Extended Forecast Discussion NWS Weather Prediction Center College Park MD 149 AM EST Sat Nov 30 2024 Valid 12Z Tue Dec 03 2024 - 12Z Sat Dec 07 2024 ...Central/East U.S. Arctic cold moderates/renews next week... ...Significant Great Lake effect snows continue next week... ...Overview... An anchoring mean upper trough will encompass much of the central to eastern United States next week, with only a very gradual shift east over time. This pattern with west/northwest winds will be favorable for continued long duration Great Lake effect to Northeast terrain focusing snows. Some snowfall accumulations will be significant in favored locations to the lee of the Great Lakes. The periodically reinforced trough aloft and cold surface high pressure originally stemming from the Arctic will cause continued colder than average temperatures migrating far southward across central and eastern parts of the country. There will be periods of temporary moderation between cold air surges and moderate return flow from the Gulf of Mexico will bring enhanced rainfall chances from Texas through the central Gulf Coast states. Meanwhile, benign weather and gradually warming temperatures are forecast for much of the West, albeit with enhanced showers best able to reach the Pacific Northwest next weekend with closer Pacific system approach. ...Guidance/Predictability Assessment... Models and ensembles now show good agreement and as a result higher confidence in the overall mid-large scale pattern through next week. Especially mid to late period though, there are some smaller scale differences particularly with shortwaves working to reinforce Eastern U.S. troughing and the specifics/frontal timing of a more defined surface low/system through the Great Lakes. Uncertainty has slowly decreased with the timing/orientation of a slow moving southern stream elongated trough/closed low near the Southwest U.S. which has implications for rainfall amounts across south-southeast Texas much of the week that gradually spreads over the central Gulf Coast states. Overall, The WPC progs for next week were mainly derived from a broad composite model and ensemble mean blend and compatible National Blend of Models. This maintains good continuity with the previous WPC forecast suite as well an latest 00 UTC cycle guidance, further bolstering forecast confidence. ...Weather/Hazards Highlights... A highly favorable pattern for Great Lake effect snow will persist well into next week. Exact snow axes and local intensities will depend on reinforcing system passages with wind directions that could vary from northwest to west day to day, but some areas downwind of the lakes will see significant accumulations, likely causing travel disruptions to include I-90 between Cleveland and Buffalo and I-81 north of Syracuse. Shortwaves and frontal systems may also support periods with additional light to moderate snows that could cover a broader area from the north-central Appalachians through favored terrain of the Northeast. Much of the rest of the country can expect mainly dry conditions next week, but there are exceptions. Return flow of moisture could start to come into the western Gulf Coast region by early next week to fuel some enhanced rainfall. This looks to be slow to spread across the central Gulf Coast region into mid-later next week. At this point, rainfall amounts are not high enough to warrant even a marginal risk on the WPC Days 4 and 5 Excessive Rainfall Outlooks, but this can continued to be monitored given anomalous moisture and modest instability. Initial upper ridging will keep the West mainly dry, but enhanced precipitation chances gradually increase for the Pacific Northwest by next weekend pending variance with extent/timing of Pacific system approach. Schichtel 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