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000
FXUS63 KDVN 210417
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1117 PM CDT TUE SEP 20 2016

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 330 PM CDT Tue Sep 20 2016

The latest sfc analysis was indicating low pressure center over
south central SD...with warm front draped southeastward to the
eastern IA/MO border and acrs central IL trying to retreat north some.
East to southeast flow to the north of it acrs the local CWA, with a
large sfc DPT gradient from the low to mid 50s in the north, to the
upper 60s to lower 70s in the far south near the boundary. Pressure
falls were increasing just to the lee of the low acrs southeastern
SD...into southern MN. Aloft, a ridge-riding vort max was seen on
water vapor imagery acrs central SD, while southerly H85 MB flow of
25-30 KTS was flowing up the plains into southwestern MN.

&&

.SHORT TERM...(This Evening through Wednesday)
ISSUED AT 330 PM CDT Tue Sep 20 2016

Tonight...Several MCS/storm cluster generation tools come together
this evening from extreme east central SD...into and acrs the
southern third of MN. Extrapolating the H85 MB jet convergent axis
targets the IA/MN border region. Thus expect more storm cluster
initiation or even an MCS along and north of the IA/MN border
tonight on nose of unseaonably THTA-E rich llvl nocturnal jet. The
big challenge for the local area is if any of this system can
eventually bleed down into the DVN`s CWA area of concern late
tonight or early Wed morning. HiRes solutions as well as the regular
models all vary from the convection staying off to the north and
northeast with the local forecast staying dry through Wed AM, to the
MCS sagging down almost into the far southern CWA, if even in a
weakening fashion, with cool pool outflow racing out ahead of it.
But support an more models lean toward some showers/storms making it
down acrs the northeastern third to half to at least I80 mainly
after 3 AM CDT and will adjust CHC POPs accordingly.

Most areas that do manage to get rain north of I80 should receive an
average from a tenth to a quarter of an inch by 12z Wed...with a few
spots in the far north possibly getting a half inch or more by
daybreak. This activity will be getting away from better forcing and
shear profiles to the north as it propagates down into the local
area, but still could see some storm lines producing wind gusts to
at least 40 mph as they push through. lows in the mid to upper 60s,
with the far south hanging up near 70 if they don`t get rain cooled
storm outflow. Will bank on enough southeasterly gradient wind of 4-
6 MPH to keep areas of dense fog from forming again, but still can`t
rule out some patchy fog especially in the south.

Wednesday...Will play the "decaying MCS/storm debris in the morning"
card through late morning acrs the north half, with more cloud
erosion in the afternoon. Low pops remaining north of I80 in the
afternoon in case of storm redevelopment on lingering boundaries, but
the main storm re-generation process will look to re-focus back to the
IA/MN border region by evening. High temps a big challenge and
plenty of bust potentail if cloud debris and showers/storms hang on
longer and push further south than expected. The air mass filtering
into the region is very summer-like and humid, supporting highs in
the upper 80s or near 90 with adequate mixing and sunshine. DPTs in
the upper 60s to lower 70s. But with storm debris possibility, will
go lower 80s in the north, to mid to upper 80s to the south. Will
need plenty of afternoon recovery to even get those values. If
nothing makes it down into the area tonight/Wed morning, then the
forecast highs may be too cool by a few degrees especially in the
north.   ..12..

.LONG TERM...(Wednesday Night through next Tuesday)
ISSUED AT 330 PM CDT Tue Sep 20 2016

Forecast focus on chance of thunderstorms and warm and humid.

Wednesday night through Friday:  Deep upper level trough settles
into the Western United States with a zonal flow across the Midwest.
This sets up a nearly stationary east/west surface boundary most
likely across southern MN into central/southern WI. However, the
front may meander a bit southward during this period depending on
the strength of outflow boundaries from thunderstorm clusters. The
main message will be that the bulk of the thunderstorm activity and
torrential rainfall should remain north of the dvn cwa during this
period. However, a few storms may drift into our northern counties
from time to time, especially north of Highway 30. Despite the
autumnal equinox arriving on Thursday this will be a summer-like
period with highs in the 80s and lows in the 60s. In addition to the
warm temperatures the dewpoints will be in the 60s so it will also
feel humid.

This weekend: In addition to the deep trough in the Rockies a
deepening trough will dive into the eastern Great Lakes/Northeast
United States. In between, an upper level ridge builds from MO to
WI. This will send a back-door weak cold front into the dvn cwa
bringing somewhat less humid and a tad cooler air. These features
should suppress any thunderstorm activity so as of now this looks to
be dry for most of the weekend.

Early next week: The rather stagnant pattern we have been in for
nearly a week finally begins to break down. This will allow for a
strong but slow moving cold front to push across the cwa from the
west. This should be accompanied by a band of thunderstorms sometime
in the late Sunday or Sunday night through Monday time frame. Behind
the front much cooler temperatures are expected.   Haase

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
ISSUED AT 1117 PM CDT Tue Sep 20 2016

Warm southeast winds will continue through the period, with
mainly VFR conditions except for some possible morning MVFR light
fog expected sites in southeast Iowa. The north, along with
northeast Iowa, will see a chance for a thunderstorm complex
arriving after 3 AM tonight, and lasting through the mid morning
hours. This may or may not occur, as the track is uncertain at
this time. I did put in a tempo group at DBQ to cover this threat
since they are the most likely to see storms. Otherwise, the main
rain and thunderstorms in the region should stay in southern
Minnesota and Wisconsin.

&&

.HYDROLOGY...
Issued at 330 PM CDT Tue Sep 20 2016

No significant rain fell yesterday which will probably result in
crests coming in slightly lower at DEWI4, MROI4, and CNEI4 than
forecast. The water in the area rivers is routed flow and is
accounted for by the river models. Looking into the future, at least
several inches of rainfall is expected for the remainder of this
week across southern MN and northern IA, which is in the headwaters
of the Cedar and Iowa Rivers that flow into eastern IA. Depending on
the actual amount of rainfall that occurs will ultimately determine
if these rivers will go above flood stage. As of now, river models
suggest the Cedar River at VINI4 and CIDI4 to approach or exceed
flood stage by early next week. Interests along the river should
monitor later forecasts.

&&

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

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...Haase
AVIATION...Ervin
HYDROLOGY...Haase