Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 242038
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
338 PM CDT SAT SEP 24 2016

.SYNOPSIS...
Issued at 337 PM CDT Sat Sep 24 2016

Low clouds continued to retreat northeastward this afternoon, with
the clearing line at 230 pm from just north of the Quad Cities to
Manchester. Under the clouds, temperatures were still in the upper
60s to lower 70s, while mid and upper 80s were common under the hazy
sunshine to the south. Visible satellite imagery showed a developing
cu field in the warm sector along and what appears to be the main
surface warm front from central IA SE through Washington to central
IL. A large complex of thunderstorms along the MO River SW into
central KS and OK was ahead of the surface cold front in an area of
high PW in the deep southerly flow between the upper ridge axis over
the MS River valley and upper low over SE MT. This upper low is
progged to push eastward sending the cold front through the region
Sunday, spreading showers and thunderstorms, followed by much
cooler weather early next week.

&&

.SHORT TERM...(This Evening through Sunday)
ISSUED AT 337 PM CDT Sat Sep 24 2016

Two primary concerns in the near term: The first is the potential
for fog over especially the northeast half of the forecast area
overnight into Sunday morning. The second is the potential for heavy
rainfall which would easily exacerbate the on-going flooding
situation.

Low level moisture and weak convergence along and north of the
nearly stationary surface boundary will favor redevelopment of fog
tonight over especially the northeast half of the forecast area.
Short term models have SE winds suggested from 5 to 10 kts,
generally on the high side for significant fog. However, where low
clouds are last to dissipate late this afternoon/early evening, and
the light winds existing along the boundary slowly washing out over
the region, will both support dense fog. For now, will have patchy
fog mentioned developing tonight and continuing into the early post
dawn hours Sunday. Otherwise, it will be rather humid with dewpoints
in the mid 60s to around 70 keeping mins well above normal.

Looking at convective trends: a deep moisture feed, sufficient
MUCAPE and upper forcing will likely keep the MCS out west going and
advancing east through central IA overnight, reaching into our
western forecast area counties toward morning. By this time, the
better convergence is mainly focused into northeast IA, with waning
instability pointing toward weakening showers and embedded
thunderstorms at best overspreading NE MO and eastern IA Sunday
morning. this is supported by the past several runs of several high
res convective allowing models. However, with another round of very
high PW (1.7 to 1.9), cannot rule out heavy rainfall rates with
these storms. Still, anticipating decent storm movement and
conditions not conducive for training cells, not anticipating enough
of a heavy rain threat to issue a watch for our areas vulnerable
from recent heavy rain event and river flooding, but will continue
to monitor trends closely.

Sunday afternoon, general model timing has the front, or
prefrontal trough, reaching the MS River around noon. This would
support afternoon redevelopment of a linear thunderstorm complex
along and ahead of the boundary in our eastern counties with upper
level support and sufficient shear for a few strong storms and
heavy rainfall. SPC has this outlined with a marginal risk area in
its day 2 outlook. Ahead of the front, temperatures should recover
into the upper 70s to lower 80s, while eastern IA will have highs
limited to the 70s.

.LONG TERM...(Sunday Night through Saturday)
ISSUED AT 337 PM CDT Sat Sep 24 2016

Sunday night...Most models and latest SREF output indicate that LLVL
Fropa process will be sweeping eastward acrs the MS RVR and into the
eastern CWA early in the period. Lead edge of in-wrapping dry slot
up into northern MN cyclone complex, will interact with back edge of
the frontal system`s deeper moisture strip to keep isolated to sctrd
showers and possibly a thunderstorm streaming up and east of the MS
RVR through at least 02z. But better thermodynamics to drive more
substantial storms by then east of the local area of concern acrs
central into northeastern IL. Dry from midnight on with increasing
west to northwest sfc wind flow behind robust front, cool air
advection making for lows well down in the 50s and even some upper
40s.

Monday through Wednesday...Monday a breezy and mainly sunny day with
west to northwest sfc wind gusts up to 30 MPH in deep mixing regime.
Deep mixing also making the most of cooling vertical profile helping
temps warm back up into the mid to upper 60s. Widespread lows in the
40s Mon night into Tue morning, and if sfc winds were not going to
maintain at 5-10 mph overnight, there could be some upper 30s.
Latest medium range model runs suggest that large cut-off upper low
will gyrate slowly south-southeastward acrs the GRT LKS and eastern
OH RVR Valley in a blocked synoptic scale pattern. But any
associated instability showers under it`s reign should stay to the
east of the DVN CWA. More seasonable temps to continue as well for
late Sep, with highs in the upper 60s to lower 70s and lows in the
40s to lower 50s.

Thursday though next Saturday...Longer range indications, as well as
upper jet trends suggest upstream omega block to adjust eastward
acrs the MO and MS RVR Valleys during the second half of the week
and into the start of the next weekend. This would maintain a needed
dry and seasonably temp regime for the local area during that time
frame.      ..12..

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
ISSUED AT 1248 PM CDT Sat Sep 24 2016

An area of low clouds and IFR conditions over eastern IA will
continue to gradually retreat north this afternoon, giving way to
VFR conditions. Tonight, this same area will likely see returning
IFR, and possible LIFR to VLIFR, especially at CID and DBQ as
lingering low level moisture leads to the redevelopment of fog and
low cigs. Confidence in these trends is low at this time. Sunday,
IFR to MVFR conditions may linger through most of the morning
with scattered showers and at least isolated thunderstorms moving
into eastern Iowa ahead of a cold front. For now, confidence in
thunderstorm occurrence is low and have brought showers into the
forecast with PROB30 wording.


&&

.HYDROLOGY...
Issued at 337 PM CDT Sat Sep 24 2016

Flooding of several of the tributary systems across Iowa is the
primary hydrologic problem today, while flooding along the
Mississippi River remains forecast for next week.

The Cedar River forecasts are the primary forecast problem today as
there is considerable uncertainty with what is going on upstream.
Measured flows from upstream have been lower than expected, but it
has been observed that the a large amount of water has spread into
fields along the river rather than continue to move through the
river system. This brings higher confidence that more attenuation is
occurring than what we had originally anticipated which would
lead to lower crests. That being said, there is the wildcard of
additional rainfall through Sunday. At this time, we don`t think
rains from this system will amount to anything substantial, but if
one storm moves over the right location, it could have an impact.
Main point is, confidence is increasing on lower crests, but with
some uncertainty still with upstream flows and future rainfall
have decided to trend the forecast downward for VINI4 and CIDI4
until we have a better grasp and can hold onto a good number.

The Wapsipinicon River at Independence has risen above major flood
stage today and will continue tor rise through Sunday morning. Going
downstream forecasts have decreased a bit since yesterday as the
models gained a better handle on the water routing down the system
so the site in Anamosa is now forecast to crest right around major
flood stage.

The Mississippi River forecasts remained fairly similar to prior
forecasts as not much changes have occurred this far as there is
exorbitant amounts of water to work through the system. Some
locations will begin to see the river rise above flood stage early
next week while others may not see flood stage until the middle
portion of the week. Crests on the Mississippi won`t occur until
late next week or into the weekend.

&&

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

$$

SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...12
AVIATION...Sheets
HYDROLOGY...Brooks


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