Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
252 AM EDT Sat Aug 24 2019
Valid 12Z Tue Aug 27 2019 - 12Z Sat Aug 31 2019
...Overall Weather Pattern...
Broad cyclonic flow aloft is expected across the northern tier of
the nation for much of the upcoming week as an upper level low
develops over southern Canada and then Hudson Bay. This is
expected to result in a broad upper level trough over the northern
Plains and extending to the Great Lakes with a Canadian surface
high in place. There will be multiple shortwave perturbations
pivoting around this main low, and will result in reinforcing cold
fronts crossing the central and northern plains. Upper level
ridging extending from Texas to California is expected to continue
through midweek, and also across the western Atlantic Ocean.
...Model Guidance Evaluation...
Model agreement has improved with respect to the large upper low
centered over Manitoba and Ontario on Tuesday, and the latest run
of the UKMET has trended closer to the model consensus compared to
its previous, more amplified run. By the end of the week, there
is general agreement for a large scale trough centered over the
Great Lakes region, with the CMC depicting the most amplified
solution, and the 12Z ECMWF flatter with the trough axis. There
has also been a trend for a stronger southwest U.S. upper ridge,
with the ECMWF and CMC being the most amplified with this. By the
end of the forecast period on Saturday, noteworthy timing
differences exist with a shortwave crossing the Dakotas and also
with a Pacific disturbance offshore, so the ensemble means provide
a better starting point for Friday and Saturday.
...Expected Weather...
A hint of fall is expected across the north-central U.S. next week
with high temperatures generally 5 to 15 degrees below normal,
which equates to high temperatures in the 60s and 70s F for much
of this region. It should continue feeling like the middle of
summer from Texas to the Great Basin and the Desert Southwest with
temperatures 5 to 15 degrees above normal, with the greatest
anomalies expected early in the week across western Texas and New
Mexico. High temperatures could exceed 110 degrees across the
lower elevations of southern Arizona and southeast California.
Areas of moderate to locally heavy rainfall will be possible ahead
of the cold front crossing the Upper Midwest and Great Lakes
region early next week. For midweek and beyond, model uncertainty
reduces confidence in placement of heaviest rainfall areas.
However, there is the potential for a corridor of enhanced
rainfall across the Central Plains later in the week.
Hamrick
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
Hazards:
- Heavy rain across portions of the south-central Plains into the
Ozarks, and from the upper
Midwest to the upper Great Lakes, Mon-Tue, Aug 26-Aug 27.
- Heavy rain across portions of the central Plains, Fri, Aug 30.
- Heavy rain along the Outer Banks of North Carolina, Mon, Aug 26.
- Flooding occurring or imminent across portions of the Northern
Plains.
- Flooding likely across portions of the Northern Plains.
- Excessive heat across portions of the interior valley of
southern California, Mon-Wed, Aug 26-Aug
28.
- Excessive heat across portions of the southern High Plains, Mon,
Aug 26.
- Much above normal temperatures across portions of western
Oregon, Tue-Wed, Aug 27-Aug 28.
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