Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 250422
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1122 PM CDT Mon Jul 24 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 236 PM CDT Mon Jul 24 2017

A very pleasant partly cloudy afternoon is taking place in most
areas, except for the small convergent lake breeze enhanced line
of stratus that has been terribly slow to mix out running from
just west of Dubuque to the Quad Cities, to near Peoria. This
central stripe is running cool on temperatures, and higher on
dewpoints than anywhere else.

&&

.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 236 PM CDT Mon Jul 24 2017

The fall-like burn off of stratus may continue into the late
afternoon. After this completely it`s process, all areas are
likely to experience a quiet and beautiful evening has cool and
dry air continue to spread southwest into the area. Lows tonight
are dependent on dewpoint, and that will locally vary with soil
wetness. There is some potential for valley fog given the wet
soils, but the winds of 5 to 8 mph will keep me from introducing
that to the forecast.

Tuesday should not see the lake stratus as was in place at sunrise
today, as the dry air will have completely established itself.
Thus, a wall to wall beautiful summer day is forecast with highs
in the lower 80s northeast to upper 80s southwest. Humidity should
remain comfortable through mid afternoon, then increase from west
to east toward evening. Even so, we`re only talking about
dewpoints reaching the upper 60s west by 7 PM.

.LONG TERM...(Tuesday Night through Monday)
ISSUED AT 236 PM CDT Mon Jul 24 2017

Forecast focus on the potential for severe thunderstorms Wednesday
afternoon and night, along with heat and humidity. Dry and
comfortable late in the week through at least early next week, with
somewhat below normal temperatures.

Wednesday through Thursday: There will be a cold front approaching
from the west on Wednesday. Ahead of the front, hot and humid
conditions can be expected with models indicating a warm axis (hot
prod) pointed into the dvn cwa. Highs should push into the 88 to 94
degree range from the Highway 30 corridor southward. With dewpoints
pushing well into the 70s, heat index values will soar to 98 to 102,
especially from Interstate 80 southward.  A heat advisory headline
may be needed for portions of the cwa for Wednesday afternoon.

Convection: Through early afternoon forecast soundings indicate a
decent cap in place. Thereafter, most of the models, including the
NAMNEST, indicate thunderstorms forming/moving into our western cwa
by late afternoon and then spreading eastward during the evening.
With sufficient shear, MUCAPES approaching 4000 j/kg, and PWAT`s to
2.5 inches, severe thunderstorms seem likely. SPC has a slight risk
for severe storms across the entire cwa. The main threats appear to
be damaging winds and frequent lightning. With PWAT values "off the
charts" torrential rainfall of an inch or two in a short time is
also likely, which may cause flash flooding in a few spots. This
system looks to be more progressive, compared to last Friday night`s
event, with little or no evidence of back-building or training of
storms. The front will push into our southern and eastern counties
after midnight, with the storms gradually weakening and diminishing.
Chances for storms continue into Thursday, mainly our southern cwa
in the morning. The GFS seems too aggressive holding onto the pcpn
in the cwa, compared to the ECMWF.

Friday through early next week: A dry period with somewhat below
normal temperatures. Models indicate a northwest flow aloft
transitioning to an upper level ridge building into the area.
Highs should be mainly in the lower 80s with lows around 60.

Haase

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
ISSUED AT 1120 PM CDT Mon Jul 24 2017

VFR conditions to prevail for at least another 24 hours as high pressure
slides east with fair skies. Winds will be light easterly overnight
at 5 MPH or less, shifting to the southeast at 5 to 10 MPH on Tuesday.

&&

.HYDROLOGY...
Issued at 1205 PM CDT Mon Jul 24 2017

River flooding remains a high concern for the Pecatonica, Rock,
Wapsipinicon, and Mississippi Rivers. The Pecatonica River at
Freeport is sitting just under major flood stage where it is
expected to stay for near the next 24 hours. This is due to
continued water moving in from upstream as well as some backwater
effects as flood waters are also entering the river just
downstream of the gage from Yellow Creek. Both of these river
systems are causing impacts in the Freeport area as water
struggles to get through the system. On the Rock, the crest was in
the Erie area late this morning. Measurements from the USGS along
with observed trends have brought forecasts down slightly from
yesterday. Crests will still be high, with both Joslin and Moline
cresting in the top 7 historical crests at 18.3 and 16.0 feet
respectively. Also of note, while the river has crested at Como,
the river here hasn`t seen levels this high since 1929.

On the Wapsi, the crest occurred at Independence lower than the
original forecast, therefore crests have been lowered downstream
at both ANSI4 and DEWI4. Will continue to watch upstream readings,
but may need to lower forecasts a bit more once confidence is in
place that all water upstream has been accounted for.

Then looking at the Mississippi, crest forecasts are just reaching
moderate flood stage at many points. Confidence is not high on
this, especially as tributary flows have been coming in lower than
expected. Thinking we`ll see a healthy minor flood event unfold on
the Mississippi.

There is rain in the forecast for Wednesday. Early model runs are
showing QPF amounts from WPC would entail a slower recession on
the Rock River, with maybe a slight upwards bump. But this would
not occur until after levels have dropped below major flood
stage.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...Haase
AVIATION...Nichols
HYDROLOGY...Brooks



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