Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Wed Apr 06 2022 Valid 12Z Sat Apr 09 2022 - 12Z Wed Apr 13 2022 ...Overview... Guidance continues to show an amplified but reasonably progressive upper pattern from the weekend into the middle of next week. A deepening trough over the West will spread rain/higher elevation snow and well below normal temperatures across the region, with the colder air and rain/snow reaching into parts of the northern and central Plains by early-mid week. Ahead of the upper trough and associated wavy surface front, moisture flowing northward from the Gulf of Mexico should promote rainfall of varying intensity over the eastern Plains/Mississippi Valley next week. Meanwhile a deep upper trough crossing the East during the weekend will produce cool weather with showers over some areas. An upper ridge moving into the region from the central U.S. will bring warmer temperatures to the eastern half of the country after the weekend. ...Guidance Evaluation/Predictability Assessment... Confidence remains fairly good for the overall pattern evolution and most aspects of the departing eastern trough. However in some respects the forecast for details of the western trough may be getting more complicated. Timing/evolution differences for energy initially over the Alaska Panhandle/Gulf of Alaska and forecast to contribute to a possible upper low within the western trough have persisted over multiple runs, with some influence on leading shortwave energy crossing the northern tier U.S. and southern Canada. Now models/ensembles are also diverging with specifics of flow over the northeastern Pacific/northwestern North America by around Monday and this issue has downstream effects on the western trough by late in the period. Looking at the 12Z/18Z guidance contributing to the updated forecast, the 18Z GFS generally trended closer to the model/ensemble mean average versus the 12Z run for leading flow across the northern tier U.S./southern Canada and the upper trough digging into the West. Guidance has become split for timing the arrival of Gulf of Alaska energy that could form a closed low as the 12Z UKMET sided with the slower GFS while the ECMWF/CMC were faster. Toward the end of the period next Wednesday the ensemble means supported an upper trough progression (its axis reaching the Rockies/Plains) near an average of the 18Z GFS and somewhat faster 12Z ECMWF. The 12Z CMC had similar timing but with an upper low track well south of other guidance. Plus its broad upper low centered over the Alaska Panhandle did not have much support. A blend of the 18Z GFS and 12Z ECMWF/CMC/UKMET early followed by trending to the 18Z GFS/12Z ECMWF with their respective ensemble means provided the most reasonable depiction and continuity for the western-central U.S. evolution as well as for the departing eastern U.S. upper trough. The most dramatic change from the new 00Z guidance is in the CMC. First it has trended slower with the Gulf of Alaska energy--joining the GFS/UKMET. This cluster would have a much stronger surface system reaching somewhere along the northern half of the West Coast than previously forecast. Then upstream changes in the CMC lead to a much faster and northward path for the core of the western upper trough, straying eastward beyond other solutions over the Plains. In contrast the 00Z ECMWF has maintained remarkable continuity given the differences and/or changes in the other models. It did trend just a bit slower, leading to a day 7 Wednesday trough progression that now matches the means. ...Weather Highlights/Threats... The upper trough currently expected to amplify into the West and approach or reach the Plains by next Wednesday will first bring rain and higher elevation snow into the Pacific Northwest and northern Rockies during the weekend. Most totals should be in the light to moderate range though some localized enhancement is possible over favored terrain. A more favorable combination of upper trough dynamics and low level upslope flow should increase precipitation over the northern-central Rockies and High Plains during the first part of next week, with the High Plains possibly seeing some snow in addition to the Rockies. There are still important uncertainties over the details of the upper trough so confidence is not great in southward extent and amounts of precipitation across central/southern parts of the West--and to some degree over the Rockies/Plains--at this time. There will also be increasing coverage and intensity of rainfall over the eastern Plains/Mississippi Valley with the establishment of moist low level flow from the Gulf of Mexico. Farther east, cold air aloft associated with the upper trough crossing the East during the weekend will promote areas of diurnally enhanced showers from the Ohio Valley/Appalachians into the Northeast especially on Saturday. Some precipitation could be in the form of snow, with the best chances across the peaks of the Central Appalachians in West Virginia. Colder air moving into the West will initially bring highs down to as much as 10-15F below normal over the Northwest/northern Rockies during the weekend. An area of minus 10-20F anomalies for highs should then reach into the Intermountain West, Rockies, and northern-central Plains by next Tuesday-Wednesday. Sunday may provide the best potential for some locations in the Northwest to see max temperatures near or below current record cold highs. Meanwhile the eastern half of the country will trend from mostly below normal temperatures (up to minus 10-20F anomalies Saturday), and potential for a late frost across parts of the southeastern quadrant of the country, to mostly above normal readings (plus 5-15F anomalies) spreading from west to east after the weekend. Rausch 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