Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Mon May 05 2025 Valid 12Z Mon May 05 2025 - 12Z Wed May 07 2025 ...A continued omega block pattern over the Lower 48 will lead to prolonged periods of unsettled weather and cooler temperatures to start the week... ...Increasing flash flood threat as well as severe weather expected for the southern Plains/Lower Mississippi Valley Monday into Tuesday... ...Locally heavy rainfall with flash flooding possible for the Greater NYC area/southern New England Monday... A blocky pattern remains in place over the Lower 48 to start the week with a slow moving upper-low over the Ohio Valley, another slow moving upper-low over the Southwest, and an upper-level ridge over portions of the northern Plains/Upper Midwest in between. The upper-low over the Southwest, which has brought unsettled weather to much of the West more broadly this weekend, will continue to bring precipitation to the Southwest/Four Corners region, eastern Great Basin, and Rockies today. Showers and thunderstorms with moderate to locally heavy rainfall are expected, with the greatest chance for heavy rainfall and some isolated flash flooding over portions of the Desert Southwest. Higher mountain elevations will see some heavy snowfall accumulations of 8-12"+, especially for regional ranges of southwestern Montana and northwest Wyoming Monday, and Colorado/north-central New Mexico Monday into Tuesday. Precipitation chances will come down significantly for the Southwest/Four Corners, Great Basin, and northern Rockies Tuesday as the upper-low shifts eastward. A more focused heavy rainfall event will develop to the east along portions of the central/southern High Plains, southern Plains, and into the Lower Mississippi Valley over the next couple of days. An influx of moist Gulf air will flow northwestward ahead of a low pressure/frontal system emerging onto the Plains coincident with the eastward progression of the upper low. The combination of this anomalously moist air, upper-level dynamic support, and upslope flow with increasing proximity to the Rockies will bring widespread showers and thunderstorms producing heavy downpours and the potential for several inches of rainfall. This will begin across portions of the southern High Plains on Monday, with a Slight Risk of Excessive Rainfall (level 2/4) in effect for the threat of scattered instances of flash flooding. In addition, cooler temperatures aloft and strengthening winds with the approach of the upper-low will lead to sufficient instability and deep-layer shear for some more intense, supercell thunderstorms. The Storm Prediction Center has included an Enhanced Risk (level 3/5) over southwest Texas with a Slight Risk (level 2/5) more broadly over the southern High Plains for the threat of several instances of very large hail along with damaging winds and a few tornadoes. Then, on Tuesday, the threat will shift north and eastward and expand in coverage along the arcing frontal system. A Moderate Risk of Excessive Rainfall is in effect across portions of the ArkLaTex and Lower Mississippi Valley where upper-level support from the low and continued storm development along a warm frontal boundary extending eastward through the region will bring repeated rounds of slow moving storms capable of heavy downpours later Tuesday and into Tuesday night which may lead to scattered to numerous instances of flash flooding. A broader Slight Risk extends northwestward across the southern Plains and into the central High Plains where increasing upslope flow along the Rockies will support widespread storms with additional scattered instances of flash flooding. Severe storms will also be possible along and south of the warm front from central Texas east through western Louisiana, with a Slight Risk of severe weather in place for very large hail, damaging winds, and a few tornadoes. Showers and thunderstorms will also continue Monday across much of the northeastern U.S. under the eastern upper-low, with storms most likely from the Lower Great Lakes east through the Mid-Atlantic and into southern New England. A more focused corridor of very moist southerly Atlantic flow along a coastal front through the greater New York City area and into southern New England may lead to some locally heavier downpours and scattered flash flooding, with a Slight Risk of Excessive Rainfall in effect. Storm chances will linger into the day Tuesday, though will become increasingly more scattered with less rainfall expected, before storms begin to come to an end late Tuesday night and into Wednesday morning. Elsewhere, some scattered thunderstorms are forecast over the Florida Peninsula ahead of a cold front Monday. The rest of the country outside of the influence of the upper-lows will see dry conditions the next couple of days. The omega block pattern will continue to lead to focused areas of both well below normal and well above normal temperatures to start the work week. Well below average highs are forecast for much of the Ohio and Tennessee Valleys under the influence of the eastern upper-low, with 50s and 60s expected. Conditions should moderate and warm a few degrees on Tuesday. Highs will be closer to average along the East Coast ahead of the upper low, with 50s and 60s in New England, 60s and 70s in the Mid-Atlantic, and 70s and 80s from the Carolinas south into Florida. Conditions will also be well below average across much of the Interior West and into the central/southern Plains under the influence of the western upper-low. Forecast highs Monday and Tuesday range from the 50s and 60s for the Rockies/Great Basin and much of the central/southern Plains to the 60s and 70s for the Desert Southwest and more southern areas of Texas. In contrast, well above average conditions continue under the upper-ridge over the northern Plains/Upper Midwest, with highs into the 70s and 80s. The West Coast will also see increasingly above average conditions as an upper-ridge builds in the wake of the upper-low, with highs in the mid-60s to mid-80s. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php