Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 140747

Area Forecast Discussion
National Weather Service Quad Cities IA IL
247 AM CDT Mon Aug 14 2017

Issued at 246 AM CDT Mon Aug 14 2017

Warm advection is now taking place over the Midwest, noted by both
the increase in nearby showers and thunderstorms, but also by the
marked increase in surface dewpoints since last  night.  Just 24
hours ago, dewpoints in the upper 40s were common in our CWA, and as
of 2 AM, we are seeing widespread dewpoints in the mid 50s to lower
60s.  The elevated warm front has been active in north central and
western Iowa overnight. The main questions today are whether this
will hold together into eastern Iowa this morning.


.SHORT TERM...(Today and Tonight)
ISSUED AT 246 AM CDT Mon Aug 14 2017

Models are split on whether this activity will last past 15Z today,
but all are running too slow on the eastward progress. This faster
progress than models had indicated will result in much higher pops
going this morning in eastern Iowa than earlier forecast, in fact if
the line can maintain good coverage, we may see a categorical
coverage event this morning over eastern Iowa. Despite this over all
QPF should be light this mornings as cell movement is quite fast
to the east around 35 mph. The showers and storms should dissipate
near the Mississippi River to the western Illinois counties by
mid morning as the LLJ decays. Cloud cover from the morning
activity will likely linger over the north half of the area this
morning, which then will likely set up a boundary in the I-80
corridor counties. This differential heating / outflow boundary
may be the focus for additional afternoon and evening storms. Any
storm that can form would have 30 to 40 kts of shear to work with
and modest CAPE values around 1000 to 1500. Thus, a strong storm
is possible, and a brief severe storm cannot be ruled out. A lack
of forcing will keep pops limited to the chance range this
afternoon, but if any mesoscale forcing can roll out along the
boundary, a cluster of storms or two are possible. Highs today
will be limited by clouds north to the upper 70s to lower 80s,
while the south half sees more sun, and likely drier conditions
through the afternoon, resulting in highs reaching the mid 80s.

Tonight, the loosely defined front will remain over the area, with
low pops continuing as isolated to scattered storms will remain
possible in isentropic lift over the boundary. Lows will remain
milder under the more widespread cloud cover and higher dewpoints.
Lower 60s north to mid 60s central and south will give the night a
more typical summer night`s feel than recent nights.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 246 AM CDT Mon Aug 14 2017

Active weather pattern expected through the long term as more August
like weather returns across the area.  Warm air and moisture will be
in place across the area along with a sfc boundary that will lead to
convection through the end of the week.  A brief stint of quiet
weather is forecast for the weekend before another round of active
weather for next week.  Most chances of rain with the exception of
Wednesday, look to be driven by mesoscale forcings, making it
difficult to time and locate showers and storms in the long term.

Tuesday... Stalled out frontal boundary lies across the CWA. Overall
lack of forcing will keep chances for rain and thunderstorms
isolated in nature.  Diurnally driven thunderstorms look possible in
the vicinity of this boundary.  Overnight, the better H85 forcing
remains west of of the area, likely leading to showers and storms
advecting into the area overnight.   Tuesday night into Wednesday
morning, some models hint at a band of waa precip across the area.
With the better moisture transport to the west, think the chances of
this are low.  Regardless, if convection to the west doesn`t fire
then we could likely see convection overnight towards Wednesday AM.

Wednesday...Ongoing convection could lead to limited chances for
strong to severe thunderstorms Wednesday afternoon.  Convective
debris could lead to cooler temps and thus lower instability.  What
is certain is that the area will see rain.  PWs above 2 inches
across the area along with sufficient moisture transport, a wave
through the area, a surface boundary and a nocturnal LLJ think that
heavy rain seems plausible across the area.  Current thinking is
that multiple rounds of showers and storms are possible Wednesday
across the area.  As far as severe chances go, the GFS has limited
shear, whereas the NAM has sufficient for organized updrafts.  This
shear is dependent on the wave structure which is different in each
model.  Therefore, my confidence in severe weather is low at this
time.  There are a lot of moving parts in this forecast, expect the
forecast and confidence to change as mesoscale features become more
readily apparent.

Past Wednesday...Largescale pattern stays zonal for the most part.
There are discrepancies between the models in this pattern so the
forecast past Wednesday is low confidence.  Guidance does agree that
Friday into Saturday look quiet across the region.


.AVIATION...(For the 06Z TAFS through 06Z Monday Night)
ISSUED AT 1138 PM CDT Sun Aug 13 2017

Confidence is highest that KCID/KDBQ will be affected with a few
decaying showers and possibly a rumble of thunder after 12z
Monday, with low VFR ceilings. Scattered storms are expected to
develop along a weak boundary by late afternoon. All TAF sites
could be impacted, but highest probability remains at KCID/KDBQ
and have left other sites dry.




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