Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Thu Feb 29 2024 Valid 12Z Sun Mar 03 2024 - 12Z Thu Mar 07 2024 ...Heavy Snow and High Wind Threat for the Western and North-Central U.S... ...Wet Pattern for the West Coast and The South... ...Guidance/Predictability Assessment... GFS/ECMWF/UKMET/Canadian model guidance solutions seem reasonably well clustered only for Sunday. A model composite looks reasonable. However, model solutions then quickly diverge. Model cycle to cycle continuity and forecast confidence has decreased significantly over the past two days with both the amplitude and timings of local weather/hazard focusing systems in multiple upper stream flows. Accordingly, the best forecast may be derived from a broad GEFS/ECMWF ensemble mean composite along with the compatible National Blend of Models in an effort to maintain the most predictable forecast components and larger scale hazards/threats signals until the pattern becomes less sensitive to initialization data. ...Overview and Weather/Hazards Highlights... A main weather story concerns the evolution of amplified upper troughing digging into the eastern Pacific that will shift earnestly over the West this weekend. This and subsequent/highly uncertain and varied additional Pacific systems will support multiple chances for periods of moderate to locally heavier precipitation through the West Coast next week. The WPC Day 5/Monday Excessive Rainfall Outlook (ERO) introduces a Marginal Risk area for coastal Oregon/northern California. There are also threats for high winds and heavy snow to spread from the West Coast states inland across the Intermountain West to the Rockies, especially for favored terrain/mountains as highlighted in the WPC Winter Weather Outlook (WWO). Valley snowfalls may develop more over time as snow levels decrease with upper system and wavy frontal cooling. This translation should also favor windy wrap-back snow development from the Northern Plains Sunday to over the Upper Midwest Monday within cold Canadian air dug on the backside of the system. Run to run guidance continuity has been less than stellar with the evolution of the weather pattern downstream over time, but protracted moisture return with wavy and now slower to propagate main fronts and a lingering/wavy coastal fronts up the East Coast all point to development of widespread showers/thunderstorms from the Mississippi Valley Monday through the Eastern Seaboard Wednesday into Thursday, but with possible main focus over the Lower Mississippi Valley/Central Gulf Coast States Monday/Tuesday. The WPC Day 5/Monday ERO introduces a Marginal Risk area. Pacific upper trough amplification and inland progression this weekend will cool temperatures over much of the West, leading to the spreading of values as cold as 15 degrees below normal, will cooled conditions lingering next week. Expect much above normal warmth will spread across much of the central and eastern U.S. this weekend into early next week before moderating. Yet another recent onset of pre-frontal springlike conditions will be highlighted by temperatures ranging upwards to 20-30+ degrees above normal to spread from the Mississippi Valley/Midwest/Great Lakes into the Northeast to again challenge record values. 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