Special Weather Statement, NWS Quad Cities, IA

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1247 AM CDT Thu Aug 12 2021

...AVIATION UPDATE...

.UPDATE...
Issued at 710 PM CDT Wed Aug 11 2021

Heat index values continue to fall below headline criteria and
heat advisory has expired.

Meanwhile, weak low level lapse rates and lack of decent
convergence has kept convection confined to north of Hwy 30 and
more isolated than earlier thought. The storms also continue to
weaken. However, the CAM's wants to develop numerous thunderstorms
south of I-80 towards midnight and into the early morning hours.
This occurs as the LLJ intensifies overnight similar to what
happened last night. We will continue to monitor convective
trends. Some locations may be vulnerable to flash flooding where
heavy rains fell last night.

&&

.SYNOPSIS...
Issued at 340 PM CDT Wed Aug 11 2021

Another extremely unstable airmass with SBCAPE 6000-7000 J/kg and
shear stronger than yesterday. A cold front was entering our far
nw cwa and thunderstorms were rapidly firing in ne IA along the
front. Several supercells were occurring in central WI where the
shear was even stronger. Another day with heat index values of 100+.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 340 PM CDT Wed Aug 11 2021

Tonight: The front will get hung up in our far nw cwa keeping the
cwa in the very warm/unstable airmass. CAM's suggest a bkn-solid
line of thunderstorms, some severe with damaging wind 70+ mph,
will slide southeast/south across the entire cwa as the evening
progresses. These storms will be thriving on the extreme CAPE.
These storms will also have frequent lightning and torrential
rainfall with PWAT's of 2 inches.

Thursday: The front will get a push southward to about I-80 by
late afternoon, in response to a deepening trough in the upper
Midwest, and deep closed low near Hudson Bay. There will be at
least scattered thunderstorms developing again in the heat of the
afternoon along and south of the front. There may be a lull in the
action for a time in the morning but this is not a guarantee.
Highs south of the front will be in the upper 80s to lower 90s
with dewpoints in the mid 70s, while to the north it will be
somewhat less humid with a northwest wind. As of now, heat index
values may touch 100 but this will depend on cloud trends. I have
less confidence on heat headlines compared to the past couple of
days. Will pass concerns to the next shifts.

As of now, SPC has a marginal risk for severe storms ahead of the
cold front, with a slight risk in our far south.

.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 340 PM CDT Wed Aug 11 2021

Thursday Night...Uncertainties going into the night period with
lingering convection and associated debris, and the frontal
placement itself. But SR-ensembles suggest it bi-secting the CWA
from southwest-to-northeast or a bit southeast of that orientation
Thu evening. Built up or lingering CAPEs of 2000-4000 J/Kg possible,
shear profiles along the front of 30 to 40 KTs under broad cyclonic
troffiness aloft still would support some strong to severe storms
along the front Through at least mid evening, before a southward
adjustment and decrease in intensity occurs into the early Friday
morning hours. Maybe a lingering heavy rain and isolated flash flood
threat in the south later Thu night, especially if the projected
lingering PWAT's of 2 inches plus pooled to lee of the LLVL boundary
are correct.

Friday through Sunday...The blend lingers POPs in the southern CWA
through Friday morning, but mean southward frontal push and sfc
ridge arrival on newer model runs suggest most of the day will be
dry. More seasonable highs in the low to mid 80s, with dry down-
mixed sfc DPTs in the low 60s to 50s, will make for a fine
refreshing day. Friday night lows in the low 60s south to mid 50s
north. More of the same for the rest of the weekend as large GRT LKS
sfc high reigns acrs the region.

Monday through next Wednesday...Upper air/jet trends suggest semi
blocked mid CONUS pattern for a mainly dry and thermally moderating
regime into mid week with mid to upper 80s by Wed. Just a low chance
for instability and weak-perturbation driven isolated/sctrd showers
Wed afternoon that might not be worth mentioning at this point.
  ..12..

