849
FXUS63 KDVN 221128
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
628 AM CDT Sat Jun 22 2024

.KEY MESSAGES...

- An active weather day is on tap today, with increasing chances
  of strong to severe storms late this afternoon through the
  evening, hot and humid conditions, as well as the potential
  for flash flooding

- A much calmer weather pattern will develop for Sunday, which will
  largely continue through Thursday

- Expect a brief interruption to the quiet conditions for
  Tuesday and Tuesday night

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 359 AM CDT Sat Jun 22 2024

Early this morning, the last of a cluster of showers and
thunderstorms continues to exit the region to the northeast, which
will lead to a brief period of dry conditions overall in our region.
We are watching a line of sub-severe thunderstorms over north-
central Iowa that has formed along the nose of a 30 to 40 knot
nocturnal low-level jet. We will need to watch this activity as it
is expected to move across our northern areas after sunrise this
morning.

Our region continues to be on the northern fringe of a large upper-
level high pressure system, currently situated over the southern
Great Plains region. Large-scale flow indicates a poleward
component, with increasing heat and moisture in our area today,
which should result in hot and muggy conditions. Additionally, a
compact mid-level shortwave impulse will eject from the Great Basin
region towards the Upper Midwest, which will set the stage for
increasing chances of showers and storms areawide as an attendant
cold front sweeps through the area. There is lots to talk about
today, so let`s break this all down:

* HOT AND HUMID CONDITIONS

Moisture from the Gulf of Mexico will advect northward around the
large upper high, which will continue to support dew points into the
upper 60s to lower 70s across most of the region. Both the ECMWF and
GEFS ensemble averages for 850 mb temperatures give values around 18
to 20 degrees C, which is a few degrees warmer than they were
yesterday. While we are expecting the morning convection to move
through our northern areas after sunrise, which should help keep
temperatures cooler there, our southern areas are more likely to
remain dry and see some daytime insolation to go along with the
already high humidity. High temperatures today will range from the
middle 80s north to the lower 90s south, particularly for areas
south of Interstate 80. Heat indices between 95 to 100 degrees are
expected for our southern areas, so we have issued a Heat Advisory
for areas along and south of I-80, excluding Bureau and Putnam
counties in Illinois. The advisory goes from noon through 7 PM
tonight.

* HEAVY RAINFALL/FLASH FLOODING POTENTIAL

The high moisture content in the air will also lead to pretty
efficient rainfall producing storms today, with a threat for flash
flooding in areas that receive repeated rounds of precipitation.
With the influx of Gulf moisture, PWAT values are progged to be 1.7
to 2.0 inches for most locations, so the strongest storms will be
capable of generating rainfall rates of 1 to 2 inches per hour,
which is quite impressive! In fact, as the cold front moves through
the region, moisture pooling along the front could result in PWATs
in excess of 2 inches. Per the SPC sounding climatology for the
month of June, if we can measure a PWAT value over 2 inches off our
evening balloon launch tonight, it would be a top 15 highest PWAT
value for the month of June in the entire period of record, dating
back to 1995! We have maintained the Flood Watch for our northern
areas, especially for areas along the Highway 20 corridor, and we
have actually extended the end time to 03z/10 PM tonight to cover
the cold front convection.

* SEVERE WEATHER POTENTIAL

As the aforementioned cold front moves through area, which the
models have delayed a bit more to having it move through late this
afternoon through the evening hours, the CAMs remain in good
agreement with a line of storms forming along it. Widespread
coverage of storms are expected, so everyone will likely see some
activity from the front. Coincident with the fropa, the mid-level
jet will intensify, with magnitudes around 40 to 50 knots per the
HREF ensemble mean for 500 mb winds. Not only will the deep-layer
shear increase to around 30 to 40 knots, but the surface-based
instability values between 1500 to 2500 J/kg will be evident ahead
of the approaching boundary. Damaging winds continue to be the main
threat with these storms. However, the tornado threat appears to
have increased a bit, with more favorable low-level shear profiles
and more clockwise-curved hodographs than what models were
indicating 24 hours ago. STP values over 1 are also evident in the
HREF ensembles compared to the previous run, so tornado potential
has increased. Large hail will be more of a secondary threat. SPC
has outlooked the entire forecast area in a Slight Risk (level 2 of
5) for severe weather.

