Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 190458
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1058 PM CST Sun Feb 18 2018

.UPDATE...

Immediate concern is Low ceilings and dense fog. We should be
fine for the most part through sunrise, then indications of a
rapid decrease in visibilites as the moisture arrives over the
cold ground. May eventually need a dense fog advisory.


&&

.AVIATION(06Z TAFS)...

VFR mid/high clouds. Will be watching stratus early this morning
as moisture increases from the south. Expect the IFR/LIFR
CIGS/vsbys to arrive after sunrise with the lower vsbys/stratus
expanding across the rest of the CWA as the morning wears on as
low level moisture advection continues.

With strong winds above the surface will continue Low level Wind
Shear in the TAFs through around midnight/early morning hours.
Rain will be overspreading the area on Monday however any freezing
rain potential will be well north of the TAF sites through the
day Monday. That freezing potential will sag further south Monday
evening possibly reaching KMSN.

&&

.PREV DISCUSSION... (Issued 900 PM CST Sun Feb 18 2018)

UPDATE...

The 00Z NAM is around 1 degree warmer in it`s surface temperatures than
the prior 18Z run. Not enough new data to make any changes to the
Ice Storm warning start time of 3 pm, especially given prior
model run`s difference of 10 degrees at 3 pm between the GFS MOS
and NAM MOS at Fond du lac. How fast the surface temperatures
drop behind the cold front/trough will be key. However the new NAM
MOS for Fond du lac at 3 pm is now 33, up from the prior cold 27.
Still areas north of the Dells to Fond du lac on the new NAM MOS
drop to or just below freezing at 3 PM.

Other concern is Low ceilings and dense fog. We should be fine
for the most part through sunrise, then indications of a rapid
decrease in visibilites as the moisture arrives over the cold
ground.

MARINE...

Still gusting to 36 knots at Sheboygan, but winds have dropped
just a little, so the Gale warning looks O.K. to end at midnight.
Have put up a Small Craft til Tuesday morning in it place
afterwards. Will likely have a brief period of light winds, but
then as the trough pushes south, northeast winds will pick up
again Monday afternoon. For now will extend the Small craft in the
south til 3 am CST.

PREV DISCUSSION... (Issued 522 PM CST Sun Feb 18 2018)

UPDATE...

Rather brisk south winds to continue but the strong gusts will
diminish with sunset.

AVIATION(00Z TAFS)...

VFR mid/high clouds well into the evening hours. Will be watching
stratus trends later tonight into Monday morning as moisture
increases from the approaching system. Lower ceilings still down
in OK so a ways to go yet. Expect the IFR/LIFR CIGS/vsbys to
arrive after sunrise with the lower vsbys/stratus expanding across
the rest of the CWA as the morning wears on as low level moisture
advection continues.

With strong winds off the deck will continue Low level Wind Shear
in the TAFs through around midnight/early morning hours as some
of the surface gustiness of the day wanes.  Rain will be
overspreading the area on Monday however any freezing rain
potential will be well north of the TAF sites through the day
Monday.  That freezing potential will sag further south Monday
evening possibly reaching KMSN.

MARINE...

35 knot sustained gust 41 knots at Sheboygan, so the gale warning
is doing well. Marine headlines look ok through midnight.

PREV DISCUSSION... (Issued 229 PM CST Sun Feb 18 2018)

DISCUSSION...

Tonight - Confidence...Medium
The southerly flow will continue and this will gradually draw
more moisture northward into the area. At this time I prefer the
more gradual approach of the 925/850 RH fields versus the quicker
NAM. Would expect winds to ease a bit overnight but expect enough
of a south wind to keep the temps from dropping off too much and
also allow for a slow but steady moisture transport. Some drizzle
potential late with the arrival of the stratus but by and large
models are keeping the precipitation return south of the state
line.

Monday through Tuesday night...Forecast confidence is high.

Confidence is very high we`ll see a lot of precipitation across
the area during this period. There is a zone of freezing rain
north of Milwaukee and Madison that has more uncertainty with it.

