Extended Forecast Discussion NWS Weather Prediction Center College Park MD 212 PM EST Wed Jan 03 2024 Valid 12Z Sat Jan 06 2024 - 12Z Wed Jan 10 2024 ...Major Winter Storm to bring Hazardous Weather across the Appalachians/Mid-Atlantic and Northeast this weekend... ...Another Major Storm to bring heavy rain/strong convection and gusty winds across the South-central U.S. and into the East early to middle of next week, with a heavy snow threat to the north... ...Dynamic Storm Systems to focus coastal rain/inland heavy snow threats over the Northwest/West this weekend and next week... ...Overview... An extremely active medium range period remains on tap with a series of major storm systems in the forecast. A leading system moves into the East this weekend, with potential for heavy rain near the coast and heavy snow across the Appalachians and interior portions of the Mid-Atlantic and New England with coastal storm development. In its wake, a next main upper trough digs into a highly unsettled West this weekend as well, focusing wintry threats for terrain/mountain snows and winds. Deep cyclogenesis than remains likely across the south-central Plains by Monday, with impressive lead moisture and instability return to fuel widespread heavy rainfall/convection and runoff issues across the south-central to eastern U.S. through next midweek. There is also a significant snow/ice threat to the north of the deep low track from the central Plains to the Midwest/Great Lakes and Northeast Monday-Wednesday, along with enhanced winds. Additional dynamic systems in the series look to move into the Pacific Northwest early next week before digging across the West into next midweek. ...Guidance/Predictability Assessment... Model and ensemble solutions certainly continue to offer uncertainties with embedded system details/focus and flow interactions, but with some improvement and steadfast development of quite the active January storm pattern to impact much of the nation over the next week. Model variances though seem reasonable enough to allow for a composite blend that produced decently defined and consistent system depictions and threat foci. The WPC medium range product suite was primarily derived from a blend of the GFS/ECMWF/UKMET/Canadian for Saturday into next Monday before mixing in some GEFS/ECMWF ensemble means to increasingly smooth the less predictable rough edges while still maintaining substantial system breath and impact potential. WPC product continuity was reasonably well maintained in this manner. ...Weather/Hazards Highlights... A major surface low tracking off the Mid-Atlantic coast Saturday into Sunday continues to show ample snow potential to the north of the low, primarily for portions of the Central Appalachians and interior Mid-Atlantic and Northeast. There may be a period of freezing rain/ice as well for parts of/lee of the Central Appalachians Saturday. Closer to the coast, and including the major DC-NYC corridor this weekend, there is plenty of uncertainty regarding precipitation type and amounts, highly dependent on the exact track of the low and availability of sufficiently cold air considering lack of a classic cold air wedge dug down over the East in advance of the main low. There is a subset of guidance suggesting these major cities could see moderate to heavy snow accumulations, which has not happened in a quite a while, but also ample potential for more modest accumulations and cold rains. A marginal risk for flash flooding remains on the Day 4/Saturday Excessive Rainfall Outlook, but was confined mainly for the coastal Carolinas and eastern Mid-Atlantic given a overall faster progression and lack of significant rainfall. The next main trough into the West will bring expanding coverage of rain and mountain snows across the Northwest and into the Four Corners region this weekend. There is a decent signal for meaningful mountain snows across parts of the Cascades, Sierra Nevada, and interior mountain ranges/southern Rockies. As the parent trough ejects into the Plains, an area of low pressure looks to form and deepen as it tracks northeastward into the Mississippi Valley and Great Lakes next week. This will tap Gulf of Mexico moisture to fuel widespread moderate to heavy rainfall across much of the Mid/Lower Mississippi Valley and the South on Monday with some severe weather potential as well along the central Gulf Coast, per the latest from the Storm Prediction Center. Rain will move into the Eastern U.S. on Tuesday and depending on snow accumulations across parts of the East early in the period, this could bring an increased risk for flooding due to excessive rain and snowmelt. A protracted period of gusty winds around the deep low looks likely as well across the East-Central U.S. to Northeastern U.S. as this system strengthens. There is also an increasing threat for a widespread swath of heavy snows and ice to the north of the low from the Central Plains to the Midwest/Great Lakes then Northeast. As aforementioned, additional dynamic systems in the series look to move into the Pacific Northwest early next week before digging across the West into next midweek. This weekend above seasonal average temperatures can be expected across the far northern tier states with anomalies generally plus 5-15F for highs, and perhaps as high as plus 15-25F for morning lows over parts of Minnesota/Wisconsin. Above normal temperatures also look to return to the Southern Plains/Lower Mississippi Valley and eventually the East early next week. The southern two-thirds of the West will likely have below normal temperatures late this week, with some cooler anomalies at least 10F below normal for highs spreading across the West into the High Plains by Sunday-Tuesday as upper troughing moves over the region. Parts of the Northwest and northern Plains should trend below normal as well, with modestly below normal temperatures across the Southern Plains/Southeast following passage of the strong cold front early next week. Santorelli/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