958
FXUS63 KMKX 151711
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1211 PM CDT Thu Aug 15 2024

.KEY MESSAGES...

- Periods of lgt-mdt rainfall and brief heavy rainfall rates
  will gradually move from west to east through the afternoon.
  Scattered storms are expected to re-develop this evening into
  the overnight but the severe potential is very low.

- Gusty southeast winds and building waves on Lake Michigan will
  create hazardous conditions to small crafts and beachgoers
  this afternoon and tonight. Thus both a Small Craft Advisory
  and Beach Hazard Statement is in effect.

- Another round of showers and thunderstorms will move across S
  WI Fri afternoon and early evening. There is a Marginal Risk
  for severe thunderstorms with damaging winds and large hail.


&&

.UPDATE...
Issued 1211 PM CDT Thu Aug 15 2024

The lgt-mdt rainfall, with brief heavy rainfall rates, will
gradually decrease in coverage through the afternoon as the low
to mid level warm, moist advection and shortwave trough move
ewd. At the sfc, the warm front will follow the pcpn but stall
over far srn WI this evening.

For tnt a couple areas of more widespread development will
focus to the north and south. A shortwave trough coming out of
NE will move into west central IL by 06Z with deep convection
expected in nrn IL. The upper low over ne ND will gradually
drift sewd with its PVA and better low level convergence
focusing over west central WI moving ewd. Thus only expect sct
showers and storm development tnt with more of a focus from
03Z-09Z with the weak passage of a sfc trough. MLCAPE of
1000-1500 J/kg can be expected with decreasing wind shear, thus
the SVR threat is very low.

For Fri-Fri nt the upper low will move across Lake Superior and
nrn WI with a shortwave trough rotating around it through srn
WI. MLCAPE around 1500 J/KG will develop ahead of this feature
and CAMs and larger scale models all agree on fairly widespread
showers and storms for Fri afternoon, lingering into the
evening. PWs will rise above 1.5 inches once again with heavy
rainfall rates expected but storm motion of 25-30 kts should
limit the urban and small stream flooding threat. Weak to mdt
deep layer shear is forecast so the SPC Day Two Marginal Risk
looks good.


Gehring

&&

.SHORT TERM...
Issued 442 AM CDT Thu Aug 15 2024

Today through Friday:

Showers will continue to gradually spread into southern WI from
the southwest through the morning as low-level WAA, nose of a
30 knot 850 mb jet, and band of low-level frontogenesis work
their way across the region. Given this low-level forcing
aligning with PWATs exceeding 1.5 inch, will continue to see off
and on periods of moderate to heavy showers through daybreak
and push east. While GLM is picking up on some sparse lightning
activity to our southwest in eastern IA/western IL, much of this
activity looks to miss our area this morning as it is anchored
to where the MUCAPE > 500 J/kg resides. Most models including
the 06z HRRR and 00z HREF keep this instability out of our neck
of the woods through the morning. Thus much of this morning
activity will likely come through our CWA as moderate to heavy
rainfall.Periods of off and on showers with a few thunderstorms this
morning and early afternoon. Then an additional round of
scattered showers and thunderstorms will be possible this
evening where a strong/severe storm or two cannot be ruled out.

We begin to see instability creep up toward a couple hundred to
1000 J/kg of MUCAPE through the afternoon. This will contribute
to thunderstorms chance picking up on the backside of the
morning round, but with the departing low-level forcing (WAA,
LLJ, and band of frontogenesis), this will result in a limited
window of thunderstorms (16z-21z) this afternoon. There still
looks to be a lull in activity for the afternoon allowing the
environment to recover a bit and may see southwestern areas of
the CWA to see MUCAPE around 1500 J/kg. While, the low-level
forcing from the morning has departed, there will be a surface
cold front paired with a mid-level impulse working its way
through the area generally after 00z. Some CAMs pick up on
additional convective redevelopment as this second round of
forcing pushes through the area, but with the later timing this
evening may work against it as we lose daytime heating.
Additionally the better environment looks more favorable further
south in IL.

