Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Sun Nov 06 2022 Valid 12Z Wed Nov 09 2022 - 12Z Sun Nov 13 2022 ...Heavy snow over the West on Wednesday, with an increasing winter storm threat in the Northern Plains on Thursday... ...Tropical disturbance could bring heavy rainfall to parts of Florida and the Southeast mid to late next week... ...Overview... An amplified upper trough over the West Coast to start the period Wednesday will translate inland over the Rockies by Thursday and strengthening into a possible closed low over the Upper Midwest/Great Lakes by early Friday. There is an increasing threat for a winter storm to develop over parts of the Northern Plains with possibly appreciable accumulating snowfall Thursday into Friday, though still plenty of uncertainty on the specifics. Meanwhile, upper level ridging will prevail across the Eastern U.S. through about Thursday before a tropical disturbance (with an increasing chance for development per the National Hurricane Center) over the Bahamas/Florida may get wrapped up into the approaching trough from the West. Confidence is increasing in at least modest rainfall spreading from parts of Florida up the East Coast. ...Guidance and Predictability Assessment... Models agree on the presence of amplified troughing over the West by the middle of next week, but continue to display plenty of uncertainty regarding speed and evolution thereafter. The 18z/Nov 5th GFS and 12z/Nov 5th ECMWF were among the first deterministic solutions to suggest a much stronger evolution of an eventual closed low over the Upper Midwest by day 5/Friday while the previous runs of the CMC and UKMET (including those available at forecast generation time) were much faster and weaker showing just an amplified shortwave through the region. However, the most recent 00z runs of the CMC and UKMET have trended more towards the GFS and ECMWF solutions (both of which had support from their ensemble means) increasing confidence in a developed surface low tracking from about the central Plains into the Upper Mississippi Valley Thursday into Friday, with sufficient cold air on the backside of the low to support a potential winter storm across portions of the Northern Plains. Again, plenty of uncertainty on the details and exactly where any potential band of heavy snow may fall, but with the most recent 00z model runs, confidence is beginning to increase in the possibility. Farther south, models also continue to trend towards the potential for a tropical or subtropical disturbance to affect Florida and parts of the East Coast mid to later this week. The National Hurricane Center has upped the potential for development through 5 days to 80 percent. Models generally track this feature westward near/north of the Bahamas and towards or over the Florida east coast before it could get swept northward by the trough moving from the Central U.S. into the East next weekend. Models continue to show plenty of variability regarding the phasing of these features later in the period. Monitor the latest outlooks and forecasts from the NHC regarding possible tropical development of this system. The WPC forecast for tonight used a mostly deterministic model blend heavily weighted towards the GFS and ECMWF through day 5, although ensemble means were introduced into the blend on day 4 a little earlier than usual just given the early period uncertainties. By 6 and 7, favored a mostly ensemble mean blend to help mitigate the late period differences both in the Central/Eastern U.S. as well as another shortwave/closed low into the Pac Northwest. ...Weather/Hazard Highlights... Heavy mountain snow and valley rain will be ongoing across parts the West on Wednesday, with the heaviest totals across the higher terrain of the Great Basin. As the trough moves inland and strengthens, a defined surface low looks to emerge out of the central High Plains deepening as it moves into the Upper Mississippi Valley by Friday. Very recent model runs have shown increasing potential for accumulating (possibly significant) snowfall across parts of the Dakotas and far northern Minnesota Thursday into Friday with a noticeable jump in the probabilities on the Day 5 winter weather outlook. Depending on strength of the low, gusty winds could accompany snowfall leading to possible blizzard conditions. It should be noted though that the specifics of this possible system remains highly uncertain as models still show some significant differences in low placement and strength which leads to a lot of variability on heavy rain/snowfall axes. Despite this, the potential for a meaningful winter storm over parts of the northern tier is there. In the warm sector of this storm, moderate to heavy rainfall is possible across parts of the Upper Midwest/Great Lakes. Despite plenty of uncertainty in the details still, the tropical disturbance moving towards Florida later this week continues to show an increasing threat for coastal and maritime impacts, including heavy rain, coastal flooding, high waves, and rip currents. Moisture from this system should move up the East Coast later in the week, although amounts and coverage remain highly uncertain still. Much below normal temperatures are expected to expand across the West through the latter part of this week associated with the deepening upper trough. The coldest air will likely be across the northern High Plains and Plains with recent forecasts showing highs in that area up to 20-30F below normal Wednesday-Friday. Many locations over the West could see daily records for cold highs through Wednesday. In contrast, well above normal temperatures will progress from the Central Plains to the East Coast Wed-Fri with widespread daily records for warm lows possible. Wednesday should be the warmest day for the Plains to the Upper Midwest with readings 10-20+ above normal. A strong cold front through this region by Thursday will usher in a much colder airmass, with high temperatures by Friday and the weekend in the Plains and Midwest as much as 10 to 20 degrees below normal. 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