422
FXUS63 KDVN 151755
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1255 PM CDT Thu Aug 15 2024

.KEY MESSAGES...

- Ongoing mainly elevated MCS on track, with minimal severe
  risk.However, heavy rainfall with the 1.9 to 2.1 inch PWAT
  feed indicated by SPC mesoanalysis still looks like the main
  impact this morning. Ponding of water in urban areas still
  looks feasible due to high rainfall rates.

-  A severe risk remains for this afternoon and evening with all modes
   of severe weather possible if storms can develop locally/in
   the DVN CWA. The most likely time frame for severe storms
   looks to be 4 to 10 PM.

- After a chance for a few isolated showers on Saturday, a
  pattern change will bring mainly quiet weather over the rest
  of the weekend and for the first half of next week.
  Temperatures look to be near normal.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 325 AM CDT Thu Aug 15 2024

Today...Large upper wave/MCV seen on several types of imagery
currently rolling acrs western into central IA ATTM, with leeside
warm air advection wing elevated MCS the main show locally. Brunt of
other south to southwestern flank convection will continue to feed
south and southeastward acrs MO along better instability gradient.
But the local activity will continue into mid morning before
supportive 20-30 KT south/southwesterly LLJ diurnally diminishes.
Looks like a low chance for any severe/precip loaded microburst
winds this morning, but the high PWAT feed mentioned above fueling
high precip rates will produce swaths of 1-3 inches of rain by the
time it winds down later this morning. Thus ponding water and some
nuisance urban/small stream flooding still possible.

Then the same uncertainty comes into play of how fast the
convective debris decays to allow for the potential warm up of temps
in the 80s and sfc DPTs in the 70s to make for high instability with
model projected SBCAPEs of 3000-4000+ J/kg. MLCAPEs may breach 3000
J/kg.  These kind of buoyancy levels with the main upper trof axis
and sfc front approaching from the west inducing effective shear
values of 35-45 KTs could be trouble if sctrd convection can take
off locally. All modes of severe including tornadoes would be
possible, and large hail up to golf ball size. But again with the
debris needed to clear/thin in time to get the heating and those
CAPE values, as well as the air getting worked over currently, a lot
of convective uncertainty exits. Fcst soundings show convective
temps in the mid to upper 80s, and fcst high temps very challenging
with the potential of values ranging from the mid 70s to mid/upper
80s. Could also see the scenario where very little or isolated
convection occurs on the fringes of the DVN CWA and more coverage
areas/prime convective initiation grounds take off to the east and
south of the local fcst area. But still with the chance of isolated
to sctrd strong storms firing in the CWA by late afternoon or early
evening, with have to cover with the adequate CHC POPs. Again if
they go locally, expect supercell structures and all modes of severe
possible with the southern into central CWA the most likely
initiation zones.

Tonight...After the evening storm/shower chances or activity
decreases, westerly post-frontal sfc winds will help temps drop into
the 60s through Friday morning. Will bank on lingering cloud cover
and the west wind speeds themselves to limit any fog production, but
it may still have to be kept in mind acrs the heavy rainfall areas
and sfc winds decouple. Spotty to isolated showers may linger in the
south and east to after midnight in lingering lift zones adjacent to
the passing boundary.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 325 AM CDT Thu Aug 15 2024

Friday...Model ensembles continue with the idea of the upper trof
evolving into a seasonably large cut-off upper acrs the northwestern
GRT LKS at week`s end.  Cyclonic steering flow wrapping around this
feature, with embedded vort spokes and more importantly steepening
low to mid level lase rates will likely produce isolated to sctrd
afternoon into evening showers and even some thunderstorms. The
northeast half of the DVN fcst area will be more at risk of this
activity. Fcst soundings show developing inverted-V soundings, and
other thermodynamic/kinematic vertical profiles that would support a
stronger cell being able to produce hail and downburst wind gusts.
Even a passing shower may produce wind gusts of 40-50 MPH if the 40-
45 KT top of the mixed layer is correct. The deep mixing profiles
will make for breezy west winds Friday afternoon, and make the most
of the thermal profiles for warm high temps in the mid to upper 80s
in many locations.

Saturday through Sunday...Latest suite of medium range ensembles and
upper jet progs now suggest the upper trof to remain adjacent to the
area enough to produce more isolated to sctrd afternoon showers in
the east on Saturday. Then eastward trof migration and northwesterly
steering flow amplification acrs the mid to upper MS RVR Valley
should make for a dry and seasonable Sunday.

Monday through Wednesday...Longer range progs suggest higher
amplified northwesterlies to the lee of large plains/Rockies upper
ridge complex, making for near to slightly below seasonable temps.
Western GRT LKS sfc ridge to prevail with fair weather. The area may
then be suspect to a clipper type wave in the steering
northwesterlies for a precip chance sometime by mid next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1239 PM CDT Thu Aug 15 2024

IFR to MVFR ceilings with low clouds will continue this
afternoon with some breaks towards the late afternoon and
evening. If some clearing is realized, some showers and
thunderstorms are expected to develop and traverse the area
during the evening hours. This would bring some MVFR conditions
in storms, but otherwise VFR conditions should prevail. MLI and
BRL will have the best chance for seeing showers or storms so
introduced a prob30. CID might see some storms near 00Z before
they more east, but opted to leave mention out due to the
uncertainty of development and placement. Overnight some
visibility reduction into MVFR category may be seen, but left
mention out of TAFs at this time.



&&

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

&&

$$

SHORT TERM...12
LONG TERM...12
AVIATION...14