Extended Forecast Discussion NWS Weather Prediction Center College Park MD 327 PM EST Fri Mar 03 2023 Valid 12Z Mon Mar 06 2023 - 12Z Fri Mar 10 2023 ...Overview... Upper flow over the lower 48 looks to transition to become less amplified next week. Strong guidance signals for individual systems in the pattern early next week become much less conclusive by later next week as forecast spread grows significantly. Through early next week, ample troughing to reinforce over the West will support periodic precipitation chances and lingering cooler temperatures, while leading energy should support a deepened surface low moving across the Plains to Mid-Atlantic/Northeast. Precipitation including some enhanced snow is likely across the Great Lakes region Monday and possibly spreading into the Interior Northeast by Tuesday, while the low's trailing front will provide a cooling trend across the central and eastern CONUS. By midweek and beyond the overall pattern becomes much more uncertain as it depends on the evolution of western Canada upper low energy as well as the details of the upper ridging over and south of Alaska. The resulting differences in upper flow pattern unfortunately lead to a wide array of possibilities regarding the sensible weather over the U.S. by the latter half of next week to further monitor over the coming days. ...Guidance/Predictability Assessment... Early in the forecast period Monday-Tuesday, model guidance remains in fairly good agreement with the overall pattern. This includes a western U.S. trough, a shortwave crossing the Midwest/Great Lakes region into the Northeast, and the latter's associated surface low. Thus early in the period, a blend of the deterministic and max clustered guidance from the 00 UTC GFS/ECMWF was used to best provide detail in a pattern with seemingly above average predictability. Models and ensembles quickly diverge by later Wednesday onward as digging/undercutting energy transfer issues with the amplified pattern atop Alaska/western Canada and the northeast Pacific wreak havoc on the pattern amplitude downstream. There have been considerable differences from model to model and run to run within the same model suite. Even the ensemble means remain not terribly agreeable though in terms of the trough positions. There was some general agreement for ridging to come into the West by day 7/next Friday along with some upper troughing/surface system response downstream over the central U.S.. The 00 UTC GEFS/ECMWF ensemble means probably match best with this scenario/latitudinal positioning, albeit with the ECMWF mean more amplified than the GEFS mean. Latest 12 UTC model run to run continuity is still not stellar, especially the GFS than now offers much deep trough amplification into the West as early as Wednesday/Thursday, further lowering forecast confidence given ample continued and aforementioned upstream sensitivities over higher latitudes. Accordingly, WPC medium range products in this time frame rely mainly on a blend of the 00 UTC GEFS/ECMWF ensemble means and WPC continuity. Overall though, predictability becomes quite low for the latter part of the forecast period and there may be more significant changes than usual in future forecasts during this time frame. ...Weather/Hazard Highlights... The upper trough over the western U.S. should continue to support periods of rain along the northern/central West Coast and snow in the higher elevations, but the best chances for higher accumulations have phased into the short range period. Light precipitation is also possible across the Rockies into the High Plains, with some slightly enhanced snow amounts in the central Rockies possible. Confidence rapidly decreases for coverage and intensity of precipitation over the West after Tuesday, with possibilities ranging from a drier trend as upper ridging approaches to persistence of precipitation with a longer duration of upper troughing, or even a transition to a more zonal and moist flow by Thursday or so. Farther east, the first system of note will be the low pressure system tracking from the Middle Mississippi Valley toward the Mid-Atlantic/Northeast Monday-Tuesday along with its trailing cold front. This will produce some rain and snow across the northern third of the central/eastern U.S., and then rain and thunderstorm chances look to increase across the south-central to southeastern U.S. by Tuesday as Gulf moisture increases. Since the airmass looks to be unstable, rain rates are likely to be high, and a Marginal Risk remains in place for day 5 in the WPC experimental medium range Excessive Rainfall Outlook. The potential may also extend into later next week for the region/vicinity, albeit with less certain support/focus. As similar areas are receiving heavy rainfall/flash flooding in the near term as well, this area may be primed to have flooding concerns, and the risk level may need to be upgraded in future cycles if there becomes better agreement in the axis of heavy rain. The forecast pattern will support breezy conditions over the Northeast Tuesday onward with some areas of terrain-enhanced snow. Late-period forecast issues over the West begin to affect areas east of the Rockies as well by Wednesday-Friday, with decreasing confidence in precipitation coverage and amounts. In general it seems that a rainy pattern may continue across the Southeast with some potential for snow around the Central Plains or so, but is quite uncertain. Below normal temperatures over much of the West should persist through the period while also spreading into the northern/central Plains next week. There will be decent coverage of highs 10F or more below normal within this area and there may be increased potential for some anomalies to reach 20F or more below normal over the central Rockies and High Plains toward next Wednesday-Friday. Meanwhile expect more above normal temperatures to extend across all but the extreme northern parts of the central/eastern U.S. during the first part of the week, in the warm sector ahead of Plains/Great Lakes/Northeast low pressure and trailing cold front. Greatest max/min temperature anomalies of plus 10-25F should be from early Monday into early Wednesday with a cooling trend coming in from the west/north with the cold front. By midweek or so, the blocky upper pattern setting up over eastern Canada and the Northeast should keep temperatures within a few degrees on either side of normal aside from above normal lows over northern New England and lows in particular near the Gulf Coast. Schichtel/Tate 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 Hazards: - Heavy rain across portions of the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Tue-Thu, Mar 7-Mar 9. - Heavy snow across portions of California, the Central Great Basin, and the Pacific Northwest, Mon-Tue, Mar 6-Mar 7. - Heavy snow across portions of the Pacific Northwest, Tue, Mar 7. - Heavy snow across portions of the Central Rockies and the Central High Plains, Mon-Wed, Mar 6-Mar 8. - Heavy snow across portions of the Upper Great Lakes and the Upper Mississippi Valley, Mon, Mar 6. - Flooding possible across portions of the Mississippi Valley, the Southern Plains, the Great Lakes, and the Ohio Valley. - Flooding likely across portions of the Lower Mississippi Valley and the Southern Plains. - Much below normal temperatures across portions of the Central Great Basin, the Northern Plains, the Northern Rockies, California, the Northern Great Basin, the Pacific Northwest, and the Southwest, Mon-Thu, Mar 6-Mar 9. - Much below normal temperatures across portions of the Plains, the Rockies, and the Upper Mississippi Valley, Tue-Fri, Mar 7-Mar 10. 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