Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 PM EDT Thu Oct 31 2024 Valid 12Z Sun Nov 3 2024 - 12Z Thu Nov 7 2024 ***Heavy rain and severe weather expected across portions of the southern and central Plains going into early next week*** ...General Overview... The first half of the extended forecast period is forecast to be quite active across the south-central U.S., with strong return Gulf of Mexico inflow into a deepening moisture channel between a Southeast U.S. upper ridge and the slow approach of an amplified upper trough and front from the West. The upper trough energy is expected to dig sharply across the Western U.S. this weekend, yielding heavy rainfall and potential severe weather across the Plains, and high elevation snows from the Northwest U.S. to the central/northern Rockies. Warm weather will continue to make headlines for the eastern U.S. with additional record highs possible. ...Guidance/Predictability Assessment... The 12Z model guidance suite features good overall agreement across the Continental U.S. going into Sunday and early next week, given a more amplified upper flow pattern evolving with a deep Western U.S. trough and a building ridge axis east of the Mississippi River. This will result in a pronounced temperature dichotomy across the country, with highs running up to 20 degrees above early November averages across the Ohio Valley early next week, and 15 degrees below average for portions of the Intermountain West. Going into the middle of the week, the models have converged on a more agreeable solution with a large positively tilted trough from the Rockies to the north-central U.S., with some differences across southern Canada and the Great Lakes region. The guidance still agrees quite well on the anomalous upper ridge just off the Southeast U.S. coast. The ensemble means were gradually increased to about 40% by next Wednesday/Thursday. ...Weather/Hazards Highlights... With a nearly continuous plume of deep-layered return flow from the Gulf between the amplifying western trough and the ridge anchored over the Southeast U.S., a multi-day heavy rain event is expected from the Southern Plains to the southern Great Lakes. This activity is expected to expand and focus along a southwest to northeast oriented axis ahead of additional frontal boundaries this weekend and into early next week as robust upper trough/closed low energy digs upstream across the Western U.S. to re-amplify the flow over the Lower 48 and vicinity. Multiple days of deep southerly, moist Gulf inflow look to increase the chances of more widespread and heavy rainfall with increasing flooding concerns despite the recent drought conditions. This includes the risk of repeat and training convection with locally high rainfall rates in excess of an inch per hour, along with favorable instability and shear parameters in place. Strong to severe thunderstorms are also likely across some of these same areas for Sunday and into Monday. After consultation with the affected weather forecast offices, and taking into account the heavy rainfall over the same general areas in the short range forecast period, a Moderate Risk is now planned across portions of northeast Oklahoma and into southeast Kansas for the Day 4 excessive rainfall outlook (12Z Sunday-12Z Monday), and the surrounding Slight Risk area will be a little larger compared to the previous issuance. For the Day 5 period period, the Slight Risk area from overnight has been adjusted slightly to the east to account for a little faster trend in the latest guidance during this time. For the Pacific Northwest, terrain enhanced precipitation can be expected, along with higher elevation snow reaching the Intermountain West/Rockies. Cooler temperatures will filter in across the West that will help spread rain into the Southwest and into the south-central Great Basin and Rockies into early next week. Meanwhile, additional Pacific system energy upstream may also bring another round of moderate precipitation back into the Northwest. Campbell/Hamrick 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