253
FXUS63 KDVN 240229
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
929 PM CDT Sun Jun 23 2024

.KEY MESSAGES...

- Heat to temporarily return early this week, with high
  confidence in 90s for highs south and west of the Quad Cities
  on Monday, and then a higher ceiling (mid 90s) and with heat
  index readings (around 100) on Tuesday, but uncertainty with
  any morning thunderstorm residual effects

- Potential (30-50%) for semi-organized thunderstorms late Monday
  night into Tuesday morning mainly north of Highway 30, with
  higher confidence in thunderstorms late Tuesday afternoon into
  Tuesday night especially along and south of I-80 that would pose
  at least a scattered heavy rain and severe threat (risk level 2
  out of 5).

- Rivers expected to rise through midweek from upstream rainfall
  last week and possibility of heavy rainfall on Tuesday and
  Tuesday night (25% chance of exceeding one inch).

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 255 PM CDT Sun Jun 23 2024

High pressure of 1013 mb will scoot over the area tonight. Warm
air advection (WAA) aloft will already be resuming overnight
and will likely result in some clouds developing late into
early Monday morning. Cannot rule out patchy fog (~10 percent
chance) in northern locations late tonight, even though not
climatologically favored, just due to wet ground and forecast
lows a few degrees below current mid 60s dew points.

Gauging by HREF and RAP solutions, any clouds early Monday
morning should depart northeast of the area as the low-level
thermal ridge builds back in. Forecast 850 mb temperatures by
mid-afternoon are 21-22C, and with full sunshine and southerly
winds, would not be surprised if a few locations in southeast
Iowa and northeast Missouri tag 94-95 degrees for a high. Dew
points are not forecast to have climbed much from the mid 60s
yet, so heat index readings are forecast in the upper 90s.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Issued at 255 PM CDT Sun Jun 23 2024

The Plains upper level ridge will start to be dampened some
again on Tuesday as a strong, slightly positively-tilted trough
tracks across southern Canada into the eastern Great Lakes
region. The quasi-zonal flow atop the ridge will be unsettled,
with a lead impulse Monday night over the Upper Mississippi
Valley. The primary synoptic front will be dragged southeastward
over the area on Tuesday afternoon and evening by the deep (sub
990 mb) low north of the Great Lakes. This is the most
favorable synoptic signal for thunderstorm coverage and
potential hazards.

For Monday night into Tuesday morning, confidence is highest in
warmth, with southerly winds of 10-15 mph not allowing much
temperature drop at all. Lows look to solidly be in the 70s
(likely to fall just short of record warm mins for the calendar
day Tuesday, June 25). Along the still strengthening front in
Minnesota into western Wisconsin on Monday evening, convection
should develop over a several hour period. Orientation of shear
vectors to the front is oblique to perpendicular, so it may
take a while to grow upstream into an organized convective
complex. However, most CAMs support an organizing morphology
with 50+ kt of mid-level flow during peak low-level jet time.
Thickness diffluence and Corfidi vectors support a southeast
propagation of cold pool-driven, organized convection, and could
mean thunderstorms moving into the northern to northeastern CWA
after midnight. Wind would be the primary threat if this
evolves, along with possibly a localized flood risk with any
backbuilding activity on the far southwest edge of such a
convective feature that would be over our already wet north CWA.

Influences of convection, even if its just a northerly wind
shift with rain-cooled outflow, will have effects on convective
evolution for Tuesday afternoon and evening. This naturally
lowers the confidence on convective details. Despite that, given
the warmth and moisture resulting in substantial instability
combined with the synoptic scale cold front moving in,
thunderstorms are likely (>60%) to redevelop along and south of
the general I-80 zone and evolve east-southeast. This may
include our entire CWA too, but again depends on details from
Monday night. The less influence on late Monday night/Tuesday
morning, the more of our area that should see Tuesday afternoon
and evening thunderstorms.

The heat on Tuesday will be part of the fuel for any
thunderstorms on Tuesday. Using NBM membership, there is 40-60%
chance of exceeding 95 degrees south of I-80, and with 850 mb
temperatures of 22-25C, that certainly is in play using
climatology for 95+ degree days in our region. Also acting as
fuel are precipitable waters around two inches (upper 5th
percentile), setting the stage for precipitation-loaded
downdrafts and potential flash flooding issues. Shear vector
orientation with respect to the front or any outflow-associated
boundary is forecast to be more oblique, and can see a clustered
convective evolution possible. As noted in previous AFD, the
forecast Corfidi vector orientation indicates training, slow-
moving storm potentail as well, but again confidence is on the
lower end on where that may be in our CWA late in the day and
throughout Tuesday evening. Currently forecast potentail for
rainfall to exceed one inch is 15-25 percent from west to east
across the CWA.

Beyond, the temperatures will ease back to normal Wednesday and
Thursday, before the GFS and ECMWF and a large membership of
their ensembles provide a return to a more active pattern. There
is a signal for a deeper synoptic scale system closer to our
latitude in the Midwest late in the week, which would mean
severe and heavy rain potential and the CSU machine-learning
probabilities already hint at these too.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 630 PM CDT Sun Jun 23 2024

VFR conditions are expected through the TAF period with periodic
SCT-BKN clouds 5-8kft agl. Northwest winds around 10 kt will
become light and variable after sunset into early Monday
morning, with the transitory passage of weak surface high
pressure. By Monday afternoon south to southeast winds will
increase to over 10 kt, with occasional gusts around 20 kt at
CID and possibly DBQ.

&&

.HYDROLOGY...
Issued at 929 PM CDT Sun Jun 23 2024

No significant changes for the Cedar River basin this evening
with the new forecasts. The rise on the Cedar River at Cedar
Rapids has been slowed some and still may reach 14 ft or
Moderate flood stage early Friday.

For the Mississippi, flood watches have been converted to flood
warnings for Dubuque Lock and Dam, Camanche, and Rock Island
Lock and Dam sites this evening. Additional warnings can be
expected in the coming days.

.Previous Discussion.

The Mississippi River is expected to reach flood stage at
multiple locations, including the Rock Island gage, by the
middle of this week. Long term we expect the Mississippi to
reach Moderate and/or Major flood stages the week of the Fourth
of July, with the crest at the Rock Island gage possibly
reaching just over 18 feet early on the Fourth of July.
However, a larger margin of error should be taken into
consideration when forecasting precipitation amounts and
locations in the 7-10 day timescale. Watches are currently out
for most of the Mississippi River and warnings will follow in
the next few as a clearer picture is drawn on what
precipitation and routed water we have coming downstream. In the
latest forecast package, we have opted to upgrade Gladstone and
Burlington to a River Flood Warning, aided by the recent
rainfall north of the area.

The Rock River is also expected to reach flood stage in Joslin,
with an increase noted into Action Stage at Moline. A River Flood
Warning has been issued for Joslin in this latest forecast
package, which is forecast to hit flood stage tomorrow
afternoon. We will continue to see additional rainfall through
this coming week, which may lead to further fluctuations in the
river levels. If heavy rainfall is seen, then increases can be
expected.

&&

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

&&

$$

SHORT TERM...Friedlein
LONG TERM...Friedlein
AVIATION...McClure
HYDROLOGY...Gross/Gunkel/Wilson