Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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547
FXUS63 KDVN 152043
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
343 PM CDT Tue Aug 15 2017

.SYNOPSIS...
Issued at 330 PM CDT Tue Aug 15 2017

A nearly stationary east-west frontal boundary extended from the
NE/KS border to southeast IA and into northern OH. South of the
front, temperatures were in the mid to upper 80s with dewpoints
in the lower 70s. North of the front, readings were in the 70s
with a northeast wind and low stratus.

MCS that has pushed slowly across southern IA during the day was
finally approaching the dvn cwa near Ottumwa, but was showing
signs of weakening. Torrential rainfall and lightning were the
main threats. An isolated storm near Burlington produced 1.40
inches of rain in 50 minutes.

&&

.SHORT TERM...(This Evening through Wednesday)
ISSUED AT 330 PM CDT Tue Aug 15 2017

Forecast focus on increasing showers and thunderstorms.

Tonight: Any showers and storms in our southern cwa should
dissipate by early this evening. Then a few showers and storms may
develop late tonight as warm air advection increases. However,
have kept pops mainly in the slight category. Lows will be in the
60s to near 70.

Wednesday: Increasing showers and thunderstorms during the day as
a sharp upper level trough swings into the Midwest. Increasing
PWAT`s and deep layer shear may allow for strong storms producing
gusty winds and torrential rainfall in the afternoon. Depending
on amount of instability (determined by cloud cover) a few severe
storms are possible if there is more heating than expected. SPC
has a marginal risk of severe storms for much of the cwa, but is
conditional on cloud cover. I will have likely pops in our western
cwa where the better forcing will exist. Highs will be in the
lower to mid 80s.


.LONG TERM...(Wednesday Night through next Tuesday)
ISSUED AT 330 PM CDT Tue Aug 15 2017

Wednesday night...Latest forcing progs and LLVL warm air advection
wing progression suggests a band of sctrd to broken thunderstorms
moving north to northeast along and north of I80 from 23z to 02z or
03z, while other storms and storm clusters form in llvl south to
southwesterlies ahead of frontal system stretched north-south acrs
central IA. This could focus more widespread shower/storm activity
acrs the northwestern half of the DVN CWA just to lee of
northeastward progressing upper trof axis from mid evening to a
few hours past midnight. With precipital water(PWATs) over 2
inches fed up acrs the CWA at that time on 35-40 KT southwesterly
LLVL flow, heavy rainfall a good bet in these areas receiving the
storm clusters, especially taking into account shear profiles of
30-40 KTs Wed evening. Could see some localized swaths of 1-2+
inches easy in 2-4 hours. Isolated 3+ inch rainfall amounts
possible. The storms will look to be more sctrd acrs the rest of
the DVN CWA, but can`t rule out a linear line tailing acrs the
southern third of the CWA as well into the overnight hours.
Rainfall amounts away from the organized clusters more in the way
of 0.25 to 0.75 of an inch.

As for severe potentail, deep layer shear/kinematic profiles support
some strong to severe storms Wed evening, but instability-
thermodynamic profiles may be marginal and becoming saturated. But,
feel at least a few severe storms will occur Wed evening and at
least Marginal risk needed. More heating build up earlier during the
day may eventually warrant a slight risk for portions of the area.

Thursday and Friday...Expect the overnight showers and storms to be
moved east out of the fcst area by 12z Thu, but lingering arrival of
both the sfc front and upper trof axis may spawn additional showers
during the day Thu, especially along and east of the MS RVR. Lag of
cool air advection and mixing west winds of 10-20 MPH increasing
behind the FROPA support highs in the upper 70s to low 80s, along as
there is some afternoon breaks in the cloud cover. Incoming ridging
for a weather lull period later Thu into Fri.

Friday night...Latest medium range model runs continue to hint at a
southeastward digging upper trof/northwest flow system for Fri night
into Sat morning. This system would produce sctrd showers and some
thunderstorm acrs the area with current model progression path, but
the 12z GFS has this system interact with a strong southerly THTA-E
feed into it`s southwestern flank to produce an MCS type system from
acrs the east central plains into the mid MS RVR Valley. A system
like this in that placement may limit moisture feed further to the
northeast acrs the local area which will be in the direct line of
the brunt of the upper system, possibly limiting precip coverage and
intensity.

Saturday and Sunday...SFC high pressure and flattening upper level
flow following the Friday night system should make for a mainly fair
weather weekend by later Sat into Sunday, along with near seasonable
temps. An increasing warm moist conveyor up around the western flank
of the eastward pushing ridge up into northern third of CONUS
westerlies will look to set up an MCS storm track somewhere acrs the
central into northern plains, and MO Valley later Sunday night. Some
chance for at least decaying portion of this activity making it into
the western CWA by late Sunday night.

Next Monday and Tuesday...The latest run medium range solutions
suggest this may be a convectively active period for the local area,
with an optimum llvl moisture feed up into short wave embedded
westerly steering flow acrs the upper Midwest. The local area may be
subject to a few rounds of storm clusters or MCS`s From Mon night
through Tue, before another digging upper level trof and northern
plains high pressure shunts the active zone to the south of the
region by mid next week. as for eclipse viewing potentail during day
Monday, hopefully convective debris from upstream storm activity, or
renewed convection on it`s remnants/MCV right overhead Monday
afternoon, doesn`t muck things up.    ..12..

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
ISSUED AT 145 PM CDT Tue Aug 15 2017

Cigs will gradually improve to MVFR this afternoon at KCID/KDBQ
and mainly VFR conds at KBRL/KMLI. A few thunderstorms are
possible in southeast IA this afternoon into early this evening.
Have kept at VCTS at KBRL. Late tonight, Cigs/Vis should lower to
MVFR/lcl IFR conds at all taf sites. Northeast to east winds this
afternoon becoming southeast by Wednesday, with wind speeds around
10 knots or less.

&&

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

$$

SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...12
AVIATION...Haase



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