Extended Forecast Discussion NWS Weather Prediction Center College Park MD 415 PM EST Mon Feb 27 2023 Valid 12Z Thu Mar 02 2023 - 12Z Mon Mar 06 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... 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 low pressure system with a rather low central pressure over the Mid-South on Friday. Widespread severe weather can be expected across the Deep South on Friday as heavy rain overspreads the mid-Mississippi Valley to the Ohio Valley Thursday night to Friday, while a wide swath of snow and wintry mix is forecast to extend from the lower Great Lakes through much of New England Friday into early Saturday. Meanwhile, the West Coast remains active with another low pressure system dropping south from the Gulf of Alaska by Saturday, possibly leading to surface cyclogenesis once again over the western High Plains going into Sunday night and Monday. ...Guidance/Predictability Assessment... Models and ensembles generally indicate above average uncertainty with the timing of the rapidly deepening cyclone over the Mid-South and how far north/south the low will track toward the northeastern U.S. late this week. The 00Z CMC and the 00Z UKmet were very slow in this regard. The 00Z ECMWF and the GFS have favored a faster and more northern track. Thereafter, models came into much better agreement with each other for the remainder of the medium-range period. The WPC medium-range forecasts were based on the 00Z EC/EC mean and 06Z GFS/GEFS on Days 3-4, with the rest of the medium-range forecasts based on 40% 00Z EC/EC mean, 40% 06Z GFS/GEFS, and 20% from the 00Z CMC/CMC mean. ...Weather/Hazard Highlights... The main weather headline will likely 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. High winds are also a good possibility Thursday into Friday morning north of the evolving frontal boundary over the central Plains where a strong surface high will be building in from the north as a cyclone deepens rapidly and tracks northeast across the Mid-South. Meanwhile, 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. 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. Across the Northeast U.S., a weaker lead disturbance is expected to bring some snow across northern Maine with rain and inland wintry mix for the rest of New England on Thursday. Surface high pressure will then build across the Eastern U.S. in time for the weekend before wintry precipitation ahead of the rapidly deepening cyclone over the Mid-South moves in later on Friday. 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. Kong/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 Hazards: - Heavy precipitation across portions of California, the Central Great Basin, the Pacific Northwest, and the Southwest, Sat-Sun, Mar 4-Mar 5. - Heavy precipitation across portions of the Northeast, the Central Appalachians, the Middle Mississippi Valley, the Mid-Atlantic, the Upper Mississippi Valley, the Great Lakes, and the Ohio Valley, Thu-Fri, Mar 2-Mar 3. - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southern Plains, and the Ohio Valley, Thu, Mar 2. - Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Thu-Fri, Mar 2-Mar 3. - Heavy snow across portions of the Northeast, the Northern Rockies, and the Northern Great Basin, Thu, Mar 2. - Heavy snow across portions of the Northeast and the Lower Great Lakes, Fri, Mar 3. - Severe weather across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southern Appalachians, the Southeast, and the Southern Plains, Thu, Mar 2. - Severe weather across portions of the Southeast, the Mid-Atlantic, the Southern Appalachians, and the Tennessee Valley, Fri, Mar 3. - Flooding possible across portions of the Middle Mississippi Valley, the Great Lakes, and the Upper Mississippi Valley. - Flooding occurring or imminent across portions of the Lower Mississippi Valley. - Much below normal temperatures across portions of the Central Plains, the Rockies, the Great Basin, the Northern Plains, California, the Pacific Northwest, and the Southwest, Thu-Sat, Mar 2-Mar 4. - Enhanced wildfire risk across portions of the Southern Plains, Thu, Mar 2. 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