Extended Forecast Discussion NWS Weather Prediction Center College Park MD 341 PM EST Mon Feb 06 2023 Valid 12Z Thu Feb 09 2023 - 12Z Mon Feb 13 2023 ...Overview... A fairly wavy and progressive pattern will remain in place through early next week. For the latter part of this week upper troughing will progress across the central to eastern U.S., with a couple of surface low pressure systems producing snow across the north-central U.S. and perhaps the Northeast, while heavy rain is a possibility in the Southeast. As an upstream upper ridge traverses across the lower 48 behind the first trough, another trough/potential upper low looks to come into the West this weekend/early next week with some timing uncertainty. Weather-wise this could produce scattered precipitation across the West, especially the Pacific Northwest, and then rain chances are expected to rise in the south-central U.S. early next week as Gulf moisture streams in ahead of the trough/low. ...Guidance/Predictability Assessment... As the medium range period begins Thursday, recent model guidance is in good agreement regarding central U.S. troughing, though exact shortwave placement remains a bit in question, while the position of a surface low over the Ohio Valley and the trailing cold front are reasonably agreeable. But by later day 4/Friday and beyond, models diverge with the timing of the trough farther west over the Pacific/California and its interface with the ridge to its east. Over the past 24 hours or so, some models have trended toward a more phased and progressive pattern with the trough Friday and into the weekend, as opposed to a southern stream upper low closing off over the Pacific like earlier models generally agreed upon. Namely, the GFS runs and the 00Z ECMWF transitioned to a more phased and progressive pattern, which also served to suppress the ridge on its western side somewhat, though thought the 00Z GFS may have been too suppressed with the ridge especially compared to ensemble members and preferred the 06Z instead. The ensemble means generally followed their respective deterministic models with a progressive trend of the southern stream trough/low. Overall it seemed prudent to lean toward a faster progression of the trough/low and the associated frontal system inland compared to its previous forecast, which the WPC forecast did by leaning toward the ECens mean as well as some deterministic GFS and ECMWF. The EC mean was considered a reasonable middle ground with an inland trend but not quite as fast as the deterministic models. However, the 00Z CMC and UKMET kept with a closed low, adding to the uncertainty for this trend. In the newer 12Z guidance cycle, the CMC trended faster, the GFS remained fast, the UKMET remained slow, and the ECMWF actually switched to be slower, closing off an upper low in the Pacific. Overall this is far from resolved, so expect potential for future changes in updated forecasts. By later Sunday into Monday, models do expect a closed low to have formed by then, admittedly with some differences in position. ...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 cold 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. Rain rates could be high given the potential for instability to be in place. 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 for Saturday. Cold fronts passing ahead of the trough in the East should lead to a transition from above normal temperatures through late workweek to near normal conditions for the weekend. 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 through the weekend. Northern stream shortwave trough passage should support modest precipitation shots repeatedly over mainly the Pacific Northwest. Uncertain eastern Pacific/West Coast upper trough/low amplification could lead to modest precipitation across the West but with uncertainty as to where this could occur, dependent on how the upper trough/low axis ends up developing. But with guidance pointing toward an upper low in the Southwest by around Monday, Gulf moisture streaming ahead of it could renew a rainfall threat in the Southern Plains to Lower MS Valley by Monday-Tuesday. Tate/Schichtel Hazards: - Heavy precipitation across portions of northern New England, Thu-Fri, Feb 9-Feb 10, and Sat, Feb 11. - Heavy rain across portions of the Florida Panhandle to the Mid-Atlantic, Thu-Fri, Feb 9-Feb 10. - Heavy rain across portions of the southern Plains to the mid-Mississippi Valley, Mon, Feb 13. - Heavy snow across portions of the upper Midwest to the upper Great Lakes, Thu, Feb 9. - Heavy snow across portions of the northern Cascades, Mon, Feb 13. - Flooding occurring or imminent across portions of the lower Mississippi Valley. - Heavy precipitation across portions of the Alaska Panhandle, Thu, Feb 9. 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