Extended Forecast Discussion NWS Weather Prediction Center College Park MD 121 PM EST Tue Jan 24 2023 Valid 12Z Fri Jan 27 2023 - 12Z Tue Jan 31 2023 ***Coldest weather so far this month expected across the Dakotas and the Upper Midwest starting this weekend*** ...Synoptic Overview... The departure of the strong low pressure system from New England late Thursday will yield an upper level pattern with broad cyclonic flow with an Alberta clipper system tracking eastward across the Great Lakes on Friday. This will herald the arrival of an arctic airmass settling southward from Canada. The strong cold front will likely spur surface cyclogenesis across the southern Plains by the weekend, but it currently appears this low should be weaker than the one that will be in place over the next couple of days. The southeast ridge is expected to remain rather strong over the Bahamas/southwestern Atlantic, and this will tend to limit the southward extent of the arctic airmass. ...Guidance/Predictability Assessment... The 00 UTC/06 UTC deterministic model guidance is in good agreement at the start of the medium range period (Friday/Saturday) depicting a highly amplified pattern with mean upper-level troughing anchored over the central/eastern CONUS and large-scale ridging over the northeastern Pacific. Small spread between the individual members of the ensemble guidance further supports this agreement. Lingering waves of upper-level energy remained embedded in the flow, one in the Great Lakes vicinity associated with a clipper system at the surface and another over the Southwest. The model blend for the WPC medium range product suite began with an even blend of the deterministic guidance, splitting the GFS contribution up between the 00 UTC/06 UTC runs. This blend also generally followed continuity from the prior forecast. Model differences rapidly increase by Sunday with disagreement over the evolution of a trough developing upstream of the Pacific Northwest. Past runs of the GFS are more of an outlier compared to the other guidance with a flatter trough while the recent 00 UTC/06 UTC runs converge towards a more similar evolution, with the caveat that significant timing/location differences exist between the guidance and spread in the ensembles rapidly increases. However, after Sunday, the 00 UTC GFS trended away from the other guidance before reversing course back with the 06 UTC run. The influence of the ensembles was introduced into the blend as the mean pattern was generally similar, including the 00 UTC GEFS mean, and the details will be further resolved when the guidance converges towards a similar solution. This is especially true for late in the period when blending across the deterministic guidance will wash out any significant details given the lack of overlap amongst the model solutions. The evolution of this feature will be important as it will have an impact on eventual precipitation chances in the West, especially if the forecast were to trend more towards the outlier runs of the GFS which are generally slower and further north with the QPF than the other guidance. ...Weather/Hazard Highlights... In the wake of the departing Northeast U.S. storm, an Alberta Clipper low will produce mainly light snow across portions of the Great Lakes region Friday. The southward plunge of a trailing cold front will advect an arctic surface high pressure down across the north-central U.S. and then into the northern Rockies/western High Plains. Expect much below normal temperatures across the north-central U.S. for the weekend into early next week, with highs running up to 15-25 degrees below normal. This would be the coldest weather since Christmas for this region, with some locations in the far Northern Plains/Upper Midwest remaining subzero for daytime highs by Sunday. This cold weather will also be expected to reach into the Northwest/northern Intermountain West. Upper trough passage combined with lower atmospheric upslope flow will produce moderate to locally heavy terrain enhanced snows down across north-central parts of the Intermountain West/northern Rockies/western High Plains Saturday and Sunday. While uncertainty remains with the evolution of the upper-level pattern over the western U.S., precipitation chances should generally increase with time in California and the Southwest as the trailing cold front eventually pushes southward, with at least some light higher elevation/interior snowfall and rain for the coast and Desert Southwest. The shortwave energy initially from the southwestern U.S. is expected to eject eastward across the Plains and support a new low pressure system over the weekend into early next week over Texas and the central Gulf Coast region. Gulf moisture return may support a corridor of moderate to heavy rainfall over portions of the central Gulf Coast states and vicinity Saturday and Sunday, with more modest rains spreading northward over the east-central U.S. into/ahead of a wavy front. Another wave over the central Gulf Coast will increase rain chances again later in the period on Tuesday. In this pattern, the pre-frontal airmass warms as upper ridging builds from the Southeast. Putnam/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