Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Fri Jan 21 2022 Valid 12Z Mon Jan 24 2022 - 12Z Fri Jan 28 2022 ...Overview... A strong eastern Pacific ridge will help to maintain a broad mean trough across a majority of the lower 48 through the middle of next week. Later in the week guidance suggests the overall pattern may begin to shift a little eastward as Pacific energy finally nudges the ridge into the western U.S. This pattern will favor temperatures that are slightly above normal over the West, variable over the Plains, and mostly below average over the East. A southern stream wave should produce an area of locally moderate to heavy rain along/north of the Gulf Coast early in the week while lighter precipitation spreads across the rest of the eastern U.S. Otherwise expect precipitation coverage and intensity to be fairly modest over most of the lower 48. ...Guidance Evaluation/Predictability Assessment... The primary forecast uncertainties involve shortwave details within the lower 48 mean trough, and by late in the week specifics of Pacific energy pushing into the ridge that drifts into the western U.S. The southern stream shortwave emerging into the southern Plains early in the week is fairly similar in the guidance, quickly shearing as it becomes embedded within fast flow. Some fine-scale surface details that have lower predictability 4-5 days out in time will still take some time to be resolved. Meanwhile guidance has been differing for specifics of one or more shortwaves dropping into the Great Basin/Rockies by Tuesday onward, with a blend approach looking best given persistent differences among the models and between consecutive runs. An intermediate solution appears ideal along the West Coast by Thursday-Friday. Recent GFS runs through 06Z have been on the slower/closed side with the Pacific energy (as was the 12Z CMC) and thus keep more ridging over the West, in contrast to the ECMWF that has been on the fast/open side with the shortwave. Their respective ensemble means are less extreme but with a tilt to their models' relative timing. The means have trended toward a stronger and faster shortwave over the past couple days, which would at least favor leaning away from the slow side of the spread. The new 12Z GFS/CMC have remained slower and closed while the new 00Z ECMWF has trended slower (albeit straying to the amplified side of the spread by early Friday), ultimately leading to better clustering for now. A 00z/06z operational model blend was effective for most of the period. Some weighting was offered to the ensembles by day 5 due to uncertainties with the Southwest shortwave. This weighting was increased to 60 percent by the end of the period to account for spread in the deterministics with respect to the incoming Pacific shortwave. ...Weather Highlights/Threats... A southern stream system tracking near the Gulf Coast Monday into Tuesday should produce an area of locally moderate to heavy rainfall across the far southern tier. Highest totals are likely be from around eastern Texas into the Lower Mississippi Valley during Monday-Monday night with a lighter trend farther eastward. Also early in the week a separate wave/front crossing the East will spread mostly light to moderate snow from the Great Lakes into the Northeast. Moisture in the northern periphery of the southern system interacting with the front may lead to some snow from the Ohio Valley into central Appalachians and could provide some enhancement farther northeast as well. Some lake effect snow will be possible after the system passes by. Another frontal system reaching the Great Lakes late in the week could bring some light snow to the region. Aided by low level upslope flow as high pressure builds into the central U.S., an area of snow will drop southward through the Rockies and High Plains during the first half of the week. The rest of the West should be dry except for possibly some light precipitation reaching the Pacific Northwest late in the week. Within the generally cold pattern over the eastern half of the country, the East Coast will start out chilly on Monday with Florida and the Northeast most likely to see min and/or max temperatures at least 10F below normal. The next Arctic surge will bring readings down to 15-25F below normal over the Midwest/Upper Mississippi Valley Tuesday into early Wednesday while well below normal readings spread south and east through the Plains and eastern U.S. into Thursday with some moderation over the East by late week. The Plains will see a warming trend Wednesday-Friday with increasing coverage of plus 10F or greater anomalies from northern into central areas. Expect the West to see moderately above normal temperatures next week. Isolated locations could see plus 10F or so anomalies. 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, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml