of the last 16 years, so snow in May is not uncommon, though a heavy snowstorm, if it materializes, would be. Denver has only received 10 or more inches of snow in the month of May 6 times in a 135 years of records, with a record total of 15.5″ set back in May of 1898.

Record high temperatures are expected to be broken across the Northeast on Thursday. Image provided by WeatherBell.
Record high temperatures are expected to be broken across the Northeast on Thursday. Image provided by WeatherBell.

Meanwhile, in the East, an early taste of summer is ongoing, thanks to a ridge of high pressure aloft, and a surface high pressure area off the East Coast. Temperatures soared into the 80s and lower 90s on Wednesday, setting several records, but the hottest day for many locations will be Thursday. High temperatures will climb into the lower to middle 90s in many locations, likely breaking records across much of the region. When you combine the heat with dewpoints well into the 60s, it will definitely feel like a mid-summer afternoon across the region. A cold front will move through the area of Friday, possibly triggering a few showers and thunderstorms, but also sending temperatures back to where they should be in the middle of May.

 

Severe Weather in the South Today, Bigger Outbreak Friday?

Severe weather is likely across portions of the Gulf Coast and Mississippi Valley today, but another, perhaps more widespread, outbreak is possible at the end of the week.

Surface analysis as of 7am CDT Wednesday April 26. Image provided by NOAA.
Surface analysis as of 7am CDT Wednesday April 26. Image provided by NOAA.

 

A strong cold front is moving into the Mississippi Valley and Texas this afternoon, and it is helping to trigger strong to severe thunderstorms across portions of the region. Ahead of the front, temperatures are into the 70s and lower 80s, with dewpoints in the upper 60s and 70s, so there’s plenty of warm, moist air in place. Behind the front, temperatures quickly drop into the 50s and 60s. Thunderstorms will continue to develop in the unstable airmass ahead of the front, with some of the storms containing large hail, heavy downpours, damaging winds, and possibly some tornadoes. Earlier this morning, some storms produced baseball-sized hail and wind gusts in excess of 70 mph in portions of Missouri, Arkansas, and Oklahoma. The threat should start to diminish across the region as we head into the overnight hours.

A more significant severe weather outbreak is possible later Friday into Saturday from the Southern Plains and Texas into portions of the Mississippi and Tennessee Valleys. Low pressure will move out of Texas and head northward, drawing warm moist air northward from the Gulf of Mexico once again. North and west of the system, much cooler air will be in place (more on that in a moment).

Models are showing that a very unstable airmass will be in place across Texas and the Lower Mississippi Valley Friday afternoon. Image provided by Pivotal Weather.
Models are showing that a very unstable airmass will be in place across Texas and the Lower Mississippi Valley Friday afternoon. Image provided by Pivotal Weather.
Models are showing that a very unstable airmass will be in place across Texas and the Lower Mississippi Valley Friday afternoon. Image provided by Pivotal Weather.
Models are showing that a very unstable airmass will be in place across Texas and the Lower Mississippi Valley Friday afternoon. Image provided by Pivotal Weather.

 

As low pressure rides along the boundary between the two airmasses, it will help to trigger strong to severe thunderstorms across the region. The threat will continue into the overnight hours Friday night, shifting into the Mississippi and Tennessee Valleys on Saturday as the system continues to progress northeastward. Some of the storms may produce torrential downpours that could trigger flash flooding, large hail, damaging winds, and tornadoes.

Portions of the Mississippi Valley could received 5-10 inches of rain between  Wednesday and Sunday. Image provided by WeatherBell.
Portions of the Mississippi Valley could received 5-10 inches of rain between Wednesday and Sunday. Image provided by WeatherBell.

