Extended Forecast Discussion NWS Weather Prediction Center College Park MD 305 PM EDT Wed Apr 06 2022 Valid 12Z Sat Apr 09 2022 - 12Z Wed Apr 13 2022 ...Overview... An amplified pattern in the medium range will begin with a trough moving out of the East while another trough deepens/gets reinforced and slowly moves eastward in the West during the first part of next week. The latter will spread rain/higher elevation snow and well below normal temperatures across the West, 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. The East should see cool weather with showers over some areas over the weekend, but an upper ridge moving from the central to eastern U.S. will bring warmer temperatures to the eastern half of the country for the workweek. ...Guidance Evaluation/Predictability Assessment... While model agreement and confidence remain good regarding the eastern trough's track eastward this weekend as it departs, and models generally show troughing amplifying and reloading over the West, there remain ample differences among guidance for the evolution of details regarding the western trough. Shortwaves that should be embedded within the trough stem from low predictability areas of the northern Pacific and near Alaska, tempering forecast confidence in any particular solution. Examples of model differences among the 00/06Z models include a narrower trough axis by Sunday in the CMC and UKMET with a hint of ridging on the western side in the Pacific Northwest compared to GFS/ECMWF guidance, as well as the strength and position of shortwaves in the north-central U.S. and digging into the western side of the trough by Monday. With the latter shortwave, models have tended to show a stronger surface reflection just offshore the Pacific Northwest but with varying positions. Into Tuesday and Wednesday, GFS and ECMWF runs continue to show a deeper and slower trough than CMC runs. But GFS runs are more phased than the ECMWF, as the EC has been indicating additional strong energy dropping into the Pacific Northwest by the end of the period. The WPC forecast generally favored the ECMWF overall in terms of the deterministic guidance, considering its persistence and continuity from run to run. The newer 12Z ECMWF has generally kept a similar pattern. Overall the WPC forecast began with a multi-model deterministic blend led by the ECMWF and GFS, but as the period progressed reduced the weighting of operational models other than the ECMWF in favor of the reasonably well clustered (albeit less detailed) EC and GEFS ensemble means to account for the increasing model differences. ...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 springtime 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. Meanwhile in the warm sector, there will 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 before a drier trend over the Eastern Seaboard early next week. 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 10-25F 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. Tate/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