Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 240514
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1114 PM CST Fri Feb 23 2018

.UPDATE...

The guidance is not handling the lower stratus to the north at
all. It`s trapped under the inversion and moving south at a pretty
steady pace. Confidence is low on how long this will survive
through the night. Some mixing should eventually cause it to
scatter out. Satellite is showing evidence of that already with
holes opening up. Will adjust temps accordingly.


&&

.AVIATION(06Z TAFS)...

An MVFR deck of clouds is spreading south into southern Wisconsin
late this evening. This is not being handled by well by nearly all
the guidance, so confidence is challenged on how it will behave
overnight. It`s already beginning to mix out as satellite shows
some holes opening up. This trend should continue overnight.
I`ll bring it into the TAF sites through about 08-09z Saturday,
followed by a period of VFR CIGS, then more MVFR CIGS push in
during the morning on Saturday. Some of these clouds are coming in
off Lake Michigan. So, rather complicated sky forecast this TAF
period. Eventually rain pushes in toward late afternoon and
conditions will quickly drop to IFR levels. If we see any snow in
the KMSN area it would be very briefly at the onset of the
precipitation.

&&

.PREV DISCUSSION... (Issued 927 PM CST Fri Feb 23 2018)

UPDATE...

Overall fcst remains on track. Main adjustment is due to stubborn
stratus lingering across the Milwaukee metro area as well as
another batch dropping south out of central WI.

MARINE...

A west wind will become strong and gust 35 to 40 kts from late
Saturday night through Sunday due to a strong low pressure system
moving from the Midwest into Ontario this wknd. Therefore a gale
watch is in effect.

PREV DISCUSSION... (Issued 543 PM CST Fri Feb 23 2018)

UPDATE...

No major changes with this update package. Stratus will continue
to erode with the drying westerly flow. There are some indications
that the low clouds could hang on across far SE WI overnight.
Otherwise, winds should become light/vrb as they swing around to
the east by morning in advance of the next storm system due in
Saturday aftn/evng.

AVIATION(00Z TAFS)...

The MVFR CIGs are in the process of clearing out. Some model
guidance indicates the stratus will not completely clear out
overnight across SE WI. Due to the light winds overnight and
plenty of moisture near the SFC, can`t rule out some patchy
fog. Guidance also suggests that IFR marine stratus may advect
inland once the wind swings around to the east Sat mrng. Not
confident in this scenario so left it out for now. Sat mrng will
be dry with increasing easterly winds and slowly lowering CIGs.
Rain or a rain/snow mix will dvlp drng the aftn from south to
north. If a mix does occur, it should be short lived with no
accumulation expected. Conditions will continue to deteriorate
into the evng.

PREV DISCUSSION... (Issued 338 PM CST Fri Feb 23 2018)

SHORT TERM...

Tonight and Saturday... Forecast Confidence is High.

The clouds are scattering out west of Madison this afternoon and
the trend will continue to the east through early evening. Skies
should mostly clear out for a period tonight, but expect high
clouds to begin streaming into the area toward morning as the next
system approaches from the southwest. The breezy west winds will
diminish around sunset. Light winds tonight will veer to the east
and increase Saturday morning. Skies should mostly clear out for
a period tonight, but expect high clouds to begin streaming into
the area toward morning as the next system approaches from the
southwest. There should be some patchy light fog inland overnight
under those clear skies.

A digging trough out west will approach the Midwest tomorrow.
Warm air advection and vorticity advection will cause precip to
develop over southern WI Saturday afternoon. The 12Z models
delayed the precip onset from prior runs since they`re picking up
on drier air it will have to overcome. Precip will spread in
quickly by late afternoon, but the type may start out as snow
initially before changing to all rain, depending on the rate of
the WAA and the temp profile. Not expecting snow accumulation.

Saturday night through Tuesday...Forecast confidence high.

Strong cyclogenesis will track from N MO to just east of
Marquette, MI for Sat nt. Strong and deep Q-vector convergence
will accompany this system via warm, moist advection on the nose
of a LLJ and PVA. The upper trough passage and cold frontal
passage will occur Sat nt. Fcst soundings are still indicating PWs
around 0.75 inches and enough elevated instability for a mention
of tstorms. Rainfall totals will range from 0.25-0.40 inches. This
should remain minimal enough to prevent another round of
flooding.

The deepening low will lead to windy conditions especially with
the passage of the cold front as lapse rates steepen. There may be
an initial burst of winds with the frontal passage that could
reach Wind Advisory criteria, but still remain close afterward
through Sun AM. The winds will be weakening through Sun PM as the
deep low moves to James Bay, Canada. The dry wly winds, eventual
sunshine, and lack of snow cover should result in temps reaching
the lower 40s for Sun. A weak sfc ridge will then pass late Sun
nt into Mon AM followed by swly winds and warm advection for the
remainder of Mon. Continued sunshine and warm advection should
boost temps to upper 40s to lower 50s. A repeat performance may
occur for Tue although lighter winds may lead to a Lake MI lake
breeze.

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

Confidence lessens for this period due to the uncertain
interaction of upper waves in the nrn and srn streams of a split
flow jet stream. Weak or fairly strong cyclogenesis may occur and
bring rain and snow to srn WI for Tue nt-Thu. Polar high pressure
may then return for Fri unless the low pressure area lingers.

AVIATION(21Z TAFS)...

Ceilings are on the rise there will be a clearing trend with the
clouds from west to east late this afternoon/early evening. Gusty
west winds that developed in the wake of a surface trough this
morning will diminish around sunset. Light winds tonight will veer
to the east and increase Saturday morning. There should be some
patchy light fog inland overnight under some clear skies.

There is a chance for some low lake clouds to spread inland
Saturday morning as winds become easterly, but not a lot of
confidence in this yet, so left it out of the TAFs. Look for the
main batch of air to saturate from the top down which means the
rain should be delayed until late afternoon or early evening.
There is a slight chance for thunderstorms Saturday evening.

MARINE...

It`s still looking like a gale event for Saturday night into
Sunday as a strong, compact low pressure system tracks across
southern MN, central/northern WI, and Lake Superior. Highest winds
should be along the leading edge of the cold front early Sunday
morning.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Gale Watch from Saturday evening through late Sunday night for
     LMZ643>646.

&&

$$

Update...Davis
Tonight/Saturday and Aviation/Marine...Cronce
Saturday Night through Friday...Gehring


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