744
FXUS63 KDVN 302316
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
616 PM CDT Sun Jun 30 2024

.KEY MESSAGES...

- Cool tonight (near record lows for some?), and one more
  pleasant day on Monday.

- Thunderstorms return to the area Monday night into Wednesday
  morning. These storms will likely lead to heavy rain as
  humidity increases. There is a chance for strong to severe
  storms Tuesday PM.

- Independence Day forecast looks wet with potential
  thunderstorms.

- Moderate to Major flooding is expected on several area rivers.
  Crests could be delayed or altered with any heavier rainfall,
  depending on where it occurs Tuesday through Friday.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 240 PM CDT Sun Jun 30 2024

It`s not hard to be distracted by the weather today, between
Hurricane Beryl (which has undergone rapid intensification over
the past 24 hours into an extremely dangerous Cat 4), and the
absolutely stunning day in progress across our region (temps
10-15+ degrees below normal highs for the date and near 70 to
the mid 70s, compliments of northerly flow off an anomalously
cool airmass across the Upper Midwest and western Great Lakes)!

High pressure will shift from the Upper Midwest to western
Great Lakes by 12z Monday, and will continue to provide
spectacular weather to the region. Tonight, cool conditions
are expected. Portions of far NE Iowa and NW Illinois in
closer proximity to the centroid of the surface high are
expected to be the coolest, as near calm to light easterly
winds and mainly clear skies allow temperatures to fall
into the upper 40s to around 50 (approaching/reaching dew
points at peak heating this afternoon). This may allow for
some patchy radiational fog in river valleys and other low
lying areas, as these readings would be near or just below
crossover temps. Elsewhere, lows will likely be in the lower to
mid 50s with more of an light ESE component to the wind and
eventually some pockets of mid/high cloudiness. These lows
generally in the upper 40s to mid 50s may be near records in a
few locations. More information on record lows for July 1st for
our main climate sites is listed in the Climate section below.

Monday we`ll see an increase in mid/high cloudiness, as warm
advection commences in the wake of departing high pressure.
Winds will increase from the ESE 10-20+ mph, but the trajectory
will be from Great Lakes through Ohio Valley ridge and thus
drier keeping it very comfortable. Some WAA precipitation may
work toward the western counties in our service area in the
afternoon, but a deep reservoir of dry air surface through 800
hPa will limit PoPs below mention, as more likely just sprinkles
if anything. Much of the warm advection will be aloft and
this coupled with some cloudiness at times should net result in
similar highs from those of today (Sunday) near 70 to the mid 70s.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Issued at 240 PM CDT Sun Jun 30 2024

Strengthening southerly flow surface to 850 hPa will continue
to usher in a return of warmer and more moist air into the
region. This along with ejecting lead shortwaves ahead of a
Northern Rockies/Great Basin trough will lead to shower and
storm chances Monday night and Tuesday, with the higher PoPs
(60-80%) favored mainly north and west of the Quad Cities.

More widespread showers and storms is expected for Tuesday
night into early Wednesday, as stronger synoptic forcing aided
by a shortwave aloft and the right entrance region of a 100-120
kt 250 hPa jet steak overspread the Upper Midwest while at the
surface a cold front moves through. The primary concern for
this period remains heavy rain and flash flooding. 00z NAEFS
and ENS continue to support PWATs climbing to 1.75 to around 2
inches by 00z Wednesday, which is 2 to 3 standard deviations
above climatology and approaches the 99.5 percentile or is near
max of their respective climatologies. Ensemble guidance
shows high probabilities of at least 1 inch from Tuesday evening
through Wednesday AM, especially across the northwest 2/3rds of
the service area. However, given the convective nature and
magnitude of the synoptic ascent doubling the PWAT would give a
general idea of the higher limit, which in this case with PWATs
around 2 inches would yield potentially higher amounts of around
4 inches. With rivers rising will be watching this heavy rain
potential closely, as this could delay or change crest forecasts
depending on where it occurs. In addition, the significant
moisture advection (IVT) and a southwesterly LLJ of 40 kt could
contribute to backbuilding and an elongated MCS and a risk of
flash flooding. This flash flood threat looks to be highest
especially across east central and northeast Iowa into
northwest Illinois, where rainfall in the past week has
accumulated 125-200+ percent of normal and soils are saturated.