Nevertheless there remains a potential for some thunderstorms
later this afternoon/evening, especially for areas south of I-94
toward the WI/IL border. Also with some meager 0-6km shear
approaching 30- 40 knots, if any storms develop and can grow
upscale this evening, still cannot rule out seeing a strong or
even severe storm or two, especially along the WI/IL border in
southwest/south-central WI. The main concern with any stronger
storm would be the damaging wind and or hail threat, but a brief
spin up would not be out of the realm of possibility given the
surface boundary and 0-3km CAPE around 100 J/kg.

In addition to storm chances, looking at some widespread
moderate to heavy rainfall today. Given the moist airmass,
prolonged period of rainfall, and PWATs topping off around 2
inches, there looks to be a high potential (>70%) for much of
southern WI to see around or more than half an inch of rainfall.
There also looks to be a potential (50-60%) for pockets of
higher rainfall exceeding 1 inch, which could result in some
localized minor flooding concerns. While any deep shower/storm
has the potential to produce such amounts, the best chances for
these higher rainfall totals seem to be for areas southwest of
Madison.

Otherwise, expect showers and storm activity to decrease
overnight. Expecting scattered shower and thunderstorm chances
pick back up on Friday as the surface low meanders across
northern WI while the mid- level trough digs down across the
Upper-Mississippi River Valley.

Lastly with the pressure gradient increasing between the
departing surface high across the eastern Great Lakes and
incoming surface low, expect southeasterly winds to increase
through the day. This will result in stronger onshore flow and
building waves along southern WI Lake Michigan beaches and
create life-threatening rip current and swimming conditions
today. Would be best to avoid swimming in these dangerous
conditions.

Wagner

&&

.LONG TERM...
Issued 442 AM CDT Thu Aug 15 2024

Friday night through Wednesday:

Low pressure gradually shifts east to MI, but some scattered
showers and a stray thunderstorm or two will be possible during
the daytime hours. Then Sunday through early next week looks
drier as the upper- level ridge builds across the central CONUS
and surface high pressure establishes itself over the Midwest.
While expecting a drier pattern through next week, still cannot
rule out some low-end rain chances as long range models hint at
some mid-level shortwaves overrunning/undercutting ridge.

Wagner

&&

.AVIATION...
Issued 1211 PM CDT Thu Aug 15 2024

Cigs below 1 kft to 1.9 kft will prevail this afternoon and
tnt. Pockets of 1-3SM BR will then form late this evening into
the overnight. The widespread showers today will decrease in
coverage from west to east this afternoon with scattered showers
and storms to redevelop this evening into the overnight. The
low stratus and BR is then expected to dissipate after sunrise
Fri. Sct-bkn035-050 cumulus are then expected by late morning
into the early afternoon followed by numerous showers and storms
for the afternoon and early evening.


Gehring

&&

.MARINE...
Issued 442 AM CDT Thu Aug 15 2024

Departing high pressure moving across the eastern Great Lakes
and incoming low pressure tracking into MN will bring increasing
southeasterly winds to Lake Michigan today. Looking at gusts up
to around 25-30 knots through the afternoon/evening along with
chances of thunderstorms as this system tracks into the Lake
Superior region. The stronger onshore winds and building
waves will result in hazardous conditions for small craft
through this evening. Low pressure then looks to linger over the
Upper Great Lakes through Friday with more southwesterly winds
before turning northerly on the backside of the low for the
weekend. High pressure looks to build into the region for the
start of next week bringing lighter winds across Lake Michigan.

Wagner

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Beach Hazards Statement...WIZ052-WIZ060 until 7 AM Friday.

     Beach Hazards Statement...WIZ066-WIZ071-WIZ072 until 1 AM
     Friday.

LM...Small Craft Advisory...LMZ643-LMZ644 until 7 AM Friday.

     Small Craft Advisory...LMZ645-LMZ646 until 1 AM Friday.

&&

$$

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