Extended Forecast Discussion NWS Weather Prediction Center College Park MD 330 PM EDT Mon Apr 11 2022 Valid 12Z Thu Apr 14 2022 - 12Z Mon Apr 18 2022 ...Overview... A strong springtime low pressure system will depart from the Upper Midwest as the period begins Thursday, with the attendant cold front sliding through the East. Behind this storm, expect lower amplitude mean flow aloft across the lower 48. Guidance generally shows a shortwave progressing into/through the West during the weekend and into the Plains/Mississippi Valley by early next week. This feature may produce another round of precipitation over the northern and eastern part of the country. Although there is some agreement with the large scale pattern, there is still plenty of uncertainty with respect to specific system/precipitation details all the way from the West Coast into the East. ...Guidance Evaluation/Predictability Assessment... The first half of the updated forecast reflected a composite of 00Z/06Z model guidance. This tilted the blend somewhat slower than the GFS for the entire sequence of northern stream features: low pressure and supporting dynamics reaching the Pacific Northwest on Thursday, the system departing from the Upper Midwest, and a weak wave that may track offshore New England. This also provided an intermediate (though slower than prior consensus) timing of the next Pacific system reaching the West by Saturday. Guidance spread for both West Coast systems would suggest below average confidence in any specific solution. Toward Sunday-Monday the 00Z CMC continues to be a fast/flat extreme with upper flow over the lower 48, requiring phasing out its contribution. The new 12Z CMC fits the consensus better. Versus the flatter 00Z GEFS run, the 06Z GEFS mean made a notable trend toward the western ridge and Plains or east-central U.S. trough depicted in the 00Z ECMWF/CMC means. ECMWF runs fall into this template but it remains to be seen if an embedded deep closed low will evolve. GFS runs have tended to lean a bit on the flatter side. Meanwhile 06Z/12Z GFS runs are somewhat south/southeast of consensus for the trough/upper low reaching the eastern Pacific by next Monday. These considerations led to placing the greatest weight on the ensemble means and 00Z ECMWF late in the period, reflecting the dominant guidance cluster while toning down ECMWF specifics. ...Weather Highlights/Threats... Some lingering snow is possible across the Upper Midwest at the start of Thursday, but the heaviest should be rapidly coming to an end as the deep low departs into Canada. However gusty winds are likely to continue into Friday with blowing and drifting of snow and possible hazardous travel conditions. The storm's associated cold front pushing through the East Thursday into Friday will bring areas of locally moderate to heavy rainfall. The best chance for heavier totals should be across parts of the Southeast where the better moisture and instability will be present. Rainfall across the Southeast could linger into the weekend as the western edge of the boundary stalls and then tries to lift north as a warm front before weakening ahead of another approaching front. Out West, a couple systems may bring rain/mountain snow to parts of the Pacific Northwest and California into the northern Rockies late this week into the weekend. Some of the activity from the West Coast into the Cascades could be moderate to heavy but there is considerable uncertainty over specifics of each system, so confidence is lower than average for determining coverage/timing of the most significant precipitation. Moisture should spread east beyond the Rockies by next Sunday-Monday as low pressure/fronts reach the central/eastern U.S. At least some precipitation across the northern tier may be in the form of snow while rainfall coverage/intensity over the East will depend on currently uncertain system details. The central Rockies/High Plains could see a brief period of strong winds around Sunday with system passage. Expect the core of below normal temperatures to persist across the northern High Plains into early next week, with daytime highs generally 20-30F below normal. Locally colder readings (especially for daytime highs) are possible late this week when some lingering daily records for lows/cold highs are possible. Over the West, Thursday-Saturday will feature chilly readings over the northern half of the region (minus 10-15F anomalies for highs) and closer to normal temperatures farther south. An upper ridge building over the region by the start of next week should bring northern locations toward normal and southern areas moderately above normal. Above normal temperatures along the Eastern Seaboard on Thursday should return to near normal next weekend. The system potentially reaching the East by next Monday could draw some of the chilly northern Plains air southward and eastward behind it, with expanding coverage of minus 10-20F anomalies. Rausch/Santorelli 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 precipitation across portions of California and the Pacific Northwest, Thu-Sat, Apr 14-Apr 16. - Heavy snow across portions of the Upper Mississippi Valley and the Northern Plains, Thu, Apr 14. - Flooding possible across portions of the Upper Mississippi Valley and the Northern Plains. - Flooding occurring or imminent across portions of the Southeast and the Middle Mississippi Valley. - Flooding likely across portions of the Southeast. - High winds across portions of the Southern Rockies, the Central Rockies, the Southern Plains, and the Central Plains, Sun, Apr 17. - High winds across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Thu-Fri, Apr 14-Apr 15. - Much below normal temperatures across portions of the Central Rockies, the Central Plains, the Northern Plains, and the Northern Rockies, Thu-Mon, Apr 14-Apr 18. 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