Extended Forecast Discussion NWS Weather Prediction Center College Park MD 208 AM EST Sun Feb 25 2024 Valid 12Z Wed Feb 28 2024 - 12Z Sun Mar 03 2024 ...Heavy Precipitation Pattern Emerging Again for the West... ...Guidance/Predictability Assessment... 12 UTC ECMWF/UKMET and ECMWF ensembles still constitute a cluster of guidance that vanguards better separated flow across much of the lower 48 this week than recent runs of the Canadian and to a lesser extent the GFS/GEFS. However, forecast spread is decreasing as we get closer in time and guidance slowly converges on a more similar scenario, bolstering forecast confidence. Overall, the WPC medium range product suite was mainly derived from the ECMWF/UKMET and ECMWF ensembles as recent trends in guidance and machine learning models toward this type of solution continue to better fit known flow biases and WPC continuity over the past day. WPC continuity is best maintained in the manner. ...Overview and Weather/Hazards Highlights... A dynamic/amplified northern stream upper trough will race from the Plains to the Appalachians Wednesday to off the East Coast early Thursday. An emerging area of showers and thunderstorms will sweep across the east-central through eastern U.S. with progression of a wavy/well defined frontal system into a moist/unstable pre-frontal environment to include lingering midweek much above normal to record warmth over the East. SPC shows some risk for severe weather with focus across the Tennessee Valley and vicinity. A post-frontal surge of cold Canadian high pressure offers transition for wrap-back snows from the Upper Ohio Valley/Great Lakes to the interior Northeast. Less progressive southern stream system energy ejection out through northern Mexico midweek may support light precipitation up into southern Arizona/New Mexico/High Plains Wednesday. Downstream translation and additional impulses support system genesis and focus, with lead return moisture to fuel an expanding area with rain/convective chances across the South/Southeast later week into next weekend. Farther upstream, a growing guidance signal in support of amplifying upper trough development/height falls over the east Pacific and gradually shift into the West will increasingly support chances for a moderate to heavier rain focus into the Pacific Northwest mid-later week that seems set to shift earnestly down the coast through California later week into next weekend to monitor. The WPC Day 4/Wednesday and Day 5/Thursday Excessive Rainfall Outlooks offer Marginal Risk areas for coastal areas of the Pacific Northwest/Northern California. There is also a significant threat for heavy snow to spread increasingly inland across the West, especially for favored terrain/mountains as highlighted in the WPC Winter Weather Outlook. 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