Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 220150

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
850 PM CDT Mon May 21 2018

Visibilities across the southeast lifted for a time late this
afternoon and early evening, but have since been dropping steadily
with many sites now at 1/4 mile. The dense fog advisory in place
looks good. The drizzle or light showers will continue into the
night as a mid level short wave moves from southeast MN and across
central/srn WI overnight.


The marine dense fog advisory continues. Winds and waves will
remain below small craft advisory levels for the next few days.


.PREV DISCUSSION... (Issued 534 PM CDT Mon May 21 2018)

A damp night is on tap. A mid level short wave over southern MN
and drifting east early this evening, won`t be exiting to the
east of Wisconsin until close to sunrise on Tuesday. The bulk of
the rain will be heading off to the northeast early this evening,
but the weak omega from this shortwave will likely just mean
persistent drizzle, scattered light showers through the night.
Dewpoints are higher than the Lake Michigan water temps, so expect
dense fog to become more widespread across the east under a light
east to northeast wind flow off the lake. The current forecast
has all this handled well.


IFR and LIFR conditions can be expected through Tuesday morning.
Drizzle or scattered light rainshowers will also persist tonight.
The combo of a very moist airmass and a cool wind off Lake
Michigan should result in very low visibilities close to the lake,
and this would include KMKE/KENW/KUES. Conditions should begin to
improve by Tuesday afternoon, but very slowly.

PREV DISCUSSION... (Issued 315 PM CDT MON MAY 21 2018)

TONIGHT AND TUESDAY...Forecast Confidence - Medium.

Weak low pressure will shift into srn lower MI by late tonight.
Areas of rain likely to persist into early this evening though
gradually decreasing from sw to ne. High pressure will nose in for
later tonight into Tuesday. The airmass will remain moist with fog
the main concern. Issued an Advisory for the lake counties earlier
and have nudged it a bit west into Waukesha/Washington based on
trends. Some models are showing higher vsbys further west into the
cwa so any further expansion will be predicated more on
trends/evolution. The low level RH progs show a good deal of
moisture lingering into Tuesday. Expecting vsbys to improve through
mid morning with the stratus likely lifting into a cu field as the
day progresses. Temps will hinge on how quick we can emerge into the
sun, but with longer days it won`t take much to reach guidance highs
inland with any sunshine that pokes through.

TUESDAY NIGHT THROUGH THURSDAY...Forecast Confidence - Medium
to High.

Expect a quiet start to the period as short wave ridging and weak
surface high pressure drift across the western Great Lakes Tuesday
night and Wednesday.  Meanwhile deeper moisture return and
increasing synoptic lift will be located upstream across the
northern Plains, spilling into MN/IA Wednesday and Wednesday night.
Both the GFS and NAM are showing more persistent high pressure
ridging over WI and the western Great Lakes on Wednesday and
Wednesday night with drier southeast flow.  ECMWF also pulling back
on QPF expected Wednesday night in western CWA.  This more
persistent ridging likely a result of weaker and farther west short
wave trof pushing into the northern Plains Wednesday night and
Thursday.  Still will need to carry schc pops for T in western CWA
Wed/Wed night as weakening mesoscale convective eddy may push
through low to mid-level ridge during this period. NAM guidance also
showing a little stronger mid-level jet max and surge of warm air
advection moving across northern IA into southwest WI on Wed.

Otherwise, expect most of the period to be dry and mild with periods
of mid-high level cloudiness and warmer temperatures.


THURSDAY NIGHT THROUGH MONDAY...Forecast Confidence - Medium.

Medium range guidance in reasonable agreement on long wave ridging
over eastern CONUS extending into the Great Lakes flattening and
succumbing to an upstream weakening short wave trof moving across
the northern Plains into the Great Lakes over the weekend.
Increasing south winds ahead of this short wave and associated
surface low pressure system and cold front will continue to pull
deeper column moisture into WI early in the period. Precipitable
water values will hover around 1.5" through Saturday.  Main period
of warm air advection Thursday night into Friday with several pieces
of 500mb short wave energy caught in increasing southwest steering
flow.  Low level jet bends over with weak axis in the vicinity of
southern WI during this period.  0-6km shear looks low but steeper
lapse rates and MUCape values potentially reaching 2K j/kg.  CIPS
experimental probability of severe analogs also show the potential
for severe weather across southern WI Friday into Saturday.  Thunder
threat will continue into Saturday night until mid-level trof and
sfc front move off to the east.  Drier and slightly cooler
conditions will return for the latter half of the holiday weekend,
especially by Lake Michigan.


Plenty of IFR/LIFR expected through tonight into Tuesday morning.
While the rains will be gradually heading out into this evening, the
moisture and increasingly lighter winds will lead to a sustaining of
the stratus and further development of dense fog. Model trends
suggest our eastern forecast area will be most vulnerable with added
moisture from Lake Michigan. Low level RH progs show a potentially
slow erosion of the stratus Tuesday morning with better improvement
during the afternoon though at best would expect the evolution to a
MVFR or VFR cu field in the afternoon.

MARINE...Main concern is the fog. Dense Fog Advisory remains in
effect into mid morning Tuesday. Otherwise light wind regime will be
in place over the next few days due to persistent influence of high


WI...Dense Fog Advisory until 7 AM CDT Tuesday for WIZ052-059-060-065-

LM...Dense Fog Advisory until 10 AM CDT Tuesday for LMZ643>646.



Tonight/Tuesday and Aviation/Marine...Collar
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