Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 211810
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
110 PM CDT Fri Jul 21 2017

.UPDATE...
Issued at 1243 PM CDT Fri Jul 21 2017

With ongoing slightly elevated showers/storms moving along the
IA/MN border region and points south to the IL/WI border, this
activity retarding main warm front retreat to the north. Also
enhanced boundary/gradient setting up from northwestern
IA...southeastward to the I80 corridor east of the Quad Cities.
Expect new thunderstorm development along and north of this
quasi-stationary boundary later this afternoon and evening, with
more shear than the past few days and ongoing plenty of CAPE feed
to support severe storms and heavy rain. New convection already
taking off near Sioux City may be our storms by early this
evening. Thus new SPC day 1 enhanced area looks on target. Bowing
segments with damaging winds, meso-vortice tornadoes or even
tornado with a supercell on a boundary all possible.

After the evening convective systems blow through, some concern
south to southwesterly LLJ may impinge on remnant outflow
boundaries or the main front itself, inducing more elevated
convection that moves along the same path(train along). This would
be from late evening and into the overnight, and may occur acrs
much of the area that got heavy rain of 1 to 2 inches last night
further west along and north of I80 out to the western fringe of
the DVN CWA. With high PWAT feed of 2 inches plus, will seriously
consider expanding the Flash Flood Watch west and south, possibly
down to I80/north half of the DVN CWA.    ..12..

&&

.SYNOPSIS...
Issued at 355 AM CDT Fri Jul 21 2017

06Z surface data has the effective boundary running from central
Indiana, across northeast Missouri, and into eastern Nebraska. Dew
points were in the 60s from the Great Lakes into the upper Midwest
with 70s across the remainder of the area.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 355 AM CDT Fri Jul 21 2017

The current headlines will remain as is. The risk for heavy rainfall
may have shifted north tonight.

Through sunrise, the second of two organized thunderstorm complexes
will move east through the area and slowly decay. The heaviest
rainfall looks to be in the I-80 corridor east of the Quad Cities.

A secondary concern through sunrise are the radar returns developing
across central and western Iowa. Some of these returns are the wind
farms. Other returns are legit showers and some thunderstorms. These
storms are developing in ascent across the boundary with the
stronger return flow aloft. These showers/storms look to impact the
far west areas around sunrise.

During the daylight hours cloud cover will slowly break up during
the late morning hours. Sunshine by mid day and into the afternoon
will result in the hot and humid conditions continuing. There are
questions as to how far north the boundary will get during the day.

Tonight, another muggy night is in store for the area. The models
have pushed the heavy rain risk further north based on the idea that
the boundary will move well north during the daylight hours. If the
boundary is further south than what the models currently indicate,
then the heavy rain risk would potentially be across Iowa/Illinois
instead of Minnesota/Wisconsin.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 355 AM CDT Fri Jul 21 2017

.LONG TERM...SATURDAY THROUGH THURSDAY

Heat and humidity will continue across much of the area on Saturday.
Organized thunderstorm complexes that develop Friday night will be
in a decaying mode Saturday morning. Boundaries left over from that
storm complex will then become the focus for diurnal convection
Saturday afternoon. An approaching cold front will move through the
area late Saturday afternoon and evening which should allow an
increase in the areal coverage of showers and storms.

Late Saturday night through Sunday night mainly dry conditions are
expected across the area as the next high pressure starts building
into the Midwest. The lower dew point air will lag behind the cold
front but will begin moving into the area in earnest Sunday night.
Temperatures should average above normal on Sunday.

Monday on...

Brief pattern change Monday through Wednesday with the flow aloft
coming from the northwest. Said pattern change will result in lower
humidity levels and temperatures close to normal.

Wednesday night/Thursday...return flow will start bringing moisture
back into the area along with the potential for more storms. The
higher dew points will start arriving on Thursday. As a result, the
model consensus has slight chance to chance pops both Wednesday
night and Thursday. Temperatures will average above normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
ISSUED AT 1243 PM CDT Fri Jul 21 2017

Incoming rounds of thunderstorms to be large impacts at most TAF
sites except maybe the BRL terminal, from late afternoon and into
mid evening with the first strong wave. Then additional storms
may fire and move along the same areas later tonight and into
early Sat morning before moving off to the east. MVFR to IFR
conditions withe the heavier bouts of storms, and concern with
sudden strong gusty winds associated with them from the west or
northwest. Heavy rain reduced VSBYS and lowered CIGs as well with
passing strong storms. Outflow boundaries will make for
challenging wind direction fcsts, plenty of variable changes
through the evening. Will leave BRL out of the mess for now, but
can`t totally rule out even this southern site form getting
impacted by storms this evening and overnight. Better conditions
coming post-frontally as Saturday progresses.   ..12..

&&

.HYDROLOGY...
Issued at 355 AM CDT Fri Jul 21 2017

Recent heavy rain in the Rock and Pecatonica River basins is
resulting in significant rises, with at least minor to moderate
flooding expected to continue into early next week. There is
potential for additional heavy rain tonight over portions of
southern Wisconsin into northern Illinois. If widespread heavy
rainfall materializes, forecast crests could be adjusted higher,
possibly into the major category at most or all forecast points.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Heat Advisory until 8 PM CDT Saturday for Benton-Clinton-Jones-
     Linn.

     Excessive Heat Warning until 8 PM CDT Saturday for Cedar-Des
     Moines-Henry IA-Iowa-Jefferson-Johnson-Keokuk-Lee-Louisa-
     Muscatine-Scott-Van Buren-Washington.

IL...Heat Advisory until 8 PM CDT Saturday for Bureau-Putnam-
     Whiteside.

     Excessive Heat Warning until 8 PM CDT Saturday for Hancock-
     Henderson-Henry IL-McDonough-Mercer-Rock Island-Warren.

     Flash Flood Watch from 4 PM CDT this afternoon through Saturday
     morning for Carroll-Jo Daviess-Stephenson.

MO...Excessive Heat Warning until 8 PM CDT Saturday for Clark-
     Scotland.

&&

$$

UPDATE...12
SYNOPSIS...08
SHORT TERM...08
LONG TERM...08
AVIATION...12
HYDROLOGY...RP Kinney



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