Extended Forecast Discussion NWS Weather Prediction Center College Park MD 151 AM EST Fri Mar 05 2021 Valid 12Z Mon Mar 08 2021 - 12Z Fri Mar 12 2021 ...Overview and Guidance/Predictability Assessment... Models and ensembles agree that an amplified eastern Pacific mean trough aloft will settle over the West next week. This trough will support rain and higher elevation snow along with the advent of below normal temperatures. Meanwhile by Tuesday-Wednesday, a shortwave expected to eject from the trough will produce a Plains system to spreads a broad area of precipitation across the central/east-central U.S.. Ahead of this evolution, eastern U.S. heights will continue to rise as ridging moves in from the central U.S. and an upper high builds from Mexico into the Gulf. This will transition much above normal temperatures from the north-central U.S. to the East. Forecast spread increases later next week with upper trough specifics in the West and frontal progressions over the central and eastern states. This reduces above normal feature predictability to more average levels. Accordingly, the WPC medium range product suite was derived from a composite of quite well clustered guidance from the 18 UTC GFS, the 12 UTC ECMWF/UKMET and to a lesser degree the 12 UTC Canadian days 3-5 (Mon-Wed) along with the 01 UTC National Blend of Models. Shifted focus to the compatible 18 UTC GEFS and 12 UTC ECMWF ensemble into days 6/7 (next Thu-Fri). Ensemble mean progressions seem consistent with amplified flow and maintain good WPC continuity. The latest 00 UTC guidance also seem in line with this forecast scenario. ...Weather/Threats Highlights... A good portion of the West has potential for at least some rain/higher elevation snow during the period under increasing influence of an unsettling and cooling mean upper trough. Heavier precipitation should extend from southwestern Oregon through favored terrain in California, with highest amounts most likely along the Sierra Nevada. Meaningful though more moderate precipitation is likely across the Interior West and Rockies. Energies ejecting into the Plains should produce a multi faceted system that tracks through northern tier locations Tuesday onward, with a broad area of precipitation extending across the northern/eastern Plains and into the east-central U.S. Some wintry weather may be possible over extreme northern locations. Farther south, there may be locally moderate to heavy rainfall from the Great Lakes/Midwest back through the mid-MS Valley and the Southern Plains currently the most likely areas to see highest rainfall totals and/or strongest convection. This will be fueled by Gulf inflow and instability. Activity will mainly focus along a wavy cold front that may tend to stall later period as upper troughing settles over the West. This could lead to a pattern with enhanced training. Much above normal temperatures will persist over the northern Plains/Midwest and expand into the Great Lakes through the first part of next week with readings generally 10-25F above normal. Daily records should be more numerous for warm lows than daytime highs. Development and gradual progression of the Plains/Midwest system and trailing front Tuesday onward will slowly push this warmth more across the eastern half of the country mid-late next week. Morning lows should remain as warm as 15-25F above normal and approach some record values while high temperature anomalies should be less extreme. Meanwhile, the West will experience a decent cooling trend spreading across the region from west to east during the period with highs tending to drop to 5-10F or so below normal. 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, winter weather outlook probabilities and heat indices 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml