Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Thu Feb 13 2025 Valid 12Z Sun Feb 16 2025 - 12Z Thu Feb 20 2025 ...Strong storm to bring heavy snow to the Northeast and locally heavy rain to the Mid-Atlantic and Southeast on Sunday... ...Overview... A deep upper trough lifting through the East on Sunday will support a strengthening surface low that should track from the Ohio Valley to the Canadian Maritimes Sunday into Monday. This storm is forecast to bring impactful winter weather and strong winds to New England and locally heavy rain to the Mid-Atlantic and Southeast. Behind this system, an elongating upper trough/low will likely linger across the northern tier of the nation while a few shortwaves/frontal systems move into the West. These systems will bring rounds of low elevation rain and mountain snow to the Pacific Northwest, Northern California, and the Northern/Central Rockies through the period. Precipitation is expected to spread into the Central/Southern Plains early next week as a low pressure system moves south across the region towards the Gulf Coast, then precipitation will expand across the South and Southeast mid-next week as the low swings along the Gulf Coast to the Southeast. Some wintry weather is expected on the northern side of this system from the Central/Southern Plains through the Mid-Mississippi and Tennessee Valleys to the Mid-Atlantic. Meanwhile, Arctic high pressure will expand south and east into the Central and Eastern U.S. through the period, resulting in multiple days of well below average temperatures. ...Guidance/Predictability Assessment... Models continue to show good agreement on the overall pattern with some differences in the details of specific systems. Since yesterday, model agreement has increased around the position, timing, and depth of the troughs over the northern tier and in the West late this weekend into early next week. Therefore, a general blend of the 06Z GFS and 00Z ECMWF/CMC/UKMET seemed to produce a good starting point for WPCs afternoon forecast. Heaviest weight was put on the GFS and ECMWF, which showed the most skill alter in the period when model spread becomes more significant. The highest uncertainty in the forecast is on day seven/Thursday when the evolution of low pressure over the Southeast becomes less clear. The GFS/ECMWF-AIFS are the most progressive with this system while the ECMWF/CMC are quite a bit slower. For WPCs forecast, ensemble means from the GEFS/ECENS were added to the blend to result in a forecast falling in the middle of the faster and slower solutions. ...Weather/Hazards Highlights... The strengthening storm lifting northeastward from the Upper Ohio Valley on Sunday will push a quick-moving cold front east across the Mid-Atlantic and Southeast. Locally heavy rainfall will be possible ahead of and along the cold front, but the threat of flash flooding will be greatly reduced as compared to Saturday. Even so, any additional rainfall in the Mid-Atlantic and Appalachians could cause some flooding concerns given the saturated soils from rainfall the day before. Wintry weather is expected on the northern side of this system as the low tracks just south of New England. A swath of heavy snow will be possible from the eastern Great Lakes through the Northeast, and a transition zone of wintry mixed precipitation will exist between the snow zone and rain to the south. Precipitation should taper off across the East Sunday night through Monday as the system moves offshore into the Atlantic, but some lingering lake effect snow is possible in the Great Lakes. The tight pressure gradient around this system may result in a period of strong, gusty winds across the Appalachians and the Northeast early next week. In the West, a Pacific system will likely continue to produce rain and mountain snow over the Pacific Northwest on Sunday. Precipitation amounts/rates are still forecast to stay below the criteria for an Excessive Rainfall Outlook area, but light to moderate precipitation will be possible. Precipitation will push east/southeast through the Rockies early next week while tapering off in the Pacific Northwest. Then, another system should bring precipitation back to the Northwest Tuesday into Wednesday with another round of light to moderate totals. Energy from the leading Pacific system should emerge east of the Rockies by Monday/Tuesday and low pressure and precipitation will develop across the Central/Southern Plains. This area of low pressure will sink south towards the Gulf Coast, then swing east towards the Southeast Wednesday/Thursday. Heavy rain will be possible across the South and Southeast, and wintry weather will be possible on the northern side of the system from the Plains through the Mid-Mississippi/Tennessee Valleys to the Mid-Atlantic. Temperature-wise, well below normal temperatures will likely prevail through the period over much of the Central U.S., with surges reaching into the Southern Plains on Sunday and again next Wednesday-Thursday. Recent colder trends in guidance suggest some locations could be at least 30 degrees below normal (especially for highs) with an increasing signal for some daily record lows/cold highs by around midweek. The East will also see significantly colder temperatures after a very brief episode of warmth along the East Coast ahead of the Sunday system's cold front. Coldest anomalies of 10-25 degrees below average over the East should extend over the Great Lakes/Ohio Valley into the Mid- Atlantic/southern New England. Expect temperatures in the West to remain fairly close to normal, with the Northwest tending to be slightly below and southern areas a little above. Dolan/Rausch 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