059
FXUS63 KMKX 041738
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1238 PM CDT Thu Jul 4 2024

.KEY MESSAGES...

- This Afternoon and tnt: Scattered showers and storms (30-40%
  chances) are expected to develop this afternoon across srn WI.
  Severe wx is not expected with these storms. A line of storms
  will then move from west to east across srn WI this evening.
  Damaging winds would be the main threat for south central WI
  with the storms gradually weakening as they move toward ern WI
  late in the evening.

- Rainfall tnt through Friday: Expect widespread totals around a
  quarter to half and inch, but areas northwest of HWY-151 have
  a 40-70% chance for totals to exceed one inch.

- Elevated water levels continue on area rivers and streams
  through the end of the week. Flood Warnings remain in effect
  in several locations.



&&

.UPDATE...
Issued 1238 PM CDT Thu Jul 4 2024

MLCAPE will continue to build to 500-1000 J/KG this afternoon
while a 700 mb shortwave trough tracks across nrn IL. The
widespread high cloud cover has kept cumulus from developing
thus far, but believe CIN will erode enough for sct showers and
storm development. SVR storms are not anticipated with this
activity.

For tnt the upper low currently over the Dakotas will track to
west central WI by 12Z Fri with its sfc low around 1006 MB in
the same vicinity. A line of strong storms is ongoing near the
sfc low and cold front from sw MN into nw IA. The HREF has a
reasonable scenario of bringing a line of strong storms from sw
WI into south central WI this evening then with gradual
weakening as CAPE declines. Overall, this is supported by a 500
mb wswly 50 kt jet nosing into srn WI ahead and within the deep
convection; thereby increasing deep layer shear to at least 50
kts. This gives some confidence for MCS development as the HREF
supports, but the strong shear also makes the timing of
weakening difficult since the MCS could maintain its strength
longer than what would be typical.

The cold front will then gradually move across srn WI late tnt
through Fri AM as the sfc low and upper wave move across central
WI. The persistent showers and scattered storms will be toward
central WI where the better warm, moist advection and PVA is
located; however, the upper trough axis will support 50-70
percent chances of rain for the remainder of srn WI. The upper
trough and moisture will then linger into the evening thus
expecting sct showers to linger.

The areas that could see widespread 1 inch rainfall amounts with
locally 2 inch amounts would be north and west of Madison
especially with the MCS this evening. Urban and small stream
flooding may occur given the saturated soils.

Gehring

&&

.SHORT TERM...
Issued 411 AM CDT Thu Jul 4 2024

Today through Tonight:

With high pressure gradually sliding eastward this morning,
Independence Day will start off dry with light winds. Dry
conditions look to persist into the start of the afternoon.
Meanwhile an area of surface low pressure over NE/IA this
morning begins get its act together through the afternoon as a
mid-level shortwave trough sweeps across the northern Plains.
Expecting this interaction to deepen the surface low as it
tracks into our neck of the woods through the evening.

Ahead of this system a stationary front across central WI is
progged to become the warm front of the developing low. With the
front already north of southern WI, expect the moisture
advection to increase through the afternoon across the warm
sector with PWATs creeping above 1.5 inches and dewpoints the
upper 60s. Instability is also expected to build across the area
with SBCAPE nearing 750- 1000 J/kg through the afternoon.
However, outside of a minor impulse of mid-level vorticity ahead
of the main trough and the surface front strewn across central
WI, there is not really a main focus of forcing to initiate
convection this afternoon across the warm sector as seen on NAM
Nest and the 06z HRRR. Additional given the weak background
flow, expecting to see a lake breeze develop this afternoon and
push inland, thus stabilizing the environment for areas behind
it and limiting the potential development this afternoon. While
not overly confident on seeing something development this
afternoon, there are still CAMs hinting at some sporadic
development through the afternoon and cannot rule out something
to develop, mainly for areas west of I-43. If anything does
develop, it would likely be brief, pop-up type shower/storm
given the lack of deep layer shear and if an outflow from a
decaying shower/storm interacts with a nearby storm, it could be
the trigger for a stray stronger storm or two capable of
producing gusty winds and small hail. Overall, there remains a
potential for an isolated thunderstorm this afternoon, but most
of southern WI should remain dry through the majority of the
afternoon.

