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000
FXUS63 KMKX 220300
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1000 PM CDT Sun Apr 21 2024

.KEY MESSAGES...

- Potential for patchy frost tonight, with more widespread
  frost/freeze concerns Tuesday and Wednesday nights.

- Elevated fire weather potential on Monday.

- Rain chances return Monday evening, continuing through
  Tuesday.

- More active pattern into late next week.

&&

.UPDATE...
Issued 1000 PM CDT Sun Apr 21 2024

Observed temperatures across the region are trending close to
prior forecast expectations, indicating that widespread frost
is unlikely tonight (hence we have not issued a frost advisory
at this time). Localized areas of patchy frost may yet develop,
especially in areas away from urban heat islands effects and the
Lake Michigan shoreline. Even in said "cooler areas", forecast
soundings from CAMs indicate impressive radiational surface
inversions (as expected with clear skies and rapidly
decelerating sfc winds tonight), yet they indicate surface
temperatures above freezing through the night. Tonight`s
residual layer features relatively slow wind speeds (around 15
knots 500 to 1000 ft AGL), but not slow enough for complete
decoupling of the lower PBL or widespread frost formation.

Elevated fire weather conditions remain a concern for Monday.
Model guidance for dewpoints has trended slightly towards the
drier direction, yet guidance for the approach of upper-altitude
cloud cover Monday afternoon has trended slightly in the
cloudier direction (which may limit afternoon mixing and
dewpoint depressions). These opposing trends suggest the
forecast for daily minimum RH around 25% for most areas (with
the potential to fall to near 20% if mixing over-performs)
remains on track.

Sheppard

&&

.SHORT TERM...
Issued 307 PM CDT Sun Apr 21 2024

Tonight through Monday night:

Clear skies and breezy northwesterly winds will continue through
tonight, with a few diurnal cumulus clouds across central and
southeastern Wisconsin dissipating into this evening. Winds will
diminish into this evening, becoming light and northwesterly.
Due to high pressure sinking farther south than previously
modeled, light southwesterly winds and mixing remains likely in
the lowest portions of the boundary layer. This would lead to
prevention of frost formation in most regions, but frost is
still possible in the Kettle Moraine and low lying areas,
including the Wisconsin River Valley. In addition, temperatures
look to only briefly fall below freezing just before sunrise,
and most areas look to remain in the 33 to 35 degree range. Held
off on any Frost Advisories due to these less than favorable
conditions for widespread frost development, but will continue
to monitor trends into this evening.

Monday, southwesterly winds increase. This will bring in warmer
temperatures, especially with minimal cloud cover in the
morning. Expecting highs in the mid-60s. In addition, relative
humidity values will fall into the 25 to 30 percent range. If
temperatures rise into the upper 60s ahead of cloud cover,
relative humidities may fall to near 20 percent. This, in
conjunction with winds becoming gusty at 25 to 30 mph during the
early to mid afternoon hours and the potential for drier air
above the boundary layer inversion to intrude downward, may
result in elevated fire weather concerns.

Southwesterly winds continue ahead of a low pressure passage to
the north Monday night. Showers are expected to develop ahead
of this passage and will progress eastward through the
overnight hours. Additional showers will continue to develop
into Tuesday morning as the parent low occludes to the east.

MH

&&

.LONG TERM...
Issued 307 PM CDT Sun Apr 21 2024

Tuesday through Sunday:

As the low pressure system advancing from the Northern Plains
toward the northern Great Lakes Region Tuesday more rain is
expected across southern Wisconsin. The signal for much of the
day to be dry is increasing as the low pressure system is
expected to weaken and elongate as it approaches the state. As the
system weakens, forecast soundings are showing increasing dry mid
and low level air moving in Tuesday morning. By the
afternoon/evening precipitation looks more likely (70-80% chance)
with the passage of the cold front. Moisture advection will help
saturate the air column with the southwest winds out ahead of this
frontal boundary. There will be a small chance (~20%) for a few
thunderstorms Tuesday evening with the passage of this frontal
boundary, but not expecting much in the way of strong or severe
storms as this time.

Dry conditions return Wednesday and Thursday as high pressure s
expected to move through the state. Wednesday will be a bit cooler
due to the northerly flow and cold air advection behind the
cold front with high temperatures expected to top out in the 50s.
This period of cooler temperature will be near normal for this
time of year and will be short lived with temperatures return to
the 60s on Thursday.

Rain looks likely (70-80%) again for the end of the work week and
into the weekend. A trough and a few shortwaves look to advect out
of the desert southwest headed toward the Great Lakes Region.
There is a fair amount of uncertainty with the timing and
location. The recent guidance has slowed this system down quiet a
bit already with the majority of the rain looking to hold off
until later Friday. Will have to keep an eye on this system moving
forward as guidance comes to a greater consensus.

Patterson

&&

.AVIATION...
Issued 1000 PM CDT Sun Apr 21 2024

Gentle southwest flow (around 5 kts) becoming light and variable
tonight under clear skies. Southwest flow picks up after sunrise
Monday, with gusty winds from noon Monday through Monday night.
Upper altitude clouds approach and thicken Monday afternoon,
with rainshowers likely Monday evening through Monday night.
Cloud ceilings are currently expected to bottom out around 5500
feet during this light rain event, allowing VFR conditions to
continue. However, a low-level jet streak is expected to deliver
fast southwesterlies (roughly 45 kts) 2000 ft above ground
level, resulting in a chance for low level wind shear Monday
night, especially if surface winds can decelerate slightly after
dark.

Sheppard

&&

.MARINE...
Issued 307 PM CDT Sun Apr 21 2024

Westerly winds have shifted to become southerly across the
northern portions of the Lake as high pressure sinks southward
into the Lower Mississippi Valley and low pressure remains in
place over northern Quebec. Winds remain light through the
overnight hours. Breezy south winds will develop Monday,
shifting westerly into Tuesday afternoon as low pressure
approaches the northern Great Lakes from Saskatchewan and
Manitoba and passes to the north. Winds could approach gale
force during this time, while winds in the nearshore regions
will reach Small Craft Advisory criteria. Winds shift to
northerly Tuesday night as the low passes eastward and a cold
front moves down the lake. Northerly gales and additional Small
Craft Advisory winds will be possible behind the front.

MH

&&

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

$$

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