Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 200456
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1156 PM CDT Sat Aug 19 2017

...06z AVIATION UPDATE...

.UPDATE...
Issued at 931 PM CDT Sat Aug 19 2017

Will likely be adding some pops into west/northwest portions
of cwa overnight for elevated convection attendant to
increasing warm advection/isentropic ascent ahead of mid level
shortwave currently aiding NE convection. Some suggestions
from latest model data of upscale growth to convection in the
Central Plains, which will tend to track e/se mostly staying to
our w/sw overnight. However, may see some increase of rain
chances toward 12z and through 18z west/south cwa between
potential convective enhanced shortwave, and veering LLJ should
feed not be interrupted.

&&

.SYNOPSIS...
Issued at 300 PM CDT Sat Aug 19 2017

A weak ridge of surface high pressure extended across far northeast
Iowa into northern Illinois through midday. Fair weather cumulus
clouds developed during the early afternoon over parts of central
and eastern Iowa, into central Illinois. The wind was light and
variable. Early afternoon temperatures ranged from 76 degrees at
Dubuque to 84 at Keokuk and Fairfield.

&&

.SHORT TERM...(This Evening through Sunday)
ISSUED AT 300 PM CDT Sat Aug 19 2017

The main issues in the short term period are fog potential overnight
and chances for thunderstorms during the day Sunday.

Expect a clearing sky tonight with a light to calm wind, providing
favorable conditions for patchy fog development. This should be most
impactful in river valleys and other low lying areas. Widespread
dense fog is not likely, and Special Weather Statements should
handle localized dense fog, if needed.

For Sunday, a short wave trough will traverse the zonal flow and
move through the area. Scattered showers and storms are possible,
mainly west of the Mississippi River. The severe weather risk
through the day is rather low, with marginal deep layer shear,
although there will likely be a few more vigorous storms to
monitor. Dewpoint temperatures will rebound into the upper 60s,
creating afternoon heat indices of 90 to 95 degrees along and south
of Interstate 80.

.LONG TERM...(Sunday Night through Saturday)
ISSUED AT 300 PM CDT Sat Aug 19 2017

Forecast focus on thunderstorms early next week then a delightful
fall-like airmass to follow for later in the week.

Sunday night through Tuesday: While there will be chances for
showers and thunderstorms Sunday night and Monday (isolated to
scattered) the more widespread activity will occur Monday night.
This is when the main upper level trough (strong forcing) will be
diving southeast across the area, along with a strong cold front.
Shear will increase and SPC has a marginal risk for severe storms
across all of the cwa. Potentially this could be upgraded to a
slight risk. PWAT`s increase to 2.3 inches so have included "heavy
rain" mention in the grids for Monday night. The rain should end
Tuesday morning.

Solar eclipse on Monday: Temperatures will be somewhat of a
challenge due to the near total eclipse (but not 100%)occurring in
the early afternoon, and the amount of cloud cover which remains to
be seen. Looking at similar events in the past our temperatures
dropped 2 to 5 degrees (partial eclipse) at peak so have adjusted
the hourly temperature grids to account for this.

Wednesday through Saturday: Delightful fall-like airmass with no
rain expected. Northwest flow aloft will be locked in place bringing
a sprawling Canadian high pressure airmass into much of the
Midwest/Great Lakes. Highs in the 70s and lows in the 50s will be
common. Would not be surprising to see temperatures dip into the 40s
in some of the favored "cold" spots.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
ISSUED AT 1147 PM CDT Sat Aug 19 2017

Main challenge is timing of any precip chances during the period.

It would appear as though some increase in shower chances is
in the offing late tonight through Sunday morning with veering
LLJ ahead of an approaching shortwave. Chances appear better
heading west of the Mississippi River aft 10z through 18z.
Can`t also rule out a few storms developing after 18z Sunday
ahead of passing shortwave, then additional storm chances by
mid to late Sunday evening mainly north of I-80 with LLJ. Have
gone with VCSH wording at most sites during favored timing with
PROB30 mention at DBQ by afternoon where some potential to be in
closer proximity to vort max and better storm chances. Overall
though lower confidence on details of convection evolution and
timing exist.


&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

UPDATE...McClure
SYNOPSIS...RP Kinney
SHORT TERM...RP Kinney
LONG TERM...Haase
AVIATION...McClure



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