Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 201736
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1236 PM CDT SAT AUG 20 2016

...AVIATION UPDATE...

.UPDATE...
Issued at 1140 AM CDT Sat Aug 20 2016

The primary cold front continues to slowly migrate through the
area late this morning, roughly from Freeport to Macomb at 11 am.
Area radars show new convection in the past half hour lighting up
just ahead of this feature and weaker bands starting to take shape
in eastern IA along a weaker boundary marking the axis of better
low level cold air advection. Several areas of weak showers
continued between these features.

With low level cold air advection, post-frontal cloud cover all
the way back to the MO river valley, and upper level forcing
focused mainly north of the area closer to a vort max over SW MN,
the potential for thunder appears too limited and has been removed
from the forecast for the rest of today. Clouds should gradually
diminish toward evening, but too late to warm readings much higher
than a few degrees above current values. This will result in much
below normal highs, optimistically near 70 in the far NW to the
mid and upper 70s in the far southeast and east.

&&

.SYNOPSIS...
Issued at 325 AM CDT Sat Aug 20 2016

Upper level trough digging into the plains this morning with a lead
wave now lifting out over the upper Mississippi valley and the main
energy with the trough over south central South Dakota.  Surface low
centered near Burlington at this time with the associated slow-
moving cold front extending from near Dubuque to Iowa City to
Kirksville. Thunderstorms spreading along and ahead of the front
with a large stratiform rain region behind it.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 325 AM CDT Sat Aug 20 2016

Forecast focus is timing of rain exiting the area then temperatures.

Cold front and associated storms are tracking most closely to the
timing of recent runs of the ECMWF, thus will use this as a general
basis for this morning`s forecast.  Main line of thunder should be
out of the forecast area by 15z with lingering stratiform rain
behind it for another couple of hours then some clearing this
afternoon.

Behind the front, cold advection will drop 850mb temps from around
16C this morning to around 10C by tonight.  With lingering showers
and frontal debris this morning, then cold advection and mixing
behind the front this afternoon, highs should hold in the 70s today.

As dew points dropping tonight into the 50s, lows will follow. Wind
should stay above 5 kts, so not an ideal setup for radiational
cooling.  However, with moist ground, will need to watch for
localized fog potential in sheltered areas.

.LONG TERM...(Sunday through Friday)
ISSUED AT 325 AM CDT Sat Aug 20 2016

Lingering cyclonic flow/CAA, steep low level lapse rates, 500 mb
shortwave(s) and sufficient moisture depth will lead to shower
chances on Sunday around the Great Lakes. Can`t rule out a few
of these showers developing down into our northeast cwa by Sunday
afternoon. BUFR soundings however, show more shallow depth of
moisture and instability (850-750 mb lapse rates 7.5-8.5c/km), with
skinny CAPE aiding perhaps more robust diurnal cumulus development
north/east of Quad Cities, while continued low level drying on
northwest winds 10-20 mph likely limits any associated precipitation
to mainly sprinkles at best. Therefore, have maintained a dry forecast
on Sunday for now. Otherwise, will see pleasant conditions on
Sunday with low humidity and below normal temperatures in the 70s.
Sunday night will bring clearing skies and diminishing wind as the
surface high pressure builds in. The ideal radiational cooling
setup looks favorable to go near to just below cool side of
consensus guidance, with 850 mb temperatures around 10c supportive
of some upper 40s in favored lower terrain locations.

Monday into Tuesday will see a warming trends to near normal, with
highs mainly in the 80s as return flow strengthens ahead of
next trough and attendant surface cold front. This system will
look to bring increasing chances for showers and storms Tuesday
night through Wednesday.

Thursday and Friday look to bring the next bout of dry and cooler
air. 850 mb temperatures are shown to drop back down around 10c
by Friday, which will lead to return of more pleasant highs in
the 70s with lows in the 50s, with some 40s possible in favored
drainage locations.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
ISSUED AT 1236 PM CDT Sat Aug 20 2016

Low clouds and scattered showers following a cold front that moved
through the area this morning will lift out of the region this
afternoon. Showers will exit east of the terminals early, but
lingering MVFR cigs will take at least until mid afternoon to
scattered out or have bases lift to VFR levels. Gusty northwest
winds overspreading the area will lose their gusts this evening,
and then drop below 10 kts overnight and trend slightly more
westward. VFR conditions are expected overnight through Sunday as
high pressure builds into the region

&&

.DVN Watches/Warnings/Advisories...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

UPDATE...Sheets
SYNOPSIS...DMD
SHORT TERM...DMD
LONG TERM...McClure
AVIATION...Sheets



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