 

Behind the storm, as colder air settles into the region, a different threat is evolving – heavy snow. While it’s getting late in the season, heavy snow is not uncommon in the Central and Southern Rockies at this time of year. Some of the higher elevations in Colorado and New Mexico could receive 1-2 feet of snow Friday into Saturday. East of the Continental Divide, especially in the High Plains, snow is also possible, especially from eastern Colorado and western Kansas into portions of the Oklahoma and Texas Panhandles. In Denver, there is still a big question as to whether to precipitation falls mainly as rain, snow, or a wintry mix. Some snow accumulation seems likely at this point, but it’s still a little too early to tell whether there will be heavy snow in the city itself.

GFS models forecast for snowfall through Sunday morning across the Plains and the Rockies. Image provided by WeatherBell.
GFS model forecast for snowfall through Sunday morning across the Plains and the Rockies. Image provided by WeatherBell.

 

Severe weather outbreaks are not uncommon at this time of year. In fact, from late March into early May is when they are most likely. The largest tornado outbreak on record occurred 6 years ago this week. Between April 25 and 28, 2011, a total of 362 tornadoes were observed from Texas to New York and portions of southern Canada, resulting in 324 fatalities, 317 of them on April 27, the most active day.

Map showing tracks of all 362 tornadoes from the April 2011 "Super Outbreak". Image provided by Encyclopedia Brittanica.
Map showing tracks of all 362 tornadoes from the April 2011 “Super Outbreak”. Image provided by Encyclopedia Brittanica.

From Record Highs to Blizzard Conditions

Much of the nation’s midsection has been enjoying temperatures more typical of April than February for the past week, with a few hundred record high temperatures broken. That is about to change, as Mother Nature will remind the region that is still February.

Numerous record highs are expected across the Plains and Midwest for one more day. Image provided by WeatherBell.
Numerous record highs are expected across the Plains and Midwest for one more day. Image provided by WeatherBell.

One more warm day is expected today, with highs well into the 60s and 70s likely setting more records. However, a cold front will sweep across the region, bringing an end to the record heat, and setting the stage for a snowstorm.

The low pressure system that brought more rain to California over the past couple of days will head eastward, bringing some snow into the Rockies today. As that system moves into the Plains on Thursday it will start to strengthen, drawing moisture northward from the Gulf of Mexico while cold air flows southward on the backside of the storm into the Northern Plains. Where these airmasses meet, snow will develop across the Central Plains states. The snow will be accompanied by winds of 20-30 mph, gusting to 40 mph or more at times, resulting in near-blizzard conditions across portions of South Dakota, Nebraska, southeastern Wyoming, and eastern Colorado on Thursday.

More than a foot of snow may fall in a swath from the Plains into the Upper Midwest. Image provided by Pivotal Weather.
More than a foot of snow may fall in a swath from the Plains into the Upper Midwest. Image provided by Pivotal Weather.

As the system heads eastward, snow will move into portions of the Mississippi Valley and the Upper Midwest on Friday. The heaviest snow looks to stay just south of the Twin Cities, but even there, moderate to heavy snow is likely. By the time the storm moves out on Saturday, a foot or more of snow is possible in a swath from the Central Plains into the Great Lakes.

Snow isn’t the only threat from this system. As the storm moves eastward, record warmth will remain in place across the Midwest. With warm, moist air in place and a strong cold front approaching from the West, strong to severe thunderstorms are possible across portions of the Lower Great Lakes and Ohio Valley on Friday. Some of the stronger storms that form may contain damaging winds, hail, and possibly tornadoes.

The Storm Prediction Center has already highlighted the Midwest as an area to watch for severe weather on Friday. Image provided by NOAA.
The Storm Prediction Center has already highlighted the Midwest as an area to watch for severe weather on Friday. Image provided by NOAA.

The system will continue to move eastward, bringing some rain to the East Coast on Saturday, but amounts should be fairly light, and additional severe weather is not anticipated.

Change is in the Air

As we head into the end of August, some familiar things start to happen. Children will start to head back to school. Baseball’s pennant races heat up while football at all levels gets ready for the start of the season. Halloween candy starts to appear in stores and it will be followed shortly by pumpkin-flavored everything. In terms of the weather, familiar things happen there too. The tropics start getting more active and the cold fronts dropping southward from Canada pack a little more punch than they usually do during the summer.

