Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 162328

Area Forecast Discussion
National Weather Service Quad Cities IA IL
628 PM CDT Fri Jun 16 2017


Issued at 330 PM CDT Fri Jun 16 2017

Broad westerlies with embedded vort max`s/short waves continue to
align acrs the plains and upper Midwest for a convectively active
period into the first half of the weekend. Slight or higher severe
thunderstorm risks continue for portions of the local area tonight
through Sat night. Then a cool down with drier weather still on
track for Sunday into early next week. Then warmer air along with
new storm chances return by mid to late next week.


.SHORT TERM...(This Evening through Saturday)
ISSUED AT 330 PM CDT Fri Jun 16 2017

Tonight...Local CAPES have reloaded back into the 2k-3k J/KG range
during the afternoon heating period. Eyes are focused on the
wave/MCV currently rolling eastward out of SD and into Northwestern
IA. Convergence along slightly elevated WAA wings currently driving
sctrd showers and some storms acrs northwestern IA. As this activity
continue to move east along the IA/MN border, it will encounter
increasingly unstable air acrs northeastern IA and flare up over the
next few hours. Latest thinking suggests that this will be where
most of the storms that will effect the local area will come from,
feeding south and southeastward during the evening and overnight
period similar to last night`s convective event. More and more
parameters such as optimum llvl thermal MCS track and propagation
vectors, suggest that the other convective system or clusters that
will look to develop soon acrs the convective spawning grounds of
eastern Neb into far western IA, will evolve and propagate
southeastward more into MO than hitting the heart of our local area.
But part of it may still clip the far southwestern CWA mainly after
midnight, although the southern CWA may be more open to the
spiraling and stratifying out northeastern flank of this system as
it plunges into the heart of MO.

As for the initial storms that will move down form the north and
effect the local area, an ensemble timing of several of the latest
available CAMs suggest them making it down acrs the HWY 20 corridor
after 7 PM, and then really expanding south and east through
midnight/1 AM down to I80. As with last night`s storms, several of
them could be severe with damaging wind gusts/outflows and Hail of
an inch or more in diameter. Extent of the PWATs and shear also
support localized heavy rain swaths of 2 inches or more where the
storms propagate. This may make the heavy rain hit areas of last
night, generally from Independence IA, east-southeastward to
Monticello and south of MT Carroll in northwestern IL, susceptible
to localized flash flooding or nuisance water issues if they get
hit by a line of storms again. Will keep the severe storm wording
ongoing generally in the slight risk areas for tonight. Low temps
similar to last night, may be cooler in rain-cooled storm outflow or
a touch warmer in the south if the storms miss to the southwest.

Saturday...Morning convective debris and it`s erosion will be a
determining factor on instability build up by afternoon for the
possible significant severe weather event Sat afternoon and evening.
Will still bank on ambient temps warming into the mid to upper 80s
with an isolated 90 here and there, combined with higher sfc dpts
pooling ahead of an incoming cool front to make for CAPE values of
2000-3500+ J/KG by mid to late afternoon. Heat index readings of 95
to near 100 degrees especially south of I80.

As for afternoon convective initiation, assessing several latest run
solutions suggest a bit later timing than previous day runs, possibly
after 4 PM. And initiation placement has also changed to possibly
right overhead or acrs the western CWA from mid to late afternoon.
Just a few solutions like the 4KM WRF erupt storms off to the
northwest of the CWA by late afternoon. Thus it is appearing more
and more like a mid afternoon through mid evening event, with
seasonably strong low to mid level wind fields  and more than
adequate vertical shear profiles to drive severe storms.

Kinematic and thermodynamic profiles suggest evolving bowing
segments acrs the area with the potential for significant straight
line wind damage swaths, possibly of 80+ MPH in apex max`s. High
WBZ`s and FZL`s make for a marginal hail threat, but some signs to
support the development of mesovortices as well on the nose of
mature bow echoes. All in all, current model assessment and potential
supports the enhanced severe thunderstorm risk acrs much of the DVN
CWA for tomorrow afternoon for a potentail widespread moderate to
higher end damaging wind event.   ..12..

.LONG TERM...(Saturday Night through next Friday)
ISSUED AT 330 PM CDT Fri Jun 16 2017

Behind the front, much cooler air will settle into the region.
Sunday will be noticeably cooler and more comfortable with highs in
the 70s and dew points in the 50s.

On Monday and Tuesday, can`t rule out scattered afternoon showers or
even a clap of thunder or two in the northwest flow aloft, so have
kept a slight chance of thunderstorms for the afternoon, although
neither widespread nor severe storms are expected.

By mid-week, northwest flow aloft will flatten into a more zonal
pattern, resulting in returning heat and humidity.  More significant
and widespread storm chances will then return by Wednesday night as
a front lays out across the area.


.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
ISSUED AT 624 PM CDT Fri Jun 16 2017

The period will begin with quiet weather, before an organized
strong line of storms moves in from northern Iowa, into southeast
Iowa and northwest Illinois. This line will move quickly, and will
bring a period of strong northwest winds, heavy rain, and possibly
small hail. After the line moves through late this evening, VFR
will return as we wait for the next line of strong storms due in
late Saturday afternoon and evening. That line will originate in
central Iowa, and race east through the entire area, with wind,
heavy rains, hail, and even a few tornadoes. Outside of storms,
south to southwest winds around 8 kts will prevail.




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