Please be weather aware today, especially with so much hazardous
weather potential! Also, with it being the weekend and lots of
outdoor events going on, it`s all the more reason to know your
safety locations at all times.

The cold front will exit the region in the late evening/overnight
hours tonight, which will end the severe threat once it is through.
Relatively cooler air will filter in behind the front compared to
what we`ve been experiencing the last few nights, with overnight
lows in the middle 60s north to near 70 south.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 359 AM CDT Sat Jun 22 2024

Sunday will be the pick day for the weekend, with much quieter
conditions expected in the wake of tonight`s fropa. Models and
ensembles are in good agreement with large upper-level ridging
developing to our west and surface high pressure building across the
western Great Lakes, leading to partly to mostly sunny skies. The
NBM is keeping our area dry Sunday into Sunday night, despite an
upper-level trough just grazing our northeastern areas late Sunday.

The only significant opportunity for showers and storms will be
Tuesday and Tuesday night, as yet another cold front passes through
the area. A look at the convective parameter space indicates
instability to be rather high with a pretty strong signal for
another hot and humid day, but the deep-layer shear values are
pretty meager. The CSU ML severe probs remains bullish on severe
potential for Tuesday, so we will have to keep an eye out for
perhaps another bout of strong to severe storms then.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 628 AM CDT Sat Jun 22 2024

VFR conditions will largely prevail through the afternoon hours
today, with the main focus being on an ongoing line of showers
and embedded thunderstorms that will move through the CID and
DBQ TAF terminals. This could bring MVFR conditions with it.
There will be a lull in showers and storms before a potent cold
front sweeps through the area late this afternoon through the
evening hours today. Strong to severe storms are possible along
this front, with strong winds being the main threat as gusts to
around 40 knots or greater are likely. Based on the general
timing from the high-res models, used TEMPO groups to highlight
the most likely timing of the storms. A wind shift will occur
due to the frontal passage, from the south to southwest ahead of
the front, to more northwesterly behind it. Then, MVFR to
perhaps IFR ceilings will move in behind the front overnight
tonight.

&&

.HYDROLOGY...
Issued at 926 PM CDT Fri Jun 21 2024

Widespread 2 to 4 inches of rain is forecast near the headwaters of
the Wapsipinicon, Cedar, and Iowa river basins in the next 24 hours.
Some localized higher amounts over 5 inches is not out of the
question as well. Much of this rain is expected in a short amount of
time overnight tonight allowing for substantial runoff. As a
result, new forecasts this evening have several sites along the
Cedar going into flood in the next 3 to 5 days. Confidence in
the placement of heaviest QPF remains very low and since it is
still 3+ days out have decided to hold issuing any flood watches
for all sites except for Vinton on the Cedar River.

On the Mainstem Mississippi, heavy rainfall amounts between 4 and 9
inches in the past 2 weeks in southern MN and western WI, will
result in rises through the rest of June and into July. Went ahead
and issued flood watches for portions of the river this evening with
more likely in the coming days.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flood Watch through this evening for IAZ040>042-051>054.
     Heat Advisory from noon today to 7 PM CDT this evening for
     IAZ067-068-076>078-087>089-098-099.
IL...Flood Watch through this evening for ILZ001-002.
     Heat Advisory from noon today to 7 PM CDT this evening for
     ILZ015-016-024>026-034-035.
MO...Heat Advisory from noon today to 7 PM CDT this evening for
     MOZ009-010.

&&

$$

SHORT TERM...Schultz
LONG TERM...Schultz
AVIATION...Schultz
HYDROLOGY...Gross