Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Wed Feb 28 2024 Valid 12Z Sat Mar 02 2024 - 12Z Wed Mar 06 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... Latest GFS/ECMWF/UKMET/Canadian model guidance solutions seem reasonably well clustered for Saturday over the CONUS and vicinity including main depcitions of a highly amplified upper trough working into the West Coast and a far downstream southern stream system finally ejecting off the East Coast. A model composite looks reasonable. However, model solutions quickly diverge Sunday with the handling of dynamic shortwaves digging into and rotating through an amplfied mean upper trough position slated to shift through the West to the Central U.S. into early-mid next week. Model cycle to cycle continuity and forecast confidence has decreased from yesterday with the amplitude and timings of these local weather/hazard focusing systems, albeit still embedded within an active and dynamic upper flow pattern evolution. Accordingly, the WPC medium range product suite was mainly derived from a GEFS/ECMWF ensemble mean composite along with the compatible National Blend of Models to isolate, maintain and depict the most predictable forecast components at these longer time frames. WPC product continuity was best maintained in this manner. ...Overview and Weather/Hazards Highlights... The main weather story concerns the evoltion of amplified upper troughing set to dig into the eastern Pacific later this week and then shift earnestly over the West this weekend. This and subsequent but uncertain additional/varied Pacific systems will support multiple chances for locally moderate precipitation foci into the Pacific Northwest over this forecast period. A leading long fetch moisture plume/Atmospheric River will shift down the coast through southern California into Saturday while easing. The WPC Day 4/Saturday Excessive Rainfall Outlook shows a Marginal Risk area. There is also a significant threat for high winds and very heavy snow to spread inland across the Intermountain West and Rockies, especially for favored terrain/mountains as highlighted in the WPC Winter Weather Outlook (WWO). Confidence continues to increase in the risk for moderate to extremely disruptive high snowfall rates/blowing snow, particularly for the Sierra Nevada. Additionally, valley snowfalls may develop more over time as snow levels decrease with upper system and wavy frontal push. This translation should also favor development of an emerging precipitation shield over the cooling Rockies/Plains by Sunday/Monday with Plains cyclo/fronto genesis. This may lead into a chance for heavy wrap-back snows in quite windy flow across the Northern Plains and Upper Midwest with Plains cyclogensis and the digging of cold Canadian air southward in the wake of this main system, as per the WWO. Downstream, widespread showers/thunderstorms look to develop across the Plains/Mississippi Valley then east-central U.S., with eventual possible focus over vicinity of the Gulf Coast States into Tuesday/Wednesday. A leading southern stream upper trough will finally exit the East Coast Saturday to prompt modest/uncertain coastal frontal lows, with a wavy trailing front with continued rain/showers lingering back across the Southeast and the Gulf of Mexico. Uncertain but gradually improving moisture return from the Gulf of Mexico and lingering onshore fetch from the Atlantic may again combine to fuel renewed areas with enhanced rain/convective chances broadly over the South to monitor for any local runoff issues early next week with downstream progression and direction of the active upper flow pattern out from the West 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. Downstream, expect much above normal pre-frontal warmth later week over the north-central U.S. that will spread to much of the central and eastern U.S. this weekend/early next week downstream of the main upper trough position and associated frontal systems. Pre-frontal springlike conditions for much of the central to eastern U.S. will feature minimum and maximum temperatures ranging upwards to 20-30+ degrees above normal over the Midwest/Great Lakes 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