819
FXUS63 KDVN 251747
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1247 PM CDT Mon Sep 25 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 222 AM CDT Mon Sep 25 2017

Another summer night is going on outside, while the pattern that has
supporting it, is beginning to change. The synoptic front, which
more or less represents the difference from late October`s cold rain
and breezy north winds, and August`s warm clear nights is found from
north central Kansas, to south central Minnesota. This front will
make slow progress towards the area today.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 222 AM CDT Mon Sep 25 2017

It will certainly be another warm day, as the entire CWA remains
east of the front today. Thus, with high confidence, another day
around 90, with dewpoints mainly in the mid 60s are forecast. The
gives heat index readings in the lower 90s for nearly all of the
area, and we will again consider that the main message. However,
the biggest question today will now include thunderstorm
coverage. Mesoscale models today, ARW, NMM, ESRL HRRR, and to a
lesser degree NAM show isolated, very slow moving thunderstorms
firing up during peak heating today. Those models all have a few
pockets of upper 60s dewpoints prior to convective initiation, and
no doubt that allows them to be more aggressive in forming
convection. Normally, I would discount that possibility, but
dewpoints near 68-69 are only a few degrees higher than what we`ve
been experiencing the past few days, and some mesoscale
convergence in our southeast winds today may allow for that to
locally occur. In any case the storms would be isolated, and slow
moving, so pops will be VERY low. The slow movement would allow
for spotty heavy rain amounts perhaps. With all guidance showing
these cells having them along and west of the Mississippi River,
I`ll have that low possibility forecast there as well, mainly
keeping Illinois dry. Tonight, a low probability shower or storm
is possible in the northwest, with dry conditions expected
elsewhere. Skies should become persistently cloudy northwest
overnight, while remaining mainly clear southeast.

ERVIN

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 222 AM CDT Mon Sep 25 2017

A chance of showers on Tuesday with a strong cold front then
temperatures much cooler in the extended, basically returning
to normal temperatures for the last week of September.

Tuesday and Tuesday night: Strong cold front arrives but forcing
weakens considerably and is mainly post-frontal, as the main upper
level trough coming out of the Rockies lifts well to our north into
the Upper Midwest. Models really diminish the qpf as the front
pushes across the dvn cwa so will keep chance pops for scattered
showers and possibly an isolated storm or two. SPC has the cwa in
only general thunder as shear is weak and instability is minimal, as
there should be extensive cloud cover. Ahead of the front
temperatures will warm into the 80s from extreme eastern Iowa into
our Illinois counties.

Wednesday through Sunday: A much more comfortable stretch of weather
as a pattern change to a deep trough in the eastern United States
takes place. This occurs as hurricane "Maria" finally lifts north
and then northeast out into the North Atlantic. While this will be a
much cooler pattern compared to the past week, temperatures should
be close to normal for late September. Highs will be in the mid 60s
to lower 70s with lows in the 40s to around 50. Rainfall during this
period appears to be slim to none.

Haase

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
ISSUED AT 1243 PM CDT Mon Sep 25 2017

Generally VFR conditions to prevail the next 24 hours. Fair skies this
afternoon will become partly to mostly cloudy tonight into Tuesday as
a broad cool front passes. Any ceilings should be above 3K AGL late
tonight and Tuesday. South winds of 5 to 15 mph will become northwesterly
Tuesday morning. Scattered showers and isolated storms coverage is
too low to include in TAF attm with greateest risk between 26/05Z and
26/15Z.


&&

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

$$

SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...Ervin
AVIATION...Nichols