Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1243 PM EST Sat Jan 11 2025 Valid 12Z Tue Jan 14 2025 - 12Z Sat Jan 18 2025 ...Arctic airmass to reinforce east of the Rockies next week... ...Overview... Into midweek the guidance shows a ridge building into the Northwest while elongated energy to the south most likely forms a closed low somewhat southwest of southern California, while deeper mean troughing extends over the northeastern U.S. into the Plains. Then shortwave energy reaching British Columbia by early Thursday will amplify south/east with time while eastern Pacific/Alaska ridging builds, by Saturday yielding a northern Canada through southwestern U.S./Rockies trough that could also include the sheared remains of the upper low previously off California. Eastern U.S. mean troughing should pass into the Atlantic by the end of the week. This pattern evolution will lead to cold temperatures over the East Tuesday-Thursday followed by another push of cold air dropping down the High Plains and vicinity by next Saturday. The Great Lakes will see a combination of lake effect and synoptic- system snow during the first half of the period. Then by next Saturday organized precipitation should develop over the east- central U.S. along a cold front, while an area of snow pushes down the northern half of the Rockies. ...Guidance/Predictability Assessment... Latest guidance shows fairly good agreement on the overall synoptic set up across the CONUS for the medium range, but plenty of uncertainty in the details. A cut off low continues to show variability on its proximity to the Southern California coast early period. Latest GFS, ECMWF, and UKMET runs have displaced this low much farther west/farther away than previous runs, but the CMC (with support from the ensemble means) continues to hold it closer to the coast. This has little impact on sensible weather initially, but may impact how much energy gets sheared from this low with the larger mean trough as it progresses eastward with time. A sharper shortwave by late week across the south-central U.S. may allow more moisture to get pulled northward and heavier precip across this region and east. The UKMET was much faster with the mean trough progression and with less sheared energy across the Southwest, so it was excluded completely from today's blend. GFS and ECMWF are slightly faster and sharper with the shortwave from western Canada into the north-central U.S.. The WPC blend for today utilized a GFS, ECMWF, and CMC blend for the first half of the period, transitioning to 60 percent GFS/ECMWF with 40 percent total of their respective means. This maintained good continuity with the previous WPC forecast as well. ...Weather/Hazards Highlights... The forecast pattern will support another surge of Arctic air that should reach the eastern half of the country by Tuesday-Thursday. Of particular note, expect areas of hazardous cold to extend from the Upper Midwest into the southern half to two-thirds of the East for one or more days during that time frame. Temperatures should be 10-25F below normal with even colder wind chills. A few locations around the upper Ohio Valley/central Appalachians could challenge daily records for cold highs on Tuesday. Cold cyclonic flow will promote periods of lake effect snow, some of it heavy, through Thursday while a frontal system may produce some light synoptic- scale snow on Thursday as well. Eastern U.S. temperatures will moderate by Friday-Saturday as a front pushes into the central U.S. and eventually Great Lakes. This front may also begin to generate precipitation over the east-central U.S. by Saturday with some heavier totals possible somewhere between the Ohio River and Gulf Coast. Elsewhere, a wavy front may bring lingering rainfall to the Florida Peninsula into Tuesday while some mostly light rain may extend into southern Texas for a time. Upper ridging that builds over Northwest through Thursday should keep most of the western U.S. dry. However, strong Interior West and Rockies high pressure through Tuesday-Wednesday will lead to a threat of high winds over parts of southern California, enhancing the fire weather conditions. Some light and scattered precipitation may reach the Northwest by late week with the arrival of a front. Then some upslope-enhanced snow may move down the eastern slopes of the Rockies Friday- Saturday behind the front. Slightly below normal temperatures over the West will moderate to near/slightly above normal into Thursday, followed by a cooler trend in the Northwest on Friday and much colder readings dropping through the northern- central Rockies on Saturday (highs 10-20F or so below normal). Warmest temperature anomalies next week should be over the northern Plains/Upper Midwest during Wednesday- Friday with some locations 10-20F above normal for highs with anomalies perhaps a few degrees higher for morning lows. The southern Plains into the South may see some above normal temperatures Friday- Saturday. Santorelli/Rausch 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