Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1058 AM EST Sun Mar 03 2019 Valid 12Z Wed Mar 06 2019 - 12Z Sun Mar 10 2019 ...Overview... The flow across the CONUS will begin the medium range in a rather amplified setup, and then gradually trend more zonal and progressive by the mid to latter portion of the forecast period as a broad upper trough initially in place across the Great Lakes/Northeast lifts out.. Shortwave energy ejecting from a mean upper trough off the West Coast will cross the country every couple days. A more significant shortwave appears likely to generate another energetic low pressure system across the central U.S. by next weekend. ...Model Guidance Evaluation and Preferences... Models/ensembles continued to show good clustering early in the medium range with respect to a mid/upper-level shortwave and surface low moving into California on Wed. As the feature moves inland Thu-Fri, consensus has improved somewhat on the amplitude, with the GFS showing a significant reduction in the amplitude of the wave as it crosses the Rockies and moves into the central U.S., and a much more suppressed frontal wave by Fri compared to previous runs. Given the improved consensus, a multi-model deterministic blend (00Z ECMWF/UKMET/CMC and 06Z GFS) was preferred from Wed-Fri (days 3-5). There is general consensus now that the development of a more significant wave of low pressure across the central U.S. should hold off until Sat when the next significant shortwave approaches. The ECMWF and GFS showed better than average consensus with respect to this next wave an the resultant surface low, which should develop in the central High Plains Fri night-Sat and then lift northeastward into the Midwest by Sat night-Sun. Additionally, some semblance of clustering of ensemble members was also evident with this feature through Sun. Spread is higher with respect to another shortwave perhaps approaching the West Coast on Sun, with some solutions keeping the feature offshore as a closed low (GFS/CMC), while the ECMWF shows a more open wave. Given these considerations, weighting of the ECENS and GEFS ensemble means was increased to comprise a majority of the forecast during days 6-7 (Sat-Sun), with some continued minor emphasis on the deterministic ECMWF and GFS solutions. ...Sensible Weather and Potential Hazards... Although the coldest temperatures will be prior to the start of this forecast period, it will still be very cold by early March standards across much of the central and eastern U.S. on Wednesday and Thursday. A large arctic high will encompass much of the U.S. east of the Rockies, and temperatures only slowly moderate by the end of the week with anomalies of 15 to 30 degrees below normal through Thursday, and a second surge of cold temperatures is expected for the northern plains and Upper Midwest through next weekend, keeping readings about 20 degrees below normal. However, much of the southern and eastern U.S. warms up to near average levels by the weekend as a storm system gathers strength across the Plains. Heavy rain and mountain snow return to the western U.S. by Tuesday night as an atmospheric river event accompanies a strong Pacific low headed towards California. The Sierra Nevada will likely get an additional 1 to 3 feet of snow, thus adding to its extensive snow pack. Significant snow is forecast for the central and northern Rockies on Wednesday and Thursday as the moisture plume advects inland, albeit not to the same degree as California. With a large storm system possibly affecting the central U.S. next weekend, widespread rain is expected to develop from portions of the lower/mid-Mississippi Valley to the Tennessee Valley and southern Appalachians as a rich supply of Gulf moisture surges northward. Depending on where the surface low develops, a band of heavy snow and windy conditions are possible across parts of the northern plains, Upper Midwest, and western Great Lakes region. Ryan/Hamrick 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