Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Tue Apr 05 2022 Valid 12Z Fri Apr 08 2022 - 12Z Tue Apr 12 2022 ...Overview... The medium range period will see an amplified and reasonably progressive pattern in the upper levels, beginning late week with an upper low/trough tracking through the East before a gradual but dramatic switch to western troughing and eastern ridging through the early part of next week. 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, while chilly temperatures over the eastern half of the country Friday into the weekend rebound to above normal levels by Monday-Tuesday. 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... Recent model guidance continues to show good agreement with the amplified pattern described above, so confidence is reasonably high for the overall pattern, but there are lingering uncertainties with the smaller-scale details. One notable detail difference occurs by early Sunday with shortwave energy within the western trough. There have been some run to run variations with a possible shortwave on the eastern side of the base of the trough around the northern Plains, causing differences in the progression of the northern stream cold front. The 00/06Z guidance cycle indicated support for the eastern shortwave, aside from the UKMET, while the newer 12Z guidance is not as excited about it. These are somewhat small differences for a day 5 forecast, but could be marginally impactful since it affects the cold frontal position, but given the small scale of the feature it may take a while longer to resolve. The western trough is forecast to gradually deepen through day 7/next Tuesday, with a possible embedded upper low over the Great Basin originating from energy over the Gulf of Alaska at the start of the period. The exact evolution of the deepening trough remains uncertain, particularly considering differences with digging energy on the west side of the trough. The ECMWF may be the most consistent of the guidance, while the 12Z CMC trended deeper than its 00Z run but the 12Z GFS trended flatter with the trough's depth due to uncertain shortwave depth and progression. With the overall good agreement especially for the first half of the period, the WPC forecast was based on a multi-model deterministic blend early on, with addition of some EC and GEFS ensemble mean guidance by the latter part of the period given typically increasing detail uncertainty. ...Weather Highlights/Threats... A coastal/triple point low pressure system forming near New England early Friday will support organized rainfall there, which should taper off by Saturday as the low moves away. However, cold air aloft associated with the upper trough will likely promote areas of diurnally enhanced showers from the Midwest/Great Lakes and Ohio/Tennessee Valleys into the Appalachians and Mid-Atlantic/Northeast through especially Saturday. Some precipitation could be in the form of snow, with the best chances across the peaks of the Central Appalachians in West Virginia. Meanwhile, precipitation should begin late this week in the Pacific Northwest and Northern Rockies and spread southeastward into next week underneath and just ahead of the incoming upper trough, eventually reaching California and the Southwest. Lower elevation/coastal rain and higher elevation snow are forecast, with enhancement of totals in higher terrain, first in the Cascades and then into the Rockies early next week as upslope flow may add to precipitation amounts. Precipitation could be in the form of snow even for northern/central parts of the High Plains as well by around Monday-Tuesday, but confidence in the details is lacking at this point. Farther southeast in the warm sector, expect rain to develop over the Mississippi Valley and vicinity during the first half of next week as Gulf moisture inflow increases. 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, with potential for a late frost across parts of the southeastern quadrant of the country, to above normal readings (plus 5-15F anomalies) from west to east by next Sunday-Tuesday. 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 Hazards: - Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Fri-Sun, Apr 8-Apr 10. - Heavy snow across portions of the Central Rockies, the Central Plains, the Central Great Basin, the Northern Plains, and the Northern Rockies, Sun-Tue, Apr 10-Apr 12. - Severe weather across portions of the Central Plains and the Southern Plains, Mon, Apr 11. - Flooding possible across portions of the Great Lakes, the Middle Mississippi Valley, the Southern Plains, the Upper Mississippi Valley, and the Northern Plains. - Flooding likely across portions of the Middle Mississippi Valley. - High winds across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Southern Rockies, the Southern Plains, and the Southwest, Sun-Tue, Apr 10-Apr 12. - Much above normal temperatures across portions of California, the Central Great Basin, the Pacific Northwest, the Northern Great Basin, and the Southwest, Fri, Apr 8. - Much below normal temperatures across portions of the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Fri-Sun, Apr 8-Apr 10. 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