Forecast Discussion
— ExtendedOverview
An amplified upper level pattern will be in place for the beginning of next week, with an anomalous ridge over the east-central U.S. supporting an early season heat wave, and a strong trough over the Rockies that will bring a round of late season snow for the higher elevations of Colorado and Wyoming. At the interface of these two features will be a strong cold front that will be crossing the Plains and Midwest with multiple rounds of heavy rainfall and strong/severe thunderstorms.
Guidance/Predictability Assessment
The deterministic model guidance suite features good overall agreement for the beginning of the period Monday, and a general model compromise works as a starting point for fronts and pressures. Looking ahead to mid-week, recent runs of the CMC have been slower with ejecting the western U.S. trough, and maintain the eastern U.S. ridge and heatwave longer than the other guidance. The GFS has trended less strong with a shortwave crossing the Midwest and Ohio Valley by Friday when compared to its 18Z run. The ensemble means were increased to about half by Friday as deterministic model spread increases.
Weather/Hazards Highlights
A dynamic storm system crossing the northern Plains to the Upper Midwest will bring widespread showers and thunderstorms from Texas to Minnesota ahead of a strong cold front. The best combination of instability and dynamics aloft is expected over Iowa and portions of adjacent states on Monday, and thus where the best lift in the atmosphere will be for heavy rainfall. Given the potential for training thunderstorms with high rainfall rates, a Slight Risk of excessive rainfall will be valid for the Day 4/Monday time period for this region. There is also a good chance for severe thunderstorms to develop in the warm sector ahead of the front, and this is something that the Storm Prediction Center is actively monitoring in the days ahead.
Going into Day 5/Tuesday, the best focus for heavy rainfall is expected to be across Texas and extending eastward to Arkansas and the Mid-South as the front drops farther to the south, and intercepts a very humid and unstable airmass. For now, a broad Marginal Risk area is valid for this time, but future upgrades to a Slight Risk are likely as the event gets closer in time with better confidence on the QPF axis placement. Additional heavy rainfall is likely going into Wednesday as well for these same general areas.
In the temperature department, heat will be making headlines for much of the Eastern U.S. for the first half of the week, with the hottest conditions across interior portions of the Mid-Atlantic into the Carolinas where highs are likely to reach the lower to middle 90s. This will likely be warm enough to establish some daily record highs before a cold front brings relief from the Ohio Valley to the Mid-Atlantic/Northeast by Thursday. The opposite will hold true for the Intermountain West and Rockies with below normal readings to start the week, and snow for the higher elevations.
Hamrick
Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at:
000 FXUS02 KWBC 150720 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 320 AM EDT Fri May 15 2026 Valid 12Z Mon May 18 2026 - 12Z Fri May 22 2026 ***Multiple rounds of heavy rain and severe storms expected for the Plains, and early season heatwave for the East Coast*** ...General Overview... An amplified upper level pattern will be in place for the beginning of next week, with an anomalous ridge over the east-central U.S. supporting an early season heat wave, and a strong trough over the Rockies that will bring a round of late season snow for the higher elevations of Colorado and Wyoming. At the interface of these two features will be a strong cold front that will be crossing the Plains and Midwest with multiple rounds of heavy rainfall and strong/severe thunderstorms. ...Guidance/Predictability Assessment... The deterministic model guidance suite features good overall agreement for the beginning of the period Monday, and a general model compromise works as a starting point for fronts and pressures. Looking ahead to mid-week, recent runs of the CMC have been slower with ejecting the western U.S. trough, and maintain the eastern U.S. ridge and heatwave longer than the other guidance. The GFS has trended less strong with a shortwave crossing the Midwest and Ohio Valley by Friday when compared to its 18Z run. The ensemble means were increased to about half by Friday as deterministic model spread increases. ...Weather/Hazards Highlights... A dynamic storm system crossing the northern Plains to the Upper Midwest will bring widespread showers and thunderstorms from Texas to Minnesota ahead of a strong cold front. The best combination of instability and dynamics aloft is expected over Iowa and portions of adjacent states on Monday, and thus where the best lift in the atmosphere will be for heavy rainfall. Given the potential for training thunderstorms with high rainfall rates, a Slight Risk of excessive rainfall will be valid for the Day 4/Monday time period for this region. There is also a good chance for severe thunderstorms to develop in the warm sector ahead of the front, and this is something that the Storm Prediction Center is actively monitoring in the days ahead. Going into Day 5/Tuesday, the best focus for heavy rainfall is expected to be across Texas and extending eastward to Arkansas and the Mid-South as the front drops farther to the south, and intercepts a very humid and unstable airmass. For now, a broad Marginal Risk area is valid for this time, but future upgrades to a Slight Risk are likely as the event gets closer in time with better confidence on the QPF axis placement. Additional heavy rainfall is likely going into Wednesday as well for these same general areas. In the temperature department, heat will be making headlines for much of the Eastern U.S. for the first half of the week, with the hottest conditions across interior portions of the Mid-Atlantic into the Carolinas where highs are likely to reach the lower to middle 90s. This will likely be warm enough to establish some daily record highs before a cold front brings relief from the Ohio Valley to the Mid-Atlantic/Northeast by Thursday. The opposite will hold true for the Intermountain West and Rockies with below normal readings to start the week, and snow for the higher elevations. Hamrick Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw $$