Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EST Sat Mar 05 2022 Valid 12Z Tue Mar 08 2022 - 12Z Sat Mar 12 2022 ...Overview... A strong ridge over the Atlantic/Gulf of Mexico and the Eastern Pacific should keep much of the CONUS within broad and reinforced troughing through most of the medium range period. Various shortwaves will progress through the flow sending low pressure into the Eastern U.S. and the central states. Amplified troughing should become established over the Rockies/Interior West by mid week, eventually pushing east into the Plains resulting in a developing low pressure area tracking into the Upper Midwest late next week. Periods of moderate to locally heavy rain are possible across the Southeast, with some wintry weather across northern areas. ...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. The initial shortwave/closed low over the Southwest should weaken as it progresses downstream, but with some timing uncertainties. The 18z/Mar 4 GFS and the 12z/Mar 4 ECMWF seemed to represent the best middle ground solution in between a faster CMC and slower UKMET. A quick look at the new 00z guidance (available after forecast generation) shows the GFS and ECMWF are a little faster than their previous runs and close to the CMC now, with the UKMET still notably slower. These subtle differences in timing may have larger impacts to potential QPF across the Southeast along a stalling frontal boundary. Energy diving into the West on Wednesday should act to reinforce and amplify troughing over the Rockies/Interior West which eventually presses east into the Plains by Friday/Saturday. This should induce cyclogenesis in the lee of the Rockies, with a well developed surface low lifting into the Upper Midwest by Friday. The 12z/18z guidance from yesterday actually showed quite good agreement timing wise for this system and so a majority deterministic blend was used through the period. Incorporated some of the ensemble means though to help smooth out the less predictable detail differences. However, the incoming 00z guidance shows much greater differences in some of the details as well as timing, with the 00z ECMWF quite a bit slower now, so uncertainty remains high with this system as a whole. ...Weather Highlights/Threats... Rain and thunderstorms will be widespread along and ahead of a cold front moving through the eastern U.S. on Tuesday. By the middle of next week, return flow moisture out of the Gulf of Mexico could result in multiple days of rainfall across parts of the lower Mississippi Valley/Southeast. Plenty of uncertainty remains with respect to rainfall totals, timing, and impacts, dependent on exactly where the boundary stalls and possible waves of low pressure. At this point, guidance suggests the better moisture stays south in areas that have been relatively dry the past few weeks, but just a small jog to the north on the axis, could bring heavier rainfall into areas which have seen above normal rain lately, increasing the threat for flooding. The next round of heavy mountain snow arrives into the West on Tuesday and Wednesday. As the surface low develops across the central U.S. Thursday-Friday, snow is likely to develop along the north side of the low from the central/northern Plains to the Upper Midwest. Exact amounts and how impactful this system will actually be remains quite uncertain at this time, but the latest WPC winter weather outlook for days 5 and 6 do show some modest potential for accumulating snow. After a mild start to the week, temperatures across the Mid-Atlantic/Northeast should moderate back towards normal Tuesday-Thursday, though above normal temperatures may arrive back on Friday ahead of the next system. Meanwhile, 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. Below normal temperatures should move into the Mississippi Valley and Midwest states by next weekend. 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 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