Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 PM EDT Mon Apr 14 2025 Valid 12Z Thu Apr 17 2025 - 12Z Mon Apr 21 2025 ...Heavy rainfall and flooding possible in parts of the central U.S. by the weekend... ...Overview... Starting Thursday a vigorous upper trough will be traversing through the Northwest as southern stream troughing setups up over the Southwest. These two features will combine to yield an upper low over the Great Basin region late in the week and with time, pivot to the south and east through the weekend. Cooler temperatures along with increased potential for precipitation, some of which may be heavy snowfall for the Northern/Central Rockies through Friday. In addition, there will be northern stream trough advancing through the north-central and northeastern U.S. accompanied by a low pressure system, as an elongated frontal system stretches from the northern tier southwestward through the south-central U.S. late week into the weekend. Rain and thunderstorms are expected with this feature along with the possibility of severe storms. Heavy rainfall and possible flooding to develop across the south-central U.S where moisture streaming ahead of the Southwest Upper Low will interact with frontal systems over the region. The greatest potential will be over the weekend. ...Guidance/Predictability Assessment... The latest runs of guidance maintain the synoptic pattern from above while hanging on to some of the tendencies observed from the the previous forecast package. The use of a multi-model approach maintained a sense of continuity and reduced some of the minor differences with the timing and location of the northern and southern stream troughing. As previously noted, the GFS is hanging on to a slow progression of the trough/low over the Great Basin/Southwest which impacts the QPF over the Central/Southern High Plains whereas the other guidance favors QPF more to the south and east of the expected frontal positions. The CMC has trended somewhat toward the GFS solution however, the ECWMF is providing the favored placement and associated details at this time. The WPC forecast was based on a blend of the deterministic guidance using the 00Z ECMWF, 06/12Z GFS, 00Z CMC, and 00Z UKMET initially while light weighting of the ECWMF and GEFS means were incorporated for the weekend and into early next week to temper the model differences. ...Weather/Hazards Highlights... Strong upper-level energy will provide support for moderate to heavy precipitation across parts of the West, stretching from the Northern/Central Rockies and High Plains across the Intermountain West into the Sierra Nevada. Colder air aloft will likely lead to accumulating snow in the higher elevation, particularly heavy across Wyoming and southern Montana with some areas of snow for the Wasatch and Sierra. Some precipitation is forecast to continue in the Four Corners states into the weekend, with possibly multiple days of snow in the Colorado Rockies. Farther east, the northern stream upper trough and a surface low pressure system will traverse the north-central Plains and Midwest on Thursday, supporting shower and thunderstorm activity. The Storm Prediction Center has identified these areas as having a severe weather risk. Given the progressiveness of the low, the locally heavy rain will have limited potential for flooding. Individual thunderstorms should move quickly but there may be repeated rounds moving west to east somewhere in the vicinity of Lower Michigan and/or Indiana/Ohio. With antecedent dry conditions and uncertainty with the axis of potential heavy rain there will not be an area for the Excessive Rainfall Outlook however will continue to monitor flooding potential. Farther south, the tail end of the frontal system in the Southern Plains should help to focus moisture advection ahead of the Southwest upper low. Some rain and storms become likely by Friday evening or night over parts of Texas and Oklahoma, with some likely lesser amounts over Arkansas/Missouri. By Saturday heavy rain is likely to continue in the Southern Plains, and this should warrant ERO areas, but this is beyond the Day 5 ERO period. The surface low and frontal system is expected to shift northeast by Sunday which will allow the rain and thunderstorms to spread into the Central/Southern Plains and the Middle/Lower Mississippi Valley. Heaviest rainfall amounts are likely to be west of the most sensitive areas of the Mississippi Valley and Ohio Valley from recent flooding. However, some rain atop recently flooded areas, and runoff from other areas into these rivers, could exacerbate ongoing flooding issues in some areas. The forecast details could change over the next few days and should be closely monitored to assess any possible impacts. Initial upper ridging across the Plains will allow for above normal temperatures there on Thursday. Above normal highs by 20-25 degrees will raise highs into the 90s from Texas to Kansas. Meanwhile cooler than normal temperatures, especially for highs, are likely to spread across the Interior West Thursday and Friday under the upper trough. Warmer than average temperatures are forecast to moderate and shift east into late week and focus across the southeastern U.S. by Sunday. Campbell/Tate 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 (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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