Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EST Thu Jan 26 2023 Valid 12Z Sun Jan 29 2023 - 12Z Thu Feb 2 2023 ***Coldest weather so far this month expected across the Dakotas and the Upper Midwest starting this weekend with dangerously cold wind chills expected*** ...Synoptic Overview... A pattern change will be evolving across much of the northern tier of the country going into the weekend and beyond as a strong cold front ushers in an arctic airmass, bringing the coldest weather since the end of December for many areas. Broad upper level troughing with cyclonic flow aloft will be in place across the north-central U.S., and the upper ridge centered over the Bahamas and Cuba will slow the progress of the front and continue to keep much of the southeastern U.S. rather mild for this time of year. Across the western U.S., an amplified shortwave trough will be tracking southward along the West Coast and then settle across the Desert Southwest by Tuesday/Wednesday, and then this will eventually reach the southern Plains by next Thursday. ...Guidance/Predictability Assessment... The 00Z guidance starts off in good shape across the continental U.S. to start the forecast period Sunday, and the timing of the shortwave tracking down the West Coast has come into better agreement. The models remain in close agreement through about Monday night, after which the 18Z GFS begins to differ with both a stronger southwestern U.S. trough and less of a trough over the Midwest and Great Lakes region. Going into next Thursday, both the 18Z and 12Z GFS are considerably stronger with the southeast U.S. ridge building northward, whereas the GEFS mean and the CMC/JMA/ECMWF all indicate more of a zonal flow pattern across the Southeast and the Mid-Atlantic with a broad trough to the north. Therefore, the GFS was not used for days 6 and 7 in the fronts/pressures forecast. However, a multi-deterministic model blend works well for days 3 and 4. More ensemble means were used going into next Wednesday and Thursday to account for greater mesoscale differences. ...Weather/Hazard Highlights... An arctic surge behind a strong cold front will be making weather headlines across much of the north-central U.S. and northern Rockies beginning this weekend and persisting into the middle of next week. Expect much below normal temperatures across the central/northern Plains to interior portions of the Pacific Northwest for the weekend into early next week, with highs running up to 25 to 40 degrees below normal from western Nebraska to central Montana, and things continue to trend colder. This would be the coldest weather since Christmas for this region, with locations from eastern Montana to northern Minnesota likely remaining below zero for highs Saturday through Monday, and perhaps into Tuesday. Wind chills could reach 40 below at times for these areas. Highs in the 0 to 10 degree range may extend as far south as northeast Colorado and northern Kansas. This cold weather will also be expected to reach into the Northwest/northern Intermountain West. While some uncertainty remains with the evolution of the upper-level pattern over the western U.S., rain and mountain snow prospects should generally increase with time in California and the Southwest as the Pacific cold front drops southward, with at least some light higher elevation/interior snowfall and rain for the southern California coast and Desert Southwest. Shortwave energy initially ejecting from the southwestern U.S. will likely support one or more surface waves of low pressure from the southern Plains/Gulf Coast into the Eastern U.S. during the weekend into early next week. Gulf moisture return may support a corridor of moderate to heavy rainfall over portions of the central Gulf Coast states and vicinity on Sunday, with more modest rains spreading northward over the east-central U.S. into/ahead of a wavy front. The Day 4 (12Z Sunday-12Z Monday) Excessive Rainfall Outlook maintains a Slight Risk area from southern Louisiana to the Florida Panhandle, where multiple rounds of heavy rainfall will be possible. Somewhat lesser probabilities of heavy rainfall exist over a larger portion of the Southeast. Another wave near the central Gulf Coast will increase rain chances again later in the period by Tuesday or Wednesday, with potential sensitivity for areas where the two episodes of rainfall could overlap. Meanwhile winter weather will be possible farther north, with locations from the Midwest into New England generally in the most favored axis for some generally light snowfall. Sufficient persistence of cold air by late in the period could increase the possibility for a transition zone of freezing rain/sleet between the rain and snow areas but any specifics have low confidence at this time. Hamrick 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, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices 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