Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 291156
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
656 AM CDT THU SEP 29 2016

...12z AVIATION UPDATE...

.SYNOPSIS...
Issued at 332 AM CDT Thu Sep 29 2016

Vertically stacked low was located over Indiana early this
morning. Our region was positioned in generally subsidence region
on northwest flank of the low, which is resulting in clear to
mostly clear skies for most of the region. However, satellite
and obs reveal considerable stratus closer to Lake Michigan
attendant to strong moisture-laden northeast flow just off the
surface. These low clouds were beginning to advect into our northwest
Illinois counties. Temperatures at 3 AM were in the upper 40s and
lower 50s, which is near normal.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 332 AM CDT Thu Sep 29 2016

Cloud trends with impact on highs, and shower chances the main
forecast challenges.

Building ridge from the Northern Plains into the Upper Midwest
will help shunt the vertically stacked low a bit further south
into Kentucky by Friday morning. Over the next 24 hours our
region will remain in cyclonic flow and subject to increasing
clouds with shower chances again mainly east, as disturbances
rotate around periphery of the low.

Today, temperatures will be quite a challenge especially for
areas along/east of the Mississippi River. Cloud trends
support more low cloudiness for skies becoming mostly cloudy
to cloudy along and east of the Mississippi River, as strong
925 mb flow of 30-35 kts pumps in moisture-laden airmass from
Lake Michigan. Have many areas in the upper 60s for highs
east of the Mississippi, but could be 2-4+ degrees too warm if
solar insolation is limited. Also, one such aforementioned
shortwaves looks to pivot back around the low and bring isolated
to possibly scattered showers to eastern counties mainly this
afternoon. Further west of the Mississippi River expect increasing
amounts of sunshine or partly to mostly sunny skies leading to
warmer highs around 70 or lower 70s in general.

Tonight, expect a westward expansion of clouds to be ongoing
by evening and through midnight, as a shortwave rotates down just
east of the Mississippi River. Will also see shower chances nudge
closer to the river. Overnight, as this wave passes and subsidence
increases expect some decrease in clouds especially north and west
sections where cooler lows in the 40s are expected. Elsewhere,
lows looks to be in the 50s.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 332 AM CDT Thu Sep 29 2016

Main forecast concern for the long term remains the closed low with
different vort maxes rotating around the low.  With low level flow
off of the lake, clouds will be the mainstay for Friday into Sunday
afternoon with chances of rain interspersed throughout the beginning
of the long term.  Chance for pops have slowed down for midweek next
week.

Main changes to the forecast for Friday and Saturday was to continue
the downward trend on temperatures.  Temperature trends in the
models continue to support lower high temps for each day.  As
previous shift noted, there is a chance for rain each day with the
best chances being Friday.  No change to this forecast.

Sunday into Monday H5 trof across the west coast finally starts to
kick out the stacked low over the Great Lakes region.  Clouds should
start to clear and temps will warm as SW brings warmer air and more
moisture into the area.

The system mid week has shown signs of slowing.  This is likely due
to the models finally grasping onto the fact that the stacked low
will be slower to move out of the area.  Coordination to remove the
POPs for Tuesday night and most of Wednesday as the ECM and GFS
start to agree on timing of the next front.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
ISSUED AT 643 AM CDT Thu Sep 29 2016

Challenging cloud forecast. Low pressure will remain over Indiana
and Kentucky during the period. Disturbances rotating around the
low will usher in bouts of cloudiness and a few showers. Early
this morning, brisk northeast winds just off the deck are ushering
in stratus with mainly MVFR ceilings at KDBQ, KBRL, KMLI, with
patchy IFR possible. With the shallow nature of the clouds and
mixing of dry air I opted to go with improving conditions to
VFR by late morning, although confidence is lower as some guidance
would like to hold onto it longer. Any showers this afternoon will
likely be confined east of the terminals. Otherwise, expect
another gusty day with north to northeast winds increasing at
15-25+ kts. Tonight, guidance suggests more low clouds will work
into the river sites late evening and overnight, with generally
MVFR ceilings although guidance would support some potential for
patchy IFR ceilings once again. A few showers may accompany these
lower clouds, but being late in the TAF cycle and lower confidence
I have left out any mention. Northerly winds will diminish to
around 10 kts with some local higher gusts possible.

&&

.HYDROLOGY...
Issued at 332 AM CDT Thu Sep 29 2016

Only changed the information about Anamosa, where it has fallen
below major flood stage.  No other changes have been made to the
forecasts overnight.

Previous discussion attached below...

Overview: Most significant change was at New Boston on the
Mississippi River where the crest forecast increased from moderate
to major flood stage. Otherwise, river forecasts are largely on
track. See site specific information in the following discussion and
in recent Flood Warning Statements.

Cedar River...

Vinton: Now below major flood stage.

Cedar Rapids: Forecast to fall below major flood stage Thursday
evening or night.

Conesville: Major flooding is occurring as river level rises
rapidly. Timing of crest forecast is Thursday afternoon into
Thursday night. Confidence is moderate to high on a crest a half
foot on either side of 18.30 feet.

Wapsipinicon River...

Anamosa Shaw Rd: Now below major flood stage.

De Witt 4S: High confidence in reaching major flood stage. Thinking
current crest forecast is on the upper end of possible outcomes.
Reasonably high probability the final crest is lower. Please monitor
for updates.

Iowa River...

Excessive amounts of water continue to propagate downstream through
the Iowa and Cedar Rivers. There is high confidence on significant
flooding. Exact timing varies by site.

Moderate confidence is associated with the crest forecasts. Current
thinking is crest forecasts are toward the upper range of what is
possible; observed crests may come in lower. Please follow forecast
information closely throughout this event.

Mississippi River...

Minor to Major flooding continues to be on track. Greatest forecast
change was at New Boston with an increased crest forecast from
moderate to major. Otherwise, latest forecasts show little to no
adjustments. Majority of the crests are projected to occur over the
weekend or early next week. Uttech

&&

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

$$

SYNOPSIS...McClure
SHORT TERM...McClure
LONG TERM...Gibbs
AVIATION...05
HYDROLOGY...Gibbs/Uttech


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