Bit of a lengthy forecast this go around, mainly as we deal with multiple potential rounds of severe thunderstorms in the US over the next few days. Looking up above, a bit of a chaotic air pattern is in place, with a decaying high-pressure system sitting over the Central Plains, a developing high-pressure system in the southwest US, and an upper-level low located over southern Canada. Aside from the severe weather, we will see the heat continue to rise in the Desert Southwest and increased potential for showers and thunderstorms across the Southeast. There is a lot to unpack here, so let us dive in and see what is going on throughout the country.
Severe weather in the Midwest and Northern Plains
Today will continue the trend of multiple days of severe weather potential for the Midwest and Northern Plains. Beginning in the Midwest, we got a substantial risk for severe weather for those in states such as Illinois, Indiana, and Kentucky. Synoptically, broad westerly flow is expected to overspread the region and be the main basis for large-scale support for organized convection. Embedded shortwaves will interact with a very moist and unstable air mass and help to trigger development by the mid-afternoon. Strong deep-layer shear, ML CAPE in excess of 2500 J/kg, DCAPE of 1000+ J/kg, and high lapse rates of 7° C/km will initially favor supercells capable of large hail and damaging winds. By the evening hours, thunderstorms coming out of Missouri should conglomerate into an MCS capable of all severe hazards. This MCS will advance eastward through the evening before exiting the region overnight.
Above is a sample sounding in central Illinois just in front of the main MCS at 7pm. A few notable features is the large amount of SBCAPE these storms will potentially utilize (3500+ J/kg), strong wind shear as evident by the turning of the wind barbs and sickle shape of the hodograph (upper right), which would help favor hail and embedded tornadoes, and how moist the vertical profile is (PW = 2.0 in and the column being largely saturated almost up to 200 mb), which would favor torrential rainfall and maybe a flash flood potential.
By tomorrow, the risk shifts slightly east into the Ohio River valley and central Eastern US. Clusters of storms are expected to form by the afternoon and move eastward throughout the day and evening hours. These storms will largely be capable of damaging winds as they progress and mature.
By early into next week, more severe weather will be possible, but this time for the northern Plains. An upper-level low and associated cold front will move in from Canada and interact with a warm and moist airmass over the northern Plains. This will help to initiate thunderstorms, some of which may be severe. Moderate amounts of ML CAPE (3500+ J/kg) will help foster and sustain powerful storm updrafts and strong horizontal and vertical wind shear will help to cause large hail and damaging winds with these storms.
Desert Southwest bakes
Looks like the heat will continue to pour on for this corner of the United States for the foreseeable future. The developing high-pressure system over the southwestern US will cause this region to crank up the temperature incrementally as we continue through next week by keeping rain chances suppressed and not allowing for the transport of large-scale air masses through the area. Areas in the Sonoran Desert and Mojave Desert will see temperatures regularly reach as high as 110°-115°, and even central California will reach between the upper 90s and low 100s throughout the week. It will be important to stay cool in this kind of heat, as it does not take long for heat-related illnesses to set in.
Showers and thunderstorms possible in the Southeast
Hopefully for what may be relief for some (depending on the time of day) in the Southeast from the oppressive heat, daily chances of showers and thunderstorms will be widespread across the area. The high-pressure system that has dominated over the last few days and has been responsible for helping to bring heat indices of up to 125°F will finally break down and more zonal flow aloft will take over. This will translate into rain chances increasing now that there is not such a lid on the atmosphere and will see these chances regularly throughout the coming week. Total rainfall accumulations will be modest, with the highest amounts around 2-3 inches locally, although heavy downpours will be possible with the stronger of these pulse storms.
Travel Impacts
Severe thunderstorms will impact travel for those in the Midwest all the way to the northern Plains over the next four days. Airport delays and cancellations across these regions may occur and alternate routes should be considered if your route goes through these areas where severe weather may occur. Outside of this, no other significant travel impacts are expected, outside of making sure your AC works while traveling in the Southwest, and the potential for travel delays for showers and thunderstorms in the Southeast.
Extended Outlook
The upper-level high over the Southwest will really be solidified by mid-week into the end of next week and will help to keep thunderstorm activity low and raise the heat. Further west and north, zonal flow with embedded shortwaves will help to provide the basis for multiple rounds of showers and thunderstorms, some possibly severe (especially in the northern Plains), well into next week. Details regarding the intensity or location of these storms is currently to be determined and further information will be come out over the following few days. Outside of this, largely seasonal summer-like conditions will exist for many.
Conclusion
Severe thunderstorms will be possible for many in the Midwest and northern Plains over the next few days. These storms will be capable of large hail, damaging winds, and possibly a tornado or two. Further area-specific weather information can be found at the National Weather Service or Storm Prediction Center and be sure to have multiple ways to receive weather information. In the southwest, the upper-level high will continue to build in over the coming week and keep the run of high temperatures around, with temperatures regularly in the upper 90s to low 100s. Ending with the Southeast US, the dome of high pressure will finally relent and allow for increased thunderstorm chances across the region, which may help bring some relief from the oppressive temperatures as of late.
