Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Sat Feb 10 2024 Valid 12Z Tue Feb 13 2024 - 12Z Sat Feb 17 2024 ...General Overview... The storm system that will be tracking across the Southern U.S. in the short range forecast period is forecast to exit the Mid-Atlantic coast Tuesday morning, with snow likely continuing into Tuesday afternoon across southern New England before tapering off later in the day. 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 by Thursday 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... The 00Z model guidance suite is in reasonably good agreement across the continental U.S. on Tuesday, with a slightly slower trend with the low exiting the East Coast. Differences become evident by 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 the ridge axis across the West Coast region. However, there is decent model agreement with the developing southern stream trough near the Gulf Coast late in the forecast period. The use of the ensemble means increased to about 50 percent by next Saturday to account for the growing mesoscale model differences elsewhere. In terms of the NBM, temperatures were reduced by 2-5 degrees about much of the north-central U.S. given the stronger signal for an arctic surface high settling in, even though the guidance has trended colder compared to this time yesterday. The QPF was also raised across the general vicinity of the Great Lakes on Friday from the NBM given the decent overall signal for a lake effect snow event. ...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 deepen upon exiting the coast. Several inches of snow is expected, especially across interior portions of 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 and points northeast, and here the forecast is more uncertain where a changeover from rain to snow will tend to limit overall accumulations. Rain will be the main precipitation type across eastern portions of the Mid-Atlantic. The quick progression of the surface low should bring an end to most of the precipitation by sunset Tuesday, and no excessive rainfall areas are currently warranted for either Day 4 or Day 5 with just light to moderate rain across western portions of Washington and Oregon on Wednesday. Looking ahead to Friday and early 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 and into the central Gulf Coast region. Additionally, the next round of organized Pacific moisture is expected to reach the West Coast on Friday and result in moderate to heavy rain for the northern half of California, and snow for the higher terrain. Farther east, the prospects for lake effect snow are increasing to close out the work week with the much colder airmass crossing the Great Lakes, with the greatest snowfall likely across central and northern Michigan. 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. Models have trended colder behind this front compared to yesterday, and things may continue to trend colder in future forecast updates. 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 by Saturday. Hamrick 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