One of those cold fronts will be moving across the Plains states and into the Midwest over the next few days. Ahead of the front, summertime heat and humidity remains in place, with temperatures well into the 80s and 90s common. Behind the front is much cooler and drier air. By Friday morning, temperatures will be 10-20 degrees below normal across much of the Plains states and Rocky Mountains as a large area of high pressure builds in from Canada. Low temperatures will drop into the 40s and 50s across the Northern Plains, with 30s and even some upper 20s from the Rocky Mountains into interior portions of the Pacific Northwest.

Temperature anomaly map based on the GFS model for Thursday morning. Image provided by Pivotal Weather,
Temperature anomaly map based on the GFS model for Thursday morning. Image provided by Pivotal Weather.

As that cooler air settles into the region, some snow is possible across the higher elevations of the Northern and Central Rockies. Snow levels will remain fairly high, but a few inches of snow may accumulate on top of some of the higher peaks in Wyoming and Colorado.

Snowfall forecast based on the GFS model through Friday morning. Image provided by WeatherBell.
Snowfall forecast based on the GFS model through Friday morning. Image provided by WeatherBell.

Ahead of the front, a warm and humid airmass will remain in place, with high temperatures well into the 80s and 90s for the next few days. As the front approaches, it will trigger showers and thunderstorms. Some of the storms could be strong to severe, with hail and gusty winds possible, along with a few tornadoes. The biggest threat looks to be heavy rain and flash flooding. Because the front will be moving fairly slowly, some of the heavier storms will linger over the same areas. Rainfall totals of 1-3 inches will be common across parts of the Eastern Plains and Mississippi Valley, with some heavier amounts possible. This will likely lead to flooding in some areas.

Expected rainfall totals across the Midwest through Friday morning. Image provided by WeatherBell.
Expected rainfall totals across the Midwest through Friday morning. Image provided by WeatherBell.

Meanwhile, in the Atlantic, we’re keeping an eye on a disturbance east of the Lesser Antilles and Tropical Storm Gaston out in the Central Atlantic. There was a third system, Tropical Depression Fiona, but it fizzled southeast of Bermuda earlier today.

Satellite loop showing Tropical Storm Gaston (far right) and a disturbance approaching the Eastern Caribbean. Loop provided by NOAA.
Satellite photo showing Tropical Storm Gaston (far right) and a disturbance approaching the Eastern Caribbean. (Click for loop) Provided by NOAA.

Tropical Storm Gaston is centered about 700 miles west of the Cape Verde Islands this afternoon, heading towards the west-northwest at 21 mph. Maximum sustained winds are near 65 mph, and additional strengthening is expected. Gaston should become a hurricane by Wednesday afternoon. The forecast for Gaston is to turn more towards the northwest, heading out in the Central Atlantic Ocean before starting to weaken in a few days. Gaston will likely bot be a threat to any land areas.

Meanwhile, a disturbance located a few hundred miles east of the Lesser Antilles is being carefully monitored for signs of development. United States Air Force Reserve Hurricane Hunter aircraft investigated the system earlier today and found it to be a weak system with an ill-defined center. Conditions are still somewhat favorable for further development, and anyone with interests in the northeastern Caribbean should continue to monitor the progress of this system. The future of this system is still a big question mark. Most of the forecast models bring the system towards the Bahamas over the next several days, though a few have the system dissipate completely before then. Once it gets to the Bahamas, there is considerable spread among the models as to where it will go, assuming it even survives that long. Some have it turn northward and head towards the Carolinas or Georgia. Some bring it into Florida, then up into the Southeast, and others bring it across Florida and into the Gulf of Mexico. As for how strong it could be, that’s an even bigger question mark. As mentioned previously, some of the models have it dissipate completely. There are other models that keep the system as a tropical depression or weak tropical storm into the Bahamas. There are others that have it as strong as a Category 2 hurricane. Once the storm actually forms (assuming it actually does), the computer models should start to get a better handle on its future.

