Extended Forecast Discussion NWS Weather Prediction Center College Park MD 154 AM EST Sat Mar 06 2021 Valid 12Z Tue Mar 09 2021 - 12Z Sat Mar 13 2021 ...Overview and Guidance/Predictability Assessment... Guidance continues to offer a strong signal that an amplified eastern Pacific mean trough aloft will settle over the West next week in a pattern with above normal forecast predictability overall. This trough will support rain and higher elevation snow along with the advent of below normal temperatures. Meanwhile by Tuesday-Wednesday, a main shortwave forecast to eject from the trough will support a Plains low pressure system to spread a broad area of precipitation across the central/east-central U.S.. Ahead of this evolution, eastern U.S. heights will tend to rise for much of the coming week as ridging moves in from the central U.S. and an upper high builds up from the Gulf. This will bring much above normal temperatures from the north-central U.S. to the East. Accordingly, the WPC medium range product suite was derived from a composite of the 12 UTC GFS/ECMWF and GEFS/ECMWF ensemble mean along with the 01 UTC National Blend of Models days 3-6 (Tuesday-Friday). 12 UTC GFS/GEFS solutions cluster slightly better with the 12 UTC ECMWF/ECENS mean than the 18 UTC GFS/GEFS. Opted to focus on mainly the ensemble means by day 7/next Saturday to account for increasing forecast uncertainty and recent run to run model continuity issues at longer time frames, especially with upper trough specifics out from the Southwest. WPC continuity is well maintained with this forecast strategy. ...Weather/Threats Highlights... Expect rain/higher elevation snow as an upper trough/low settles into the West/Southwest in separated southern stream flow. Heavier precipitation will focus over favored terrain in California, with highest amounts most likely for the Sierra Nevada and coastal ranges. Some meaningful precipitation will also spread across the Interior West and the Rockies with upper trough, ejecting impulses and frontal system progressions. Energies ejecting into the Plains will support frontal low pressure systems with a precipitation focusing into the south-central Plains, Mid-Mississippi Valley, and Midwest/Great Lakes/Ohio Valley with Gulf moisture pooling. Some wintry weather may be possible over extreme northern locations. Activity will focus near a wavy cold front that may tend to stall as upper troughing settles over the West, leading to some training. Much above normal temperatures will persist over the northern Plains/Midwest and then expand into the Great Lakes through the first part of next week with readings generally 10 to more than 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