Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 210844
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
344 AM CDT SUN AUG 21 2016

.SYNOPSIS...
Issued at 330 AM CDT Sun Aug 21 2016

The latest surface analysis was indicating seasonably deep low
pressure center just north of the GRT LKS, still maintaining some
cyclonic flow back to the mid and upper MS RVR Valley. Further to
the west was a large ridge complex acrs the plains and MO RVR
Valley. Aloft...mid/upper level moisture flow channels on the
current water vapor loop was indicating the axis of the midwest L/W
trof was currently shifting east of the MS RVR Valley. The latest
SFC Obs were showing that much of the DVN CWA had cooled into the
upper 50s.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Sun Aug 21 2016

Today...battle between incoming ridge gradient and lingering
cyclonic flow will make for west to northwest winds of 10 to 20 MPH
from late morning through mid afternoon, before they start to
diminish into the evening as ridge axis approaches from the west.
Some wrap-around stratocu in the lingering llvl cyclonic flow may
clip the far northeastern fcst area this morning, otherwise just
some ambient CU today probably not more than scattered coverage.
Even in rather deep mixing regime today, incoming cool advection
vertical profiles support most areas not warming past of the middle
70s. Temps may only range in the low to mid 70s north of the Hwy 30
corridor, while a few of the warmer bias areas along and south of
I80 push 77 or 78 degrees this afternoon. SFC DPTs will look to mix
down into the mid to lower 50s in some locations. All in all an
ideal day for this time of year.

Tonight...with passing ridge axis overhead for a quick decrease to
light or calm winds after sunset along with clear skies, temps
should really drop off this evening. H85 MB cool ridge rule supports
lows in the lower 50s to around 50, with a chance for some upper 40s
in the cool air drainage locations north of I80. Several 00z run
models want to begin southerly return flow on backside of the passing
ridge late tonight before sunrise, which if it occurs, would limit
the cool potential especially west of the MS RVR. But looking out
west and northwest currently acrs western IA and the MO RVR Valley
where the incoming airmass is at, there is already plenty of lower
50s and even some upper 40s. For now will go widespread lower 50s
except in the far south where will keep mid 50s. Will also keep some
upper 40s already introduced in the cool air drainage locations of
the Wapsi Valley. Will match neighboring offices to the east and
northeast with some patchy fog mention in NW IL where SFC winds will
stay calm the longest thru sunrise Mon morning, but confidence for
more widespread fog is low. It may just occur in the river valleys.

.LONG TERM...(Monday through next Saturday)
ISSUED AT 330 AM CDT Sun Aug 21 2016

Main focus is around mid-week when the next seasonably strong
cold front looks to bring showers and storms, and the potential
for heavy rainfall.

Monday and Monday night, high pressure will remain the dominant
weather feature, while gradually shifting into the Ohio Valley.
Developing southerly flow during the day should lead to moderating
temperatures, with highs climbing back around normal (around 80F
to 85F). Lows on Monday night will largely be dependent on just
how much the boundary layer decouples under mainly clear skies.
More decoupling, or lighter winds will lead to cooler lows in the
range of 55F to 60F per progged 850 mb temperatures around 15C.
Meanwhile, more mixing or stronger winds will likely keep lows in
the 60s. For now the forecast is with the consensus, which is a
good compromise or blend of the two scenarios, with mainly upper
50s to around 60F on lows.

Tuesday and Tuesday night, the models have been pretty consistent
with ejecting a low-amplitude trough from the Central Plains into
the Upper Midwest ahead of a stronger trough and associated height
falls traversing the Northern Rockies. This will hold the main
cold front and attendant low to mid level FGEN forcing at bay well
to our west. However, strengthening warm advection attendant to
strong, dynamically induced low level jet (40-50 kts) will likely
result in increasing shower and storm chances by late afternoon
and especially Tuesday night. A developing low on the southern end
of the cold front over Kansas, coupled with a warm front extending
eastward near the Missouri and Iowa border may allow for some
organization or upscale growth into a nocturnal MCS, which would
be most favored over about the southwest 1/2-2/3rds of the cwa.
Ample shear is shown with 0-6km of 30-35+ kts for a few stronger
storms possible with gusty winds and perhaps some hail. However,
the main threat will be potentially heavy rainfall with
precipitable water values ramping up to around 2 inches by 12z
Wednesday.

Wednesday and Wednesday night, will see continued chances for
showers and storms. May see a period of relatively lower
precipitation coverage on Wednesday as low level jet wanes with
passage of shortwave, with forcing mechanism mainly weak frontal
convergence and continued broad warm, moist advection ahead of the
slow moving front nearly parallel to mid and upper level flow.
Wednesday night looks to bring renewed increase in coverage and
uptick in intensity as height falls and upper diffluence attendant
to Ontario shortwave overspread the slowly advancing cold front.
Yet again another round of heavy rainfall would be the main
concern, with precipitable water values still between 1.5 to 2
inches. Hopefully the rain can be spread around, but if we do
pick on the same areas repeatedly then likely would have some
flooding concerns.

Any lingering rain chances on Thursday look to taper off early with
the passage of the cold front. Then, should see a 18+ hour period
of refreshingly cool and dry weather Thursday night into Friday
night as high pressure quickly traverses the region. However, the
flow aloft will remain west/southwest and so the front is not
expected to go far and will likely pull up stationary just south
of the cwa by Friday. Upper level energy lifting out of the
southwest and isentropic lift over the front will likely lead to a
return of rain chances later Friday night and at least through the
first half of next weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
ISSUED AT 1125 PM CDT Sat Aug 20 2016

VFR and clear aviation conditions through the next 24 hours are
expected, with northwest winds under 10 kts until mid morning
Sunday, and raising back to around 10-12kts again by mid morning
Sunday. Beyond this, little hourly change is expected in conditions.

&&

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

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...McClure
AVIATION...Ervin


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