Computer model forecasts for the track of a disturbance approaching the Eastern Caribbean. Image provided by Tropical Tidbits.
Computer model forecasts for the track of a disturbance approaching the Eastern Caribbean. Image provided by Tropical Tidbits.
Computer model forecasts for the intensity of a disturbance approaching the Eastern Caribbean. Image provided by Tropical Tidbits.
Computer model forecasts for the intensity of a disturbance approaching the Eastern Caribbean. Image provided by Tropical Tidbits.

Widespread Severe Weather in the East Starting to Wind Down

Severe weather has been widespread across the eastern half of the nation for the past 2 days, but high pressure will bring much quieter conditions this weekend.

A cold front has been slowly dropping southward over the past 2 days, replacing warm and humid air with cooler and drier conditions. Ahead of the front, strong to severe thunderstorms have cut a large swath of damage.

Reports of severe weather from Thursday June 16. Image provided by the Storm Prediction Center.
Reports of severe weather from Thursday June 16. Image provided by the Storm Prediction Center.

 

On Thursday, severe weather was widespread across the Mid-Atlantic states from mid-afternoon through the late evening hours. There were over 250 reports of damage from wind gusts as high as 77 mph, with a majority of the reports concentrated in West Virginia, Virginia, and Maryland, including the Washington, DC metropolitan area, where thunderstorms dropped 2.58″ of rain in just a couple of hours at Dulles Airport. In addition to the wind damage and heavy rain, hail as large as baseballs was observed with some of the strong storms. One tornado was also confirmed in Barnes Gap, Pennsylvania.

While most of activity quieted down in the evening, thunderstorms flared up across North Dakota and Minnesota. A cluster of storms moved across the state early in the morning, producing baseball-sized hail near Bismarck. Wind gusts as high as 80 mph were also reported across the region.

Radar loop for the Southeast from Friday afternoon June 17. Loop provided by the College of DuPage.
Radar loop for the Southeast from Friday afternoon June 17. Loop provided by the College of DuPage.

 

By Friday afternoon, activity started to flare up again across the Southeast ahead of the cold front. A line of strong to severe thunderstorms quickly developed from Mississippi to South Carolina and began to march southward. Widespread wind damage was reported across the region as wind gusted as high as 70 mph in some of the stronger storms. These storms also produced torrential rainfall, with 2.32″ falling in one hour in Columbus, Mississippi.

Reports of severe weather from Friday June 17. Image provided by the Storm Prediction Center.
Reports of severe weather from Friday June 17. Image provided by the Storm Prediction Center.

 

Across the Plains states, under sunny skies temperatures soared well into the 90s and lower 100s on Friday.  Another cold front moving into the Western Plains provided the necessary lift to trigger thunderstorms across portions of Kansas and Nebraska. Once the activity got going, it quickly exploded into a large cluster of strong to severe thunderstorms. In McCook, Nebraska, the temperature reached 99 degrees during the afternoon with a dewpoint in the upper 60s to lower 70s. As a severe thunderstorm moved into the region, it produced a wind gust to 72 mph and dropped over 2 inches of rain on the area. It also sent temperatures tumbling into the middle 60s.

Radar loop for Kansas and Nebraska from Friday afternoon June 17. Loop provided by the College of DuPage.
Radar loop for Kansas and Nebraska from Friday afternoon June 17. Loop provided by the College of DuPage.

 

Much quieter conditions are expected over the weekend as a large area of high pressure builds into the eastern half of the nation. Sunshine and seasonably warm temperatures are expected for most of the region, with thunderstorm activity mostly confined to the Gulf Coast, near the dying frontal boundary that produced severe weather over the past few days, and the Northern Plains, where a strong cold front will slowly move through this weekend.

Heavy Rain in the Plains and Mississippi Valley Tuesday

 

After Sunday’s cold front ushers in cooler and drier air for Monday in the Northern Plains, a warm front will push north Tuesday. This warm front is attached to a low pressure system that will be moving northeast through the Rockies and into the Northern Plains. Areas in between the northward moving warm front and the southeastward moving cold front could see some strong to severe thunderstorms on Tuesday. This would mainly occur in the eastern Central Plains and portions of the Middle Mississippi Valley where convective energy, CAPE, and turning of the winds, shear, overlap to be able to support these storms.

