Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 252026
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
326 PM CDT SUN SEP 25 2016

.SYNOPSIS...
Issued at 326 PM CDT Sun Sep 25 2016

At 19Z the surface cold front was bisecting the forecast area
roughly from Galena S-SW just west of the Quad Cities to near
Burlington. A broken line of thunderstorms has fired well ahead of
this boundary from S central WI through south into central IL. Brisk
west winds over eastern IA were pulling in an airmass in central
Iowa with temperatures in the 60s and dewpoints in the 50s. Ahead of
the boundary, temperatures were in the 80s wiht dewpoints in the
upper 60s to lower 70s. An upper level trough was evident on water
vapor imagery pushing out of the Dakotas into western MN and NW IA
with visible images showing an extensive deck of stratocu along and
east of this axis.

&&

.SHORT TERM...(This Evening through Monday)
ISSUED AT 326 PM CDT Sun Sep 25 2016

Temperatures are the primary focus as an incoming fall airmass with
much cooler, drier air brings a sharp contrast to the very warm and
humid conditions over the past week. Tonight, the post frontal weak
showers, appearing to be mainly virga on area radars, will exit to
the east this evening following the frontal passage. Low and mid
level clouds may be slow to move out this evening until the upper
trough axis passes through the region after midnight with subsidence
and weakening surface winds. Dewpoints in the 40s over the northern
plains will advect into the forecast area by morning with 850 mb
temperatures around 5 deg C supporting lows from the upper 40s NW to
lower 50s SE.

Monday will have a definite fall-like feel, with gusty west to NW
winds from 15 to 25 mph by late morning through afternoon and
temperatures only reaching into mid 60s to around 70.


.LONG TERM...(Monday Night through Sunday)
ISSUED AT 326 PM CDT Sun Sep 25 2016

Monday night...Clear and seasonably cool Mon night with H85 MB cool
rule support widespread lows in the low to mid 40s, with even some
upper 30s possible in cool air drainage locations. But that would be
with clear and calm conditions for optimum radiational cooling.
Since we are forecasting mixing winds maintaining at least 5-10 mph
overnight, will side more with widespread mid 40s, with both some
lower 40s and upper 40s in spots.

Tuesday and Wednesday...Main challenge this period in a blocked
pattern is if cut-off upper cyclone can drop south-southwest enough
out of the northern GRT LKS and spiral a portion of it`s associated
stratocu shield and even some embedded showers acrs eastern portions
of the CWA Tue night into Wed. The 12z ECMWF is the most bullish in
this westward gyration with showers acrs the eastern 2/3`s of the
CWA Tue night, then some diurnal flare up again on Wednesday in
building column instability. Other solutions keep most of the precip
to the east of the local area or just swipe the eastern fringe with
instability showers on Wed ala 12z GFS. For now will raise non-
mentionable POPs acrs the eastern third this period. Will also keep
the more seasonable temps going with highs generally in the mid to
upper 60s and lows in the 40s. Some deeper mixing and more
insolation in drier airmass will also support a few 70 degree
readings especially in the west/southwest.

Thursday through next Sunday...General longer range trends suggest
omega block to reign acrs the mid conus for dry and seasonable
weather into the upcoming weekend. But will have to keep watch on
the closed eastern cyclone for a westward retrograde toward the area
like the latest ECMWF run suggests by this weekend. But longer range
upper jet trends/teleconnections suggest the more normal looking 12z
GFS may have a better handle for late in the period. ..12..

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
ISSUED AT 1242 PM CDT Sun Sep 25 2016

A cold front moving through the region this afternoon will produce
scattered showers and thunderstorms. At noon, these were forming
along the MS River between the Quad Cities and Dubuque and will
push east out of the TAF sites at the start of the forecast
period. Light showers and pockets of MVFR ceilings, immediately
along the wind shift may impact the terminals until 2 pm. Gusty west
to northwest winds behind the front this afternoon will likely
diminish this evening, then resume gustyness Monday morning as
cooler and much drier air flows into the region.

&&

.HYDROLOGY...
Issued at 1242 PM CDT Sun Sep 25 2016

Flooding of several of the tributary systems across Iowa remains the
primary hydrologic problem for today, while flooding along the
Mississippi River continues to be forecast for the upcoming week.

Cedar River:

Forecast for major flooding continues. Vinton has now surpassed 20
feet and is still rising, placing it at the second highest level on
record (unofficially). Confidence on the crest forecasts at Vinton,
and more so at Cedar Rapids and Conesville, are moderate due to
uncertainty with effects of attenuation as the high water routs
downstream.

The crest at Cedar Rapids was lowered a half foot down to 23.0 feet,
but may be lowered further if Vinton crests below current forecast
and effects of attenuation become more apparent. Either way, well
above major flood stage is likely at Cedar Rapids from Monday
morning into the middle of the week. Major flood stage is forecast
at Conesville by the middle to end of the week.

Iowa River:

Excessive amounts of water continue to rout 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.

Low to 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

The Wapsipinicon River at Independence experienced a large flow
surge above the Major Flood stage last night, making for some
uncertainty on the associated local flow contributions. The crest
was adjusted upward, but recently the river level trends have slowed
possibly indicating the Wapsi may finally be near crest at IDPI4
around 19.3 or 19.4 feet. Routing this enhanced recent flow from
Independence downstream has produced increased crest forecasts of up
to 2 feet higher at Anamosa Shaw Road, and up to a half foot higher
near De Witt. Ranges at these two downstream sites may vary over the
next 24 hours because of unknown attenuation factors.

The Maquoketa River near Maquoketa also showed an overnight rise and
will reach the lower end of minor Flooding early this afternoon,
before dropping back down below flood stage tonight.

The Mississippi River forecasts continue to show only minor or
little adjustments in handling the large amounts of routed water
coming from upstream that will work though the main stem system.
Some locations will begin to see the river rise above flood stage
early this upcoming week, while others may not see flood stage until
the middle portion of the week. Crests on the Mississippi won`t
occur until late week or into next weekend. Just minor adjustments
of a slowed rise late in the week at Keokuk LD19 and Gregory Landing
due to flow cut back at the Red Rock Dam on the Des Moines River.
..12..

&&

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

$$

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



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