Extended Forecast Discussion NWS Weather Prediction Center College Park MD 309 AM EDT Sun Mar 20 2022 Valid 12Z Wed Mar 23 2022 - 12Z Sun Mar 27 2022 ...A strong low pressure system will continue to cause precipitation in the eastern U.S. midweek, with severe storms in the Southeast, locally heavy rain, and wintry weather across the northern tier... ...Overview... The most active weather during the medium range period will be around midweek, as a potent upper low and a surface low pressure system track from the Mid-Mississippi Valley to the Great Lakes region. Rain is forecast to spread ahead of the associated cold front with some embedded heavy totals, while severe thunderstorms are possible in the Southeast. Meanwhile on the cold northern side of the system, springtime snow and mixed precipitation are possible from the Great Lakes region to the interior Northeast. As a ridge builds into the West, warm temperatures including some possible record highs particularly for California are forecast. The upper level pattern looks to stagnate over the weekend with an East Pacific trough, Intermountain West ridge, and eastern U.S. trough, which will lead to overall dry conditions. ...Guidance Evaluation/Predictability Assessment... Model guidance from the 12/18Z yesterday cycle continues to agree with a potent rounded upper low in the central U.S. supporting a surface low over the Middle Mississippi Valley day 3/early Wed. These features should move northeastward Thu, but with some model differences on the upper-level feature staying closed or opening up. The WPC forecast leans toward a solution with the low remaining closed, favoring the ECMWF/CMC and their means. The GFS/GEFS guidance shows a more open pattern by that time, but the main outlier for the 12Z cycle appeared to be the UKMET, with a more strung out trough holding back more energy into northern Mexico than current consensus, looking like some guidance from previous cycles but it is now one of the main holdouts. Then by Friday it separates northern and southern stream energy with the northern stream tracking likely too quickly. Other than the UKMET, despite the differences in timing of phasing, the progression of the trough/low eastward is mostly more agreeable. Models have stuck with the trend for an occluded surface low spreading more precipitation on the northwestern side. By around day 5/Fri and beyond, the troughing should slowly lift, though additional energy digs from the north to reinforce troughing across the East through the weekend, with some typical differences in shortwave energies and thus timing for cold fronts and low pressure systems. Namely, ensemble guidance generally showed low pressure near Maine or the Canadian Maritimes around Sat, but the 12/18Z deterministic guidance showed a local high around there with lows north and south. The 00Z guidance seems to be more in line with the ensemble consensus. Meanwhile there is rather good consensus for periods of ridging in the West with its axis shifting slowly eastward late in the week. Shortwaves moving across the Northwest could suppress the northern side around Thu-Fri, but most guidance other than the CMC has the ridge rebuilding for the weekend. The incoming 00Z suite of guidance shows a similar pattern but with typical wiggles in the details. The WPC forecast was based on an initial blend of the 12Z ECMWF, 12/18Z GFS, and 12Z CMC, just excluding the UKMET in terms of the deterministic models. Ensemble mean guidance was phased in around day 5 and increased somewhat through days 6-7, but only to about 40 percent given fairly good agreement for the large scale pattern even in the ECMWF/GFS in particular. ...Weather Highlights/Threats... Another rainy day is expected as the medium range period begins Wednesday as ample Gulf of Mexico moisture flows into the low pressure system tracking across the central U.S. Storms could be severe across the Deep South down to the central/eastern Gulf Coast per the Storm Prediction Center. Furthermore, widespread rain is likely across the East, which could potentially cause some isolated flash flooding in some areas from the southern/central Appalachians eastward. North and west of the low track, snow and wintry precipitation are possible, with the highest probabilities for notable snow in the Upper Great Lakes region. Wintry mix or snow could also occur particularly in higher elevations of the interior Northeast north of a warm front on Wednesday-Thursday and as a western Atlantic low develops by early Friday. Showers could linger into late week across the East with generally light amounts expected, but perhaps with more moderate amounts as a front lingers in Florida, which could cause localized flooding issues if rain falls atop saturated soils. A mainly dry pattern is expected for the western and central U.S. for the latter part of the week, though with some Pacific Northwest and Northern Rockies light precipitation possible before a more widespread moisture surge next weekend. The strong upper ridge building into the West will lead to a broad area of highs 10-20F above normal Wednesday-Sunday with slightly higher localized anomalies possible. There is potential to reach daily record highs across California Wednesday to Friday and spreading eastward into the Intermountain West and Southwest as the ridge axis shifts east. Leading upper level troughing should support temperatures 10-20F below average across the central/southern High Plains Wednesday. The cooler air should moderate closer to normal by the latter part of next week as it progresses eastward. Ahead of the trough and cold fronts, generally warmer than normal conditions are likely across much of the eastern third of the U.S. for much of the week, transitioning to near normal temperatures by Friday and Saturday and a cooldown associated with a secondary cold front in the Great Lakes by Sunday. Isolated record highs are possible over parts of Florida Tuesday-Wednesday. Tate 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