Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1226 PM EST Sat Jan 11 2020 Valid 12Z Tue Jan 14 2020 - 12Z Sat Jan 18 2020 1730 UTC Update... A blend of the 00Z ECMWF/GFS was used extensively during days 3-5 (Tue-Thu) for this update. These solutions were fairly similar with low pressure crossing the Great Lakes Tue-Wed, and the next low pressure system following quickly behind it, moving from the mid-Mississippi Valley to the lower Great Lakes/Northeast as it is forecast to deep rather quickly Thu-Fri. Still some spread among the guidance by Fri as to how quickly the system move east, although a component of this is also how quickly energy transfers from the inland surface low to a new triple point low across New England on Fri. A number of ensemble members continue to show the primary surface low back across the Great Lakes Fri morning, while the consensus of deterministic guidance has shifted farther east. Farther west, consensus is relatively good among the guidance on a relatively deep low pressure system expected to approach the Pacific Northwest Wed-Thu, although there are still a few ensemble members that are slower and/or weaker. By later in the extended forecast period, a trend was noted among the latest guidance for a bit slower solution with the next shortwave crossing the Rockies Thu night/Fri and moving into the central U.S. Fri night/Sat. Followed this trend and slowed the progression of a low pressure system expected to develop across the central U.S. by Fri-Sat in this update. Overall, a shift toward heavier weighting of ECENS/GEFS ensemble means was shown during days 6-7 (Fri-Sat), with some continued use of small components of the ECMWF/GFS. Ryan Previous Discussion (issued at 0535 UTC)... ...Weather Pattern/Hazard Highlights and Guidance/Predictability Assessment... A deepened closed low/trough is still expected to shift from the Canadian Rockies eastward across southern Canada to the Canadian Maritimes Tuesday-Friday. A cold Arctic airmass coincident with lower atmospheric high pressure will spill southward through the Northwest and the central and eastern U.S. Expect a stark temperature contrast across this front that will divide areas with much below and much above values that near records. Recent GFS runs seem too aggressive with arctic air, but WPC remains settled between the GFS and alternate guidance that may prove too benign given the pattern. Meanwhile underneath, an amplified mid-upper level mean trough will periodically be reinforced with eastern Pacific storm energies that dig over an unsettled western U.S. next week. In particular, guidance has trended in support of a deepened/well organized low offshore the Pacific Northwest Wed/Thu that would enhance maritime hazards and inland flow/weather. WPC QPFs and 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. Snows over the northern High Plains/Rockies would be enhanced by periodic post-frontal lower level upslope flows. Upper trough energies and 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 and undercutting the Arctic airmass. The preferred GFS/ECMWF/Canadian now offer quite similar system evolutions Tue-Thu including a deepening low from the central Plains to the Northeast, but the UKMET does not develop the low much, so some uncertainty lingers. There is also uncertainty with potential cyclogenesis ahead of the northern stream cold surge along lead fronts by day 6-7, so an ensemble mean forecast approach was used. Overall, the pattern seems to favor moderate rainfall potential next week from the south-central U.S. to the Appalachians overtop the shielding Southeast ridge. The pattern also offers a widespread snow/ice threat in the cooled northern tier of the central and eastern U.S. as deepening frontal waves wrap moisture into the region, especially Wed/Thu and then again with more uncertainty heading into next weekend. This threat is also shown by WPC progs, grids, QPFs and winter weather outlook probabilities. 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 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