Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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910
FXUS63 KDVN 151120
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
520 AM CST Wed Nov 15 2017

...12Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 329 AM CST Wed Nov 15 2017

Surface cold front at 3 am was bisecting Iowa, running from a weak
low pressure center near Minneapolis through central IA into far
northwest MO. Well out ahead of the front, mid level instability
was leading to scattered showers across far eastern Iowa and much
of northern IL, with a few cloud to cloud lightning strikes
limited to just east and well south of forecast area. Further
west, area radars showed an axis of light rain or drizzle moving
into eastern Iowa, in the upper forcing ahead of the attendant
mid level shortwave over eastern SD and eastern NE. As this front
progresses east, the light precipitation will end this morning,
followed by a breezy afternoon. After a break Thursday, the next
system in the active, semi-zonal flow is expected to bring the
next round of rain Friday into Friday night.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 329 AM CST Wed Nov 15 2017

Challenges today center around the ending precipitation, then
cloud and temperature trends this afternoon and tonight. Current
timing of the cold front will sweep the showers, then drizzle and
light rain east of the area by late morning. Cold air advection,
and a tight pressure gradient behind the front will lead to brisk
northwest winds of 20 to 30 mph this afternoon. There is low
confidence, however, in just how much clearing will occur.
Satellite imagery shows an axis of stratus dropping south
southeast across the Dakotas into an axis of clear skies under
strong mid level subsidence behind the shortwave trough.
NAM/WRF forecast soundings show a shallow layer of moisture
trapped below an elevated inversion, especially across our north
this afternoon into this evening, which will need to be watched as
it would affect temperatures. For now, will keep an optimistic
clearing trend with deep mixing leading to early afternoon
temperatures recovering into the upper 40s to mid 50s, despite
the cold air advection.

Tonight, high pressure becomes centered over central Iowa by 12z,
with light winds allowing temperatures to cool into the mid to
upper 20s. For now, will keep partly cloudy skies going across
the north with mostly clear skies elsewhere. If stratus is indeed
more extensive than models advertise, these low temperatures will
be too cold.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 329 AM CST Wed Nov 15 2017

Quiet and dry conditions will be seen Thursday and Thursday night as
the next storm system moves toward the area. High temperatures
Thursday will be below normal.

Friday/Friday night the storm system moves through the area.
Initially the atmosphere will be quite dry across the area so it may
be late Friday morning before precipitation occurs. Atmospheric
profiles indicate precipitation will be mainly in the form of rain
or a rain/drizzle mix. If precipitation develops prior to late
morning, the potential is there for a rain/snow mix or possibly a
little sleet before changing over to all rain.

The track of the system is still somewhat uncertain which brings
into question the overall risk of thunderstorms Friday night and
precipitation type late Friday night. Although the risk of
thunderstorms is low, thunderstorms may occur south and east of a
Prophetstown, IL to Memphis, MO line.

Just prior to sunrise Saturday, precipitation in the far northwest
part of the area may go over to a rain/snow mix.

Saturday on...

The storm system exits the area Saturday morning with nearly all of
the area dry during the afternoon. A rain/snow mix may be seen in
the highway 20 corridor early Saturday morning and for areas
north/west of Cedar Rapids.

Saturday night through Tuesday, the model consensus has quiet and
dry conditions for the area. Storm tracks are well to the north and
south of the area. The global models are suggesting a dry frontal
passage occurring in the Monday to Tuesday time frame.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday Morning)
ISSUED AT 520 AM CST Wed Nov 15 2017

Very low IFR conditions ahead of a cold front will impact the TAF
sites early this morning. Improving conditions will then follow
along with south winds veering to the northwest and becoming gusty
by afternoon as high as 20 to 30 kts. There is somewhat low
confidence in how fast conditions will improve from IFR to MVFR
through the morning as ceilings lift and the drizzle and fog
dissipates. For the afternoon through tonight, VFR conditions are
likely at all but the DBQ terminal, where there is a good
potential for MVFR conditions due to lingering clouds around 2000
ft. All sites are forecast with VFR conditions for overnight, but
will continue to monitor trends as there is a possibility that low
clouds may return or even linger through the day to result in
MVFR conditions.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

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



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