286
FXUS63 KMKX 211022
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
422 AM CST Thu Nov 21 2024

.KEY MESSAGES...

- A brief but heavy round of snow will affect the Thursday
  morning commute. Expecting 1-4 inches of snow accumulation
  across most of southern Wisconsin along with northwesterly
  winds gusts of 35-45 mph. A Winter Weather Advisory is in
  effect between 6 AM and Noon for most of southern WI. The
  headline was expanded westward to include Dane County.

- Strong northwest winds will become north this afternoon, with
  gusts up to 45 mph at times. A Wind Advisory is in effect for
  most of southern WI. Small Craft Advisories and Gale Warnings
  remain in effect in nearshore and open water zones of Lake
  Michigan.

- The next widespread precipitation chances arrives Monday,
  with mostly rain being favored at this time.

&&

.SHORT TERM...
Issued 421 AM CST Thu Nov 21 2024

Today and Tonight:

The light snow lingered through much of the overnight hours.
Temperatures hovered in the upper 20s to around 30 with steady
westerly winds. This gave plenty of time for the surface
pavement temperatures to drop down to around freezing. We have
some higher returns showing up on radar over southern WI now (4
AM) and these are pockets of steady snow with visibility down to
3 miles at times. This snow is due to a vorticity max swinging
through the area. Light accumulations are possible with this.

The very beginning of the main show is arriving in the Fond du
Lac area now (4 AM). This leading edge is light, but there is an
area of slightly better snowfall rates upstream, currently from
Appleton to Manitowoc. Even better snowfall rates are in Green
Bay. The reason for the tiers of snow intensity are due to the
various forcing mechanisms. Vorticity advection aloft is along
the leading edge. The deformation zone around a deep low over
northern Lake Michigan is the reason for the heavier snow.

The surge of heavier snow should accelerate as the low tracks
down the lake this morning, so the timing of the heavier snow
will be between 8 and 10 AM. The deep surface low will track
southward along the center of Lake Michigan today, reaching the
southern tip around 4 PM. Warmer air is wrapping into the back
side of the surface low and will therefore make its way down
into southern WI by noon and help transition our snow into rain.

Headline decisions: With our air temperatures primed from a long
night of below-freezing temperatures, the round of steady snow
will create hazardous travel conditions with even the smallest
amount. This happening during the morning commute makes the
situation worse. While the forecast snowfall amounts did not
change much, the anticipated travel hazards warranted an
expansion of the Winter Weather Advisory another tier of
counties westward. One other reason for this expansion is the
insistence of the models to swing the deformation zone westward
a bit on the tail end of the precip to sit over Dane county into
late morning.

In our previous messaging, we combined the strong winds with the
winter weather hazard. I think the windy conditions (gusts up to
45 mph) will last longer than the snow and also affect more
areas than what the impactful snow will, so I separated the
hazards. There is a Wind Advisory for roughly the northern two
tiers of counties from 12-22Z and the southern two tiers (plus
Sauk) from 15-00Z. Marquette county is not in a headline. The
area and timing of the wind advisory was created to blend well
with neighboring offices. The bottom line is that it will be
windy. The winds will help to greatly reduce the visibility
while it is snowing.

There is still some concern that mixing might not be deep enough
to tap into the 40-50kt winds at 2000 ft, but there is a strong
enough signal that we felt the need to have a Wind Advisory.
Once the low tracks into southern Lake Michigan this afternoon,
models are showing a rush of very strong northerly winds down
the lakeshore, well after the precip ends there.

Cronce

&&

.LONG TERM...
Issued 421 AM CST Thu Nov 21 2024

Friday through Wednesday:

Upper-level ridging begins to build in overnight Friday and into the
start of the weekend. A few passing shortwave troughs to the north
will flatten the ridge a bit, thus limiting the warm up potential.
Nevertheless, still looking at drier conditions with temps warming
back up into toward normal highs in the 40s for Saturday and Sunday.
Cannot rule out seeing a few location approach the 50F on Sunday as
well, but GEFS and ENS as well as the 01z NBM are not too excited
with <30% chance of exceeding 50F on Sunday. Otherwise upstream long
range models prog a shortwave trough to develop across the northern
CONUS and swing into the Upper Midwest overnight Sunday into Monday.
The accompanying surface low looks to lift in from the Plains and
track across the region and will bring the next opportunity to see
some precip. Given the warmer temp trend, any precip is likely come
in the form of rainfall, but if the low tracks further south, it may
put us more on the colder side of the weak low and could see a bit
of a mix to snow with the early next week system. However, still a
bit of spread between model suites on the this systems track.

As we head deeper into the holiday week, expect the CAA on the
backside of the early week system to bring in a colder, Canadian
airmass. Will see this colder, drier airmass settle across the area
through the middle of next week with daily highs in the 30s and
nightly lows in the 20s and possibly upper teens.

Wagner

&&

.AVIATION...
Issued 421 AM CST Thu Nov 21 2024

There are pockets of steady snow moving across southern WI early
this morning. Reduced visibility and a couple tenths of
accumulation are expected. The main snow is over east central WI
and will be dropping through southern WI this morning. Peak
snowfall rates will occur from north to south between 7 and 10
AM. Snow may linger into late morning toward Madison. Overall,
expect snow to change over to rain late this morning, but timing
of that is still uncertain.

MVFR ceilings will become IFR in the snow. Very strong northwest
winds will become northerly by late afternoon as they taper off.

Cronce

&&

.MARINE...
Issued 421 AM CST Thu Nov 21 2024

There was a slight change in the timing of the Gale Warnings. They
are in effect from 12 AM to 6 PM CST today in the northern half, and
from 6 AM Thursday to 12 AM CST Friday across the southern half.
The Nearshore gale now runs from 6 AM to 9 PM.

Low pressure of 29.3 inches over far northern Lake Michigan will
track down the axis of Lake Michigan today, reaching the far
southern tip by late afternoon while weakening to 29.5 inches. Snow
and rain will reduce visibility along the area of low pressure.
Expect west- northwesterly gales of 35 to 45 knots today near the
center of the low. The majority of these gusts will be across
western portions of the lake. Northerly gusts in the wake of the low
will taper off from north to south through mid evening as low
pressure fills and exits to the east. Northwesterly winds continue
through Friday, with gusts around 30 knots expected in the southern
half as high pressure of 30.2 inches builds into the northern
Plains.

Cronce

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Wind Advisory...WIZ047-WIZ051-WIZ052-WIZ057-WIZ058-WIZ059-
     WIZ060 until 4 PM Thursday.

     Winter Weather Advisory...WIZ047-WIZ051-WIZ052-WIZ057-WIZ058-
     WIZ059-WIZ060-WIZ063-WIZ064-WIZ065-WIZ066-WIZ069-WIZ070-
     WIZ071-WIZ072 until noon Thursday.

     Wind Advisory...WIZ056-WIZ062-WIZ063-WIZ064-WIZ065-WIZ066-
     WIZ067-WIZ068-WIZ069-WIZ070-WIZ071-WIZ072...9 AM Thursday
     to 6 PM Thursday.

LM...Gale Warning...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 until midnight
     Friday.

     Gale Warning...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ868 until 6 PM Thursday.

     Gale Warning...LMZ643-LMZ644-LMZ645-LMZ646 until 9 PM Thursday.

     Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646 until 6 AM
     Thursday.

&&

$$

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