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FXUS63 KDVN 082345
AFDDVN

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

...00z AVIATION UPDATE...

.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
in the Excessive Rainfall Outlook. 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 00Z TAFS through 00Z Thursday Evening)
ISSUED AT 638 PM CDT Wed Jul 8 2020

VFR conditions anticipated through tonight and into Thursday with
light southerly winds. Storms are possible at anytime on Thursday
into Thursday night ahead of an approaching upper level
disturbance. Best coverage will likely favor later in the PM
and Thursday evening. Since this is toward the end of the TAF
period and just beyond, and lower confidence exists on coverage
I've opted to keep out any mention of precipitation for now. This
will likely be added with future forecasts as details become
better defined. In addition, there will be a threat of a few
strong/severe storms with gusty winds the main hazard.

&&

.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...McClure
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