####018006475#### FXUS02 KWBC 220646 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 246 AM EDT Mon Apr 22 2024 Valid 12Z Thu Apr 25 2024 - 12Z Mon Apr 29 2024 ...Severe thunderstorms and heavy rain possible for the Plains and Mississippi Valley late this week and again this weekend... ...Overview... The upper level pattern will be fairly consistent through the medium range period, featuring mean troughing over the western U.S. and a ridge shifting over the East Coast. A couple shortwaves will eject from the base of the trough in the West across the Central U.S., which will trigger rounds of active, and potentially hazardous, weather across portions of the Plains and Mississippi Valley. Persistent troughing over the western U.S. will result in a prolonged period of unsettled weather for the region with rain at low elevations and snow at high elevations. Ridging over the East Coast will keep the weather calm through most of the period, but a cold front will move towards the Northeast over the weekend, bringing precipitation back to the region. ...Guidance/Predictability Assessment... The main features of interest will be the upper level shortwaves that could potentially produce severe thunderstorms and heavy rain in the Central U.S. late this week and again over the weekend. Models are in good agreement on the timing and location of the first shortwave, bringing it across the Southwest on Thursday and across the Plains to the Upper Midwest on Friday. Model agreement decreases further out in time, so there is more spread surrounding solutions for the second shortwave over the weekend, though the amount of spread is fairly typical for this time range. Most of the spread derives from how the models are handling upstream energy moving southeast from the Gulf of Alaska. The ECMWF is more progressive with this feature while the GFS is a bit slower. A pure deterministic blend was used for the first half of the WPC forecast with a nearly even blend of the 18Z GFS and 12Z ECMWF/CMC/UKMET. For the second half of the period, ensemble means were introduced to the blend to help smooth out some of the model differences, but the majority of the blend was still composed of deterministic models to help keep some definition of the secondary shortwave feature. ...Weather/Hazards Highlights... Thursday and Friday, an upper level shortwave will move northeast across the Central U.S. and will be accompanied by a surface low pressure system. Low pressure will strengthen over the Central Plains on Thursday, then the system will move towards the Upper Midwest on Friday, pulling a warm front north across the south- central and eastern U.S. and a trailing cold front from the Mid- Mississippi Valley to the Southern Plains. This system is forecast to produce showers and thunderstorms over portions of the Plains and Mississippi Valley, and the ingredients (instability and moisture) will be in place for locally heavy rainfall totals. A Marginal Risk area remains in place over the Central Plains and Mid-Mississippi Valley in the vicinity of the developing surface low in the Day 4 (Thursday) ERO. Precipitation will become more widespread on Friday, and another Marginal Risk area was introduced for much of the Mississippi Valley and eastern portions of the Plains in the Day 5 (Friday) ERO. In addition to heavy rainfall, severe thunderstorms will be possible ahead of a dryline in the warm sector of this system, and the Storm Prediction Center has highlighted portions of the Plains and Mississippi Valley in the Severe Weather Outlook for Thursday and Friday. Isolated to scattered severe thunderstorms will be possible, and severe storm threats may include damaging winds, large hail, and tornadoes. On the western side of the dryline, strong winds and low humidity will create and increased wildfire risk for portions of New Mexico, west Texas, the Texas and Oklahoma panhandles, and far southeastern Colorado. Over the weekend, the second upper level shortwave will move northeast across the Central U.S. and create a precipitation pattern that will look very similar to the first system. A low will strengthen over the Central/Southern Plains Saturday and move towards the Upper Midwest Sunday into Monday, bringing another round of showers and storms to portions of the Plains and much of the Mississippi Valley. Precipitation chances will also spread into the Ohio Valley and Northeast over the weekend as the leading system moves over the top of the East Coast ridge. In the West, mean upper troughing will allow precipitation chances to persist across much of the region through the end of this week, but drier conditions will likely develop over the Southwest on Sunday and Monday. Precipitation will fall as rain at lower elevations and as snow at higher elevations. Daily high temperatures will likely remain slightly below normal across the West, but highs may return to near normal in the Southwest Sunday and Monday after precipitation comes to an end. Temperatures will trend above normal across much of the south- central and eastern U.S. as a warm front lifts north later this week, and high temperatures will likely reach the 70s and 80s for much of these regions. Highs could reach the 90s and potentially over 100 degrees for portions of south Texas by Saturday. Dolan 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 $$