599
FXUS63 KDVN 210858
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
358 AM CDT Fri Jun 21 2024

.KEY MESSAGES...

- Another hot day expected today, with highs in the lower 90s along
  and south of Highway 30

- Increasing chances (20 to 50%) of showers and storms after
  midnight tonight, with an outside chance of a strong storm

- More robust thunderstorms are expected Saturday afternoon and
  evening, with some strong to severe storms possible

- Generally dry conditions return for Sunday through Thursday,
  with another round of convection Tuesday and Tuesday night

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 356 AM CDT Fri Jun 21 2024

Things have calmed down quite a bit from yesterday evening`s
convection, with largely dry conditions observed across the area. A
low-level thermal inversion, which has developed across our far
northern areas, has resulted in a low stratus deck, and some areas
of fog will be possible early this morning along the Highway 20
corridor.

The overall synoptic pattern hasn`t changed a whole lot over the
last few day, with a large upper-level high anchored over the
southern Great Plains region. We remain on the far northern side of
the upper high, with a low-amplitude trough developing over the
northwestern CONUS and an upper-level jet streak over the Dakotas
into northern Minnesota. The heat dome continues to be strong, with
temperatures expected to warm to the upper 80s north and the lower
90s south for highs. A warm frontal zone continues to be draped
across far northern Iowa into southeastern SD, where a large complex
of thunderstorms has developed early this morning, which should
translate eastward. This complex, plus additional convection
expected later on along the warm front, could graze our far northern
areas later on, which would influence temperatures if they make it
into our area. However, the CAPE gradient does appear to remain
north of us, so the convection is likely to remain anchored along it
and stay away from our region. Humidity today should be slightly
lower compared to the last few days, so although it will be another
hot day, heat indices should remain below 100 degrees, precluding
the need for heat headlines.

Shortwave ridging will become more likely in our region late tonight
as mid-level shortwave impulses sink southward. This will support
increasing chances (20 to 50%) of showers and storms. Both shear and
instability appears to be pretty meager, with deep-layer shear less
than 25 knots and most-unstable CAPE from the HREF less than 1000
J/kg, so more likely non-severe storms should result. Still, there
is an outside chance of a strong storm, and SPC does have a Marginal
Risk, or level 1 of 5, for areas along and north of a Freeport, IL
to Van Horne, IA line.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 356 AM CDT Fri Jun 21 2024

As we go through the day Saturday, the aforementioned low-amplitude
trough over the northwestern CONUS gradually moves eastward with
time, and an attendant surface cold front will sweep through our
area during the afternoon to evening time frame. Instability will
increase to around 1500 to 2500 J/kg of surface-based CAPE per the
HREF ensemble mean, and strengthening mid-level westerlies around 35
to 45 knots will result in deep-layer shear increasing to 30 to 40
knots, so more supportive of strong to severe convection. Low-level
shear and mid-level lapse rates remains a bit more limited, but PWAT
values near daily records (2+ inches) per the SPC sounding
climatology for the Quad Cities area should help support strong,
damaging wind gusts as the main hazard, with large hail and isolated
tornadoes as secondary threats. As such, SPC has expanded the Slight
Risk, or level 2 of 5, for areas along and northwest of a Keokuk, IA
to Sterling, IL line, with Marginal Risk elsewhere. Timing of the
front remains uncertain, given the differences among the CAM
guidance, but confidence remains high for a Saturday afternoon
arrival.

After the front moves through late Saturday night, a much more
pleasant day is expected Sunday, with lots of sunshine and more
seasonal temperatures and humidity. Sunday is definitely looking
like the pick day for the weekend! In fact, the large-scale pattern
appears to support a period of mostly dry conditions through
Thursday, thanks to upper-level ridging developing over the
Intermountain West states and surface high pressure settling into
the upper Midwest. The only other opportunity for showers and storms
appears to be for Tuesday and Tuesday night, as yet another compact
upper-level trough and attendant surface cold front crosses the
area. The timing of the front per the latest global models does
appear to be advantageous for more strong to severe storms,
especially with the CSU ML severe probs suggesting strong to severe
convection with a hot and humid air mass again in place, so we will
need to watch Tuesday as well.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1254 AM CDT Fri Jun 21 2024

Largely VFR conditions are anticipated through the TAF period.
Early this morning, we will mainly be focused on DBQ, where an
IFR stratus deck has developed, evident on the GOES-East nighttime
micro satellite imagery showing the southern extent of this low
stratus along the Highway 20 corridor. It is uncertain just how
persistent that low stratus will linger at DBQ, but the
majority of the model guidance has it staying around 500 ft
through the early morning hours. Some MVFR fog is also possible
there as well for a time this morning. Some isolated storms are
possible this afternoon and evening.

&&

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

&&

$$

SHORT TERM...Schultz
LONG TERM...Schultz
AVIATION...Schultz