Extended Forecast Discussion...UPDATED NWS Weather Prediction Center College Park MD 256 PM EDT Fri Mar 22 2024 Valid 12Z Mon Mar 25 2024 - 12Z Fri Mar 29 2024 ...Heavy snow likely to continue into Monday for parts of the north-central Plains and Upper Midwest... ...Heavy rain threat across the Lower Mississippi Valley to Southeast early to midweek... ...Overview... A strong low pressure system forecast to intensify and track across the central Plains to the Upper Midwest Monday-Tuesday should bring heavy snow to the north-central U.S., north and west of the low track. Expect strong winds and very cold temperatures with this system as well. On the warm side of the system, heavy rain associated with strong thunderstorms ahead of a relatively potent cold front will likely lead to flooding issues across the Lower Mississippi Valley and Southeast Monday-Tuesday, with some uncertainty beyond that in how much rain may fall along the East Coast. Meanwhile, one or more Pacific systems should bring increasing totals of rain and mountain snow to the Northwest and then into the Rockies mid-late week. Some of this moisture may reach the northern Plains by next Friday. ...Guidance/Predictability Assessment... Latest guidance shows better than average clustering for the strong Plains through Upper Midwest storm during the first half of the week. There are still some detail questions along and ahead of this storm's cold front, with one or more possible low- predictability waves for which most guidance shows a reasonable signal in principle. As the overall upper trough continues eastward later in the week, the primary forecast problem is how much flow separation may occur and at what longitude--affecting surface low position and depth. ECMWF runs have been showing more separation and farther westward position, with ECens runs understandably less separated aloft but likewise somewhat west. 00Z ECMWF/06Z GFS-GEFS runs have attempted some convergence though, with the ECMWF shifting a little east and GFS/GEFS somewhat west. 00Z ECMWF- initialized machine learning (ML) models show some scatter with their mean appearing to support a solution close to an average among the 06Z GFS/GEFS and 00Z ECMWF/ECens. The 00Z CMC becomes a slow extreme after midweek, not just over the East but for the rest of the lower 48 and vicinity as well. Farther west, the 00Z UKMET was initially the odd model out with a more suppressed Pacific low track by Wednesday. By next Friday recent GFS runs have leaned a little south with the next potential system nearing the Pacific Northwest. While there is decent model/ensemble clustering for this Friday system, there is more diversity among the ML models for what the upper details will look like and how they will reflect at the surface. Therefore will monitor the potential for adjustments in the dynamical guidance. Based on the comparisons among latest guidance, the first part of the updated forecast started with mostly the 06Z GFS/00Z ECMWF with a little 00Z CMC. Then the forecast phased out the CMC while increasing 06Z GEFS/00Z ECens input to 60 percent by late in the period. ...Weather/Hazards Highlights... The deep surface low tracking from the central Plains to Upper Midwest (and its upper level support) will produce an impactful multi-hazard weather event for early-mid next week. A widespread late season winter storm should be ongoing Monday with heavy snow accumulation (8+") likely from northeastern Nebraska into eastern parts of the Dakotas, much of Minnesota, and far northwestern Wisconsin, as this region will be on the colder side of the low with a deformation zone developing. High winds due to the deep surface low could lead to blizzard conditions in some areas. Timing/track uncertainty may change the eventual location of the impactful winter weather, but the risk for disruptions to daily life and hazardous travel is likely. High winds are also possible southward across the Plains on Monday behind the cold front, though with drier weather. Farther south ahead of the cold front, ample moisture streaming in and a strong jet aloft will support heavy rain and potentially severe thunderstorms for the Lower Mississippi Valley Monday, shifting into the Southeast on Tuesday. Slight Risk areas are in place in the Days 4-5 Excessive Rainfall Outlooks due to the potential of a likely squall line causing rain rates of 2+" per hour. Most guidance suggests the areal coverage of heavy QPF and localized maxima should be somewhat lower on Tuesday compared to Monday, but still have a Slight Risk given sufficient guidance signal that the squall line will likely last into Tuesday over Mississippi/Alabama, with significant rainfall possibly extending into parts of Tennessee as well. Latest guidance themes favored a little eastward/northeastward expansion of this Day 5 Slight Risk area for the afternoon update. By mid-late week, the stormy weather crosses the Florida Panhandle north into the Carolinas and eventually up the Eastern Seaboard, but with considerable uncertainty in rainfall coverage/amounts from the Mid-Atlantic northward after midweek. Some lingering moderate snow is possible across parts of the south-central Rockies on Monday, with light amounts elsewhere across the Intermountain West. The Pacific Northwest could see some moderate lower elevation rain and higher elevation snow amounts Monday, with increasing totals by Tuesday-Wednesday and expanding into California as upper troughing and low pressure approach. Some moderate to heavy precipitation should expand into the Intermountain West by mid-late week, and will continue to monitor the potential for further expansion of the precipitation possibly in the form of snow to affect the north-central Plains once again by Thursday or Friday. Much colder than average temperatures (more comparable to January) are likely for the northern and central High Plains in the wake of the strong Plains/Midwest storm. Highs will only be in the 20s and 30s for these areas on Monday. The central U.S. will see a warming trend going into the middle and late part of next week, though Montana and the Dakotas will still remain chilly by late March standards. The West should see generally cooler than average highs and near average lows next week. Meanwhile the East should see a warming trend early-mid week ahead of the Midwest storm's cold front and then near to slightly below average temperatures central/south after frontal passage. The Northeast may remain a little above average, especially for morning lows. Rausch/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 WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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 https://www.wpc.ncep.noaa.gov/#page=ovw