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796
FXUS63 KDVN 271818
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
118 PM CDT TUE SEP 27 2016

...AVIATION AND HYDROLOGY 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 18Z TAFS through 18Z Wednesday Afternoon)
ISSUED AT 1251 PM CDT Tue Sep 27 2016

VFR conds through this afternoon into the evening, then cigs
gradually becoming MVFR from north to south over the remainder of
the taf sites overnight into Wednesday morning. West to northwest
winds sustained 15 to 20 knots with gusts to around 25 knots this
afternoon, diminishing to less than 10 knots tonight. North winds
10 to 15 knots on Wednesday.

&&

.HYDROLOGY...
Issued at 1251 PM CDT Tue Sep 27 2016

River forecasts largely on track. See site specific information
in following discussion and in recent Flood Warning Statements.

Cedar River...

Vinton: Major flooding continues. Forecast to fall below major
flood stage Wednesday afternoon or evening.

Cedar Rapids: Currently cresting near 22 feet (unofficially the
second highest on record). Expected to remain above 21.5 feet into
this evening before beginning to steadily fall.

Conesville: Major flood stage is also forecast here by Wednesday
evening, persisting into the weekend. Forecast crest confidence
is moderate due to uncertainty associated with the effects of
attenuation as the high water routes downstream.

Wapsipinicon River...

Independence: Forecast to fall below flood stage by Wednesday
morning.

Anamosa Shaw Rd and De Witt 4S: High confidence in reaching major
flood stage, moderate to high on the crest forecasts which have
been adjusted down slightly - partly based on flow measurements
taken yesterday evening at Anamosa.

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. Uttech

Main Stem Mississippi River...

Minor to Major flooding continues to be on track, with the sites
hitting Major flood stage being Keithsburg, Gladstone LD18, and
Burlington. In the ongoing assessment of routing water from
upstream, as well as tributary input, the latest forecasts show
little to no adjustments from previous runs from last night.
Generally most sites have kept the same crest value, or have been
adjusted a tenth or two of a foot downward. Besides at Dubuque
(Thursday into Friday), crests on the Mississippi at most of the
sites are forecast to occur over the upcoming weekend. Then most of
the same gage sites are projected to start to experience river level
decreases Monday into next Tuesday. With higher confidence that the
river will not reach the flood stage at Bellevue LD12, have dropped
the river flood watch for that site.     ..12..

&&

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

$$

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