330
FXUS63 KDVN 181112
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
612 AM CDT Sat May 18 2024

.KEY MESSAGES...

- There is a Marginal risk (level 1 of 5) of severe weather
  today west of the Mississippi River. Scattered showers with
  isolated storms are possible late this afternoon and evening.

- Above normal temperatures this weekend, with high temperatures
  in the upper 80s each day.

- Active pattern returns early next week, with several rounds of
  storms Monday through Wednesday. Severe weather becoming more
  a concern on Tuesday.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 329 AM CDT Sat May 18 2024

Quiet and mild conditions were observed early this AM across the
forecast area. Temperatures are 3 to 8 degrees warmer compared
to 24 hrs ago. The latest water vapor imagery and upper air
analysis, shows the CWA is currently in-between two main weather
systems of interest across the CONUS (strong shortwave tracking
across the lower MS RVR valley and another shortwave moving
across Montana). Weak upper level flow was also overhead, with
our 00z DVN sounding showing winds under 20kts through the
entire column up to 300 mb.

Another warm and mostly sunny day is in store today to start
the weekend! With the slightly warmer start and 850mb temps
expected to be 2C warmer today, raised highs a few degrees
area-wide into the mid to upper 80s. A weak cold front will
track across Iowa this afternoon and evening, bringing with it a
chance of scattered showers and isolated thunderstorms. Forcing
along the front is not overly impressive and better dynamics
will be displaced further north. However, 00z hi-res models and
the HREF all continue to support a broken line of
showers/storms occurring after 5pm across our northwest counties
and moving east southeast.

Regarding the severe potential, this will be a high CAPE-low
shear scenario where a narrow corridor of multi-cell and pulse
type storms may occur. Strong daytime heating will allow
building MLCAPE values near 1500 J/Kg and moisture pooling ahead
of the front (PWs near 1.5"). While deep layer shear is
forecast under 25kts with strong west southwesterlies displaced
behind the front, can`t rule out a few strong cells occurring
with an isolated severe hail/damaging wind report. For this
reason, SPC has a Day 1 Marginal (level 1 of 5) risk for severe
weather west of a line from a line from Galena IL, to Mt
Pleasant IA, to Memphis MO. The severe potential will quickly
diminish after sunset tonight.

Weak high pressure behind the front will bring clearing skies and
dry conditions overnight tonight, with lows dropping into the
middle 50s to lower 60s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 329 AM CDT Sat May 18 2024

An active southwest flow weather pattern will develop early
next week, with several waves moving through the local area.
Timing and strength of these waves still differs from model to
model and run-to-run. However, the 00z ensembles still suggest
that Monday and Tuesday will have the potential for severe
weather with plenty of CAPE/Shear for storms to work with. The
00z GEFS supercell composite parameter shows values of 3-5 for
Monday/Tuesday. Additionally, the 12z ECMWF EFI also continues
to show values around 0.7 for the CAPE/Shear combination for 00z
Wednesday. These all point to a severe weather risk each day.
SPC has now outlined our entire area in a Day 3 Marginal risk
(level 1 of 5) on Monday. Strong capping aloft may prevent much
activity locally until late Monday evening and overnight where
an MCS may develop just to our west and propagate east into our
CWA.

Tuesday...this period is becoming more of one to monitor in the
coming days. A warm front will lift north across the CWA in the
morning, placing us in the warm sector. With a deepening surface
low and trough lifting northeast, strong thermodynamics and
kinematics will be in play by the afternoon and evening allowing
for convection to rapidly develop possibly into a linear QLCS.
All modes of severe weather will be possible and more details
to come in later updates. In addition, some heavy rainfall will
be possible with this event, with PWs around 1.5 to 1.7 inches,
which would be above the 90th percentile for this time of year.

Wednesday On...additional showers and storms will be possible
late week. However, model timing differences in shortwaves
moving through the flow precludes changing the PoPs, which are
in the 15 to 30 percent range for each 6 hr period through
Friday. There will be some dry hours, but when this will occur
is still in question. Temperatures will return to more
seasonable values by late week, with highs in the 70s and lows
in the 40s.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 603 AM CDT Sat May 18 2024

VFR conditions are expected through the TAF cycle. A weak cold
front will track across Iowa this afternoon and evening, with a
broken line of scattered showers and isolated thunderstorms
developing along it. Confidence in storm coverage is low with
several differing model solutions and because of this have left
out mention in the TAF for now. If storms were to hit a
terminal, it would occur at CID/DBQ in the 00-03z time frame.
Any showers/storms that do occur will quickly dissipate after
sunset with loss of daytime heating. Behind the cold front,
winds will switch out of the northwest and remain under 12 kts.

&&

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

&&

$$

SHORT TERM...Gross
LONG TERM...Gross
AVIATION...Gross