Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1129 AM EDT Sat Jul 20 2019
Valid 12Z Tue Jul 23 2019 - 12Z Sat Jul 27 2019
...Overview and Guidance/Predictability Assessment...
Amplified upper-level pattern expected to be in place through much
of the medium range, with persistent upper ridging centered across
the Four Corners region and amplified upper troughing,
transitioning to broad cyclonic flow, across the eastern half of
the CONUS. Upper troughing is expected to push a cold front off
the Eastern Seaboard by day 3 (Tue), with the trailing end of the
front extending from the Florida Panhandle to South Texas. Models
show consensus that this front should stall by day 4 (Wed) and
linger through the remainder of the forecast period as it
gradually washes out. Farther west, shortwave energy reaching the
Pacific Northwest on days 3-4 should move a cold front inland,
reaching the northern High Plains by day 5 (Thu), where forward
progress should begin to slow somewhat as the southern end of the
front runs into the higher heights from the southern Rockies to
the Southern Plains.
Overall, the majority of model/ensemble guidance was relatively
agreeable through much of the extended forecast period. A
multi-model deterministic blend (00Z ECMWF/UKMET/CMC/06Z GFS) was
used as a basis for the forecast during days 3-4. The UKMET/CMC
were dropped starting on day 5 as their solutions begin to differ
from consensus, particularly the CMC which differed substantially
with the evolution of the shortwave expected to reach the Northern
Plains by late Thu, closing off the feature and holding it farther
west across the Canadian Rockies. The forecast during days 5-7 was
based heavily on the ECMWF/GFS and ECENS/GEFS ensemble means, with
gradually increasing weight on the means trough time.
...Weather Highlights/Threats...
The frontal boundary expected to stall off the Eastern Seaboard
through the medium range is expected to focus numerous showers and
thunderstorms. The most widespread convection and the greatest
potential for areas of heavy rainfall should occur from
eastern/coastal North Carolina southward across the coastal plain
to the Florida Panhandle Tue-Thu. Showers/storms may lessen in
coverage/intensity by late next week as the surface front washes
out. The shortwave/frontal system moving from the Pacific
Northwest to the Northern Plains/Upper Midwest should bring an
increase in shower/storm chances to the Upper Midwest by late next
week. Meanwhile, daily scattered storms will be possible across
the central/southern Rockies as some degree of monsoonal moisture
manages to spread into the upper ridge.
Below average temperatures are expected across a large area in the
wake of the cold front moving off the East Coast Tue. High
temperatures are forecast to be 5 to 10 deg F below average from
the Southern/Central Plains to the Southeast/Mid-Atlantic Tue
through late in the week. Temperatures are expected to gradually
moderate some by Thu-Sat across the Mid-Atlantic, but areas from
the Southern Plains to the Southeast should remain below average
due to elevated clouds and scattered precipitation north of the
frontal boundary.
Ryan
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