Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Fri Nov 1 2024 Valid 12Z Mon Nov 04 2024 - 12Z Fri Nov 08 2024 ...Heavy rain and severe weather expected across portions of the central U.S. into early next week... ...Overview... The central U.S. will be the most prominent focus for active weather during portions of next week. In particular, continuing into Monday expect an area of heavy rainfall over parts of the Plains/Midwest as southern Plains upper dynamics eject northeastward while the leading wavy front interacts with abundant moisture contributed by strong Gulf inflow. Then most guidance shows shortwave energy arriving from the Pacific and dropping into the Rockies/Four Corners region, possibly closing off an upper low after midweek. This feature may produce additional rainfall over the southern Plains and vicinity late in the week but likely with lighter totals than in the preceding event. An area of rain and higher elevation snow should pass through the Pacific Northwest and move south through the Rockies with the progression/evolution of the energy aloft. This pattern will favor very warm temperatures (likely including some daily records) over the East and below normal readings over most of the Interior West and Rockies. Meanwhile, the National Hurricane Center is monitoring possible Caribbean tropical development that may emerge into the Gulf, with typically broad guidance spread for track and timing. ...Guidance/Predictability Assessment... While the agreement does not extend to rainfall amounts over the Mississippi Vally and vicinity by Tuesday, there is otherwise a solid guidance consensus regarding the details of ejecting southern Rockies energy and leading wavy surface front during the first part of the week. Then models and ensembles diverge for incoming Pacific energy that is most likely to dig southward over the Interior West/Rockies. While there is a lot of spread within the full ensemble envelope, enough members cluster well enough for the means to suggest an upper low closing off over the Four Corners region by next Thursday-Friday. The 18Z GFS/12Z ECMWF/12Z CMC all fit this scenario as well. Among new 00Z runs, the ECMWF remains a bit on the western side with the upper low while the GFS/CMC have shifted eastward. A number of 12Z machine learning (ML) models offer potential for the upper low/trough to reach the Plains by next Friday though one is slow like the new 00Z ECMWF. As this energy separates, northern stream flow should trend toward broad troughing over the northeastern U.S. and eastern Canada while western Canada and the northwestern U.S. see mean ridging ahead of a couple strong systems near Alaska. As for the possible Caribbean tropical development tracking into the Gulf, latest CMC and ECMWF AIFS runs are on the fast and eastern side of the spread with Gulf Coast/Southeast effects already by late next week. Among other guidance the most common theme by next Friday is a position over the central or southwestern Gulf. This is in line with extrapolation of yesterday's WPC/NHC coordinated depiction through Thursday. Guidance comparisons led to starting the updated forecast with a 12Z/18Z operational model composite during the first half of the period and then a transition toward the 18Z GEFS/12Z ECens means and operational runs (more GFS/ECMWF than CMC). ...Weather/Hazards Highlights... Strong deep-layer flow from the Gulf of Mexico ahead of a wavy front pushing through the central U.S. will contribute abundant moisture to a heavy rain event expected to continue from the weekend into the first part of next week. The Storm Prediction Center is also monitoring severe weather potential over parts of the central/southern Plains. Currently the relatively higher potential for repeat and training convection with locally high rainfall rates extends from around eastern Oklahoma/western Arkansas northeastward into northern Illinois, corresponding to the Slight Risk area in the Day 4 Excessive Rainfall Outlook. This region will initially see dry ground conditions but some rainfall is likely in the shorter term leading into Day 4. The coverage of significant rainfall will likely decrease by Day 5/Tuesday as the upper dynamics and primary frontal wave continue northeastward. However lingering moisture/instability may promote some additional rainfall, with considerable spread among guidance for amounts. The Day 5 ERO depicts a Marginal Risk area from the Lower Ohio Valley southwestward as a reasonable starting point given the forecast uncertainty. Incoming Pacific dynamics will bring an episode of terrain-enhanced rain and higher elevation snow to the Pacific Northwest early in the week with precipitation then dropping south through the Rockies, plus with some rainfall developing over the Plains. Specifics for Rockies/Plains totals will be sensitive to the details of flow aloft. A broad area of well above normal temperatures will drift across the eastern half of the country, with gradual progression of a couple fronts eventually leading to some moderation by late week. Warmest anomalies should be for morning lows, with some areas 20F or more above normal for one or more days, but daily records will be possible for both highs and warm lows during early-mid week. In contrast, a majority of the Interior West and Rockies should see chilly temperatures for most of next week with readings tending to be 5-15F below normal. Rausch 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