Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 231514 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1014 AM CDT Tue May 23 2017

.UPDATE...

500 mb low will slowly slide southeast from southern Minnesota to
central Iowa today, then into northeast Missouri tonight. It will
then slide further to the southeast on Wednesday. Differential
cyclonic vorticity advection from several vorticity maxima will
aid upward vertical motion this afternoon into tonight. In
addition, there will be some low level confluence/convergence
from the passing weak surface low.

These should help combine to bring numerous showers to the area
by this afternoon, lingering into tonight. Forecast soundings also
show some weak mean layer CAPE with steep low to mid level lapse
rates and cold 500 mb temperatures. Thus, kept the isolated
thunder wording for this afternoon into this evening. Small hail
is possible with any storms. Some showers may linger into
Wednesday as well, with low level moisture remaining with some
upward vertical motion.

Cloudy skies with the expected 925 mb temperatures should bring
highs to the lower 60s across the area. Cloudy skies and some
showers tonight into Wednesday should keep lows in the upper 40s
tonight, with highs Wednesday in the 50s lakeside to around 60
well inland.

Wood

&&

.MARINE...

Some fog may develop over the nearshore waters of Lake Michigan
today into tonight, with light winds and the moist airmass over
the area. Not expecting dense fog at this time.

The pressure gradient will increase Wednesday into Wednesday
evening, as the surface low moves further to the southeast of the
region. Gusty north to northeast winds are expected by later
Wednesday morning into early Wednesday evening. Frequent gusts to
around 25 knots appear likely during this time. This will help
generate elevated waves of 3 to 5 feet as well. A Small Craft
Advisory will likely be needed during this time.

Wood

&&

.PREV DISCUSSION... (Issued 538 AM CDT Tue May 23 2017)

AVIATION(12Z TAFS)...

A weak wind flow across the area coupled with ample low level
moisture has lead to areas of IFR and MVFR CIGS across southern
WI this morning. CIGS will lift to predominantly MVFR levels this
morning with VFR conditions expected during the afternoon from
about Milwaukee to Madison and points south. However, an
increasing northeast flow off Lake Michigan tonight will allow
the lower conditions to return this evening, with IFR cigs/vsbys
expected across the southeast.

Look for scattered showers and isolated thunderstorms to develop
by mid to late morning and become widespread this afternoon into
this evening. The showers will diminish in coverage later tonight.

Winds will back to the southeast by early afternoon, then
northeast this evening.

PREV DISCUSSION... (Issued 252 AM CDT Tue May 23 2017)

SHORT TERM...

Today and tonight...forecast confidence is high.

A closed mid level low will continue to drift south from
Minnesota into Iowa today. This is part of a very large trough
system that extends up to James Bay, Canada. Temps aloft are quite
cold in the core of the low, down to -22C. At the surface, a low
pressure center will drift across southern Wisconsin with
dewpoints in the 50sF. The weak convergence associated with the
low, coupled with the steep lapse rates due to the moist low
levels and cold temps aloft will lead to scattered showers and
isolated thunderstorms. Short wave perturbations rotating around
the upper low will help to encourage precip development. The rain
should focus best along the weak low level trough axis during
peak heat this afternoon where convergence will be maximized. This
could lead to some localized heavy rain. That axis should be
centered right over the middle of southern Wisconsin. Given the
cold temps aloft, some small hail might fall out of out an over
productive shower/storm. No severe weather is expected today. The
activity will continue into tonight, but will begin to taper off
with the diminishing diurnal trends.

LONG TERM...

Wednesday and Thursday...Forecast confidence is medium to high:

The upper level low will continue to move slowly through the area
on Wednesday. This will keep shower chances going across southern
Wisconsin. Below normal temps will continue with the precip
chances and mostly cloudy skies.

Should see a break in the precip on Thursday as the low pulls
away. Still looks like there should be a decent amount of
sunshine. High temps are expected to be back near normal, except
for cooler conditions near Lake Michigan.

Friday through Memorial Day...Forecast confidence is medium:

Multiple shortwaves are expected to move through the area Friday
through Memorial Day. This will bring a daily chance for showers
and storms. No day looks like a washout through this upcoming
holiday weekend, but unfortunately no day looks completely dry
either. On a more positive note, there will probably be some
sunshine at times and temperatures are expected to remain around
normal values for late May.

AVIATION(06Z TAFS)...

We should see a lull in the shower activity early this morning.
But, this will pick back up by mid to late morning and continue
into tonight. A few thunderstorms are possible this afternoon and
evening, no severe weather is expected. Low pressure slowly
approaching from the west resulting in diminishing winds with high
low level rh lingering over southern WI. Seeing some increase in
sct-bkn MVFR clouds across southern WI so expect this trend to
continue as low edges closer during the late night into Tuesday
morning.

MARINE...

Low pressure developing and moving by to the south of Lake
Michigan will bring persistent northeast winds that will likely
build large waves resulting in small craft advisory conditions
Wednesday through Wednesday night.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

Update...Wood
Today/Tonight and Aviation/Marine...Davis
Wednesday THROUGH Monday...DDV


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