Extended Forecast Discussion NWS Weather Prediction Center College Park MD 427 PM EDT Tue Apr 19 2022 Valid 12Z Fri Apr 22 2022 - 12Z Tue Apr 26 2022 ...Weekend storm likely to bring heavy precipitation/strong winds to the Northern Plains and a heavy rainfall threat to some areas farther south... ...Weather Pattern Overview... The upper level pattern over the continental U.S. will become more amplified by the end of the week and into the weekend as a large synoptic scale Pacific trough progresses through the West, supporting surface cyclogenesis across the High Plains by Friday night. An embedded upper low should track northeastward through the Northern Plains during the weekend, bringing strong low pressure through the this region and the Upper Midwest. This storm should produce significant snowfall over some areas in the cold sector along with varying intensity of rainfall to the east as well as potentially heavy rainfall farther south over the Plains/Mississippi Valley along the trailing wavy front. Meanwhile, a downstream upper ridge axis building over the eastern U.S. should lead to a considerable warming trend over some areas for the weekend but cool high pressure may persist for a time over the Northeast/northern Mid-Atlantic. Another Pacific upper trough should approach the northwestern U.S. by the beginning of next week. ...Model Guidance Evaluation... The updated forecast utilized a blend of 00Z/06Z operational models early and then trended to a combination of models and 06Z GEFS/00Z ECMWF means. This approach yielded only typical run-to-run adjustments through most of the period. By early next week, most guidance has displayed a trend toward a slower/more elongated upper trough behind the strong northern tier storm--resulting in a slower and more wavy trailing surface front that was reflected in the update. 06Z/12Z GFS runs have gone back to a faster progression though. As for the strong northern tier storm, there is still a fair degree of timing spread with the GFS fastest and UKMET/CMC slowest. Multi-run trends show the GFS/GEFS coming back to the ECMWF/ECMWF mean so at the very least the fast side of the spread appears less likely. Thus far trends have not been pronounced enough to include more than minority weight of the UKMET/CMC. Some track spread is also evident and forecast weather over some areas will be very sensitive to specifics. For the upper trough nearing the West Coast by late in the period, models/ensembles are good at depicting the overall feature in principle but vary with some details. The 12Z GFS is particularly strong with some leading shortwave energy reaching the West by late Sunday-Monday. This ultimately affects its progression of the central U.S. trough. ...Sensible Weather/Threats... Confidence continues to improve for the general forecast of a strong storm emerging from the Rockies and tracking into the Dakotas/Upper Midwest late this week into the weekend. Best potential for significant snowfall will be from favored terrain within the Great Basin/north-central Rockies and then through eastern Montana/northeastern Wyoming and the western half of North Dakota (to the immediate west of the surface low track). Strong winds around the low could produce blizzard conditions for some areas if model forecasts persist. There is still some uncertainty for the track and speed of the storm, so continue to monitor forecasts for refinements to the details. Locations in warmer air to the east may see rainfall of varying intensity, including some pockets of locally moderate to heavy activity. The wavy cold front extending southward from the storm may provide a focus for heavy showers and thunderstorms from Sunday into the early part of the next work week, with added contribution from lingering upper trough energy and input from Gulf moisture advecting northward ahead of the front. This will likely be in the form of multiple mesoscale convective complexes with repeating rounds of convection/training, and some strong to severe storms are also possible. Currently the best potential for highest rainfall totals exists from parts of the southern half of the Plains into or a bit south of the Middle Mississippi Valley. The upper trough approaching the West late in the period should bring light to moderate precipitation to the Pacific Northwest early next week. Expect unseasonably cold temperatures to persist over far northern parts of the Plains through the period with North Dakota in particular seeing highs 15-30F below normal for multiple days. The West will see more variable temperatures, with minus 5-15F anomalies late week into the weekend but followed by a west-to-east moderating trend with increasing coverage of above normal readings early next week. Clouds/precipitation may bring below normal highs to the Pacific Northwest next Tuesday though. A major warming trend is likely for the central/southern Plains on Friday and then much of the eastern half of the nation going into the weekend. Central Plains locations could see highs up to 20-30F above normal on Friday. Plus 10-20F anomalies should be more common farther east. Also humidity levels should increase in response to deep southerly flow ahead of the central U.S. storm system. One exception to the eastern warmth should be over the Northeast/northern Mid-Atlantic where cool surface high pressure/ridging may prevail for multiple days. A back door front expected to settle over the Mid-Atlantic could provide a sharp contrast between cool air to the north and warmth to the south and west. Rausch/Hamrick Hazards: - Heavy precipitation across portions of northwestern Wyoming, southwestern Montana, and the Wasatch of Utah, Fri, Apr 22. - Heavy precipitation across portions of the northern Plains into northern Minnesota, Fri-Sat, Apr 22-Apr 23. - Heavy snow across portions of the northern High Plains, the Black Hills, and into nearby Rockies, Fri-Sat, Apr 22-Apr 23. - Heavy rain from across portions of the central and southern Plains into the mid-Mississippi Valley and the Midwest, Sun-Mon, Apr 24-Apr 25. - Heavy rain across portions of the upper Mississippi Valley, Fri-Sat, Apr 22-Apr 23. - Severe weather across portions of central to northern Plains, Fri, Apr 22. - Flooding possible across portions of the Southeast. - Flooding occurring or imminent across portions of the lower Savannah River and near/west of Jackson, Mississippi. - Flooding likely across portions of central South Carolina. - High winds across portions of the central and southern Rockies into central and southern High Plains, Fri, Apr 22. - High winds across portions of the northern High Plains and into the northern Rockies, Fri-Sun, Apr 22-Apr 24. - Much below normal temperatures across portions of the northern Plains, Sat-Tue, Apr 23-Apr 26. - Enhanced wildfire risk across portions of the central and southern Rockies into the nearby High Plains, Fri, Apr 22. - Enhanced wildfire risk across portions of the southern High Plains into the foothills of the southern Rockies, Sat, Apr 23. 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