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Much Needed Rainfall For the Northeast

Winters in the Northeast can be often feel long and cold, leaving residents of the region longing for sunny, warm days in the Spring and Summer. This year, they got quite a lot of them, which didn’t draw too many complaints. However, because it was so sunny and warm, much of the region is now in the midst of a very serious drought.

Latest drought update that shows more than two-thirds of the Northeast experiencing some form of drought. Image provided by the National Drought Monitor

A persistent ridge of high pressure kept the Northeast dry and warm through much of the Spring and Summer. Most of the cold fronts that tried to move through the region were starved for moisture, thus their main effects were to cool temperatures and lower humidity for a day or two. Thunderstorm activity was common, but aside from localized downpours, there really hasn’t been a widespread heavy rain event across much of the region for several months. That could be changing this week.

A slow-moving cold front will move across the region on Tuesday, bringing showers with it. While the rain likely won’t be too heavy, it should be widespread, which is good news for an area that needs all the rain it can get. The front will likely stall out right along the coastal plain, which may keep the shower activity going into Wednesday right along the coast. However, changes in the weather pattern are coming that promise to bring even more rain to the area.

GFS forecast showing an upper-level low pressure area sitting over the Appalachians Friday morning. Image provided by Pivotal Weather.

An upper-level low pressure system will drop southward from the Great Lakes and take up residence across portions of the Ohio Valley and Appalachians. It will likely stay there for several days, before lifting out to the northeast this weekend. However, with the upper-level low pressure area just sitting there, low pressure will essentially remain in place at the surface as well across the same area. This will result in periods of rain and showers across much of the area right through the week. While the rain may be briefly heavy at times, persistent rainfall over several days can add up, with some areas possibly receiving 1-3 inches of rain between Tuesday and Friday, with some heavier amounts possible. Rainfall deficits in this area are on the order of 5-10 inches, so much more is needed, but this is definitely a good start.

GFS model forecast for rainfall through Saturday morning. Image provided by Pivotal Weather.

Of course, this beneficial rain may not impact the entire Northeast. For New England, the forecast is much trickier. With the low setting up well to the southwest of the area, high pressure will try to build in from the north. This will bring cool and dry conditions into much of northern New England this week. As for southern New England, where the effects of the drought are the most pronounced, the forecast depends entirely on where the low and high set themselves up. If the high is the dominant feature, much of southern New England can expect dry and cool conditions, with gusty east to northeasterly winds bringing some clouds and drizzle in off the Atlantic at times. If the low sets up a bit closer to the region, then the forecast will trend more towards a damp scenario with periods of showers for the next several days. At this point, it’s still a little too early to tell which scenario will be the correct one.

The Feel of Fall is Arriving

Astronomical fall begins on September 22 at 10:21am EDT, but meteorological fall is defined as the period between September 1 through November 30. While it can and does still feel like summer across parts of the nation, there are more and more signs that summer is winding down.

As the nights start to grow a little longer the farther north you go, the cooler air starts to build up a little more, especially as you head into Canada and Alaska. The cold fronts that drop down from Canada and into the Northern US start to pack a little more punch. One of those fronts is moving across portions of the Upper Midwest and the Great Plains today. The airmass moving into the Rockies and Northern Plains behind the front is sending temperatures as much as 15 to 25 degrees below normal this afternoon.

Temperatures will be 15 to 25 degrees below normal across the Northern Rockies and Northern Plains today behind a cold front. Image provided by Pivotal Weather.

As that airmass settles in, low temperatures will drop into the 30s and 40s across the Northern Plains and Rockies tonight. Frost advisories and freeze warnings have been posted for western portions of North Dakota for Tuesday morning. By Wednesday morning, the coldest air will move over Minnesota, where low temperatures could drop into the upper 20s and 30s. Additional frost and freeze advisories will likely be issued for this region.

GFS model forecast for low temperatures across Minnesota Wednesday morning. Image provided by WeatherBell.

Cold temperatures aren’t the only noteworthy item with this cold front. As the cold air surges into the Rockies, precipitation will accompany it. That precipitation will likely fall as snow in many areas, mainly at elevations above 5000 feet. Across some of the higher peaks, more than a foot of snow could accumulate over the next day or two. Winter Weather Advisories have been issued for portions of northern Wyoming as a result.

GFS model forecast for snowfall through Wednesday morning. Image provided by WeatherBell.

