Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 211957

Area Forecast Discussion
National Weather Service Quad Cities IA IL
257 PM CDT SUN AUG 21 2016

Issued at 257 PM CDT Sun Aug 21 2016

NW winds on the northeast periphery of high pressure centered over
southeast Kansas were advecting a cool, dry airmass into the region
this afternoon. Temperatures were only in the lower to mid 70s with
dewpoints in the 50s across the forecast area. Aloft, a trough axis
was over the Great Lakes, low over southern British Columbia, and a
broad ridge in between over the northern rockies.


.SHORT TERM...(This Evening through Monday)
ISSUED AT 257 PM CDT Sun Aug 21 2016

Main focus is on temperatures as high pressure migrates over the
region overnight with warm advection setting in on Monday. Scattered
to broken cumulus in the weakly cyclonic flow currently over the
forecast area will dissipate with sunset, followed by a clear and
cool night as the surface and upper level ridges push eastward. With
the center of the high progged to be over southern IL by 12z and
weakly confluent, subsident flow aloft, the low levels should remain
decoupled through the night. Nearly calm winds and a deep dry
airmass should lead to temperatures at least as low as the
widespread lower 50s observed from the MO river valley westward the
previous night and have thus stayed on the low side of MOS guidance
and the previous forecast with lows around 50 north to the mid 50s
south. Any fog looks likely to be shallow in nature and not worthy
of mention.

A southerly return flow resumes Monday, but little change in low
level moisture fields is expected based on the airmass source region
over the central and southern plains where dewpoints were mainly in
the 50s today. Thus, anticipating only few to scattered diurnal cu
for mostly sunny skies. Mixing into the warm advection underway at
850 mb, temperatures should at least reach the lower 80s. This will
also lead to gusty south winds by afternoon, perhaps higher than
guidance suggests, in the range of 15 to 25 mph over the western
half of the area.

.LONG TERM...(Monday Night through Sunday)
ISSUED AT 257 PM CDT Sun Aug 21 2016

Main forecast concerns in the long term is the boundary and a couple
of waves that transect the area through the long term.  Heavy rain
and isolated strong storms could be possible Tuesday night into
Wednesday evening.

Tuesday, ridge will be moving just east of the CWA as the southwest
flow returns to the area.  This will aid in bringing more moisture
and warmer temps to the area.  Tuesday will be mostly dry as a wave
moves across the central plains for the upper Midwest late in the
day and overnight into Wednesday.  Guidance has been consistent with
this occurring.  Slight differences in timing are still at issue,
however the overall placement is not. Split H5 flow, with deeper
wave to the north and a stronger shortwave over the central United
States will aid in bringing a cold front south into the Mississippi
River valley.  H85 jet will set it`s sights on western Iowa and then
veer into eastern Iowa Wednesday morning.  This, coupled with the
cold front will lead to widespread rain and convection, especially
across the Iowa and MO counties.  As the quick wave moves out of the
area, the progression of the cold front will be slowed. When the
deeper wave lumbers across Canada and south into the US the cold
front will become more progressive. This will set up a zone for
showers and thunderstorms through the area on Wednesday and into
Thursday before fropa clears us out.

Heavy rain and strong thunderstorms are possible overnight Tuesday
with a lingering heavy rain threat through Thursday.  PWAT values
near 2 inches and Corfidi vectors favoring training storms will be
possible Tuesday night. The limiting factor to heavy rain is that
the LLJ veers through the period.  That veering establishes good low
level shear across the area.  The GFS and NAM both have 35+ kts of
deep layer shear, strong enough for organized updrafts.  The 12Z NAM
is more bullish with the shear, especially in the low levels as
surface winds back in response to a meso low that the model tries to
form across the area. While this is likely convective in nature, it
does show that the environment would be conducive for strong to
severe storms if a strong enough MCS can form.  Right now the SPC
has the area in a marginal risk for severe weather.  WPC has a 5 day
rain total near 3 inches across the southern CWA.  Models range in
totals from 1 to 3 inches for this period as well.  Flooding could
definitely become a concern into Wednesday, especially if some areas
see repeated rounds of thunderstorms.

Past Thursday morning, few changes to the long term were made.
Pleasant conditions return again, before the flow becomes more
active and warmer, more humid air makes its voyage into the area.
Another wave is possible this coming weekend.  Chances for rain and
thunderstorms return.


.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
ISSUED AT 1209 PM CDT Sun Aug 21 2016

A ridge of high pressure will provide VFR conditions through the
forecast cycle as it migrates east across the region. Northwest
winds around 10 kts will diminish to light and variable, then
become light southerly Monday morning. There is a low potential
for late night and early morning fog, which at this time appears
likely to be shallow and not impact any of the TAF sites.


.DVN Watches/Warnings/Advisories...


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