929
FXUS63 KDVN 022339
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
639 PM CDT Tue Jul 2 2024

.KEY MESSAGES...

- Flash flood watch is in effect for much of the area until 1
  AM. Very heavy rainfall is possible with any storm through
  tonight. There is a Moderate Risk (level 3 of 4) for excessive
  rainfall and flash flooding generally for our parts of SE IA.
  A Slight Risk area encompassed the rest of the area.

- Severe thunderstorms are possible 3 PM to 10 PM, with all
  hazards possible. The Severe Risk is highest (level 3 of 5) in
  our southwest CWA.

- Showers and storms are possible on Independence Day as a warm
  front lifts north through the area followed by a cold front.
  There is a Marginal Risk for the western third of the CWA.

- Moderate to Major River Flooding continues, with further
  changes to river forecasts expected as we transition from
  predicted rainfall to observed rainfall over the next 36 hrs.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 320 PM CDT Tue Jul 2 2024

Not much has changed with the going short term forecast. We
have expanded the Flood Watch to include the NW IL counties.
Heavy rain will be likely with any storm that develops as well
as in areas that see multiple rounds of storms. A strong wave
will move across the area tonight pushing a cold front through
the area. The level of moisture in the air is extremely high and
will increase as a LLJ aims into the area. A band of PWATs of 2
to 2.5 inches will be moving across the area late this PM and
tonight. By this evening, near record or record PWAT values
will be possible for our area! The HREF has 2 to 2.4 inch
PWATs initially across the NW CWA with it translating across
the southern, and especially southwestern, CWA during the
evening into the late night. WPC has introduced a Moderate Risk
for excessive rainfall and flash flooding in parts of our
western and southwestern CWA counties in IA.

A warm front is lifting into the area this afternoon. Satellite
has shown a good degree of sunshine across much of the CWA.
There is a wide range in temps across the area with upper 60s in
rain cooled areas along highway 20 to the mid and upper 80s
south. Dew points around 70 are seen in those southern areas
with higher values in south central IA. MLCAPE of 2000-2500 J`kg
are estimated just south of the warm front. This could further
increase to over 3000 J/kg. As SPC indicated, there is moderate
deep layer shear evident on TOP sounding of 40 kt of 0-6 km
bulk shear. This could be enhanced along the frontal boundary,
so the position of the boundary will be critical to monitor. All
modes are in play, with damaging winds, tornadoes, and large
hail all possible. Damaging winds with water-loaded downbursts
possible.

This is expected to affect our NW CWA 3 to 6 PM, and into the
Dubuque to Iowa City to Ottumwa areas 5 to 7 PM, and then along
and east of the MS River in the 7 to 9 PM time frame. The severe
potential is expected to decrease after dark and as the main
line of storms moves into the eastern CWA. SPC has issued a
Tornado Watch for much of the area except our northern IA
counties, and Stephenson, Hancock and McDonough in IL until 9 PM.

Precip chances exit the area NW to SE overnight. Dry conditions
are expected Wednesday with sunshine.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Issued at 320 PM CDT Tue Jul 2 2024

Wednesday night...The next upstream short wave/upper trof will
look to propagate eastward acrs the northwestern plains, with
some LLVL baroclinic tightening in convergence zone to the lee
of this process from acrs KS into MO. Frontal and storm outflow
from earlier in the day also to enhance the baroclinicity from
west-to-east acrs these southern areas. With nocturnal southerly
LLJ impingement on the LLVL front, the MCS spawning grounds
appears right now to be acrs KS into western MO, with resultant
convective system possibly propagating acrs MO into southern IL
through Thu morning. Some chance northeastern flank may make it
acrs the southern DVN CWA if even in an slightly elevated
fashion and will need POPs for that potential. We probably won`t
need anymore rainfall in those areas after tonight, so it could
be hydro-sensitive.

Thursday the 4th...We could have more showers and storms developing
and creeping further northward up toward I80 Thu morning on the west
or northwestern flank of the southern IL/SE MO MCS if southwesterly
LLJ streams up that portion along with ongoing short wave lift.
Locally heavy rainfall again a possibility over areas that probably
by then will be run-off/flood sensitive. As the upper trof axis
continues to approach acrs central IA, there may be further
northward sctrd convection developing acrs central into eastern IA
along and inverted sfc trof Thursday afternoon into the evening.
With the projected slow movement of the upper trof, sctrd to
isolated showers/storms may linger well into the night. The
potential for strong to severe storms is uncertain at this time, but
there may be some adequate shear. Thursday high temps challenging
with the cloud and precip possibilities, but will advertise 50
percentile low 80s for now.

