Severe Thunderstorm Warning 108, NWS Quad Cities, IA

Area Forecast Discussion
National Weather Service Quad Cities IA IL
247 PM CDT Wed Jul 8 2020

.SYNOPSIS...
Issued at 159 PM CDT Wed Jul 8 2020

At 2 PM, A stationary frontal boundry stretched a surface low
near Huron South Dakota southeastward to KDBQ and then to south
of Chicago. There is no change in dewpoint or temperature across
the frontal boundry. Dewpoints were in the mid to upper 70s with
air temperatures in the upper 80s to lower 90s across the area.
Heat indices were around 100. Scattered showers and thunderstorms
were popping up across eastern Iowa and northwest Illinois.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 159 PM CDT Wed Jul 8 2020

The main forecast concerns were chances of storms through the
period. There remains disagreements between all of the models
(synoptic/CAMs) on the timing and placement of precipitation
through the short term.

Currently, isolated showers and thunderstorms are on going across
the area this afternoon and expect them to continue into the
early evening. The shear is weak across the area today but once
again the downdraft CAPE is high which may lead to microburst s
this afternoon into this evening.

A heat advisory remains in effect until 7 PM this evening.

Tonight into Thursday, a lead piece of shortwave energy will move
across the after 06 UTC tonight and could bring scattered showers
and storms to the area during the morning hours. A second,
stronger convectively enhanced vort max will roll across the area
18z Thursday to 00 UTC Friday. The GFS and operational NAM track
this feature north of I-80 while the ECMWF and Canadian bring the
vort max south of Interstate 80. CAPE will be similar to today
with 3000 to 4000 J/KG forecast across the area but 0 to 6 km
shear slightly stronger as the moves into the area and increasing
the shear to 20 to 30 knots. Severe storms will be possible. The
main threats will be damaging winds and increasing helicity in
the afternoon and more cyclonically curving hodographs mean that a
tornado may occur as well. The storm prediction center as the
northern half of the area in a slight risk of severe storms and
the rest of the area under a marginal risk. The primary threat for
severe weather is a window from

Additionally, precipitable water values of 1.80 to 2.00 inches
will lead to threat for heavy rain and potential flash flooding.
The Weather Prediction Center has a slight risk of heavy rainfall
across the whole area.

.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 159 PM CDT Wed Jul 8 2020

Key Messages:

1.  Storms should be ongoing at the beginning of the period.
2. Slightly cooler weekend with additional chances for precipitation
for the weekend.
3. Heat dome returns to the area and pushes the MCS track
north of the CWA.

Discussion:

At the beginning of the period, showers and storms should be ongoing
across the CWA.  The coverage and intensity of any storms should be
tied to a MCV across the area.  With the MCV being strongly tied to
convection tonight, confidence in where it will be is low due its
mesoscale nature.  If it does move across the area, this will
increase shear enough to lead to organized updrafts and thus a
better risk for severe weather.  The main threat looks to be strong
wind gusts with any severe weather.  That said, there is a pseudo
warm front and a wave is expected to move along this boundary.  Any
thermal boundaries in this environment may be enough to pose a low
threat for tornadoes.  For this to occur a lot has to come together
and I am not confident in this occurring.  On the other hand, high
PWATs, with shear and slow moving storms will set the stage for
heavy rain from any storm.  WPC has the area in a slight risk ERO.
If the MCV does not move across the area, expect weaker convection
and less coverage.

After this, the pattern shifts to NW flow with a few waves that move
through it.  This means there is a chance for rain and storms again
this weekend.  The timing of these waves are different between each
model and thus lead to low forecast skill for the weekend.  There
will be sun and quiet weather this weekend along with a chance for
rain.

After this, the ridge  moves back in across the west and shifts the
low track north of the CWA as we see the return of 90s with
dewpoints in the 70s.  Another round of heat advisories could be
needed next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
ISSUED AT 1230 PM CDT Wed Jul 8 2020

VFR conditions are forecast through the TAF period. This
afternoon, scattered diurnally driven cumulus field will be over
the area with ceilings around 5kft. Scattered thunderstorms are
possible today but they are expected to remain east of KMLI and
KBRL so they were left out of the TAFs.

Isolated showers and storms are possible after 09 UTC Thursday
through the morning hours but confidence is low at this time that
will impact any specific TAF site.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Heat Advisory until 7 PM CDT this evening for Benton-Buchanan-
     Cedar-Clinton-Delaware-Des Moines-Dubuque-Henry IA-Iowa-
     Jackson-Jefferson-Johnson-Jones-Keokuk-Lee-Linn-Louisa-
     Muscatine-Scott-Van Buren-Washington.

IL...Heat Advisory until 7 PM CDT this evening for Bureau-Carroll-
     Hancock-Henderson-Henry IL-Jo Daviess-McDonough-Mercer-
     Putnam-Rock Island-Stephenson-Warren-Whiteside.

MO...Heat Advisory until 7 PM CDT this evening for Clark-Scotland.

&&

SYNOPSIS...Cousins
SHORT TERM...Cousins
LONG TERM...Gibbs
AVIATION...Cousins

Hazardous Weather Outlook
National Weather Service Quad Cities IA IL
314 AM CDT Wed Jul 8 2020

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-090815-
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-
314 AM CDT Wed Jul 8 2020

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...TODAY AND TONIGHT

Hot and humid conditions will be seen this afternoon heat index
readings up to 103, a heat advisory is in effect for the area.

There may also be some isolated afternoon thunderstorms, mainly
along and east of the Mississippi River.  The strongest storms may
produce isolated damaging wind gusts and small hail.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

Very warm and humid conditions will continue Thursday through
Tuesday with afternoon heat index readings in the 90s.

Thunderstorms will be possible each day through Sunday. The Storm
Prediction Center has a slight risk of severe storms for
Thursday. The primary severe risk Thursday looks to be damaging
winds. Beyond Thursday it is too early to determine any severe
risk.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated today or tonight.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
325 PM CDT WED JUL 8 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0324 PM     HAIL             3 W BETTENDORF          41.56N 90.54W
07/08/2020  E0.70 INCH       SCOTT              IA   TRAINED SPOTTER

&&

TJG

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
328 PM CDT WED JUL 8 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0327 PM     TSTM WND DMG     1 ESE DAVENPORT         41.55N 90.59W
07/08/2020                   SCOTT              IA   LAW ENFORCEMENT

            TREE BLOWN DOWN AT 35TH AND MARQUETTE.

&&

TJG

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
331 PM CDT WED JUL 8 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0800 PM     HEAVY RAIN       1 NW ELMOVILLE          42.27N 90.06W
07/07/2020  M1.70 INCH       JO DAVIESS         IL   TRAINED SPOTTER

&&

TJG

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