Extended Forecast Discussion NWS Weather Prediction Center College Park MD 211 AM EST Mon Nov 07 2022 Valid 12Z Thu Nov 10 2022 - 12Z Mon Nov 14 2022 ...Potentially significant winter storm likely for the Northern Plains on Thursday... ...Tropical disturbance will likely bring heavy rainfall from Florida to the Mid-Atlantic later this week/weekend... ...Overview... An amplified upper trough over the West to start the period Thursday is forecast to develop into a closed low over the Upper Midwest/Great Lakes by early Friday. Confidence continues to increase for a potentially significant winter storm to develop over parts of the Northern Plains with likely appreciable accumulating snowfall Thursday into Friday, though still plenty of uncertainty on the specifics. Meanwhile, upper level ridging will continue Thursday into Friday across parts of the Eastern U.S. before a tropical disturbance (that remains quite likely to develop into a subtropical or tropical storm per the National Hurricane Center) over the Bahamas/Florida is likely to get wrapped up into the approaching trough from the West. This system likely will bring widespread heavy rainfall to parts of Florida and spreading up the Eastern Seaboard Friday and Saturday. ...Guidance and Predictability Assessment... The majority of the models are now in agreement on amplified troughing over the West becoming a well developed closed upper low by early Friday over the Upper Midwest. There is still plenty of lingering uncertainty though on the exact track of the associated surface low and thus the positioning of the heaviest wintry precipitation in the cold sector on the backside of the low. Compared to previous shift, WPC stayed pretty close to continuity until better trends north or south become more apparent. Overall though, confidence is increasing for a high impact to potentially signfiicant winter storm, but the details on placement and timing remain much more uncertain and are likely to continue to shift slightly over the next couple of days as this event moves into the short range period. WPC generally leaned more towards the better clustered GFS, ECMWF, and UKMET, as the CMC was a little more east/quicker with the system than consensus. Farther south, the NHC continues to show high likelyhood on the formation of a tropical or subtropical storm reaching the East Coast of Florida by early Thursday. The guidance in the medium range period generally track this system across central/northern Florida before it eventually gets picked up by the midlatitude trough and accelerates up the Eastern Seaboard. While there is good agreement on this overall track, the timing continues to be highly uncertain with some models showing a quicker phasing and transition up the coast, and some wanting to bring it more into Florida and possibly the eastern Gulf before moving northward. A middle ground solution is preferred at this point, most close to the deterministic ECMWF. Finally, out West, ridging should build in behind the trough by Friday, but a lot of uncertainty thereafter on the next system into the Northwest with some guidance suggesting a closed low over/near the Pacific Northwest coast early next week. The WPC forecast trended quickly towards the ensemble means late period to account for the uncertainties. ...Weather/Hazard Highlights... A well defined surface low looks to emerge out of the central High Plains on Thursday deepening as it moves into the Upper Mississippi Valley by Friday. With model runs continuing to show the potential for accumulating and possibly significant snowfall across parts of the Dakotas and far northern Minnesota Thursday into Friday, the probabilities in the Winter Weather Outlook for Day 4 continue to increase, with widespread greater than 70% probabilities from northern South Dakota into far northern Minnesota. Depending on strength of the low, gusty winds could accompany snowfall and lead to possible blizzard conditions and dangerous travel. Again, while a meaningful winter storm over parts of the northern tier continues to become more likely, the specifics in the placement of the heaviest snow axis remain in question and are dependent on the low placement and strength. In the warm sector of this storm, moderate to heavy rainfall is possible across parts of the Upper Midwest and into the Great Lakes, with a chance for strong thunderstorms as well. Additionally, there could be an axis of freezing rain and/or sleet between the snow and rain though placement is still very uncertain. Coastal and maritime impacts, including coastal flooding, tropical-storm-force winds, heavy rainfall, rough surf, and beach erosion are possible associated with the tropical disturbance near/over Florida and the Southeast. Slight risks are on both the day 4 and 5 experimental Excessive Rainfall Outlooks from Florida/the Southeast coast (day 4) and into the eastern Carolinas (day 5) to show the potential for flash flooding from tropical rains. The area may have to shift or be upgraded in future forecasts depending on rainfall amounts and the track of the tropical system. Moisture from this system should move up much of the East Coast into the weekend though with more uncertainty in the amounts and coverage. Temperatures over the Rockies and Great Basin should finally begin to moderate some by Friday, but still remaining below normal. The coldest air will likely be across the northern High Plains and Plains as the period starts with recent forecasts showing highs in that area up to 20-30F below normal through the upcoming weekend. In contrast, well above normal temperatures will progress from the Midwest to the East Coast Thursday-Friday with widespread daily records for warm lows possible and a handful of record highs as readings soar 15 to 25 degrees above normal. A strong cold front through this region late this week will usher in a much colder airmass, with high temperatures by the weekend in the Midwest as much as 10 to 20 degrees below normal. The cooler temperatures will also reach the East this weekend, and Sunday to Monday looks to be near or below normal for almost the entire CONUS. 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, 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