Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Tue Apr 05 2022 Valid 12Z Fri Apr 08 2022 - 12Z Tue Apr 12 2022 ...Overview... Today's guidance is consistent in advertising a dramatic switch in the amplified upper level pattern from late this week into next week, with an initial western ridge/eastern trough ultimately evolving to a western trough/eastern ridge. This evolution will lead to some dramatic temperature changes during the period as much above normal temperatures over the West on Friday trend toward well below normal readings by the first part of next week and chilly temperatures over the eastern half of the country Friday into the weekend rebound to above normal levels by early next week. Meanwhile rain and higher elevation snow will spread over the West and low level Gulf inflow should eventually contribute to rainfall over the Mississippi Valley and vicinity. A showery pattern over the East during Friday-Saturday under the upper trough should give way to drier weather thereafter. ...Guidance Evaluation/Predictability Assessment... 12Z/18Z operational models were in good agreement for most aspects of the forecast during the first half of the period. The main exception was with the 18Z GFS depiction of a questionably strong shortwave (with an embedded upper low) crossing the northern Plains and southern Canada around Sunday. Recently there have been some modest trends toward more height falls reaching across the northern tier and southern Canada, pushing the Plains cold front a little farther southeast, but the 18Z GFS specifics have minimal support from other model/ensemble guidance. The new 00Z GFS shows favorable trends. Consensus still shows an upper low over the Great Lakes as of Friday, followed by uncertainty over exactly how the core of the upper trough will evolve as it lifts out. The updated forecast using an operational model composite kept 18Z GFS weight low enough to minimize the questionable details over the northern Plains by Sunday. From late weekend through next Tuesday the primary focus of the forecast will be the deepening upper trough over the West, with a potential embedded Great Basin upper low originating from energy over the Gulf of Alaska at the start of the period. Recent ECMWF/CMC runs have been fairly consistent with this evolution, as have the ensemble means. The 18Z and 00Z GFS runs look better after the 12Z run was suspiciously slow to bring this energy into the West. Farther east there is some spread for how shortwave energy may round the eastern ridge, with effects on a surface front expected to extend from the Plains into the Great Lakes (and possibly beyond) by day 7 Tuesday. A blend of the 18Z GFS/12Z ECMWF-CMC and 18Z GEFS/ECMWF mean represented the consensus well while accounting for typically increasing detail uncertainty. ...Weather Highlights/Threats... The upper trough amplifying into the West will spread rain and higher elevation snow across northern and central parts of the region, eventually reaching some southern areas late in the period. Best potential for some enhancement beyond light/moderate activity will be over favored terrain in the Cascades late this week into the weekend and then the northern-central Rockies by Sunday-Monday and possibly into Tuesday. Low level upslope flow may add to precipitation totals along the Rockies. Farther east, expect rain to develop over the Mississippi Valley and vicinity during the first half of next week with an increasing flow of Gulf moisture. The main area of organized rainfall with the broad system affecting the East late this week should depart from New England on Friday with the northward progression of a frontal wave. However cold air aloft associated with the upper trough will likely promote areas of diurnally enhanced showers from the Midwest into the northern half to two-thirds of the East into Friday-Saturday. Some precipitation could be in the form of snow between the Midwest and Appalachians. The West will see one more day of very warm to hot temperatures on Friday with highs reaching 15-25F above normal especially from California into the Great Basin, with some daily records for highs/warm lows. Then the upper trough steadily deepening over the region will bring a pronounced cooling trend. Much of the Northwest/northern Rockies may see highs of 10-15F below normal by Sunday and highs of 10-20F below normal should be common over a majority of the West as well as northern High Plains by next Tuesday. Meanwhile the eastern half of the country will trend from mostly below normal temperatures (up to minus 10-20F anomalies) Friday-Saturday to above normal readings (plus 5-15F anomalies) from west to east by next Sunday-Tuesday. 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