Extended Forecast Discussion NWS Weather Prediction Center College Park MD 150 PM EST Thu Jan 20 2022 Valid 12Z Sun Jan 23 2022 - 12Z Thu Jan 27 2022 18Z Update: The 12Z model suite is in excellent agreement on the overall synoptic scale pattern through about early Tuesday, with broad cyclonic flow aloft with a deep trough anchored over the central-eastern U.S., and a ridge off the West Coast. A shortwave trough tracking around the eastern periphery of that ridge sinks southward across the Intermountain West, with the past few runs of the GFS being quite amplified by Wednesday with this feature, and the overnight run was an outlier solution compared to the ensemble spaghetti plots. Therefore, the GFS was weighted less for the second half of the forecast period. In terms of QPF, there was a slight increase in rainfall totals for the central Gulf Coast region, and a slight decrease across the Mid South. Otherwise, the majority of the forecast remains on track and the previous discussion is appended below for reference. /Hamrick ...Pattern Overview and Guidance/Predictability Assessment... Models and ensembles are in good agreement with the amplified mean flow over the lower 48 highlighted by an upper ridge off/along the West Coast and an upper trough over the central to eastern U.S.. Guidance now offers more characteristic run to run continuity issues with embedded systems within the larger scale flow over time in a pattern with seemingly near normal forecast predictability. Accordingly, the earlier issued WPC medium range product suite was mainly derived from a composite of the the reasonably well clustered solutions of the 18 UTC GFS and 12 UTC ECMWF/UKMET/Canadian along with the 01 UTC National Blend of Models for days 3/4 (Sunday/Monday). Transitioned to a composite of the compatible 18 UTC GEFS and 12 UTC ECMWF ensemble means along with the NBM for days 5-7 (Tuesday-next Thursday). This along with some applied manual adjustments consistent with uncertainty maintains decent WPC product continuity that also remains generally in line with a similar composite plan from newer 00 UTC guidance. ...Weather Highlights/Threats... A weekend southern stream Southwest U.S/northern Mexico closed low offers some snow potential for the Southern Rockies/High Plains. The system will eject eastward across the U.S. southern tier early next week and wave genesis on a lingering trailing front over the Gulf of Mexico will induce lead moisture return from the Gulf of Mexico to fuel a moderate swath of precipitation within a cooled airmass from Texas eastward across the Gulf Coast/Southeast. This may include some snow/ice on the northern periphery of precipitation. The next in a series of Arctic Blasts will again spread far south over the central and eastern U.S. Monday-next Thursday as another mean flow reinforcing upper trough digs southeastward from Canada. Transitory frontal enhanced upslope snows will dig through the cooling Rockies and adjacent High Plains. Northern stream upper system passage and frontal low genesis on the leading edge of Arctic air starting Monday should support a windy snow swath from the Dakotas through the Upper Midwest/Great Lakes. Low development through the Great Lakes/Northeast Tuesday into Wednesday and trailing cold frontal passage across the East favors lingering lake effect along with some threat of plow-able snows from the Appalachians through the Northeast. System evolution becomes complex offshore and into the Canadian Maritime by midweek as the aforementioned southern stream system phases/lifts on the lead periphery of the amplified northern stream upper trough. Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook 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