Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 PM EST Fri Mar 04 2022 Valid 12Z Mon Mar 07 2022 - 12Z Fri Mar 11 2022 ...Heavy rain potential across the Ohio Valley into Monday... ...Overview... The medium range period begins Monday with broad troughing (with embedded shortwaves) across the central U.S. pushing a cold front into the East. This setup brings a threat for heavy to excessive rainfall across the Ohio Valley, with snow to the north. Shortwaves should weaken in the flow as they progress downstream as heights begin to rise over the East Coast. Out West, a strong ridge over the east Pacific should allow for shortwaves to keep reinforced troughing over the Rockies, which eventually should press east into the Plains by late next week. ...Guidance Evaluation/Predictability Assessment... Reasonably good model agreement continues for the large scale pattern over the last couple of model cycles, but with typical timing and detail differences remaining, some of which could be impactful to sensible weather. There is good consensus for elongated low pressure along the cold front at the beginning of the period Monday, with lingering differences in the exact placement of the surface low or two dependent on shortwave differences. The cold front moving eastward has trended a bit faster compared to the previous forecast as the low tracks quickly across the Northeast. A blend of the deterministic guidance favoring the GFS and ECMWF worked well for this system. Farther west, energy diving south along the West Coast on Monday produces differences that become more notable Tuesday and beyond. Models have been waffling on how much energy is held back across the Southwest Tuesday, with the bulk of 00Z guidance showed a slower track and a possibly closed low compared to the previous cycle, though the 06Z GFS was open and faster. This trend toward a slower/stronger solution was reflected in the WPC 500mb charts. The newer 12Z guidance still shows a bit of spread, with the CMC now among the faster/weaker guidance after the past few runs of it being slow, but overall model consensus is still slower compared to about a day ago. The details of this feature remain uncertain Tuesday and then beyond as it ejects eastward with varied timing--which influences the Gulf of Mexico return flow and timing of rainfall beginning across the southeastern quadrant of the country. Another factor to consider with that is the trough's eastward extent for the latter half of the week, which appears to have trended westward (allowing for higher heights in the East) over the past couple of days, keeping rain chances in the forecast. By midweek through Thursday and Friday, the next shortwave arrives into the Northwest, which should help to reinforce broad troughing over the Rockies which eventually pushes into the Central U.S. by the end of the week. There are some timing differences regarding both the trough axis and the associated surface front and developing low pressure. ECMWF runs have generally been slower than GFS runs, and the WPC forecast for the latter part of the period attempted to take a middle ground approach by phasing in and increasing the proportions of the reasonably agreeable ensemble means, with some inclusion of the deterministic runs for a little added system definition. ...Weather Highlights/Threats... Rain and thunderstorms will be widespread along and ahead of the cold front moving through the eastern U.S. early next week. The axis of the heaviest rain by Monday is forecast from the lower Ohio Valley into the central Appalachians and northern Mid-Atlantic. Flooding and flash flooding are possible particularly in areas that see repeat/training convection and in areas where soils are already wet, and newly experimental Slight Risks of excessive rainfall remain in place for day 4. A swath of wintry precipitation could develop on the north side, with light to moderate amounts possible from into the Great Lakes and interior Northeast. Then by the middle of next week, Gulf moisture could return to the Lower Mississippi Valley and Southeast, but uncertainty remains with respect to rainfall totals and timing, all dependent on a stalling boundary and possible waves of low pressure. The West should see a break in the precipitation on Monday, but mountains snows return by Tuesday and beyond for the Pacific Northwest and especially the Rockies. There remains some potential, but low confidence, on snowfall into the northern Plains/Upper Midwest late week as low pressure may develop over the central states. Temperatures should feel very mild for the south-central to eastern part of the U.S. on Monday ahead of the cold front, with temperatures 10 to 30 degrees above average and dozens of daily record high minimum and maximum temperatures possible. Temperatures should moderate back to near normal after the frontal passage on Tuesday. The West and parts of the central U.S. will generally be cooler than average through much of the period, but particularly for the second half of the week as more substantial troughing develops and pushes southeast along with cold high pressure. Temperatures should trend cooler with anomalies 10 to 30 degrees below normal possible across the northern and central Plains, and as far south as Texas and Oklahoma by Friday. Tate/Santorelli 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 rain across portions of the Southeast, the Mid-Atlantic, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Wed-Thu, Mar 9-Mar 10. - Heavy rain across portions of the Southern Appalachians, the Great Lakes, the Mid-Atlantic, the Central Appalachians, and the Ohio Valley, Mon, Mar 7. - Heavy snow across portions of the Northeast and the Great Lakes, Mon, Mar 7. - Severe weather across portions of the Southeast, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Mon, Mar 7. - Flooding possible across portions of the Central Great Basin. - Flooding occurring or imminent across portions of the Middle Mississippi Valley, the Central Great Basin, the Ohio Valley, the Northern Rockies, and the Tennessee Valley. - Flooding likely across portions of the Central Great Basin. - Much below normal temperatures across portions of the Central Plains and the Southern Plains, Mon-Tue, Mar 7-Mar 8 and Fri, Mar 11. - Much below normal temperatures across portions of the Central Plains, the Middle Mississippi Valley, the Southern Plains, the Upper Mississippi Valley, and the Northern Plains, Fri, Mar 11. - Much below normal temperatures across portions of the Central Rockies, the Central Plains, the Upper Mississippi Valley, the Northern Plains, and the Northern Rockies, Wed-Fri, Mar 9-Mar 11. - Much below normal temperatures across portions of the Central Rockies and the Central Plains, Mon-Fri, Mar 7-Mar 11. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml