Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 262345
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
645 PM CDT FRI AUG 26 2016

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 315 PM CDT Fri Aug 26 2016

18Z surface data has high pressure over the upper Midwest with a low
in eastern Kansas west of KEMP. A frontal boundary runs east from
the low into the Ohio Valley. Dew points were in the 50s and 60s
north of the front with 70s along and south of the front.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 315 PM CDT Fri Aug 26 2016

Through late afternoon mainly dry conditions should be seen across
the area with possibly a few light showers across the south third of
the area.

There has been a fairly consistent signal from the RAP indicating
showers and eventually thunderstorms will develop across the
southeast half of the area during the evening. This scenario is
supported by the weak radar returns across eastern Missouri and an
approaching upper level disturbance in water vapor imagery. The
northwest half of the area should eventually see showers and
possibly a few thunderstorms develop prior to midnight.

By or after midnight, the convection that develops during the
evening will grow upscale into an organized thunderstorm complex.
The southeast half of the area should have the better areal coverage
along with the potential for locally heavy rainfall.

The nocturnal thunderstorm complex that develops tonight will exit
the area Saturday morning. Thus areal coverage of precipitation will
decrease during the morning roughly from west to east.

Boundaries left over from this convection will then provide the
focus for diurnal convection that develops Saturday afternoon.
Potential cloud cover from the morning does raise questions about
how much convection will develop during the afternoon.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 315 PM CDT Fri Aug 26 2016

The extended forecast begins with the somewhat poorly organized
convective potential this weekend and early week, followed by at
least two likely dry days under a passing high pressure system at
the surface. This dry period will likely not completely appear
obvious in our forecast grids until tomorrow when blends hopefully
let go of the very low pops remaining in the mid week periods.

The air mass in place in the Midwest continues to support highs
mainly in the 80s, and lows in the mid 60s to lower 70s. This will
be accompanied by rather high humidity, especially for early
September, at least under the high pressure moves in for Wed-Thu.
Looking beyond, the GFS amplifies a huge upper high, while the ECMWF
builds a broad trof into the rockies. Climatology could support
either one this time of year, and confidence is low.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
ISSUED AT 640 PM CDT Fri Aug 26 2016

VFR conditions will give way to episodes of MVFR conditions between
27/03Z and 27/08Z at all or most of the terminals as an area of showers
and thunderstorms passes. After 27/08Z low end VFR to MVFR conditions
due to 1-4K AGL ceilings will persist with risk of light precipitation
into mid morning on Saturday as a warm front passes. Skies will become
partly cloudy to mostly sunny after 27/15Z after the warm front passes.
Light easterly winds will shift to the south and southwest by Saturday
morning.

&&

.HYDROLOGY...
Issued at 1017 AM CDT Fri Aug 26 2016

Area rivers are still rising for the most part, including the
Mississippi River. Todays forecasts show the Iowa river near
Conesville and Wapsipinicon River near DeWitt approaching or
exceeding flood stage in a week mainly due to routed flow from
upstream. We have chosen not to issue a warning or watch, as this
is still a ways out, and the flood peak flows upstream are likely
to attenuate some more that we feel are modeled currently in the
forecast, resulting in possibly lower river levels a week from now
that what is currently forecast. This is also true for the
Mississippi River, when you look at today`s forecast compared to
yesterday. The Turkey River input upstream has been dropped
several thousand CFS, on today`s run, thus the flood forecast for
Burlington (well downstream) has been lowered a bit below flood
stage. All that said, this is often the case of routed flood water
from a heavy rain event, but does not account for additional
rainfall beyond today. Rivers are running higher than normal, and
soils are generally saturated. Additional heavy rains could result
in increased river forecasts.
ERVIN

&&

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

$$

SYNOPSIS...08
SHORT TERM...08
LONG TERM...Ervin
AVIATION...Nichols
HYDROLOGY...Ervin


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