Extended Forecast Discussion NWS Weather Prediction Center College Park MD 140 AM EDT Sat Mar 16 2019 Valid 12Z Tue Mar 19 2019 - 12Z Sat Mar 23 2019 ...Overview... A blocking mid/upper-level ridge initially centered from the Pacific Northwest to western Canada early next week is forecast to very slowly shift eastward through the forecast period while a mean upper-level trough very initially across the Great Lakes/Northeast slowly lifts out. Strong westerly flow across the North Central Pacific will split as it encounters the ridge, with some shortwave energy directed north into the higher latitudes of Canada and the rest separating into the southern stream. Stronger height falls may approach the Pacific Northwest by late next week as the upper ridge axis shifts east to toward the High Plains. ...Guidance Assessment/Preferences... Models/ensembles show above average agreement at the larger scales through the period. Some differences remain when it comes to the details of specific systems, but guidance over the past day has shown some trends worth nothing. Models have trended more amplified with shortwave energy digging into the Midwest Tue-Wed. The GFS has generally lagged the majority of other guidance on this trend while the FV3 has generally been close to the consensus. Farther west, the trend has also been toward the deeper solutions with southern stream energy reaching California by Wed, with the GFS also lagging to some extend on this trend. Finally, models show broad agreement that an amplified trough should approach the Pacific Northwest by next weekend, although given the time frame solutions differ on the precise timing, amplitude, and structure of this feature. Given these considerations, a blend of the ECMWF/CMC/UKMET/FV3-GFS was used as a forecast starting point during days 3-5 (Tue-Thu), with more weight shifted toward the ECENS and NAEFS ensemble means during days 6-7 (Fri-Sat). ...Weather Highlights and Hazards... Widespread and potentially heavy rains should be ongoing Tue-Wed across the southern half of the Florida Peninsula as a wave of low pressure moves along a surface front stalled south of the state. Farther west, the the Pacific system tracking into California should spread rain and high elevation snow into the Sierra Nevada, Great Basin, and central/southern Rockies by next Wed-Fri, with some localized enhancement of precipitation over favored terrain possible. Moisture increasing ahead of the system by Fri may also bring an increase in showers and thunderstorms to portions of the Southern Plains, with locally heavy rain possible. Finally, the stronger height falls and a cold front approaching the Pacific Northwest by Fri-Sat may bring a return of rains and mountain snows to that area. The eastern U.S. will begin the forecast period with chilly temperatures beneath the broad upper trough (highs 5 to 10 deg F below average), but these should gradually moderate to near seasonal averages by Thu. Meanwhile, high temperatures will be 5 to 15 deg above average Tue-Wed from the Pacific Northwest to the northern Rockies, and these anomalies will spread east into the Midwest by next weekend. 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