Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Wed Nov 13 2024 Valid 12Z Sat Nov 16 2024 - 12Z Wed Nov 20 2024 ...Overview... Troughing over the West by this coming weekend will split sending northern stream energy through the northern Plains/Upper Midwest, while southern stream energy drops south and then eastward early next week. This should help induce cyclogenesis in the lee of the Rockies with a modestly deep storm ejecting northeastward through the Central U.S. next Tuesday and Wednesday. The pattern would support heavy rainfall potential from the south-central Plains into the Mississippi Valley by late this weekend into early next week, with some snow possible on the backside of the low depending on cold air filtering in behind this system. Another atmospheric river will bring a round of heavy rain and mountain snows to the Pacific Northwest this weekend. This should reload and help deepen mean troughing over the West resulting in a rather active and amplified pattern across the CONUS by next week with strong troughing shifting through the Central U.S. and ridging over the East and West coasts. Meanwhile, guidance continues to suggest some sort of tropical development emerging out of the Caribbean and into the southern Gulf of Mexico next week. ...Guidance/Predictability Assessment... The guidance shows good agreement on the overall large scale pattern across the CONUS for the upcoming medium range period, but plenty of uncertainty in the details and evolution of individual systems. The main area of uncertainty continue sot lie with the deep Western trough which may briefly close off a low in/around northwest Mexico before it moves eastward. The models show better agreement this should track northeastward inducing strong surface low pressure that tracks through the Central U.S. next week. More uncertainty surrounds the next shortwave into the West which should reload and deepen the mean Western trough leading to some differences in exactly how energy gets incorporated into the trough and how quickly it moves eastward. Farther south, the guidance has been trending towards an emerging tropical threat out of the Caribbean into the southern Gulf, but still quite a bit of uncertainty on potential impacts to parts of the Southeast. See tropical outlooks from the National Hurricane Center for the latest information on this potential. Was able to utilize a GFS/ECMWF/CMC blend for the first few days of the WPC progs tonight. Quickly trended more towards the ensemble means late period to account for increasing uncertainty with the West to Central U.S. trough. This generally maintains good continuity with the previous WPC forecast, but maybe a little quicker with surface low/frontal progression through the Plains- Mississippi Valley. ...Weather/Hazards Highlights... Precipitation should increase in intensity and coverage across parts of the Four Corners region into the south- central Plains/Mississippi Valley beginning this weekend, with the overall setup supporting a heavy rain threat from the south-central Plains into the middle Mississippi Valley Sunday-Monday. Exact amounts, location, and impacts remain very uncertain but there is enough signal to introduce a broad marginal risk on the Day 5/Sunday Excessive Rainfall Outlook from northern Texas into Oklahoma. Depending on cold air filtering in behind the system, some snow may be possible across the Rockies into the northern Plains early-mid next week. Generally wet conditions is expected to accompany the cold front late period as it pushes into the east-central states and Great Lakes. Out West, another atmospheric river will support heavy rain and mountain snows across the Pacific Northwest this weekend. Marginal risks are highlighted on both the Day 4 and 5 EROs. Moisture from whatever tropical threat emerges out of the Caribbean may begin impacting parts of Florida mid next week, but there is a lot of uncertainty in exact impacts and amounts from this. But this will need to continue to be watched. Above normal temperatures will progress eastward with time from the Central U.S. Saturday, enveloping the East by Sunday into Monday. Daytime highs could be 10-15 degrees above normal in some spots. Out West, temperatures will trend much cooler with time as upper troughing amplifies over the region and persists into next week. 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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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