Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 170426
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1126 PM CDT Tue May 16 2017

.UPDATE...

Thunderstorms are focused across northern Wisconsin along the warm
front. More thunderstorms are tracking northward from Iowa into
southern MN this evening and these will continue to progress into
west central WI overnight. South central and southeast WI is
expected to remain dry tonight.

Wednesday morning, the upper low will begin to dig into the
Plains and Upper Midwest. This forcing, along with mid level
frontogenesis, could lead to showers and thunderstorms across
south central WI mid Wed morning. Lots of uncertainty here, but if
this happens, then that might diminish our chances for severe
thunderstorms in this area Wed afternoon if we end up with cooler
temperatures than forecast.

If we can realize our full instability potential, the best chance
for severe thunderstorms will be during the mid afternoon hours
and probably from Madison westward. Decent 0-1km shear and good
0-6km bulk shear, around 1000 j/kg of CAPE, and strong forcing
from the approaching 500mb shortwave will give us the conditions
for possible severe storms. Large hail, damaging wind and
tornadoes are all possible. Model soundings are showing the strong
capping inversion standing strong through late afternoon east
of Madison, so that is why the greater severe threat is west.

&&

.MARINE...

Gusty southerly winds are expected during the daytime hours once
again Wednesday and Thursday. A small craft advisory is in effect
until Thu afternoon.

&&

.PREV DISCUSSION... (Issued 222 PM CDT Tue May 16 2017)

DISCUSSION...

Tonight and Wednesday...Forecast confidence is medium:

Ongoing thunderstorms may limp into the west later tonight into
Wednesday morning as the overnight convection wipes out.
Otherwise, looks like a mild and dry night for southern Wisconsin,
with forecast low temperatures fairly close to average highs for
this time of the year.

Focus tomorrow will be on the potential for another round of
strong to severe storms. Low pressure will lift from Kansas
tomorrow morning to northwest Iowa by the evening hours. A warm
and moist airmass will remain in place across southern Wisconsin
during this period. In addition, the low level jet associated with
the low will nose into the area from the south during the
afternoon. Given enough daytime heating after previous
convection/clouds wind down, should see ample instability develop
by the afternoon hours. This could lead to a round of storms
moving west to east from late afternoon into the evening hours.
SPC has upgraded most of the forecast area into a Slight Risk for
severe storms tomorrow. This certainly seems reasonable given the
instability and wind fields.

Temps will likely be warmest in the east tomorrow where there
should be less clouds and somewhat warmer temps aloft. Less
certainty in the west given the cloud/precip potential in the
morning and then redevelopment in the afternoon. It won`t take
much sunshine though to push temps up toward 80.

Thursday into Friday...Forecast confidence is medium.

The surface low will be over central Wisconsin at sunrise on
Thursday, lifting off quickly to the northeast during the day. We
will be pretty stable at that point, but we could have some
lingering rain in the morning, drying out for the afternoon. It
looks mostly dry through Friday as high pressure will be in place
between the exiting low to the northeast and another approaching
from the southwest. The southeast will still be rather warm on
Thursday with the cooler air advection holding off a bit longer
there. Cooler northwest of Madison. Friday temps will be the
coolest of the week with highs only in the 50s, and likely only
40s along the Lake Michigan shore due to an easterly wind.

Saturday and Sunday...Forecast confidence is medium.

Another deep low pressure system will lift into the Upper Great
Lakes over the weekend. The GFS takes the low up across Iowa and
Minnesota, west of our area, while the ECMWF is farther east,
tracking across our western forecast area. Either way it looks
pretty wet on Saturday with things hopefully drying out by Sunday
afternoon. This system should be more stable than the previous
ones. Although we may see some thunderstorms, they shouldn`t be
very strong.  Highs will generally be in the 60s with cooler
readings near the lake on Saturday due to an onshore wind.

Monday and Tuesday...Forecast confidence is low.

There is plenty of uncertainty for early next week. Most of Monday
looks dry, but another low may be approaching from the west
northwest introducing more chances of rain.

AVIATION(18Z TAFS)...

It still looks like the low level jet ahead of approaching low
pressure will result in some low level wind shear this evening
into the early morning hours of Wednesday.

Shower/storm chances will gradually increase in the western
forecast area later tonight into Wednesday morning. Decent chance
more widespread storms will affect much of the forecast area by
later afternoon into the evening hours.

Outside of lower visibilities within thunderstorms tomorrow, VFR
conditions are expected to prevail through the TAF forecast
period.

MARINE...

Southerly winds will continue to pick up this afternoon,
remaining gusty through mid-week as low pressure moves through the
region. Without much of an onshore component to the winds, waves
should generally stay in the 3 to 5 foot range the next couple
days. Left the Small Craft Advisory timing as is for now.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 4 PM CDT Thursday for LMZ643>646.

&&

$$

Update...Cronce
Tonight/Wednesday and Aviation/Marine...DDV
Wednesday Night through Tuesday...Davis



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