860
FXUS63 KDVN 181810
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
110 PM CDT Sat May 18 2024

.KEY MESSAGES...

- Scattered showers and storms will wane after sunset tonight.
  There is a Marginal risk (level 1 of 5) of severe weather
  today west of the Mississippi River.

- Boundary stalls south of the area as temperatures again reach
  well into the 80s as chances for thunderstorms return late.

- 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 109 PM CDT Sat May 18 2024

Temperatures well into the 80s today were found area-wide.
Dewpoints in the upper 50s to low 60s made it feel somewhat
nicer than the middle of July. To the west of the area, a cold
front was located across the center of Iowa. A shortwave passing
north of the area today will drag this front through the area
this afternoon and into the evening. The boundary will then
stall out across southern portions of the area. This boundary
on Sunday will separate the higher moisture air from the drier
air. Nonetheless, we will see highs again in the 80s, but with
drier air than today. With that boundary in place across the
south, we could see some thunderstorms redevelop along the front
later in the day and move east towards us late.

Most of the impactful weather will likely be ongoing at 00z
tonight as the cold front moves through the area. Guidance has
CAPE building ahead of the front to around 2000 J/kg this
afternoon. Shear looks very weak, so updraft organization is not
expected. Pulse like storms are expected if they develop. The
main question today is forcing. The main upper level forcing is
way north, so the front and daytime heating will be the main
drivers for thunderstorm development. CAMs have either a broken
line of storms or not much with the exception of the highway 20
corridor. Dprog/Dt of the HRRR shows run to run variability with
some having convection down to highway 30 the rest further
north. The NAMnest has convection all the way through the CWA.
Think the best chance for storms is highway 20 north. In a nod
to the NAMnest, did keep schc south through I80. Am not too big
on severe today. Could see near severe wind gusts and hail,
especially due to the steeper lapse rates, but don`t expect
cells to have much longevity to really get going.

&&

.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 /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 109 PM CDT Sat May 18 2024

VFR conditions are expected through the period. Winds will
slacken tonight and then could become gusty again later in the
period. There is a very low (<20%) chance for thunderstorms at
CID and DBQ this afternoon. There are disagreements between
guidance about this occurring. As such, have left out of the
TAFs at this time.

&&

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

&&

$$

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