Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
331 PM EDT Fri Jul 19 2019
Valid 12Z Mon Jul 22 2019 - 12Z Fri Jul 26 2019
...Excessive Heat Episode Winds Down Over The Mid-Atlantic...
...Overview and Weather Highlights/Threats...
A hot and humid airmass across the eastern half of the CONUS from
the weekend will continue to be suppressed south to the Gulf Coast
under a developing upper trough and associated cold front Monday
through Tuesday.
The cold front will continue to be a focus for widespread
convective thunderstorms as it pushes south through the southern
Plains, Tennessee Valley, and Mid-Atlantic Monday night and to the
Gulf Coast Tuesday. The front looks to slow or stall as waves of
weak low pressure progress along the front over the southern
Mid-Atlantic Monday night into Wednesday. Moisture and instability
pooling ahead of this front and frontal waves should enhance
rainfall, with heavy downpours and resultant flash flooding
concerns.
The cold front will stall over the Gulf Coast through midweek and
likely bring relief to both heat and drought conditions in the
Southeast. However, the presence of a stalled front along the Gulf
Coast in July should lead to 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 through
these areas.
Continued upslope flow to the southern Rockies as the cold front
sags south Monday night into Tuesday could lead to localized flash
flooding.
A ridge persists from the Four Corners to the Canadian Prairies
into Wednesday before the next low/trough from the Pacific
Northwest begins to over top it. Expect monsoonal convection over
the Desert Southwest and Intermountain West through at least
midweek.
...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 low and 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 ejects east into Canada and over the top of the ridge
Wednesday into Thursday with heights rebounding in the Pacific
northwest. 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 preference to deterministic models
through Day 5 with inclusion of some 06Z GEFS and 00Z ECENS means
for Days 6 and 7. The larger differences toward the end of next
week involve the handling of cyclone energy over Canada and over
the northeast Pacific with the Canadian ensembles much more varied
than the GEFS or ECENS. The best agreement is with the persistent
anticyclone over the Four Corners by next Friday.
Jackson
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 Lower Mississippi Valley, the
Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the
Southeast, and the Southern Plains, Tue-Thu, Jul 23-Jul 25.
- Heavy rain across portions of the Northeast, the Central
Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern
Appalachians, and the Ohio Valley, Mon-Tue, Jul 22-Jul 23.
- Flooding occurring or imminent across portions of the Lower
Mississippi Valley, the Upper Mississippi Valley, and the Northern
Plains.
- Flooding likely across portions of the Upper Mississippi Valley
and the Northern Plains.
- Excessive heat across portions of California and the Southwest,
Wed-Fri, Jul 24-Jul 26.
- Excessive heat across portions of the Southeast and the
Mid-Atlantic, Mon, Jul 22.
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