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209
FXUS63 KDVN 251136 AAA
AFDDVN

Area Forecast Discussion...UPDATED
National Weather Service Quad Cities IA IL
636 AM CDT SUN SEP 25 2016

...12Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 331 AM CDT Sun Sep 25 2016

Early this morning, weakening convection and showers were on the
CWA`s doorstep. Overall motion of the cells have been to the north
with a very slow easterly propagation of the line. These showers
and isolated rumbles of thunder will slowly make its way into the
area through day break. The best forcing for these showers and
thunder will slide north of the CWA. To our west, a cold front was
just entering the state of Iowa. This cold front looks to be the
gateway for more fall like weather.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 331 AM CDT Sun Sep 25 2016

Main forecast concern for the short term are the chances for rain
and thunder and the QPF associated with them. At this time, it
appears that many of the areas with cresting rivers today, will
not see much total rainfall, as the better chance for organized
thunderstorms and heavy rain will be east of the Mississippi River
this afternoon.

Llvl forcing for organized convection and rain is weakening this
morning. This means that showers will diminish in intensity and
coverage through the morning. Hires guidance and QPF suggests that
little to no rain should fall across western zones this morning.
Current forecast has less than 0.25 inches in Buchanan County.
This is likely overdone base on current radar trends. Think that
this rainfall will have little to do with current crest forecasts
in Independence.

Later this morning a cold front will roll across the state of
Iowa. This front looks to be crossing the Mississippi river
between 18z and 21z today. Sporadic clearing will limit overall
instability in front of the front. Deep layer shear of 20 to 30
kts will likely limit the chance of severe weather. Current
thinking from SPC is that a wet microburst is possible. Based on
CAMs and regional gridded and spectral models, it appears that the
best chances for thunderstorms will be just out of the CWA to the
east. Have kept chc pops for most of the area with the exception
of likelies in the afternoon close to our eastern border.

Tonight, the main focus turns to the strong H5 vort advection and
resultant strong CAA. This will likely keep the BL coupled and
lead to winds in the 10 kts with gusts near 20kts realm. Drier air
will rush into the area for Monday morning.

.LONG TERM...(Monday through Saturday)
ISSUED AT 331 AM CDT Sun Sep 25 2016

Little change to theme of forecast with mainly dry conditions and
near to below normal temperatures.

Models forecast the upper trough over the Upper Mississippi Valley
on Monday to deepen into a closed low while dropping slowly south
across lower Michigan into midweek. This will keep the area under
deep cyclonic flow through Wednesday with west to northwest winds,
gusty at times early in the week, ushering in the coolest air of the
young fall season with highs in the 60s to lower 70s and lows in the
40s to lower 50s through Wednesday. Will have to watch for periodic
bouts of clouds and possibly sprinkles or a few brief light showers
by Tuesday into Wednesday over northeast cwa, but have maintained
dry forecast as forecast soundings show limited moisture depth. The
ECMWF is most aggressive and an outlier with very light QPF on
Wednesday, as it`s a bit further west with the low near Lake Michigan
and brushes cwa with a vort max. In addition the flow turns more
northeasterly especially over northern Illinois, which may aid in
bringing some lake-enhanced moisture. All this adds up to needing to
watch the Wednesday timeframe for possibly some introduction of
precipitation chances, and also increasing cloud cover and lowering
highs.

Late week into next weekend, have continued with a dry forecast and
moderating temperatures, as surface and upper level ridging build
in. The one potential fly in the ointment is the ECMWF for the past
couple of runs has remained consistent with retrograding the large
upper low back towards the Midwest by next weekend. This would
likely yield more clouds and cooler highs, but for now have kept
with consensus dry forecast and temperatures warming near to
slightly above normal.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday Morning)
ISSUED AT 627 AM CDT Sun Sep 25 2016

MVFR visbys should start to improve a couple of hours after 12z.
IFR clouds associated with ra off to the west should become MVFR
by the time they affect CID and DBQ today. A cold front will push
through the area leading to a wind shift and winds gusting to near
20 kts this evening and overnight.

&&

.HYDROLOGY...
Issued at 331 AM CDT Sun Sep 25 2016

Flooding of several of the tributary systems across Iowa is the
primary hydrologic problem today, while flooding along the
Mississippi River remains forecast for next week.

The Wapsipinicon River at Independence is above major flood stage
and continues to rise. Crest forecasts have been revised upward to
18.5 feet, but it`s looking more likely that it will go higher thus
anticipate additional updates and impacts. Due to the increase at
Independence, the crest forecast at Anamosa Shaw Road has also been
revised up to 22.5 feet for Tuesday.

The Cedar River forecasts are the primary forecast problem today as
there is considerable uncertainty with what is going on upstream.
Measured flows from upstream have been lower than expected, but it
has been observed that the a large amount of water has spread into
fields along the river rather than continue to move through the
river system. This brings higher confidence that more attenuation is
occurring than what we had originally anticipated which would lead
to lower crests. That being said, there is the wildcard of
additional rainfall through Sunday. At this time, we don`t think
rains from this system will amount to anything substantial, but if
one storm moves over the right location, it could have an impact.
Main point is, confidence is increasing on lower crests, but with
some uncertainty still with upstream flows and future rainfall have
decided to trend the forecast downward for VINI4 and CIDI4 until we
have a better grasp and can hold onto a good number.

The Mississippi River forecasts remained fairly similar to prior
forecasts as not much changes have occurred this far as there is
exorbitant amounts of water to work through the system. Some
locations will begin to see the river rise above flood stage early
next week while others may not see flood stage until the middle
portion of the week. Crests on the Mississippi won`t occur until
late next week or into the weekend.

&&

.DVN Watches/Warnings/Advisories...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...Gibbs
SHORT TERM...Gibbs
LONG TERM...McClure
AVIATION...Gibbs
HYDROLOGY...McClure/Brooks