Extended Forecast Discussion NWS Weather Prediction Center College Park MD 303 PM EST Fri Jan 10 2020 Valid 12Z Mon Jan 13 2020 - 12Z Fri Jan 17 2020 1730 UTC Update... A multi-model blend including the 00Z ECMWF/CMC/06Z GFS was used as a forecast starting point during days 3-5 (Mon-Wed) for this update. For days 6-7 (Thu-Fri), the forecast relied more heavily on the ECENS ensemble mean along with some continued use of the deterministic ECMWF. The GFS continues to be much more aggressive with spreading an arctic air mass southward and eastward across the central/eastern CONUS relative to the ECMWF, to the degree where the two pieces of guidance showed nearly a 40 deg F spread for high temperatures across portions of the central U.S. on day 7. Actual forecast temperatures were somewhere in between, with a nod toward the warmer ECENS guidance (not near as warm as the deterministic ECMWF, however). Overall, changes to the forecast from continuity were relatively small. Made a westward adjustment to the position of a low pressure system crossing the eastern Great Lakes Wed night/Thu morning, as a number of solutions/ensemble members continue to suggest a track farther west, despite the eastward shift in much of the deterministic guidance from yesterday. Based on a building ridge between Hawaii and Alaska next week and the associated teleconnections, continue to feel that there is the potential for the southeastern U.S. subtropical ridge to be stronger than indicated by recent deterministic runs, which would result in a more amplified flow pattern across the CONUS and a surface low track a bit farther west by later next week. At a larger scale, the ECENS and the GEFS means showed a fairly significant difference by late next week, with the ECENS showing a broad upper trough across the interior West, with anticyclonic upper-level flow across the East, and the GEFS showing a ridge axis near/just east of the Rockies and broad cyclonic flow farther east. The described pattern over the north central Pacific supports something more like the ECENS, and thus this was weighted quite a bit heavier than the GEFS late in the extended forecast period. Ryan Previous Discussion (issued at 07 UTC)... ...Weather Pattern/Hazard Highlights and Guidance/Predictability Assessment... A closed low/trough will shift from the Canadian Rockies eastward across southern Canada to the Canadian Maritimes Monday-next Friday and a cold arctic airmass coincident with lower atmospheric high pressure will spill southward through the Northwest and the central and eastern U.S. in the wake of passage. This offers a threat for a swaths of snow across the U.S. northern tier of the central and eastern U.S., albeit with mainly modest QPF. Meanwhile underneath, an amplified mid-upper level mean trough will periodically be reinforced with eastern Pacific energies that dig over an unsettled western U.S. next week. WPC winter weather outlook probabilities show a widespread snow threat over the Northwest that may work down to lower elevations given the extent of cold air filtration. Activity will spread down into the Sierra and out across the north-central Great Basin/Rockies with system progressions. Trough energies and associated surface systems will tend to eject east-northeastward out from the West over the central and eastern U.S. overtop a lingering and warming/stabilizing Florida mean ridge. There remains much uncertainty with potential cyclogenesis scenarios in advance of the northern stream cold surge and along lead fronts, but the pattern seems to favor the heaviest rainfall potential next week from the lower MS Valley and Mid-South through the Southeast overtop the shielding Florida ridge. The latest models and ensembles are tending to converge upon a more common solution with mid-scale systems embedded within complex and progressive flow over the lower 48 states. This bolsters forecast confidence a bit, but recent runs of the ECMWF have been erratic and still offer more variance than desired. Accordingly, the WPC medium range product suite was primarily derived from a composite blend of the more compatible and run to run stable 18 UTC GFS and 12 UTC ECMWF ensemble mean along with the 00 UTC National Blend of Models. This blend maintains good WPC forecast continuity. Schichtel Hazards: - Heavy precipitation across portions of the Pacific Northwest, Wed-Thu, Jan 15-Jan 16. - Heavy precipitation across portions of the Northeast and the Great Lakes, Thu-Fri, Jan 16-Jan 17. - Heavy rain across portions of California and the Pacific Northwest, Wed-Thu, Jan 15-Jan 16. - Heavy rain across portions of the Southeast, the Mid-Atlantic, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Mon-Tue, Jan 13-Jan 14. - Heavy snow across portions of California, the Central Great Basin, the Pacific Northwest, the Northern Great Basin, and the Southwest, Tue-Fri, Jan 14-Jan 17. - Heavy snow across portions of the Central Rockies, the Central Great Basin, the Northern Rockies, the Northern Great Basin, and the Northern Plains, Mon-Tue, Jan 13-Jan 14. - Flooding possible across portions of the Central Plains, the Lower Mississippi Valley, the Southern Plains, the Middle Mississippi Valley, the Northeast, the Great Lakes, and the Ohio Valley. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Pacific Northwest, and the Northern Plains. - Flooding likely across portions of the Great Lakes, the Middle Mississippi Valley, the Lower Mississippi Valley, the Southern Plains, and the Ohio Valley. - Much below normal temperatures across portions of the Northern Rockies and the Northern Great Basin, Mon-Wed, Jan 13-Jan 15. - Much below normal temperatures across portions of the Central Plains, the Upper Mississippi Valley, the Northern Plains, and the Northern Rockies, Mon-Fri, Jan 13-Jan 17. - High significant wave heights for coastal portions of California and the Pacific Northwest, Wed-Thu, Jan 15-Jan 16. - Much below normal temperatures across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Jan 13-Jan 14. - Much below normal temperatures across portions of the Alaska Panhandle, Mon-Thu, Jan 13-Jan 16. 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