Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 212013
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
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.

.EXTENDED PERIOD...

.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.

&&

.AVIATION(21Z TAFS)...

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
pressure.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...

WI...Dense Fog Advisory until 7 AM CDT Tuesday for WIZ052-059-060-
     065-066-071-072.
LM...Dense Fog Advisory until 10 AM CDT Tuesday for LMZ643>646.


$$

TONIGHT AND TUESDAY/AVIATION/MARINE...PC
TUESDAY NIGHT THROUGH MONDAY...MBK



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