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Area forecast discussion...updated 
National Weather Service quadrant cities Iowa Illinois
331 PM CDT Thursday Aug 21 2014

issued at 211 PM CDT Thursday Aug 21 2014

As of 2pm CDT a surface low had moved into west central Minnesota
with a warm front stretching from the surface low to msp and then
southward to Kalo to kbrl. South of that warm front dewpoints were
in the lower to middle 70s with temperatures in the middle to upper 80s.
A remnant mesoscale convective vortex was moving eastward across Iowa with rain showers
and isolated thunderstorms along and to the north of Interstate


Short term...(this evening through friday)
issued at 211 PM CDT Thursday Aug 21 2014

Models are in good overall agreement with the placement of
features but model initialization appears to be too far south with
these features. The main forecast concern over the next 24 hours
will be chances of precipitation and temperatures.

Mesoscale convective vortex continues to move eastward across eastern Iowa this afternoon
with continued scattered rain showers and isolated
thunderstorms north of a line from Fairfield to Galesburg. Expect the
showers and thunderstorms to exit to the east as lift associated
with the mesoscale convective vortex exits into Illinois by 00 UTC.

A low confidence forecast over the next 24 horus as disturbances
moving across the region provide weak lift for shower and
thunderstorm initiation. There are several flies in the ointment as
convective potential will be limited by cloud cover from decaying
convection. The NAM...GFS...and Gem all agree in overspreading the
region with lift this evening with much weaker lift from the
European model (ecmwf). It will also appear that track of lift may be too far to the
south given the placement of vorticity maxima in the models. The
high resolution convective models continue to fester showers and
thunderstorms along the warm front and warm advection Wing through
06 UTC on Friday with the coarser models moving an mesoscale convective system across the
region between 06 and 12 UTC on Friday. Will leave 30 to 40
percent probability of precipitation in the forecast for this.

This lift will pass to the east by 12 UTC on Friday and will
expect thunderstorms to come to an end by this time. Temperatures
for Friday are some concern given the lingering clouds of the last
couple of days and their effect on our temperatures. Expect middle
and high level clouds to linger across the region through the day
on Friday working to inhibit the solar insolation and have thus
lowered temperatures by a couple of degrees. If clouds linger or
are thicker high temperatures may need to be lower by a few more
degrees. Another disturbance will arrive from the west late in the
period with increasing chances of showers and thunderstorms.

Long term...(friday night through thursday)
issued at 211 PM CDT Thursday Aug 21 2014

The broad ring of fire pattern will continue through early
Saturday...before the upper pattern becomes more amplified as the
large Bermuda high shifts west and becomes stronger.
Then...eventually the upper ridge will shift east allowing a
stalled front from Kansas through Wisconsin to move east. The result
will be many days of low chance probability of precipitation...with dry weather most likely
Saturday night through Sunday evening. Like mentioned
yesterday...though low confidence exists in any period...the weather
is high impact. Our forecast could easily go two ways on several
days...either the mesoscale convective system stays north resulting in hot and humid
conditions and potential heat advisory levels of heat index...or
like today...mesoscale convective system remnants keep the County Warning Area cooler.
will be difficult to impossible to have a day to day high confidence
going this mesoscale processes with nightly mesoscale convective system activity
will determine the position of the west to east front.

Our forecast is hot...certainly worthy of advisory should it
verify...however given low confidence on any days mesoscale convective system placement...we
will hold off on issuing a headline at this time. We can take this
day by day...especially since today has not been near advisory
criteria. In the end...this forecast will either verify heavy rain
and storms or advisory heat...but not both.

The front eventually moving into the region Monday...should bring
another good chance for storms...and until its passage...the threat
for near advisory levels of heat will also persist.


Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1236 PM CDT Thursday Aug 21 2014

A middle level cloud are moving across eastern Iowa ahead of a
disturbance moving into the central part of the state. Regional
radar showed scattered showers and thunderstorms moving into
eastern Iowa and northwest Illinois mainly to the north of
Interstate 80. Ceilings and visibilities were VFR at all taf sites
with the exception of kdbq were MVFR ceilings were in place.

Showers and thunderstorms will continue through approximately 21
UTC ahead of the current disturbance moving across the Iowa.
Ceilings should remain VFR at kcid and kmli but there may be
periods of MVFR visibilities in showers and thunderstorms. Kdbq will
continue to fluctuate between VFR and MVFR and drop as low as LIFR
as the stronger showers and thunderstorms move through the region.
Another round of thunderstorms will be possible overnight
beginning prior to 06 UTC but the placement of these thunderstorms
is a problem as they may be farther to the north as the warm front
lifts out of the area. Expect a middle level deck to overspread the
region Friday morning after 12 UTC depending on where the
thunderstorms track. Winds will shift from southerly to
southwesterly after 12 UTC on Friday in the wake of the overnight


Dvn watches/warnings/advisories...


short term...cousins
long term...Ervin

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