Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 251748
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1248 PM CDT Tue Jun 25 2019

...18Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 315 AM CDT Tue Jun 25 2019

A few showers were noted in northern IA with a lone pesky shower
in Jackson county IA which is slowly fading. Otherwise, skies were
clear to partly cloudy.

A cold front extended from western MN to northern NE.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 315 AM CDT Tue Jun 25 2019

Severe storms possible late this afternoon/evening with very large
hail and damaging winds.

Today into this evening: Forecast soundings indicate a capping
inversion through mid afternoon which should suppress any
convection. Meanwhile, sunshine should push temperatures in the
mid 80s with dew points in the mid 60s. This will build up SBCAPES
to 3000-4000 J/kg, sfc- 3km shear increases to 45 knots (strong)
especially in our southern cwa, and freezing levels 12,300 ft agl
which is ideal for hail. This sets the stage for severe storms to
develop late this afternoon through the evening hours. This is
when the cap breaks as moisture convergence increases ahead of an
advancing front, a short wave arrives and the convective
temperature has been reached. With the strong shear and high CAPE
very large hail is possible along with damaging winds. This will
be especially true in any supercell that forms. Eventually storms
that congeal into clusters/lines would enhance the damaging
winds. Forecast sounding suggest tennis ball size hail (perhaps
larger) and 70+ winds are possible. An isolated tornado or two is
also possible. SPC has a slight risk for severe storms with
enhanced risk just to our sw.

Overnight: Convection gradually ends as forcing shifts off to our
east. Lows will be in the lower to mid 60s.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 315 AM CDT Tue Jun 25 2019

Beginning on Wednesday, ridging will be building so a pretty warm
day is in store for the area. Despite good warming at the surface,
temperatures aloft will also be warming, with 850mb temperatures
reaching 20-21C by 00Z Thursday. The warming aloft will likely keep
much of the area capped through the day as it will be hard to reach
convective temperature. Thermal profiles from forecast soundings do
indicate that convective temperatures may be reached to cause
isolated to scattered thunderstorms late in the afternoon/early
evening. Plentiful instability in place, so thunderstorms are
possible if convection is able to develop but not anticipating much
of a severe threat with deep layer shear in the 20-30kt range. Also,
the mean winds will be less going to the south into the ridge axis,
so while any activity over the northern CWA will move ok to the
east/southeast, anything going south will have much slower movement
and could produce some isolated heavy rains. At this point not
expecting any widespread activity.

Wednesday night into Thursday the top of the ridge will be placed
over the Upper Mississippi River region. The low level jet does
pulse up over the plains and focuses into eastern South Dakota
and western Minnesota. There is quite the spread in model
solutions on if there will be enough convergence at the nose of
the LLJ to develop convection. The CAP will likely remain in place
so if elevated convection doesn`t develop it could be a rather
quiet night. Essentially, confidence is quite low on the
occurrence on showers and storms and the areal extent hit by rain.

On Thursday, the models are in agreement with a fairly potent
shortwave trough moving over the ridge to provide precipitation
development from Thursday through Friday morning. Chances for
thunderstorms will be highest over the northern half of the forecast
area generally along and north of I-80. In fact, the strongest
forcing with this shortwave trough will be further north so the
highest chances for rain will be up over Minnesota, Wisconsin and
far northern Iowa. Lots of instability to work with as MU CAPE
values are indicated to be 5K-6K as temperatures in the 80s and
dewpoints around 70 degrees are expected. With deep layer shear at
or less than 30kts, not expecting supercells locally, but can`t rule
out a severe MCS moving across the area Thursday night if things
come together right and storms are able to develop into a line and
become surface-based.

Following the Thursday system, ridging builds into the region over
the weekend, with a hot and humid conditions expected. Temperatures
in the mid 80s to the low 90s is looking likely as 850mb
temperatures soar to 23-24C. Generally dry conditions are expected
at least Friday and Saturday as the ridge builds and shifts the
storm track for any MCS activity to the north. There may be a
breakdown slightly of the ridging allowing energy to push southward
into Iowa and Illinois by Monday and Tuesday so thunderstorm chances
return.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
ISSUED AT 1240 PM CDT Tue Jun 25 2019

At least scattered storms likely to develop this evening into
early overnight, with a weakening cap ahead of a sagging cold
front. This has been handled with VCTS wording at all sites for
now. Several of the CAMs have shifted the storm track further
north into areas south of I-80, which if occurs would lead to
better coverage and likelihood of impact at BRL terminal, and
possibly MLI and CID. Will continue to assess convective trends
and be ready to amend if needed. Storms will have a risk for large
hail and damaging winds. Conditions are likely to go into lower
MVFR to IFR for a time with any storms. Outside of the
precipitation expect VFR conditions. Gusty SW winds 15-30 kts will
taper off this evening to light and variable.

&&

.HYDROLOGY...
Issued at 315 AM CDT Tue Jun 25 2019

While rain continues to be in the forecast for the next week there
looks to be enough of a variety in the placement of the heavier
rains that a concentrated area to cause extensive river rises is not
currently expected. Therefore, on the tributaries, those that are
still seeing rises should expect the rises to level off and start
falling in the next few days. Along the Mississippi River, impacts
of the rain may be negligible with a slight delay in the
recession expected for most locations, with receding levels
continuing.

There is enough uncertainty in the rainfall forecast though and with
plentiful moisture to work with that could cause heavy downpours and
slow moving storms, anyone with interests on rivers should stay
tuned to later forecasts for any changes.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Brooks
AVIATION...McClure
HYDROLOGY...Brooks


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