Some snow is also possible across the higher elevations of the Sierra Nevada as the cooler air spreads into the West. While accumulations will be minor, this will likely be the first snowfall of the year for this region. Across the rest of the Golden State, temperatures will likely be 6 to 12 degrees below normal on Tuesday, with highs only in the 70s to lower 80s, a welcome change from the 90s and 100s they’ve had for most of the summer.

While this front will bring cooler air into the Northeast later this week, one thing it won’t do unfortunately, is bring beneficial rainfall to the region. It will produce showers and some thunderstorms, and while a few of the storms may contain heavy downpours, they’ll be very localized. Across much of the region, rainfall totals will be generally under half an inch. This will do little to put a dent in the severe drought that much of the region is currently experiencing. Rainfall deficits of 5 to 10 inches below normal since the beginning of March are common across the region.

Rainfall deficits across the Northeast from March 1 through August 31. Image provided by the Northeast Regional Climate Center.

While this early taste of fall moving into much of the Northern US this week is not uncommon for mid-September, it might not be repeated much this fall. Long-range forecasts are showing the likelihood of a warmer than normal fall across much of the United States.

Drought Continues in the Northeast, Is Relief in Sight?

A persistent pattern over the last several months has left much of Northeast in a drought. According to the most recent update from the National Drought Monitor, portions of Western New York and also Central New England are experiencing severe drought.

Update from August 2 on drought conditions across the Northeast, Image provided by NOAA.

Heavy showers and thunderstorms have been common across the Mid-Atlantic states recently, eliminating any drought concerns, but the bulk of the rainfall has remained well south or well north of areas that need it the most.

Map shopwing percent of normal rainfall from May 1 through July 31 across the Northeast. Image provided by the Northeast Regional Climate Center — Map showing percent of normal rainfall from May 1 through July 31 across the Northeast. Image provided by the Northeast Regional Climate Center

According to data from the Northeast Regional Climate Center, the period between Marc 1 and August 2 is the driest on record for several locations across New York and New England, including cities such as Lawrence, MA, and Elmira and Batavia, NY. Other locations, such as Hartford, CT and Hingham, MA, are in the Top 5 driest March 1-August 2 on record. Many rivers and streams across the region are at near record low levels. Water restrictions and/or bans are in effect for hundreds of cities and towns across the region.

A cold front will cross the region on Saturday, producing scattered showers and thunderstorms. While some of these storms could be locally heavy, most places will receive just light rainfall, which will barely put a dent in the drought. The bigger concern on Saturday is for severe weather across the Northeast. While the timing of the front won’t be optimal for a severe weather outbreak, conditions will be favorable for some strong to severe thunderstorms, especially across Southern New England and southeastern New York during the afternoon hours. Some storms may produce strong winds along with hail and brief downpours.

GFS model forecast for rainfall through Saturday night. Image provided by WeatherBell.

Once the front moves through, high pressure builds back in with sunshine and dry conditions for the first half of the upcoming week. Another front will move through on Wednesday with a chance for some additional showers and thunderstorms before stalling out across the region. Exactly where that front stalls out will be critical, as waves of low pressure are expected to ride along it, bringing chances for some much-needed rainfall. If the front stalls along the southern New England coast, then some significant rainfall could fall across much of New York and Southern New England. If the front stalls out across the Mid-Atlantic states, then the heaviest rain would be focused there, and not where it is needed most. The forecast models are split on where the front will stall out, so it’s too early to get a good idea of which idea might be correct. However, if history is any indication, then expect the front to stall out to the south. Droughts feed on themselves, which leads to an old forecasting rule of thumb – “When in drought, leave it out”.

Satellite loop showing a disturbance in the Gulf of Mexico. Loop provided by NOAA. — Satellite loop showing Tropical Storm Early moving into eastern Mexico and a disturbance in the northeastern Gulf of Mexico. Loop provided by NOAA.

Normally, when the Northeast experiences a drought in the summer, it ends with heavy rainfall from a tropical system, or the remains of a tropical system that made landfall elsewhere. Tropical Storm Earl is moving into eastern Mexico this evening, but it is not expected to have any impacts on the US. However, there is a cluster of thunderstorms in the northeastern Gulf of Mexico that needs to be watched. While development of a tropical cyclone is not expected over the next few days, the system could slowly organize. The main impact from this system will be heavy rainfall across the Gulf Coast, especially in portions of Florida and southern Georgia. Some models are showing the potential for 5-10 inches of rain over the next few days. This will almost certainly lead to flooding in parts of the region.

