652
FXUS63 KDVN 121024
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
524 AM CDT Mon May 12 2025

...Updated for 12z 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
  heat (low-mid 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 TUESDAY NIGHT/...
Issued at 310 AM CDT Mon May 12 2025

A cutoff low, which has been loitering in the Lower Mississippi
Valley over the past few days, will open up /weaken/ while
meandering northward into the Ohio Valley over the next couple
of days. This system despite passing largely to our south/east
will bring some changes to our weather over the next couple of
days with increasing cloud cover, and steadily rising dew points
leading to a more humid airmass (particularly for Tuesday as
PWATs climb to around 1.3 inches, which would be above the 90th
percentile for all DVN raobs for May 13th per SPC sounding
climatology). This increase in moisture along with some
instability that develops (0-3km MUCAPE around 1000 j/kg) will
support diurnally driven convection primarily on Tuesday (30-
50% coverage). Wind shear will be quite weak and thus not
expecting any organized activity or severe threat, but very
weak steering flow and the anomalously high PWATs will
support some heavy downpours of which the 00z HREF LPMM picks
up on with its depiction of some small pockets of 1-2" rain
amounts. We could certainly use the rain. Unfortunately, not
everyone will see rain and any amounts >1" look to be localized.

As for temperatures, most notable will be the transition to much
warmer nighttime lows (upper 50s and 60s) aided by the
increase in low level moisture and cloud cover. Daytime highs
will be mainly in the 80s both days, although confidence is
somewhat lower for exact highs on Tuesday being modulated
by convection and cloud cover which could limit highs to the 70s
for some.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 310 AM CDT Mon May 12 2025

Mid level ridging will build in behind the departing low for
Wednesday, which will foster a strong warm-up during an already
warm week. Increasing SSW low level flow and attendant warm
advection will boost 925 hPa temperatures into the range of 20C
to 24C, which with superadiabatic low level lapse rates will
support highs from 83F to around 90F. A very summer-like feel!
Some diurnally driven airmass convection also can`t be ruled out
Wednesday afternoon, but the coverage should be fairly isolated
with the building heights aloft.

Still have to keep an eye on the potential for nocturnal organized
convection /MCS/ moving into parts of the area late Wednesday
night and early Thursday morning. The convective spawning grounds
look to be across parts of the Dakotas and Nebraska by late
Wednesday afternoon, as large scale ascent increases atop a
surface cold front. Should convection in these areas grow
upscale and become surface based then there`s the potential
for it to slide E/SE along a lifting warm front, riding the
conceptually favorable +19C to +24C 850 hPa thermal gradient
for MCS evolution/track with an ideal LLJ of 25-35 kt depicted
veering into the area by 12z Thursday. This could contain some
severe wind threat if this were to materialize, but confidence is
low on this scenario/potential.

Thursday, a warm front will lift through the area setting the stage
for a day of windy and unusually hot conditions. The ECMWF
Extreme Forecast Index (EFI) depicting values greater than 0.8 and
positive Shift of Tails (SoT) values to 1 for Max T on Thursday
continue to support the idea of an anomalous or very unusual event,
which has been a consistent signal for the past several days. In
fact yesterdays 12z ECMWF EFI is indicating values of 0.95 to 0.99
into west central Illinois meaning that 45 of the 50 ECWMF ensemble
members are predicting an extreme event! This supports the idea of
record highs in the low to mid 90s for some, especially
south/east portions of the service area. Records at the main
climate sites (BRL, CID, DBQ, MLI) are 90-94F for May 15th,
established back in the early 1940s (end of the Dust Bowl
years). Given the strong anomalous temperature signal it begs
the question of whether could we see something ridiculous happen
like somewhere reach awfully close to 100F, especially after
seeing what happened yesterday in parts of E North Dakota and NW
Minnesota which saw highs of 97F to 100F! Closer inspection
shows 925 hPa temperatures were in the range of 25C to 30C in
those areas yesterday, which a local office study years ago
(covering years 1874 to 2012) showed that 925 hPa temp range
correlated to nearly all of the 100 degree days in that span at
MLI except for two. And the reason this is pointed out is
because the Canadian model from 00z does show 925 hPa
temperatures climbing to 25C to near 30C by Thursday evening.
Past experience suggests though that the Canadian model can
exhibit a warm bias, but the ECMWF deterministic has 925 hPa
temperatures around 25C to 26C. Also, several of those ECMWF
ensemble members referred to earlier do show highs in the upper
90s at MLI, BRL and MQB. The point to be made with all of this
is that we should be preparing for a brief but potentially intense
period of heat Wednesday (near 90F) for some, but especially
Thursday particularly from the QC Metro and points to the south
and east!

The other thing we`ll be monitoring for Thursday is the potential for
severe storms with all of the heat and instability, and a strong
shortwave ejecting across the Upper Midwest in negative-tilt fashion.
Kinematic and thermodynamic parameter space continues to be very
favorable for severe weather. The main problem is the potential for
a strong capping inversion/EML to overspread the area while the better
forcing for ascent is focused more to our north/west. This could limit
storm development until a cold front moves in, but timing of this is
uncertain and if the frontal passage is more at night will it be able to
sufficiently erode the cap and allow storms to develop. No question the
environment would support severe storms with possibly all hazards IF
storms were to develop, and that`s the main question and uncertainty
which continues to preclude us from much messaging of the SPC 15% risk
(Slight risk). Stay tuned in the next few days as we learn more details
and can better refine this risk.

Beyond, there`s low confidence on the forecast in particular timing/
location of rain chances. This all hinges on just where the front
will likely hang up as it parallels the mid/upper flow, and then
serve as a focus for additional periodic shower/storm chances as more
energy ejects out from the west and interacts with the low/mid level
baroclinic zone and moisture. For now have let the NBM ride for the
weekend, which leads to a dry day Saturday before the rain chances
return on Sunday into Monday. Temperatures will also be cooling down
closer to seasonal normals heading through the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 520 AM CDT Mon May 12 2025

VFR conditions are expected through the period with easterly winds
generally 5-15 kt. An isolated shra/tsra is possible near to
south of BRL and MLI terminals 20z-01z as moisture increases
with a lifting low over the Lower Mississippi Valley, but the
probability (10-20%) remains too low for mention.

&&

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

&&

$$

SHORT TERM...McClure
LONG TERM...McClure
AVIATION...McClure