Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Wed Feb 22 2023 Valid 12Z Sat Feb 25 2023 - 12Z Wed Mar 01 2023 ...Major Northern Tier U.S. winter storm to track away from New England Friday... ...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 will. A significant winter storm will be winding down Friday as the progressive eastern U.S. flow pushes the system offshore the Northeast. Heavy coastal rain and higher elevation/inland snow will spread across parts of California and the Southwest late this week into the weekend as temperatures drop with an upper low tracking southward near the California coast Friday-Saturday and reaching into the Southwest by Sunday. This upper low feature will exit into the south-central U.S. early next week and will be the focus for increasing rain and thunderstorm from the Plains to the Mississippi Valley. There will be potential for severe with this system. Meaningful precipitation will likely continue to the East Coast. Mixed precipitation including ice could be a threat along the rain/snow transition zone draped across portions of the Midwest/Great Lakes. Wintry precipitation may also extend into New England. Behind this system, precipitation will rebound again over the Pacific Northwest/Northern Rockies and then push south into California next weekend into early next week as another system approaches. The amplified pattern will lead to significant temperature extremes on both sides of the spectrum, with above average max/min temperatures over the East and below average max/min temperatures for the West--especially into Friday. ...Guidance/Predictability Assessment... The timing and location of the upper low, initially in the proximity of California, continues to waffle with the latest runs of guidance. Like previously noted, the GFS and GEFS means initially lead on the eastern edge of consensus while the EMCWF has lags behind as it tracks across the Southwest. Once again, these two solutions swap places due to differences in weak shortwave energy arriving from the Pacific (ahead of a stronger amplifying trough). The models and the ensemble means also advertise a fairly strong surface low by Monday, with the majority at least as deep as the 980s mb. Then guidance suggests that a triple point wave should form near New England by next Tuesday. Additionally, toward the tail end of the extended forecast the guidance depicts an upstream trough with above average clustering as it approaches the Northwest. Overall an average of the latest operational models, with a little ensemble mean input late, provided a good intermediate representation of individual systems while offering stable continuity as well. ...Weather/Hazard Highlights... Lingering snow along with gusty winds across the Northeast should be winding down by Friday night/early Saturday morning. The system dropping south near the California coast late this week will bring the potential for multiple feet of snow in some higher elevations across California and Interior West over the course of several days. The flow ahead of the upper low may produce the best focus for enhanced moisture into favored terrain along the southern California coast. Given the potential for at least a couple of inches of rainfall with the potential for runoff, the experimental Day 4 Excessive Rainfall Outlook maintained a Marginal Risk for portions of southern California. The upper low will spread less extreme amounts of rain/higher elevation snow into Arizona and parts of the Rockies. Then expect this system to spread a broad area of precipitation from the Plains through the East. The most likely region for the highest accumulations is the Midwest although some uncertainty persists in specifics given the model differences for timing and track. Since this airmass will not be as chilly as the previous, there may be less coverage of wintry precipitation or at least a potential transition among precipitation types. Probabilities are somewhat higher for enough cold air to be in place for a period of meaningful snow over New England, depending on the details of coastal low development around next Tuesday. 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. Expect another episode of precipitation to arrive over the Pacific Northwest/Northern Rockies by next weekend into early next week, with the best focus for rain and mountain snow shifting into California by next Monday-Tuesday. With the frontal passage colder air will filter in and may lead to daily temperature reading of 10F to 20F below normal highs over New England into Saturday. However 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. From the weekend into next week, the Southwest will tend to see the coldest anomalies for daytime highs within a generally cool pattern for most of the West. 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 Hazards: - Heavy precipitation across portions of California and the Pacific Northwest, Mon-Tue, Feb 27-Feb 28. - Heavy precipitation across portions of California and the Southwest, Fri-Sat, Feb 24-Feb 25. - Heavy precipitation across portions of the Great Lakes, and the Upper Mississippi Valley, Mon, Feb 27. - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, and the Southern Plains, Sun, Feb 26. - Heavy snow across portions of California, the Pacific Northwest, and the Northern Great Basin, Sun-Mon, Feb 26-Feb 27. - Heavy snow across portions of the Central Great Basin, California, and the Southwest, Fri, Feb 24 and Mon, Feb27. - Heavy snow across portions of the Northeast and the Lower Great Lakes, 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. - Much below normal temperatures across portions of the Northern/Central Plains, the Northeast, the Great Basin, the Lower Great Lakes, the Northern/Central Rockies, California, the Upper/Middle Mississippi Valley, and the Pacific Northwest, Fri-Sat, Feb 24-Feb 25. 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