Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 AM 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. 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... No single model/ensemble mean was preferred through the period, due to larger than average differences off the Pacific Northwest and Florida (Dorian) in the 12Z/18Z guidance. For Dorian, a blend of the 18Z GFS, 12Z Canadian, and 00Z/29 ECMWF offered a reasonable starting point nearest the 03Z NHC track that would take Dorian into south Florida then slowly northward into coastal Georgia. Please consult that latest information from NHC on Dorian. In the Pacific Northwest, guidance was quite varied 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 the 12Z/18Z GFS runs were among the fastest of any model/ensemble member. 12Z Canadian represented a modest middle ground solution that seemed prudent given the uncertainty. By midweek, northern stream troughing will wrap through the Great Lakes/Northeast but again there remains 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 as another shortwave digs through western/central Canada. Favored an 18Z GFS/12Z ECMWF blend to maintain a coherent Dorian depiction. ...Sensible Weather... Dorian will bring strong winds, heavy rain/flooding, and storm surge to parts of Florida into Georgia 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 along/ahead of the northern tier cold front. The Southwest/Four Corners states may see isolated to scattered rain but with generally light amounts. 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 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