Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Mon Jan 08 2024 Valid 12Z Thu Jan 11 2024 - 12Z Mon Jan 15 2024 ...Another major storm to impact the East-Central to Eastern U.S. with snow/rain/wind threats and an arctic blast envelops much of the North-Central U.S.... ...General Overview... In the wake of the departing surface low exiting the Northeast U.S. late Wednesday, an improving weather trend commences going into Thursday across the Eastern U.S. as high pressure briefly settles in across the region. However, this will be rather short lived as the extremely active weather pattern continues with another potent low pressure system getting better organized across the south-central U.S. by Friday morning in response to an amplifying upper trough approaching from the Rockies. This low should track in the general direction of the Ohio Valley and Great Lakes region by Saturday with more bad weather expected for many areas that will be hammered earlier in the week. In addition, a strong Arctic front will herald the coldest weather of the season thus far across much of the north-central U.S. for the second half of the week and into next week. ...Guidance/Predictability Assessment... For the next big system developing across the southern Plains Friday, the models all agree that a potent southern stream trough/shortwave exiting the Rockies Thursday will begin acquiring negative tilt by Friday evening across the Midwest, allowing rapid surface cyclogenesis to occur downstream. Guidance has also shown a significant stronger trend with the surface low as it approaches the Great Lakes, with both the GFS and ECMWF indicating central pressure close to 970 mb over eastern Michigan and potential for triple point low development Saturday by New England. The guidance now agrees better on a shortwave approaching the Pacific Northwest late Saturday that will eventually move inland across the Intermountain West/Rockies, eventually downstream toward The South. For the WPC fronts/pressures progs and forecast weather grids/threats, a multi-deterministic model blend along with the NBM and WPC continuity offers a solid starting point in the forecast process, with more weighting towards best clustered GFS/ECMWF then GEFS/ECMWF ensemble means over time, but forecast predictability seems to hold above normal through medium range time scales. For the lake effect snow later in the forecast period, the NBM again appeared too low with amounts, so the QPF was roughly doubled for this region. ...Weather/Hazards Highlights... Unfortunately, another strong low pressure system is forecast to rapidly develop over the south-central U.S. by Thursday night into early Friday, and this could affect similar areas of the central and eastern U.S. compared to the low in the short range forecast period, tracking from northern Texas to the Ohio Valley and then the eastern Great Lakes based on the latest model guidance. There will likely be a band of significant snow extending from at least Missouri to Michigan associated with the deformation zone/wrapping moisture northwest of the surface low, and the highest probabilities of this are generally southeast of the highest snowfall totals expected with the system early in the week. Given the strong pressure gradient that will be in place, many places could experience blizzard conditions. With strong cold air advection in the wake of this low pressure system, lake effect snow is expected to increase downwind of the Great Lakes by the weekend, and potentially heavy at times. Additional rounds of heavy rain and strong to severe thunderstorms are also likely for much of the South/Southeast going into Friday, and then spreading quickly northeastward along the East Coast going into Friday night and Saturday. This rainfall will also be falling over highly saturated soils owing to recent and upcoming rainfall and snows, and given the QPF signal for some 1-3+ inch rainfall totals across portions of the Mid-Atlantic and Northeast, a Slight Risk of excessive rainfall certainly seems warranted for the Day 5 period on Friday/Friday night from northern Virginia to western MA, and a broader Marginal Risk area extending southward along the spine of the Appalachians and a separate area across portions of KY and TN. In terms of temperatures, an Arctic blast is expected for the Northern Plains/Rockies to close out the week with widespread double digit subzero lows for the Dakotas and into Montana, and some subzero highs, with anomalies as much as 35 degrees below normal and the potential for some daily record lows. The arctic airmass will also drop southward west of the continental divide throughout the central and northern Intermountain West, and also spread down across the central to east-central U.S. over time, but modified as it progresses southeastward. Upstream, a continued series of highly dynamic Gulf of Alaska/western Canadian amplifying systems will maintain and periodically rejuvenate a highly unsettled and wintry pattern late this week for a good portion of the West. There is a strong signal in the guidance for this shortwave energy to spread down from the Pacific Northwest to north-central California into the Sierra. There is a moderate to locally heavy rainfall signal for coastal Oregon/northern California to monitor outlined by a Day 5/Friday ERO Marginal Threat area. There should also be widespread terrain/mountain enhanced snows farther inland across the northern Intermountain West into the Rockies with continued system progressions. This energy is slated in less certain form to work increasingly downstream in a southern stream into the south-central U.S. in an emerging pcpn pattern. Hamrick/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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw