West Allis, Wisconsin 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

126
FXUS63 KMKX 221009
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
409 AM CST Sun Dec 22 2024

.KEY MESSAGES...

- Freezing drizzle may occur later tonight into Monday morning,
  with slick spots on roads possible.

- Some light snow mixing in Monday morning and afternoon in
  northern parts of the area may occur, with light rain mixing
  in Monday afternoon to the south.

- Temperatures will slowly warm today into Monday, with above
  normal temperatures then expected through the rest of the
  upcoming week.

&&

.SHORT TERM...
Issued 409 AM CST Sun Dec 22 2024

Today through Monday night:

Area of middle level clouds will continue to move southeast into
the area this morning, and this should help temperatures remain
steady or slowly rise. Warm air advection develops in earnest
today and tonight, as south southeast winds become gusty within
a tight pressure gradient. There may be a few periods of
scattered clouds this afternoon, before more clouds move in for
tonight. Highs today should rise into the upper 20s to lower
30s.

The warm air advection into tonight will help transport low
level moisture into the area, with the moisture perhaps becoming
more deep through the air column by Monday late morning or
afternoon. There is an absence of ice crystals in the air column
later tonight into Monday morning for a good part of the area,
so this may lead to the development of freezing drizzle. Surface
temperatures will be steady or slowly rising to around 30
degrees later tonight into Monday morning, supporting the
freezing drizzle potential.

This should bring some slick spots to area roads later tonight
into Monday morning. Travel impacts could be more widespread if
the freezing drizzle is the predominant weather type, so a
Winter Weather Advisory may be needed in later forecasts for
later tonight into Monday morning.

A potent 500 mb shortwave trough and some frontogenesis response
in the middle levels should shift through the area later Monday
morning into the afternoon. These features should bring some
light snow mixing in across northern portions of the area, as
long as the deeper moisture arrives. Accumulations should be
under one half inch, but may be enough to bring slick roads.

Temperatures may warm enough in the low levels to bring a mix
of light rain to southern portions of the area as well in the
afternoon. As the precipitation ends Monday evening, there may
be some lingering light freezing drizzle, as ice crystals are
lost with drier air working in. All in all, keep up with the
forecast for later tonight into Monday evening.

Wood

&&

.LONG TERM...
Issued 409 AM CST Sun Dec 22 2024

Tuesday through Saturday:

High pressure will cross the Upper Great Lakes on Tuesday. It
looks like a subsidence inversion and some mid level warm air
advection will give us a mostly cloudy day. Light winds and a
high around 35 degrees can be expected.

For Christmas Day, an upper trough crossing Lake Superior will
be slightly ahead of and not phase with a weaker upper trough
sliding across the Mid Mississippi River Valley. The precip from
both areas of forcing should miss southern Wisconsin, although
drizzle is possible. Highs will be a notch warmer, in the upper
30s, with continued light winds.

A much weaker mid level shortwave may bring some light rain to
southern Wisconsin Thursday afternoon and evening. The ECMWF is
more excited about this than the GFS. The subtle forcing
introduces inherent uncertainty in the precip chances, but
temperatures will be just above freezing so no impacts are
anticipated.

Our upper levels will transition into a southwest flow pattern
with a train of waves rounding the base of an expanding upper
trough over the western U.S. late in the week. The first low
will arrive Thursday night or Friday. Since temperatures at the
surface and aloft will be above freezing, with lows in the upper
30s and highs in the lower to mid 40s, the precip will be in
the form of rain.

The GFS wants to phase the upper lows over the Midwest while
the ECMWF is showing a more progressive pattern without phasing.
If the GFS phased solution pans out, a little colder air will
wrap into the back side of the system over the weekend, although
we should remain above freezing for our area. This messy and
relatively mild upper flow pattern looks like it will persist
into the new year.

Cronce

&&

.AVIATION...
Issued 409 AM CST Sun Dec 22 2024

Mid level clouds overspread southern Wisconsin overnight and
they will stick around through much of the day. The light
returns we are seeing on radar over central Wisconsin are
associated with those mid level clouds and no precipitation is
reaching the ground.

Cloud bases may lower to around 5000 feet AGL but remain VFR
through this evening. Look for increasing southerly winds this
afternoon into tonight. Low level wind shear is expected
tonight, due to winds up to 45 knots at around 2000 feet AGL.

With temperatures just below freezing today and tonight,
freezing drizzle is possible early Monday morning, as low level
moisture moves into southern Wisconsin. IFR ceilings are
possible. The drizzle may transition to light snow Monday,
mainly toward central Wisconsin, before diminishing early
Monday evening. Some light rain may also mix in Monday afternoon
toward the southern terminals like Janesville and Kenosha.

Cronce

&&

.MARINE...
Issued 409 AM CST Sun Dec 22 2024

Low pressure around 29.9 inches will move from western to far
northeastern Nebraska today. The low then shifts into southeast
Minnesota tonight and across northern Lake Michigan into
northern Lake Huron Monday.

South winds will increase and become gusty by this afternoon
and linger tonight into Monday morning, becoming southwest. A
few gale force gusts are possible tonight into Monday morning
across the open waters of Lake Michigan. There is a small
chance that more frequent gales may occur during this time, but
held off on a Gale Warning for now.

A period of mixed precipitation, with snow, freezing drizzle
and rain should accompany the passage of the low.

A Small Craft Advisory is in effect from Noon CST today until
Noon CST Monday for the nearshore waters of Lake Michigan from
Sheboygan Wisconsin to Winthrop Harbor Illinois. Gusty south
winds 15 to 25 knots with gusts to 30 knots are expected, with a
few gale force gusts to 35 knots possible. Winds will shift to
the southwest Monday morning. Elevated waves of 5 to 8 feet are
expected this afternoon and tonight, before slowly subsiding on
Monday.

Winds will shift to the north and weaken behind a passing cold
front later Monday into Monday night. Lighter winds will return
on Tuesday, as high pressure around 30.4 inches builds into the
region.

Wood

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...noon
     Sunday to noon Monday.

&&

$$

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