Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 221220 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
720 AM CDT Mon May 22 2017

.UPDATE...

Showers over north central IL are associated with 850-700mb
theta-e advection. The showers are tracking east and could clip
southern WI by late morning. More showers are expected to the
south of that area, with the low level theta-e advection later
today. These should evolve into scattered thunderstorms over
northern IL and spread into far southern WI late this afternoon.
The latest HRRR run has backed off the coverage of thunderstorms
over srn WI a little.

The next area to watch will be along a weak cold front as it
tracks into southwest WI later this afternoon. Showers and storms
are looking likely along it, and there should be enough
instability for a few stronger storms. The timing of this front is
still uncertain, but it`s looking like early evening now. The
front is expected to stall over south central WI tonight.

&&

.AVIATION(12Z TAFS)...

Showers and thunderstorms will develop over northern IL and
southwest WI this afternoon and track east to the lake by late
afternoon into early evening. Coverage of these storms across
southern WI is still uncertain, so check the radar often this
afternoon. A few storms could be strong with small hail and gusty
winds.

MVFR ceilings and visibility are anticipated late tonight as
winds become light and low level moisture lingers.

&&

.PREV DISCUSSION... (Issued 335 AM CDT Mon May 22 2017)

Today and Tonight...Forecast Confidence is Medium...

The upper low over southern Ontario will shift a little to the
east today but leave behind an upper trough that extends back over
MN. Meanwhile, a weak cold front will track across the Midwest.
Ahead of this cold front, southwesterly flow will usher modest
low-level moisture into northern IL and southern WI this
afternoon.

This moisture and the fairly steep mid level lapse rates will
yield sufficient CAPE for thunderstorms late this afternoon into
the early evening. SPC kept the portions of south central WI
included the marginal risk for severe storms. This is mainly west
of Madison and Janesville. The latest meso models suggest that
thunderstorms might develop across northern IL around 4 to 5 pm
today and track northeast through far southern WI until early
evening. A few thunderstorms could be strong and one or two might
produce a 60 mph wind or 1-inch hail.

More showers with a few thunderstorms are possible along the cold
front as it slides southeast through south central WI in the 6-8
pm time period. Instability will drop off overnight with the
weaker surface and upper level flow approaching, so only a chance
of showers.

Highs today should get up to around 70 with a good amount of
morning sunshine, gusty southwest winds and warm air advection.
Overnight lows should remain elevated in the lower/mid 50s due to
cloud cover and lingering showers within the warm sector of the
system.

LONG TERM...

Tuesday through Thursday...Forecast confidence is medium to high:

An upper level low will slowly move through the area Tuesday and
Wednesday. This will bring multiple rounds of showers to the
forecast area. Left a slight chance of thunder in Tuesday
afternoon per model instability. This pattern will result in
mostly cloudy skies and more below normal temperatures for
Tue/Wed.

Should see a break in the precip on Thursday as the low pulls
away. Looks like there could even be some sunshine. High temps are
expected to be back near normal, except for cooler conditions near
Lake Michigan.

Friday through Sunday...Forecast confidence is medium:

Warm advection with a passing shortwave will bring a chance for
showers back into the area later Friday into Friday night. Could
be a few rumbles of thunder too.

Wet weather seems likely over the weekend as well as low pressure
passes through. It probably won`t rain all weekend, but models
aren`t in great agreement with the timing/placement of the low, so
precip chances ended up being spread out through the weekend. Will
probably see a few storms over the weekend too.

Temps are expected to be back around normal for Friday through the
weekend.

AVIATION(06Z TAFS)...

Some MVFR CIGS still linger over the area, mainly north of
Milwaukee and Madison now, and they will continue to lift north
tonight. VFR conditions will prevail into the early evening on
Monday. However, a low pressure system and weak frontal boundary
will push in from the west Monday afternoon and evening, bringing
increasing clouds again along with a chance of showers and
thunderstorms toward evening. Look for breezy southwest to west
winds during the afternoon, ahead of the low. As the low moves
overhead Monday night, the weak pressure pattern and increased
moisture may lead to a quick development of MVFR then IFR
CIGS/VSBYS during the late evening and overnight hours.

MARINE...

Gusty southwest winds are once again expected during the daytime
heating hours this afternoon into the early evening. Gusts up to
25 knots are anticipated, so a Small Craft Advisory is in effect
from noon to 9 pm. Highest waves will be toward the open waters.

Brisk northeast winds will probably reach small craft advisory
criteria on Wednesday.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory from noon today to 9 PM CDT this evening
     for LMZ643>646.

&&

$$

Update...Cronce
Today/Tonight and Aviation/Marine...Cronce
Tuesday THROUGH Sunday...DDV


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