Extended Forecast Discussion NWS Weather Prediction Center College Park MD 154 PM 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 into the middle of next week. This trough will support rain and higher elevation snow along with the advent of below normal temperatures. Meanwhile, a main shortwave forecast to eject from the trough Tuesday-Wednesday will support a Plains low pressure system to spread a broad area of precipitation across the central/east-central U.S.. There has been a general model tendency to eject this initial low pressure wave from the northern Plains to central Canada into the northern stream, while another low pressure center develops over the central High Plains in connection with the southern stream wave ejection. 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. Toward the end of next week, models generally agree that a cold front will progressively move through the Northeast, whereas the trailing portion of the front should become nearly stationary from the central/southern Plains to the Mid-Mississippi Valley, where there is a decent model signal for an axis of heavy rain to develop. Low pressure waves that form and track along the front would be instrumental in producing the heavy rain axis. However, the timing of these waves will be difficult to resolve until we get closer in time toward the event. Accordingly, the WPC medium range product suite was derived from a composite of the 00Z ECMWF/00Z EC mean and the 06Z GFS/GEFS with smaller contributions from the 00Z CMC/CMC mean. Beginning on Day 6, more of the 06Z GEFS together with the 00Z EC mean were used to account for the increasing forecast uncertainty due to recent run to run model continuity issues at longer time frames. 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 precipitation focusing into the south-central Plains, Mid-Mississippi Valley, and Midwest/Great Lakes/Ohio Valley with the return of Gulf moisture. 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, possibly 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 anomalous. 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. Kong/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