Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 348 AM EDT Sun May 04 2025 Valid 12Z Sun May 04 2025 - 12Z Tue May 06 2025 ...A continued omega block pattern over the lower 48 will lead to prolonged periods of unsettled weather and cooler temperatures into early next week... ...Locally heavy rainfall with flash flooding possible for southern New England Monday... ...Scattered instances of flash flooding as well as severe weather forecast for the southern High Plains Sunday and Monday... An omega block pattern over the Lower 48 is in place this morning as a strong ridge builds between a pair of upper-level lows over the Ohio Valley and California/Southwest. This will bring prolonged periods of unsettled weather and cooler temperatures to portions of the eastern and western U.S. while north-central areas see dry conditions and well above average temperatures. First, in the East, the upper-low over the Ohio Valley as well as an accompanying occluded/cold front arcing southeastward along the Lower Great Lakes and East Coast will continue to bring widespread showers and thunderstorms over the next couple of days. Moderate to locally heavy rainfall can be expected given the slow progression of the front, with isolated flash flooding possible on Sunday. On Monday, more focused very moist, onshore flow from the Atlantic ahead of the cold front over portions of southern New England will lead to the threat of a few more scattered instances of flash flooding, with a Slight Risk of Excessive Rainfall (level 2/4) in effect. The southern portion of the cold front over the Southeast/Carolinas will make the most eastward progress, bringing an end to rain chances for these areas during the day Monday as the front clears the coast, while rainfall lingers into Tuesday for the Lower Great Lakes and Northeast. Forecast temperatures broadly throughout the Great Lakes and Southeast will remain below average the next couple of days, particularly for the Ohio/Tennessee Valleys, with highs mainly in the 50s and 60s. Conditions will be closer to average along the East Coast ahead of the slow moving front, with highs in the 60s and 70s for New England and the northern Mid-Atlantic and the 70s and 80s for the southern Mid-Atlantic/Carolinas. To the west, widespread precipitation chances also remain in the forecast across much of the West under the influence of the second upper-level low. Showers and thunderstorms throughout the northern Rockies, Great Basin, Four Corners region, and Southwest today will shift a bit eastward on Monday, bringing greater chances into areas of the central Rockies and the adjacent High Plains as areas of the western Great Basin dry out. Moderate to locally heavy rainfall, with some isolated flash flooding possible, is most likely over the western Great Basin Sunday and the eastern Great Basin Monday. Higher mountain elevations will see accumulating snowfall, particularly over portions of the northern/central Rockies on Monday, with totals of 4-8", locally higher, expected. A more focused corridor of showers and thunderstorms along with more widespread heavy rainfall is expected over the southern High Plains as anomalously high moisture from the Gulf flows northwestward ahead of a surface frontal system emerging from the mountains over the region. A Slight Risk of Excessive Rainfall is in place for portions of northeastern New Mexico Sunday with another Slight Risk over portions of the Texas Panhandle/western Texas on Monday where the potential for rain rates of 1"/hr and 2-4" totals may lead to some scattered instances of flash flooding. In addition, sufficient instability given the moisture in place and cooler air aloft with the approaching low, along with increasing upper-level winds, will lead to the threat of some severe weather. The Storm Prediction Center has outlined portions of southeastern New Mexico with a Slight Risk (level 2/5) Sunday mainly for the threat of large hail. Another Slight Risk in place Monday across portions of western Texas for the threat of very large hail, damaging winds, and a few tornadoes. In contrast to the unsettled weather to the north, portions of southwestern New Mexico will remain very dry ahead of the approaching upper-low, with the combination of low humidity and gusty winds prompting a Critical Risk of fire weather (level 2/3) from the Storm Prediction Center for Sunday. Conditions across much of the west and into the southern Plains will be below average given the upper-low overhead and widespread precipitation. Forecast temperatures Sunday are mainly in the 50s and 60s across the Interior West with 60s and 70s in the Desert Southwest and southern Plains. The West Coast will be cooler and below average as well on Sunday, with highs in the 50s and 60s, before a warm up into the 60s and 70s on Monday as the upper-low shifts eastward. Elsewhere, dry conditions and well above average temperatures are expected across north-central portions of the country as the upper-ridge builds overhead. Highs will be in the 70s and 80s Sunday across the northern/central Rockies, northern/central Plains, and Upper Midwest. Some locations across the northern High Plains may approach 90, upwards of 30-35 degrees above average for this time of year. The approach of the upper-low and an accompanying eastward moving cold front will bring much cooler temperatures to the northern/central Rockies and adjacent High Plains Monday as highs fall into the 50s and 60s. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php