Extended Forecast Discussion NWS Weather Prediction Center College Park MD 157 PM EST Fri Mar 05 2021 Valid 12Z Mon Mar 08 2021 - 12Z Fri Mar 12 2021 ...Overview and Guidance/Predictability Assessment... Global models and ensembles agree very well 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 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.. There is a general model trend toward larger separation between the northern stream near/across the Canadian border and the developing low in the Plains, resulting in a faster motion of the low heading into Canada and a general northward trend of the rain axis across the Midwest/Mid-MS Valley during the second half of next week. 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 respect to 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 the 00Z ECMWF/00Z EC mean and the 06Z GFS/GEFS with smaller contributions from the 00Z CMC/CMC mean. Beginning on Day 5, more of the 06Z GEFS together with the 00Z EC mean were used to account for the increasing forecast uncertainty. Good WPC continuity is maintained. ...Weather/Threats Highlights... A good portion of the West has potential for at least some rain/higher elevation snow during the period as a cool mean upper trough settling in across the region. 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 northern Rockies, with some snow lingering into late week for the central Rockies. Energies ejecting into the Plains should support a low pressure system that tracks through the northern tier states from Tuesday onward, with a broad area of precipitation extending across the northern Plains to the Great Lakes into the interior Northeast, and down into the Midwest and the Ohio Valley. Some wintry weather may be possible over extreme northern locations. There may be locally moderate to heavy rainfall from the Great Lakes/Midwest. The mid-MS Valley and the southern Plains will be susceptible to the highest rainfall totals and/or strongest convection fueled by Gulf inflow and instability. Activity will mainly focus along a wavy cold front that may tend to stall later in the 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 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. 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