Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 271151
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
651 AM CDT TUE SEP 27 2016

...12Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 329 AM CDT Tue Sep 27 2016

Clear and cool is the rule early this morning. 3 AM temperatures
were mainly in the mid 40s to lower 50s, which is actually close
to normal lows for the date. Further north satellite shows
considerable low clouds arcing from northern Minnesota through
northern Wisconsin. Deep low pressure was found over southwest
Ontario early this morning. Regional radar loop shows some
showers rotating down through the Great Lakes region in the deep
cyclonic flow, with a more notable area over northeast Minnesota
and across Lake Superior attendant to a pronounced shortwave
diving down the backside of the Ontario low. This shortwave will
brush the region tonight bringing some showers to areas especially
north/east of the Quad Cities.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 329 AM CDT Tue Sep 27 2016

The near vertically stacked low over Ontario is forecast to sag
south to the vicinity of southern Lake Michigan by Wednesday
morning. In doing so, it will slosh extensive clouds and some
light showers into the region, as early as later this afternoon
far northern cwa, then over all but the far southern cwa tonight.
Moisture will remain somewhat limited, but cold advection and
differential CVA-driven forcing ahead of pronounced shortwave
should be more than sufficient to squeeze out periodic light
showers/sprinkles with again the best potential north/east of the
Quad Cities, where amounts generally a few hundredths to isolated
near 0.10 inch possible.

As for today, expect another repeat of breezy northwest winds
15-25+ mph with deep mixing with sunny skies except northern
sections where expect increasing clouds later this afternoon.
Based on soundings and mixing to near or above 850 mb supports
highs from the mid 60s north to a few mid 70s far south. Also,
anticipate dew points once again lowering into the 30s for areas
especially south of Highway 30. This will likely result in minimum
relative humidity levels of 25-30 percent and combined with the
gusty winds will again lead to high fire danger mainly in agricultural
fields where they are still near 90 percent cured.

Lows tonight look to be mainly in the 40s to near 50 degrees with
the warmest readings expected north/east beneath more widespread
low clouds.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 329 AM CDT Tue Sep 27 2016

Main forecast concern for the long term is what happens to the upper
level closed low that is slowly propagating to the east across the
Great Lakes and the sensible weather it brings to the area. Guidance
is starting to come to agreement in the long term on solutions,
however it should be noted that the models usually are too slow with
cut off low progression.

Wednesday, main forecast change is in the high temps for the day.
Closed off low will continue to advect in cool H85 temps and cloud
cover into the area. Lowered highs into the low 60s across the
area.  Wouldn`t be surprised to see this go lower with H85 temps at
+3C.  Winds will make for blustery sensible weather conditions on
Wednesday. Some isolated showers associated with being under the
H5 low will affect the eastern CWA.

Thursday, the low lumbers oh so slightly to the east allowing for
warmer temps and a reduction in the chances of rain across the
eastern CWA.

Thursday on, models are starting to agree with a retrograded low.
How this plays out and where it moves too will greatly affect our
sensible weather.  Most of the blended models are warmer than the
current operational runs.  Dprog Dt of the GFS shows a trend towards
a retrograded low. Think the trend towards cooler highs and possible
chances for rain and clouds due to the closed low moving back west
will start showing up in the blends today.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday Morning)
ISSUED AT 642 AM CDT Tue Sep 27 2016

Expect gusty west to northwest winds at 15-25+ kts again by late
morning through afternoon. An upper level low moving through the
Great Lakes will usher in clouds later today and tonight, with
mainly VFR ceilings although anticipate some bouts of MVFR ceilings
and light rain showers/sprinkles with highest confidence at KDBQ
while lower confidence at KCID and KMLI.

&&

.HYDROLOGY...
Issued at 329 AM CDT Tue Sep 27 2016

No changes to the river forecasts were made on this shift.
Everything still appears to be on track.  Previous discussion is
attached below.

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...McClure
SHORT TERM...McClure
LONG TERM...Gibbs
AVIATION...McClure
HYDROLOGY...Gibbs/Uttech/12


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