-- Discussion containing changed information from previous version are highlighted. --
149
FXUS63 KDVN 231746
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1246 PM CDT Thu May 23 2024

...18z Aviation Update...

.KEY MESSAGES...

- A pleasant day is on tap today across the area, with lots of
  sunshine.

- A line of thunderstorms is expected to move through the area
  late tonight, which could bring some strong to severe
  thunderstorms with it, with additional chances of showers and
  storms to redevelop Friday afternoon.

- A quiet start to the Memorial Day weekend is expected for Saturday,
  with more chances of showers and storms on Sunday. Some
  storms Sunday could be strong to severe.

- Active conditions will continue into Monday before drying out on
  Tuesday and Wednesday.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 423 AM CDT Thu May 23 2024

If you have outdoor plans, today will be a great day! An area of
high pressure, which has settled across the Ohio River valley early
this morning, will result in dry conditions under mostly sunny
skies. Some diurnal cumulus clouds are expected for areas along and
north of Interstate 80, with southerly winds around 10 to 15 mph.

Late tonight, after midnight, we are expecting an MCS to develop
ahead of an upper-level trough that will gradually become more
negatively-tilted with time. A mid-level shortwave trough will
enhance large-scale forcing for ascent, along with a 30 to 40 kt
southerly low-level jet. Most-unstable CAPE values per the HREF
ensemble mean and various deterministic guidance should be around
1000 to 2000 J/kg, with deep-layer shear around 25 to 35 knots.
Steep mid-level lapse rates should also be in place, so we are
expecting mainly a wind and hail threat with this overnight MCS. As
such, SPC has expanded a Marginal Risk (level 1 of 5) into our
western tier of counties. One thing to watch for with this MCS is
the potential for mesovortex tornadoes to develop along the line. In
general, the motion of the MCS will be from west to east, with RAP 0-
3 km shear vectors oriented more southwest to northeast. If any
convective elements can translate northeastward, which some guidance
is suggesting, concurrently with a surge/bowing segment of the line,
there could be some embedded tornadoes with this threat. Generally,
the timing of this MCS in our region is between 6 AM and Noon Friday.

Attention will then quickly turn to another round of convection
Friday afternoon and early evening. A surface cold front is expected
to sweep through the area from west to east, and given southerly
flow/WAA in the wake of the MCS, dew points are expected to increase
to the lower to middle 60s. Additionally, some temperature recovery
is expected to occur behind the MCS, which will help temperatures
warm to the upper 70s to near 80 ahead of the front, leading to
destabilization. Deep-layer shear doesn`t appear to be as strong,
due to a lack of LLJ dynamics, but instability appears to be
greater, with mixed-layer CAPE values around 1500 to 2500 J/kg.
Steep mid-level lapse rates should remain in the area ahead of the
front, as well. With this said, SPC has introduced a Slight Risk
(level 2 of 5) generally for areas along and east of the MS River,
with a Marginal Risk elsewhere. The main hazards will be strong
winds and large hail, once again, with a secondary threat for an
isolated tornado.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 423 AM CDT Thu May 23 2024

Eventually, the thunderstorms from Friday afternoon will move off to
the east by the evening hours, leading to a quiet night Friday night
as an area of high pressure settles in. Skies should be partly to
mostly sunny on Saturday as the high pressure dominates the area.
Eventually, conditions will become more active for Sunday and
Monday, as a low-amplitude mid-level trough develops over the
Intermountain West region and approaches. There is some uncertainty
on how things will evolve on Sunday, given some differences in the
ensembles on the speed and strength of the trough. WPC cluster
analysis appears to show differences in the 500 mb heights and
anomalies, with the GEFS a bit more bullish on a strong trough,
while the ENS and CMCE are weaker on the height anomalies. The
strongest signal for any strong to severe thunderstorms appear to be
along and south of Highway 34 in our southern CWA, given the ECMWF
EFI indicates values between 0.5 to 0.7 there, suggesting a lower-
end severe potential. Just before this discussion was sent, SPC sent
the severe outlook for Sunday, and they have broadened the going
Slight Risk to now include most locations along and south of Highway
30. The better upper-level jet dynamics does appear to remain well
to our south in the southeastern MO, southern IL, KY, TN region,
where there is an Enhanced Risk.

Our active pattern isn`t over though! Monday appears to also have
chances of showers and storms in our region, as the aforementioned
trough finally moves over us. The threat for severe weather should
remain south of us, closer to the base of the trough, as we will
have more of a northerly flow regime. Monday could be a gusty day,
but we are not outlooked for severe weather at this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
-- Changed Discussion --
Issued at 1232 PM CDT Thu May 23 2024

VFR conditions are expected through midnight before a
thunderstorm complex moves through the region late tonight and
early Friday morning. PROB30 groups continue to be utilized to
identify the time periods most favorable for storms, and have
been added in this TAF for KMLI/KBRL where confidence is
increasing for storms.

Southerly winds around 5 to 10 knots are expected through this
evening, with a few gusts up to 20 knots.
-- End Changed Discussion --

&&

.HYDROLOGY...
Issued at 1030 PM CDT Wed May 22 2024

Watch/Warnings:

Issued a Flood Watch for Cedar River at Cedar Rapids for
potential to reach into the minor flood category in about 36 to
48 hours.

Canceled the flood warning for the English River at Kalona. It
crested near 14.2 feet earlier this afternoon and fell below
flood stage during the late afternoon. It will continue to
fall.

Most of the river forecasts are starting to be based on routed
flow. Some attenuation is still possible as the crest wave makes
its way through the river systems over the next two to seven
days. Because of this, confidence in some forecasts, especially
those forecast to reach flood stage or a respective flood stage
category beyond day 4, remain lower.

Continued the watches for the Wapsi at DeWitt and the Cedar at
Conesville which have over 2 days before reaching flood stage.
Warnings continue at Anamosa, Marengo, and Sigourney with no
category changes.

Overall, this evenings crest forecasts have come in slightly
slower and at or lower than prior forecast levels. Fore example,
the Skunk River at Sigourney is now a half foot lower with a
forecast crest a half foot over the Major stage.

Forecast adjustments and possible additional watches/warnings
will be made Thursday morning. Stay tuned.

&&

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

&&

$$

SHORT TERM...Schultz
LONG TERM...Schultz
AVIATION...Speck
HYDROLOGY...14