Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 212033
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
333 PM CDT Tue Mar 21 2017

.SHORT TERM...

TONIGHT AND WEDNESDAY...Forecast Confidence is medium.

The primary concern is for the chance of lake effect (LE)
precipitation this evening immediately adjacent to Lake Michigan.
Onshore winds will prevail through the night, and 850mb to water
temperature differences are in the 9C to 13C range which would
support LE precip. Most guidance has an abbreviated period this
evening where the atmosphere is saturated from 850mb to the surface
right along the lake, and that period is when LE precip is most
likely.

Not confident that any precip will materialize, and as is always the
case with LE precip, it`s very difficult to nail down exactly where
any bands will set up. Further complicating matters, in the early
evening we will be dropping through the 30s and into the 20s, so we
may see a mix of rain and snow before changing to all snow.
Therefore decided to just go with isolated precip through the
evening.

Otherwise, strong CAA will set up behind this afternoon`s front,
resulting in cold temperatures tonight and tomorrow. Not going too
crazy with low temperatures this tonight despite the strong CAA
and mostly clear skies because winds will remain elevated through
the night, allowing some warmer temps to mix down. High pressure
builds in tomorrow, resulting in cool, sunny conditions.

.LONG TERM...

Wednesday night through Sunday...Forecast Confidence is Medium to
High:

Models remain in good agreement showing low pressure moving slowly
through the region late in the week and over the weekend. High
confidence remains that this will bring a long period of rain
chances back into the area later Thursday through Saturday,
possibly lingering into Sunday. Kept mention of thunder Thursday
afternoon through Friday morning, as models are still showing some
elevated instability.

Near normal temps Thursday should warm back above normal Friday,
though not great confidence in temps Fri for any given location
of the front. The front is progged to bisect the forecast area
during they day, which would result in quite a spread of temps
south to north across southern Wisconsin. Won`t take much of a
frontal budge north or south to result in big temp forecast
changes for areas near the the front. Should see cooler temps for
the weekend, especially near the lake under onshore winds.

Monday and Tuesday...Forecast Confidence is Medium:

Another system is expected to bring light rain Monday into Monday
night, with dry weather returning Tuesday. Went with a model blend
for temps, given a decent spread between milder GFS and cooler
ECMWF/Canadian solutions.

&&

.AVIATION(18Z TAFS)...

Wind shift occurred a bit earlier than expected, but otherwise the
forecast remains on track. Clouds should reach MKE in the
late afternoon/early evening, with cigs gradually lowering in the
hours following the frontal passage. MSN should be far enough west to
avoid most cloud cover once the high clouds move out.

As onshore winds set up this evening, conditions become marginally
favorable for lake effect snow (LES) along the lake. Confidence
for LES is not especially high, and as always, it`s very
difficult to nail down exactly where any LES will set up.
Therefore only carrying VCSH for now and will adjust as necessary
if and when the LES become apparent. Any snow accumulations will
be light.

&&

.MARINE...

Marine sites have been flirting with 20kt winds all afternoon, and a
few locations have reached into small craft criteria, so SCA is
still on schedule to begin at 4pm. Winds will remain elevated and
out of the north though the night, allowing waves to build through
the night.

Winds look to pick up again ahead of an approaching low pressure
system on Thursday, so another SCA may be needed at that time.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 10 AM CDT Wednesday for LMZ643>646.

&&

$$

Tonight/Wednesday and Aviation/Marine...BSH
Wednesday Night through Tuesday...DDV



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