127
FXUS63 KDVN 121958
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
258 PM CDT Mon May 12 2025

.KEY MESSAGES...

- Slow moving showers will move in from the east later today
  into tomorrow. Some thunder is possible with the strongest
  shower.

- 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 257 PM CDT Mon May 12 2025

Closed low over the lower Great Plains and Lower Mississippi
River Valley started to lumber north and east of the area today.
A couple of shortwaves through the flow were leading to
increased lift into the area. In a more atypical fashion we
started to see low level moisture return to the area from the
east today. Dry low level air kept rain at bay for the day and
will likely keep it at bay through the early evening with the
exception of IL south of I-80 where some scattered showers are
possible this evening.

Overnight, expect shower activity to diminish, however, expect
llvl moisture to return. With the upper level low elongating,
expect to see more showers tomorrow. With increased BL we could
see some thunderstorms as well. Most of the area won`t see rain,
however some showers may not move all that fast leading to
bullseyes of heavier rain tomorrow. Really small impacts, maybe
some ponding of water. But not real widespread rain across the
area.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 257 PM CDT Mon May 12 2025

Previous long term AFD remains valid and brilliantly explains
the heat threat we see Wednesday into Thursday. As is typical
with our heat dome set ups we could be on the edge of the ring
of fire and overnight MCSs activity could cause the forecast to
bust. Thursday remains a high bust potential forecast, with high
impacts if it doesn`t bust. The ECMWF and GFS do have timing
differences still, in a nod to uncertainty with Thursday`s
forecast.

Prev Discussion
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 /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1228 PM CDT Mon May 12 2025

VFR conditions are expected through tomorrow mid morning as
better chances for rain moves into the area. Expect MVFR
cig/vsbys and even a chance of IFR cigs with any showers. Low
chance for a rumble of thunder as well with those showers.

&&

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

&&

$$

SHORT TERM...Gibbs
LONG TERM...Gibbs/McClure
AVIATION...Gibbs