Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 PM EST Sat Feb 10 2024 Valid 12Z Tue Feb 13 2024 - 12Z Sat Feb 17 2024 ...Northeast Coastal Storm Heavy Snow/Gusty Wind Impacts to linger into Tuesday... ...General Overview... A developing and wet storm system across the Southern to Eastern U.S. in the short term is forecast to exit the Mid-Atlantic coast and deepen into a potent coastal storm into Tuesday, with impactful wrap-back snow now likely continuing into Tuesday afternoon across southern New England before tapering off. A quasi-zonal flow pattern develops across much of the nation in the wake of this storm system, and a pattern change is expected to evolve across the north-central U.S. as an arctic airmass drops southward from western Canada with a return to below normal temperatures. Meanwhile, an upper level ridge is likely to become established over the West Coast states by the end of the week, and this will tend to limit the progression of offshore Pacific storm systems until about Saturday when the next round of organized precipitation moves inland across California. Elsewhere, some light snow showers are possible from the northern Rockies to the Upper Midwest with weak shortwave passages, and lake effect snow across the Great Lakes region Friday night into Saturday. ...Guidance/Predictability Assessment... Latest models and ensembles remain in reasonably good agreement across the continental U.S. for Tuesday, with a slightly slower trend recently with the main system exiting the East Coast that would extend wrapback snow/wind potential a bit across southern portions of the Northeast that day. Differences become more evident Wednesday with the extent of trough amplification over the north-central U.S. and the timing of shortwave features in the northern stream flow, and also with the extent of Pacific system energies and moisture to undercut amd work onshore into the West Coast. However, there is decent model agreement with the developing southern stream trough near the Gulf Coast late in the forecast period. Accordingly, a composite model blend for best detail on Tuesday was quickly substituted by GEFS/ECMWF ensemble usage Wednesday into next weekned to account for the growing mesoscale model differences. In terms of the NBM, temperatures were reduced across much of the north-central U.S. given the ongoing signal for an arctic surface high to settle in. QPF was reduced inland into the West Coast states into at least late next week given model uncertainties with onshore system onset in complex flow over the eastern Pacific undercutting higher latitude blocking flow. The ensemble mean pattern does support an eventual wetter pattern into next weekend to monitor. The QPF was also raised across the general vicinity of the Great Lakes Thursday into Friday from the NBM given the decent overall signal for some lake effect snows. ...Overview and Weather/Hazards Highlights... Widespread snow will likely be ongoing Tuesday morning across much of the Northeast U.S. as the surface low continues to re-develop/deepen upon exiting the coast. Impactful snow is expected, especially across interior portions of the northern Mid-Atlantic through southern New England where snow is the primary precipitation type throughout the event. The rain/snow line comes close to the major metropolitan areas along Interstate 95 from Philadelphia through New York and southern New England, and there the forecast is more uncertain where a changeover from rain to snow should tend to limit overall accumulations. Rain will be the main precipitation type across eastern portions of the Mid-Atlantic. The quick progression of the system should bring an end to most of the heavier rains by Tuesday, so no WPC Excessive Rainfall areas seem warranted at this time. Elsewhere and looking ahead to Friday and next Saturday, a low pressure system is expected to develop over the western Gulf and advect increasing moisture northward and over a developing warm front, and this will likely result in widespread showers and thunderstorms across southern Texas that may then quickly overspread the Gulf Coast states and the Southeast in an emerging enhanced rainfall pattern to monitor. While there is quite a bit uncertainty in the models all next week over the eastern Pacific, the next main round of organized moisture is expected to reach the West Coast heading into next weekend. The strongest ensemble signal favors an emerging rain signature for the northern half of California, with snow for the higher terrain. Farther east, the prospects for lake effect snow are increasing to close out next week as much colder airmass crosses the region. Temperatures are expected to be generally 5 to 15 degrees above mid-February averages across much of the Midwest region on Tuesday and Wednesday with slightly below average readings over the Desert Southwest and the northern Rockies. Going into late Wednesday, a strong cold front dropping south from western Canada is expected to herald the arrival of an arctic airmass across the Northern Plains and bring a return to below average temperatures from Montana to the Dakotas and northern Minnesota through the end of the week, perhaps up to 20 degrees below average. Meanwhile, much of the remainder of the U.S. should have temperatures generally within 5 degrees of climatological averages to close out the work week, followed by colder conditions across much of the central and southern Plains through later next week with the southward march of the cold airmass. Hamrick/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, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw