Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 160455

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1155 PM CDT Sat Jul 15 2017


Issued at 241 PM CDT Sat Jul 15 2017

Surface high pressure is sliding off to our southeast and flow is
becoming more southwesterly which is bringing back higher dew
points and warmer temps. 70+ dew points have moved into all but
the easternmost part of Iowa as of 19Z.

A shortwave trough embedded in the northwest flow was located in
southeast SD - southeast MN, and with an associated surface cold
front, is the potential weather maker tonight.


.SHORT TERM...(This Evening through Sunday)
ISSUED AT 241 PM CDT Sat Jul 15 2017

CAM and non-CAM models are in general agreement in bringing
weakening line of thunderstorms into the northern part of the CWA
late this evening and overnight. Can`t rule out the potential of a
lingering severe storm in a moderate CAPE/shear environment with
hail and wind being the main threats.

Developing cap will be a hindrance to the western reach of the
storms. Best chances for stronger storms looks to be along and
east of the Mississippi and in the northeast part of the CWA, with
even better chances further northeast into WI where pressure
rise-fall couplet is currently set up.

The weak cold front pushes into the southern part of the CWA
Sunday where it could be the focus for a few non-severe
thunderstorms tomorrow afternoon. Max temps will vary from around
80 in the northeast CWA behind the front to near 90 in the
southwest CWA where frontal passage may not occur at all.

.LONG TERM...(Sunday Night through Saturday)
ISSUED AT 241 PM CDT Sat Jul 15 2017

Well above normal temperatures are expected for much of next week
along with increasing humidity levels. There is a very real
possibility of heat index readings above 100 in the Tuesday through
Thursday time frame.

Sunday evening lingering showers and some thunderstorms will be seen
across the extreme south that will dissipate with sunset. The
remainder of the area will see dry conditions. Temperatures will be
at or slightly below normal.

Monday/Monday night quiet and dry conditions will be seen across the
area with temperatures at or slightly below normal. Attention then
turns to the increasing humidity levels.

Starting Tuesday, the models bring back the heat with dew points
increasing during the day. The morning hours will be dry but
boundaries from the previous night`s thunderstorm complex may allow
some diurnal convection to develop in the afternoon over the far
northwest areas.

Tuesday night on...

High dew points will be common Tuesday night through Thursday. A
diurnal change should be observable with higher dew points during
the day than at night.

IF diurnal convection develops over the far northwest Tuesday
afternoon, then convection is possible in mainly the highway 20
corridor Tuesday evening. The current model consensus has slight
chance to low chance pops for that area.

After midnight Tuesday night and continuing into Wednesday evening,
dry conditions are expected along with hot and humid conditions.

Late Wednesday night through Thursday night the question becomes
where do the nocturnal organized thunderstorm complexes develop and
track. Here the models disagree. Some of this disagreement is where
the next frontal boundary sets up. Internally, the models are
pointing toward MN/WI. Boundaries created by these storm complexes
may move into the area and generate new convection. If this scenario
occurs, convection would develop late at night and dissipate during
the morning. Boundaries created from this convection would then
allow afternoon/evening convection to develop across the area.

Adding to these questions is an additional signal of another front
moving through the area on either Thursday or Thursday night.

Given all these uncertainties, the model consensus has slight chance
to low chance pops for the area late Wednesday night through
Thursday night. Not every location will see rain. Those that do have
the potential to see up to an inch of rain.

Friday into Saturday the models diverge on their respective
solutions. The overall large scale signal that is loosely agreed
upon is high pressure over the Great Lakes with the better return
flow across western Iowa and the Plains. The key appears to be how
far south does the previous front get before it stalls.

If the front stalls south of the area, the potential is there for
much of the area to remain dry Friday into Saturday. The exception
would be the normal diurnal convection that develops in the
afternoon and dissipates with sunset. At night, the key question is
where does the organized thunderstorm complex develop and track.

The above scenario has support from the ECMWF and GFS.

The CMC on the other hand stalls the front across the area. An
organized thunderstorm complex develops along the front in northwest
Iowa that moves through the area late Friday night and Saturday.

Given all these uncertainties, the model consensus has mainly slight
chance pops Friday/Friday evening with chance pops late Friday night
into Saturday.


.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
ISSUED AT 1146 PM CDT Sat Jul 15 2017

Anticipate continued weakening of storms as they drift southward
from WI into N IL overnight. Given the uncertainty have left out
any mention of precip in the terminals, but will continue to
monitor trends and amend if needed. Otherwise, cold front will
push across the terminals overnight through mid morning. In the
wake cooler n/ne winds and low level moisture will likely aid
some low cloud development with additional lake enhanced clouds
potentially advecting into portions of northeast IA and northwest
IL. DBQ is most likely to see some mvfr cigs and have gone with
a tempo group mid morning through early afternoon. There is a low
chance of ifr clouds. Elsewhere expect sct-bkn mainly vfr cu
by mid morning through afternoon decreasing late. Winds turn from
e/ne at 4-8 kts on Sunday. A few showers and storms are possible
in the afternoon, but indications are these should mainly be south
of BRL terminal.




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