Severe weather potential may exist by Tuesday PM/evening, as
deep layer shear 0-6km increases to 40-50+ kts aided by the
approaching shortwave trough. Models try to build in the
instability during this time, especially west of the Mississippi
River with MLCAPE increasing to 1000-2000+ j/kg. Initial
supercell potential will exist before upscale to a line of
storms would be favored with a wind threat, provided sufficient
destabilization occurs. As previous shift mentioned, one thing
to watch for is any potential OFBs from Tuesday AM convection,
which could serve as focii for redevelopment and an earlier
severe/flash flood threat Tuesday PM, otherwise Tuesday
evening/night would be most favored. If rain/clouds persist for
much of Tuesday that could limit instability or keep the primary
instability axis further west. Bottom line, extent of
instability and initial placement and timing of the surface
convergence will play a key role in how far east/south the
severe threat reaches.

A brief respite in the wet weather is expected Wednesday AM/PM,
but the emphasis is on brief as the surface boundary looks to
have a play on the area perhaps as early as late Wednesday
night/early Thursday AM with convection potential increasing
(30-60%) south of I-80. Then, the shower and storm potential
increases over the rest of the area on the 4th of July into
Thursday evening, as a vigorous shortwave trough evolves into
a closed low while traversing near the international border to
the north. Ensembles point to PWAT values of 2+ inches pooling
near and south of the boundary supporting a heavy rain threat.
The frontal location will be critical to where this heavy rain
threat eventually sets up, and will bear watching in the coming
days given the ongoing river flooding and saturated soils in some
areas. Probably still a ways off to cancel fireworks, but it
does look likely to have storms around and most of us may have
to rely on Mother Nature to provide the fireworks.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 613 PM CDT Sun Jun 30 2024

A clear, VFR night is in store for Iowa and western Illinois.
Light north winds will gradually switch to east this evening,
then to the southeast and increase to around 12 kts Monday after
sunrise. Some passing altocumulus clouds will brush through
southeast Iowa, with bases well above 6kft tonight and Monday.

Otherwise, though VFR, there will be a chance for some showers
and storms in northeast Iowa, arriving Monday evening, most
likley after 00z Tuesday.

&&

.HYDROLOGY...
Issued at 1135 AM CDT Sun Jun 30 2024

New forecasts this morning for the tributary rivers have come in
slightly lower for the Cedar River at Conesville, Iowa River at
Wapello, and the Wapsipinicon River near De Witt. However, no
changes to the expected flood category were made. The crest on
the Cedar River has gone through Cedar Bluff and should reach
Conesville by Monday morning. A return to an active weather
pattern will bring a heavy rain risk Monday night through
Wednesday that may result in renewed rises on many tributary
rivers. Those with interests along the tribs should monitor
future forecasts, especially Monday evening when the bulk of the
1-3 inch rainfall will be incorporated into the river model.

On the mainstem Mississippi, no change to the expected flood
categories with the new forecasts this morning. Broad crests are
now shown from Dubuque to Fulton LD13 late in the 7 day
forecast. A widespread heavy rain event (1-3" amounts across
much of eastern IA into southern WI) is anticipated in the
Monday evening through Wednesday time frame which may have an
impact on expected rises and delay the crest downstream.
Residents and interested individuals/businesses should monitor
future forecasts for any changes to the river rises.

&&

.CLIMATE...
Issued at 145 PM CDT Sun Jun 30 2024

Record low temperatures for July 1

Burlington......51 in 1918
Cedar Rapids....43 in 1924
Dubuque.........47 in 1995
Moline..........48 in 1988

&&

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

&&

$$

SHORT TERM...McClure
LONG TERM...McClure
AVIATION...Ervin
HYDROLOGY...Gross
CLIMATE...McClure