Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
427 PM EDT Tue Jul 30 2019
Valid 12Z Fri Aug 02 2019 - 12Z Tue Aug 06 2019
...16Z update...
No major changes were needed to the overnight medium range
package. Model guidance continues to handle the overall pattern
well over the CONUS, while struggling a bit with energy over the
eastern Pacific and Gulf of Alaska, especially late in the period.
Decided the best compromise was the 06Z GFS, 00Z EC mean, and the
00Z NAEFS. The 00Z ECMWF kept the energy more northward toward the
Gulf of Alaska. Downstream, model differences exist with another
upper trough over south-central Canada. The 00Z GFS is stronger
with this low compared to other guidance, but on the other hand,
the 00Z and 06Z GEFS means have less troughing extending southward
from this feature into the Great Lakes region. Therefore, chose to
lean away from those solutions in favor of better clustering of
other guidance.
For additional information and details about sensible weather,
please see the previous discussion.
Tate
...Previous Discussion...
...Overview and Guidance/Predictability Assessment...
Fairly typical summertime pattern will feature an upper high over
New Mexico with troughing lifting out of the Pacific Northwest,
through Canada, and settling into the Great Lakes by next week. A
break in the subtropical ridge will favor a trough over the
northeastern Gulf of Mexico as well. The models/ensembles have had
a tough time resolving the Pacific flow into western North America
which continued through the 12Z/18Z cycle. However, the 18Z GFS
and 12Z ECMWF clustered well enough with their ensemble means so
that a consensus blend sufficed as a starting point Fri-Sun. By
next week, the ensembles were much quicker to dig height falls
into the Great Lakes/Northeast than the deterministic runs but the
trend in the ensembles is for a more-defined and slower solution.
In light of quicker continuity, a position midway between the two
camps was reasonable for now since there continues to be
uncertainty upstream with ridging into the Gulf of Alaska which
may modulate the orientation of the flow across southern Canada.
Elsewhere, a blended solution worked well with fewer changes in
lower latitudes.
...Weather Highlights/Threats...
Monsoonal moisture will focus rainfall over CO/NM around the upper
high this weekend before possibly shifting back westward into
eastern Arizona next week. Coastal Washington will see some rain
as a cold front moves inland Friday before drying out. Downstream,
a wavy frontal boundary from the central Plains eastward to the
mid-Atlantic will favor precipitation along and to the south of it
with scattered mainly afternoon shower/storms. East of Florida, an
emerging tropical wave may bring increased rainfall to parts of
the Sunshine State, the Bahamas, and perhaps into the coastal
Carolinas. Finally, the High Plains/Upper Midwest will see the
Canadian system pull its fronts eastward along with higher chances
of rain/convection Sat-Tue.
Temperatures will be a bit cooler than average over the central
states with higher chances of precipitation. Milder than average
temperatures are expected over the Great Lakes and Northeast ahead
of the northern tier system this weekend. Elsewhere, temperatures
will be within a few degrees of typical early August values.
Fracasso
Hazards:
- Heavy rain across portions of the Central Plains, the Central
Rockies, the Central Great Basin,
the Southern Rockies, the Southern Plains, and the Southwest,
Sun-Tue, Aug 4-Aug 6.
- Heavy rain across portions of the Central Plains, the Middle
Mississippi Valley, the Lower
Mississippi Valley, and the Southern Plains, Fri-Sat, Aug 2-Aug 3.
- Heavy rain across portions of the Southeast, Fri-Sun, Aug 2-Aug
4.
- Flooding possible across portions of the Upper Mississippi
Valley and the Northern Plains.
- Flooding occurring or imminent across portions of the Lower
Mississippi Valley and the Northern
Plains.
- Flooding likely across portions of the Northern Plains.
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