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
ISSUED AT 1238 AM CDT Thu Aug 12 2021

A frontal boundary continues to sag southward through KMLI and is
expected to washout before reaching KBRl. Showers and
thunderstorms are developing early this morning near KBRL and to
the east of KMLI. These storms will bring MVFR to possibly IFR
visibilities to KBRL over the next 3 hours before the storms shift
eastward. At this time, I do not expect showers or storms to
impact the other TAF sites overnight.

After 12 UTC, expect winds to switch back to the south or
southeasterly ahead of anther cold front that move across the TAF
sites in the 18 to 00 UTC time range. A prob 30 group was added at
KBRL and KMLI for thunderstorm potential along and ahead of the
front. Currently have lower confidence at KCID and KDBQ.

&&

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

UPDATE...Haase
SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...12
AVIATION...Cousins

Hazardous Weather Outlook
National Weather Service Quad Cities IA IL
730 PM CDT Wed Aug 11 2021

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-130030-
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-
730 PM CDT Wed Aug 11 2021

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...TONIGHT

Numerous thunderstorms are expected south of Interstate 80 after
midnight. The main threats are gusty winds, frequent lightning and
torrential rainfall. Flash flooding is possible where heavier rain
fell recently.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

Severe storms are possible Thursday afternoon and evening ahead of
a cold front, mainly south of a line from Stockton, Illinois to
Belle Plaine, Iowa where the Storm Prediction Center has a
Marginal Risk. There is a slight risk south of Highway 34. The
main severe weather threat will be damaging winds. Heavy rainfall
and frequent lightning will also be possible.

Very warm and humid conditions will linger through Thursday along
and south of Highway 30, where heat index readings near 100 are
possible in the afternoon.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected tonight.

Haase

Special Weather Statement
National Weather Service Quad Cities IA/IL
209 AM CDT Thu Aug 12 2021

IAZ088-089-099-ILZ025-034-120730-
Henderson IL-Hancock IL-Henry IA-Des Moines IA-Lee IA-
209 AM CDT Thu Aug 12 2021

...A strong thunderstorm will impact portions of north central
Hancock, southwestern Henderson, southeastern Henry, southern Des
Moines and northern Lee Counties through 230 AM CDT...

At 207 AM CDT, Doppler radar was tracking a strong thunderstorm over
St. Paul, or 11 miles northwest of Fort Madison, moving east at 40
mph.

HAZARD...Winds in excess of 40 mph, torrential rainfall and pea size
         hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

This strong thunderstorm will be near...
  West Point around 210 AM CDT.
  Lowell around 215 AM CDT.
  Danville and Middletown around 225 AM CDT.
  Burlington around 335 AM CDT.

Other locations in the path of this storm include West Burlington and
Iowa Army Ammunition Plant.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 4065 9160 4083 9162 4089 9100 4060 9100
TIME...MOT...LOC 0707Z 266DEG 35KT 4074 9151

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

Sheets

Special Weather Statement
National Weather Service Quad Cities IA/IL
239 AM CDT Thu Aug 12 2021

IAZ089-099-ILZ025-026-034-035-120815-
Warren IL-Henderson IL-McDonough IL-Hancock IL-Des Moines IA-Lee IA-
239 AM CDT Thu Aug 12 2021

...A strong thunderstorm will impact portions of northeastern
Hancock, southern Henderson, southwestern Warren, northwestern
McDonough, south central Des Moines and northeastern Lee Counties
through 315 AM CDT...

At 237 AM CDT, Doppler radar was tracking a strong thunderstorm over
Carman, or near Burlington, moving east at 45 mph.

HAZARD...Winds in excess of 30 mph, torrential rainfall and pea size
         hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

This strong thunderstorm will be near...
  Stronghurst around 250 AM CDT.
  Raritan around 255 AM CDT.

Other locations in the path of this storm include Roseville.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4059 9122 4083 9124 4085 9060 4056 9061
TIME...MOT...LOC 0737Z 270DEG 40KT 4073 9108

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...30 MPH

Sheets