GFS model forecast for rainfall across the Gulf Coast through Tuesday. Image provided by WeatherBell.

The ideal situation would be for some of this moisture to be drawn northward and ride along the front into the Northeast, finally bringing significant rainfall to the area. While this is a possibility, it does not seem like a likely scenario at this point. In fact, some of the models show the moisture remaining in place across the Northern Gulf of Mexico right through the week, with heavy rain and thunderstorms continuing across the region.

When in Drought, Leave it Out

“When in Drought, Leave it Out”

We don’t know who first coined that phrase, but like most meteorological rules of thumb, it tends to hold true most of the time. Currently in New England, especially Southern New England, a drought currently grips the region.

Latest update from the U.S. Drought Monitor.

A persistent pattern has led to warm and dry conditions across the Northeast for the past several months. While scattered showers and thunderstorms have produced locally heavy rainfall in some areas recently, widespread rainfall has been lacking. Many cold fronts have come across the region with little rainfall and coastal storms are rare in the summer to begin with. Even waves of low pressure passing south of New England along stalled out cold fronts have been too far south to produce much rain across out area.

Rainfall since the start of April has been well below normal across the Northeast. Image provided by the Northeast Regional Climate Center.

The dryness has been most noticeable since the beginning of June. Since June 1, Boston’s Logan Airport has recorded just 1.99″ of rain. This is the driest June/July on record in the city. The current record is 2.03″ from 1949. If Boston does not receive more than 0.04″ before Sunday night, a new record will be set (more on that later). In Worcester, the 3.18″ during the same timeframe is the 4th lowest total on record. In Lowell, 3.12″ of rain has been reported since June 1. This is the 8th lowest total on record.

Is there any relief on the way? A cold front will move across the region late Thursday and early Friday, then stall out south of New England. A wave of low pressure will ride along the wave, passing south of us on Friday. This wave will produce locally heavy rain and thunderstorms across the Ohio and Tennessee Valleys on Thursday, before it heads for the Mid-Atlantic states Thursday night. The question then is, how far north does the low and its associated rain shield get. This is the same situation we often see in the winter when trying to determine if a storm will miss us completely, bury us with heavy snow, or come too close and give us rain instead of snow. Thankfully, we don’t have to worry about snow for another 3-4 months at least.

Right now, there are several different solutions among the models, which have a rather large impact on the forecast.

GFS model forecast for total rainfall through Saturday night. Image provided by WeatherBell.

GEM model forecast for total rainfall through Saturday night. Image provided by WeatherBell.

NAM model forecast for total rainfall through Saturday night. Image provided by WeatherBell.

For the past few months, as we’ve mentioned previously, most of these storms have passed too far south to have much of an impact on us. For this reason, we’re inclined to lean that way with the forecast for Friday as well. Droughts feed on themselves, which is how the expression at the top of the page came into existence. When the ground is dry, there is even less moisture available for approaching systems. When there’s less moisture available, less rain falls. When less rain falls, the drought gets worse. So how do you break a drought? When you have one in the summer, usually, the answer is with a tropical system. Either a tropical storm/hurricane comes up the coast and slams into New England dumping copious amounts of rain on us, or one hits farther down the coast (North Carolina or the Gulf) and weakens inland and the remains of it move this way with heavy rainfall. The Summer of 1955 was hot and dry like this one has been. Then, in the span of a week in August, two Tropical Storms (Connie and Diane) brought record rainfall to the region, with widespread flooding. Of course, that’s not the preferred scenario. A more gradual transition to a wetter pattern is the best case scenario, but that isn’t how is usually works.

Speaking of the tropics, things may be starting to heat up. Since a record-setting June, there hasn’t been any activity at all in the Atlantic in July, but that could be changing. A tropical wave moved off the coast of Africa on Tuesday, producing plenty of shower and thunderstorm activity. Although some of that activity diminished today, conditions are still favorable for some development over the next few days. The odds of the system becoming a tropical depression are still fairly low, and the odds of it impacting any land, let alone New England are still fairly remote.

Model forecasts for the track of a tropical disturbance in the Eastern Atlantic. Image provided by the University of Wisconsin.

Model forecasts for the intensity of a tropical disturbance in the Eastern Atlantic. Image provided by the University of Wisconsin.

