566
FXUS63 KDVN 110533
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1233 AM CDT Thu Jul 11 2024

.KEY MESSAGES...

- There is a chance (40-60%) of scattered showers and
  thunderstorms this afternoon/evening. An isolated severe storm
  or two will be possible with heavy downpours, gusty winds, and
  funnel clouds the main threats.

- Increasingly humid Friday and into next week. Heat indices
  well into the 90s and even low 100s are forecast Sunday and
  Monday.

- Sunday through Tuesday, while thunderstorms will very likely
  (80%) fail to develop, if they do, severe thunderstorms would
  be possible.

- Moderate to major river flooding continues on the Mississippi
  River with most sites crested or cresting in the coming days.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 258 PM CDT Wed Jul 10 2024

19z WV satellite shows an upper trough advancing south-southeastward
over southern MN with multiple shortwaves rotating around this
feature over SW MN, IA, and NW IL. Per radar and visible/IR
satellite, thunderstorms have already developed in the CWA and two
the our west in S central IA.

This afternoon and evening, expect additional thunderstorms as
temperatures at the surface rise into the 80s and temperatures aloft
cool considerably as the upper trough advances overhead, allowing
MLCAPE to rise to 1000-2000 J/kg. WHile deep layer shear is lacking,
this should be enough buoyancy for stray severe hail to be possible.
Additionally, presence of a surface mixed layer suggests a risk for
a severe wind gust or two and the otherwise unorganized updrafts
collapse, with this risk tempered by the shallow nature of the
surface mixed layer, resulting in DCAPE values of only around 800
J/kg. Finally, given the pattern - an upper trough moving overhead,
a well-mixed boundary layer, and the presence of outflow boundaries
providing areas of vertical vorticity - cannot rule out funnel
clouds and a brief non-supercell tornado.

Moving ahead to tonight, light winds and near-surface moisture
courtesy of the afternoon/evening convection may lead to the
development of fog. With GLAMP/HREF/SREF probs suggesting around a
25-35 percent chance for visibility reductions, perhaps even under a
mile, have introduced patchy fog into the forecast for a few hours
very late tonight.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 258 PM CDT Wed Jul 10 2024

Thursday, last gasp shortwave looks to rotate southward west of
the departing upper trough. A few showers and thunderstorms may
develop, but continued lack of shear suggests the chance for a
severe thunderstorm is very low.

Friday through Tuesday, return flow due to high pressure in the
southeastern CONUS will cause conditions to become noticeably
more humid with dewpoints in the 70s favored by the weekend. As
this occurs, heights aloft build, with the potential result
being triple digit heat index values during the afternoon Sunday
and Monday afternoons.

Along with the potential for hazardous heat and humidity,
multiple ridge riding shortwaves look to eject downstream over
the Upper Midwest Sunday through Tuesday. Given the moist
advection regime described above, MLCAPE may approach 3000 J/kg
as winds aloft increase, with sfc-6km bulk shear perhaps
topping 40 kts Sunday and Monday evenings. All that said, the
operative word in MLCAPE is potential as those warm
temperatures aloft will very likely (80%) keep a tight lid on
proceedings. Thus, while overall pattern - and CSU ML outlooks -
suggest a chance for severe thunderstorms, have only included
thunderstorms of any kind in the official forecast for NE IA and
NW IL those afternoons.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1222 AM CDT Thu Jul 11 2024

A slow moving shortwave will rotate through the forecast area
today, bringing additional chances of showers and thunderstorms.
In the near term, this will be confined to areas north of I-80
and have included a TEMPO at CID for this possibility. South of
I-80, fog will be a concern early this AM with Nighttime
Microphysics channel already showing signs of development. Have
not gone as low as some guidance suggested which was widespread
LIFR cigs/vsbys, but went IFR for now and will continue to
monitor trends this morning. Thunder potential this afternoon
too low for mention at this time, but if it occurred the most
likely terminals impacted would be MLI/BRL.

&&

.HYDROLOGY...
Issued at 124 PM CDT Mon Jul 8 2024

Precipitation in the next few days, especially in Iowa, is expected
to be dry or very light. Thus, routed flow will continue on all of
our rivers.

The Mississippi River is currently cresting at major levels upstream
of Camanche, IA, and near crest through Illinois City.  The crest
may take 1 to as much as 3 days to pass. From Le Claire to
Burlington, the respective crests will commence within the next 1 to
2 days.

Keokuk is now forecast to crest within Moderate Flood category
beginning Friday.  Gregory Landing is forecast to remain near 19.5
feet through the week.

Tributary Rivers:


The Cedar River at Cedar Rapids crested below flood stage and will
fall over the next several days.

On the Cedar River at Conesville, minor flooding will continue. It
will see a secondary crest near 14.4 feet Wednesday night into
Thursday.

The Wapsipinicon River at Dewitt is forecast to remain in
moderate flooding category through late on Friday.

The Iowa River at Oakville is seeing high water levels due to
backwater affects from the Mississippi River. It is forecast to
remain near 11.4 or 11.5 feet through midweek and then rise to near
12.1 feet late Thursday into Friday.

&&

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

&&

$$

SHORT TERM...ARX/77
LONG TERM...ARX/77
AVIATION...Gross
HYDROLOGY...Gunkel