266
FXUS63 KDVN 211744
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1244 PM CDT Sat Sep 21 2024

.KEY MESSAGES...

- Marginal Risk for severe storms late this afternoon into
  tonight for the far NW CWA.

- Damp and much cooler for Sunday and Monday with highs in the
  mid 60s to lower 70s, which is slightly below normal.

- Dry conditions are expected to prevail Tuesday through
  Thursday with high temperatures in the low to mid 70s.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 158 AM CDT Sat Sep 21 2024

Today will be the last of the stretch of summer-like warmth in
this stretch, as a cold front approaches the area tonight. In
the mean time, a complicated forecast is in store today, with a
wide spread in short term model guidance surrounding convective
placement and timing.

There were several 00z CAMS suggesting that the convection well to
our south would expand northeastward into our south 1/2 early this
morning.  This trend has yet to begin, with southern storms tracking
east/southeast as of 1 AM. In addition, there is a low level dry
pocket from northeast Missouri through our CWA, thus any rain
processes will need to be elevated through the morning today.

As mentioned in the evening update AFD, there are a handful of CAMS
suggesting afternoon strong storm development today. However,
looking at members that favor this, they all have dew points in the
68 to 72 range along the Mississippi River by early afternoon, with
temperatures in the upper 80s to lower 90s.  This same area is
currently much drier, with dew points in the 55 to 60 range. Thus,
the surface based storm threat is probably over forecast by those
more aggressive models this past evening, and we prefer a timing
more focused on the frontal movement, during the evening hours, and
that should favor a multicell environment rather than supercell. SPC
has continued to show a marginal, level 1 of 5, risk in our
northwestern CWA, once again more focused on the cold frontal timing
tonight.

Storms this afternoon( if they occur) and tonight, are forecast to
have 1500 to 2500 MUCAPE prior to the development of storms, with
some potentail DCAPE available as well. This should favor
strong downdrafts with stronger/tall cores, and potentially
some large hail, through mid level lapse rates are not
particularly steep (6- 6.5).

The overall QPF maximum has now shifted south of our CWA in the mean
guidance with amounts now generally 0.25 to 1 inch, but there
remains some CAMS showing swathes of 1-2 inches for our area.
These amounts could delay some harvesting, but otherwise would
be seen as beneficial rainfall.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 158 AM CDT Sat Sep 21 2024

Sunday, an upper wave will move through the area, with little to no
available surface CAPE, thus, rain or showers/weak storms are
expected to be rather widespread, with moderate amounts under 1
inch possible. The increasing northeast wind, and cold advection
will keep our temperatures steady in the 60s to low 70s Sunday,
and mainly in the 60s for Monday.

The upper trof will influence our area into Tuesday, with some
shower chances continuing in the southern CWA.  As dry air arrives,
the overnight lows will drop to the upper 40s to lower 50s, making
for chilly mornings that reflect the upcoming fall season.

Slow moderation is forecast by late week, along with a slight chance
for rainfall.  Late week highs remain forecast in the 70s, and lows
in the 50s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1235 PM CDT Sat Sep 21 2024

Scattered showers and a few thunderstorms near MLI and BRL are
expected to diminish early this afternoon, with VFR prevailing
at the terminals into this evening. Additional development of
isolated showers and storms are possible from this evening
through early tonight, but with low areal coverage anticipated.
A more widespread area of rain and embedded thunder is possible
late tonight into Sunday morning, which will likely be accompanied
by MVFR/IFR ceilings and MVFR visibilities. Confidence remains
low on the exact timing and location of any storms through the
period.

&&

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

&&

$$

SHORT TERM...Ervin
LONG TERM...Ervin
AVIATION...Uttech