350
FXUS63 KMKX 180932
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
432 AM CDT Sat May 18 2024

.KEY MESSAGES...

- Chance of isolated thunderstorms Saturday evening

- Warmer and more humid today through Sunday

- Rain and a chance of thunderstorms Monday and Tuesday

&&

.SHORT TERM...
Issued 432 AM CDT Sat May 18 2024

Today through Sunday:

On the western edge of exiting high pressure this morning dry
and quiet weather is expected to continue. Some ground fog has
developed mainly in low lying areas across southern Wisconsin.
Fog is very patchy with many areas maintaining visibilities of 4
SM or greater. Overnight temperatures have been higher,
especially in our larger urban landscapes which has kept the dew
point depression high (effectively preventing dense fog). While
temperatures will continue to decrease until after the sun has
risen, many areas may not reach the dew point value and thus
will evade any dense fog. Southerly winds will begin to increase
this morning as well which will aid in preventing further fog
development.

Clear skies and another warm day is ahead of us here in southern
Wisconsin today. Given the warmer temperatures this morning and
the fact that temperatures overperformed yesterday, daytime
highs were bumped up a bit. To further support the slightly
increase temperatures is the 925mb temperatures near 22 degrees
and adiabatic lapse rates. This will bring surface temperatures
closer to 86 to 88 degrees.

This evening a low pressure system to our north will drag a
frontal boundary across the state. The best of the synoptic
forcing and moisture is expected to stay to our north. Guidance
has been pretty bullish with this line of showers and isolated
storms especially across central Wisconsin where the synoptic
forcing will be weak due to the distance from the low pressure
system. Many of the guidance have mid level dewpoints much
higher than what is currently in place and upstream from us,
which includes when the breezy southerly winds kick in this
afternoon. Which likely contributes to the bullish response. Now
there will be great sfc based instability with clear skies and
warm temperatures and the weak frontal boundary will provide
some lift even with how weak it is. So there is a small chance
(roughly 20-30% chance) across south central Wisconsin for some
showers and a couple rumbles of thunder this evening. This line
of showers should be diminishing and falling apart as it travels
eastward as the timing puts the frontal boundary moving through
after dark. Thus the chance showers becomes a slight chance (15%
or less) across southern and eastern portions of the forecast
area. Overall, not super enthused about the chance for rain this
evening, but given the weak lift and great instability any
available moisture no matter how small could be squeezed out.

Beyond this, dry and quiet weather will remain for much of the
day Sunday. A low pressure system will be advancing from the
Rocky Mountain west and central Plains for Sunday night into
Monday. This system has ever so slight increased its speed
meaning a slightly earlier arrival in POPs than previously.
Regardless of this slight shift much of the day will remain dry
and cloud cover will increase throughout afternoon. Sunday is
expected to be slightly cooler than today with high temperatures
in the 60s along the lakeshore to near 80 inland.

Patterson

&&

.LONG TERM...
Issued 432 AM CDT Sat May 18 2024

Sunday night through Friday:

Sunday night into Monday the first of a number of upper level
shortwaves will traverse Wisconsin. The associated sfc low
pressure system will traverse the Great Lakes Region. Timing
still remains the biggest concern with this system as
discrepancies will remain. The current guidance trend has
brought this system through a bit earlier than previous runs.
Regardless of the timing of this system the potential for a few
thunderstorms remains with warm sfc temperatures bringing in
some instability and modest 0-6km wind shear. If the diurnal
heating trend over the previous days continues to overperform
then the instability could increase even more and with the mid
and upper level support a few stronger to severe storms cant be
out of the question. The overall concern for any strong storm
Monday would be wind and some hail.

The next shortwave trough and surface low eject into the Great
Lakes Region Tuesday afternoon will be a much better showing on
the severe weather potential. Out the gate the low pressure
system look deeper and stronger than the previous. Guidance
soundings are indicating there would be some steep mid level
lapse rates with warm temperatures and good sfc instability.
This has resulted in higher CAPE values. 0-6 km shear wont be
anything to scoff at either , thus the SPC 15% probability
remains for all of southern Wisconsin. As this system pulls
through the area the organized convection will likely be along
or ahead of a cold front. Rain will likely linger on the back
side of this system Wednesday with a more stratiform rain set
up.

By the end of the work week, high pressure looks to make a
return. This will bring a return some more dry and quiet
conditions. Some of the ensembles try to bring in another weak
low pressure system, but these solutions are greatly outnumbered
by those with high pressure. Thus some low end POPs did make
there way into the forecast for Friday, but dont expect that to
persist for long.

Patterson

&&

.AVIATION...
Issued 432 AM CDT Sat May 18 2024

Widespread VFR conditions are expected to continue through the
period. Patchy ground fog early this morning could bring a brief
period of MVFR conditions, but visibilites are expected to
remain 4 SM or greater. Lake shore terminals that are closer to
the marine air will have the best chance of seeing these 4 SM
visibilites. Light and variable winds tonight will become
southerly and slightly increase by this afternoon. This evening
a weak cold front is expected to traverse the region causing
winds to shift to northerly. An isolated to scattered
shower/storm will be possible as this boundary pushes through.
The best chance for an rain will be across south central
Wisconsin. Clear skies will return behind this frontal boundary
for Sunday.

Patterson

&&

.MARINE...
Issued 432 AM CDT Sat May 18 2024

The last of the dense fog across Lake Michigan has or will
dissipate as we approach sunrise this morning. The few small
pockets of dense fog along the west central lake have been
shrinking over the last couple of hours. Satellite shows the
majority of the lake clear, thus the Dense Fog Advisory has
ended. The light and variable winds this morning will become
southerly and increase slightly. While winds will be breezy,
both winds and waves will remain below small craft criteria. The
light and variable winds return Sunday. Monday and Tuesday
winds will again switch to southerly and increase as low
pressure systems move into the Great Lakes Region bringing
chances for thunderstorms.

Patterson

&&

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

&&

$$

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