Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EST Tue Feb 28 2023 Valid 12Z Fri Mar 3 2023 - 12Z Tue Mar 7 2023 ***Major storm system is expected to produce widespread heavy rain and severe thunderstorms from the interior Gulf Coast sates to the Ohio Valley and Mid-Atlantic, as well as snow for the Great Lakes and New England late this week*** ...Synoptic Overview... The main weather headline going into the end of this week will continue to be the potent low pressure system tracking from Arkansas to the Northeast, with widespread strong thunderstorms, heavy rain, and wintry weather. The storm exits the East Coast early Saturday with surface high pressure building in through Monday. The western U.S. continues to have unsettled conditions as a strong low pressure system drops southward from the Gulf of Alaska and reaches the general vicinity of the Pacific Northwest by Saturday night, and then lingers off the coast whilst slowly weakening. Going into early next week, a new storm system is likely to gather strength across the central and southern Plains ahead of a building western U.S. upper trough. ...Guidance/Predictability Assessment... Models and ensembles generally offer well clustered solutions going into the end of the week, and a GFS/ECMWF blend offered a good forecast starting point for fronts and pressures, although the 12Z CMC/UKMET were a bit farther southwest with the low. Over the past 36 hours of model runs, there has been an overall trend for a slower storm progression, including the latest 00Z ECMWF, so there is still some uncertainty on exact timing. By the end of the forecast period early next week, the synoptic scale agreement is fairly decent for a day 7 forecast with a broad upper low over the West Coast and a broad ridge axis over the Midwest, but greater model differences exist across the Great Lakes and Northeast, so the use of the ensemble means was increased to about 50% by this time. ...Weather/Hazard Highlights... The storm system that is currently affecting California is progged to reach the general vicinity of Arkansas/Missouri by Friday morning with a expansive area of moderate to heavy rainfall extending east across much of the Ohio Valley. Strong to severe thunderstorms are a good possibility across portions of the Deep South and extending to the southeast U.S. coast on Friday where favorable kinematic and instability parameters will exist in the warm sector. Farther north, another round of impactful snow is looking more likely from the southern Great Lakes to the interior Northeast, with some locations possibly getting over a foot of snow accumulation by early Saturday. Given the expected strength of the surface low, strong winds will also be a factor to contend with across much of the Midwest and Ohio Valley. A deep upper trough is forecast to evolve over the West this weekend that will increase coastal rain and heavy inland snow from northern California to Washington state. It appears the northern mountains of California and especially the central and northern Sierra will be adding to the already very impressive snow pack, and lighter snow across the central and northern Rockies. In terms of temperatures, much of the southeastern U.S. should have readings of 10-20F above average on Friday in the warm sector of the low pressure system. Readings should return to with 5 degrees of climatological averages by next weekend for most areas east of the Rocky Mountains. The southeast U.S. upper ridge will once again exert its influence across much of the south-central U.S. going into early next week with temperatures easily 5-15 degrees above early March levels along with increasing humidity levels near the Gulf Coast. The West will continue to feel like the middle of January through the weekend with the Intermountain West and Rocky Mountains consistently having highs on the order of 10-20F below normal, which will equate to highs in the 20s and 30s for most areas north of the Utah/Arizona border. 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