183
FXUS63 KDVN 120422
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1122 PM CDT Sun May 11 2025

...Updated for 06z Aviation...

.KEY MESSAGES...

- Scattered slow-moving showers Tuesday (30-50% coverage) with
  a few t-storms possible.

- A warm week, with a strong likelihood in at least near record
  warmth (low 90s) for part of the area during a windy Thursday.

- A chance within the region for severe t-storms late Wednesday
  night through Thursday given a strong weather system and
  inherent warm air mass, however storm coverage is low
  confidence with this pattern at this distance.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 259 PM CDT Sun May 11 2025

A splendid day for the mothers across much of the Midwest. The
air mass is particularly dry with humidity values between 15
and 30 percent across the area this afternoon. This dry air mass
with surface ridging and a clear evening sky will allow for
larger diurnal range again. Some cirrus from the south late
will keep minimum temperatures up from last night, with upper
40s north to mid 50s south.

The beautiful weekend was provided in part by the rex block
setup which basically is a quasi-stationary upper ridge over a
stationary closed upper low. That low will meander northward
toward our area on Monday, but do think the suppression from the
ridging and inherent dry air mass will stifle much for showers
during Monday, apart from maybe a few along and south of U.S.
Highway 34 during the afternoon and evening. The 850 mb
temperatures warm a smidge over the area from today, and should
support highs a few degrees warmer. If the suppression limits
much for clouds north of I-80 and dew points remain lower than
what short term guidance is indicating, mid 80s look to be
realized along/north of I-80.

&&

.LONG TERM /MONDAY THROUGH SUNDAY/...
Issued at 259 PM CDT Sun May 11 2025

Tuesday:
The northward-tracking upper low will broaden/weaken into
Tuesday as a lobe of its center moves over the CWA. The 500 mb
heights will be 570 dm (basically at normal), and the mid-level
temperatures also near normal. With surface dew points more
confidently expected to be near 60F and higher RH values in the
lower troposphere, inhibition should be overcome for showers
especially during peak heating. The CAPE above -10C (a lightning
proxy) looks to be very limited, but convective temperatures
still should be reached. So the trend for showers continues to
nudge upward with also expansion in area of those PoPs. The
center or pivot of that upper level vorticity lobe would be most
likely to see higher coverage of slow-moving showers that could
provide isolated pockets exceeding one quarter of an inch.

Wednesday:
The air mass becomes a little warmer on Wednesday yielding more
of a "lid" on shower development. Northwest Illinois may still
be able to sprout some, but low confidence in that. Temperatures
should climb a few degrees, maybe even entering the upper 80s
category in parts of eastern Iowa and northeast Missouri.

Wednesday Night-Thursday:
The upper low just offshore of the Pacific Northwest today will
move eastward through the week and re-deepen midweek (near 3
standard deviations below normal at 500 mb heights) as a
subtropical jet becomes phased into the southern side of the
trough. This will help it to go quickly from neutral to negative
tilt on Thursday. This supports warm and windy, and an
environment that conceptually could be conducive to strong,
organized storms most favored at the north end of the
instability gradient during peak heating and into the nighttime
hours. That spatiotemporal aspect is where confidence is low if
things will line up for severe chances for our area.

An already warm air mass will have southwesterly low-level flow
boost it even more with a quick-moving but strong low-level
thermal ridge characterized by 850 mb temperatures of 17 to 21C.
If unaffected by A.M. convection (likely for at least along/south
of I-80), this will support Thursday highs to reach if not top
90 by a few degrees. This is even more strongly supported by the
EC Extreme Forecast Index (EFI) indicating a strong likelihood
in a highly anomalous thermal event centered south of I-80 in
our area. About one third of model guidance indicates highs at
or above 93F in that general area, and low 90s are very much in
play north of there too. With this being still early season
heat (normal first 90F in the Quad Cities is May 30), this would
be in the record territory for our climate sites, and also
something we will have to message more with regard to early
season heat safety if the signal remains.

Regarding thunderstorms, with the upper low deepening and mass
response increasing Wednesday Night over the Plains States into
the Upper Missouri River Valley, there could easily be convective
development (some robust?) Wednesday night in those areas.
Looking at forecast steering vectors and orientation of the
MUCAPE gradient and 850-300 mb thickness diffluence, organized
convection would likely be north of the area. However, it would
be close and at this distance, predictability of any specific
convective motion is low. If this were to produce
clouds/rain/outflow into the northern CWA, temperatures would
likely be several degrees cooler. With the quickly tightening
and evolving pressure gradient and very warm surface
temperatures, gusty winds are almost a given. NBM probabilities
of 35+ mph gusts are on the order of 20-40 percent -- sizable
for 5 days out in the warm season.

Today`s deterministic guidance has had a few trends, and caution
should be used reading into these much at this distance. But
those trends just to note are: 1.) nudged quicker with the
thermal ridge/instability plume (east of our CWA by 00Z Friday)
and 2.) overall system a bit deeper and farther northwest. Those
may seem contradictory, but rapidly deepening systems in the
Midwest with such a strong southwesterly jet (110+ kt at 250 mb)
on its southern periphery can have such an evolution, with the
system dry tongue from the Southwest advecting in drier column
air. This would favor the greater convective coverage east of
the CWA, with even a scenario where most of the CWA sees no rain.
Machine learning-based output comparing past scenarios to the
forecast GEFS and EPS output also indicate the relative maximum
being east of the area. Certainly too early to lock that in
stone, and the SPC Day 5 Outlook for awareness captures the
threat at this distance very well.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1111 PM CDT Sun May 11 2025

VFR conditions are expected through the TAF cycle with E/SE winds
generally around 10 kt that could occasionally gust near 20 kt
Monday afternoon. Isolated shra and tsra can`t be ruled out
near BRL and MLI late Monday afternoon and early evening as
moisture increases with a lifting low over the Lower Mississippi
Valley, but the probability (10-20 percent) is too low for mention.

&&

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

&&

$$

SHORT TERM...Friedlein
LONG TERM...Friedlein/McClure
AVIATION...McClure