Cooler and drier air (green colors) moving into the Northern Plains behind a cold front.
Cooler and drier air (green colors) moving into the Northern Plains behind a cold front. Courtesy of College of Dupage.
A warm front nestled between North and South Dakota.
A warm front nestled between North and South Dakota. Courtesy of College of DuPage.
Showalter Index showing possible instability in the Northern Plains, but higher values occur in the Eastern Central Plains and Middle Mississippi Valley.
Showalter Index showing possible instability with negative values in the Northern Plains, but even lower negative values occur in the Eastern Central Plains and Middle Mississippi Valley. Courtesy of AccuWeather.
Severe weather categorical outlook for Tuesday showing the highest probability of severe weather in the Central Plains and Middle Mississippi Valley.
Severe weather categorical outlook for Tuesday showing the highest probability of severe weather in the Central Plains and Middle Mississippi Valley. Courtesy of the Storm Prediction Center.

Farther north along the warm front in the Northern Plains, factors like limited sun exposure, saturated atmospheric columns and a lack of a shear/CAPE overlap may preclude strong to severe thunderstorms all together. There is some question as to how far north the warm front will be able to push into North Dakota so if it is able to push farther north and allow more sun, some strong to possibly severe thunderstorms may occur. At the very least, some thunderstorms may be embedded in what does appear to be a heavy rain event as a result of a vigorous upper level disturbance that appears to go negatively tilted in the upper levels of the atmosphere. This negative tilt allows for a strong draw of moisture into the system as a result of a strong low level jet stream. At the same time, very moist low levels and total column precipitable water values between 1.5 and 2 inches get wrapped around the northeastward moving low pressure system bringing the potential for a heavy rain event into the Northern Plains. Furthermore, large scale lift as a result of a collocated upper level jet stream will help to support the event. All told, 1 to 2.5 inches of precipitation in 24 hours from morning Tuesday to morning Wednesday seems reasonable for this event, but could be higher in any embedded thunderstorm.

The vigorous possibly negatively tilted energy moving into the Central and Northern Plains.
The vigorous possibly negatively tilted energy moving into the Central and Northern Plains. Courtesy of College of DuPage
Strong low level jet in the Northern Plains along with the Central Plains and Middle Mississippi Valley helping fuel heavy rain and strong to severe thunderstorms respectively.
Strong low level jet in the Northern Plains along with the Central Plains and Middle Mississippi Valley helping fuel heavy rain and strong to severe thunderstorms respectively. Courtesy of College of DuPage.
Forecast rainfall totaling 1 to 3 inches. Possibly higher in any thunderstorms from Tuesday morning to Wednesday morning.
Forecast rainfall totaling 1 to 2.5 inches. Possibly higher in any thunderstorms from Tuesday morning to Wednesday morning. Courtesy of the Weather Prediction Center of NWS.

 

It is also interesting to note that the ECMWF model contains around an inch less of precipitation than the GFS model, with the NAM model being closer to the mean of the two models despite the ECMWF model reaching the above parameters. With this in mind, it appears any flooding risk would be low, but could still occur if the higher end of the precipitation range is realized.

 

The low pressure system is forecast to move away from the Northern Plains allowing for drier air to come in for Wednesday and Thursday. However, clouds are forecast to return as another low pressure system ejects off the Rockies for Friday allowing for some more rain.

 

 

 

Severe Weather In the Northeast on Saturday?

For the second weekend in a row, there is a threat for severe weather across parts of the Northeast. Unlike last weekend, when the threat was centered on areas from the Delmarva Peninsula southward to the Carolinas, the threat on Saturday is focused on the Northeast.

Strong to severe thunderstorms moved across the Midwest Friday evening. Loop provided by College of DuPage NexLab.
Strong to severe thunderstorms moved across the Midwest Friday evening. Loop provided by College of DuPage NexLab.

