Extended Forecast Discussion NWS Weather Prediction Center College Park MD 358 PM EST Thu Jan 26 2023 Valid 12Z Sun Jan 29 2023 - 12Z Thu Feb 02 2023 ...Coldest weather so far this month expected across the Dakotas and the Upper Midwest starting this weekend with dangerously cold wind chills expected... ...Overview... Latest guidance continues to show an upper pattern dominated by mean troughing from a closed low near northwestern Hudson Bay southwestward through the western U.S., while an upstream ridge over the eastern Pacific eventually migrates over or just inland of the West Coast. This pattern will support a broad area of well below normal temperatures over the western/central U.S. with the coldest anomalies over parts of the Rockies/High Plains. At the same time an upper ridge meandering over Cuba and the Bahamas will tend to keep the Southeast on the warm side relative to normal. Between these two temperature regimes, shortwave energy and the combination of a couple wavy fronts along with periods of Gulf inflow should support a couple of significant precipitation events east of the Rockies with rainfall to the south/southeast and some wintry weather in the colder air. An upper low/trough digging into the western U.S. mean trough will also support some locally enhanced rain and higher elevation snow. ...Guidance/Predictability Assessment... In contrast to 24 hours ago when the GFS was in the minority for its depiction of a more amplified West Coast trough/embedded upper low, the 00Z/06Z guidance made a notable shift in that direction with a fair amount of follow-through in the 12Z cycle. Representative of some of the spread/variability in recent days, the 00Z GFS had switched back to a more open/progressive feature but the 06Z/12Z runs returned to a slower and more closed evolution (though a bit faster than the 00Z ECMWF and 00Z/12Z CMC by day 7 Thursday). Ensemble members are still quite varied and not surprisingly yield an open trough in their respective means, while the 12Z UKMET made a significant change to a more open feature with northern stream phasing versus its 00Z run. Overall preference was to incorporate 00Z/06Z majority trends early-mid period while keeping some ensemble mean influence later given the ongoing uncertainty. Behind this system, there is still a fair amount of variability for how Pacific energy may intrude upon the mean ridge expected to reach the West Coast around midweek. The 00Z GFS considerably flattened the ridge but most other models/means have held onto a stronger ridge to varying degrees. The 06Z GFS was closest to consensus in principle while the 12Z GFS has trended toward more southeastward amplitude for the upper trough approaching by day 7 Thursday. One other forecast problem involves the surface evolution over the East toward midweek. Trends over the past day have been for a more suppressed wavy front, but there are still extremes on either side of that trend. The new 12Z UKMET is representative of a solution closer to consensus from 24 hours ago while the quick passage of a more amplified than consensus northern stream shortwave across the east in the 06Z/12Z GFS leads to much stronger high pressure over the East next Wednesday. The ECMWF/CMC and the three ensemble means represent the majority cluster for this aspect of the forecast. ...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 from this weekend into the middle of next week. Expect much below normal temperatures across the central/northern Plains to interior portions of the Northwest for the weekend into early next week, with highs running up to 25-40F below normal from the central High Plains into parts of Montana. 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 at least on Sunday-Monday. 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. The remainder of the Interior West will also be quite cold, with Monday-Tuesday being the days likely to have the greatest coverage highs 15-25F below normal with gradual moderation thereafter. While some uncertainty remains with the evolution of the upper-level pattern over the western U.S., the trough expected to drop southward and associated surface reflection should produce a period of rain and higher elevation snow across southern California and the Southwest/southern Great Basin with some localized enhancement possible within a broader area of moderate totals. 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 Southeast 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 across parts of this region with this afternoon's update extending the SLGT area into parts of Georgia and the southern tip of South Carolina based on guidance consensus for a band of heavy rainfall where the ground is wet from recent rainfall. More waviness near the central Gulf Coast and the upper system emerging from the Southwest will likely increase precipitation across the southern tier again during the latter half of the period. Winter weather will be possible to the north/northwest of the rain area, 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. The forecast over the southern part of the Plains will depend on the uncertain specifics of the Southwest upper trough/low with some significant rain and/or snow possible depending on the feature's evolution/track. Rausch/Hamrick Hazards: - Heavy precipitation across the Ozarks, portions of the lower/mid Mississippi Valley, the Tennessee Valley, and into the southern Appalachians, Tue-Wed, Jan 31-Feb 1. - Heavy rain from portions of the lower Mississippi Valley into the Southeast, Sun-Mon, Jan 29-Jan 30. - Heavy rain from portions of eastern Texas into the Deep South, Tue-Wed, Jan 31-Feb 1. - Heavy snow across portions of the central Rockies and northern New York, Sun, Jan 29. - Heavy snow across portions of the central Rockies and central Arizona, Mon, Jan 30. - Much below normal temperatures across much of the northwestern U.S. into the northern and central Plains, Sun-Wed, Jan 29-Feb 1, spreading into much of the Midwest by Thu, Feb 2. 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