Now that we’re approaching the beginning of August, these waves should start to move off the coast of Africa every few days. At least a few of these will eventually become tropical systems as we approach the peak of hurricane season, which is late August into late September. Another area to watch is down near the Bahamas. Sometimes tropical systems form in this region, and they can quickly strengthen and head up the coast within a couple of days, which is exactly what Hurricane Bob did in August of 1991.

Intense Heat Across the Plains Will Spread into the Southwest

A ridge of high pressure over the Plains states will slowly shift westward over the next few days, with intense heat across the Plains heading for the Desert Southwest.

High temperatures soared well into the 90s across the Southern Plains on Wednesday, but when the humidity was factored in, the heat index exceeded 100-110 degrees in parts of the nation’s midsection. Only a few showers and thunderstorms provided scattered relief to the region. On Thursday, with similar conditions expected across much of the Southern Plains and parts of the Mississippi Valley, heat advisories have been posted for much of the region. High temperatures will be well into the 90s once again with some triple digit readings expected. When the humidity is factored in, heat index values will be in the 100-115 degree range across the region.

Forecast for heat index values for Thursday afternoon. Image provided by WeatherBell

While the nation’s midsection has been enduring the heat, a trough of low pressure has been keeping the West cool for the past few days. Temperatures have been as much as 10 to 20 degrees below normal, especially across the Pacific Northwest. Across the higher elevations of the Cascades, several inches of snow has been reported.

Forecast for 500mb heighs for Sunday June 19. Image provided by Pivotal Weather. — Forecast for 500mb heights for Sunday June 19. Image provided by Pivotal Weather.

While the Northwest will remain cool into the weekend, much warmer weather will move into the Southwest as a ridge of high pressure builds westward. By Saturday, temperatures will be 10-20 degrees above normal in the Desert Southwest. For a place that is “normally” hot, anomalies that big can break records. In Phoenix, high temperatures could approach 120 degrees on Sunday. The record high for that day is 115, set in 1968.

High temperature forecast for Sunday June 19. Image provided by WeatherBell. — High temperature forecast from the GFS model for Saturday June 18. Image provided by WeatherBell.

High temperature forecast from the GFS model for Sunday June 19. Image provided by WeatherBell.

Excessive heat watches have been posted for much of the Southwest from Saturday through Tuesday. The hottest days look to be Sunday and Monday, when high temperatures will likely exceed 110 degrees in Las Vegas, and could approach 120 degrees in Phoenix and Yuma. In Death Valley, California, high temperatures on Sunday and Monday could approach 125 degrees.

Even at night, there will be little relief, as low temperatures may only drop into the 80s to lower 90s across the area. In Death Valley, temperatures may only drop below 100 degrees for a couple of hours.

While temperatures may drop a few degrees later in the week, the ridge of high pressure is expected to remain in place across the Southwest right through the end of the month, keep temperatures above to well above normal.

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. Courtesy of College of Dupage.

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. 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. 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. 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.

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.

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.

Tropical Depression Two Develops – Threat to the Carolinas?

The second tropical depression of the 2016 Hurricane Season has developed in the Western Atlantic Ocean.

As of 8pm EDT Friday, Tropical Depression Two was centered approximately 400 miles southeast of Charleston, South Carolina, and was moving towards the west-northwest at 13 mph. Maximum sustained winds are near 35 mph, and additional strengthening is expected.

Infrared satellite loop of Tropical Depression Two. Loop provided by NOAA.

The storm is expected to continue on a general west-northwest track into Saturday, with some modest strengthening possible. If the system attains maximum sustained winds of 39 mph or more, it would be named Tropical Storm Bonnie. This may occur on Saturday. However, many of the forecast models are indicating that the system may not strengthen much over the next few days, due to a combination of, wind shear aloft, and sea surface temperatures that are only marginally warm enough to sustain a tropical cyclone. Most of these models do show a track towards South Carolina over the next 24-48 hours.

Model forecasts for the strength of Tropical Depression Two. Image provided by tropicaltidbits.com

Model forecasts for the track of Tropical Depression Two. Image provided by tropicaltidbits.com

A tropical storm warning has been posted for most of the South Carolina coastline, from the Savannah River to Little River Inlet. Showers and thunderstorms should begin to move into the region later on Saturday, with some locally heavy rainfall totals expected. Wind gusts to tropical storm force will likely be confined to the immediate coast.