Low pressure is moving across Lake Superior this evening, with a warm front extending east and southeast from the system across the eastern Great Lakes and into Virginia. A cold front trails the system into the Dakotas and Wyoming. South of these two fronts a very warm and humid airmass is in place, with temperatures well into the 80s and 90s on Friday. Dewpoints were in the 60s to lower 70s across much of the region as well. As the cold front moved into the Upper Midwest, it helped ignite a line of strong to severe thunderstorms. These storms produce golfball-sized hail and wind gusts as high as 76 mph as they cross Minnesota and Wisconsin Friday afternoon and evening.

Usually, strong to severe thunderstorms diminish during the evening hours as they lose the heating of the sun. However, with the warm and humid air in place across the Midwest, these storms will likely continue to march eastward overnight ahead of the cold front.

Radar loop predicted by the NAM model from Friday night into Sunday night. Loop provided by College of DuPage NexLab
Radar loop predicted by the NAM model from Friday night into Sunday night. Loop provided by College of DuPage NexLab

Forecast models indicate that this line of thunderstorms will move across portions of New York and Pennsylvania Saturday morning and afternoon before moving into portions of New England. How far north and east the warm front moves will help determine where the best chance for severe weather will be located.

High temperature forecast for Saturday afternoon based on the WRF model. Image provided by WeatherBell.
High temperature forecast for Saturday afternoon based on the NAM model. Image provided by WeatherBell.
Dewpoint forecast for Saturday afternoon based on the WRF model. Image provided by WeatherBell.
Dewpoint forecast for Saturday afternoon based on the NAM model. Image provided by WeatherBell.

Right now, it looks like the warm front will only make it into New York and southwestern New England before the cluster of showers and thunderstorms arrives. Some of the stronger storms could produce downpours, strong winds, and hail across portions of New York, Pennsylvania, and New Jersey.

Across New England, the threat for the afternoon seems less, with more typical showers and thunderstorms expected. However, this does not mean that the threat is zero. If the warm front were to make progress farther northward, the threat would increase. The bigger threat in this region could come at night. The warm front should eventually push through during the evening, allowing the warm and humid air to move into Southern New England. As the cold front continues it eastward march, another round of showers and thunderstorms will likely develop along and ahead of it. As these storms move across New England overnight, some of those storms could produce heavy downpours and strong winds.

Forecast for 500mb heights and winds based on the WRF model. Image provided by Pivotal Weather.
Forecast for 500mb heights and winds based on the NAM model. Image provided by Pivotal Weather.

After the cold front moves through Saturday night, skies should become partly to mostly sunny across the Northeast on Sunday with near-to-below normal temperatures expected. An upper-level low will slowly move across the Gulf of Maine early next week, keep temperatures near or below seasonal normals while heat and humidity dominate the remainder of the eastern two-thirds of the nation.

The Heat is On Across the Plains

A large ridge of high pressure will shift from the West coast into the Nation’s midsection over the next few days, bringing with it some of the hottest weather so far this year to the Plains states.

Temperature anomalies for the past 30 days across the nation. Image provided by WeatherBell.
Temperature anomalies for the past 30 days across the nation. Image provided by WeatherBell.

A persistent ridge of high pressure has been anchored across the West for the past few weeks, keeping temperatures well above normal for much of May and early June. Numerous records were set across the region, even in normally hot locations like the Desert Southwest, where temperatures exceeded 110 degrees several times. In Death Valley, California, which is frequently the nation’s hotspot, the first 8 days of June have averaged 10.6 degrees above normal, with high temperatures exceeding 115 degrees each day.

While the West has been baking, temperatures across the Plains states have been 1 to 3 degrees below normal for the past month. That is about to change as the ridge slides eastward. By the end of the week and the weekend, the ridge will be centered across the Plains and doesn’t look to move that much right through next week.

