Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Mon Feb 06 2023 Valid 12Z Thu Feb 09 2023 - 12Z Mon Feb 13 2023 ...Guidance/Predictability Assessment and Weather/Hazard Highlights... An initially potent southern stream upper trough will eject northeastward from the MS Valley through the Northeast Thursday/Friday as a kicker upper trough digs southeastward through the Rockies to the south-central U.S., amplifying downstream of a building upper ridge over the West. In this pattern, a lead surface low will deepen and track across the Midwest/OH Valley Thursday before exiting through the Northeast Friday. Gulf moisture inflow/instability and right entrance region upper jet/height falls support will combine with the associated frontal system to produce a widespread swath of rainfall across the Appalachians and Eastern Seaboard. Heaviest potential and some risk of runoff issues with repeat/training of cells to monitor in the coming days may be along a trailing front to slow over the moist soils of the Southeast as the upstream upper trough is carved out over the south-central U.S. and subsequently works slowly eastward. Meanwhile, cold air draped to the north of the system and several potent shots of Canadian air in the wake of system passage will also offer a threat for wrapback and lead flow snow/ice on the northern periphery of the expanding precipitation shield out from the central Plains through the Great Lakes and interior Northeast and southern Canada. Expect lake-effect snows into the weekend given lingering cold/windy flow. Upper trough energy slated to lift from the Southeast to up the East Coast for the weekend and modest coastal low genesis and Atlantic inflow could renew a mainly interior Northeast snow threat to monitor. Latest 00 UTC guidance has converged a bit more on a more common system evolution and timings, but there is a ways further to go. While there is a growing guidance signal for the amplification of the overall flow significantly by later week across the nation and adjoining oceans, subsequent precipitation re-emergence may otherwise be limited. Northern stream shortwave trough passage should support modest precipitation shots repeatly over mainly the Pacific Northwest. Modest precipitation with uncertain eastern Pacific/West Coast upper trough/low amplification may organize over south-central CA and the Southwest by the weekend with expected carving out of a closed low to monitor given guidance uncertainties, but forecast spread is reduced with latest 00 UTC guidance bolstering forecast confidence compared to earlier ECMWF/Canadian/ECENS runs that were slower and GFS/UKMET/GEFS runs that were more progressive. Overall now, a composite blend of 00 UTC model and ensemble guidance seems to provide a reasonable forecast basis overall for the pattern evolution and main systems through medium range time scales. 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml