285
FXUS63 KDVN 011701
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1201 PM CDT Mon Jul 1 2024

...Updated for 18z Aviation...

.KEY MESSAGES...

- Beautiful day ahead of us, with temperatures in the 70s and
  increasing clouds. High pressure will slowly push east today,
  with increasing moisture ahead of the next wave.

- Several rounds of showers and storms are expected from Tuesday
  night through Wednesday morning, with chances retuning again
  Wednesday night through Thursday. Severe weather and flash
  flooding are both possible with any storms, especially Tuesday
 PM, as repeating storms are expected.

- Unfortunately, Independence Day is looking to be a wet day, as
  a warm front brings the potential for widespread showers and
  storms once again. Too soon to determine severe risk.

- Moderate to Major River Flooding continues, with further
  changes to the forecast expected due to fluctuations in the
  QPF forecast.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 240 AM CDT Mon Jul 1 2024

High pressure will be the rule through the day, leaving us with
another beautiful day, with temperatures in the 70s throughout.
Today will be very similar to yesterday, with the main difference
being an increase in cloud cover. This increase in cloud cover can
be attributed to increasing moisture, as ridging builds overhead and
LLVL southerly flow kicks in. The best of the moisture return will
be west of the forecast area through the day, which is a good thing,
as a large bout of energy pushes through the area today, as a
wave develops over the Rockies. With such dry air in place
today, we are not expecting any precipitation with this.

Tonight, we start to see the moisture increase slowly from the west.
The main focus for this moisture will be along our western border,
especially in our northwest. In these areas, PWATs will quickly rise
into the 1.75-2.00" range, favoring heavy rainfall in any storms
that develop. Guidance does not have the best grip on when we will
start to see precipitation, with the HREF being a good happy medium
at the moment. Currently, the HREF starts to introduce measurable
precipitation to our west around 09-12z tonight, which is about 4-
7am local time. Thus, this will be quite late, with chances
increasing through the day tomorrow. This will be discussed more
below. We are not expecting much on the side of excessive
rainfall with any storms that we get tonight, as convection
seems to be more scattered in nature, rather than widespread
heavy rainfall.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 240 AM CDT Mon Jul 1 2024

Much of the forecast below is from the previous forecast package, as
they covered this event very well. Some updates were made,
resulting from latest trends in guidance, but the big picture
largely remains the same. Up front, one of the more notable
changes was the introduction of an Enhanced Risk (level 3/5)
for Severe Weather in southeast Iowa, with all hazards in play.
Also, with several chances for heavy rain this week, we may need
to start considering headlines for the Flash Flood Potential,
especially as we approach Tuesday night and then again Thursday.

More widespread showers and storms are expected Tuesday afternoon
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. This will be especially true
through the nighttime hours, which seem to be the best chance
for widespread heavy rainfall. The primary concern for this
period remains heavy rain and flash flooding. NAEFS and ENS
continue to support PWATs climbing to 1.75 to around 2.00 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 1.00 inch from Tuesday evening
through Wednesday AM, especially across the northwest 2/3rds of
the service area, with 60-90% favorability amongst guidance.
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 2.00
inches would yield potentially higher amounts of around 4.00
inches. With rivers rising, we will be watching this heavy rain
potential closely, as this will lead to fluctuations in the
river forecast. In addition, the significant moisture advection
(IVT) and a southwesterly LLJ of 40 kt could contribute to
backbuilding and an elongated MCS, resulting in 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, as deep layer
shear 0-6km increases to 35-45+ 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 growth into a line of storms, transitioning
to 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
a focus for redevelopment and an earlier severe/flash flood
threat Tuesday PM. Otherwise, Tuesday evening/night would be
most favored for the severe. 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 a surface warm front passes north into
the area 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
2.00+ 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. With this forecast in mind,
we may be preparing to see more of nature`s fireworks, rather
than actual fireworks.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1157 AM CDT Mon Jul 1 2024

VFR conditions expected to persist through this evening. There
is a slight chance (10-20%) for a brief shower late this
afternoon and early evening at KCID and KDBQ, however there is a
copious wedge of dry air sub-cloud and so it may be more
sprinkles than anything with no impacts. By later tonight and
Tuesday morning (after 06z through 15z), the shower and storm
chances will be increasing with a veering SW low level jet and
abundant moisture advection with the greatest chances at KCID and
KDBQ requiring prevailing SHRA/TSRA mention, with lower chances
PROB30 at KMLI while potential appears too low for mention at KBRL
right now. MVFR to local IFR conditions (mainly for visibility) will
be found in the storms and heavier showers. Winds will be predominantly
from the E/SE around 10-15 kt and then occasionally gust 20-25 kt.
LLWS is possible at KCID and KDBQ late tonight/Tuesday morning, but
too much uncertainty as winds may not decouple completely tonight and
marginal criteria precludes mention with the 18z TAFs.

&&


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

&&

$$

SHORT TERM...Gunkel
LONG TERM...Gunkel/McClure
AVIATION...McClure