Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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719
FXUS63 KDVN 261737
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1237 PM CDT MON SEP 26 2016

...AVIATION AND HYDROLOGY UPDATE...

.SYNOPSIS...
Issued at 336 AM CDT Mon Sep 26 2016

Early this morning, a much more seasonable airmass surged into the
area. Dewpoints in the low 40s to upper 30s were found across NW
Iowa and SW MN. Temperatures in this area were in the low 50s to
upper 40s. High clouds were slowly moving out of the area as the
cold front surges east into Indiana and KY. A strong vort max
aloft will lead to windy conditions today across the area.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 336 AM CDT Mon Sep 26 2016

Main forecast concern in the short term is the dewpoint and wind
forecasts as fire danger for field fires could be very high today.
Rather quiet and cooler short term forecast is the main sensible
weather impact.

High pressure will further entrench across the area today as upper
level closed low slowly slides to the east. Shortwaves through
this flow will lead to winds in the 15 to 20 kt range this
afternoon with possible gusts to 30 kts. NAM and GFS soundings
suggest mixing to 825 hPa. H85 winds are near 40 kts, so some of
this flow will translate into gusty winds. With the deep mixing,
think that dewpoints will be lower than what many of the spectral
and regional models have. Looking at the CAMs, it appears that
dewpoints across the southern CWA will likely result in afternoon
min RH values near 25. While most of the native grasses have not
cured much, many fields are near 90 percent cured. With those
values and the wind and RH, it appears that field fires could be a
concern today. Will be issuing a SPS to discuss this threat.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 336 AM CDT Mon Sep 26 2016

The upper trough in the vicinity of Lake Superior on Tuesday is
shown to deepen into a closed low while shifting slowly southward
along Lake Michigan through Wednesday. This will maintain deep
northerly flow through mid-week ushering in the coolest air of the
early fall season.

Tuesday will start off with considerable sunshine but during the
afternoon expect increasing clouds over northeast Iowa into
northwest Illinois, as a PV anomaly rotates down backside of sagging
upper low. With the increase in clouds may come a chance of showers
late in the day, but better chances look to occur Tuesday night over
the northeast third to half of the cwa as the PV anomaly sweeps
down across the region. Any rainfall amounts look to be very light
and mainly a trace to a few hundredths of an inch. Prior to the
arrival of the clouds Tuesday PM, deep mixing will fuel more gusty
northwest winds 10-20+ mph, while thermal parameters support a
general range from the lower 60s far north to the lower 70s south.
Clouds and spotty light precipitation Tuesday night may aid in
warmer lows in the upper 40s to near 50 degrees over the northeast
while mainly mid to some lower 40s elsewhere.

Wednesday looks to be trending toward a cloudy and rather cool day
as the core of the cold air aloft traverses the region. Will also
have a chance at some light showers or sprinkles again mainly over
the eastern half of the cwa. Highs in some areas of far northeast
Iowa and northern Illinois could struggle to hit 60 degrees if skies
were to stay overcast, with 850 mb temperatures generally around 4C
to 5C supporting lower 60s with a few mid 60s possible southwest with
any length of solar insolation.

Late week into the weekend there remains uncertainty with the
overall pattern and eventual track of the upper low. The consensus
favors the region becoming more under the influence of surface and
upper level ridging Thursday into Friday, with temperatures
moderating closer to normal. As the upper ridge builds in the upper
low will become cutoff and blocked with developing rex block over
the Great Lakes. Over the weekend, as a trough comes ashore in the
west the ridging breaks down and the ECMWF shows the upper low
retrograding back toward Lake Michigan on Saturday. It has been
consistent with this idea, but remains a western outlier. Should
this occur then would likely see more clouds along with cooler
temperatures and even a chance of showers for our eastern counties
mainly late Friday through Saturday. However, despite the ECMWF
consistent westerly track of the retrograding low this weekend, it
remains west of it`s ensemble mean and all other guidance.
Therefore, the forecast for Friday through the weekend is toward the
consensus further east track with less influence resulting in dry
conditions and near normal temperatures of mostly 70s for highs and
50s for lows.

&&

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



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