Special Weather Statement, NWS Quad Cities, IA

Area Forecast Discussion
National Weather Service Quad Cities IA IL
105 AM CDT Thu Jul 19 2018

...06Z AVIATION UPDATE...

.UPDATE...
Issued at 945 PM CDT Wed Jul 18 2018

Radar trends indicate some virga/sprinkles have developed in mid
level clouds between OTM and CID in the past 90 minutes. As waa
increases tonight, more showers and eventually some storms will
develop on the theta e gradient that will move into the area from
Missouri and central Iowa.

Forecast is being updated to reflect the addition of sprinkles
ahead of the expected development of waa precipitation later
tonight.

&&

.SYNOPSIS...
Issued at 243 PM CDT Wed Jul 18 2018

A very pleasant summer day is at hand outside with the main warm
moist advection axis still well west of the area. This has resulted
in a mostly sunny day, and temperatures in the lower to mid 80s,
with dewpoints in the lower to mid 60s. For July, this is pretty
nice.  Thunderstorms earlier today were found along the elevated and
surface warm fronts, generally along the Missouri River. That
frontal zone will set up closer to our area tonight and Thursday.

&&

.SHORT TERM...(This Evening through Thursday Night)
ISSUED AT 243 PM CDT Wed Jul 18 2018

Tonight, dry weather should linger though the evening, as we are
discounting models that produce surface based convection beyond a
few isolated sprinkles in the north and southwest. This activity
should wane quickly if it forms. Otherwise, the night's rain chances
will wait for the wing of warm advection showers and storms arriving
after midnight from the west. These showers should be high based and
progressive, thus offering only beneficial rainfall potential.  By
morning, the Iowa side will see a scattered to broken area of storms
and showers moving northeast, reaching the Mississippi by mid to
late morning, and northwest Illinois by early afternoon. Again, this
activity should be high based, and mainly a rain and lightning
producer.  By afternoon, the threat for additional surface based
activity will be increasing in all areas. The afternoon and evening
will be acting on deep layer shear, and steeper mid level lapse
rates than earlier storms. Models have shifted south with the entire
system, especially the upper low for Thursday. That includes data
from ensemble GFS too, and I think this is a summer equivalent to
seeing a clipper shift south with a track the day prior to the
event. That will likely increase our chances for significant
rainfall compared to earlier runs and and forecasts, as well as
warrant cooler temperatures for highs Thursday and likely Friday.

Severe storms will bring a threat for damaging winds in short line
segments, and marginally severe hail (CAPE not too high). Tornadoes
cannot  be ruled out, though this will be tough to pin down
locations this far out, as low level backed winds will be required
for low level rotation to be intense.

ERVIN

.LONG TERM...(Friday through Wednesday)
ISSUED AT 243 PM CDT Wed Jul 18 2018

At the beginning of the period, the upper level low will slowly move
to the east.  Wrap around moisture and cold air will likely lead to
showers and some thunderstorms across the area.  Expect this
activity to be widely scattered through the period.  This low will
be slow to move out of the area as a wave moves north in front of it
along the east coast.  There will be chances for rain showers and
thunderstorms through the early part of the weekend.  One thing that
will be different are the dewpoints.  Drier air is expected, so
heavy rain is not expected from any of these showers.

Past Friday, much cooler and drier air is forecast for the area. The
weekend looks to be very beautiful again. Drier air and much cooler
temperatures.  The CPC outlook is for below average temperatures
next week.  We could see highs in the 70s most days.  A reprieve
from the heat.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
ISSUED AT 104 AM CDT Thu Jul 19 2018

Developing high-based showers and thunderstorms over central and
southeast Iowa will affect the terminals through the rest of
tonight and have this handled with TEMPO groups. There is low
confidence in how long these showers and thunderstorms will linger
into the daylight morning hours and for now have opted to mention
with vicinity wording. Overall, VFR conditions should prevail
through midday. Another round of more organized, and possibly
strong thunderstorms is then expected from mid afternoon into
early evening. Will initially have broad four hour windows with
prob30 wording to cover these, with later forecast updates likely able
to narrow down to more specific timing.

&&

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

UPDATE...08
SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...Gibbs
AVIATION...Sheets

Hazardous Weather Outlook
National Weather Service Quad Cities IA IL
248 PM CDT Wed Jul 18 2018

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-192000-
Buchanan-Delaware-Dubuque-Benton-Linn-Jones-Jackson-Iowa-Johnson-
Cedar-Clinton-Muscatine-Scott-Keokuk-Washington-Louisa-Jefferson-
Henry IA-Des Moines-Van Buren-Lee-Jo Daviess-Stephenson-Carroll-
Whiteside-Rock Island-Henry IL-Bureau-Putnam-Mercer-Henderson-
Warren-Hancock-McDonough-Scotland-Clark-
248 PM CDT Wed Jul 18 2018

This Hazardous Weather Outlook is for portions of north central
Illinois...northwest Illinois...west central Illinois...east
central Iowa...northeast Iowa...southeast Iowa and northeast
Missouri.

.DAY ONE...THIS AFTERNOON AND TONIGHT

Scattered thunderstorms are possible mainly west of the
Mississippi River tonight. Severe weather is not expected, but
lightning will be the main risk.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

Thunderstorms are possible across the area Thursday and Friday.
There is a potential for severe storms and the Storm Prediction
Center has placed a Slight Risk over much of the outlook
area Thursday. The main severe weather risk is damaging winds,
large hail, and locally heavy rainfall. An isolated tornado will
also be possible in the afternoon and evening hours.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed this afternoon or tonight.

Haase/Sheets/Ervin

Special Weather Statement
National Weather Service Quad Cities IA/IL
344 AM CDT THU JUL 19 2018

IAC095-107-190945-
Keokuk-Iowa-
344 AM CDT THU JUL 19 2018

...THUNDERSTORMS PRODUCING HEAVY RAIN WILL AFFECT KEOKUK AND
SOUTHWESTERN IOWA COUNTIES UNTIL 445 AM CDT...

At 337 AM CDT, radar indicated a slow moving cluster of
thunderstorms with heavy rain centered near What Cheer, or near
Sigourney. These storms were moving northeast at 10 mph.

Minor flooding of area creeks and streams is possible, as radar
estimates have indicated rainfall of amounts over 2 inches has
fallen since midnight. Additional rainfall amounts over 1 inch can
be expected with rainfall rates as high as 1.5 inches per hour
possible due to the slow moving storms.

Minor flooding is possible. If you are driving and encounter a
flooded roadway, Turn around, don't drown. Most flood deaths occur in
vehicles.

LAT...LON 4151 9241 4151 9230 4171 9230 4166 9196
      4127 9195 4118 9241
TIME...MOT...LOC 0837Z 239DEG 9KT 4138 9228

Sheets