Extended Forecast Discussion NWS Weather Prediction Center College Park MD 324 PM EST Mon Feb 03 2020 Valid 12Z Thu Feb 06 2020 - 12Z Mon Feb 10 2020 ...Excessive rainfall threat for the Southeast and Mid-Atlantic... ...Heavy snow risk across the Northeast... 1830 UTC Update... Overall, the GFS and ECMWF showed relatively good consensus at the large scale through the medium range. Differences were primarily confined to relatively small timing/intensity differences of features, such that a blend of the solutions yielded a good result reflective of the overall guidance consensus. Thus, a blend of the 06Z GFS/00Z ECMWF was used as a basis for this forecast update, with increasing weight placed on ECENS/GEFS ensemble means through time. Changes to continuity were relatively small. Ryan Previous Discussion (issued at 0523 UTC)... ...Weather/Hazard Highlight and Guidance/Predictability Assessment... Amplified upper troughing with northern and dynamic southern stream energies will work from the Central Plains on Thursday and then cross the eastern U.S. on Friday as reinforcing impulses run over top then dig downstream of a building upper ridge over the West. These impulses and onshore flow will favor a renewed wet pattern from the Pacific Northwest to the Great Basin/Rockies where the threat of heavy snows will again focus into favored terrain/mountains. A feed of mid-higher level eastern tropical Pacific moisture and increasingly deep layered Gulf of Mexico inflow ahead of the approaching upper trough and favorable jet support/instability will fuel an expanding heavy rainfall and local runoff threat from the Southeast to the Appalachians/Mid-Atlantic. SPC also still shows a severe weather risk across the Southeast on Thursday. Cold post-frontal high pressure will dig through the Midwest as lead high pressure dams ahead of the system into the Northeast. Wrap back flow on the northwest periphery of the precipitation shield and theta-e advection into the receding cold air over the northern Mid-Atlantic/Northeast will favor a heavy snow/ice swath threat. Activity will be enhanced by deepening frontal waves lifting from the Gulf Coast to the Appalachians and Northeast Thur-Fri prior to frontal exit into the western Atlantic. With the exception of the CMC (which is much slower than the consensus), models and ensembles have converged more upon a better clustered forecast with this overall scenario, at least at moderate to larger scales, bolstering forecast confidence. WPC favored a blend of the latest GFS/ECMWF with smaller amounts from the ensemble means to smooth out the details. This maintains good continuity with the previous shift. The next system/shortwave enters the Pacific Northwest next weekend, and models indicate this could drop down the West coast resulting in a possible closed low over central California by day 6. This should pull precip from the Pacific Northwest southward into California and the central Great Basin days 6 into 7, with snowfall likely in the higher terrain. The models show better consensus on this feature at least compared to previous days, but the details still need to be worked out. A 50/50 ensemble means with the GFS/ECMWF blend approach is preferred given the lingering uncertainty. Santorelli/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 Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Thu-Fri, Feb 6-Feb 7. - Heavy rain across portions of the Northeast, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, and the Southeast, Thu-Fri, Feb 6-Feb 7. - Heavy snow across portions of the Central Plains, the Northeast, the Central Great Basin, the Northern Plains, the Northern Rockies, the Central Rockies, the Northern Great Basin, and the Great Lakes, Thu-Sat, Feb 6-Feb 8. - Severe weather across portions of the Southeast and the Southern Mid-Atlantic, Thu, Feb 6. - Flooding possible across portions of the Northeast, the Central Appalachians, the Northern Great Basin, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Pacific Northwest. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Pacific Northwest, and the Northern Plains. - Flooding likely across portions of the Southeast and the Mid-Atlantic. 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