Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
252 AM EDT Fri Aug 16 2019
Valid 12Z Mon Aug 19 2019 - 12Z Fri Aug 23 2019
...Weather Pattern Overview...
A zonal upper level flow pattern is expected across the
north-central U.S. with a broad upper level ridge over the
southern tier states to begin the forecast period early next week.
By mid-week, the pattern is expected to become more amplified
with a weak trough axis evolving across the eastern U.S. and the
upper level ridge becomes more established over the Rockies, which
is in response to a building trough over the northeast Pacific.
By the end of the week, a cold front is expected to cross much of
the eastern U.S. with the upper level trough axis situated over
the Northeast U.S.
...Guidance/Predictability Assessment...
There is good overall deterministic model and ensemble agreement
with the synoptic scale pattern on Monday, with the main exception
being a more amplified trough over the Ohio Valley with the past
few runs of the GFS, with a few ensemble members also supporting
this. This difference continues into mid-week with more troughing
along the East Coast and more GEFS members supporting it. The
UKMET appears stronger and more expansive with the upper level
ridge over the south-central U.S. Towards the end of next week,
model differences remain with the timing of the northeast Pacific
trough as it tracks inland across southwest Canada. The 00Z ECMWF
is faster with the progression of this trough axis over Alberta on
Thursday, whereas the EC mean is farther back and the GFS/GEFS
mean even slower. To address these differences, the medium range
forecast was based mainly on a deterministic model blend with
slightly greater weighting towards the ECMWF, and then more
towards the GEFS and EC means for the end of next week.
...Sensible Weather...
Temperatures are expected to remain above average across a large
portion of the nation through Tuesday, compliments of the upper
level ridge, with the exceptions being across parts of the
Southeast owing to increased cloud cover and showers/storms, and
also for the northern Plains. The heat is expected to be most
pronounced across the central High Plains and across the Desert
Southwest, with highs of 10 to 15 degrees above normal. This will
equate to widespread triple digit heat for those areas. Cooler
and less humid conditions will likely be in place across much of
the north-central U.S. and extending to the East Coast to close
out the week after the passage of the cold front.
In terms of rainfall, there will likely be scattered areas of
moderate to locally heavy rainfall across parts of the Midwest and
also near the Gulf Coast, with most events resulting in less than
1 inch in any 24-hour period. At the end of the forecast period
late Friday, it is worth noting that the GFS/GEFS ensemble members
are hinting at the possibility of a heavy rainfall event near the
central/western Gulf Coast region, but confidence in this scenario
is limited at this time.
Hamrick
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