Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 272035
AFDDVN

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

.SYNOPSIS...
Issued at 335 PM CDT Tue Sep 27 2016

Upper low swirling across the Great Lakes region was slowly
dropping southward. The leading edge of a solid area of
stratocumulus/stratus was nearing Highway 20. A strong vort max
was dropping southward on the west side of the low and was
spreading rain into central MN and western WI. Under the thick
cloud cover afternoon temperatures there were rather chilly, only
in the upper 40s to mid 50s.

Across the dvn cwa there has been plenty of sunshine again today
with afternoon temperatures rising into the mid to upper 60s
north to the mid 70s south. Another good mixing day with dewpoints
in the 30s with relative humidity in the lower to mid 20s. West
to northwest winds have been gusting to around 30 mph.

&&

.SHORT TERM...(This Evening through Wednesday)
ISSUED AT 335 PM CDT Tue Sep 27 2016

Forecast focus on rain chances, cloud trends and temperatures.

Tonight: The upper low will continue to slide southward into
northeast IL vicinity by sunrise, with the vort max rotating
across the dvn cwa overnight. The rain currently in WI and MN will
spread southward, with the vort max, into the cwa as the evening
progresses. The bulk of the showers should be across roughly our
northeast half, with the area of rain pushing off to the east of
the cwa towards morning. We will have likely pops in nw IL east
of the track of the vort max, with only chance pops farther west
and south. With the cloud cover spreading southward over the cwa
temperatures will be somewhat warmer compared to last night.
Minimum temperatures should bottom out in the upper 40s to around
50. Rainfall amounts are expected to be a tenth of an inch or less
at most locations.

Wednesday: A much cooler day is in store! The upper low will
gradually move into northern Indiana later in the day. However,
cyclonic flow/cold pocket aloft associated with the low will keep
the cwa in extensive cloud cover. While the main energy and
showers will be well to our east, can`t rule out at least isolated
showers along and east of the MS River. Based on upstream
temperatures, we have lowered highs somewhat from the previous
forecast. With 850 mb temperatures of only 3 to 4+C this should
translate to surface readings ranging from the upper 50s in far nw
IL to the mid 60s in our far south. This is at least 10 degrees
below normal for late September.

.LONG TERM...(Wednesday Night through Tuesday)
ISSUED AT 335 PM CDT Tue Sep 27 2016

Wednesday Night...Stacked sfc-300mb low drifts to the SE through the
Ohio Valley. Northerly sfc winds are forecast locally as skies
become partly to mostly clear. It will be cool in the mid 40s to
lower 50s and dry.

Thursday...500mb upper-low spins over the Ohio Valley. Sfc temps
will respond to clear to partly cloudy skies, rising into the upper
60s to lower 70s. The exception is over the far east (Bureau and
Putnam Counties). The edge of the stratus deck could linger through
much of the day. If this scenario plays out, forecast temps are
likely too warm there. All-in-all it will be a nice fall day.
Although, we will have to contend with NNE winds of 10-20 mph
(isolated higher gusts along/east of the Mississippi R.).

Friday and Saturday...Model discrepancies exist as models struggle
on projecting evolution of the cut-off upper-low. The trend is to
retrograde the low further to the NW. The ECMWF/Canadian are
furthest to the NW, the GFS/NAM not as much. Adjusted temps down a
few degrees which is probably not cool enough - especially if the
non-American model solutions verify.

The forecast message is higher confidence that stratus clouds will
overspread much of the CWA from the E/SE, scattered mainly light
showers are possible, sfc winds will be higher, and there is
potential for cooler highs than currently forecast. Would not be
surprised if forecast temps trend cooler over next few model runs.

Sunday and Monday...Model suite in reasonable agreement weakening
the upper-level low on Sunday and tracking it to the NE through
Michigan. This will be a pleasant stretch of weather in the upper
60s into the 70s with little, if any, chance for precip through
Monday afternoon. Uttech

&&

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



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