####018006492#### FXUS02 KWBC 221858 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 PM 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 amplified and progressive as a couple of shortwaves/embedded upper lows progress west to east across the country. Initial troughing over the East Thursday- Friday will be replaced with strong ridging this weekend which should help steer system northward into the Upper Midwest/Great Lakes. This overall pattern will support rounds of active, and potentially hazardous, weather across portions of the Plains and Mississippi Valley, and a prolonged period of unsettled weather for the West 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 models continue to show good agreement on the large scale upper pattern during the medium range period, but plenty of disagreement in the details still. There are some minor timing differences with the first shortwave as it lifts through the Central U.S. Thursday- Friday, but a general blend of the latest deterministic models seemed to provide a good starting point. Also plenty of timing uncertainties with the second shortwave early next week. As of the 00z/06z models, the CMC was faster with this shortwave than the other guidance and so the late period WPC blend for today was based on a non-CMC compromise, including the latest ensemble means with the GFS/ECMWF. However, there is a faster trend in the new 12z guidance suite that came in after forecast generation time, so this will need to be watched. Overall though, good consistency was maintained between the overnight and the new day shift progs. ...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 portions of the Central Plains and Mid-Mississippi Valley in the vicinity of the developing surface low in the Day 4 (Thursday) ERO, but dry antecedent conditions may limit the overall threat. Precipitation will become more widespread on Friday, and another Marginal Risk continues 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-Friday. On the western side of the dryline, strong winds and low humidity will create an 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. Again, increasing threats for severe weather per the Storm prediction Center which has an area highlighted on Saturday across parts of the southern/central Plains. The southern portion of the cold front associated with this feature may stall early next week, and increase heavy rain chances again across portions of the central Gulf Coast. 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. Santorelli/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 $$