Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 201553

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1053 AM CDT Sun Jun 20 2021

(Issued 1055 AM CDT Sun Jun 20 2021)

We are starting to see how things may evolve today with the 2
rounds of showers/storms. Currently we are seeing showers really
fighting drier air in the low levels preventing showers from
pushing into southern Wisconsin. Models suggest we should moisten
up but we are still waiting on that though it is likely delayed
somewhat. Thus not as much rain should be expected with this first
round. This could allow for some additional warming of the
southeast perhaps increasing instability, giving some storm
chances early this afternoon. With the very strong forcing
throughout and very strong wind shear any storms could easily
become organized and strengthen. However models are very down on
storm chances early this afternoon with the first round.

For the second round of storms models suggest better chances for
stronger storms though its a bit more conditional and fairly
restricted to the southern half of the CWA. Shear will remain
strong so any storms that develop with have potential to become
strong but lack of instability is the primary uncertainty.



(Issued 341 AM CDT Sun Jun 20 2021)

Today through Monday:

Today will bring some storms and showers across southern
Wisconsin. There will be good upper level support throughout the
day with a shortwave trough passing through southern Wisconsin
during the late morning and afternoon hours that is followed
quickly by another trough during the evening hours. The mid level
winds will be out of the south and southwest throughout the day
bringing consistent warm air and moisture advection. For the
first round of storms and showers during the late morning and
afternoon hours the forcing along the shortwave and increasing
moisture will allow storms/showers to fire across southern
Wisconsin. However, there is a lack in the instability during the
morning hours that could hinder storm development and intensity.
Wind shear will be increasing throughout the morning before it
evens out around 35 knots. The better instability will be along
the Wisconsin and Illinois border so its not out of the question
for a stronger storm to develop across far southern Wisconsin.

The second round of storms is expected to pass with the cold front
and main trough later in the day. There will be plenty of low
level shear to work with and the low level jet is expected to
push into the area. The question remains on if there will be
enough instability to produce stronger storms. The best
instability will be just across the border in northern Illinois.
If it can warm back up enough ahead of the front by either the
high level clouds dissipating or increased warm air advection then
the environment could destabilize. Given enough instability storms
will reach severe limits. Similar to the first round of
storms/showers, the better severe threat will be toward the
Illinois border.

After the passage of the cold front, winds will shift to
northwesterly and become gusty overnight through Monday. High
pressure will build in from the high plains on Monday bringing
clearing skies and dry weather. The winds are expected to
gradually weaken late Monday afternoon as the pressure gradient
slackens and high pressure moves into the Great Lakes Region.



(Issued 341 AM CDT Sun Jun 20 2021)

Monday night through Saturday:

A weak sfc ridge will move across the area for Mon nt into early
Tue. Good radiational cooling in an already cool airmass will drop
temps into the 40s. High temps only in the upper 60s to lower 70s
for Tue, but could be slightly cooler depending on the timing of
increasing cloud cover.

Sly flow and warm, moist advection then begins in earnest Tue nt-
Wed. 1000-500 mb thicknesses will rise from a low of 546-552 DM
Tue AM to 570 DM for Wed afternoon. Chances for showers and storms
Tue nt, which may linger into Wed. Srn WI will then be on the srn
periphery of quasi-zonal flow for later Wed into Thu and on the
edge of the mid level cap of 10-12C. Sfc temps will return to near
normal on Wed and well into the 80s for Thu with increasing
humidity. At least a couple shortwave troughs with the zonal flow
and a passing cold front on Fri will bring likely PoPs for showers
and storms and possibly a good amount of rain.  A cooler and more
pleasant airmass for Sat, but will maintain chances for showers
and storms as an upper trough approaches from the nw.



(Issued 1055 AM CDT Sun Jun 20 2021)

The confidence in potential for storms during the day today has
come down with still decent chances for showers though we still
could see some MVFR CIGS chances for that also seem somewhat
reduced. A second additional round of thunderstorms/showers is
expected to move through southern Wisconsin along a cold front
during the evening hours. CIGS are expected to drop to 900 to 800
feet AGL and VSBYS could drop to 6 SM in the vicinity of any
storm. South to southwesterly winds will persist throughout the
day before shifting to northwesterly winds behind the passing cold
front. Northwesterly winds overnight through Monday will be gusty
at times.



(Issued 341 AM CDT Sun Jun 20 2021)

The weak high pressure in the western Great Lakes Region will
gradually move easterly early this morning as a low pressure
system approaches from the southwest. The low pressure is
expected to move northeast across Lake Michigan tonight. Showers
and thunderstorms will be possible across the lake as the low
pressure passes. Winds will become south to southeasterly ahead
of the low today, then pick up out of the northwest behind the low
Monday. A Small Craft Advisory is in effect for the nearshore
waters from early Monday morning through Monday afternoon for the
gusty northwesterly winds. Wind will then become light again on
Tuesday as high pressure moves back into the area.



LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...1 AM Monday
     to 3 PM Monday.



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