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Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
315 PM CDT Monday Oct 23 2017

Tonight and Tuesday - forecast confidence...medium.

A 150+ knot speed Max will dive south-southeast from
the northern Great Plains into the mid Mississippi Valley today,
as troughing digs equatorward into the upper Midwest and western
Great Lakes. As the upper wave approaches, surface low pressure
will rapidly deepen while progressing from northern Indiana
towards far northern lower Michigan by tonight. Rain showers will
begin pushing back into our area from the west later this
afternoon with chances increasing tonight as forcing for ascent
arrives via jet-level divergence and increasing DCVA. The rain
should end from west to east on Tuesday as deep layer troughing
slowly pushes away to our east. A very strong pressure gradient
will ensue on Tuesday as the low deepens over lower Michigan.
While there is still some uncertainty in the evolution and
ultimate mixed layer depth, northwesterly wind gusts at least into
the 30 to 45 mph range are expected. With it being a bit too close
for Comfort, went ahead and pulled the trigger on a Wind
Advisory, in collaboration with our neighboring offices. Looks
like a good indoor day for Wednesday given the combination of cool
temperatures, high wind, and rain.

Tuesday night through Thursday - forecast confidence...medium.

Over the past 24 hours, short term guidance has been varying its
tune in regards to location and strength of isentropic lift/warm air
advection event sliding southeast from southern Canada. 00z
guidance backed off on strength of this weak system and shifted it
well to the north into southern Canada. Only the European model (ecmwf) kept the
weak event progressing rapidly southeast across Wisconsin late
Tuesday night and Wednesday morning. 12z GFS has flip-flopped and
is now carrying weak lift across central and northeast WI during
this period with light qpf grazing the northeast County Warning Area. Meanwhile 12z
European model (ecmwf) remains consistent with earlier runs in showing vigorous mid-
level short wave moving rapidly southeast across western and
southern Wisconsin. NAM solution farther east over eastern
Wisconsin, while GFS even farther east over northeast WI into
Southern Lower Michigan. Enough weak layer q-vector convergence and
higher rh to warrant returning small pops for rain and snow showers
to the area for about a 6 hour period. Also, impressive burst of
700h potential vorticity advection with mid-level lapse rates of 6.5

Low level thermal structure still shows a mix of rain and snow
or all snow may occur with this event during the Wednesday morning
commute. If full potental vorticity is realized and European model (ecmwf) solution
turns out correct, then briefly lower visibilities with -shsn could
impact Wednesday morning commute. Too much uncertainty at this
point to include in severe weather potential statement.

Some moderation in temperature is expected Wednesday night into
Thursday ahead of next in a series of amplifying short wave
trofs that will move through the upper Midwest and Great Lakes
around Thursday. Strengthening low pressure will move across
Wisconsin later Thursday into Thursday night dragging another
strong cold front through the area. Even colder air will surge
in to finish off the work week. The atmosphere is expected to
be pretty dry so no -shra are expected with the frontal passage.

Extended period...

Thursday night through Monday - forecast confidence...medium.

Medium range guidance in good agreement on amplifying long wave
trof over the Great Lakes and upper Midwest remaining
nearly station through the weekend on into the following
week. In fact, both GFS and European model (ecmwf) show secondary area of
low pressure sagging southward from Canada into the Great
Lakes early in the weekend. This will reinforce the
unseasonably cold conditions expected over the area, and
linger the cold into Monday. 925h temperatures will drop
below zero on Friday and remain in the 0 to 5c range
through the period. A few periods of rain and snow showers are
expected with below freezing nighttime temperatures looking more
likely, pending cloud cover and boundary layer mixing.

GFS 500h standardized anomalies not as encouraging for next week as
yesterday, with below normal heights now lingering through the first
days of November.


Aviation(21z tafs)...lower MVFR deck across the east has been a bit
slower to mix out, so kept ceilings lower a bit longer at the
eastern taf sites. Otherwise look for prevailing VFR conditions this
afternoon, with rain chances increasing this evening. Ceilings late
tonight will drop to at least MVFR, and potentially lower. Haven't
advertised this in the tafs just yet, but further shifts will need
to assess this possibility. Strong and gusty winds will develop
towards Tuesday morning, with surface gusts reaching around 35
knots. A period of low-level wind shear is possible before the
surface winds pick up, but it appears too marginal to include in
most of the tafs just yet. Wet and windy conditions will persist into
Tuesday evening.



Northwest winds will increase this evening into Tuesday as a
strong low pressure system develops over lower Michigan and tracks
north. A Small Craft Advisory is in effect for late tonight, with
a Gale Warning in effect for Tuesday into Tuesday night. Mariners
should exercise extreme caution during this period.


Mkx watches/warnings/advisories...

WI...Wind Advisory from 7 am to 7 PM CDT Tuesday for wiz046-047-051-

Lm...Small Craft Advisory from 6 am to 9 am CDT Tuesday for

Gale Warning from 9 am Tuesday to 4 am CDT Wednesday for

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