Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Sat Mar 30 2024 Valid 12Z Tue Apr 02 2024 - 12Z Sat Apr 06 2024 ...Heavy rain threat from Pennsylvania to New Jersey along with strong to possibly severe thunderstorms down the spine of the Appalachians on Tuesday... ...New England coastal storm with maritime hazards/high wind/coastal flooding along with heavy snow threat Wednesday- Thursday... ...Widespread precipitation/cooling for the West mid-late week... ...Pattern Overview, Guidance/Predictability Assessment, and Weather/Hazards Highlights... The medium-range period will begin with a low pressure system developing from across the mid-Mississippi to the Ohio Valley. Model guidance continues with the ongoing trend of slowing down the upper trough that is forecast to lift northeastward across the central Plains. This trend has helped strengthen a low pressure wave farther back over the mid-Mississippi Valley on Tuesday while keeping another wave farther downstream near the upper Ohio Valley. The best dynamics will support heavy rain likely from Pennsylvania to New Jersey on Tuesday while an axis of moderate to heavy rain extends southwestward down the spine of the Appalachians well ahead of a cold front where minor adjustments to the Marginal Excessive Rainfall risk area was necessary. Some strong to possibly severe thunderstorms are expected to accompany this axis of enhanced rainfall. Wednesday will likely feature cyclogenesis over the eastern U.S., with New England likley being impacted by a significant nor'easter by Thursday. There are two important contributors to the cyclogenesis. An upper trough associated with a surge of cold air from central Canada is forecast to dive toward the upper Great Lakes on Tuesday. Given the ongoing slowing trend of the upper trough lifting across the central Plains, models are trending toward having an double-barrel low pressure system as it tracks toward the New England coast. The slower lifting of the trough over the central Plains will also help keep a stronger low back across the Great Lakes while keeping the cold air in place over New England. As a result, the chance of heavy snow, instead of heavy rain, has continued to increase from central New England through all of Maine on Thursday. Meanwhile and significantly on the colder northern side of storm system, there will be a significant threat for lake-effect snow bands and snow squalls out from the Great Lakes and through the Interior Northeast Tuesday to Thursday as depicted by enhanced WPC Winter Weather Outlook probabilities. Toward the end of next week, models show very good agreement on a highly amplipied upper pattern across the U.S. with ridge building over the central U.S. as the deep low slowly pulling out of the Northeast and the next upper trough digging just off the West Coast. A strongly amplifying upper trough/closed low and leading and wavy cold front/secondary Canadian cold surge digging into the West should act to cool temperatures and spread enhanced precipitation and windy/unsettled flow to include coastal rains down through California along with a prolonged period with interior and terrain/mountain snows increasingly inland across much of the West midweek into next weekend. Depicted areas of precipitation are currently on the modest to moderate side given track/moisture, but ample upper support and favored terrain lift may lead to locally heavier focus and activity to monitor. The WPC Winter Weather Outlook shows the greatest snow probabilities over Northwest to northern Intermountain/Rockies terrain/mountains. Kong/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