Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM EST Sun Jan 22 2023 Valid 12Z Wed Jan 25 2023 - 12Z Sun Jan 29 2023 ...Heavy rain and inland snow threat from the Ohio Valley to the interior Northeast for Wednesday through early Friday... ...Synoptic Overview... A well organized low pressure system tracking from the Gulf Coast to the Northeast U.S. during the middle to end of the week 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 across interior portions of the Northeast. This will be in response to an amplifying shortwave trough aloft that will quickly exit the East Coast by Friday morning. 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. By next weekend, a new storm system will likely get better organized across the Southern Plains as a much colder airmass drops southward from Canada across much of the Midwest and Northern Plains. ...Guidance/Predictability Assessment... The 00Z model guidance suite is in above average synoptic scale agreement through Thursday, including the track of the strong surface low across the Eastern U.S. and the ridge axis across the West. One of the things the models have been struggling with over the past couple of days is the breakdown of the West Coast ridge by shortwave energy originating from the Gulf of Alaska, and the past few GFS/GEFS runs have maintained the ridge longer than the CMC/ECMWF. The ECMWF is faster with the arrival of the shortwave reaching the Pacific Northwest, with the CMC between the timing of the ECMWF and GFS. By next Sunday, the ECMWF is supporting the development of a closed low near the West Coast, whereas the other guidance is weaker with this. The WPC fronts and pressures forecast was primarily derived from a nearly multi-deterministic model blend for Wednesday and Thursday, followed by less of the GFS owing to differences with the western U.S. ridge going into Friday and the weekend. The ECENS was favored more than the GEFS mean going into the weekend since the CMC mean was much closer to the ECENS and had a more favorable pattern evolution. ...Weather/Hazard Highlights... The next major storm system is forecast to develop over Texas/Louisiana on Tuesday and then track northeast across the Ohio Valley on Wednesday, and then 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 southern Georgia and across the Piedmont of the Carolinas and Virginia, with the potential for some 1 to locally 2 inch rainfall totals, and also across southern New England and Long Island, NY. 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 then likely across the Appalachians through interior areas of the Northeast as the secondary low develops, with heavy rain and gales up the coast as the low continues to intensify. Much of this snow will be falling over areas that get significant accumulations from the event on Sunday-Monday. A broad expanse of below average temperatures are expected from the Intermountain West to the central Gulf Coast on Wednesday in the wake of the Eastern U.S. low pressure system, and mild air along the East Coast ahead of the front. Nothing too anomalous appears likely going into Friday, but 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. Meanwhile, mild conditions will likely return to much of the southern and eastern U.S. with some return flow off the Gulf of Mexico. 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, 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