Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Sat Nov 23 2019 Valid 12Z Tue Nov 26 2019 - 12Z Sat Nov 30 2019 ...Several Major Storms for the Thanksgiving Holiday Period... ...Guidance/Predictability Assessment... The latest models and ensembles show much better than average forecast clustering/predictability regarding the evolution of a shortwave trough exiting the Central Rockies at the beginning of the period (Tuesday), and steadily deepening as it lifts into the Great Lakes and the Northeast by Wednesday. This should spin up an impressive cyclone at the surface which tracks across the Central Plains and Midwest Tuesday into early Wednesday, exiting New England by late Wednesday. Model agreement and run-to-run variability on the timing and intensity of this system has improved within the past 24-36 hours, with most deterministic and ensemble means showing a similar track for this feature. The preferred blend for this system was a composite of the GFS/ECMWF, the GEFS/ECMWF ensemble means and the National Blend of Models. This maintains good continuity with the previous WPC forecast and depicts a significant storm system to message. Another focus for highly threatening weather is also out West where models and ensembles continue to show very amplified troughing and an upper level low dropping down the West Coast starting by mid next week that persists and is reinforced into later next week. The sharp digging of a potent upper jet and height falls that acts to carve out the anomalously amplfied system is well supported by upstream mid-upper ridge amplification pumped up by farther upstream potent northeast Pacific and Bering Sea low/storm activity. This is a high predictability event at medium range time scales, especially for the day 3-5 time frame. There remains some question on how quickly the energy begins ejects though by days 6-7 (Fri-Sat). Suspect lead main energies will eject through the Rockies into the Central U.S. with some vigor heading into next weekend, but reinforcing energy will still maintain a base trough over the West. The progressive 12 UTC GFS seems the outlier compared to most other models and ensembles including the 12 UTC GEFS. ...Weather Highlights/Threats... Moderate to locally heavy precipitation is likely Tuesday into Wednesday on the north and west side of the surface low from the Central Plains to the Upper Midwest. Some accumulating snows may be possible on the northern edge of the precipitation shield. As the storm lifts into the Northeast on Wednesday, wintry precipitation is possible across northern/interior New England. Depending on surface low intensity, a period of high winds may also accompany this system. Heavy mountain snows are likely from the Washington/Oregon Cascades and the Sierras on Tuesday, spreading into the Great Basin and Rockies Wednesday-Friday as the upper trough amplifies along the coast. Snow levels will drop significantly. Another round of potentially heavy rainfall with a threat of runoff problems are also especially likely across Southern CA and the Southwest (including burn scars) by mid to late next week. Rainfall is also likely from portions of the Southern Plains to the Tennessee Valley as multiple shortwave impulses round the base of the Western U.S. trough and tap some mid-upper level moisture from the tropical east Pacific. The biggest temperature anomalies will focus across the Western U.S. through much of the period with daytime highs averaging 10 to 20 degrees below normal. In response to this trough, ridging builds across the south-central U.S. which should bring a return of above normal temps (anomalies +5 to +10 degrees) to this region by the end of the period. In the East, above normal temperatures Tuesday and Wednesday should moderate back to normal or slightly below normal at the end of the week. Schichtel Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml