Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 200439

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1139 PM CDT FRI AUG 19 2016


Issued at 856 PM CDT Fri Aug 19 2016

A slow moving line of weak to moderate showers and thunderstorms
is continuing to move east, while individual cells move north. The
outflow from the storms entering our northwestern counties is
capable of strong winds gusts around 35 mph, but as they move
slowly east, this will likely weaken. I have pulled back on the
heavy rain threat overnight, as the line just is not holding up on
intensities. The elevated cells over southeast Iowa will continue
to lift north, and should merge with the line around 10 pm. This
should not bring a significant increase in intensity.


Issued at 310 PM CDT Fri Aug 19 2016

18Z surface data has a boundary running from northwest Indiana, to
just north of KDVN and up into the KALO area. The main cold front
ran from northeast Wisconsin to a weak low near KRST, and then into
southeast Nebraska. Dew points were in the 70s from the Great Lakes
to the Gulf Coast ahead of the front. Behind the front dew points
were in the 50s and 60s across the northern and central Plains.


.SHORT TERM...(This Evening through Saturday)
ISSUED AT 310 PM CDT Fri Aug 19 2016

Through late afternoon the more focused convection will be north of
highway 30 an west of the Mississippi. Convection here is taking
advantage of the outflow boundary from the nocturnal convection and
an instability gradient. Across the remainder of the area, isolated
convection will be possible during the warmest period of the day.

This evening more convection will slowly start developing across the
area as forcing ahead of the cold front increases. Some storms may
produce locally heavy rainfall due to their slow movement and the
high moisture content of the atmosphere. After midnight, forcing and
moisture increases significantly across the area. Widespread
convection will develop along the frontal zone and slowly move east
through sunrise that may produce locally heavy rainfall.

Saturday...the cold front sweeps through the remainder of the area
during the morning. Convection will be widespread at sunrise. By
late morning and continuing into the afternoon, the widespread rain
will end from west to east and become more scattered in nature.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 310 PM CDT Fri Aug 19 2016

Cooler and drier conditions following Saturday`s cold frontal
passage will be the big story from Saturday night through Sunday.
Gradual warmup back to near normal temperatures to follow next week,
with a slow moving frontal system bringing our next chances for rain
from Tue night through Thursday.

Saturday night through Sunday: Initially cyclonic low level NW flow
Saturday night will be advecting cooler and much drier air into the
area. Increasing subsidence overnight should erode any lingering
clouds from SW to NE. Latest guidance backed previous forecast lows
in the lower to mid 50s over most of the area and only minor tweaks
were made. The incoming high pressure ridge rolls through the area
Sunday, causing NW winds to become light by evening. 850 mb
temperatures and MOS support highs only in the lower 70s north
and mid to upper 70s south.

Temperatures moderate back closer to late August normals early next
week, with highs back in the 80s. Sunday night still looks to be the
coolest, with clear skies and light winds leading to lows around 50
to the mid 50s and possibly a few degrees cooler if the timing of
the ridge axis slows some and the airmass remains dry. An increasing
surface pressure gradient building Monday into Tuesday will result
in a breezy period as winds could reach 15 to 25 mph by Tuesday
afternoon.  POPs move back into the forecast Tuesday night with a
possible warm advection wing ahead of the main front kicking off
thunderstorms, which pushes through with higher pops for showers and
thunderstorms Wednesday into Wednesday night. Model agreement and
forecast confidence wanes from Wed onward, with differing depictions
of the timing and placement of a wave of low pressure tracking along
the front. For now, this will require keeping pops from Wed night
into Thu, until this system is better resolved. Confidence is higher
that Friday should be dry with surface high pressure over the area.
This results in highs back in the 70s to near 80, lower humidity
and overnight lows in the 50s Friday night.


.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1130 PM CDT Fri Aug 19 2016

As of 11 PM, the widespread showers and thunderstorms associated
with a cold front are nearing the Mississippi River, but coverage
is most widespread well west towards central and eastern Iowa.
Thus far, cigs remain mainly at or above 3000 ft with the storms,
but that is expected to lower to MVFR and possibly IFR overnight
as the rainfall continues to increase in coverage. While
individual storms will be short lived through the early morning
hours, the potential continuous enough to warrant a VCTS for
several hours, and moderate rain and MVFR cigs following that
through the early morning hours. Winds will switch to northwest
after sunrise Saturday, and increase to gusty levels during the
morning. Eventually this will bring in drier air, after a MVFR
morning with cigs around 2-3000 ft.


.DVN Watches/Warnings/Advisories...


LONG TERM...Sheets
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