Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Mon May 20 2024 Valid 12Z Mon May 20 2024 - 12Z Wed May 22 2024 ...Continued severe weather and excessive rainfall threats over the central U.S. into mid-week... ...Cool conditions with periods of shower and storm chances from the Rockies to the Pacific Northwest... ...Well above average, Summer-like temperatures to start the week across much of the central/eastern U.S.... An energetic upper-level pattern featuring multiple shortwaves emitting from a broader long-wave trough over the western U.S. will continue a period of active weather over the central U.S. this week. An initial shortwave/accompanying surface frontal system will bring showers and thunderstorms to portions of the Upper Midwest/Great Lakes Region by early Monday. A few more robust thunderstorms will be possible immediately ahead of the wave over northeastern Illinois and adjacent Wisconsin/Indiana, where the Storm Prediction Center has issued a Slight Risk of severe weather (level 2/5) for the threat of some damaging winds and large hail. Some locally heavy downpours and isolated flash flooding will also be possible. Further west, lee cyclogenesis is expected over the central High Plains as the long-wave trough further amplifies, helping to reinforce a frontal boundary draped across the region. Moist upslope flow north of this boundary is expected to lead to thunderstorms by Monday afternoon, with an Enhanced Risk of severe weather (level 3/5) over northeastern Colorado and southwestern Nebraska as some of the more robust storms may produce very large hail, significant damaging winds, and a few tornadoes. A broader Slight Risk extends northeastward along the front through the central Plains into the Upper Midwest. Increasing storm coverage Monday evening with the potential for some locally heavy downpours will also bring the threat for some isolated flash flooding from northeastern Colorado northeast into northwestern Iowa. Moisture spreading northwestward into portions of the northern High Plains/Rockies will bring moderate precipitation chances here as well, with some locally heavy snowfall totals possible for higher mountain elevations. Another shortwave ejecting from the longwave western trough will bring a broader, greater chance for severe weather and flash flooding to portions of the Midwest Tuesday. The accompanying surface low pressure/frontal system will deepen and lift northeastward from the Plains into the Upper Midwest, with an expansive warm sector from the Southern Plains northeastward through the Lower Missouri and Upper Mississippi Valleys. Both supercells and more organized convective systems are expected amidst strengthening low and upper-level wind fields and strong instability. An Enhanced Risk of severe weather is in place for the threat of tornadoes, some strong, significant damaging winds, and large hail. In addition, a deep influx of moisture as well as the strong forcing associated with the deep surface low will help to promote heavy downpours. With more numerous storms expected in vicinity of the surface low, a Slight Risk of Excessive Rainfall (level 2/4) has been issued for portions of central/southern Minnesota and northwestern Wisconsin for the risk of some scattered instances of flash flooding. Lingering shower and thunderstorm chances will also extend back west through the central Plains into the central/northern Rockies. Elsewhere, a few thunderstorms will remain possible over the Florida Peninsula through at least Tuesday. An upper-low/frontal system dropping southward from northwestern Canada will spread showers and storms into the Pacific Northwest/northern Great Basin Tuesday, with some locally heavy rainfall possible along the coastal ranges and Cascades. A broad area of well above average temperatures is expected over much of the central/eastern U.S. with ridging in place ahead of the trough over the West. Highs in the 80s and even low 90s will be common, even in more northerly locations from the Great Lakes into the Northeast. Sweltering heat continues over portions of southern Texas into the southern High Plains as highs soar into the 90s and 100s. In contrast, much cooler, below average temperatures are expected to the north and west of the system over the Plains under the influence of the western trough. Highs from the Pacific Northwest into the Great Basin, northern/central Rockies, and northern/central Plains will be in the 50s and 60s. Highs will be closer to average in the Southwest with 80s and 90s forecast. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php