Extended Forecast Discussion NWS Weather Prediction Center College Park MD 249 PM EDT Mon Mar 17 2025 Valid 12Z Thu Mar 20 2025 - 12Z Mon Mar 24 2025 ...Snowstorm on Thursday in the Midwest/Great Lakes... ...Overview... The guidance agrees on a flow pattern that has some amplitude but remains progressive. This pattern favors multi-day unsettled and wet weather for the West/Northwest this week, with an enhanced moisture/rain focus into the Pacific Northwest and terrain enhanced heavy snow potential inland across the Northwest to the Rockies. Expect less defined rainy periods for the Central to Eastern U.S. may become better organized later period contingent on emerging return inflow with expected upper flow amplification. ...Guidance/Predictability Assessment... Models and ensembles show good agreement, albeit with uncertainty in details as is typically the case. The WPC forecast blend was comprised of even parts of the GFS/ECMWF/CMC/UKMET early on, before including the NAEFS/ECMWF ensemble means this weekend into early next week for the pressures, winds, fronts, QPF, and PoPs which should account reasonably for any lingering uncertainty. The remainder of the grids were more strongly tied to the 13z NBM output. ...Weather/Hazards Highlights... A series of Pacific low pressure/frontal systems will move into the West/Northwest and trigger repeating rounds of precipitation through the weekend. Moderately heavy rain and mountain snow are likely in the Pacific Northwest where moderate moisture will be channeled onshore. The WPC Day 5/Friday Excessive Rainfall Outlook maintains a Marginal Risk area for portions of the coastal ranges of northwest OR and WA given compounding effects of multiple days of precipitation which may lead to local runoff issues. There will also be periodic heavy snow threats inland as enhanced by terrain across the Northwest to the north- central Rockies. These Pacific systems are forecast to move east across the Central and Eastern U.S. Friday through the weekend and may produce mainly modest precipitation chances this week, but activity may intensify into next week given potential system organization with expected upper flow amplification, particularly across portions of the Midwest and Southeast. A big weather story surrounds a late season winter storm expected to produce blizzard conditions for parts of the north-central U.S. into midweek. A low pressure system will track from the Central Plains to the Upper Midwest and reach the Great Lakes by Thursday. The storm will have a wrap-around heavy snow threat on the northern side of the low track, and the tight pressure gradient around the system will likely produce strong gusty winds that could create blizzard conditions. This windy system forms a new center near Chesapeake Bay which moves just offshore the New England Coast late Thursday into Friday, and some wintry weather can be expected in northern/interior New England and the higher terrain of the Central Appalachians. Showers and thunderstorms with a trailing/wavy cold front of this system will work across and sweep offshore the East Coast Thursday. Roth/Schichtel 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