Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 232314

Area Forecast Discussion
National Weather Service Quad Cities IA IL
614 PM CDT Wed Aug 23 2017


Issued at 330 PM CDT Wed Aug 23 2017

High pressure was centered over the central part of Iowa this
afternoon leading to early fall like weather. Afternoon fair
weather cumulus clouds have formed across the area. Otherwise
temperatures in to 70s with low RH were reported across the area.


.SHORT TERM...(This Evening through Thursday)
ISSUED AT 330 PM CDT Wed Aug 23 2017

Two main forecast concerns in the short term forecast. The first
is the slight chance for rain across the area tonight into
tomorrow morning as a wave advects south into the Great Lakes and
the other are the temperatures tonight. Guidance is suggesting
clouds but with the clear skies and low Td and at sunset, could
see temps plummet.

All guidance suggests low end QPF across the far northern CWA as a
wave advects in from the NW flow. The HRRR has been consistent
with a band of light to moderate showers across northeast and east
central Iowa towards daybreak. Main concern is that the best H5
forcing is to the north and east of the area and with dry air any
rain that forms will have a hard time making it to the ground.
With low confidence in this occurring, decided to keep schc pops
across the far NE and the rest of the area dry. This will need to
be watched by later shifts to determine if there is a greater
chance for rain later.

As far as temps tonight go, its going to be a race between
temperatures dropping fast and clouds moving in. With temps this
morning in the upper 40s, decided to keep them in the low 50s
across the area. Once the clouds move in think that the temps at
that time will be close to the actual lows. As far as lows went,
went with MOSguide and tweaked a few degrees here or there for

.LONG TERM...(Thursday Night through next Wednesday)
ISSUED AT 330 PM CDT Wed Aug 23 2017

Thursday night and Friday...LLVL ridge will look to maintain acrs
the western GRT LKS, while upper ridge undercutting upper wave/trof
shifts slowly eats acrs the central plains. The jury is still out on
how much low to mid level moisture lee side elevated warm air
advection wing will have to utilize to try and produce some showers
acrs the MO RVR Valley and IA, and suspect that the western CWA will
just have some AC, virga, or few sprinkles trying to spill in from
the west at times later Thu night into Fri morning. Still some
chance of at least patchy fog in the eastern fcst area late Thu
night/early Fri morning closer to lingering ridge axis and least/
last in line for some cloud cover. Will play Thu night lows at the
coolest of guidance, or even undercut them in the east, again closer
to the ridge axis and light convergent easterly sfc wind regime.
with ongoing dry low to mid level east-southeast fetch, like the
drier 12z run NAM for Fri...again probably just mid level clouds and
mainly virga trying to make it into the western and northwestern
CWA. Below normal temps continue to end out the week. ELevated wing
of WAA showers to the lee of increasingly blocked northeastern
plains upper low, will then look to gather more organization Fri
night, but mainly along and north of the CWA acrs MN into WI.

Saturday and Sunday...The latest run medium range models continue to
suggest a general blocked pattern to maintain over the weekend acrs
the GRT LKS, with increasing influence from the southwestern Gulf
tropical system, as well as other waves off the Atlantic coast. If a
cut-off upper low forms acrs MN By Sat night west of upper ridge
lobe over the eastern GRT LKS and James Bay, a regional Rex Block
may keep this feature almost in place or just allow it to slowly
gyrate southward acrs or near the local area Sunday and into early
next week. Thus while Sat may largely be dry, sctrd shower chances
will then look to increase acrs the local area later Sat night into
Sunday. with early indications of limited moisture feed into this
system, just see light showers and sprinkles by Sunday, but
associated cloud cover and evapo-cooling may make the fcst highs in
the upper 70s to around 80 hard to attain.

Monday through next Wednesday...If the latest trends on the medium
range guidance and ensembles area correct, the blocked upper low
will look to rotate almost overhead Mon into Tue, for continued
cloud cover and sctrd shower chances. Would think and thunder threat
embedded in the showers will be limited to only the afternoon, if
any happens at all. Temperatures will continue to be tied to cloud
cover and precip trends and fcst highs possibly optimistic this
period. Will have to watch trends of the western Gulf to lower MS
RVR Valley tropical system, as well as possible waves along the
Atlantic as they will be big players in the synoptic scale pattern
evolution how long the upper system lingers locally early to mid
next week.    ..12..


.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
ISSUED AT 612 PM CDT Wed Aug 23 2017

Light north to northwest winds under 10 kts will become light and
variable overnight, and turn east to southeast Thursday morning,
while remaining under 10 kts. Some increase in mid level clouds
above 10kft is expected, and a few very light sprinkles/virga may
also occur, but no visibility restrictions are expected at any
airport in eastern Iowa and northwest Illinois through Thursday




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