Extended Forecast Discussion NWS Weather Prediction Center College Park MD 207 AM EST Tue Feb 01 2022 Valid 12Z Fri Feb 04 2022 - 12Z Tue Feb 08 2022 ...Heavy snowfall beginning to exit northern New England by the start of the medium range period... ...Overview... A positively tilted and reinforced mean trough aloft should hold strong across much of the CONUS through the medium range period (Friday-Tuesday), as strong upper riding builds over both the western Atlantic and the eastern Pacific (and periodically extending into parts of the west). On Friday, a shortwave moving through the Northeast will drive a potent cold front off the East coast, with potentially heavy wintry precip likely coming to an end on the north side of this system. Meanwhile, the next shortwave/possibly brief closed low will weaken as it moves over the Southern Plains, and combine with energy to the north. This weekend, uncertainty begins to increase over details of additional shortwaves dropping down the east side of the ridge in the West (with some guidance support for a Southwest closed low Sunday-Tuesday) as well as a series of northern stream shortwaves which should support a train of northern tier waves into early next week. Troughing across the East by next Tuesday may induce low pressure off the East Coast, but most guidance at this time shows it tracking well enough east for avoid any impacts along the coast. ...Guidance Evaluation/Predictability Assessment... A general blend of 12z/18z model guidance from yesterday provided a good representation of consensus for days 3-4 Friday-Saturday. In this time frame, frontal waves along the cold front in the East should consolidate into a single low that ultimately tracks away from New England while a weak wave and frontal system reach the northern tier. There remain some minor north-south differences in cold frontal placement early Friday, but mostly just the typical run-to-run model fluctuations. The GFS has been consistent the past several runs in a little farther southward push of the front/colder air, which ultimately would bring wintry precipitation farther south into parts of the Mid-Atlantic on Friday. The last few runs of the ECMWF (including the new 00z run for today) has been shifting ever so slightly southward though as well so even though the GFS seems to be a cold outlier right now, it cannot be completely ruled out. By this weekend, the greatest point of uncertainty continues to be with a shortwave dropping into the Northwest and a potential break off of southern stream energy ultimately resulting in a closed low lingering over/near the Southwest. The GFS has been very consistent with a much stronger/deeper closed low, while the rest of the guidance supports a little bit more consolidation between northern/southern stream energy through the Rockies into the Central Plains. At this point, the GFS is a big outlier, but does have support from some ensemble members (and older runs of the ECMWF). WPC prefers the weaker solution as offered by the deterministic ECMWF/CMC and ensemble means, leaning away from the much too deep GFS. For northern stream shortwaves/frontal waves, just mainly minor timing differences through the weekend easily handled by a general model blend. One point of concern is evolution/interaction of late period northern/southern stream energy to induce surface low development off the East Coast. The 12z/yesterday ECMWF brought this low much closer to the East Coast than most other guidance, but the 00z run seems to have trended farther offshore again, and more inline with the ensemble means. Given the increasing late period detail differences across the board, the WPC forecast leaned fairly heavily on the ensemble means. ...Weather Highlights/Threats... Troughing into the Ohio Valley/Northeast on Friday and a leading wavy cold front through the East will continue the threat for potentially significant snows across mainly northern New England on Friday. There likely will be a band of moderate to heavy sleet/freezing rain just to the south of this in the transition zone as well, with lingering uncertainties on how far south it extends (possibly into parts of the Mid-Atlantic). Heavy rainfall across the South at the end of the short range period will mostly have ended by Friday morning as the better moisture feed gets cut off from the Gulf. Some lingering, moderately to locally heavy showers, are still possible across parts of the Southeast along the cold front. Elsewhere, northern tier systems may produce a couple episodes of light and scattered snowfall. Mostly light rain/mountain snow should accompany a couple systems brushing the Pacific Northwest and possibly extending into the northern Rockies. Significant guidance differences with separate streams of energy aloft lead to low confidence in the coverage and amounts of precipitation over the South and East from the weekend into the start of next week. Some precipitation type issues may come into play depending on how far north the moisture shield extends. Areas ahead of the eastern U.S. cold front will continue to see above average (+10-15F) anomalies for highs, with more anomalous overnight morning lows on Friday. Arctic high pressure settling across the central U.S. and into the Midwest behind the front will bring very cold temps to especially parts of the southern Plains where daytime highs 20-25 degrees below normal are possible. Points north and east should be slightly less extreme through still areas of generally -10-20F highs. Temperatures should moderate and slide eastward this weekend, with many places east of the Plains back to near normal values by early next week. Upper ridging trying to build across the northern/central Plains Monday-Tuesday of next week could bring a period of much above normal temperatures to this region. The West Coast states should be near normal into weekend, trending slightly warmer the rest of the period owing to amplified ridging across the East Pacific. Santorelli 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, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml