Extended Forecast Discussion NWS Weather Prediction Center College Park MD 223 AM EST Fri Feb 23 2024 Valid 12Z Mon Feb 26 2024 - 12Z Fri Mar 01 2024 ...Overview... An upper ridge traversing the central and eastern U.S. for the first half of next week will spread much above normal temperatures to the Plains and Midwest and then the East. Meanwhile northern and weaker southern stream troughing looks to track into the West and bring cooler temperatures, lower elevation rain and higher elevation snow, and windy conditions from the West Coast to the Rockies through early next week. Downstream translation may then support emerging genesis of systems and precipitation pattern from the south-central U.S. to the Midwest/Great Lakes onward into midweek, along with a post-frontal/trailing southward surge of a cold Canadian high pressure airmass to offer some wintry potential, albeit with much uncertainy and less than stellar continuity for this period and onward. ...Guidance/Predictability Assessment... Guiidance remains in reasonably good agreement that a northern stream system will cross southern Canada/northern tier of the U.S. towards the Northeast early next week as weak ridging in the southern stream proceeds the upper-level energy to the west, transitioning from northwestern Mexico/the Southwest eastward across the Southern Plains towards the Southeast. Initial shortwave energy following the ridge should bring subsequent cyclogenesis/surface system development over the Plains, lifting northeastward towards the Midwest. The general pattern shifts towards mean troughing in the West early next week as the upstream energies approach. The main forecast challenge for next week remains with how a strong northern stream trough dropping south upstream from the northeastern Pacific and closed upper-low in the southern stream off the coast of California progress and evolve together across the CONUS through next week. Deterministic models and ensembles over the past few days have favored stream upper trough phasing over the West early next week with a northern stream trough drops across the Pacific Northwest and the southern stream closed low breaking down as energy ejects eastward over the Southwest/California/Baja. Machine learning systems mostly did not favor significant phasing of these system with more independent downstream progression of potent northern stream energies. This seems to make more sense as the strong upper jet flow over the Pacific introduces very uncertain phasing timing issues, as well as the historic tendancy for closed southern stream systems to linger in separated flow. 12 UTC guidance started to show a dent in model/ensemble thinking, but with only the 12 UTC ECMWF/ECMWF ensembles making a change away from phasing. Given the aforementioned thought process though, the WPC product suite has now embraced a solution with much less phasing next week and shifted continuity closer to the ECMWF ensemble mean given lingering uncertainties. While either forecast camp remains plausible, updated information from the latest 00 UTC guidance cycle does now also have the UKMET joining the ECMWF/ECMWF ensemble based solution. ...Weather/Hazards Highlights... As troughing comes into the West early next week, precipitation will spread into the Pacific Northwest and northern Rockies into Monday, including snow that could be heavy over favored terrain. Precipitation may now spread through California and into the Intermountain West by Monday, then out through the Rockies Tuesday given less likely stream phasing and northern stream upper trough progression. Additional moisture ahead of additional systems upstream over the Pacific will continue precipitation chances in the Pacific Northwest then California through Wednesday-next Friday. Overall, the highest likelihood for winter-related impacts is in the Cascades, Sierra, and portions of the Northern/Central Rockies, though most of the regional higher elevation mountain ranges will at least see some snow through the period. Widespread strong, gusty winds are also expected across much of the West, particularly for higher elevations, as a couple frontal systems pass through, lingering the longest along the eastern ranges/foothills of the Rockies and immediate High Plains. Precipitation chances will begin to increase Tuesday into Wednesday across much of the eastern half to third of the country as moist southerly flow increases ahead of the approaching upper-level trough and surface low pressure/frontal system from the West. Most precipitation will be in the form of rain given anomalous lead warmth, but some snow on the backside of the low and cold front for the Upper Midwest/Great Lakes. The WPC Winter Weather Outlook has increased probabilities there given the low and post-frontal cold onset. Some rainfall amounts could be moderately heavy, particularly for the Ohio Valley, with multiple rounds of rain possible through at least midweek. In addition, the moist, unstable airmass as well as increasingly strong winds aloft with the approaching trough will bring the chance for some severe thunderstorms, with the Storm Prediction Center highlighting this threat from the Southern Plains to Middle Mississippi Valley Tuesday and into the Mid-South and Ohio/Tennessee Valleys Wednesday. Later week precipitation focus may spread over the East, then return/linger over the South, but guidance is murky on the scenario to be monitored closer to the event. The central U.S. will see quite mild to warm temperatures early next week underneath an upper ridge. Temperatures of 20-35 degrees above average will expand throughout the Plains and Mississippi Valley, putting actual temperatures into the 80s and even 90s in Texas by Monday-Tuesday while 60s reach as far north as South Dakota and Iowa, with potential for widespread records. The upper trough and cold front pressing eastward should cool temperatures down closer to normal or a few degrees below in the central U.S. by midweek, but temperatures could already start to rebound by Thursday. The well above normal to possibly record-breaking temperatures will get shunted eastward ahead of the upper trough/underneath the upper ridge into the east-central and then eastern U.S. Tuesday-Thursday. 70s should be widespread across the Southeast and could even reach as far north as the Mid-Atlantic. Meanwhile the West is forecast to see near to slightly above normal temperatures into Sunday, but cooling to below normal particularly in terms of highs by Monday-Tuesday as upper troughing comes in. Schichtel 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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw