Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 PM 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... There is decent large-scale agreement over the next week but plenty of uncertainty in the details and evolution of individual systems. Uncertainty persists 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. The WPC blend was comprised of a combination of the ECWMF/GFS/CMC for the start of the extended period and then included increasing weights of the EC and GEFS ensemble means from the midpoint to the end of the period. This approach maintained continuity from the previous forecast to dampen the increased uncertainty with the West to Central U.S. trough with time. ...Weather/Hazards Highlights... The coverage and intensity of precipiation across portions of the Four Corner to the Southern/Central Plains/Mid-Mississippi Valley will increase over the weekend; which will boost the threat for heavy rain for the Plains and Mid-Mississippi Valley for the start of the week. Given the degree of spread amongst the guidance, specifics for amounts, location and degree of impacts remain very uncertain; however there continues to be a signal focusing in the vicinity of northern Texas into Oklahoma. As such, WPC has maintained a D5 Marginal Risk for excessive rainfall for that region. 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. For the West another atmospheric river is expected to support heavy rain and mountain snows across the Pacific Northwest this weekend. WPC is maintaining the Marginal risks that are highlighting portions of the Coastal and Cascades ranges 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 seasonal normal temperatures will spread from the central U.S. to the East by Sunday into Monday leading to daily maximum temperatures to climb 10 to 15 degrees warmer in a some locations. For the western U.S., it will be trending cooler as upper troughing amplifies over the region and persists into next week. Campbell/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