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000
FXUS63 KDVN 240427
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1127 PM CDT FRI SEP 23 2016

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 310 PM CDT Fri Sep 23 2016

Rain has finally ended at mid-afternoon in the dvn cwa with the
stronger forcing and low level convergence shifting into MN. This
has triggered a band of thunderstorms lifting northeast into
central MN. A nearly stationary east-west frontal boundary was
located near Highway 34. To the north of the front low clouds and
temperatures in the mid 60s to mid 70s were noted, while to the
south temperatures were in the upper 80s with sunshine. Isolated
showers are still possible this afternoon across our north in the
axis of higher PWAT`s.

Water vapor movie loops indicated upper level ridging building
into the area from the south as a deep trough moves into the
Rockies. This shifts the forcing and main area of thunderstorms into
the Plains and Upper Midwest.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 310 PM CDT Fri Sep 23 2016

Forecast focus on dry weather in the short term.

Tonight: Upper level ridging will continue building into the cwa
from the south as surface high pressure builds into the Great
Lakes out of Ontario. The strong forcing will be well out in the
Plains and Upper Midwest regions. This should keep the cwa dry
tonight. The nearly stationary east-west frontal boundary should
remain in place, with low clouds and patchy to areas of fog
expected to the north of the front. Minimum temperatures should
range from the lower to mid 60s north to the upper 60s far south.

Saturday: The front should get a nudge to the north as strong
upper level trough moves into the Plains, but the ridge will
remain over the dvn cwa. The forcing remains to our west so a dry
day expected. After low clouds and patchy fog in the morning
skies should become mostly sunny by afternoon. This will push
afternoon temperatures into the 80s at most locations, except
upper 70s in our far north along Highway 20.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 310 PM CDT Fri Sep 23 2016

Major change to a much needed stretch of cool and dry weather is the
main story for the long term. However, in the near term, a
progressive frontal system will bring another round of showers and
thunderstorms from late Saturday night through Sunday. This setup is
not likely to result in heavy rain or have much impact on river
flooding.

Saturday night into Sunday: The upper low over northern UT is
progged to push eastward, nudging the upper ridge eastward with a
surface cold front driving through the forecast area Sunday. The
current timing is likely to result in diurnally waning showers and
thunderstorms reaching into the western half of the forecast area
late Sunday night with weak support from warm advection and upper
forcing. This activity will redevelop Sunday, likely along and east
of the MS river during the day, with minor model timing differences.
While precipitable water will again be high on the S-SW flow feeding
into the prefrontal axis, the linear, progressive nature of the
convection along and ahead of the front will be supportive of
perhaps some locally heavy downpours, heavy rainfall of the
magnitude the area has seen over the past several days is not
supported. Total rainfall is likely to be more in the range of a
quarter inch with local amounts of a half to three quarters of an
inch possible, which is likely to have only minor impacts to area
river flooding. Ahead of the front, highs should reach at least the
uppr 70s, while lower 70s are forecast in the west, which may need
to be adjusted if the front further slows. Will keep rain chances
going over mainly the east Sunday night, but leave out thunder as
instability and upper forcing diminishes and exits eastward.

Monday will bring an abrupt change to more typical fall weather as
850 mb temperatures, progged to cool into the lower single digits
celsius in the ensuing cold air advection, would limit highs to the
60s. Brisk west winds due to a somewhat tight surface pressure
gradient and possible lingering strato cu in the cyclonic upper flow
of the passing upper low, will make it feel even cooler.

Tuesday through Friday: Cool high pressure will be in control
through Wednesday with highs limited to the 60s to lower 70s and
overnight lows in the 40s. A return flow will moderate temperatures
back to daytime highs in the 70s and lows in the 50s Thursday and
Friday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1124 PM CDT Fri Sep 23 2016

Low clouds that covered the entire region all day are now
completely moved out of eastern Iowa, but some fragments of the
cloud deck in Illinois continue to be seen near Lake Michigan.
Models are not handling that, and it is concerning that the clouds
remain over northeast Illinois, so clouds could become more
widespread again overnight. Thus, a low confidence forecast is
being issued with pessimistic MVFR/IFR forecast at DBQ and
optimistic VFR mainly forecast for CID/MLI/BRL as they are already
clear and somewhat dry advecting from the east surface winds off
Lake Michigan. Saturday should see partly cloudy VFR weather in
all sites, especially after 15Z when any morning light fog or low
clouds mix out.

ERVIN

&&

.HYDROLOGY...
Issued at 310 PM CDT Fri Sep 23 2016

Heavy rains across the area last night created some additional
flooding concerns across the area. Primarily along the Maquoketa
River which had not had the heavy rains previously. Currently, the
Maquoketa River at Manchester is nearing crest, just over Major
Flood Stage. In other areas, the river models are continuing to get
a handle on all of the rainfall. Some locations upstream in the
Cedar River Basin have been running higher than originally forecast
which has caused a rise in the forecasts along the Cedar River and
areas downstream of the confluence with the Iowa River.
There is still a bit of question on these exact crest levels, as
there could be changes up to a foot. That being said, these levels
are the 2nd highest in historical history and do have confidence that
it will be a significant event.

Looking at the Mississippi River, the forecast crests for many
locations continues to be just outside of the 7 day forecast as we
would expect the crests sometime next weekend. Many locations will
reach well over flood stage so have felt confident enough to issue
flood warnings for a good portion of the river. There are a few
areas that don`t receive impacts until they observe higher flows
and have continued with Flood Watches as there is less confidence
in reaching flood stage.

Forecasts will likely be updated and changed periodically over the
coming days. Please stay tuned to the current statements as well as
the AHPS pages for current information.

&&

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

$$

SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Sheets
AVIATION...Ervin
HYDROLOGY...Brooks/Uttech