The setup remains unchanged. A powerful low level jet, fluctuating
in intensity and orientation, will provide an impressive flux of
moisture into the area from time to time. The focused low level
frontogenesis over southern Wisconsin is strong and will also
fluctuates in intensity as it response to the jet. The right rear
quad of the upper jet will be favorably located over the area
providing the opportunity for deep omega. The climatological value
of the moisture profile is nearly maxed out across our far
southeast. The NAM continues to have the lower QPF values, while
the GFS/ECMWF and especially the Canadian are still in the 1 to 2
inch range, or higher in some cases. This, coupled with the
lingering icy snowpack and frosty ground has prompted the issuance
of a flood watch for parts of south central and southeast
Wisconsin. Contingencies forecasts from the River Forecast Center
suggest some rivers across our southern tier counties could exceed
flood stage.

The freezing rain/ice concern...the biggest challenge with the
ice is determining just how far south the very shallow arctic
airmass will wedge under the very strong warm layer aloft. As an
example of this contrast, the NAM, across Green Lake and Marquette
counties shows the cold layer bottoms out at -8C at 1000ft above
ground level while the warm layer at 3000ft is +7C. The GFS is
similar, just not as extreme on the high and low end.

With an increasing northeast flow at the surface, it will be tough
for temps north of Madison to stay above freezing on Monday and
they should begin to collapse by mid afternoon. At this point, the
threat for freezing rain will begin north of Madison and
Milwaukee. The intrusion of the cold air will filter farther south
Monday night and so will the threat for the freezing rain.

We`ll see a surge of warmer air and another round of rain on
Tuesday. This could push the freezing rain threat back north out
of the forecast area. The rain then finally pushes southeast of
the area Tuesday night, bringing and end to the hazardous weather.

This is an incredibly complex scenario with a very tight
temperature gradient across southern Wisconsin. The model guidance
doesn`t handle very shallow arctic airmasses very well, so
expected adjustments as the event unfolds.

Wednesday - Confidence...Medium to High
High pressure will be building in. Cold advection and a push of
drier air will make for a needed reprieve from the prior days.

Thursday - Confidence...Medium
Would tend to favor the consensus of the GFS and GEM on keeping
the dry look with the influence of high pressure in place. The
ECMWF spreads light qpf into the area with a vort max well to our
northwest but the high still looks dominant. So favor the drier
look.

Thursday night through Saturday - Confidence...Medium
Active southwest flow returns. Again sticking with the consensus
of the GFS and GEM for the arrival of the next better push of
moisture with another round of rain, mixed precipitation or snow.
The models show there could be 2-3 rounds of precipitation as a
few waves move northeastward within flow.

Sunday - Confidence...Low
Some disparity on how quick things wrap up with the GFS showing a
dry day with precip off to our east. Meanwhile the GEM and ECMWF
suggest precip lingers. Will stick with the blended pops which
keep a pop in our southeast.

AVIATION(18Z TAFS)...VFR mid/high clouds well into the evening
hours. Will be watching stratus trends later tonight into Monday
as moisture increases from the approaching system. Lower ceilings
still down in OK so a ways to go yet. Will start nudging vsbys
down late tonight in the far SC WI with some lower vsbys/stratus
expanding across the rest of the CWA as the morning wears on as
low level moisture advection continues. With strong winds off the
deck will have LLWS in the TAFs for a period tonight as some of
the surface gustiness of the day wanes. Rain will be overspreading
the area on Monday however any freezing rain potential will be
well north of the TAF sites through 00z. That freezing potential
will sag further south Monday evening possibly reaching KMSN.

MARINE...Marine headlines look ok through midnight. Getting some
gusts pushing gale criteria in the north so status quo for now.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Flood Watch from Monday evening through late Tuesday night for
     WIZ063>066-068>072.

     Winter Weather Advisory from 6 PM Monday to 6 PM CST Tuesday for
     WIZ059-062-063.

     Ice Storm Warning from 3 PM Monday to 6 PM CST Tuesday for
     WIZ046-047-051-052-056>058.

LM...Small Craft Advisory until midnight CST tonight for LMZ644>646.

     Small Craft Advisory from 6 PM Monday to 6 AM CST Tuesday for
     LMZ643.

     Gale Warning until midnight CST tonight for LMZ643.

&&

$$

Update...Hentz
Tonight/Monday and Aviation/Marine...Hentz
Monday Night through Sunday...Davis



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