Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Sun Nov 24 2019 Valid 12Z Wed Nov 27 2019 - 12Z Sun Dec 01 2019 ...Several Major Storms for the Thanksgiving Holiday Period... ...Guidance/Predictability Assessment... Model guidance in good agreement continues to indicate a tight shortwave trough will spin up into a closed upper low in the Upper Midwest by day 3/Wed, with good agreement in the 06Z GFS and GEFS mean as well as the 00Z ECMWF and UKMET. The 12Z model cycle has come in with this idea as well, so with good run-to-run continuity, a multi-model blend was used for this feature which is likely to spin up a strong surface low. These features track east-northeast on day 4/Thu, affecting the Northeast. The other main feature in the medium range is the anomalously deep (3-4 standard deviations below normal for 500 mb heights) upper low moving through the West midweek onward. The guidance is well clustered through day 3-5 but start to diverge day 5-6 (Fri-Sat), with the 06Z GFS and (to a lesser extent) the GEFS ejecting energy eastward more quickly than other models like the EC. Given this can be a common bias for the GFS suite, the forecast hedged more toward the 00Z deterministic EC and EC mean, with some incorporation of the GEFS to account for forecast uncertainty. The new 12 ECMWF, however, seems to move the low farther eastward more quickly than its previous run, matching fairly closely with the 12Z GFS. So the timing and the exact track remain uncertain at this time for this feature, but it appears the the associated surface low could end up around the same location (Upper Midwest/Upper Great Lakes region) as the earlier low on Wed. Overall these choices maintained good continuity with the previous WPC forecast. ...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. Accumulating snows are becoming increasingly likely on the northern edge of the precipitation shield--see the short range winter weather forecast for more. As the storm lifts into the Northeast on Wednesday, wintry precipitation is possible across northern/interior New England. A period of high winds appears likely to accompany this system as well. Meanwhile, heavy mountain snows are likely across the Great Basin and Rockies Wednesday-Friday with snow levels expected to drop significantly due to the anomalously low 700 mb heights. 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. Heavy rainfall is also possible from portions of the Southern Plains to the lower Ohio 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 northwest edge of this precip shield across eastern New Mexico/Texas Panhandle may also see accumulating snowfall with surface high pressure and sufficiently cold air diving southward across the Plains. With the next potential storm system winding up in the Central U.S. into next weekend, accumulating snows (potentially heavy or significant) are possible to the north and west of the surface low from the Northern Plains to the Upper Mississippi Valley next Friday and Saturday. 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 on Wednesday should moderate back to normal or slightly below normal at the end of the week. Tate/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