Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 170932 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Quad Cities IA IL
432 AM CDT Mon Jul 17 2017

Issued at 323 AM CDT Mon Jul 17 2017

High pressure over the western Great Lakes was supplying much of the
forecast area with a seasonably cool and dry airmass early this
morning. Aloft, a ridge axis was located over the Missouri River
Valley into MN with a trough downstream over the Ohio Valley and
Great Lakes. Both features are expected to migrate eastward today,
providing near to below normal temperatures and low humidity to
start the work week. This will be short-lived as a pattern change
brings back heat, humidity and storm chances for much of this


.SHORT TERM...(Today and Tonight)
ISSUED AT 323 AM CDT Mon Jul 17 2017

The low level light east to southeast flow out of the Great Lakes
high will keep low humidity and relatively mild temperatures in
place through today. With the light flow, temperatures should
recover to afternoon highs in the the lower to mid 80s from
northeast to southwest under the near full sunshine. Dewpoints
initially as low as the 50s over portions of eastern IA and
northwest Illinois, will likely return to the 60s by afternoon due
to moisture contribution from mature crops. Little change is
expected overnight, outside perhaps some high level thin
cloudiness. This, combined with light surface winds gradually
veering to the south, should lead to slightly warmer mins, from
around 60 northeast to the mid 60s in the south and southwest.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 323 AM CDT Mon Jul 17 2017

Forecast focus on many challenges during the extended period. There
will be a zonal flow with strong westerlies across the upper
Midwest, while a heat dome persists in the mid MS Valley.

Tuesday: This is when the heat dome begins to push northward into
our southern cwa, where afternoon highs will push into the lower
90s. Dewpoints will be rising into the lower 70s with heat index
values pushing into the upper 90s. In our north, where debris clouds
from convection to our west and north will hold afternoon
temperatures in the mid 80s.

Tuesday night: An MCS that develops well to our northwest Tuesday
afternoon may spread into our northern cwa during the night. Severe
storms are possible in our far nw later in the evening. However,
models indicate a weakening trend after that as the MCS tracks
across our north. As of now, SPC has a slight risk of severe storms
in a small portion of Highway 20 in northeast IA, with a marginal
risk a bit farther southeast. The main threat will be damaging winds
and large hail.

Wednesday through Saturday: Models indicate a potentially very
active period with several rounds of thunderstorm complexes tracking
east/southeast across MN/WI/northern IA/northern IL. This would be
on the edge of a strong cap with the heat dome centered in the
central Plains/mid MS Valley. With strong westerlies in the upper
Midwest providing decent shear, and endless supply of high CAPE, any
of these complexes could be severe. PWAT`s will be increasing to
well over 2 inches with thunderstorm complexes producing several
inches of rain in a short time. Any repeating (training) storms
would yield much higher rain amounts. The tricky part of the
forecast is timing these complexes that may impact the dvn cwa,
and how far south this may push a cold front or cold pool. Thus,
the reason for chance pops in nearly every period of the extended.

Temperatures will be a challenge depending on where the storm
complexes track, and associated cloud cover. For now, the thinking
is our southern cwa (closer to the heat dome) will be most favored
for several days of heat advisory criteria (Wednesday through
Saturday). This technically would mean excessive heat warning
criteria for later shifts to consider, but it is too soon as of this
writing. Maximum temperatures roughly from Interstate 80
southward would be in the mid 90s with dewpoints well into the 70s
to lower 80s. This would soar heat index values to 100 to 107. In
our northern cwa, closer to or actually impacted by
thunderstorms, the highs there should remain in the 80s.

Sunday: The ECMWF indicates a strong upper level trough diving
southeast across the area, breaking down the heat dome, and sending
a strong cold front sweeping through the area. However, the GFS is a
day slower with the front not arriving until Monday of next week.



.AVIATION...(For the 06Z TAFS through 06Z Monday Night)
ISSUED AT 1131 PM CDT Sun Jul 16 2017

VFR conditions are anticipated to dominate the TAF cycle as
easterly low level flow advects in drier air. Toward
daybreak there is a low chance of patchy ground fog and
MVFR visibilities at the terminals.




...corrected long term segment...

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