Severe Thunderstorm Warning 337, NWS Quad Cities, IA

Area Forecast Discussion...UPDATED
National Weather Service Quad Cities IA IL
814 PM CDT Thu Aug 15 2024

.KEY MESSAGES...

- A severe risk remains through 11 pm timeframe with isolated to
  widely scattered thunderstorms. Hail and damaging winds are
  the main threats.

- A pattern change will bring mainly quiet weather to the area
  Saturday night through next Thursday. Temperatures look to
  be near normal.

&&

.UPDATE...
Issued at 813 PM CDT Thu Aug 15 2024

Severe Thunderstorm Watch 623 remains in effect for southeast
Iowa and northeast Missouri until 11 PM CDT tonight. Storms
continue to develop across the area ahead of a eastward moving
cold front but have struggled to strengthen to severe limits in
eastern Iowa and northeast Missouri. An inversion exists on the
00 UTC DVN sounding around 840 mb. There are steeper lapse
rates above the inversion resulting in most unstable CAPE to
around 2800 J/KG. Model soundings do show a cooling or weakening
of the inversion. Low level flow is weak but mid to upper level
flow is faster resulting in 0 to 6 km shear of 40 to 45 knots
mostly in the mid to upper levels. CAMs have been supportive of
some increase in coverage of these storms through 10 PM. Think
that hail and damaging winds are the main threat from any storms
that intensify this evening.

Winds are forecast to remain light across the area tonight and
given recent rains and abundant low level moisture patchy to
areas of fog are possible tonight after 3 AM.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 258 PM CDT Thu Aug 15 2024

Tonight, uncertainty remains with possible storm development
after 6 pm in western parts of the CWA. Trends of the HRRR have
been to delay the time of development, which is now showing
closer to 6 or 7 in our western CWA. The NAMNEST has only shown
some activity in the far SW after 8 pm. MUCAPE values of 2 to 3K
J/kg build into the area late this afternoon and evening. This,
along with mid level lapse rates over 7 C/km and moderate shear,
will all some supercells to be possible with strong winds,
hail, and tornadoes all a threat. The caveat is whether the
clouds that have been over the area most of the day will clear
in time for needed heating for development. Some temps in the
low 80s are seen in south central IA as of 2 pm. Moisture is
plentiful, with dew points in the lower and middle 70s area
wide. Due to these uncertainties, kept POPs in the chance
category. As for timing, it looks like areas west of the MS
River will see activity from 6 pm to 10 PM, with the eastern CWA
seeing it 9 pm to about midnight or 1 am. Overnight, any
showers or storms will exit to the east. Some patchy fog is
possible overnight, but left mention out of grids for now. Lows
will be in the 60s.

Friday, a secondary cold front will sweep across the area as
the surface low moves across northern WI. Sunshine will prevail
south of Highway 30, while clouds and even some shower and
thunderstorm chances will be possible to the north. SPC has NW
IL in a marginal risk area for wind gusts and hail. Highs will
top out in the lower 80s north to upper 80s south.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 258 PM CDT Thu Aug 15 2024

Largely quiet weather dominates the Quad Cities CWA in the long
term as the upper low currently situated over the ND/MN border
slowly migrates east over the next several days putting the area
into northwest flow. Temperatures are expected to sit generally
right around average through Tuesday with highs in the upper
70s/lower 80s and lows in the upper 50s/lower 60s. Temperatures,
combined with manageable humidity levels (especially early next
week), should make for overall pleasant weather. The focus over
this weekend will be on the upper low Saturday as it pushes
into Lower Michigan, which could provide enough forcing for a
few wrap-around showers over the far eastern portions of our
area. The most favored time for shower activity comes during the
daytime hours on Saturday. Still, generally low chances (<35%)
of precipitation exist, so not expecting anything in the way of
widespread rainfall.

Shower chances diminish Sunday and beyond as the upper low exits
and high pressure builds in. Mid-level ridging builds in by midweek
which will nudge temperatures back up into the upper 80s late
week.

Siemianowski

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 632 PM CDT Thu Aug 15 2024

TAFs are currently VFR ahead of a cold front that is moving
across central Iowa. Isolated showers and thunderstorms are
possible through 06 UTC with the best chance currently at KCID
from 1 to 3 UTC. Periods of MVFR to IFR conditions are possible
in any showers and storms. Stronger thunderstorms could produce
winds up to 40 knots but confidence is low on what TAF sites
this would occur at. Conditions will improve to VFR after 06
UTC and continue through the remainder of the period. Winds will
turn to the west behind the front with gusts up to 20 knots
possible after 15 UTC on Thursday.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.

&&

UPDATE...Cousins
SHORT TERM...14
LONG TERM...12/14
AVIATION...Cousins

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