Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
112 AM EDT Sat Jul 20 2019
Valid 12Z Tue Jul 23 2019 - 12Z Sat Jul 27 2019
...Overview and Weather Highlights/Threats...
A cold front will continue to be a focus for widespread showers
and thunderstorms as it pushes south through the southern Plains,
lower MS Valley, and southeast Tuesday and to the Gulf coast by
Wednesday. However, the presence of a stalled front along the
Gulf Coast in July should lead to showers and storms, along with a
localized flash flood risk. Temperatures behind the front will
fall below normal across the central to southern Plains to the
mid-lower MS Valley and southeast owing to how far south the front
penetrates.
Waves of weak low pressure progress along the front over the
southern Mid-Atlantic Tuesday and Wednesday. Moisture and
instability pooling ahead of this front and frontal waves should
enhance rainfall, with heavy downpours and resultant flash
flooding concerns.
Continued upslope flow to the southern Rockies as the cold front
sags south Monday night into Tuesday could lead to localized flash
flooding. Expect monsoonal convection over the Southwest and
Intermountain West each day as pockets of moisture and instability
occur around the periphery of the large scale high.
Several model/ensemble members depict a 700-500 mb wave crossing
the northern Plains Fri and into the upper MS Valley/upper Great
lakes Sat. This should increase probability of showers/storms in
these locations/days.
...Guidance/Predictability Assessment...
There continues to be overall good large scale agreement among
global deterministic and ensemble guidance through the middle of
next week with the setup of a trough over the Pacific Northwest, a
ridge over the interior West, and a Hudson Bay low with a trough
extending south across the eastern U.S.
The Pacific Northwest trough ejects east into Canada and over the
top of the ridge Wednesday into Thursday with heights rebounding
in the Pacific northwest Fri until the next upper trough
approaches Sat 27 Jul. The closed anticyclone persists over the
central to southern Rockies, and mid-upper trough remains over the
northeast and Mid-Atlantic. A weakness with a 500 mb trough drifts
west from the Gulf of Mexico into southern TX.
The timing and amplitude differences of the upper troughs are
small enough to warrant a blend of the deterministic 18z
GFS/12z-00z ECMWF along with the 18z GEFS and 12Z ECENS means for
Days 3 through 7. The larger differences toward the end of next
week involve the handling of cyclone energy over Canada and over
the northeast Pacific. The best agreement is with the persistent
anticyclone over the Four Corners by Friday 26 Jul and drifting
into AZ Sat 27 Jul.
Petersen
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