Extended Forecast Discussion NWS Weather Prediction Center College Park MD 141 AM EST Thu Jan 04 2024 Valid 12Z Sun Jan 07 2024 - 12Z Thu Jan 11 2024 ...Major Winter Storm to continue bringing Hazardous Weather across parts of the Northeast into Sunday... ...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 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 will be exiting the East on Sunday, with some potential for lingering hazardous weather across parts of the Northeast. In its wake, a next main upper trough will be digging through 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 gusty 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... The latest guidance continues to offer above average agreement on the larger scale pattern, but plenty of uncertainties in the details of embedded systems and flow interactions. Regardless, there is high confidence in a very active January storm pattern across much of the nation for at least the next week. With the weekend storm exiting the East coast by the start of the medium range period (Sunday), the main focus will be on the storm likely to develop and impact much of eastern half of the country next week. Models show good agreement on a deepening trough across the West Sunday, but begin to have some timing uncertainties as the system kicks out into the Plains and tracks across the Midwest Mon-Wed. Elsewhere, plenty of uncertainty as a series of shortwaves moves across the Northwest next week, with potential for another low pressure system to move into the north-central U.S. next Wednesday-Thursday. The WPC medium range product suite for tonight used a blend of the deterministic guidance for Sunday-Monday, before incorporating some of the GEFS/ECENS ensemble means to help smooth out the smaller scale differences. Did continue some lessening parts of the deterministic solutions late period to help maintain reasonable system definition. This approach maintained very good continuity with the previous WPC forecast. ...Weather/Hazards Highlights... The major surface low bringing snow and ice to parts of the Mid-Atlantic/Northeast will be exiting the East Coast by Sunday, but there could still be some hazardous weather across parts of New England, including moderate to heavy snows and gusty winds. The next main trough into the West will bring some rain and mountain snows across the Four Corners region on Sunday with a decent signal for meaningful snow accumulations across parts of the 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. Given ample moisture and instability, and rainfall expected in the short range period, a slight risk was included on the Day 5 Excessive Rainfall Outlook tonight, with a broad marginal for surrounding areas across the Deep South. Rain will move into the Eastern U.S. on Tuesday and depending on snow accumulations across parts of the East this weekend, 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. Additional dynamic systems in the series look to move into the Pacific Northwest early next week with rounds of moderate to heavy rainfall expected for the coastal ranges and foothills of the WA/OR Cascades. Given the ongoing wet pattern across this region later this week/this weekend, a marginal risk was added to the Day 5/Monday Excessive Rainfall Outlook for this region. Heavy snows are expected in the higher terrain of the Cascades, with rain and mountain snow also extending into parts of the interior West through Wednesday. Temperatures should generally trend cooler across much of the Western U.S. into next week as mean troughing remains anchored over the region. Daytime highs 5-15 degrees above normal are expected Sunday-Monday with some slight moderation Tuesday-Wednesday, before trending even colder next Thursday, with widespread highs 10-20 degrees below normal across interior portions of the West and extending into parts of the central and northern Plains. Ahead of the next storm system in the Central U.S. early next week, temperatures across the East will likely be moderately above normal. Santorelli 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