Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 271742
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1242 PM CDT WED JUL 27 2016

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 339 AM CDT Wed Jul 27 2016

High pressure centered over northern Illinois was leading to
another night with light winds, mostly clear skies and typical late
July nighttime temperatures in the 60s. Occasional ground fog was
being reported at some of the more fog-prone sites in eastern IA
and nw IL. Satellite imagery showed cirrus from upstream
convection overspreading central IA, reaching into east central IA
at 2 am. This was from an MCS over central NE, which was flanked
by smaller complexes over SE CO and NE SD into western MN.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 339 AM CDT Wed Jul 27 2016

Main challenge is centered on chances for showers and thunderstorms
as an increasingly more active upper level W-NW sends series of mid
level impulses over region. Today, remnant high clouds from the
upstream nocturnal convection are on track to spill over the area,
likely in a thinning stage. This should be enough, however to keep
temperatures near to perhaps a bit cooler than Tuesday across the
central and north, while mixing into warm advection aloft should
boost highs in the far south and southwest into the mid and upper
80s. Elevated moisture transport, and enhanced forcing should focus
showers and thunderstorms well to the north and northwest during the
most of the day, which is the general trend in convective allowing
models. Some of this activity may spill into the far the northwest
counties of the forecast area by late afternoon, where model MUCAPES
push 1500 to 2000 J/KG and have added slight chance pops. These same
models also depict isolated convection over west central and northern
IL in the afternoon, where there is another axis of building
instability, and a potential very weak surface boundary. Confidence
not great that this will occur and have kept this area dry for now.

Tonight, there is a better signal backing a wave of scattered
showers and thunderstorms moving through the forecast area overnight
as a deepening shortwave traverses the region. Have maintained
higher chance pops across the north where the forcing is greater.
Instability wanes considerably after midnight, and it may end up
being more showers versus thunderstorms, especially toward morning.
Without strong convection and limited moisture, expecting QPF to be
light, generally less than a quarter inch in most areas.

.LONG TERM...(Thursday through next Tuesday)
ISSUED AT 339 AM CDT Wed Jul 27 2016

Thursday and Friday...The 00z run GFS and ECMWF in general agreement
of digging short wave trof aloft acrs the mid and upper MS RVR
Valley, over some llvl convergence either around a sfc wave or
inverted trof feature acrs the CWA for occasional showers and a few
thunderstorms Thu into Thu evening. Cloud cover, northerly boundary
layer flow, and low to mid level saturation will make for below
normal temps Thu in the upper 70s to lower 80s. If less cloud cover
occurs or more breaks, then some areas to push the mid 80s. Lift
along with the main wave shifts off to the east and takes the more
organized showers with it as Thu night progresses. Just some lighter
sprinkles and maybe some fog left in the system`s wake late thu
night into early Fri morning. Lows in the low to mid 60s. The latest
medium range models continue to suggest broad backdoor sfc ridging
to slip down acrs the upper MS RVR Valley and western GRT LKS on
Fri. Would think the CWA would be mainly dry but both the GFS and
00z ECMWF break out spurious light precip acrs the area during the
day Fri into Fri evening. Probably from another vort and some column
instability embedded in broad cyclonic flow aloft. May try and keep
POPs to slight CHC for now. If we get and maintain enough cloud
cover, projected thermal profiles support highs being held down in
the 70s acrs much of the area on Fri.

Saturday and Sunday...The CWA will look to remain under similar
condtions Sat as Fri, with lingering troffiness aloft. Even with the
low to moderate POPs fcst acrs the area, many hours of the day
should be dry for outdoor activities. Some slight thermal moderation
to help temps back into the upper 70s to lower 80s. The latest 00z
medium range model runs suggest thermal ridge to start to amplify up
the western plains during the second half of the weekend. the
general idea is for associated eastern flank return flow warm front
to organize and be a convective focal point acrs the central plains
into the lower OH RVR and TN Valleys thru the day Sunday. If this
further south placement verifies, the CWA could remain largely dry
Sat night into Sunday. But longer range signals of some retreat
northward potential of this feature would open up at least the
southern third or so of the fcst area to elevated storm clusters
Sunday night into Mon morning.

Monday and next Tuesday...longer range indications suggest this
early week period to be a transition window as the upstream heat
dome tries to build eastward. After some WAA-type showers and
storms on Mon, the 00z GFS then firmly shunts the thermal ridge axis
overhead for a hot Tue with highs at least in the lower 90s acrs
much of the area if not even some mid 90s. The GFS also shunts the
storm track/ring of fire northward acrs the Dakotas to northern GRT
LKs next Tue thru Wed. The 00z run ECMWF keeps the area more
unsettled and on the northeastern periphery of the high and thus
open up to ridge-riding storm clusters or MCS type features Mon
night into at least early Wed. But when it`s not storming or
convective debris impacted, the Euro also suggests highs in the
upper 80s to lower 90s for next Tue and Wed.    ..12..

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
ISSUED AT 1237 PM CDT Wed Jul 27 2016

Mainly VFR conditions should be seen across eastern Iowa and
northern Illinois through 00z/28. There are pockets of MVFR cigs
that may briefly impact a TAF site. After 00z/28 VFR conditions
should continue with areas of MVFR with showers. Although not
included in the 18z TAFs, an isolated thunderstorm cannot be ruled
out. A period of MVFR conditions may develop between 06z/28 and
sunrise Thursday due to patchy fog.

&&

.DVN Watches/Warnings/Advisories...
IA...None.
IL...None.
MO...None.
&&

$$

SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...12
AVIATION...08



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