Extended Forecast Discussion NWS Weather Prediction Center College Park MD 235 PM EDT Thu Mar 23 2023 Valid 12Z Sun Mar 26 2023 - 12Z Thu Mar 30 2023 ...Overview and Guidance/Predictability Assessment... The guidance is agreeable on the idea of progressive flow under the base of a mid-level cyclone across Hudson Bay across much of the Lower 48, with an amplifying trough eventually setting up shop out West mid next week, but disagree with the details. Late in the period, the 00z Canadian/00z ECMWF are more along the lines of the ensemble means in digging in a trough in the West and having it move at a slower pace, which also fits the general flow pattern which favors a slower moving system well away from the Hudson Bay mid-level cyclone. A compromise of the 06z GFS, 00z Canadian, and 00z ECMWF was used to start with for the surface pressures, 500 hPa heights, winds, and QPF, before blending in some of the 00z ECMWF/00z NAEFS ensemble mean solutions thereafter, which took care of the GFS quick bias with the system moving across the West into the Plains late in the period. The 13z NBM was strongly relied upon for the remainder of the grids, as usual. ...Weather/Hazards Highlights... The system departing from New England on Sunday leaves behind a wavy front over the Gulf Coast/Southeast, where ahead of a shortwave moving across the Plains sufficient moisture and instability is expected to exist to foster areas of heavy rain/thunderstorms due to cell training near and north of the front. This led to the day 4 (12Z Sunday-12Z Monday) Excessive Rainfall Outlook having a Slight Risk area in and near a line running from southern Mississippi through central Georgia. For day 5 (12Z Monday-12Z Tuesday), a Marginal Risk area remains in the outlook for a lingering heavy rainfall threat, with less consensus for specifics than the previous day due to the uncertainty inherent to this time frame. The system crossing the Plains into east-central U.S. should produce some precipitation of varying intensity, with snow possible in the northern part of the moisture shield. The details become more uncertain closer to the East Coast due to the track and depth of a low offshore. The most recent trend in the guidance was to slow the system down, and some modest probabilities for a a few inches of snow/0.25"+ of sleet are now advertised in the vicinity of southeast NY. Parts of the Interior West (next Monday through next Wednesday) and Rockies/High Plains (Sunday as well as next Tuesday and next Wednesday) should see some areas of heavy snow. The developing storm in the far eastern north Pacific by the start of next week suggests an increasing potential for strong winds along and offshore the coast. Moisture near and ahead of the system could bring some heavy rainfall/mountain snow to locations from the central West Coast into the Sierra Nevada. The day 5 Excessive Rainfall Outlook has a Marginal Risk area corresponding to the arrival of this Pacific moisture for portions of Oregon and northern California. Should the related upper trough deepen and/or slow down, the risk for excessive rainfall would be delayed and potentially shift and/or be more significant depending how strong the trend becomes. Expect much of the West and portions of the northern Plains to see below normal temperatures (roughly 10-20F) during the period. Coldest readings over the West will likely be through Sunday-Monday when parts of the Great Basin into central Rockies may see temperatures up to 30F below normal. Northern Plains locations should see highs consistently 10-20F below normal with some even colder readings possible early-mid week. Some of the cold air may spill into the central Plains on Sunday-Monday where a few locations may approach or set daily records for cold highs and/or lows. Areas along the East Coast, and especially the Southeast, should see above normal temperatures Sunday into Monday and slightly below normal readings around next Tuesday-next Wednesday due to cold northerly flow. Roth 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, experimental excessive rainfall outlook, 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/#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