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382
FXUS63 KDVN 261955 CCA
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
254 PM CDT MON SEP 26 2016

.SYNOPSIS...
Issued at 250 PM CDT Mon Sep 26 2016

Skies were sunny across the dvn cwa with nary a cloud due to a
very dry airmass. Dewpoints have dropped into the lower to mid 30s
(models were not low enough) with 2 pm temperatures in the mid
60s to lower 70s. After about 11 days in a row with highs in the
80s to near 90 this is a welcome change!

Strong low pressure was situated near Lake Superior with high
pressure in the central Plains. Tight gradient was over the dvn
cwa with west to northwest winds gusting to around 35 mph. Soundings
indicated mixing to around 850 mb with momentum transport pulling
down 35 knot winds at the top of the mixed layer.

To the north in the cyclonic flow there was extensive cloud cover
from northern MN into central/northern WI and into northern Lower
MI. In those areas 2 pm temperatures were only in the upper 40s to
mid 50s, along with some light rain and drizzle.

&&

.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 250 PM CDT Mon Sep 26 2016

Cool and dry in the short term.

Tonight: A clear and cool night is in store with low pressure over the
Great Lakes and high pressure well to our south. With the very dry
airmass in place there should be a large diurnal swing in temperatures.
Winds will diminish quickly by sunset with decoupling of the
boundary layer. However, with west to northwest winds remaining
near 10 mph for much of the night this should prevent a total
free-fall of temperatures. We will continue to forecast minimum
temperatures in the 40s.

Tuesday: Another sunny day is expected for most of the cwa. The
exception will be our far north where an increase in stratocumulus
is expected in the afternoon. This will occur as a strong short
wave rotates southward around the Great Lakes upper low. Any rain
should remain in Wisconsin during the day. With the filling low
the gradient will relax some so winds will not be as strong as
today. With that said, some gusts may still approach 25 to 30 mph.
Temperature-wise this will be a rather cool day again with highs
ranging from the mid 60s north to the lower 70s south.

.LONG TERM...(Tuesday Night through Monday)
ISSUED AT 250 PM CDT Mon Sep 26 2016

Tuesday Night...Cool in the 40s. Light showers likely over the far
northeast CWA, tapering to slight chances along an Independence to
Iowa City to Moline line. Large and deep tropospheric low forecast
to move southward through the Western Great Lakes into Wednesday
morning. Lobes of enhanced vorticity rotating around the low will
provide some lift from DCVA; however, moisture is limited.

Wednesday...Cloudy, cool, and breezy under the cold core upper low.
Expect the sky to have a classic fall look - gray low overcast
(stratocumulus clouds). Highs are forecast in the lower to middle
60s. Maintain slight chances for light showers in the counties east
of the Mississippi River and along/north of I-80. Thinking most
areas will not receive measurable rain. Lows are forecast in the mid
40s to lower 50s.

Thursday...500mb upper-low finally pulls away to the east into the
Ohio Valley which will take most of the low stratus with it. Sfc
temps will respond, rising into the upper 60s to lower 70s. Winds
won`t be quite as strong, staying in the 10-20 mph range for the
afternoon. Looks like a nice fall day!

Friday through Sunday...Model discrepancies exist as models struggle
on projecting evolution of the, now cut-off, upper-low. The ECMWF
has consistently been retrograding the upper-low back to the west
which is at odds with other model guidance (GFS/Canadian). Current
model blend forecast favors a warmer/drier solution in the 70s.
The ECMWF brings low stratocumulus, scattered light showers, and
cooler temps in the 60s back into E Iowa/NW Illinois/NE Missouri.
Will have to wait for lower model variance before forecast
confidence can increase during this period. Uttech

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
ISSUED AT 1237 PM CDT Mon Sep 26 2016

VFR conds through this taf cycle. Strong low pressure over Lake
Superior with high pressure in the central Plains. West to
northwest winds sustained 15 to 25 knots with gusts to 30 to 35
knots this afternoon, then quickly diminishing to less than 10 knots
after sunset. West to northwest winds on Tuesday increasing to
sustained 15 to 20 knots with gusts to 25 to 30 knots.

&&

.HYDROLOGY...
Issued at 1237 PM CDT Mon Sep 26 2016

Cedar River...

Vinton: Major flooding continues. Vinton is currently cresting near
21.79 feet (second highest level on record unofficially) and should
begin to slowly fall later today.

Cedar Rapids: Now exceeding 20 feet and quickly rising. The crest
forecast remains at 23.0 feet - from Tuesday morning into the
afternoon. Confidence is high on a crest between 22 to 24 feet due
to the amount of flow measured upstream at Vinton and Palo.

Conesville: Major flood stage is also forecast here by the middle to
end of the week. Forecast crest confidence at Conesville is moderate
due to uncertainty associated with the effects of attenuation as the
high water routes further downstream.

Wapsipinicon River...

Independence: River level continues to fall rapidly. Forecast to
fall below major flood stage by this evening.

Anamosa Shaw Rd and De Witt 4S: High confidence in reaching major
flood stage, moderate to high on the crest forecasts. But increasing
confidence observed crests will not come in well below (a foot or
more) current forecasts.

Iowa River...

Excessive amounts of water continue to propagate downstream through
the Iowa and Cedar Rivers. There is high confidence on significant
flooding, especially during the middle to end of the week. Exact
timing varies by site.

Moderate confidence is associated with the crest forecasts, or by
how much a river level exceeds either moderate or major flood stage
due to attenuation of the routed flow. Please follow forecast
information closely throughout this event. ..Uttech..

Main Stem Mississippi River:

Minor to Major flooding still on track. In the ongoing assessment of
routing water from upstream, as well as tributary input, the latest
forecasts continue to show only minor or little adjustments from
forecasts last night. Generally a few tenths of a foot adjusted down
from Dubuque on down toward the Camanche area. Trib input from the
Wapsipinicon River keeping forecasts similar or even a tenth or two
higher south of Camanche to north of Keithsburg, then forecasts are
similar or drop off a tenth or two again from Gladstone LD18 on
southward. Some locations will begin to see the river rise above
flood stage over the next day or two, while others may not see flood
stage until the middle to later portion of the week. Crests on the
Mississippi won`t occur until late week or over the upcoming
weekend. Several sites, from Muscatine on northward to Dubuque, are
projected to start to experience river level decreases by Sunday
into next Monday Oct 3rd. Have kept Bellevue LD12 in a river flood
watch for now, with a projected broad crest(below the 17 FT flood
stage)at around 16.3 feet Friday into Saturday. ..12..

&&

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

$$

SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Uttech
AVIATION...Haase
HYDROLOGY...12/Uttech