Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 291143

Area Forecast Discussion
National Weather Service Quad Cities IA IL
643 AM CDT MON AUG 29 2016


Issued at 334 AM CDT Mon Aug 29 2016

Slow moving thunderstorms that produced locally heavy rainfall
Sunday evening have since dissipated across the forecast area,
giving way to another humid and warm night. Since midnight, very
isolated showers and thunderstorms have been limited to central
Iowa while the weak low level convergence boundary along the I-80
corridor in the local area has since become inactive. Area radars
show stronger, more organized storm clusters over southeast NE and
northern MN. Satellite IR and fog channel imagery showed mid and
high level clouds from the evening convection thinning out
overhead, with additional high cloud cover from on-going
convection upstream drifting eastward toward the area.


.SHORT TERM...(Today and Tonight)
ISSUED AT 334 AM CDT Mon Aug 29 2016

Initial short term challenges center around possible redevelopment
of at least isolated showers and thunderstorms, along with potential
fog formation early this morning. Otherwise, the unchanging weather
pattern today through tonight points toward a forecast based largely
on persistence. This will lead to another day of potential locally
heavy rainfall and possible flash flooding, on at least a local
scale, as seen the past couple days.

Fog is developing much slower tonight than last night, likely due to
the cloud cover that is just now thinning over the area. For now,
will be keeping patchy fog mentioned over most of the area going
until shortly after sunrise as the potential is still there for
fog formation with the wet ground in many locations and dewpoints
still in the upper 60s to lower 70s.

Will continue the slight to low chance pops for showers and
thunderstorms through the morning. Like yesterday, more widespread
coverage will likely wait until convective temperatures in the lower
80s are reached around midday and have increasing pops along these
lines. Have also raised highs a few degrees in most locations to the
mid 80s, which is warmer than most guidance, but yet a degree or two
cooler than Sunday. Surface dewpoints should again recover into the
lower 70s, leading to another muggy day with afternoon heat index
readings into the 90s over especially the south. This low level
moisture, along with continued PW values well into the 1.5 to 1.8
inch range, will support heavy rainfall. Another favorable
factor will be weak winds, both at the surface and aloft.
Rainfall amounts of 1 to 2 inches in less than an hour will again
be a threat over the area as slow moving storms evolve on storm
scale boundary interactions during the afternoon and early evening
hours. The potential for flash flooding will be greatest over
areas that received very heavy rainfall in this regime the past
couple days, mainly over east central IA into far NW IL.
Confidence is not high enough to go out with a flash flood watch
at this time, but convective trends will again need to be closely
monitored today through this evening.

Overnight, the axis of weak low level convergence and high moisture
levels will require keeping at least slight to low end chance pops
for showers and thunderstorms going through the night. Fog will
again be a threat, but have initially confined a mention of patchy
fog where the potential looks highest. Similar to tonight, low
temperatures will be no cooler than the mid 60s to around

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 334 AM CDT Mon Aug 29 2016

Main forecast concerns in the long term are the chances for rain and
thunderstorms at the beginning of the long term and then again at
the end of the period.  The first period of storms looks to be
continuation of the past couple of days.  The end of the week looks
to be slightly better in terms of largescale forcing.  The period
between these two chances of rain looks to be early fall like with
low humidity and highs in the low to mid 70s.

With little change to the current pattern and PWATs in the 1.50 to 2
inch range, expected more of the same for Tuesday and into
Wednesday.  On Wednesday, a cold front ushers the boundary that has
caused all of the rain and thunderstorms across our area the past
few days, to move south of the area.  Until then, expect more
mesoscale diurnally driven thunderstorms that could be slow moving.
Some areas could see up to 2 inches of rain if the storms do not
move much, while others see little to no rain.

NNW flow will usher in more cooler and drier air for the end of the
week.  With it, a reprieve from the rain.

Towards the end of the period, largescale flow turns to a broad SW
pattern.  Shrtwvs through the flow will cause showers and
thunderstorms.  In response to this flow H85 flow becomes stronger,
increasing the threat for strong storms and possibly the return of
nocturnal MCSs across the region.  Heavy rain will also be a
possibility.  It looks as though the beginning of Labor Day weekend
looks great and then Sunday into Monday, showers and thunderstorms
return. Saturday may be the best day for a Labor Day grill out.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday Morning)
ISSUED AT 643 AM CDT Mon Aug 29 2016

IFR to VLIFR conditions due to low clouds and fog should be
limited to MLI and DBQ and last only a couple hours early this
morning. Scattered, slow moving thunderstorms developing over
south central IA at 11z were timed to move through the terminals
late this morning with TEMPO groups, but this is somewhat low
confidence due to the disorganized nature of convection expected
today. This was then followed with PROB30 groups for additional
late afternoon thunderstorms with otherwise prevailing VFR
conditions. Thunderstorms with isolated to scattered coverage are
expected well into the evening hours, but confidence was too low
to include in these outer periods of the TAFs. Lingering moisture
likely lead to more fog tonight, which was included at MVFR levels
after midnight.


Issued at 334 AM CDT Mon Aug 29 2016

Most of the rain that occurred in the past 24 hours, fell in the
Cedar and Wapsi valleys.  Rises at Conesville and Dewitt have been
noted sooner than forecast.  Even with this additional rain think
that we have more than 24 hours until Conesville gets near flood
stage.  Would like to wait and see what the morning forecast brings
before changing this to a warning. As for the rest of the sites,
with confidence around 50% and over 24 hours until they reach flood
stage, decided to continue the current watches.  The next couple of
days could bring more isolated rain amounts near or greater than 2
inches.  This means that some sites may have additional rises and/or
sooner flooding than currently forecast.  At this time, the forecast
for many of the sites in flood watches, is for crests in the minor
flood category.


.DVN Watches/Warnings/Advisories...


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