Extended Forecast Discussion NWS Weather Prediction Center College Park MD 206 AM EST Thu Feb 23 2023 Valid 12Z Sun Feb 26 2023 - 12Z Thu Mar 02 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. There will be potential for severe thunderstorms to develop along and ahead of this system along with meaningful precipitation for the East Coast. Snow, mixed precipitation and possibly ice is expected on the northern periphery of the precipitation shield from northern portions of the Midwest and the Great Lakes region with mainly snow extending to New England. There may be a greater snow potential given model signals for a coastal/offshore wave to form. In the wake of this system another round of precipitation will overspread the Northwest, Intermountain West, Northern Rockies, California and parts of the Great Basin 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 storm tracking from near California through the Northeast and then the next system that amplifies into the longer-term West Coast mean trough will be the main features for the extended period. The timing differences on the ejection of the first system remains unresolved but the guidance has a decent handle on it. The UKMET remains the slower extreme of the global guidance therefore was not utilized while the GFS is persistently faster, especially over the Plains. Consensus favors a quite strong low/trough 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. The models/ensembles continue to support that a triple point low will form over/near New England and then trend offshore.The latest WPC preferred blend leaned heavier on the ECWMF, but also the CMC and 18Z/12Z runs of the GFS. This maintained continuity from the previous forecast. ...Weather/Hazard Highlights... Heavy snow will spread across portions of California and Southwest this weekend as an upper low enter the Southwest. Additionally, the southern California coast will continue to have heavy rain. As this system moves eastward the broad area of precipitation will follow suite, spreading from the Plains to the East. Conditions are favorable for the heaviest rainfall to occur over the Central Plains and the Midwest, where copious amounts of 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. WPC has an experimental Marginal Risk identified for the Day 4 period. Most of the precipitation will likely fall in liquid form as the airmass will not be as chilly as the previous system. There will be 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. Light to moderate mountain snow will spread across the Northwest this weekend as a weakening front approaches. However, a stronger system approaching the West Coast late weekend/early 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 for the beginning of the extended but will trend back toward seasonal average. Meanwhile the strong upper high over southern Florida/Cuba will maintain warmer temperatures 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. Campbell/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 - 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