Extended Forecast Discussion NWS Weather Prediction Center College Park MD 203 AM EST Mon Jan 23 2023 Valid 12Z Thu Jan 26 2023 - 12Z Mon Jan 30 2023 ...Heavy snow threat from the Ohio Valley/Great Lakes to the interior Northeast for Wednesday/Thursday... ...Synoptic Overview... A well organized low pressure system will track across the Ohio Valley to the Northeast through this period through Thursday, with a wind-driven rain near the coast and moderate to heavy snow from northern portions of the Ohio Valley/Great Lakes across interior portions of the Northeast. This will be in response to an amplified shortwave trough aloft that will quickly exit the East Coast by Friday. Following this system will be a relatively weak Alberta Clipper that streams across the Great Lakes region Friday with an associated trailing cold front. Colder air will filter into the CONUS with shortwave passages/height falls to combine with upslope fetch to spread some terrain enhanced snows down across north-central parts of the Intermountain West/Rockies/High Plains. Energies dug into the West then eject downstream to support a new system that may organize late period over the Southern Plains as the cold Canadian airmass sinks increasingly southward. ...Guidance/Predictability Assessment... The latest runs of the global guidance and their respective ensemble means continue to show above average predictability through most of the extended forecast period. However there are still some differences toward the latter periods with how to resolve complex Alaska/Gulf of Alaska system energies in the models down into the Western U.S. to the lee of an amplified eastern Pacific upper ridge, and also with even less certain undercutting eastern Pacific system energies and phasing issues. The WPC medium range product suite was primarily derived from a composite blend of seemingly well clustered and consistent guidance from the 18/00 UTC GFS, 00 UTC ECMWF/UKMET/Canadian/EC ensemble mean and the 01 UTC National Blend of Models (NBM). This approach helped maintain some forecast to forecast continuity. ...Weather/Hazard Highlights... The leading major storm system is expected to lift northeast across the Ohio Valley Wednesday, reaching the Northeast U.S. Thursday as a new surface low is forecast to develop near the coast and becomes the dominant low. Concentrated areas of moderate to heavy rainfall will likely focus from the Florida Panhandle to southern Georgia. This is where Gulf of Mexico moisture will be pooling in proximity to the trailing front which may yield 1 to 2+ inches. Further north, a swath of wintry weather is anticipated from the northern Ohio Valley/eastern Great Lakes. Heavy snow is additionally likely across the Appalachians through interior areas of the Northeast as the secondary low develops, with gales up the coast as the low continues to intensify. Much of this snow will be falling over areas expected to get significant accumulations from the lead storm on Sunday-Monday. A broad expanse of below average temperatures are expected from the Intermountain West to the central Gulf Coast on Wednesday and onward in the wake of the Eastern U.S. low pressure system, with mild air along the East Coast prior to frontal passage. A return to much colder conditions is looking likely across the Northern Plains and Upper Midwest as an arctic airmass moves in behind the departing clipper low, with highs running up to 15-25 degrees below normal potentially across portions of Montana, the Dakotas, and Nebraska on Sunday. Cold air will also eventually filter through the Northwest/Intermountain West. Meanwhile downstream, mild conditions will likely return to much of the southern and eastern U.S. with some return flow off the Gulf of Mexico. Campbell/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, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices 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