088
FXUS63 KMKX 120919
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
419 AM CDT Fri Jul 12 2024

.KEY MESSAGES...

- Patchy fog possible over the Wisconsin River Valley and in
  low-lying spots through sunrise.

- Confidence in above-normal high temperatures continues to
  increase during the Sunday to Monday timeframe. Heat indices
  between 95 and 100+ degrees are possible both Sunday and
  Monday afternoon.

- Active weather returns Saturday afternoon through Monday, with multiple
  rounds of showers and storms anticipated. Some storms could
  be strong to severe.

- Drier, quieter conditions return by the middle of next week.

&&

.SHORT TERM...
Issued 417 AM CDT Fri Jul 12 2024

Today through Saturday:

Synopsis/Mesoanalysis: Regional surface observations place an area
of low pressure over the Lower Peninsula of Michigan early this
morning. Resulting light winds, clear skies, and attendant
radiational cooling have driven pockets of fog development through 3
AM, with satellite imagery showing the most widespread development
over the river valleys of central Wisconsin and low-lying areas of
south-central Wisconsin. Anticipate that said areas of fog will
continue through sunrise, quickly burning off with the onset of
daytime heating this morning. In the mid-levels of the atmosphere, a
pronounced subtropical high pressure center will remain entrenched
over the Four Corners through the duration of the short term period.
Positioned downstream of said feature, west-northwest mid to upper
flow will prevail across the Northern Plains and western Great Lakes
through Saturday night. Southerly winds will gradually increase by
Saturday afternoon as the aforementioned high pressure pushes east,
allowing a moist & unstable air mass to advect into southern
Wisconsin. Tied to a series of shortwaves embedded within the west-
northwest upper flow pattern, periods of showers and thunderstorms
are possible Saturday afternoon and night within said air mass. A
few storms could be strong to severe.

Rest Of Tonight: Can`t rule out pockets of fog through daybreak,
particularly across the Wisconsin River Valley and in low-lying
spots across south-central and southeastern Wisconsin. Fog will
quickly burn off following sunrise and the onset of daytime heating.
Slow down, use low beam headlights, and allow for extra following
distance if briefly encountering areas of reduced visibility on the
roads through sunrise.

This Afternoon: Anticipate high temperatures in the low to mid 80s
away from Lake Michigan under mostly sunny skies. Have kept the
entirety of the area dry in the overnight update, though a few
diurnally-driven showers/thundershowers are possible over north-
central Wisconsin. Said isolated potential was depicted in a pair of
the 00Z Friday CAMs, with the 06Z NAM Nest and HRRR continuing to
hint at development to the north of the area. Sub-15% precip
probabilities were maintained given the aforementioned placement,
though trends will nevertheless be monitored over the coming
forecast updates. Should precip signals shift south, mentionable,
slight chance (15-24%) PoPs may need to be inserted over our
northern tier of counties.

Saturday & Saturday Night: Periods of showers and storms will be
possible from as early as mid-afternoon Saturday through the
overnight hours. Development will be closely affiliated with
MCV`s/convectively-enhanced shortwaves connected to thunderstorms
developing over the Northern Plains this afternoon. A broad
consensus pointing toward strong/severe storm development over north-
central MN and northwestern WI during the afternoon hours is
apparent, with activity pivoting into southeastern Wisconsin during
the evening and overnight hours in its decaying stages. Less certain
is any additional development that may occur across the area on
Saturday afternoon. A minority of 00Z CAM solutions -- namely the
HRRR -- depict such development along/ahead of an encroaching MCV
during the mid-late afternoon hours Saturday. Said development would
be better-phased with peak heating, and would pose some
strong/severe potential given an overlap of 2000+ J/kg of MLCAPE &
~20-25 knots of effective shear depicted in forecast soundings.
Gusty winds would be the primary concern. Regardless of how
thunderstorm development evolves, all activity will be capable of
producing heavy downpours given 1.5-1.9" precipitable water values
in place across the area. Progressive storm motions should preclude
a more substantial flooding threat from materializing.


