Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 261755
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1255 PM CDT Fri May 26 2017

.UPDATE...

&&

.AVIATION(18Z TAFS)...

Upper level disturbance moving out of NE IA will spread SHRAs
across sthrn WI this aftn. Most of the activity should remain
along and S of I-94. System is fcst to pull away this evng
leaving scattered VFR clouds tonight. Winds become lght/vrb
overnight as weak SFC ridge moves thru which will set the stage
for some radiation fog. Best chances will be across SW WI which
should be the first areas for clouds to thin tonight. Another area
of concern is a band of fog that dvlpd this mrng along the
lakeshore. Expect this band to persist into Sat with IFR VSBYs.

&&

.PREV DISCUSSION... (Issued 1113 AM CDT Fri May 26 2017)

UPDATE...

An MCV (Mesoscale Convective Vortex) is rolling through eastern
Iowa this morning and will continue to move through northern IL
this afternoon. Southern WI will be on the northern fringe of the
showers today. There is just a little bit of instability, so we
could see a couple rumbles of thunder. No severe storms.

More clouds today and a persistent onshore wind will lead to
slightly cooler temps than previously forecast.

MARINE...

Webcams near the lakeshore indicate dense fog in most areas, so
expanded and extended the marine dense fog advisory. The
conditions with these higher dewpoints over the relatively cool
lake will lead to areas of dense fog across much of Lake Michigan
through midday Saturday.

PREV DISCUSSION... (Issued 557 AM CDT Fri May 26 2017)

UPDATE...

Fog and stratus has been moving south down Lake Michigan and it`s
clipping the lake shore counties, especially around Sheboygan. The
bulk of this stuff will stay out over the lake, but some of the
shoreline areas could see the fog for a time during the morning.
I expect this to mix out by early afternoon.

With regard to the system passing by this afternoon, the new 06z
NAM has generated a similar solution to the GFS with a very
intense mid level short wave lifting up here this afternoon. It
too looks overdone, but our current pops/rain are sufficient for
any precip that moves into southern Wisconsin. We`ll be watching
trends closely to see how this stuff moves northeast out of
eastern Iowa this morning. The majority of the heavy rainfall
should stay south of the border.

AVIATION(12Z TAFS)...

Low stratus and fog has been moving down Lake Michigan and it is
threatening to move into KMKE for a time this morning. That would
produce IFR CIGS/VSBYS. Confidence isn`t high on what this stuff
is going to do, so for now, may just play it scattered and keep it
VFR. But, caution advised that conditions could deteriorate
quickly. The threat of the fog and stratus should disappear by
early afternoon. Otherwise, look for a round of showers or a
thunderstorm rolling across far southern Wisconsin this afternoon
into early this evening as a weak disturbances pushes through.
Conditions are expected to remain VFR through the TAF period, the
obvious caveat being the lake stratus/fog.

PREV DISCUSSION... (Issued 315 AM CDT Fri May 26 2017)

Saturday and Sunday...Forecast confidence is medium.

A mid level shortwave will approach from the southwest but models
differ on whether it will move across southern WI. Surface flow will
be weak across the region with low pressure well to the southwest
and north, so a lake breeze is possible. A weak frontal boundary
will be draped across the region providing the focus for some
showers and thunderstorms. There is some surface based cape. With
the exception of the GFS, models are showing a better chance for
precip Saturday night as an upper trough approaches and surface low
pressure tracks across Illinois and into Michigan. The GFS keeps us
much drier keeping this system further south.

On Sunday an upper low will drop from Canada to over the Upper Great
Lakes region. An upper trough will swing through on Sunday with
surface based instability yielding a chance for showers and
thunderstorms. A cooling trend will start with the influence of the
upper low. No severe weather is expected during this period.

Memorial Day and Tuesday...Forecast confidence is medium

Several lobes of vorticity will rotate through the region as the
upper low lingers over Quebec. There are small chances for showers
each afternoon. No severe weather is expected. Thunder chances
diminish Tuesday as surface temperatures cool and warm air advection
at the mid levels reduces instability. Steep low level lapse rates
will promote mixing and breezy winds.

Wednesday through Friday...Forecast confidence is low.

The upper low will slowly move east later in this period but won`t
entirely lose its grip on the region. Mid level flow will still be
out of the northwest. Models really diverge at this point. The GFS
is showing a low level jet nosing into the region Wednesday with a
frontal boundary moving through Wednesday night. This results in
precip through Thursday and is looking interesting for thunder
potential. The ECMWF, on the other hand, does not agree and is
quicker to bring high pressure over the region.

AVIATION(06Z TAFS)...

VFR conditions are expected through most of the TAF period. There
is some lower stratus moving south down Lake Michigan and there
is plenty of uncertainty with its behavior. It`s possible this
could make it south to the Milwaukee and Kenosha areas by around
sunrise this morning. CIGS would likely be around 500ft. Will be
watching this closely. Some showers could push through southern
Wisconsin, mainly this afternoon, but the bulk of the showers and
lower CIGS will remain south of Wisconsin. Winds will be light
southeast, generally less than 10kts.

MARINE...

Marine conditions are expected to remain favorable, below small
craft advisory levels, through the holiday weekend.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory until 1 PM CDT Saturday for LMZ643>646.

&&

$$

Update...99
Today/Tonight and Aviation/Marine...99
Saturday THROUGH Thursday...99



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