Same cannot be said for this evening as the shortwave trough
pushes into WI aligning the more favorable dynamics and forcing
with the ample moisture and instability. The main focus for
shower and thunderstorm development this evening will be the
surface low deepening to sub-1008mb and cold front extending
south from it. Areas west of I-39 will see this activity develop
sooner, generally thinking between 00z-04z and with the better
forcing, increasing LLJ to around 30 knots aligning with
lingering instability, cannot rule out seeing a stronger storm
or two capable of producing gust winds. However, the potential
remains low, especially if this convection is delayed by a few
hours. Otherwise, expect the showers and thunderstorm chances to
spread east through the evening with areas east of I-39 seeing
things develop a bit late mainly between 02z- 06z.

Showers chances persist overnight as the surface low begins to
occlude over central WI through Friday. While thunderstorm
chances are progged to gradually diminish overnight with the
loss of instability, there may be enough MLCAPE for some
embedded storms to persist into Friday.

As for rainfall, there is a high potential for most areas to
pick up to a quarter of an inch of rainfall and any heavier
rainfall exceeding a half an inch will likely be associated with
the scattered thunderstorms activity. While the thunderstorm
activity through this evening looks to be progressive/moves
quickly, areas that see repeated/persistent rainfall can pick up
locally high amounts exceeding one inch, especially for areas
closer to the surface low north of HWY-151. Any additional
rainfall to any swollen rivers may contribute to additional
rises and localized river flooding.

Wagner

&&

.LONG TERM...
Issued 411 AM CDT Thu Jul 4 2024

Friday through Wednesday:

Will continue to see showers and thunderstorms persist through
much of Friday on the back side of departing low pressure.
However, the latest medium range models and tail end of the CAM
runs show a bit less coverage. Nevertheless, the lingering
rainfall on the backside of the low will be lighter in nature
given the better forcing shifting east. Should start to see
drier conditions Friday night as northwesterly winds develop and
bring in a dry airmass.

Saturday is looking drier as mid-level ridging sets up over the
region and surface high pressure tracks south of the area. Then
an active pattern returns for the later half of the weekend
into early next week as a series of shortwave troughs traverse
the region. The first of these shortwave troughs looks to impact
the Upper Great Lakes region Sunday into Monday bringing
another shot at showers and thunderstorms. Additional waves are
possible into the first half of next week, bringing additional
bouts of showers and thunderstorms, but uncertainty due to model
differences.

Wagner

&&

.AVIATION...
Issued 1238 PM CDT Thu Jul 4 2024

VFR conditions will prevail this afternoon and evening but areas
of MVFR Cigs and vsbys may occur following thunderstorms. Widespread
stratus development with Cigs of 600-1900 feet are then
expected to develop from west to east early Fri AM through late
Fri AM with the passage of low pressure and a cold front.
Intermittent showers and isold storms will continue during this
time, while Cigs will rise to 1-3 kft for Fri afternoon.


Gehring

&&

.MARINE...
Issued 411 AM CDT Thu Jul 4 2024

Weak high pressure over IL this morning will continue to slide
eastward. Winds will remain lighter and vary from the west-
southwest to the east through the afternoon. Will see winds
begin to pick up into this evening across Lake Michigan as as
low pressure coming in from the Central Plains deepens over WI
tonight. This low pressure will gradually track eastward across
the middle of Lake Michigan into Friday with south-southwesterly
winds over the southern half while winds across the northern
half will be more north-northeast. These winds will remain
fairly breezy with gusts to 20-25 knots. The low will continue
to track into eastern Ontario/Quebec for Saturday bringing
breezy northwesterly winds across Lake Michigan for Saturday
before turn back to the south as an area of high pressure slides
up the Ohio River Valley into Sunday.

Wagner

&&

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

$$

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