Quigley

&&

.LONG TERM...
Issued 417 AM CDT Fri Jul 12 2024

Saturday night through Thursday:

Synopsis: The beginning of the long term period will be marked by a
stagnant synoptic pattern across the CONUS, with subtropical high
pressure persisting over the Four Corners, and a warm/muggy air mass
entrenched across the western Great Lakes & Upper Mississippi
Valley. The hottest temperatures of the period are expected Sunday
and Monday, when heat advisories may become necessary over portions
of the area. Additional showers and storms are anticipated Sunday
afternoon and evening, with strong to severe storms possible.
Changes in the prevailing pattern will begin to occur Sunday night
through Monday, when an upper trough initially centered over
northern Canada will dig southeast into Ontario and the Hudson Bay.
Attendant surface cyclogenesis will occur along the Ontario-Quebec
border vicinity beneath the encroaching upper trough, with the
feature dragging a cold front across the state Monday afternoon &
evening. Additional showers and storms are thus forecast Monday
afternoon and evening along/ahead of the front, with additional
severe storms possible. The cold front is progged to push southeast
of the area by Tuesday afternoon, encouraging a west-northwest wind
shift across the area. Said wind shift will usher a noticeably
drier, Canadian air mass into southern Wisconsin, with the end
result being a much quieter conclusion to the long term period.

Sunday & Sunday Night: A combination of high temperatures in the low-
mid 90s & dew points in the 70s will drive widespread heat indices
in the mid-upper 90s, with readings approaching/exceeding triple
digits possible over south-central and southeastern Wisconsin. Heat
Advisories thus may become necessary in some locations Sunday. The
next round of showers and storms is anticipated Sunday afternoon and
evening. Regional forecast soundings depict a stout EML in the 850-
700 mb layer, so afternoon initiation zones will depend heavily on
any leftover surface boundaries from Saturday night`s storms, as
well as the crossing points of any shortwaves embedded within
northwest flow aloft. Mesoscale uncertainties aside, the
aforementioned forecast soundings depict high to extreme amounts of
surface-based instability beneath the EML, which combined with an
overlapping 30-35 knots of effective shear would support organized
severe weather potential in any thunderstorms during this portion of
the period. Will continue to monitor trends in the guidance and
adjust the forecast accordingly over the coming cycles.

Monday & Monday Night: Hot high temperatures and muggy conditions
will once again support elevated heat indices, with readings likely
being a touch lower compared to Sunday. A final round of showers and
storms is anticipated as a cold front crosses the area. Forcing
mechanisms are a bit more certain compared to Sunday given the
approach of the aforementioned front, as well as increasing DPVA
ahead of the encroaching Hudson Bay trough. Nevertheless, precise
placement of storm development will once more depend on any leftover
boundaries from Sunday/Sunday night convection. Will thus continue
to monitor trends on the finer scale forecast details and make
forecast adjustments as necessary. Forecast soundings depict a
similar environment to Sunday, with strong surface-based instability
beneath the EML overlapping with sufficient effective shear to
support organized severe potential in Monday`s activity.

Quigley

&&

.AVIATION...
Issued 417 AM CDT Fri Jul 12 2024

Apart from some patchy FG this morning, VFR conditions prevail
through the duration of the period at all southern Wisconsin
terminals. Sky conditions will remain mostly clear, with a few upper
cirrus decks based near FL250 occasionally passing overhead. Winds
will remain light & variable during the overnight, with prevailing
east-southeast winds expected during the daytime hours.

Quigley

&&

.MARINE...
Issued 417 AM CDT Fri Jul 12 2024

Light winds prevail across the open waters this morning, which has
allowed areas of fog to form over the northern third of the lake.
Visibilities below one mile will be possible within areas of fog,
with a dense fog advisory in effect through 9 AM CDT/10 AM EDT this
morning. Fog is expected to dissipate following sunrise, giving way
to continued light winds this afternoon. Isolated showers and storms
are possible over the open waters Saturday afternoon and evening,
with better chances for showers and storms arriving Sunday & Monday
as 998 mb low pressure develops over Ontario. A few storms could
become severe on Sunday and Monday. Winds will turn out of the west
and northwest on Tuesday as a cold front moves across the open
waters.

Quigley

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory...LMZ261-LMZ362-LMZ364-LMZ563 until 9 AM
     Friday.

&&

$$

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