Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 162000

Area Forecast Discussion
National Weather Service Quad Cities IA IL
300 PM CDT Sat Sep 16 2017

Issued at 259 PM CDT Sat Sep 16 2017

Very warm and seasonably humid conditions were found across the
forecast area this afternoon with sunshine and somewhat breezy
south winds ahead of a cold front that reached from western upper
Michigan, south across western Iowa to the Texas panhandle.
Scattered showers and a few thunderstorms occurring along and east
of the boundary since this morning over central Iowa have
continued to weaken as they migrate east-northeast into an
environment with less favorable upper level moisture and deep shear.
Light showers or sprinkles were reaching into areas west of an
Independence to Fairfield line as of 2 pm, cooling temperatures
into the lower 80s, while readings in the mid 80s to around 90
were found over rest of the forecast area.


.SHORT TERM...(This Evening through Sunday)
ISSUED AT 259 PM CDT Sat Sep 16 2017

Main challenges is coverage and intensity of showers and possible
thunderstorms as the cold front gets nudged east-southeast through
the forecast area late tonight by an upper level trough moving
through the northern Rockies. In the near term, convective
allowing models continue to spread the weak convection well ahead
of the front eastward into eastern IA this evening in a
dissipating fashion, but agree with synoptic models that more
widespread activity will be focused along and behind the advancing
front from late evening through early morning, or roughly 11 pm
in the west, exiting the southeast by 8 am. Will keep only slight
to low end chance pops in the evening going for what will likely
be showers with perhaps isolated thunderstorms, then higher pops
overnight for the activity along the boundary. With modest forcing
and waning instability by that time, the potential for
thunderstorms, likely occurring as the boundary moves in, will
diminish overnight with just showers by the early daylight hours
as the system exits the southeast. Rainfall amounts will be less
than a quarter inch in most locations.

Sunday will likely start out with a low overcast as a large area
of post frontal stratus currently reaching from northwest IA and
eastern NE north to the Canadian border overspreads the region.
This should clear out from northwest to southeast during the
afternoon as 850 mb winds turn northwest and advect in cooler and
drier air. This will limit high temperatures to mainly the 70s
with noticeably lower humidity by afternoon as dewpoints lower
into the 50s.

.LONG TERM...(Sunday Night through Saturday)
ISSUED AT 259 PM CDT Sat Sep 16 2017

A broad southwesterly upper level flow with subtle shortwaves moving
through this flow will continue throughout the extended forecast
period. 12Z Saturday model runs prog that a deep 500 MB longwave
trof will develop over the western CONUS while an upper level ridge
remains over the eastern U.S. The models prog a chance of showers
each day as moisture from the Gulf of Mexico advects toward the
upper Mississippi Valley. HOWEVER, the long range forecast is NOT
suggesting a wet week with significant rainfall.

Monday and Tuesday, 12Z Sat model runs prog that Monday will be
mainly dry with temperatures in the mid 70s. The chances for showers
and possible thunderstorms, increase Monday night into Tuesday as a
subtle upper level shortwave passes overhead of a weak quasi-
stationary surface boundary lying close to the area. Tuesday
afternoon and overnight look to be dry. Temperatures on Tuesday will
be warm with afternoon highs in the mid 80s and overnight lows in
the mid 60s.

On Wednesday, a 500 mb shortwave and surface cold is expected to
move across the upper midwest providing another chance for showers.
Temperatures will continue to be summer like with afternoon highs in
the mid 80s and overnight lows in the mid 60s.

Thursday through Saturday, Forecast confidence is low. A broad
southwest flow aloft continues with a chance of showers each day.
However, the timing of upper level impulses that could produce
showers varies greatly between models this far out in the future.
High temperatures will be in the mid 80s with lows in the the mid


.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
ISSUED AT 1238 PM CDT Sat Sep 16 2017

Scattered thunderstorms in central Iowa occurring well out ahead
of a cold front are expected to remain west of the terminals
through this evening. This will keep VFR conditions in place with
south winds and scattered mid level clouds. Late tonight, this
front will push through eastern Iowa and northwest Illinois,
accompanied by scattered weakening showers and isolated
thunderstorms. At this time, the potential for thunderstorms is
too low to mention at the terminals and prob30 groups for showers
were utilized. Low clouds behind the front look likely to bring
IFR conditions into at least CID and DBQ for Sunday morning, while
ceiling were kept just above 1000 ft for now at MLI and BRL.
Conditions will likely improve to VFR at all sites Sunday




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