Extended Forecast Discussion NWS Weather Prediction Center College Park MD 201 AM EST Mon Feb 26 2024 Valid 12Z Thu Feb 29 2024 - 12Z Mon Mar 04 2024 ...Heavy Precipitation Pattern Emerging Again for the West... ...Guidance/Predictability Assessment... Model and ensemble forecast spread continues to decrease through medium range time scales in amplifying upper flow, bolstering forecast confidence. Favor a blend of compatible guidance of the GFS/ECMWF/Canadian/UKMET for Thursday into Saturday, albeit with a bit more weighting applied to the ECMWF/UKMET that have performed better recently. Predictability seems to remain at above normal levels later weekend into early next week and a composite of the GEFS/ECMWF ensemble means and best compatible GFS/ECMWF seems to provide a good forecast basis along with the National Blend of Models through these longer time frames. WPC product continuity is well maintained with this plan. ...Overview and Weather/Hazards Highlights... A leading/main southern stream upper trough with origins over the East Pacific will eject eastward from northern Mexico and traverse The South/Southeast Thursday and Friday as a surface low/frontal system takes position over the Gulf of Mexico. Moisture return from the southern Gulf and easterly fetch from the Atlantic are expected to fuel an area with rain/convective chances. Locally heavy downpours may focus over the Central Gulf Coast. This area will monitored for any runoff issues, but no ERO threat area has been issued at this time given relatively high Flash Flood Guidance values. Rain/showers will linger over the Southeast this weekend with more, but weaker impulses in a similar pattern. Upstream, there continues to be a very strong guidance signal that an amplified upper trough digging into the eastern Pacific later this week will shift over the West this weekend. This will increasingly support chances for a moderate to heavier rain focus into the Pacific Northwest mid-later week that along with an associated/moderate long fetch moisture plume will shift steadily down the coast through southern California later week into the weekend to monitor. The WPC Day 4/Thursday and Day 5/Friday Excessive Rainfall Outlooks (EROs) offer Marginal Risk areas for coastal Oregon through Northern California. There is also a significant threat for high winds and heavy snow to spread inland across the West, especially for favored terrain/mountains as highlighted in the WPC Winter Weather Outlook. However, valley snowfalls will develop more over time as snow levels decrease with upper system and wavy frontal translation. This translation should also favor development of an emerging precipitation shield over the cooling Rockies/Plains by Sunday/next Monday that may include snows on the northwest periphery of activity. Upper trough amplifciation and inland march by the weekend will cool temperatures over much of the West, leading to maximum values of as much as 10-15 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/lead frontal system working over the West. Spring maximum temperatures ranging upwards to 20-30 degrees above normal will spread from the Midwest toward the Northeast to offer potential for some 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