Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 PM EDT Fri Aug 30 2019 Valid 12Z Mon Sep 02 2019 - 12Z Fri Sep 06 2019 ...Hurricane Dorian forecast to affect Florida and parts of the Southeast U.S. next week... ...Overview... Upper pattern next week will feature ridging over the Four Corners/Southern Plains as well as in the western Atlantic as the jet stream remains along the U.S./Canadian border. This leaves Hurricane Dorian to move northward over/near the Florida peninsula, and eventually along/just inland of the Southeast coast. In the northern stream, positively-tilted troughing out of the northeast Pacific into WA/BC will gradually stream eastward in weakened fashion while additional shortwaves will round the upper low over Hudson Bay/northern Quebec. ...Guidance Evaluation and Preferences... Larger than average differences off the Pacific Northwest and Florida (Dorian), continues in the latest suite of model guidance. For Dorian, a blend of the 06Z GFS, 00Z Canadian, and 00Z ECMWF offered a reasonable starting point nearest the 15Z NHC track that would take Dorian into south Florida then slowly northward into coastal Georgia/South Carolina. Please consult the latest information from NHC on Dorian. In the Pacific Northwest, guidance continues to show variation on how to take a shortwave or weakly closed upper low inland (i.e., at what strength and speed). Trend may be quicker/weaker, but deterministic runs are showing less than stellar run-to-run continuity even on days 3-4. The 06Z GFS has slowed down slightly from its 00z run, more closely resembling the 00z CMC, but the 00z ECMWF/UKMET both remain slower and deeper with the system. By midweek, northern stream troughing will wrap through the Great Lakes/Northeast but again there remains some timing/amplitude differences in the ensembles. No real trend was noted in the ensemble systems but it appears this lead trough may swing through about a day ahead of when Dorian might be picked up. By the end of the week, height falls may attempt to push into the Pacific Northwest again as another shortwave digs through western/central Canada. Models also struggle to resolve the details of this system as well. The blend for Dorian (GFS/CMC/ECMWF) seemed to work well for the rest of the CONUS, along with WPC continuity from the previous shift. Increased the usage of the ensemble means (ECENS/GEFS) by days 6-7 to help mitigate unresolved details in the deterministic runs. ...Sensible Weather... Dorian will bring strong winds, heavy rain/flooding, and storm surge to parts of Florida into the Southeast per the current forecast. Daytime maxes would be suppressed by a few degrees along its track but the larger negative anomalies will be over the Northern Plains into the Great Lakes Tue-Thu behind a cold front. Away from Dorian, rainfall coverage should be fairly limited over the lower 48, with the exception being along/ahead of the northern tier cold front. Locally strong to severe thunderstorms are possible along this boundary as well, particularly Monday in the Northern Plains/Upper Midwest. The Southwest/Four Corners states may see isolated to scattered rain but with generally light amounts. Santorelli/Fracasso 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 Hazards: - Heavy rain across portions of the Great Lakes and the Upper Mississippi Valley, Mon-Tue, Sep 2-Sep 3. - Heavy rain across portions of the Southeast and the Mid-Atlantic, Mon-Fri, Sep 2-Sep 6. - Heavy rain across portions of the Northeast, Mon, Sep 2. - Heavy rain across portions of the Northeast, Wed, Sep 4. - Severe weather across portions of the Central Plains, the Upper Mississippi Valley, and the Northern Plains, Mon, Sep 2. - Flooding possible across portions of the Central Plains, the Southeast, the Middle Mississippi Valley, and the Southern Plains. - Flooding occurring or imminent across portions of the Northern Plains. - High winds across portions of the Southeast and the Mid-Atlantic, Mon-Fri, Sep 2-Sep 6. - High significant wave heights for coastal portions of the Southeast, Mon-Wed, Sep 2-Sep 4. 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