Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1150 AM EDT Sun Sep 08 2019
Valid 12Z Wed Sep 11 2019 - 12Z Sun Sep 15 2019
...Potential for record heat to continue for the lower Mississippi
Valley and Southeast...
...Overview and Guidance Evaluation/Preferences...
An upper-level ridge is forecast to remain rather entrenched from
the lower Mississippi Valley to the Southeast through much of the
medium range. Meanwhile, initially splitting upper flow from the
eastern North Pacific into western North America will consolidate
as a stream of relatively vigorous upper shortwaves traverse the
CONUS northern tier. Farther south, an easterly wave is forecast
to approach Florida and the coastal southeastern U.S. by the
upcoming weekend, traversing the southern periphery of the
expansive upper ridge.
For the start of the medium range period, a blend of the 00Z
ECMWF/CMC and 06Z GFS was used, which represented consensus well
with the synoptic features across the Northern Plains. For Day 5
onward, model differences became more significant, particularly
with the evolution of troughing over the Pacific Northwest and
northern Rockies. The 06Z GFS was considerably faster with the
shortwave energy coming out on Day 6 and 7 (Sat-Sun) while the
ECMWF/CMC were slower and a bit more amplified. This matched
better with the ensemble means and consensus, so less weight was
given to the GFS late in the forecast period, with more weight
toward the ECENS/NAEFS ensemble means. The 00Z ECMWF/CMC offered
some utility for day 6-7, so some of it was incorporated into the
blend as well.
...Weather Highlights/Threats...
Heavy rain will be possible across much of the Northern Plains and
Upper Midwest Wed-Thu in association with a deepening surface low
pressure system crossing the region. Models suggest the potential
for at least a couple inches of rainfall across a relatively wide
area. The easterly wave approaching Florida and the Southeast U.S.
by late in the week is expected to increase shower and
thunderstorm activity, with locally heavy rains possible.
Increasing rain, potentially moderate to heavy, will also be
possible across the mountain ranges of the Pacific Northwest by
late week as upper troughing progresses into the region.
Hot conditions are expected to persist across portions of the
south central and southeastern U.S. through much of the upcoming
week. High temperatures are forecast to be 5 to 15 deg F above
average across a large area from the Ohio Valley to the lower
Mississippi Valley and the Southeast. Several record high
temperatures are possible each day, especially from the lower
Mississippi Valley to the Southeast where highs may soar well into
the 90s, perhaps approaching 100 deg at a couple locations.
Ryan/Taylor
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