Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 230021 AAA

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
721 PM CDT Thu Jun 22 2017


A few thunderstorms are developing out ahead of the main line,
within the warm sector. They are not forming along a radar-defined
boundary, but it`s roughly in the area of surface convergence
between north winds and south winds. The RAP mesoanalysis
indicates 1000-2000 CAPE south of the I-94 corridor that is
finally becoming uncapped. Bulk shear is not too shabby, around 30
kt. A few of these storms are intense, but are not growing too
high yet to support large hail. There was a report of pea size
hail in Waukesha.

Now for the evolution of the main line of storms that is expected
to track through southern WI later this evening... I think the
kicker of this convection that is focused along an elevated
frontal boundary is going to come from a shortwave trough way up
in northern MN. As it tracks southeast, this front will finally
start to move southeast. Timing is still uncertain, but the
showers are starting to get into our area now. Potential for
severe is limited. Thus, SPC dropped our area into a marginal risk
this afternoon.



Scattered storms are expected early this evening. Then a main line
of storms will track southeast through southern WI from late
evening through overnight hours. Timing is still uncertain of this

Period of MVFR ceilings possible behind the front late tonight.
Quiet weather expected Friday.


.PREV DISCUSSION... (Issued 342 PM CDT Thu Jun 22 2017)


Tonight...Forecast Confidence is Medium.

Latest SPC Day 1 Outlook has shifted most of the Slight Risk for
severe storms southward into northern Illinois, with a Marginal
Risk across most of the area. This is mainly in response to most
of the area seeing cloudy skies with on and off showers and
isolated storms for most of the day. There have been some breaks
in the southern parts of the area, with the north remaining

The best mean layer CAPE will be south of the state line, with
lower values along with some mean layer CIN in most of the area.
The best deep layer shear is in northern portions of the area,
with lower amounts to the south. Thus, it appears that areas near
and south of the Illinois border have the best shot at strong to
severe storms.

Mesoscale models still have convection developing across the area
by middle evening and pushing southeast with the cold front, with
the HRRR developing convection by 00Z to the north of the area.
Continued high PoPs for thunderstorms tonight, ending northwest to
southeast later tonight. Gusty winds, hail and heavy rainfall
still are the main hazards, with the best chances for isolated
severe storms near the Illinois border.

Friday through Monday...Forecast confidence medium.

A large polar trough will become established over much of ern
Canada and the Great Lakes for the weekend into early next week.
Cold advection on nwly sfc winds will increase late Fri aft-eve
but high temps on Fri will reach 75-80F beforehand. Otherwise nwly
sfc winds and unseasonably cool temps will prevail for the
weekend and Mon. High temps from 65-70F are expected with lows in
the upper 40s to middle 50s. A fairly strong shortwave trough will
bring good chances of showers Sat nt especially north of Madison
and Milwaukee. The chances of showers will continue for Sun-Mon
given cold temps aloft and potential weak vorticity maximums.

LONG TERM...Tuesday through Thursday...Forecast confidence

High pressure will finally settle over the area Mon nt-Tue
followed by a pattern change to more zonal flow across the nrn
USA. Thus warmer temps and higher humidity expected ahead of an
approaching shortwave trough and cold front for Wed-Thu.

AVIATION(21Z TAFS)...Gusty south to southwest winds should
linger until early evening in southern portions of the area.
Weaker winds will be found in cloudy areas to the north. Ceilings
should remain above 3000 feet this afternoon.

Thunderstorms are expected to slide southeast across the area
tonight, from northwest to southeast. They will spread southeast
during the evening, then end later tonight. Look for visibilities
down to 2 miles, and ceilings down to around 2000 feet. These may
be lower in any stronger storms. Gusty winds, hail and heavy
rainfall are possible, with the best chances for isolated severe
storms near the Illinois border.

May see ceilings around 2000 feet linger after the storms exit
the area later tonight into Friday morning, before mixing out.
West winds should become gusty by the afternoon hours. Some
diurnal cumulus clouds are possible as well.


Small Craft Advisory continues until 00Z Friday south of Port
Washington. Gusty south to southwest winds are expected until
early evening before weakening.

Thunderstorms are then expected to slide southeastward across the
area tonight. The timing for the nearshore waters of Lake
Michigan should be generally between 03Z and 09Z Friday. The best
chances for isolated severe storms will be toward Winthrop Harbor
Illinois. Gusty winds and hail are possible.

May see gusty west northwest winds reach Small Craft Advisory
levels at times on Friday, with cooler and drier air moving into
the region. Good mixing and a tight pressure gradient will help
with mixing these gusts to the surface. Highest waves will be over
the open waters.




Tonight/Friday and Aviation/Marine...Wood
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