Extended Forecast Discussion NWS Weather Prediction Center College Park MD 248 PM EST Thu Nov 24 2022 Valid 12Z Sun Nov 27 2022 - 12Z Thu Dec 01 2022 ...Snow likely across higher elevations of the West into next week... ...Heavy Rain and severe weather possible across parts of the South and into the Ohio Valley Tuesday-Wednesday next week... ...Overview... A fairly progressive upper pattern is in store for much of next week. The upper low located in the Southern Plains during the short range period should be lifting into the Mid-Mississippi Valley as the medium range period begins early Sunday, while a surface low also tracks quickly northward across the northeastern quadrant of the U.S. and spreads precipitation along the low track and the trailing cold front in the Mid-Atlantic to Southeast on Sunday. Most precipitation will be rain, but there could be some light snow in higher elevations of the interior Northeast. Then troughing is set to dig and amplify across the western U.S. Monday-Tuesday, mountain snow chances shifting from the Pacific Northwest to the central Great Basin and Rockies. As the trough shifts eastward, the current forecast shows a consolidating surface low pressure system to shift from the central Plains into the Midwest for Tuesday-Wednesday, with some snow possible north and west of the low for the Northern Plains into the Upper Midwest. Confidence continues to increase for severe weather and heavy rainfall potential ahead of this system across parts of the south and into the Ohio Valley. ...Guidance and Predictability Assessment... Latest 00z/06z guidance shows fairly good agreement on the initial upper low as it shifts into the Midwest on Sunday. Behind this, another much weaker shortwave should quickly move through the southern Plains into the Midwest Sunday-Monday. Though the 00z CMC was a slower outlier, the 12z run today did speed up and seems more in line. Attention then shifts out West as a trough begins to dig through the West Monday-Tuesday, and into the central and eastern U.S. Wednesday-Thursday. Guidance and ensembles show minor timing differences early in the week with this potentially high impact system, but do show some meaningful differences in amplitude. The 00z (and new 12z) runs of the CMC and UKMET are notably less amplified and faster (later period) than the GFS and ECMWF. The ensembles also show some variability but would favor a bit more amplified solution. Minor differences in the upper pattern become more important at the surface with a complex surface low evolution in the central U.S.. These differences are pretty typical for this forecast lead time though, and the daytime guidance does show somewhat better agreement for the eventual track of the consolidated low into southeastern Canada by day 7/Thursday. Models are also reasonably consistent with showing another bout of troughing coming into the Northwest late in the period, but with more differences in the timing. The WPC forecast used a general blend of the deterministic guidance led by the 06z GFS and 00z ECMWF for the early part of the period. Left the CMC and UKMET out after day 4 in favor of the ensemble means in order to depict a more amplified trough over the West. The forecast gradually transitioned to half GEFS/EC ensemble mean with the GFS and ECMWF by days 6-7. This helped to mitigate some of the model details differences and also maintained good agreement with the overnight WPC forecast package. ...Weather/Hazard Highlights... Gulf moisture is forecast to stream into the eastern U.S. ahead of the upper and surface lows moving from the Mid-Mississippi Valley northeastward and produce widespread rain chances on Sunday for the East. With this low track, most areas are likely to see rain rather than wintry precipitation, with the exception of higher elevations of the Interior Northeast where snow could fall. A fairly progressive system should lessen overall flooding concerns. The Pacific Northwest into the Northern Rockies can expect increasing precipitation on Sunday in conjunction with a couple of frontal systems. Precipitation is then forecast to spread southward across California and eastward into the Great Basin and Rockies by Monday as the noted upper trough continues digging into the region. Lower elevation rain and higher elevation snow will be likely. At this point it looks like the heaviest snow should be across the Cascades into the Wasatch to Wind River Mountains and the Northern/Central Rockies, with more uncertainty for heavy precipitation in California/the Sierra Nevada. Yet another round of troughing could increase chances for additional precipitation in the Northwest by Wednesday-Thursday, with even some potential for lower elevation snows too. Low pressure system development/consolidation still looks likely in the central U.S. by around midweek, bringing precipitation chances to central and eastern portions of the lower 48. Widespread, potentially heavy rainfall looks possible across parts of the Mississippi Valley into the Ohio/Tennessee Valleys and Appalachians. There also remains potential for snow on the backside of the low as it tracks northeastward into the Midwest Tuesday-Wednesday, with a possible focus of snow from the eastern Dakotas into the Upper Midwest. Sufficient moisture and instability in the warm sector could lead to severe weather, with SPC already highlighting the chance in their outlook for next Tuesday across parts of eastern Texas into the lower Mississippi Valley. Details regarding this potentially high impact system will vary as it gets closer in time, so stay tuned to future forecast updates. Slightly cooler than normal highs could linger in the south-central U.S. on Sunday, while milder than normal temperatures are possible in the East with anomalies for lows around 10-20F and highs around 5-15F above normal. But more widespread cooler than normal temperatures are likely to expand across the western half of the U.S. Monday-Wednesday as deepening troughing takes hold. Anomalies of 15-25F below average may focus across the northern High Plains Monday and spread south into the Great Basin and central High Plains Tuesday. Meanwhile, the south-central and east-central U.S. could see above normal temperatures ahead of the western trough. Then the cold air continues marching eastward to flip most areas to below normal by next Thursday. Santorelli/Tate 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 Hazards: - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Tue-Wed, Nov 29-Nov 30. - Heavy snow across portions of the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Sun, Nov 27 and Wed-Thu, Nov 30-Dec 1. - Severe weather across portions of the Lower Mississippi Valley and the Southern Plains, Tue, Nov 29. - Flooding occurring or imminent across portions of the Southeast. - High winds across portions of the Southern Rockies, the Southern Plains, and the Southwest, Tue, Nov 29. - High winds across portions of the Northeast and the Great Lakes, Wed, Nov 30. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices are at: 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