Extended Forecast Discussion NWS Weather Prediction Center College Park MD 233 AM EDT Sat Aug 31 2019 Valid 12Z Tue Sep 03 2019 - 12Z Sat Sep 07 2019 ...Hurricane Dorian forecast to affect Florida and parts of the Southeast U.S. next week... ...Overview... Upper ridging over the Four Corners/Southern Plains and western Atlantic will help to funnel Hurricane Dorian northward near/along the Florida coast next Tue/Wed. As troughing in the northern stream swings through the Great Lakes Wednesday, it will begin to tug the system northeastward near/along the Carolina coast as additional height falls push through Ontario Friday. Troughing off the west coast will slowly ease inland and be replenished upstream. ...Guidance Evaluation and Preferences... Models/ensembles have gravitated toward a more common solution off the west coast and near Florida with the larger players in the forecast, but differences remain in timing/track/strength of said features. In the west, consensus agrees on a sub-1000mb low in northern Minnesota Tue lifting into Canada and dragging its cold front eastward/southeastward into the southern Appalachians late Wed/early Thu. Most disagreement lied in Canada but this also translated into differences in frontal timing from the Northeast through the Ohio Valley (quicker GFSs, slower ECMWF/UKMET/Canadian). Ensembles suggest somewhat of a quicker pattern in the northern stream, so the 18Z GFS was not unreasonable. To the south, 03Z NHC track was closest to the 18Z GFS followed by the 12Z UKMET/ECMWF which was a good blended starting point over the CONUS as well. By next Fri/Sat, enough height falls should dig south toward Dorian (assuming it will be that far north) to start to tug it northeastward as the surface front lies astride the cyclone. Split between the 18Z GFS and 12Z ECMWF would bring Dorian (likely in extratropical transition) near the 40N/70W benchmark by next Saturday but ensemble spread was encompassed in a nearly 1000km by 1000km area so confidence was low. Please consult the latest information on Dorian from the National Hurricane Center as changes in the short term track/speed will have large affects on the forecast for late next week. ...Sensible Weather... Dorian will bring strong winds, heavy rain/flooding, and storm surge to parts of Florida into the Southeast per the current forecast but will be tied to its proximity to the coast. Northern Plains into the Great Lakes and Northeast will see cooler temperatures (10-15F below average) Tue-Thu behind a cold front that will sink toward the Southeast. Should Dorian lift northeastward as expected later next week, the heavy rain threat would follow through coastal NC as the system moves offshore. Quite uncertain of any effects on New England later next week. 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 and in the Pacific Northwest as the upper trough moves into WA/OR. 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