Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Sat Oct 28 2023 Valid 12Z Tue Oct 31 2023 - 12Z Sat Nov 4 2023 ...Synoptic Overview... The strong cold front that will deliver the coldest air mass so far this season is expected to clear the southeast U.S. coast by Tuesday morning, and then clear the Florida Peninsula by late Wednesday, with a strong surface high building in behind the front. A couple of reinforcing upper troughs will give this colder airmass some staying power across much of the central and eastern states, with perhaps the first notable lake effect snow event of the season, and a low pressure system developing off the New England Coast. The airmass should gradually modify some going into the end of next week, and a Pacific storm system approaching the northwestern coast will increase the prospects for rain and mountain snow to close out the work week and into next Saturday. ...Guidance Evaluation/Predictability Assessment... Question marks still remain for the development of a coastal surface low off the New England Coast mid-week. The past few runs of the GFS/GEFS have been consistently more progressive with a potent mid-upper level northern stream trough across the Great Lakes region, and the past few ECMWF/ECENS/CMC runs have also been consistent with a slower and a little more amplified solution, which also has some support from the UKMET and ICON models. WPC continuity also favors the slower side of the non-NCEP guidance for this forecast cycle, and this results in a low developing closer to the coast due to the incoming shortwave trough, in contrast to the GFS which has the low well to the east of the model consensus. Looking ahead to the end of the week and next Saturday, the GFS is also more progressive with the Pacific trough and front moving inland across the Intermountain West, and the ECMWF is stronger with a second trough approaching the Pacific Northwest on Saturday. The ensemble means accounted for about half of the forecast blend by next Saturday. ...Weather/Hazards Highlights... In contrast to the heavy rainfall expected over the next couple of days across the south-central U.S., the extended forecast going into early next week features a return to much quieter conditions in terms of rainfall across the entire country. The rainfall expected behind the strong cold front and in association with the offshore Atlantic low should be below the thresholds of any excessive rainfall headlines. There may be some locations that get 0.5 to 1 inch of rainfall on Tuesday and into early Wednesday near the Mid-Atlantic coast, but the intensity is expected to be only light to moderate. For the Day 5 period Wednesday into Wednesday night, moist onshore flow increases across western portions of Washington and Oregon with the potential for 1 to 2 inches of rainfall across the west-facing terrain, but the intensity is also expected to be limited here, so no excessive rainfall headlines are warranted at this time. Depending on the potential evolution of an offshore low around midweek, some moisture is expected to be advected inland across coastal portions of the Northeast U.S., with rain for the big cities and perhaps some snow for the higher inland terrain. Some lake effect snow could also make headlines from Michigan to Upstate New York as a strong surge of cold air advection rushes across the warmer lake waters, with a few inches of accumulation possible for some areas. Looking ahead to the end of the week, showers and mountain snow is likely to make a return from Washington to the northern Rockies, with some heavy snow likely for the higher mountain ranges. The cold airmass ushered in by the strong cold front engulfs all of the central and eastern U.S., by Tuesday, and then cooler weather returns to the Florida Peninsula by Wednesday. Widespread anomalies on the order of 15 to 25 degrees below average for this time of year are expected from the western High Plains to the Ohio Valley, and then the East coast gets the coldest weather of the week on the first day of November on Wednesday. The first frost/freeze of the season is expected for a vast expanse of the south-central U.S. and also extending into the major metro areas of the Northeast U.S. going into the middle to end of the week. This airmass should then modify going into Friday and beyond as a more zonal flow pattern evolves. 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