Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 241748
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1248 PM CDT SAT SEP 24 2016

...AVIATION UPDATE...

.UPDATE...
Issued at 1126 AM CDT Sat Sep 24 2016

At 11 am, visible satellite showed the sw edge of the low clouds
was roughly along an a line from Williamsburg through Columbus
Junction in IA to Alexis IL, eroding slowly to the northeast.
Under the low clouds, temperatures have struggled into the upper
60s to around 70 with lingering light fog, while to the south,
sunshine and weak warm advection on light SE surface winds had
warmed temperatures into the mid and upper 70s. The main synoptic
front, based on even warmer surface temperatures and more
southerly surface winds, appeared to be further to the southwest,
from west central IA SE through Centerville to Quincy.

Cloud cover will continue to slowly erode from SW to NE, but it is
looking less likely that the clearing will reach the area from DBQ
to Freeport this afternoon. E-SE winds and limited mixing under
the frontal inversion will also limit warming. Have lowered highs
today to the mid 70s in this area, ranging to the upper 80s in SE
IA, far NW MO and adjacent W central IL. Even this may be a bit
optimistic by a few degrees, considering the low sun angle and
unfavorable low level winds.

&&

.SYNOPSIS...
Issued at 331 AM CDT Sat Sep 24 2016

H5 ridge across the area this morning led to quiet weather.
Easterly sfc winds were ushering slightly lower dewpoints into the
area. This flow was aiding in creating a stratus deck. To our
west, a closed off H5 low was slowly lumbering across the Great
Plains. This low will slide closer to the area in the short term.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 331 AM CDT Sat Sep 24 2016

Main forecast concern for the short term are the chances for rain
and thunder later in the period towards daybreak Sunday. As with
most closed off lows, the models are usually faster than what
occurs. The current forecast calls for a slightly slower frontal
passage.

For the most part today will be a continued taste of summer with
temps in the 80s across the area, with possibly 90s in the
southern CWA. The sfc boundary will shift north in response to the
H5 low advecting in from the west. This will allow for upper 60
dewpoints to advect into the area, leading to a warm and humid
Saturday across the area.

Overnight tonight, a slower progression of the cold front has lead
to delayed arrival for pops with most of the chance for rain
closer to 12z across the western CWA. This system is a much more
progressive system than last nights weak H85 flow and flash
flooding. Moisture convergence along the sfc feature is weakening
during the period so it appears that most of the rain will be in
a weakening state when it approaches the CWA. Hires cams suggest
that precip will be scattered and weakening as well during this
time. Our current pops may be overdone near 12z, however decided
to keep likely pops across the west as confidence in lower pops is
lower than I`d like to change the forecast. The rain that is
forecast during the short term will likely not exasperate ongoing
flooding as the storms should be moving much faster than last
night.

.LONG TERM...(Sunday through Friday)
ISSUED AT 331 AM CDT Sat Sep 24 2016

Rain likely on Sunday followed by much cooler and drier into
midweek then moderating temperatures and continued dry late
week.

Anticipate a gradual waning in intensity of pre-frontal showers and
possibly a few storms Sunday morning, with some flare-up possible
by afternoon along and east of the Mississippi River provided
enough solar insolation, which is in question. Progged MUCAPES by
afternoon over the eastern CWA are in the 1500-2000+ J/KG range
based on temperatures in the lower 80s and dewpoints in the upper
60s, but bulk shear is marginal at around 20 kts 0-6km. As a
result, do not anticipate severe weather at this time but an
isolated couple of strong storms may be possible if thermodynamic
parameters are realized, which again are in question and dependent
on degree of solar insolation. Ribbon of deep tropospheric
moisture is depicted with the front, with precipitable water
values shown of nearly 2 inches. This may support brief heavy rain
with the stronger cells, but overall progressive nature of front
and weakening large scale ascent look to limit rainfall amounts to
generally below 0.5 inch, which is good news for area rivers as
this amount would have little if any impact on levels.

Advancing dry slot in wake of front and undercutting an Upper
Mississippi Valley low should lead to decreasing clouds and
diminishing rain chances Sunday night into early Monday morning.
Much cooler conditions expected by Monday morning on gusty
northwest winds, with lows Sunday night in the upper 40s to mid
50s.

Monday through Friday looks like an extended period of dry weather,
and exactly what is needed with many area rivers experiencing
flooding. The core of the cool air is forecast to rotate through
the region on Monday into Tuesday on the backside of a slowly
departing Great Lakes low, with 850 mb temperatures shown around
4C to 6C. This will lead to slightly below normal and near
typical early fall-like temperatures with highs in the 60s to
near 70 degrees and lows in the 40s to near 50 degrees. Mid to
late week and upper ridge looks to build toward the region, which
will bring moderating temperatures along with a continuation of
dry conditions.

&&

.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 331 AM CDT Sat Sep 24 2016

The only change since yesterday afternoon is that a flood warning
has been issued for the English River at Kalona. CFS from Parnell
gauge would support Kalona breaching flood stage, however likely
to see some attenuation of water as it moves downstream and thus
could be close to whether it reaches FS or not, and have noticed a
marked slowing in the ascension of the river recently. Parnell
crested only a few hours and has already quickly dropped below FS,
thus any flooding at Kalona likely to be short-lived.

Previous discussion...issued 310 pm 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.
&&

$$

UPDATE...Sheets
SYNOPSIS...Gibbs
SHORT TERM...Gibbs
LONG TERM...McClure
AVIATION...Sheets
HYDROLOGY...McClure/Brooks/Uttech


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