Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 241809 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1209 PM CST Fri Feb 24 2017

.UPDATE...

No change to headlines. Drizzle will continue across southern WI
through the day as the surface low tracks through northeast IL.
the depth of the low clouds is around 4000 feet, all warmer than
the snow growth zone, which is resulting in widespread drizzle and
freezing drizzle, depending on the surface temperature. Removed
chance of thunderstorms for the rest of the day, as the better
instability is well to our east.

Moderate snow is still occurring in southeast MN within the
850-600mb frontogenesis zone. That band of fgen will march east
through WI tonight. Expect drizzle to change over to freezing
drizzle during the evening hours, and then change to snow with the
fgen band (and deeper cloud depth allowing for ice crystals). Snow
will taper off from west to east beginning early Saturday morning.
Flurries could linger through mid Sat morning.

Timing of freezing drizzle in southeast WI this evening is still
a little uncertain due to the possible dry slot and exact surface
temps. We may need to add a county or two to the winter weather
advisory by mid afternoon.

&&

.AVIATION/18Z TAFS/...

Drizzle is expected through the evening hours, with freezing
drizzle in areas northwest of Mineral Point to Madison to Fond du
Lac. Freezing drizzle will expand east from late afternoon into
the early evening, then change over to snow from west to east from
late evening into the overnight hours. 1 to 2 inches snow
accumulation expected.

Mainly IFR category ceilings with visibilities down to 2 to 4SM
are expected. Gusty northeast winds today will back north this
evening and northwest overnight. Look for light snow showers to
taper off from west to east Saturday morning.

&&

.MARINE...

Extended Gale Warning to 2 pm north of Port Washington as strong
low draws closer and gradient remains tight. Small Craft Advisory
with gusty winds persisting as low shifts into lower Michigan
later today. Northeast winds will back to the northwest overnight.

&&

.PREV DISCUSSION... /Issued 353 AM CST Fri Feb 24 2017/

TODAY AND TONIGHT...Forecast Confidence Is Medium.

Strong upward vertical motion from low level frontogenesis response
fields and low level jet nose helping drive precipitation across the
area. Mix of rain and freezing rain, with some snow and sleet,
continues across the Winter Weather Advisory area. Mainly rain is
occurring elsewhere. Elevated convection also continues to push
through the area, producing several reports of pea size hail along
the way.

This area of strong upward vertical motion will push north and east
of the area this morning. Mesoscale models suggest that there may be
more light precipitation developing along the 850 mb
convergence/baroclinic zone for the rest of the morning into the
afternoon. Some of these models are not as optimistic with more
precipitation developing. Thus, some uncertainty here with trends
into this afternoon. For now, will bank on low level convergence to
continue to generate light precipitation into the afternoon.

One issue will be the potential for a period of freezing rain moving
east across the area not in the current Winter Weather Advisory this
evening, before the change to light snow later tonight. The ice
crystals are lacking during the evening, and forecast soundings are
showing potential for freezing rain developing. This will battle the
milder road temperatures in this area, which may limit the extent of
any icing.

Still, this may cause hazardous travel conditions this evening.
Thus, the Winter Weather Advisory may need to be expanded across the
rest of the forecast area for this evening. Later shifts can re-
evaluate this potential, as it would not occur until this evening.
The Advisory continues as is across the rest of the area.

The change to light snow is still on track for this evening and
overnight west to east across the area. Snowfall amounts should be
in the 2 to 3 inch range toward the Dells and Montello, with lower
amounts to the south and east.

SATURDAY - Confidence...Medium
500 millibar low center proggd to be over ern WI in the morning. In
the low levels we will be well in the cold advection regime with
amplifying thermal trough. Gusty nw winds and the lingering light
snow associated with the upper low will make for wintery morning.
This system is then proggd to exit in the afternoon so have kept
pops confined to the morning for now. Any additional morning
accums look like about 1/2 inch or so. many areas will remain in
the 20s for highs.

SUNDAY - Confidence...Medium
Models continue to show a weak mid level wave riding through with
light or no qpf. Surface/850 low tracks to our north with weak
reflection of trough in the low levels. So for now just small pops
in our far north. 925 temps will bounce back to near zero celsius so
some modification in temps from the chilly Saturday.

MONDAY - Confidence...Medium Still looks dry as weak ridging slides
off to the east. A bit of a return flow sets up but low level winds
primarily southeast and rather weak. Precip with next system stays
to our south.

MONDAY NIGHT THROUGH WEDNESDAY - Confidence...Medium
Next low is still proggd to track across WI on Tuesday and then
shift off to our northeast Tuesday night into Wednesday. At this
time it still looks like a mostly warm system for us with some
mixiness possible at times within the initial moist push Monday
night into Tuesday. However the 00z ECMWF keeps much of this to our
south. Meanwhile the GEM and GFS both show a good slug of precip
with the waa but the GEM is much faster bringing this in Monday
evening while the GFS holds off until the daytime Tuesday. The
mid/upper level dynamics arrive Tuesday and Tuesday night with
both the GFS and ECMWF showing the 850 low tracking across WI this
period. COld advection regime starts later Tuesday night with
some possible wraparound light snow into Wednesday. GFS is more
bullish with the light qpf while the ECMWF shows very little or
nothing at all on Wednesday.

THURSDAY - Confidence...Medium
Another shortwave moves in from the northern Plains within the
northwest flow aloft. GFS and ECMWF are in decent agreement this far
out while the GEM shows nothing. This one looks like it would have
more cold air to tap left in place behind the last low. So some
accumulation potential with this clipper type system.

AVIATION/12Z TAFS/...Area of winter precipitation will continue
early this morning across the area, with a rain and freezing rain
mix in northern and western portions of the area, including
Madison. Mainly rain is expected elsewhere. Elevated thunderstorms
should continue to move through for the next few hours as well.

There may be a period of light precipitation for a time this morning
into the afternoon. Mainly freezing rain and rain should linger in
the northern and western areas, including Madison, with ice
accumulations up to 0.20 inches. Mainly rain is expected elsewhere.
Some uncertainty here with how widespread any light precipitation
will be.

There may be a period of light freezing rain pushing east across the
area this evening, before changing to light snow. Some uncertainty
here with this occurring. Snowfall amounts of 1 to 3 inches are
forecast mainly later this evening into early Saturday morning,
highest toward the Dells and Montello.

Mainly IFR category ceilings with visibilities down to near
alternate minimums are expected. Gusty northeast winds today will
back north tonight.

MARINE...Extended Gale Warning through 15z today to account for
stronger winds to potentially gale levels as strong low draws
closer and gradient remains tight. Gale Warning will eventually
transition to a Small Craft Advisory with gusty winds persisting
as low shifts into lower Michigan later today.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 AM CST Saturday for WIZ046-047-
     051-052-056>060-062-063.

LM...Small Craft Advisory until 6 PM CST Saturday for LMZ644>646.

     Gale Warning until 1 PM CST this afternoon for LMZ643.

&&

$$

UPDATE...MRC
TODAY/TONIGHT AND AVIATION/MARINE...Wood
Saturday THROUGH Thursday...Collar


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