Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Sun Feb 26 2023 Valid 12Z Wed Mar 01 2023 - 12Z Sun Mar 05 2023 ...A series of active winter storms to threaten the West and a late week storm offers a heavy rain/severe weather threat across the southern to eastern states along with a snow/ice threat from the cental Plains/Midwest to the Northeastern states... ...Synoptic Overview... It remains the case that the month of March is expected to begin like a lion across much of the south-central U.S. as a potent southern stream disturbance generates a well defined surface low over the Southern Plains on Thursday, and then is forecast to track across the Mid-South and then exit the East Coast Friday night. A weaker lead disturbance is expected across the Northeast U.S. prior to this event on Thursday. Surface high pressure then builds across the Eastern U.S. in time for the weekend. Meanwhile, the West Coast region remains active with another low pressure system dropping south from the Gulf of Alaska by Saturday, and surface cyclogenesis is once again possible over the western High Plains going into next Sunday. ...Guidance/Predictability Assessment... Models and ensembles generally offer well clustered solutions into Wednesday/Thursday and a composite seems to provide a good forecast starting point along with the National Blend of Models. The larger scale pattern evolution seems well forecast into longer time frames as well from the Pacific into the West, but still offers increased forecast spread with ejecting and potentially significant system energies and main weather focus across the east-central to eastern U.S., albeit with less forecast spread than yesterday. Recent GFS runs seem a bit of an outlier with the northern shift of main system and weather focus, but even the ECMWF and other guidance continues to overall shift partially in that direction. Overall, the WPC product suite was mainly derived from the 00 UTC ECMWF and GEFS/ECMWF ensemble means along with the National Blend of Models to account for recent trends closer toward the middle of the overall forecast envelope. ...Weather/Hazard Highlights... The western U.S. will continue to remain unsettled/cold going into midweek as the upper trough rebuilds, with heavy snow likely over the Four Corners states while snowfall intensity begins to wane across the Sierra as the surface low tracks inland. High winds are also a good possibility Thursday north of the evolving frontal boundary over the Central Plains where a strong surface high will be building in from the north. The pattern remains very active for the West later week as well with the digging of subsequent shortwave systems into the region, with a threat for heavy snow for parts of the Northwest. Much deeper upper trough amplification/height falls/cooling to dig into the West next weekend would enhance activity and spread effects/coverage deeper into California and the Intermountain West/Rockies. Downstream, heavy rain and strong to severe thunderstorms, as per SPC, are likely to develop across portions of the South/Mid-South and south-central Appalachians late Wednesday into Thursday, and there is a Marginal Risk area for Day 4 in the excessive rainfall outlook for portions of that area. Additional rainfall is becoming more likely into the end of the week, and some of this may be heavy at times from the Mid-South/South through the Appalachians/Mid-Atlantic where the best forcing for ascent is likely to reside with approach of a dynamic southern stream system whose lead deep Gulf moisture inflow via a strong low level jet may support repeat and training of cells. The potential exists for a couple inches of rainfall going into Friday, and a new "Slight Risk" area for excessive rainfall is now warranted for the Day 5 period to address the growing threat given moist soils from recent/upcoming activity. There is also a growing guidance signal supporting a swath of heavy snow/ice on the northern periphery of the overall/expanding precipitation shield from the central Plains through the Midwest to especially the north-central Appalachians/Mid-Atlantic and Northeast where amounts would be further enhanced with development of well organized inland low and eventual deep coastal storm to further monitor for precise axis/track. In terms of temperatures, much of the central/eastern U.S. should have readings of 10-20F above normal through Thursday, and potentially up to 25 degrees above normal on Wednesday across the Ohio Valley. Readings should return to with 5 degrees of climatological averages by next weekend for most areas east of the Rocky Mountains. The West will see a persistent cool pattern through the entire week with the Intermountain West and Rocky Mountains most consistently having highs on the order of 10-20F below normal, but nothing all that extreme in terms of arctic blasts is currently expected, with the exception of some 10s for highs across North Dakota and Minnesota Wednesday and Thursday. Hamrick/Schichtel 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