Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 121959

Area Forecast Discussion
National Weather Service Quad Cities IA IL
259 PM CDT Thu Oct 12 2017

Issued at 259 PM CDT Thu Oct 12 2017

Stubborn low stratus covered the entire dvn cwa with the west edge
of the clouds from Mason City, IA to Columbia, MO. Some patchy
drizzle lingered into the afternoon. The clouds were keeping
temperatures below normal again with mid afternoon readings in the
mid 50s to lower 60s.

Meanwhile, warmer temperatures were noted in the central and
southern Plains with readings well into the 70s to lower 80s.


.SHORT TERM...(This Evening through Friday)
ISSUED AT 259 PM CDT Thu Oct 12 2017

Forecast focus on cloud trends tonight then a chance of showers
and a few thunderstorms Friday afternoon.

Tonight: Clouds should continue to gradually erode from the
southwest into portions of our western and southern cwa. However,
stratus may linger in our northeast cwa much of the night. Later
shifts will need to monitor these cloud trends as confidence is
lower than usual. Lows will be in the lower to mid 50s.

Friday: Low pressure will develop in the central Plains with a
warm front developing along Highway 34 in se IA/western IL.
Models indicate increasing warm air advection/moisture return
especially during the afternoon. Elevated scattered showers and a
few thunderstorms should increase along a zone of elevated
frontogenesis and low level warm air advection. The models seem to
want to focus the better forcing mainly north of Interstate 80
and this is where we will focus the pops. As the afternoon
progresses the coverage of the precipitation will increase and by
late in the afternoon we will be at likely pops. Extensive cloud
cover in our northern cwa will keep temperatures much cooler
compared to our far south closer to the warm front. Highs will
range from the mid to upper 60s along Highway 20 to around 80 in
extreme northeast Missouri. HAASE

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 259 PM CDT Thu Oct 12 2017

A wet and stormy period remains forecast for Friday night through
Saturday night. Models are individually variable on placement of the
warm front and low track. The primary forcing for showers and
thunderstorms Friday evening will be elevated in nature, as surface
CAPE will be pretty much a non factor until later Saturday.
Incredibly high moisture content will be spreading over the area,
with good convergence along the I-80 corridor through Highway 20
during the evening and overnight. As discusses in earlier AFD
issuances, this is a anomalous amount of deep moisture, and heavy
rain potential will already be on the increase Friday night, as
there will be some potential for repeat/training storms due to the
moisture transport into a quasi-stationary boundary with only a weak
short wave to move through. A far stronger, possibly closed off low,
short wave will move through quickly Saturday and Saturday night.

The result of this strong wave interacting with a exceptionally
moist air mass with a seasonally stong baroclinic zone should be a
low passage over the CWA Saturday evening. That favorable timing,
brings together dynamics, deep moisture, and backed winds in a
deeply sheared atmosphere. Thus, repeat rounds of convection will be
likely as the warm front tries to be pushed north over the north half
of the area, but I think this will be a much more stationary
boundary that some models suggest. With a Fall airmass over the
Upper Midwest, the stable cool air will not quickly evacuate north
of the surface front. The low, should ride along it as forecast, but
should mainly focus storms to a triple point over the CWA not push
them into MN/WI as the GFS forecasts. This all points to heavy rain
amounts, of 1 to 3 inches, especially along and north of Interstate
80.  In addition, severe storms, with hail and possible surfaced
based storms near the stalled boundary could bring a tornado threat
Saturday afternoon/evening. That potential should transition to a
linear wind threat, heavy rain threat again in the evening, as a
very strong cold front shifts through. This Fall strength cold front
will bring  breezy night and breezy Sunday to the Midwest.

Sunday through Thursday appear dry, and increasingly pleasant as
zonal flow brings plains warmth back to the region.


.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 101 PM CDT Thu Oct 12 2017

Mainly MVFR/ocnl low VFR conds through this taf cycle.
South winds less than 10 knots.




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