Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 272312
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
612 PM CDT Thu Jul 27 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 318 PM CDT Thu Jul 27 2017

The main cold front extended from central MO to central Il and was
sagging southward. A secondary weak front or trough was moving
through northern IL (seen on visible satellite imagery) and was
producing a few showers on this boundary, but was east of the dvn
cwa. Despite the HRRR wanting to generate showers in the dvn cwa
there has been no evidence on radar as of yet. Will hang onto the
slight pops this afternoon just in case.

Northeast winds were coming off the Great Lakes with much drier
air across MN/WI/MI where dewpoints were in the 50s at many
locations. Across the dvn cwa, dews ranged from the mid 60s north
to the lower 70s south.

&&

.SHORT TERM...(This Evening through Friday)
ISSUED AT 318 PM CDT Thu Jul 27 2017

Forecast focus on delightful weather for the end of July.

Tonight: With loss of heating the cumulus clouds will dissipate
giving way to a clear and comfortable night, as dewpoints continue
to lower on northeast winds. Lows should range from 60 at
Freeport, Il to the mid 60s in extreme northeast MO.

Friday: High pressure building into the Great Lakes will bring a
fantastic day with comfortable humidity and light northeast winds.
Other than scattered fair weather cumulus clouds dotting the
landscape, there will be plenty of sunshine. Afternoon highs will
push into the upper 70s to lower 80s at most locations. ..Haase..

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 318 PM CDT Thu Jul 27 2017

Friday night through the weekend...Latest run medium range models in
good agreement of suggesting long wave trof to continue to dig south
and establish acrs the Appalachians and Atlantic seaboard this
period, while broad upper ridge engulfs the west half of the CONUS.
Resultant amplifying northwest fetch will allow for a seasonably
robust llvl high pressure system to dump down out of Canada and
backdoor it`s way down the western GRT LKS this period. Looking at
extent of projected air mass influx, drier column from the sfc on
up, and thicknesses generally suggest lows at night well down in the
50s, with afternoon highs in the upper 70s to lower 80s. More areas
may have trouble making it out of the 70s on Saturday depending on
mix out depth, will have to go above H85 MB to get the 80s. H85 MB
ridge cool rule supports lows down in the low to mid 50s for much of
the CWA for both Fri and Sat nights.

Monday through next Thursday...Projected upper jet trends and extent
of the western ridge mass indicate the synoptic scale pattern to
adjust little and remain almost blocked until later in the week. The
air mass acrs the region will look to modify and warm back up to
normal levels this period. Looking at longer range trends, it
appears that ridge-riding wave energy will try to propagate
southeastward into the GRT LKS and re-enforce the troffiness from
the GRT LKS on eastward. In the process, it will try and shunt a sfc
front down acrs the local area from the north sometime Wed into Thu,
which may act as a focus for shower and thunderstorm development
during the afternoon and evening. But most of the medium range
solutions suggest marginal moisture feed and convergence into this
boundary and there may not be much organization to any convection...
sctrd diurnal clusters to isolated showers/storms both Wed afternoon
and possibly Thu. The 12z ECMWF really washes out this feature to
the south By next Thu and suggests most of the day to be dry. The
12z GFS of course is wetter and more bullish, festering rounds of
showers and storms from Wed into Thu acrs portions of the area.
Unless there can be a more enhanced low to mid level draw into the
front from the southwest to utilize some monsoonal influences,
currently see the 12z ECMWF solution becoming more viable for the
long range.      ..12..

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
ISSUED AT 612 PM CDT Thu Jul 27 2017

VFR conditions will be the rule overnight through Friday as high
pressure builds into the western Great Lakes. There is a low
potential for patchy shallow ground fog, which is not mentioned in
the forecasts.

&&

.HYDROLOGY...
Issued at 318 PM CDT Thu Jul 27 2017

Only isolated showers and maybe a thunderstorm will be possible
this afternoon, thus no real additional impact expected to the
flood sensitive river basins. An extended period of dry weather is
still on track across the entire area from tonight through at
least next Tuesday night. This dry weather will allow area
waterways to go below flood stage and allow the saturated ground
across northeast Iowa and northwest Illinois to dry out. But
elevated readings on all area waterways are still expected into
early August.

Wapsipinicon River...

Moderate flooding is ongoing at Anamosa Shaw Road, but the gage that
was determined to be reading incorrectly has been adjusted to 18.8
feet. Still forecast there to start falling tonight and drop below
Moderate Flood Stage by late Friday morning. Major flooding still on
track near DeWitt by Saturday morning.

Rock River...

Major flooding continues along the Rock river. Joslin is falling
after a brief jump in the river level there from the storms over
that basin yesterday evening. Como will experience a secondary crest
around 13.2 feet by Friday afternoon. Moline continues to slowly
fall with the potential of dropping below Major Flood Stage there by
Sunday morning.

Pecatonica River...

Flooding continues along the Pecatonica River. The Winslow area is
observing significant flooding, with the crest near that location as
of Thursday morning. Downstream at Freeport the river should start
rising again as the crest makes its way downstream. However, the
timing of the rise and how much higher the river will go is still
uncertain as there is significant spreading of the water across the
rural areas. The current forecast is for the river to crest around
15.6 feet, but it could be up to 0.3 ft higher or lower than that.

Mississippi River...

Flood warnings remain in effect for minor flooding from Muscatine
down to Burlington, although Muscatine should drop below flood stage
this afternoon. The flood crest is at Gladstone L&D 18, and
currently approaching Burlington. Keithsburg appears to be slowly
falling and thus has crested earlier this morning.

&&

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

$$

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



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