National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KDVN 230452
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1152 PM CDT Thu Jun 22 2017

...06Z AVIATION UPDATE...

.UPDATE...
Issued at 629 PM CDT Thu Jun 22 2017

At 6 pm CDT, KDVN radar an isolated pocket of spiraling light
rain showers associated with a MCV remnant from last night`s
storms over KS entering southeast Iowa. Further north, a band of
weakening showers that previously had a few embedded weak
thunderstorms, reached from the Waterloo area northeast into far
southwest WI. With the main synoptic cold front still well to the
northwest, and a capped environment over the forecast area, these
features will remain weak through early evening and tonight`s
anticipated thunderstorms have yet to develop.

Have fine tuned the forecast for these features in updates and
will continue to monitor trends this evening for anticipated
upstream storm development.

&&

.SYNOPSIS...
Issued at 323 PM CDT Thu Jun 22 2017

A frontal boundary stretches from central Nebraska northeastward
into northern Iowa and into Southern Wisconsin. Scattered showers
continue north of Interstate 80. Temperatures ranged from the
upper 70s along the Highway 20 corridor to the mid 80s in
southeast Iowa and northeast Missouri. Dewpoints were in the upper
60s to lower 70s.

&&

.SHORT TERM...(This Evening through Friday)
ISSUED AT 323 PM CDT Thu Jun 22 2017

The main forecast concern this period are chances of thunderstorms
tonight into Friday morning. Large scale models are in good
overall agreement and CAMs are resolving the current features a
little better.

Models depict a cold front sliding southeastward across the region
from basically 06 utc to about 09 UTC Friday. The best lift is
slightly offset from the convergence along the front and the best
RH. Surface base CAPE is currently ranging from 1500 to 2500 J/kg
across the region. The better 0 to 6 km shear is just ahead of the
front and will probably need the arrival of the front to initiate
storms across the north and then move southeastward with the front
across the region. The main threats will be hail and winds ranging
from 60 to 70 MPH. For these reasons, there is slight risk of
severe thunderstorms across the region. The convergence of the
front and synoptic lift will be needed to overcome the CAP to our
north and develop thunderstorms that will move into our region.
There is also an isolated flash flood threat with increasing deep
moisture.

This is expected to be a progressive system with the front moving
through and high pressure building into the region for the end of
the work week. Temperatures will be slightly below normal for
Friday.

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 323 PM CDT Thu Jun 22 2017

.Mainly dry, and exceptionally pleasant conditions will be found
from Friday through Monday, as a seasonally strong upper trof digs
over the eastern 1/3 of the country. This upper trof will draw down
a surface high from central Canada, with dry dewpoints in the 40s
and 50s, and highs in the mid 60s to mid 70s over the upper Midwest.
There should be a daily increase in cumulus during the afternoon
hours each day, and with some passing upper energy, some isolated to
scattered showers and weak thunderstorms are possible. However,
despite this rain threat, the days should be viewed as dry days for
the most part. Any rain should quickly evaporate within a few
minutes of falling in the dry air.

Moving on to mid week, after a period of moderation under the high,
moisture is expected to return to the Midwest for Tuesday through
Friday as a series of waves pass through in zonal flow aloft. The
GFS/GEM/and EC all hit the area with a at least 1 if not multiple
MCS during this period. With a sustained southerly flow headed into
the warm front during that period, PWAT values probably will be
seasonally high given the convergence into the upper Midwest.
Therefore, a seasonal risk for both severe weather and heavy rains
is expected in this time frame. As to what days that occur, and
whether it is multiple events, or just one, is going to have to wait
until the pattern evolves.
ERVIN

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday Night)
ISSUED AT 1132 PM CDT Thu Jun 22 2017

At least scattered coverage of thunderstorms is anticipated to persist
overnight ahead of a cold front. Have gone with tempo wording at
most TAF sites trying to target a 2 hour window of highest probability
ahead of the northerly wind shift prior to 12z. Some guidance
continues to suggest MVFR to possibly IFR ceilings in the wake of
the storms and cold frontal passage. While lower conditions can`t
be ruled out given ample low level moisture and cool advection I have
left out any mention as confidence too low given lack of lower ceilings
post frontal per latest obs. Northerly winds may occasionally gust to
around 20 kts on Friday by mid morning through afternoon before
diminishing with sunset, as conditions remain VFR during this timeframe.

&&

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

$$

UPDATE...Sheets
SYNOPSIS...Cousins
SHORT TERM...Cousins
LONG TERM...Ervin
AVIATION...McClure