Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Sun Jan 5 2025 Valid 12Z Wed Jan 08 2025 - 12Z Sun Jan 12 2025 ...Arctic blast persists for the central/eastern U.S. this week... ...Overview... A quieter weather pattern is expected to develop mid-week with only light precipitation forecast across the nation, except for in the Great Lakes where cold northwesterly flow will rejuvenate lake effect snows. Heavier precipitation will return later this week as a frontal system moves into the West and low pressure develops along the Gulf Coast. The frontal system in the West will approach the coast on Friday and move across the region this weekend with widespread precipitation from the Northwest to the northern and central Rockies. The Gulf system is forecast to bring widespread precipitation from the Gulf Coast to the Southeast late this week, and precipitation may spread up the East Coast as it moves offshore this weekend. There is a significant amount of uncertainty surrounding the evolution of the system as it moves towards the East Coast, and the timing and location of this system will be important for determining impacts. ...Guidance/Predictability Assessment... Model guidance remains in good agreement on the weather pattern through mid-week, but model spread increases significantly Friday through the weekend as they try to resolve the low pressure system evolution over the Southeast and East Coast. The ECMWF has shown the best run-to-run consistency with this feature while the GFS has tended to flip flop a bit, and the CMC and UKMET seem to be the furthest from the general model consensus and the ensemble mean solutions. The 00Z ECMWF and 06Z GFS were in good agreement the track and placement of the surface low, bringing it across the Carolinas and strengthening the low offshore of the Northeast. The 12Z guidance has come in a bit weaker, and is favoring a more eastward track, which would pull the system away from the coast and reduce potential impacts for the Mid-Atlantic and Northeast. Due to spread/uncertainty and low predictability, confidence is low in the forecast along the East Coast for Saturday and Sunday. A general model blend of the deterministic GFS/ECMWF/CMC/UKMET was used for the first two days of the period (Wednesday and Thursday), with more weight placed on the GFS and ECMWF. For Friday onwards, the CMC and UKMET were removed from the blend and the ECENS and GEFS ensemble means were added in increasing amounts. ...Weather/Hazards Highlights... Mid-week, the quieter weather pattern will result in limited precipitation hazards. Lake effect snows will periodically be rejuvenated by deep cold surges, and light to modest precipitation will focus down through the Rockies and north-central U.S. with an emerging surface system. There will also be chances for precipitation over portions of the Southwest and southern Plains underneath an upper closed low that will move south over this region. Precipitation chances will increase over the southern Plains, Lower Mississippi Valley, and Gulf Coast by Thursday as energy from the upper low spreads northeast. Anomalous moisture will focus over the western Gulf Coast as a low pressure system strengthens over the western Gulf, and heavy precipitation will be possible in portions of Texas and Louisiana. Latest model trends show increasing precipitation in this region, so a Marginal Risk area will likely be added to the Day 5/Thursday Excessive Rainfall Outlook to account for localized flood potential. While the Gulf low strengthens, cold air in place over the southern Plains may support some mixed/icy wintry precipitation Wednesday and Thursday during the overnight hours. Temperatures will drop below freezing overnight for most of the state, and even portions of South texas could be cold enough for some icy precipitation. Wintry precipitation will move northeast with the system towards the Tennessee Valley and central/southern Appalachians on Friday. As the Gulf system progresses, precipitation will spread across the Southeast on Friday and expand north across the eastern third of the nation Friday into the weekend. Heavy precipitation potential will be strongly dependent on the timing and placement of the low pressure system, which is highly uncertain at this time. If the low moves quickly offshore and strengthens away from the coast, then impacts will be limited, and impacts will be more likely with a slower low that strengthens closer to the U.S. coastline. The weather pattern will favor the continuation of well below normal temperatures east of the Rockies through at least this weekend. Notable cold is possible in the far northern tier, but this should not be record breaking. Temperature anomalies of 10-20 degrees below normal are also likely from the central Plains and Mid-Mississippi/Ohio Valleys through the Appalachians, especially as temperatures remain quite cold for snow covered areas from a major lead short range winter storm. Meanwhile, upper ridging in the western U.S. will offer slightly above normal temperatures prior to possible breakdown later period that would support organized rain/terrain snow potential from the Northwest to the Rockies. Dolan/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