Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 190245
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
845 PM CST Wed Jan 18 2017

.UPDATE...
Moist low levels under a shallow inversion is resulting in an
expansion northward of the stratus that never mixed out earlier
today. Visibilities should also come down some later tonight. But,
there appears to be enough mixing/wind at inversion height to
keep the fog from getting too dense. Forecast temperatures look on
track, not really moving much overnight.

&&

.AVIATION/06Z TAFS/...

IFR CIGS are expected through about mid to late morning on
Thursday. The low stratus over southern Wisconsin this evening is
a result of a moist boundary layer beneath a shallow temperature
inversion. There is decent wind at the inversion height
/20-25kts/. This makes the behavior of the stratus a bit
uncertain. It`s possible we could see some holes open up or the
clouds just continue to push north with clearing across the south
due to these winds. Those winds should also help to keep VSBYS up
around 3SM or better. Some rural areas will likely drop to 1SM.
In these situations, it`s generally tough to get any decent
stratus clearing, so will play it pessimistic. If we do get
improvement Thursday morning, we`ll just see conditions
deteriorate quickly again Thursday evening as rain and mild temps
push in ahead of an approaching low. So, IFR into Thursday
morning, lifting to VFR by 17z Thursday, then back to MVFR or IFR
Thursday evening, continuing into Friday.

&&

.MARINE...

Southwest winds will gradually diminish overnight,
become southerly Thu, and easterly Fri. Conditions are expected
to remain below small craft advisory levels through the remainder
of the week.

&&

.PREV DISCUSSION... /Issued 329 PM CST Wed Jan 18 2017/

SHORT TERM...

Tonight and Thursday... Forecast confidence is medium.

The main uncertainty for tonight is sky cover. Skies managed to
clear across much of central WI and now southern WI. We should have
mainly clear skies by dark, except for far southern WI where there
will just be breaks in the clouds. The dark is going to do one of
two things. It is going to strengthen the inversion and the
lingering low level moisture that is trapped will be enough for a
low stratus deck again, OR the drier air will win and keep skies
clear with a lack of mixing beneath the inversion.

Winds will diminish overnight. The strong inversion and lingering
low level moisture support yet another night of low clouds and areas
of fog. There could be dense spots again, but probably not
widespread.

it will take a while for the low clouds and fog to erode away Thu
morning. Mid level clouds will spread in just as the low clouds are
dissipating, so not a lot of sunshine expected, especially toward
the IL border. Warmer air will be working into southern WI ahead of
the approaching system, so highs in the lower 40s are expected.

Thursday night through Saturday...Forecast confidence medium.

A wave of low pressure will track from the Middle MS River Valley
to the Lower Great Lakes for Thu night and Fri while the large
upper low currently over the High Plains lifts newd into WI as a
negative tilt upper trough. Deep Q-vector convergence is depicted
with warm advection in the lower levels and decent PVA aloft.
Believe surface temps and road temps will remain above freezing
with some uncertainty toward central WI. Widespread rainfall is
expected Thu night and will linger into Fri AM.

Another strong negative tilt shortwave trough will then track nwd
from the central Great Plains into MN for Fri night and Sat. This
will maintain relatively mild temps and small chances of light
rain over srn WI.

LONG TERM...Sunday through Wednesday...Forecast confidence
medium.

A large low pressure area will track from the Lower MS River
Valley to New England during this period. A weak inverted trough
will extend into WI during this time. Small chances of light rain,
sometimes snow, is forecast along with the continuation of
relatively mild temps.

AVIATION/00Z TAFS/...The low clouds cleared out of central WI all
the way down to MSN. Clouds in southern WI will have some breaks
around dark. The question is whether or not the clouds will fill
back in this evening.

There is a better chance of low clouds and fog developing once
again late tonight and taking a while to erode Thu morning. Ceilings
will be below 1000 feet, and likely below 500 feet toward morning.

Rain will spread into southern WI from sw to ne early Thu evening
and persist through the night.

MARINE...Southwest winds will gradually diminish overnight,
become southerly Thu, and easterly Fri. Conditions are expected
to remain below small craft advisory levels through the remainder
of the week.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

UPDATE...Davis
TONIGHT/Thursday AND AVIATION/MARINE...MRC
Thursday NIGHT THROUGH Wednesday...Gehring


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