Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM EST Mon Feb 20 2023 Valid 12Z Thu Feb 23 2023 - 12Z Mon Feb 27 2023 ...Major winter storm to track along the Northern Tier of the U.S. this week... ...Record cold possible in the West while record warmth is possible in the Southeast... ...Overview... A significant winter storm will be moving through the Northern Plains and Upper Midwest, and eventually into the Interior Northeast. Heavy higher elevation snow will also continue over a large portion of the West, focusing farther southward later in the week before chances increase once again over the Pacific Northwest/Northern Rockies into next weekend. Widespread rain and thunderstorm chances are possible from the south-central U.S. northeastward with severe weather possible. Mixed precipitation including ice could be a threat across the rain/snow transition zone draped across portions of the Midwest/Lower Great Lakes. The amplified pattern will lead to significant temperature anomalies with above average max/min temperatures over the East and below average max/min temperatures for the West. ...Guidance/Predictability Assessment... The large scale pattern is becoming more amplified as a deep, large-scale trough develops over the western CONUS as an anomalously strong upper level high builds off the Southeast coast. There is general model consensus with this setup and decent clustering of the position of a potent shortwave (originating from a short range southern stream closed low) moving quickly from the Southern Plains across the Midwest on Wednesday and enhancing some heavy rain potential. The models maintain their clustering as another round of strong energy and a surface low tracks across the Midwest to Northeast Thursday-Friday, leading to high confidence in the forecast for a major winter storm. Thus, the first two days of the extended forecast were a compromise of the 12Z ECWMF, CMC, UKMET and the 12Z/18Z GFS. Meanwhile through the latter part of the week, additional upper-level energy is forecast to dig into the trough's western side and maintain it. Although the model consensus remains fairly good, the run to run waffling has persisted with this trough and energy, namely if this causes a closed low to pinch off around California or its vicinity by Friday or Saturday while the northern stream flow progresses eastward. Within the cluster, a majority of the guidance is favoring a slower progression and the last few runs of the GFS has been edging toward a faster pace. Although its on the eastern edge of the solutions some of the ensemble means resemble the placement of the GFS, thus it was not discounted but utilized in lesser amounts. The latest ECMWF continues to lean toward the slowest solution however the ensemble means were a little less so and closer to the CMC which is near the middle of the spread. For the later periods the inclusion and weighting of the GEFS and EC Ensemble means were increased. ...Weather/Hazard Highlights... A winter storm will be spreading widespread precipitation across the Northern Tier of the country through Thursday. Over the central U.S., a northern-stream shortwave will help to initiate a low pressure system forecast to track eastward across the Central Plains and into the Midwest. This system will usher in significant heavy snowfall along and to the north of the surface low track across the Northern Plains and Upper Midwest. Gusty winds and snow could likely lead to local blizzard conditions. Snow potential will increase for the Interior Northeast/New England through Friday as an additional wave of low pressure intensifies to the east and the entire system moves off the East Coast. Then by late week into the weekend, chances for precipitation are forecast to increase again for the east-central U.S., with the heaviest amounts possible in the Ohio Valley and into the Central Appalachians, but with some uncertainty at this time. Widespread heavy snow chances and very cold temperatures will continue over much of the West through Friday as an energetic upper-level trough deepens over the region and a couple of frontal systems pass through. The focus for heavier snow chances will generally shift southward over California and the Interior West through Friday. Multiple feet of snow are likely in some Western higher elevations throughout the week. Additionally, some very strong, gusty winds will accompany the southern of the two frontal systems passing through southern California, the Southwest, and into the adjacent Southern High Plains around midweek. Precipitation looks likely to return to the Pacific Northwest/Northern Rockies by next weekend, while this forecast cycle also shows precipitation remaining over southern California and the Southwest with the slower trend in the upper low. Given the amplified flow across the country, there will regions of below and above seasonal normal. Daily temperature values of 20F to 40F degrees below normal , especially for the daily maximums, can be expected from the Northern Rockies to the High Plains through Friday. The western U.S. should see temperatures more around 10F to 20F below average, but this could be enough to set or tie some record lows especially in lower elevations of the Pacific Northwest by Thursday-Friday. Record cold high temperatures could expand farther into the Interior West and High Plains, with perhaps a few record lows as well. In contrast, portions of the south-central U.S. and much of the East will get to enjoy milder temperatures of 10F to 30F above seasonal average. Dozens of warm low and high temperature records, with the biggest areal coverage currently expected on Thursday, when many records could be broken by several degrees. The Southeast should be the most persistently warm, and monthly record highs cannot be ruled out given the robust upper-level high centered near Florida. Cold fronts passing through the Southern Plains to Ohio Valley and Mid-Atlantic will moderate temperatures closer to normal in those areas by late week. Campbell/Tate 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