Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Fri Jan 3 2025 Valid 12Z Mon Jan 06 2025 - 12Z Fri Jan 10 2025 ...Arctic blast/Winter storm to bring heavy snow and hazardous ice from the Central Plains to the Mid-Atlantic... ...Overview... A highly favorable guidance signal remains in place in support of the development of a winter storm by Sunday from the Central Plains to Mid-Mississippi and Ohio/Tennessee Valleys through the Appalachians and the Mid-Atlantic, lasting into the med-range period Monday for eastern areas. Heavy snow is likely, along with significant sleet and a wavy transitional zone of ice/freezing rain from the Mid-South to the south-central Appalachians/Mid- Atlantic. On the southern side, heavy rain and thunderstorms are likely over parts of the Lower Mississippi and Tennessee Valleys and Southeast. The weather is forecast to quiet down in terms of precipitation after this system, aside from periodic Great Lake effect snow enhancement with reinforcement of Arctic flow and areas of mainly light precipitation in the western and central U.S., but much colder than average temperatures are likely to persist through the week in most areas east of the Rockies. There is also an uncertain signal for far south-central U.S. rain/winter precipitation development into later next week to monitor given separated southern stream flow system ejection potential. ...Guidance/Predictability Assessment... Model and ensemble forecast spread continues to slowly improve for med-range time scales over the past few guidance cycles, including for the latest 00 UTC cycle. Larger scale flow evolution now seems more commonly shared by most guidance well into next week in a pattern with seemingly above normal predictability, but continued local system and focus issues still linger into shorter range time scales. However, a forecast plan utilizing a composite model and ensemble solution along with the National Blend of Models seems to provide a more consistent and reasonable forecast basis that along with targeted manual adjustments highlights the main threat impacts and messaging. This solution maintains good WPC product continuity. ...Weather/Hazards Highlights... It very much remains the case that the upcoming short to med-range range winter pattern from the weekend into early next week will be especially impactful for a broad swath of the central to eastern U.S.. An upper trough in the central U.S. Sunday will produce a consolidating surface low in the Southern Plains. Precipitation is expected to push across the eastern half of the U.S. with this low and good dynamical support aloft. Cold air in place will favor widespread heavy snow that will be heavy across areas from the Central Plains, Mid-Mississippi Valley, and Ohio Valley Sunday. Snow will push into the Mid-Atlantic Sunday night into Monday. Just to the south, there is a relatively broad transitional area that will see impactful mixed precipitation types, transitioning between multiple p-types and/or seeing snow and sleet/freezing rain. Potentially significant sleet and freezing rain are possible across the Ozarks east to the Tennessee Valley and south-central Appalachians/Mid- Atlantic. WPC is issuing Key Messages for this winter storm. Meanwhile farther south in the warm sector, expect lingering trailing frontal showers and thunderstorms to spread eastward into and across the Southeast into Monday. Great lake effect snow will become rejuvenated with cold and brisk flow behind the main low pressure system and within later next week cold pattern amplitude. Light to modest precipitation including higher elevation snow is expected to spread focus out from the Northwest through the Rockies next week, and eventually the Northern Plains with an emerging surface low. Farther south, there are some chances for precipitation from the Southwest to Southern Plains and Lower Mississippi Valley dependent on uncertain timing/ejection of a potentially amplified southern stream system. An emerging precipittaion pattern may unfold into later next week and with the cold air in place from Texas eastward, some areas will need to monitor the onset of some wintry precipitation. Colder than normal temperatures are likely across the central and eastern U.S. underneath rounds of upper troughing and with cold surface high pressure systems. Notable cold is possible in the northern tier, with even high temperatures barely reaching 0F and lows between -10F and -20F in some areas. This should not be record breaking, but the cold could still be hazardous as wind chill values may dip below -20F to -30F. Temperature anomalies of 10-20 degrees are also likely across parts of the northern/central Plains to Middle Mississippi and Ohio Valleys to Appalachians into much of next week, especially if areas are snow covered and hold temperatures down. Meanwhile, initial upper ridging in the western U.S. will allow for slightly above normal temperatures in the Intermountain West, and 10-20 degrees above normal anomalies in the south-central U.S. Sunday will cool to below normal behind a cold front by Monday. The upper pattern in the West is uncertain by midweek next week, causing temperatures to be in question, but there may be a trend toward warming for parts of the West. 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 (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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