Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1141 AM EDT Wed Jul 10 2019
Valid 12Z Sat Jul 13 2019 - 12Z Wed Jul 17 2019
...Potential Tropical Cyclone Two to bring heavy rain to the lower
Mississippi Valley this weekend...
...Overview and Guidance/Predictability Assessment...
...Weather Highlights/Threats...
A significant focus of the medium range forecast continues to be
with the eventual track and sensible weather effects of Potential
Tropical Cyclone Two that may develop during the next day or so
over the northern Gulf of Mexico. The updated forecast remains
fairly close to ongoing continuity (which stemmed from the WPC-NHC
coordination yesterday) and reflects the first official advisory
from the NHC as of 10AM CDT. This was best represented by a 2/3rds
00Z ECMWF to 1/3rd GFS (00Z/06Z) blend which was just west of the
overnight progs. This takes the system into Louisiana and points
northward slowly but steadily in weak flow aloft. Expect heavy
rainfall to accompany this system from the Gulf Coast northward,
with highest totals likely to be near the central Gulf Coast/Lower
Mississippi Valley. Gulf inflow to the east of the system as well
as a stalled front to the north may promote relative maxima in
addition to the rainfall closer to the center. Please consult the
latest NHC advisory for more information.
Elsewhere the guidance continues to agree rather well with the
overall pattern. An upper ridge will prevail over the southern
half of the Rockies, likely with a very slow southward drift with
time. At the same time an eastern Pacific mean trough will make
slow progress toward the Pacific Northwest coast. Individual
shortwaves will eject from the trough and be carried along in
progressive flow across the northern U.S./southern Canada then
into a shallow mean trough that covers the Northeast. Continuity
looks good at the moment for the best-defined waves/frontal
systems affecting the northern states. These fronts will provide
a focus for episodes of showers and thunderstorms. The northern
Plains into Upper Mississippi Valley still appear to have the best
potential for some locally heavy activity due to fronts stalling
for a time before lifting northward ahead of the next wave in the
series. For the upper trough nearing the Pacific Northwest, the
ECMWF mean has been the most consistent over recent runs though
latest GEFS means are now similar. As expected the operational
model runs vary with shortwave details that have low
predictability, ultimately favoring a model/mean blend for a
deterministic forecast. The overall mean trough will keep the
chances for occasional light to isolated moderate rain in the
forecast over parts of the Pacific Northwest. Opted to retain an
increasing weight of the previous forecast by next Tue/Wed which
were reflected in less detail by the latest 00Z ECMWF ensemble
mean and 06Z GEFS mean.
A majority of the western and northern U.S. should see above
normal temperatures during the period with anomalies for morning
lows tending to be somewhat greater than for daytime highs. Some
pockets of plus 10F or greater anomalies are possible. Expect the
best emphasis for warmest readings versus average to shift from
the western states during the weekend into the northern
Plains/Upper Mississippi Valley and expanding toward the Northeast
during Mon-Wed. Clouds and rainfall near and east of the system
tracking northward from northern Gulf should keep daytime highs
below normal for a period of time.
Fracasso/Rausch
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