Extended Forecast Discussion NWS Weather Prediction Center College Park MD 117 PM EDT Sat Mar 21 2020 Valid 12Z Tue Mar 24 2020 - 12Z Sat Mar 28 2020 ...Guidance/Predictability Assessment... The upper flow pattern for next week is expected to feature cold troughing across the western U.S. with zonal to southwesterly flow over the central/eastern U.S. In this flow, a series of progressive shortwaves and associated/complex surface based systems will traverse through the active southern stream, bringing episodes of organized precipitation in a warm pattern. The phasing or lack of between northern and southern streams and multiple weaker storm systems through the flow lead to an overall average to below average forecast confidence for individual storms and associated weather impacts. The WPC forecast was initially based heavily on a blend of the 00Z ECMWF/UKMET during days 3-5 (Tue-Thu). These solutions were well-clustered with the ensembles for a low pressure system off the New England coast on Tue. The same holds true for another wave of low pressure expected to develop across the Southern Plains early Tue, crossing the Ohio Valley Tue night/Wed, and moving once again off the New England coast on Thu. These solutions were also comparable along the West Coast during that time frame with a broad, positively-tilted trough digging southward Tue-Thu, and with northern stream shortwave energy crossing the Northern Plains/Midwest. By days 6-7, leaned heavily toward ECENS/GEFS ensemble means, along with some continued limited use of the ECMWF. As the Pacific energy moves east in the southern stream during this time frame, models show typical timing and amplitude differences. Ensemble means helped to smooth out these differences and find some degree of consensus. The ECMWF was a little faster than the ensemble consensus with this shortwave across the central U.S. by days 6-7. Some degree of consensus exists, however, that an area of low pressure should develop across the Southern Plains in response to this shortwave on Fri, and lift eastward or northeastward by day 7. The level of suppression of this system as it move east-northeast is unclear at this time, with the current forecast leaning more toward the ECENS idea of a less suppressed and deeper system crossing the Midwest/Great Lakes next Sat. ...Weather/Hazard Highlights... Expect an active wintry pattern for much of the West next week as broad areas of moderate rains and terrain enhanced snows periodically overspread the region with approach and passage of several lead systems and eventual upper trough amplification. Highest totals for the period should be over the Sierra Nevada while favored terrain along much of the West Coast. The Great Basin/Southwest and Rockies will likely see episodes of organized precipitation as well. Energy ejecting from the West in flat flow offers potential for a swath of rain/convection from the Mid-MS Valley/Mid-South to the Mid-Atlantic/Northeast Tue-Wed with low/frontal system passage and moderate lead return moisture inflow. Progressive flow nature should limit heavy rainfall/runoff issue potential. This system could produce another round of accumulating snows for portions of the Northeast, most likely for interior areas. The potential low pressure system across the central U.S. by Fri-Sat could produce a broad area of showers and thunderstorms from the Central Plains/Mid-Mississippi Valley to the eastern U.S. The system also has the potential to produce severe thunderstorms in parts of the Southern Plains, Arklatex, and Mid-Mississippi Valley on Fri (see SPC Day 4-8 Convective Outlook/Discussion) - although confidence in the specifics is low at this time. Schichtel/Ryan Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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