Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EST Sat Nov 23 2019 Valid 12Z Tue Nov 26 2019 - 12Z Sat Nov 30 2019 ...Guidance/Predictability Assessment... Models seem to be coming into much better agreement regarding the evolution of a shortwave trough exiting the Central Rockies at the beginning of the Period (Tuesday), and steadily deepening as it lifts quickly into the Upper 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, and 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-hours, with most deterministic and ensemble means showing a similar track for this feature. The exception to this is the 12z/Nov 22 UKMET which has a much weaker upper shortwave/surface low. The preferred model blend for this system was a general model compromise of mostly deterministic 12z/Nov 22 ECMWF and 18z/Nov 22 GFS, with small contributions from the ECENS and GEFS means. This maintains good continuity with the previous WPC forecast. After this, the focus shifts out West where models continue to show very amplified troughing and an upper level low dropping down the West Coast in the middle to latter part of next week. Models and ensembles show good agreement on this feature in the day 3-5 time frame, but there remains question on how far south the height falls dig and how quickly the energy begins shifting inland by days 6-7 (Fri-Sat). The GFS remains faster and farther south with the upper low compared to the ECMWF and CMC, with the ensemble means representing a good middle ground solution. Thus, preferred a mostly ensemble mean (ECENS/GEFS) blend on days 6-7, but did keep a small percentage of the ECMWF because it was the deterministic model which most closely resembled the ensemble means. ...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. Another round of potentially heavy rainfall is also possible across the Southwest 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. 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. Santorelli 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