Extended Forecast Discussion NWS Weather Prediction Center College Park MD 334 PM EST Wed Feb 22 2023 Valid 12Z Sat Feb 25 2023 - 12Z Wed Mar 01 2023 ...Significant storm system to track from the Southwest into the Northeast from late this week into early next week... ...Record cold possible in the West while record warmth is possible in the Southeast... ...Overview... An amplified mean trough aloft will remain present near the West Coast and strong progressive flow downstream, between an upper low north of Hudson Bay and an upper ridge gradually sagging south from southern Florida to Cuba. Associated with the first individual West Coast system, an upper low initially just offshore California and then pushing inland, heavy coastal rain and higher elevation/inland snow will continue across parts of California and the Southwest into the weekend. The upper low feature will exit into the south-central U.S. early next week and will be the focus for increasing rain and thunderstorms from the Plains to the Mississippi Valley. Severe weather is also possible with this system. Meaningful precipitation will likely continue to the East Coast. To the north of the rain area, snow and mixed precipitation including ice could be a threat over the northern Midwest/Great Lakes. Wintry precipitation should also extend into New England, with perhaps greater snow potential given model signals for a coastal/offshore wave to form. Behind this system, precipitation will rebound again over the Pacific Northwest/Northern Rockies and then push south into California and other parts of the West next weekend into next week as a weakening leading front and a trailing stronger system arrive. The amplified pattern will lead to significant temperature extremes on both sides of the spectrum, with the West tending to be on the chilly side and the southern two-thirds of the central/eastern U.S. most consistently seeing above average readings. ...Guidance/Predictability Assessment... The two dominant features of interest continue to be the storm tracking from near California through the northeast and then the next system that amplifies into the longer-term West Coast mean trough. There are continued timing differences with the ejection of the first system but overall today's solutions are clustered better than they were 24 hours ago, especially by way of the GFS trending faster over the Plains. GFS runs are still waffling in consecutive 6-hourly runs with the 00Z and new 12Z runs a tad slower than the guidance average and the 06Z run slightly fast. The 00Z UKMET was a notable slow extreme due to being slow with the upstream weak shortwave reaching the West Coast on Sunday. Model guidance still suggests the system will be quite strong over the Midwest/Great Lakes, with operational runs tending to reach as deep as 975-985 mb around Monday. Depending on exact track and depth, the system as currently forecast (and at least plausible given the sharp and negatively tilted nature of the upper system) could challenge some February sea level pressure records at select locations. Then models/ensembles offer a good signal that a triple point low will form over/near New England and then trend offshore, with the 12Z GFS/CMC trending somewhat to the ECMWF in principle (but not quite as slow by Wednesday). For the next upper trough reaching the West Coast, the 00Z ECMWF and 00Z-12Z GFS/GEFS align in their historically respective slower and faster roles. Latest UKMET/CMC runs side more toward the ECMWF/ECMWF mean. A blend reflecting this proportion of guidance provides a good starting point in light of typical predictability/model error 6-7 days out in time. With support from the means in principle, a composite of the 00Z ECMWF/CMC and average of the 00Z/06Z GFS provided a good starting point for depicting the majority ideas of significant features through the period. ...Weather/Hazard Highlights... The upper low entering the Southwest from just offshore California this weekend will produce additional heavy snow over parts of California and the Southwest, along with continued heavy rain along the southern California coast after heavier activity on Friday. The experimental Day 4 Excessive Rainfall Outlook maintains a Marginal Risk with this area of heavy rainfall potential along the southern California coast. Then expect this system to spread a broad area of precipitation from the Plains through the East. The most likely region for heaviest rainfall extends across parts of the Central Plains and Midwest. With latest guidance converging on this area for anomalous moisture (up to plus 3-3.5 standard deviations in the ensemble means and 4+ sdevs in the operational models) and some instability to allow for potentially heavy short-term rainfall rates, the experimental Day 5 Excessive Rainfall Outlook will likely introduce a Marginal Risk area from a sliver of northern Oklahoma into northern-northeastern Iowa. Since this airmass will not be as chilly as with the previous storm, there may be less coverage of wintry precipitation or at least a potential transition among precipitation types in the Upper Midwest/Great Lakes. There may be some issues for locations receiving snow from the previous system and rain from this one. Meanwhile probabilities for significant snow are somewhat higher over New England, depending on the details of coastal/offshore low development around next Tuesday. Current model trends support such an offshore low that would hold colder air/snow over parts of New England. This system may produce some very strong and gusty winds through its existence, from California and the Southwest into the High Plains and through the eastern half of the country. A weakening front should bring some light to moderate rain/mountain snow into the Northwest during the weekend. A stronger system approaching/arriving from Sunday into next week will likely bring heavier precipitation to the West Coast region, with highest totals expected along the central West Coast and the Sierra Nevada. A broader area of precipitation should spread farther inland across the West. Cold high pressure reaching New England behind a late-week front may lead to temperatures of 10F to 20F below normal highs over the region on Saturday. Expect a gradual return toward normal thereafter. Meanwhile the strong upper high over southern Florida/Cuba will keep temperatures warm over the South with some record highs possibly lingering into early next week. The system expected to affect the central/eastern U.S. early next week may bring another northward surge of unseasonably warm temperatures (plus 10F to 25F anomalies) to areas east of the Rockies. The West will see a persistent cool pattern from the weekend through the first half of next week, with locations over California and the Southwest/Great Basin most likely to see highs of 10F or more below normal on one or more days. Rausch/Campbell 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 - Heavy precipitation across portions of California and the Pacific Northwest, Sun-Tue, Feb 26-Feb 28. - Heavy precipitation across portions of the Great Lakes and the Upper Mississippi Valley, Mon, Feb 27. - Heavy precipitation across portions of the the Northeast and the Great Lakes, Mon-Tue, Feb 27-Feb 28. - Heavy rain across portions of California, Sat, Feb 25. - Heavy rain across portions of the Central Plains, the Northern Plains, the Great Lakes, the Southern Plains, and the Ohio Valley, Sun-Mon, Feb 26-Feb 27. - Heavy snow across portions of California, the Central Great Basin, the Pacific Northwest, the Northern Great Basin, and the Southwest, Sun-Tue, Feb 26-Feb 28. - Heavy snow across portions of the Central Great Basin, California, and the Southwest, Sat, Feb 25. - Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Sun, Feb 26. - Heavy snow across portions of the Central Rockies, the Northeast, the Central Great Basin, the Northern Rockies, and the Northern Great Basin, Mon-Tue, Feb 27-Feb 28. - Severe weather across portions of the Central Plains and the Southern Plains, Sun, Feb 26. - Flooding possible across portions of the Middle Mississippi Valley, the Great Lakes, and the Ohio Valley. - Flooding occurring or imminent across portions of the Lower Mississippi Valley. - High winds across portions of the Southern Rockies, the Central Plains, the Southern Plains, and the Southwest, Sun, Feb 26. - High winds across portions of the Great Lakes and the Ohio Valley, Mon-Tue, Feb 27-Feb 28. - Much below normal temperatures across portions of California and the Southwest, Sat-Tue, Feb 25-Feb 28. - Much below normal temperatures across portions of the Northeast, Sat, Feb 25. - Much below normal temperatures across portions of the Southwest, Sun, Feb 26. 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