Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
110 AM EDT Fri Jul 09 2021
Valid 12Z Mon Jul 12 2021 - 12Z Fri Jul 16 2021
...Excessive Southwestern Heat Persists into Next Week...
...Pattern Overview with Weather Highlights/Hazards...
The ongoing heat wave under upper ridging will continue for the
Great Basin to CA and the Southwest into early next week with
temperatures 10-20F above normal through Tuesday. Several daily
high temperature records are likely through Tuesday in these
areas. The model consensus is leading to gradually lowering
heights with a developing modest northwest US trough, with the
highest heights drifting south into southern CA/AZ.
With high along over the southeast, another area with above normal
temperatures will be the mid Atlantic to the lower Great Lakes/NY.
This includes the Washington, DC to Baltimore, Philadelphia, and
New York City corridor.
The forecast indicates potential for showers/thunderstorms over
the Southwest/Southern Rockies with pockets of enhanced 700 mb
relative humidity in place to support diurnal activity with
instability peaking each afternoon/evening.
Locally heavy rainfall may occur along a slow moving front in the
Midwest to the lower MS Valley on Sunday as fueled by
return/pooling Gulf Moisture and instability. A break develops
with the front decaying afterward. The next frontal wave brings
heavy rainfall potential into Iowa and Missouri Wed and Thu 15
July, possibly developing into the adjacent Midwest and Ohio
Valley by the end of next week.
...Guidance/Predictability Evaluation...
The WPC medium range product suite was primarily derived from a
blend of guidance from the 18 UTC GFS/GEFS, 12 UTC operational
ECMWF/Canadian global. The guidance is in better than average
agreement in the anticyclone over the southwest and southeast.
The primary differences are the timing/amplitude of the 700-500 mb
trough over the Northwest coming into the mean upper Midwest and
then Great Lakes trough. An equally weighted solution among the
12z ECMWF/12z Canadian/18z GFS/18z GEFS Mean was used to mitigate
the differences.
Petersen
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook 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