Friday...Longer range projections suggest upper low complex to
meander eastward acrs WI, with cool pool aloft effects making for
isolated to wdly sctrd instability showers possible acrs the area,
especially north of I-80. Ambient cumulus, a few showers and the
cool pool itself may keep temps in the 70s to around 80, so a below
normal day for July.

Saturday and Sunday...Medium range ensemble patterns hint at rather
broad upper troffiness establishing or more accurately getting re-
established acrs much of the upper midwest by another digging
northern stream upper wave into the upper MS RVR Valley. Hopefully
most of Saturday will be dry ahead of this incoming process with
moderating temps back into the 80s. There may be a few showers and
storms in the north Sat night, but as the upper trof axis slides
overhead, Sunday afternoon and evening may be a better chance for
isolated to sctrd showers and storms to occur. Seasonable temps in
the low to mid 80s Sunday.

Early next week...Upper jet and synoptic scale feature progs suggest
the longer wave upper trof to linger and even deepen acrs much of
the mid to upper MS RVR Valley this period. This would allow for
wdly sctrd shower and storm development in the afternoon heating
under this feature. The unorganized buoyancy pop up type precip
warrants only low CHC POPs at this juncture inn time. Near
seasonable to somewhat below normal temps this period.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 639 PM CDT Tue Jul 2 2024

IFR conds in a line of severe thunderstorms moving through the
taf sites this evening. There will be locations with 55-65 kts,
along with isolated tornadoes and torrential rainfall. A couple
of hours afterwards there will be some storms still lingering.
Later tonight into Wednesday VFR conds return with west winds
around 10 kts in the wake of the front.

&&

.HYDROLOGY...
Issued at 455 PM CDT Tue Jul 2 2024

New Today:

Maquoketa River at Manchester is in a Warning now for Minor
flooding.

Mississippi River at Keokuk is now expected to crest in Major
Category.

Discussion...

Overall the forecasts along the MS River have been increased and
are trending to rise slightly faster than prior forecasts.
Locations from Dubuque to Keokuk are expected to crest over their
respective Major Flood Stage levels. At Gregory Landing, a crest
in the Moderate category is expected. The crest is forecast near
Dubuque and Bellevue on July 4th and 5th, with sites from
Fulton to Keokuk seeing a crest between July 6th and 8th.

On the Maquoketa at Manchester, recent heavy rains from earlier
today and rain expected this evening is expected to push it
over flood stage late tonight and early tomorrow morning. It
should drop below flood tomorrow afternoon.

Showers and storms tonight area expected to produce torrential
downpours as we are seeing a very moisture-laden air mass moving
across the area. In addition, some areas may see repeated rounds
of heavy rain-producing storms. Rainfall totals of 1 to 3
inches are possible across much of the area tonight, with
locations south and west of a line from Cedar Rapids, to Iowa
City, to Mount Pleasant, to Memphis possibly seeing 2 to 4
inches or more! There is a Moderate Risk (level 2 of 4) for the
aforementioned area. Flash flooding will be possible. Seek
higher ground if you get a warning and never drive into flood
waters!

Observed rainfall amounts in the past 24 hours upstream of
DeWitt were not as high as forecast. The crest is still expected
to be in the Major flood category, but will be delayed and
slighly lower.

Additional rises are expected on the Iowa, Cedar, English,
Wapsipinicon and Maquoketa river basins.

Additional flood watches and warnings are possible over the
next 24 hours.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flood Watch until 1 AM CDT Wednesday for IAZ040>042-051>054-
     063>068-076>078-087>089-098-099.
IL...Flood Watch until 1 AM CDT Wednesday for ILZ001-002-007-009-
     015-016-024>026-034-035.
MO...Flood Watch until 1 AM CDT Wednesday for MOZ009-010.

&&

$$

SHORT TERM...14
LONG TERM...12
AVIATION...Haase
HYDROLOGY...14