Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 PM EST Mon Nov 25 2019 Valid 12Z Thu Nov 28 2019 - 12Z Mon Dec 02 2019 ...Increasing confidence in a major winter storm for the Thanksgiving Holiday Period... ...Pattern overview and Guidance/Predictability Assessment... A robust upper-level low over the California/Great basin region will spin up a potent winter storm that will spread rain and snow from southern California across the Southwest, Southern/Central Rockies, Plains and into the Great Lakes, Ohio Valley and Mid-Atlantic region by through the course of the extended forecast. Numerous shortwaves will round the base of the western trough into the Central Plains Friday and Saturday as the surface low pressure system tracks northeast over the Rockies. A strong upper-level jet will increase the divergence aloft while enhancing the orographic lift, which will aid in the development of higher rain and snow amounts across this region. Additionally, tight pressure gradients with this system along with the initial intense pressure/height falls will result in very strong winds over much of the Southwest U.S. The ECWMF, GFS and their mean have been persistent in the evolution of this feature, at least through the weekend (day 6)- beyond that there are noticeable timing and location differences for QPF across the Great Lakes and East Coast. As such, a blend comprising of these solutions made up a majority of the forecast. The CMC and UKMET continued to be slower with the progression of the low lifting out of the Great Basin/Four Corners region and it had the QPF shifted west of the rest of the guidance. ...Weather Highlights/Threats... Heavy mountain snows are likely across parts of the Central Great Basin, Desert Southwest and Rockies through Friday, with snow levels expected to drop significantly. Additionally, another round of heavy rainfall with a threat for runoff problems is likely across Southern California and the Southwest (including burn scars) Friday. As the surface low moves out into the Plains, a swath of heavy to potentially significant accumulating snowfall is possible to the north and west of the low from the Northern Plains to the Upper Mississippi Valley and Upper Great Lakes Friday and Saturday. Depending on surface low intensity, a period of strong winds could accompany this system cause blowing and drifting snow. These conditions would make for hazardous travel across this region, especially with increased Holiday traffic. Across the South, shortwave energies tapping into mid-upper level moisture from the tropical East-Pacific will result in heavy to possibly excessive rains shifting from the Southern Plains to the Ohio Valley along and ahead of the main cold front. Much of the Western states will have much below normal temperatures, with some locations as low as 20 to 25 degrees below seasonal average. For the Gulf region, temperatures will be warm and above average, spreading northward into the Ohio Valley Friday and Saturday. Once the front passes through the central U.S. the temperatures will moderate and trend cooler. Campbell 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 Hazards: - Heavy precipitation across portions of the Central Great Basin and California, Sun-Mon, Dec 1-Dec 2. - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Central Great Basin, the Tennessee Valley, the Middle Mississippi Valley, California, the Southern Plains, the Ohio Valley, and the Southwest, Thu-Fri, Nov 28-Nov 29. - Heavy rain across portions of the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Middle Mississippi Valley, the Southern Appalachians, the Great Lakes, and the Ohio Valley, Sat-Sun, Nov 30-Dec 1. - Heavy snow across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Northern Rockies, the Southern Rockies, the Northern Great Basin, the Southern Plains, and the Southwest, Thu-Sat, Nov 28-Nov 30. - Heavy snow across portions of the Central Plains, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Fri-Sun, Nov 29-Dec 1. - Heavy snow across portions of the Northeast and the Great Lakes, Sun-Mon, Dec 1-Dec 2. - Severe weather across portions of the Central Plains 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