Extended Forecast Discussion NWS Weather Prediction Center College Park MD 426 PM 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... ...Nicole to impact Florida and the East Coast later this week/weekend... ...Overview... An amplified upper trough centered over the Rockies early Thursday should 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 and strong winds Thursday into Friday, though with continued uncertainty for the specifics. Meanwhile, upper level ridging will continue Thursday into Friday across parts of the Eastern U.S. before what is now Subtropical Storm Nicole (likely tropical by the medium range period) reaching Florida is likely to get picked up ahead of the approaching Rockies/Plains trough. Nicole will likely bring widespread heavy rainfall and gusty winds to parts of Florida Thursday and spreading up the Eastern Seaboard Friday and Saturday. A rebuilding upper ridge over the Northeast Pacific/northwestern North America will likely yield mean troughing over much of Canada into the lower 48 by the weekend and early next week, along with below normal temperatures over much of the country. ...Guidance and Predictability Assessment... There is still meaningful spread for the developing northern tier storm during the latter half of the week, with latest GFS runs and 00Z ECMWF on the stronger and/or southwestern side of the spread and the 12Z UKMET farthest northeast as of early Friday. The new 12Z ECMWF has trended farther northeast than its prior run, highlighting the continued uncertainty with important details. Preference sided with an intermediate solution based on guidance available through the 06Z cycle. Ahead of this system, guidance shows some shuffling/trending for Subtropical Storm Nicole which should gain a more tropical character in coming days per National Hurricane Center forecasts. 12Z guidance trends are generally faster with the northward progression of Nicole along the East Coast as the upper trough approaches. Farther west, models and ensemble members are all over the place for exactly how initial eastern Pacific shortwave energy may split to produce one or more Pacific upper lows/shortwaves (which may or may not reach the West Coast), with the rest of the energy rounding a larger scale mean ridge and dropping into southern Canada and the lower 48. There may also be a southern stream that carries shortwave energy across the eastern Pacific and far southern tier U.S. Thus confidence confidence ultimately becomes quite low for shortwave details across much of the eastern Pacific and within the broad mean trough covering Canada and the lower 48. The updated forecast started with an operational composite and some localized manual adjustments during the first part of the period to reflect preferences for the northern tier storm and official NHC track for Nicole. Then the blend transitioned to about half models and half ensemble means to balance the increasing detail uncertainty while holding onto some definition of features where feasible. Resulting specifics near the West Coast from Saturday onward do not reflect any confidence in that specific evolution, and indeed the new runs have changed. ...Weather/Hazard Highlights... A well defined surface low looks to emerge out of the central High Plains on Thursday and deepen 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 gradually, with widespread greater than 70% probabilities from western-central 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 exact low track 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. There could be an axis of freezing rain and/or sleet between the snow and rain areas, but again dependent on details of the low. Coastal and maritime impacts that include coastal flooding, tropical storm force winds, heavy rainfall, rough surf, and beach erosion are possible associated with Nicole near/over Florida and the Southeast. The days 4 and 5 experimental Excessive Rainfall Outlooks depict Slight Risk areas from parts of Florida and the Southeast coast (day 4) and into the eastern Carolinas/coastal Mid-Atlantic (day 5) to show the potential for flash flooding from tropical rains. These areas 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. An approaching cold front will likely help to provide some focused enhancement of rainfall. Expect much of the West/Rockies into the Northern Plains to see below normal temperatures through the first part of next week. The coldest air will likely be across the northern High Plains and Plains Thursday-Saturday with highs in that area up to 20-30F below normal. Some locations in the Great Basin may see similar anomalies. 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 crossing 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-Monday look to be near or below normal for almost the entire CONUS. Rausch/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 Hazards: - Heavy precipitation across portions of the Upper Mississippi Valley and the Northern Plains, Thu-Fri, Nov 10-Nov 11. - Heavy rain across portions of the Northern/Central Plains, the Upper/Middle Mississippi Valley, the Mid-Atlantic, the Southeast, and the Great Lakes, Thu-Fri, Nov 10-Nov 11. - Heavy rain across portions of the Northeast, the Central/Southern Appalachians, the Mid-Atlantic, the Southeast, the Great Lakes, and the Ohio Valley, Fri-Sat, Nov 11-Nov 12. - Heavy snow across portions of the Northern/Central Plains, and the Upper Mississippi Valley, Thu, Nov 10. - Severe weather across portions of the Northern/Central Plains, and the Upper/Middle Mississippi Valley, Thu, Nov 10. - Flooding possible across portions of Florida. - Flooding occurring or imminent across portions of Florida. - High winds across portions of the Northern/Central Plains, and the Upper/Middle Mississippi Valley, Thu, Nov 10. - High winds across portions of the Southeast, Thu-Fri, Nov 10-Nov 11. - Much below normal temperatures across portions of the Northern/Central Plains, Fri-Sat, Nov 11-Nov 12. - Heavy precipitation across portions of mainland Alaska, Sat, Nov 12. 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