A strong ridge of high pressure is currently setup across the Southwestern and Central United States. It will become one of the strongest high pressure systems on record for the Jun 19th to June 21st time frame in terms of geopotential height. Geopotential height measures the distance above ground level that a certain pressure occurs. For example, if one were trying to find a pressure of 500 mb at 8AM on Sunday June 18th over Albuquerque, New Mexico, one would need to rise up 5970 meters into the sky (as found by the morning observational sounding balloon). These geopotential height readings will reach all time highs during this weekend and into the workweek, especially the early part of it.
The ideal gas law has been getting a lot of press lately as a result of the Patriots’ “Deflate Gate”, but we can use it here to prove that when there is more space for air to move around in, higher geopotential heights for example, we can approximate that the air temperature will be warmer than normal in those circumstances. In the Southwestern United States, during the time that this anomalously strong high pressure system will be overhead, above normal temperatures are forecast by the National Weather Service (NWS). In fact, the NWS is forecasting temperatures in the Southwestern United States to soar past previous records by as much as 3 degrees in Tucson, Arizona on Sunday, as much as 4 to 5 degrees in Winslow, Arizona and 3 to 4 degrees in Los Angeles, California on Monday and as much as 4 degrees in Las Vega, Nevada on Tuesday.
This certainly won’t be good news for those battling wildfires in the Southwest with the record high temperatures being forecast in those areas. The warm temperatures allow areas to become even drier and that allows for better fuel for wildfires. One positive is that winds won’t be as strong with high pressure around the region.
Another piece of this pattern that we will have to watch for is that when high pressure sets up in the West, a trough of low pressure sets up in the East or Northeast. This occurs during our short term pattern and often results in severe weather in the form of mesoscale convective systems (MCS’s). These often form along the periphery of the high pressure system, especially to the north of the high pressure ridge, and ride to the southeast. The main thing that keeps these systems going is a large difference in temperature over a short distance not only horizontally, but also vertically. So the area between the warm air to the southwest and the cooler air to the northeast is the first place to look, but one would also need a disturbance moving through and possibly even a large change in temperatures at a location from the surface to the low to mid-levels of the atmosphere. With all of this in mind, MCS’s may occur along the line from the Northern Mississippi Valley to the Tennessee Valley and move toward the Southeastern United States generally along the path that the mid-level winds take it. This track would shift east as the ridge shifts east later in the week if the do continue to form.