Extended Forecast Discussion NWS Weather Prediction Center College Park MD 213 AM EST Mon Jan 6 2025 Valid 12Z Thu Jan 09 2025 - 12Z Mon Jan 13 2025 ...Arctic blast persists for the central/eastern U.S. this week... ...Overview... Lingering cold northwesterly flow will still support Great Lake effect snows into later this week. Meanwhile, organzied precipitation will return later this week as a frontal system moves into the West and low pressure develops off 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 downstream Gulf system is tricker given uncertain southern stream upper trough energy ejection from the Southwest U.S./Northern Mexico. The pattern eventually does seem to support the development of 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 over the Gulf and especially as it moves towards/up the East Coast and western Atlantic, and the timing and location of this system will be important for determining impacts. ...Guidance/Predictability Assessment... Recent models and ensembles continue through the latest 00 UTC versions to offer quite a run of less than stellar cycle to cycle forecast continuity, with system timings and split flow phasings/interactions variances that span the entire med-range forcast period. Given greater than normal uncertainties, opted to invoke an ensemble mean and composite forecast plan approach with usage of guidance from a blend of the GEFS/ECMWF ensemble mean and the National Blend of Models. This seems to best capture guidance that best maintains WPC product and threat messaging continuity with depiction of one possible subset of system timings, albeit in reasonably similar main guidance storm tracks. ...Weather/Hazards Highlights... Lake effect snows will periodically be rejuvenated by deep cold surges into later this week as light to modest precipitation will focus down through the Rockies and north-central U.S. with an forcassurface system genesis. There will also be chances for precipitation over portions of the Southwest and southern Plains with return flow response as an upper closed low settles and approaches. 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. While deepest instability and heaviest rains may focus offshore, guidance shows ample western then central Gulf Coast state precipitation potential, so Marginal Risk areas have been introduced to the Day 4/Thursday and Day 5/Friday WPC Excessive Rainfall Outlook to account for localized flood potential. While the Gulf low moderatly strengthens,cold air well in place over the southern Plains may support some mixed/icy wintry precipitation into Thursday. 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 may translate with the system towards the Tennessee Valley and central/southern Appalachians/Southeast on Friday. As the Gulf system progresses, precipitation may expand northeastward across the East Friday into Saturday. 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 this wek for snow covered areas from an ongoing major lead winter storm. Meanwhile, upper ridging in the western U.S. will offer slightly above normal temperatures prior to breakdown heading into the weekend. 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