Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Mon Mar 17 2025 Valid 12Z Thu Mar 20 2025 - 12Z Mon Mar 24 2025 ...Winter Storm to impact Upper Midwest/Great Lakes to northern Northeast as an unsettled/wet pattern works over the Northwest... ...Overview... Guidance overall agrees that a few different low pressure systems will move generally west to east across the lower 48 this week. A potent low pressure system will strengthen significantly to the lee of the Rockies and track towards the Upper Midwest midweek, then move across the Great Lakes and Northeast later week. A wrapback swath of heavy snow and gusty winds are expected on the northern side of the storm track from the Central Plains to the Upper Midwest, with expected blizzard conditions in some areas. Some wintry weather is also expected in the Northeast, with the highest chances in northern/interior New England given coastal low development. Two other main low pressure systems are forecast to then move west to east across the nation, but will be quite a bit weaker than the first lead system. 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 again show good agreement on the overall weather pattern through the medium range period, with reasonably good agreement on individual storm systems as well. Forecast confidence is above average overall with a guidance composite, albeit with more uncertainty in details late in the period that seem well mitigated consistent with predictability by the blending process. The WPC forecast blend comprised of near even parts of the GFS/ECMWF/CMC/UKMET and GEFS/ECMWF/Canadian ensembles seems in line with the National Blend of Models and WPC product continuity. ...Weather/Hazards Highlights... 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 deepened 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 will push east across the Northeast Thursday into Friday, and some wintry weather can be expected in northern/interior New England. Some wintry weather may also be possible in 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. Upstream, a series of Pacific low pressure/frontal systems will move into the West/Northwest and trigger repeating rounds of precipitation through next 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 initiated a near coastal Marginal threat area given compounding effects of multiple days of precipitation 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. 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