Map showing heights at the 500mb level across the United states on Friday June 8. Image provided by Pivotal Weather.
Map showing heights at the 500mb level across the United states on Sunday June 12. Image provided by Pivotal Weather.
Map showing heights at the 500mb level across the United states on Friday June 15. Image provided by Pivotal Weather.
Map showing heights at the 500mb level across the United states on Friday June 17. Image provided by Pivotal Weather.

With the ridge of high pressure in place, temperatures will soar well into the 90s across the Plains states and adjacent portions of the Mississippi Valley for much of the remainder of the week, with some triple-digit heat possible across parts of the Dakotas, especially Friday and Saturday.

High temperature forecast based off of the GFS model for Friday June 10. Image provided by WeatherBell
High temperature forecast based off of the GFS model for Saturday June 11. Image provided by WeatherBell

Some relief will settle into the Northern Plains in the form of a cold front early next week, but the heat will continue from the Southern Plains and Texas eastward into the Southeast. Across these areas, humidity levels will be higher, with dewpoints rising into the 60s and 70s. The result will be heat index values well over 100 degrees across parts of these areas.

The ridge will also act to suppress thunderstorm activity across the Plains states for much of the remainder of the week. Cluster of thunderstorms may develop across the Northern Rockies and ride over the Ridge and into the Great Lakes and eventually the Northeast later in the week. One of these clusters could produce some severe weather across the Eastern Great Lakes and Mid-Atlantic states on Saturday.

Severe Outbreak Possible in the East, Tropical Trouble in the Gulf?

The weather will become quite active across both the East and the Gulf later this weekend and into early next week.

A strong cold front will slowly make its way eastward this weekend, likely reaching the East Coast Sunday night. Ahead of the front, with a warm, humid airmass in place, showers and thunderstorms will develop, some of which will become strong to severe. Widespread severe weather isn’t expected on Saturday, but there is a risk for some strong to severe storms from the Great Lakes into the Ohio Valley.  Sunday will be a different story. The ingredients will be in place for a severe weather outbreak from the Mid-Atlantic states into the Carolinas.

GFS forecast of Lifted Index values for Sunday afternoon. Image provided by Pivotal Weather
GFS forecast of Lifted Index values for Sunday afternoon. Image provided by Pivotal Weather
GFS forecast of CAPE values for Sunday afternoon. Image provided by Pivotal Weather
GFS forecast of CAPE values for Sunday afternoon. Image provided by Pivotal Weather

As temperatures rise into the 80s to lower 90s, the airmass will become increasingly unstable. CAPE, which is short for Convective Available Potential Energy, is a measure of instability through the atmosphere. CAPE values of 1000-3000 J/kg are expected from the Delmarva Peninsula into the Carolinas Sunday afternoon. These values are indicative of moderate instability in the atmosphere. The “Lifted Index” is the difference in temperature between the atmosphere at 500mb (about 18,000 feet) and a parcel of air from the surface that is lifted to 500mb. A negative value is indicative of unstable conditions. On Sunday, forecast models are showing values between -4 and -9 across the Mid-Atlantic states.

While Sunday may start off cloudy with showers across parts of the region, breaks of sunshine should develop by early afternoon, with showers and thunderstorms developing along the eastern slopes of the Appalachians. Thunderstorm activity will likely organize into a line that will march eastward, reaching the Washington/Baltimore area by late afternoon, and the Richmond/Norfolk area towards evening. The main threats with any storms that do develop are strong winds, hail, and heavy downpours, with a few tornadoes also possible.

Meanwhile, Tropical Storm Bonnie has redeveloped east of North Carolina this evening. As of 5pm Friday, Bonnie was centered about 285 miles east of Cape Hatteras, NC, moving towards the east at 13 mph. Maximum sustained winds are near 40 mph. Bonnie is expected to head out into the open waters of the Atlantic over the weekend while steadily weakening.

Satellite loop of Tropical Storm Bonnie from Friday afternoon. Loop provided by NOAA.
Satellite loop of Tropical Storm Bonnie from Friday afternoon. Loop provided by NOAA.

