Extended Forecast Discussion...amended NWS Weather Prediction Center College Park MD 323 AM EST Mon Feb 27 2023 Valid 12Z Thu Mar 2 2023 - 12Z Mon Mar 6 2023 ***Major storm system is expected to produce widespread heavy rain and severe thunderstorms from the Gulf Coast to the Ohio Valley and Mid-Atlantic, and snow for the Great Lakes and New England late this week*** ...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 Sunday night and Monday. ...Guidance/Predictability Assessment... Models and ensembles generally offer well clustered solutions going into the end of the week, and a GFS/ECMWF/UKMET seems to provide a good forecast starting point for fronts and pressures, although the 12Z CMC was a bit farther southwest with the low developing over Texas, so the 12Z run for fronts/pressures was given less weighting. The 00Z model guidance suite is featured with a stronger GFS solution across the Mid-South and Ohio Valley, and the CMC weaker. There has been an overall northwestward trend with the low and the axis of highest QPF over the past 24 hours, and a little slower trend in the storm system exiting the East Coast. By the end of the forecast period next Monday, the synoptic scale agreement is decent for a day 7 forecast with a broad upper low over the West Coast and a broad ridge axis over the Plains. However, given mesoscale differences, the use of the ensemble means was increased to about 50% by this time. ...Weather/Hazard Highlights... The Pacific Northwest and the northern Rockies will continue to remain rather unsettled and cold going into Thursday as the upper trough rebuilds, with heavy snow likely over the Cascades and northern Idaho. 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. A deeper upper trough evolving over the West next weekend is expected to increase coastal rain and inland snow from northern California to Washington state. The main weather headline will be the increasing potential for heavy rain and strong to severe thunderstorms to develop from the ArkLaTex region to the Ohio Valley on Thursday, and there is a Slight Risk area for Day 4 in the excessive rainfall outlook for portions of that area. Additional rainfall is likely going into Friday from Ohio to Pennsylvania, and moderate to heavy snow from Upstate New York to central/northern New England. Most of this precipitation should exit the East Coast by midday Saturday. In terms of temperatures, much of the southern/eastern U.S. should have readings of 10-20F above normal for the end of the week. 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 weekend with the Intermountain West and Rocky Mountains consistently having highs on the order of 10-20F below normal, but no major Arctic blasts are currently expected. Hamrick 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