Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 252108

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
408 PM CDT WED MAY 25 2016

.TONIGHT AND THURSDAY...Forecast Confidence Is Medium.

A broken north to south line of showers and thunderstorms continues
to slide northeast across Green Lake to Rock Counties. More showers
and storms were seen extending into north central Illinois. These
showers and storms were being driven by the main 500 mb shortwave
trough moving northeast through the region, as well as some focused
850 mb warm air/moisture advection. HRRR model has handled this
convection fairly well, and takes it out of the far east by middle
evening. Will follow this general trend with high pops shifting
northeastward into this evening.

A quasi-stationary surface boundary extended northwest to southeast
across the area as well, with a sharp temperature gradient. This
boundary has been helping some storms intensify, and per earlier SPC
Mesoscale Discussion may serve to add some low level rotation
potential to any storms that cross it. This will need to be watched
for quick spin-ups over the next few hours.

SPC has entire area in a marginal severe risk, which implies
isolated severe storms possible. Given the mean layer CAPEs to
around 1000 J/kg, and deep layer shear of 30-plus knots, could see
an isolated severe storm occur.

Other issue to watch is slow movement of storms, which may drop
heavy rainfall in a short period of time. This would bring minor
street flooding possibilities in urban and low lying areas.

Chances for showers and storms later this evening into Thursday are
more uncertain. HRRR and NAMNest try to bring a slowly decaying band
of showers and storms into the western area after 09Z Thursday, with
other mesoscale models dry or taking this area to the south of
Wisconsin. Area does get into warm sector airmass, as warm front
moves northward. Not a lot to latch onto as far as forcing for
upward vertical motion during this time period. For now, will keep
lower end chance pops for later tonight, with lower pops on
Thursday. A good part of Thursday may end up dry.

Some fog is possible later tonight into Thursday morning, with dew
points in the lower 60s and light winds. Areas near the lake may see
some fog as well later this evening. Warm temperatures are expected
tonight into Thursday. Highs in the middle 80s are expected over
most of the area with south southwest winds Thursday. They may get a
bit warmer if area remains precipitation-free and fewer clouds


All models bring weak short wave energy into srn WI overnight
Thursday night, with the 18Z NAM depicting a hefty meso-scale
convective vorticity maxima over the sw by 06Z. Will start dry in
the evening then trend pcpn in from sw to northeast with
strengthening 850mb winds/convergence. Better chances move in with
surface boundary lifting through the CWA Friday, followed by a short
wave for Friday night affecting mainly western sections of the CWA.

In spite of the precipitation still expect highs Friday to reach
around 80 inland with a south wind, with lakeside areas cooler
with onshore southeast winds. Expect lows in the lower to mid 60s
both nights.


Shower and storm chances continue with a persistent series of
vorticity maxima moving across the area ahead of the main 500 mb
trough, with the forecast area in the warm sector as the surface low
tracks to the west. Again, not an all-day rain but no one period
with low enough PoPs to have dry. Clouds and pcpn will hold highs
in the mid-upper 70s.


Models have slowed passage of the mid-level trough through the
region Sunday...keeping higher chance PoPs in the forecast into
Sunday evening. Mid-level flow becomes a bit more zonal over the
Upper Midwest for Monday before backing ahead of another trough
crossing the northern inter-mountain states into the Northern Plains
Monday night into Tuesday night...picking up a short wave in the
Central Plains and lifting it up into the area Tuesday/Tuesday

While overall pattern similar, timing/location differences in the
details lead to slight chance/chance PoPs through the extended.
Above normal temperature trend continues, but not as warm as this



Expect a broken line of showers and thunderstorms to continue to
move northeast across TAF sites through about 03Z Thursday. VFR
category conditions will prevail, though may see visibilities down
to fuel alternates in any showers/storms. Brief gusty winds and
small hail may occur as well. Easterly winds are expected at the
eastern sites into this evening, with south to southeast winds at

Should see mainly quiet weather for most of the rest of tonight into
Thursday across TAF sites. There are outside chances for showers and
storms later tonight into early Thursday morning at Madison, but not
enough confidence to mention in TAFs at this point. Most of Thursday
may end up dry.

There should be a period of light fog and low clouds across the area
later tonight into Thursday morning. May see ceilings down to or
even below 1000 feet above ground level between 09Z and 15Z
Thursday, with visibilities down to around 2 miles. Some uncertainty
here with the timing and how low ceilings and visibilities will get.



A Marine Dense Fog Advisory continues for Sheboygan to Port
Washington until 00Z this evening. Webcams there continue to show
dense fog at Sheboygan. The rest of the waters do not show much in
the way of fog, but chances should increase later tonight with
higher dew points and warmer air moving back into the area. The
showers and storms should help improve visibilities by early this
evening. Fog should develop again later tonight into Thursday, as
more warmth and moisture move into the area.

The fog should linger through the upcoming weekend, as warm and
moist air lingers over the region. May see some dense fog at times,
as the moist airmass lingers over the cool lake waters.


.MKX Watches/Warnings/Advisories...
LM...DENSE FOG ADVISORY until 7 PM CDT this evening for LMZ643.



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