Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1158 AM EDT Thu Jul 18 2019
Valid 12Z Sun Jul 21 2019 - 12Z Thu Jul 25 2019
...Widespread Excessive Heat Persists into Monday...
...Overview and Weather Highlights/Threats...
A hot and humid airmass across the eastern half of the CONUS will
be suppressed south to the Gulf Coast under a developing upper
trough Sunday through Tuesday. Excessive heat ahead of the
associated cold front will continue to warrant heat headlines
until the cold frontal passage. The abbreviated heat wave will
remain problematic for those working or recreating outdoors,
individuals sensitive to heat, especially the elderly and animals.
The cold front will be a focus for widespread convective
thunderstorms as it pushes south from the Central Plains, Midwest
and Northeast Sunday night and into the southern Plains and
Southeast Monday. The front looks to slow or stall with frontal
wave development over the southern Mid-Atlantic Monday through
Tuesday. Moisture and instability pooling ahead this cold front
and frontal waves should enhance rainfall amounts and increase the
risk for flash flooding, particularly where the front slows.
The cold front will eventually sag toward or to the Gulf Coast by
midweek and likely bring relief to both heat and drought
conditions in the Southeast, though the persistence of the front
for several days with convergence of Gulf moisture looks to lead
to at least localized flash flooding concerns.
North of the tail end of this cold front there will be enhanced
upslope flow to the central/southern Rockies as it sags south
Sunday night into Tuesday which could lead to localized flash
flooding.
A ridge builds from the Four Corners to the Canadian Prairies
Sunday night through Tuesday and persists at least through
Wednesday before the next low/trough from the Pacific Northwest
begins to over top it. Expect monsoonal convection over the Desert
Southwest under this developing ridge starting Monday and
expanding up the Intermountain West through at least midweek.
...Guidance/Predictability Assessment...
There is overall good large scale agreement among global
deterministic and ensemble guidance in the early to middle parts
of next week with the setup of a strengthening trough over the
Pacific Northwest, a building ridge over the interior West, and a
trough digging from the Great Lakes. Details with shortwave
energy, particularly as it rounds the ridge and into the eastern
trough is understandably varied among guidance. The 00Z and 06Z
GFS/GEFS is more amplified with the eastern trough and brings it
to the Gulf Coast earlier than the 00Z ECMWF/ECENS. However,
overall the timing and strength differences are small enough to
warrant a general deterministic model blend with the 00Z/06Z GFS
and 00Z ECMWF/CMC/UKMET for days 3-5 with equal weighting of the
06Z GEFS/00Z ECENS for days 6 and 7 along with some of the
deterministic 06Z GFS/00Z ECMWF/CMC.
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
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