Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1045 AM EST Sat Mar 02 2019 Valid 12Z Tue Mar 05 2019 - 12Z Sat Mar 09 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. Shortwave energy ejecting from a mean upper trough off the West Coast will cross the country every couple days. Meanwhile, a broad upper trough initially in place across the Great Lakes/Northeast should gradually lift out by the middle to end of the next work week. ...Model Guidance Evaluation and Preferences... Models/ensembles continue to show good clustering with respect to an energetic upper shortwave and low pressure system approaching the West Coast Tue night-Wed, such that a multi-model consensus forecast was preferred. As this feature moves into the central Rockies by Thu, the same model differences as yesterday continue to plague this feature. The GFS continues to keep a more amplified shortwave across the Rockies and into the central U.S., while the consensus of other guidance continues to weaken the wave as it encounters broad weakly anticyclonic upper low. The differences increase further by Thu night-Fri with the GFS spinning up a deep cyclonic across the central plains/Midwest, while the consensus of other guidance keep a weaker and more suppressed surface low across the southern plains. Ensemble means continue to provide little in the way of support for the GFS solution, and it was thus rejected starting Thu night-Fri. Flow in the northeast Pacific becomes a bit more chaotic by late in the forecast period, with the ECMWF/CMC showing some degree of shortwave energy undercutting the North Pacific/Gulf of Alaska ridge, and the GFS keeping a stronger ridge intact. There is some consensus, however, that an additional shortwave should move into the western U.S. on Fri and then reach the central Rockies by Sat. The ECMWF and CMC solutions showed the best agreement with the ensemble consensus on this feature. Given these considerations, the forecast was initially based on a multi-model deterministic blend (00Z ECMWF/UKMET/CMC and 06Z GFS) during days 3-5 (Tue-Thu). For days 6-7 (Fri-Sat), the forecast was shifted to heavier ensemble mean (ECENS and NAEFS) weighting, with some continued emphasis on the 00Z ECMWF/CMC solutions as well. ...Sensible Weather and Potential Hazards... Cold temperatures will continue to make headlines at the beginning of this forecast period, with a strong arctic surface high in place across the central/eastern U.S. High temperatures on Tuesday of 20 to 35 degrees below average are expected across much of the Plains eastward across the Midwest and Ohio Valley. This equates to widespread subzero and single digit low temperatures, and highs only in the teens and low 20s for many of those areas. Temperatures will only slowly moderate through midweek with temperatures 15 to 30 degrees below normal also extending eastward towards the Mid-Atlantic and Northeast. The magnitude and coverage of the cold temperatures will abate some by the end of the week, but below normal temperatures will continue for many areas through the end of next week. Heavy rain and mountain snow are expected to make a return to the western U.S. by Tuesday night as an atmospheric river event accompanies a strong Pacific low headed towards California. Heavy rainfall across the lower elevations of California may lead to some flooding problems, and heavy snow in the Sierra Nevada will add to the already extensive snow pack. Significant snow is forecast for the central and northern Rockies by Wednesday and Thursday as the moisture plume spreads inland, albeit not to the same degree as California. Rain is expected to become become widespread from portions of the lower/mid-Mississippi Valley to the Tennessee Valley by Fri into Sat as a warm front sets up ahead of a developing central U.S. low pressure system. 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