As the storm nears the coastline it will start to slow down as the upper-level steering currents start to weaken. A turn towards the north is possible, but if the turn occurs too early, it would prevent the storm from making landfall in South Carolina, but would make a landfall in southeastern North Carolina a bit more likely. Residents along the coast from Georgia to North Carolina should keep an eye on the storm’s progress, as it will likely have a significant impact on the holiday weekend forecast.

The storm will also have an indirect impact on the weekend forecast for much of the remainder of the East Coast. As the upper-level flow becomes south-to-north along the East Coast, it will take moisture from the storm and send it northward, ahead of a cold front. This will result in periods of heavy rain for the Mid-Atlantic states later on Sunday, and the Northeast on Monday. Rainfall totals of 1-2 inches or more are expected, and while it will ruin plans for barbecues and beach days, the region has not received much rain this Spring, so any moisture that does fall is needed.

Rainfall forecast from the GFS model for the weekend. Image provided by Pivotal Weather — Rainfall forecast from the GFS model for Sunday and Monday Image provided by Pivotal Weather

The 2016 Hurricane Season got off to an extraordinarily early start when Hurricane Alex formed back in January. Alex became the first January tropical system in the Atlantic when it acquired subtropical characteristics south of the Azores on January 13. It became a full-fledged hurricane on January 14, the first January hurricane in the Atlantic since Alice in 1955. Alex crossed the Azores on January 15, before weakening to a tropical storm and then becoming extratropical later that day as it headed out in the open Atlantic.

Hurricane Season in the Atlantic Starts on June 1

June is a little more than a week away, and while that marks the start of meteorological summer, it also marks the start of Hurricane season in the Atlantic Basin (North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico).

Hurricane season in the Atlantic runs from June 1 through November 30, but it got off to an extraordinarily early start in 2016 when Hurricane Alex formed back in January. Alex became the first January tropical system in the Atlantic when it acquired subtropical characteristics south of the Azores on January 13. It became a full-fledged hurricane on January 14, the first January hurricane in the Atlantic since Alice in 1955. Alex crossed the Azores as a strong tropical storm on January 15, and eventually head out in the open Atlantic transitioning to an extratropical cyclone on January 17. The next storm that forms will be given the name Bonnie.

Name list and pronunciation for the 2016 Atlantic Hurricane Season

Is the early start a harbinger for an active hurricane season? Not necessarily. What will be more of a factor is the developing La Nina in the Pacific Ocean. In an El Nino, such as the one we had in 2015, the subtropical jet stream is stronger, which inhibits storm development as the jet stream effectively cuts the tops off of storms before they can develop. In a La Nina, the subtropical jet is weaker, allowing easterly winds to dominate, which allows the storms to develop.

Map showing all tropical systems across the Atlantic Basin from the 2015 Hurricane Season. Image provided by the National Hurricane Center.

The presence of El Nino or La Nina is just one of many factors that go into whether a hurricane season is active or quiet, but most predictions are for activity to be more common than in 2015 and above normal. In a normal season, the Atlantic Basin sees 12 named storms, of which 6 become hurricanes and 3 become major hurricanes (Category 3 or higher on the Saffir-Simpson Scale). While there are plenty of hurricane forecasts out there, these were pioneered by Dr. William Gray, who recently passed away after over 50 years in the field. His research team at Colorado State University continues his work, and for this season is calling for 14 named storms, of which 8 could become hurricane, and 3 major hurricanes.

An active season doesn’t guarantee that a storm will make landfall in the United States though. In 2010, there were 19 named storms, 12 hurricanes, and 5 major hurricanes. Only 1 storm, Tropical Storm Bonnie, made landfall in the United States. On the flip side, 1992 was a quiet season, with just 7 named storms, 4 hurricanes, and 1 major hurricane, with the first named storm not forming until August 16. Of course, that first storm was Andrew, which slammed into South Florida on August 24 as a Category 5 hurricane, one of just 3 Category 5 storms to ever make landfall in the United States.

The peak of the season usually occurs from mid-August through late September, but an early start isn’t unusual. On average, the first name storm of the season occurs on July 9, with the first hurricane forming around August 10. In 2015, there were two tropical storms during May and June (Ana and Bill), while 2012 saw 4 named systems (Alberto, Beryl, Chris, and Debby) with 1 hurricane (Chris) forming before the end of June.

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

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.