Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
107 AM EDT Fri Jul 19 2019
Valid 12Z Mon Jul 22 2019 - 12Z Fri Jul 26 2019
...Excessive Heat Episode Winds Down Over The Northeast and Mid
Atlantic...
...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.
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 waves of
weak low pressure progressing along the front over the southern
Mid-Atlantic Monday through Tuesday. Moisture and instability
pooling near this front and frontal waves should enhance rainfall
amounts, with localized heavy downpours and resultant flooding
concerns.
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. The front will focus showers and
storms along the Gulf coast into Florida. The temperatures behind
the front 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.
There will be enhanced upslope flow to the central/southern
Rockies as it sags south Sunday night into Tuesday with resultant
showers and storms, 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 trough over the Pacific
Northwest, a building ridge over the interior West, and a trough
drifting east from the the Great Lakes and Ohio Valley to the
northeast and Appalachians.
The Pacific Northwest trough moves downstream into Canada next
Wed-Thu with heights rebounding in the 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 blend of the models and ensemble means
with the forecasts consisting of an equally weighted average of
the 12z ECMWF/12z ECMWF Ensemble Mean/18z GFS/18z GEFS Mean/12z
Canadian Global. The larger differences towards 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 region (CO/UT/AZ/NM) by next Fri
26 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