Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 220227 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
927 PM CDT Thu Mar 21 2024

.KEY MESSAGES...

- Snow will overspread the area tonight, continuing through the
  morning on Friday. The heaviest snowfall rates are expected to
  occur during the morning hours on Friday, including during the
  morning commute.

- A band of enhanced snowfall is expected to occur with this
  system, but there continues to be uncertainty with the
  placement of this band.

- Good chance (70-80%) for precipitation Sunday through
  Tuesday, initially in the form of snow, with warmer
  temperatures and rain by Monday.

&&

.UPDATE...
Issued 927 PM CDT Thu Mar 21 2024

The 600-700mb warm air advection snow is well underway across
central MN and central WI this evening. There are multiple bands
of snow south of there that are due to 925-850mb warm air
advection. One of those bands is slowly progressing eastward
into the Madison area, and this one is getting a boost from
700mb frontogenesis as well. There is very dry air in the low
levels, so the radar reflectivity makes it look worse than it
actually is since not much of that is hitting the ground.

Over time, expect the lower layers to saturate and allow the
600-700mb WAA snow to accumulate across much of southern WI
between midnight and 6AM. Everyone should get accumulating snow
up to a few inches by this time while temperatures are in the
upper 20s to around 30. The low level WAA should translate south
of the WI/IL border overnight.

We are expecting frontogenesis to be the main player in
producing a heavy snow band across some portion of southern WI
Friday morning between roughly 6 AM and 1 PM. The 00z models are
on their way in and they seem to have a handle on the banded
snow developing over northeast Iowa which will continue to trek
eastward through southern WI, primarily along and south of I-94.

There is still no real convincing evidence that can push me over
the edge to issue a warning and be confident in that location at
this time. Seeing things unfold on radar is helping to get a
better picture, but a few more hours to see where the best fgen
bands are going to line up will be helpful. I am also concerned
that bands will be transient enough to blanket the area with a
decent amount of snow (3-6"), but only be intense for short
periods of time.

Cronce

&&

.SHORT TERM...
Issued 320 PM CDT Thu Mar 21 2024

Tonight through Friday night:

Focus continues to be on snowfall tonight and Friday. A few
light echoes are already overhead, but dry air in the low
levels (dewpoint depressions on the order of 25 degrees in some
cases) will have to be overcome before anything makes it to the
ground.

We should start to see snow begin to reach the ground late
tonight, associated with warm advection aloft pushing in from
the northwest. That area of snow will expand in coverage
overnight. By daybreak, look for an enhanced band or two of snow
to develop, associated with an area of frontogenesis. This is
currently most favored along and just south of the I-94/US 18
corridor, but the "envelope" of reasonable solutions ranges from
north of the Interstate to as far south as northern Illinois.
Outside of this band of snow, most areas should see 2-5 inches
of snow by the time precipitation ends Friday. Wherever that
band tracks, however, totals will likely be in the 6-8 inch
range, with very heavy snowfall rates through the morning hours
tomorrow.

There was a lot of consideration given to upgrading part of the
current Winter Weather Advisory to a Winter Storm Warning for
the morning hours tomorrow. However, it is prudent to give
things another 6-8 hours to try and resolve the location and
intensity of the band, and not include counties unnecessarily
in a warning.

Impacts from this event will largely be driven by snowfall
rates and timing, not exact snow amounts. Those rates,
unfortunately, look to be maximized during the morning hours
tomorrow, likely impacting the morning commute in many
locations.

Snow will end from west to east from late morning through early
afternoon tomorrow. Temperatures tomorrow will be in the low to
mid 30s, warmest to the west where precipitation will end
earlier. This should give at least some time for melting before
temperatures fall into the teens tomorrow night, when refreeze
may become a concern.

Boxell

&&

.LONG TERM...
Issued 320 PM CDT Thu Mar 21 2024

Saturday through Thursday:

High pressure passing by to the north of the region should bring a
dry Saturday to the area. Temperatures look to remain in the 30s
with north to northeast winds.

Models and ensembles seem to be in decent agreement with general
trends regarding the next low pressure system to affect the
region, mainly Sunday into Tuesday. Low pressure should shift from
the Central High Plains Sunday into western Iowa on Monday, then
into northern Wisconsin or western Lake Superior Tuesday. There
remains some uncertainty with the low track for Monday into
Tuesday in the ensemble output.

Still, it appears that warm air and moisture advection will push
into the region later Saturday night into Sunday, with thermal
profiles still cold enough for snow across the area. However, the
better upward vertical motion fields should remain to the
northwest of the forecast area during this period, and increasing
southeast winds may help bring a feed of dry air, which may delay
the onset of precipitation until perhaps Sunday night or Monday.
So, further refinements with PoPs are expected for the Saturday
night into Sunday night/Monday morning period.

As the low shifts into the region Monday into Tuesday, the
associated low level frontogenesis with the cold front should
bring more organized precipitation. Any snow would mix with and
change to rain later Sunday night into Monday morning, as the warm
air advection continues and brings the warm sector airmass into
the area. There is a small chance for thunderstorms with the
frontal passage Monday afternoon or night, if high enough
dewpoints move into the area.

Some deterministic models and ensembles suggest there is also the
possibility of a dry slot shifting into the region after the
frontal passage for Monday night or Tuesday. This may bring the
ending time for precipitation up sooner than currently forecast.
Thus, there will be more adjustments to PoPs and QPF as this event
draws closer. Nearly all ensemble members suggest measurable
precipitation for this event. There seems to be more uncertainty
about the timing of the rounds of precipitation, so keep up with
the forecast. Ensembles and models agree that gusty winds should
occur Sunday night into Tuesday as the low shifts toward and
through the region.

At this time, ensembles suggest a dry period for the middle of
next week, with temperatures remaining on the cool side.

Wood

&&

.AVIATION...
Issued 927 PM CDT Thu Mar 21 2024

Snow will overspread the region overnight and slowly taper off
from northwest to southeast through mid afternoon. Ceilings and
visibility will fall overnight as snow increases in intensity.
The heaviest snowfall rates are expected to occur during the
morning hours on Friday, when visibility of less than 1 mile and
rates approaching 1" per hour are possible in some locations
along and south of I-94.

Winds tonight and most of Friday will be from the east and
southeast, turning northerly Friday afternoon.

Boxell/Cronce

&&

.MARINE...
Issued 320 PM CDT Thu Mar 21 2024

Winds will become more easterly tonight as high pressure pushes
eastward across the eastern Great Lakes. A Small Craft Advisory
is in effect for the nearshore on Friday due to elevated waves.

Low pressure will pass by to the south of the lake tonight and
Friday, with winds turning more northerly late Friday as the low
moves east of the region. Breezy northerly winds will continue
Saturday, before becoming easterly again on Sunday. Winds may
reach gale force at times Monday and Tuesday as a stronger low
pressure system moves through the region.

Boxell

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory...WIZ046-WIZ047-WIZ051-WIZ052-WIZ056-
     WIZ057-WIZ058-WIZ062-WIZ063-WIZ067-WIZ068...1 AM Friday
     to 1 PM Friday.

     Winter Weather Advisory...WIZ059-WIZ060-WIZ064-WIZ065-WIZ066-
     WIZ069-WIZ070-WIZ071-WIZ072...1 AM Friday to 4 PM Friday.

LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...10 AM
     Friday to 4 PM Friday.

&&

$$

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