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fxus63 kdvn 211137 
afddvn

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
637 am CDT Fri Jul 21 2017

..aviation update...

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 12z tafs through 12z Saturday morning)
issued at 632 am CDT Fri Jul 21 2017

Decaying thunderstorm complex across eastern Iowa and northern
Illinois has produced a new band of thunderstorms and rain from near kmli to the
northeast of kmcw. This band of thunderstorms and rain will slowly move east and
likely affect kdbq/kmli with a period of IFR/MVFR conditions.
After 15z/21 expect VFR conditions with high density altitudes.
Isolated rain showers/thunderstorms and rain may or may not occur prior to sunset. After
00z/22 VFR conditions are expected but another nocturnal thunderstorms and rain
complex is expected to develop over the upper Midwest.

&&

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...
Iowa...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 Iowa-Iowa-Jefferson-Johnson-Keokuk-Lee-Louisa-
Muscatine-Scott-Van Buren-Washington.

Illinois...heat advisory until 8 PM CDT Saturday for Bureau-Putnam-
Whiteside.

Excessive heat warning until 8 PM CDT Saturday for Hancock-
Henderson-Henry Illinois-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.

&&

$$

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