Extended Forecast Discussion NWS Weather Prediction Center College Park MD 148 PM EST Sun Jan 22 2023 Valid 12Z Wed Jan 25 2023 - 12Z Sun Jan 29 2023 ...Heavy snow threat from the Ohio Valley/Great Lakes to the interior Northeast for Wednesday/Thursday... ...Synoptic Overview... There continues to be strong support for the development of a well organized low pressure system to track across the Ohio Valley to the Northeast U.S. Wednesday/Thursday that will be the main story making weather headlines during this forecast period, 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. In the wake of this storm will be a weaker Alberta clipper that will track southeast across the Great Lakes region on Friday with a trailing cold front behind it. Frontal passage will drop a cold Canadian airmass into the lower 48, 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 down across our fine nation. ...Guidance/Predictability Assessment... The WPC medium range product suite was primarily derived from a composite blend of seemingly well clustered and consistent guidance from the 06 UTC GFS, 00 UTC ECMWF/UKMET/Canadian, the 13 UTC National Blend of Models (NBM) and WPC continuity Wednesday into Friday in an active pattern with above normal predictability. 12 UTC guidance now also remains in line with this forecast strategy. However, there remains ample concerns heading into next weekend with the disparate model handling of 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 mainly from the GFS. Accordingly prefer an ensemble mean solution to mitigate some of these differences and run to run variations. Of the ensemble systems, prefer the ECMWF ensemble mean whose more amplified upper trough development down through the West Coast seems to fit best with considering upstream upper ridge amplitude, recent model trends, WPC continuity and pattern history. ...Weather/Hazard Highlights... The next major storm system is forecast to track northeast across the Ohio Valley on Wednesday, reaching the Northeast U.S. by Thursday as a new surface low is forecast to develop near the coast and becomes the dominant low. The best heavy rainfall potential exists from the Florida Panhandle into southern Georgia with thunderstorms along a Gulf moisture pooling trailing cold front and up into coastal areas of the Northeast with enhanced Atlantic inflow with the low. There is potential for some 1 to locally 2 inch rainfall totals. Meanwhile there will likely be a noteworthy swath of wintry weather from the northern Ohio Valley/eastern Great Lakes on Wednesday, where a swath of enhanced deformation zone snows will be possible. 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. 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, 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