Extended Forecast Discussion NWS Weather Prediction Center College Park MD 425 PM EST Tue Mar 08 2022 Valid 12Z Fri Mar 11 2022 - 12Z Tue Mar 15 2022 ...Winter storm threats for parts of the Mid-South to the interior Northeast Friday-Saturday... ...Heavy rainfall likely across portions of the Southeast on Friday... ...Overview... A potent shortwave in the southern Rockies and a northern stream shortwave through the Midwest early Friday will combine to support strong cyclogenesis into the Eastern U.S. by Saturday. This classic spring system will feature snow and cold to the north/northwest of the surface low, and warm/wet conditions ahead of the cold front. Upper flow should then become quasi-zonal Sunday-Monday with a weak shortwave into the Northwest, though may amplify with time as it reaches the East on Tuesday. The next shortwave should reach the Pacific Northwest by next Tuesday as well. ...Guidance Evaluation/Predictability Assessment... The latest runs of the models continue to gain confidence with the melding of the two streams to produce a winter storm system that will impact the central and eastern U.S. Friday into Saturday. There remains some timing differences with the passage of the cold front which is being reflected in the placement of the QPF and the expected amounts. The GFS has isolated maximums focused on Gulf side of Florida, while others have streaks of higher amounts across northern/northeast Florida and into the Carolinas. As previously noted, GFS had been running faster but it (along with the UKMET) are now in within the cluster of acceptable guidance. WPC continued to favor a slightly slower, yet progressive evolution for this feature which consisted of a blend of the 00Z ECWMF/CMC/UKMET and 06/00Z GFS through the weekend/early next week before including increasing weights of the ECWMF ensemble mean and GEFS mean for the remainder of the forecast. After the exit of the eastern U.S. system the models are struggling a bit with the quasi-zonal flow over western half of the country. The Pacific Northwest will have an increase in precipitation as shortwave energy tracks through. Inclusion of the means for the latter half of the forecast helps to reduce the noise and uncertainty. These are details that will take until the short range period to fully resolve. So it's hard to throw any solution off the table at this point. ...Weather Highlights/Threats... Deep moisture drawn northward up the Southeast/Mid-Atlantic states will aid in sustaining showers and thunderstorms near the frontal boundary over the region. There will be periods of moderate to heavy rainfall, especially for portions of Florida and southeast Georgia. This boundary should finally become absorbed/pushed east/lift northward with the strong cold front on Saturday though. Rainfall will come in waves over the Southeast, some of which could be heavy and flooding/flash flooding may be a threat especially where multiple rounds of convection train over the same areas and combined with heavy rainfall the previous day in the same region. Given this potential, the WPC day 4 (Friday) newly experimental excessive rainfall outlook highlights a slight risk area from the Florida Big Bend to southeast Georgia. Cold air pouring into the Central U.S. behind the developing storm system into Friday will support rain changing to snow behind the front Friday evening, with accumulations possible as far south as the lower Mississippi Valley. The central low pressure associated with this system is expected to deepen rapidly over the Northeast, which may allow for areas of heavy snowfall for the Great Lakes and interior Northeast. The arctic airmass behind the front will bring daytime highs 20-30+ degrees below normal as far south as Texas on Friday. Overnight lows across the northern Plains and in higher elevations of the Rockies are likely to be near or below zero for many locations. Modifying some with time, the cold air will shift into the Midwest on Saturday and the Eastern U.S. on Sunday following the frontal passage (with above normal temps ahead of it). Even for parts of northern Florida and the Southeast, low temperatures Sunday morning could be near or below freezing with record lows possible in some locations. By next week, parts of the West and central U.S. may see moderately above normal temperatures as periodic upper ridging slides through. Campbell/Santorelli Hazards: - Heavy snow across much of the interior Northeast, the upper Ohio Valley and nearby Appalachians, Sat, Mar 12. - Heavy precipitation across the higher elevations of the Pacific Northwest, Sat-Tue, Mar 12-Mar 15. - Heavy rain across the lower elevations of the Pacific Northwest into northwestern California, Sun-Mon, Mar 13-Mar 14. - Heavy precipitation across portions of the interior Mid-Atlantic into New England, Sat, Mar 12. - Heavy rain across portions of the Southeast and the Mid-Atlantic, Fri-Sat, Mar 11-Mar 12. - Heavy rain across portions of southeastern New England and southern/Downeast Maine, Sat, Mar 12. - Heavy snow across portions of the northern Rockies, Sun, Mar 13. - High winds across much of the Northeast into the Mid-Atlantic, Sat-Sun, Mar 12-Mar 13. - Severe weather across portions of the Southeast, Fri, Mar 11. - Flooding possible across portions of the Ohio Valley. - Flooding occurring or imminent across portions of the Ohio/Tennessee Valley. - Much below normal temperatures through the Great Plains and into the central/southern Rockies, Fri-Sat, Mar 11-Mar 12. - Much below normal temperatures from the Great Lakes and Ohio Valley down through the Deep South, southern Appalachians, and much of the Southeast, Sat-Sun, Mar 12-Mar 13. 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 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml