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