Extended Forecast Discussion NWS Weather Prediction Center College Park MD 149 AM EST Sun Mar 07 2021 Valid 12Z Wed Mar 10 2021 - 12Z Sun Mar 14 2021 ...Overview and Guidance/Predictability Assessment... Models and ensembles continue to show a strong signal that an amplified southern stream upper trough/low will settle over the West/Southwest this week in a pattern with above normal forecast predictability. This trough will support rain and higher elevation snow along with the advent of below normal temperatures. Lead energies forecast to eject from the trough will support a quite wavy and slow moving central to eastern U.S. front whose Gulf moisture and instability pooling will fuel a focus for locally enhanced rainfall and training convection. Ahead of this evolution, eastern U.S. heights will tend to rise for much of the coming workweek as ridging moves in from the central U.S. and the Gulf of Mexico. This will bring much above normal temperatures from the north-central U.S. to the East. Toward the end of the week and next weekend, models generally agree that a cold front will progressively move through the Midwest and down through the East in response to amplified northern stream upper trough passage whereas the trailing front will become nearly stationary from the central/southern Plains to the Mid-Mississippi and into the Ohio Valley, where there is ample 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 periodic heavy rains. However, the timing of the waves will be difficult to resolve until we get closer to the event. The WPC medium range product suite for days 3-5 (Wed-Fri) was derived from a composite of the 18 UTC GEFS mean, 12 UTC ECMWF ensemble mean and best clustered 12 UTC ECMWF along with the 01 UTC National Blend of Models. Opted to focus primarily on guidance from the ECMWF ensemble mean next weekend. WPC continuity is well maintained with this forecast strategy. In contrast, 18 UTC GFS system timings are increasingly less well clustered with the WPC preferred blend, but the experimental GFS was more in line. The GEFS mean also increasingly became an outlier solution with a faster ejection of the main Southwest U.S. upper trough. ...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 lingering into this period for the Sierra Nevada and coastal ranges. Some meaningful precipitation will also spread across the Interior West and Rockies with the upper trough/low, 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 and pooling of Gulf moisture and instability. Some wintry weather may be possible over northern locations. Activity will focus near a wavy trailing cold front that will tend to stall as upper troughing settles over the West, possibly leading to cell training. There is increased forecast spread with respect to the eventual ejection and increasingly neutral tilt of the main Southwest upper trough next weekend, but height falls and instability may invigorate precipitation potential for the south-central Rockies/Plains with deformation and terrain/upslope flow. This includes a wintry threat focus from the Rockies to the High Plains as lead cold air filters southward through the central and eastern U.S. 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