Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EST Sun Feb 11 2024 Valid 12Z Wed Feb 14 2024 - 12Z Sun Feb 18 2024 ...General Overview... A quasi-zonal flow pattern develops across much of the nation in the wake of the departing East Coast 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, a weak upper level ridge is likely to become established over the Intermountain West by the end of the week, and this will tend to slow the progression of offshore Pacific storm systems until about Friday 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 Wednesday, with a slightly slower trend with the low exiting the East Coast. Differences become evident by the end of the week with the extent of the ridge axis across the West Coast region and the arrival of lead Pacific shortwave energy 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 weekend to account for the growing mesoscale model differences elsewhere. In terms of the NBM, temperatures were reduced by 2-4 degrees across much of the north-central U.S. given the stronger signal for an arctic surface high settling in for the second half of the work week. The QPF was also raised across the general vicinity of the Great Lakes on Friday/Saturday from the NBM given the decent overall signal for a light to moderate lake effect snow event. ...Overview and Weather/Hazards Highlights... A relatively quiet period of time is expected across the nation on Wednesday with most areas remaining dry, and some light snow across the north-central U.S. and the Northern Rockies. There will likely be some Pacific moisture moving inland across the Pacific Northwest, but model guidance varies more than usual for this region and overall rainfall totals are expected to be modest. Therefore, no risk areas are warranted for the Day 4 excessive rainfall outlook on Wednesday. Looking ahead to Thursday and Friday, 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. The guidance favors Deep South Texas for heaviest rainfall totals on Thursday, and a Marginal Risk is planned for the Day 5 excessive rainfall outlook. More heavy rain is likely across portions of the Deep South going into the Friday-Saturday time period as the surface low tracks towards the Southeast U.S. Coast. 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 Wednesday and then across he Mid-South and Ohio Valley region on Thursday. Meanwhile, 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 Minnesota through the end of the week, perhaps up to 25 degrees below average across portions of Montana, but not quite as cold as the previous arctic blast back in mid-January. Meanwhile, much of the remainder of the U.S. should have temperatures near or slightly below climatological averages going into next weekend. 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