 

While June is usually quiet in the tropics, another area of disturbed weather in the western Caribbean is being monitored for development this weekend. A cluster of showers and thunderstorms will head towards the Yucatan Peninsula this weekend and then turn more towards the north and head into the Gulf of Mexico. For several days now, forecast models have been indicating that this system could become a tropical depression or tropical storm over the Gulf early next week.

Computer model forecasts for the strength of a potential tropical system in the Gulf of Mexico. Image provided by Tropical Tidbits
Computer model forecasts for the strength of a potential tropical system in the Gulf of Mexico. Image provided by Tropical Tidbits
Computer model forecasts for the track of a potential tropical system in the Gulf of Mexico. Image provided by Tropical Tidbits
Computer model forecasts for the track of a potential tropical system in the Gulf of Mexico. Image provided by Tropical Tidbits

Most forecasts are for the storm to turn more toward the northeast early next week and cross the Florida Peninsula as a tropical depression or weak tropical storm. While winds aren’t expected to be strong, the main impact will be heavy rainfall. The storm could drop as much as 4-8 inches of rain on the Sunshine State next week, especially the southern half of the state. Heavy rain fell on portions of the region during May, so additional heavy rain could lead to flooding in parts of the area.

 

Severe Weather Outbreak Across the Southern Plains on Tuesday

While the attention has been on heavy rain and flooding across portions of southern and eastern Texas recently, areas to the north of there will be in the spotlight early next week.

Severe Weather Outlook for Tuesday from the Storm Prediction Center
Severe Weather Outlook for Tuesday from the Storm Prediction Center

All of the ingredients appear to be coming together for a severe weather outbreak from Kansas into northern Texas on Tuesday. Low pressure, both at the surface and aloft will move out of the Rockies and across the Central Plains on Tuesday. Ahead of the storm, warm, moist air will flow northward from the Gulf of Mexico into Texas and the Southern Plains. A cold front trailing the system will provide the lift needed to initiate thunderstorm development during the afternoon hours across the region.

Forecasted CAPE (Convectice Available Potential Energy) for Tuesday evening. Image courtest of WeatherBell.
Expected CAPE (Convective Available Potential Energy) for Tuesday evening. Image courtesy of WeatherBell.

As the storms move into south-central Kansas, central Oklahoma, and north-central Texas, they will encounter a very unstable airmass. The above map shows the forecast of Convective Available Potential Energy (CAPE) across the Southern Plains for Tuesday evening. CAPE is a measure of instability through the depth of the atmosphere, and is related to updraft strength in thunderstorms and is measured in Joules of energy per kilogram of air. A CAPE value of 1000 or less is considered “weak” instability, a value of 1000-2500 is “moderate” instability, a value of 2500-4000 is “strong” instability, and over 4000 is “extreme” instability. Areas shaded in purple on the map have values over 4000 Joules/kg, with some of the lighter purple shading in excess of 4500 Joules/kg. With this much instability in place, it won’t take much for storms to quickly become severe, with strong winds, large hail, torrential downpours, and tornadoes all possible.

Late April and early May are a time when severe outbreaks can be common across the Central and Southern Plains. If this outbreak does pan out, it will fall on the 25th anniversary of another outbreak across parts of the same area. On April 26, 1991, a total of 54 tornadoes were observed from Iowa and eastern Nebraska into portions of Missouri, Kansas, Oklahoma, and northeastern Texas, resulting in 21 deaths.

Plot of all 55 tornadoes that were reported on April 26, 1991 across the Central and Southern Plains. Image courtesy of the Storm Prediction Center
Plot of all 54 tornadoes that were reported on April 26, 1991 across the Central and Southern Plains. Image courtesy of the Storm Prediction Center

 

There was one F5 tornado reported that day – the one that moved across portions of Wichita, Kansas, including McConnell Air Force Base, before devastating the town of Andover, Kansas.

Residents of this region should pay attention to the forecast over the next few days and keep an eye to the sky if they have outdoor plans for Tuesday.

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