Extended Forecast Discussion NWS Weather Prediction Center College Park MD 231 AM EDT Thu Apr 21 2022 Valid 12Z Sun Apr 24 2022 - 12Z Thu Apr 28 2022 ...Significant late season winter storm this weekend along with potentially heavy rainfall over portions of the Southern Plains and Mid-MS River Valley... ...Weather Pattern Overview... An amplified flow pattern is expected to start the period as the Northern Plains deep low lifts into Canada while a strong Southeast ridge extends northward through much of the eastern U.S.. The associated trailing cold front southward could bring a localized heavy rainfall threat Sunday into Monday over portions of the Southern Plains to the Ozarks and Mid Mississippi Valley. By Tuesday-Wednesday, gradual progression of the mean pattern will bring moderate upper troughing to the East, a ridge to the Rockies/Plains, and a trough into the eastern Pacific/West Coast. Much below normal temperatures may persist for a while over the far northern parts of the Plains while well above normal readings are possible over a majority of the eastern half of the country through the weekend. ...Model Guidance Evaluation... This forecast cycle the model agreement remains fairly clustered and agreeable aside from the CMC and to some degree the UKMET which were slower with the progression of the trough axis moving from the northern tier toward the Northeast. The ECMWF continued to be the best proxy through the period as the GFS was on the faster side of the model spread but overall the GFS/ECMWF show fairly good agreement through much of the forecast period such that higher weights of the two were included in the forecast blend this cycle. How the northeast closed low evolves mid to late week is still uncertain and the timing of the next system in the Northwest has continued uncertainty but through day 6-7, the deterministic runs offered enough value to be considered. To maintain some continuity, the ECENS/GEFS means were included days 5-7. ...Sensible Weather/Threats... The strong/significant winter storm affecting the Northern Plains will be continuing at the start of the medium range with the surface low likely to be centered across northern Minnesota. Wrap around precipitation underneath the closed low will likely continue snow showers and with a strong/tight pressure gradient, strong winds will likely continue blowing snow and reduced visibility at times. Conditions improve by early next week as the low weakens more into southern Canada. Meanwhile, further south, the trailing cold front slows and stalls over portions of the Southern Plains to Mid-Mississippi River Valley. Southerly flow ahead of it will draw up warm, moist air that intersects the boundary. An increasing low level jet Sunday night into Monday morning should focus a few mesoscale convective systems that have the potential to train and repeat over the same areas. The latest forecast guidance suggests potential for multi-inch totals during the Day 4 period (ending 12Z Monday April 25) across an area from northeastern Texas through eastern Oklahoma, western/northwest Arkansas into southern/southwest Missouri. The Day 4 Excessive Rainfall Outlook Slight Risk was maintained this cycle with minor adjustments based on the latest model trends which showed a nudge to the south/southeast for the heavy rain axis. Stream flows and precipitation anomalies are above normal for much of the Slight Risk area due to recent heavy rainfall and there is potential for additional rainfall leading up to Day 4. Guidance is still in the process of resolving the timing and wave details of the surface front so changes in the most likely coverage and magnitude of rainfall totals are certainly possible. The front then begins to accelerate with a progressive and amplified trough axis swinging through - this will spread lighter rainfall across much of the eastern U.S. during the Tuesday through Wednesday period. Generally unsettled weather but light precipitation will spread across the northern portions of the Pacific Northwest next week as a series of shortwaves move through the flow underneath a closed upper low positioned off British Columbia. Timing and specific details are still uncertain in the lower confidence weather pattern but overall several opportunities for precipitation though at this time nothing looks too significant. The weekend storm system will bring both much above normal and much below normal temperatures to portions of the CONUS Sunday through the middle of next week. Ahead of the system, expect seasonably warm temperatures across the eastern U.S., especially Sunday high temperatures across the eastern Great Lakes where highs could top 20 degrees above normal. Warm temperatures continue Monday but to a lesser degree. The exception to the eastern warmth is for the coastal Northeast areas and perhaps into the Mid-Atlantic where surface high pressure present may keep temperatures on the cooler side. A front meandering to the south could lead to a sharp contrast between cool air to the north and warmth to the south and west, increasing the challenge of temperatures forecasting over the region. The West will see more variable temperatures, with minus 5-15F anomalies over the Intermountain West/Rockies late in the weekend followed by a west-to-east warming trend with increasing coverage of above normal readings. Warmest highs of 10-15F above normal are likely to extend from the Great Basin/Southwest into the central High Plains during Tuesday-Wednesday. At the same time clouds/precipitation ahead of the upper trough nearing the West Coast may bring slightly below normal highs to the Pacific Northwest. Rausch/Taylor 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, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices are at: 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