329
FXUS63 KMKX 050235
AFDMKX

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

.KEY MESSAGES...

- Cold front with a broken line of thunderstorms crossing the
  region from west to east overnight. Isolated severe storms
  cannot be ruled out, but storms are expected to gradually
  weaken over time.

- Rainfall tnt through Friday: Expect widespread totals around a
  quarter to half and inch, but areas northwest of HWY-151 have
  a 50-80% 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 935 PM CDT Thu Jul 4 2024

A cold front currently spans from east-central Iowa to central WI,
gradually drifting east. A broken line of thunderstorms is organized
along it, with another storm cluster stretching east of the line
towards Beaver Dam / Juneau along a weak mesoscale warm front /
remnant outflow boundary, moving north. The cold front and
associated thunderstorms will move west to east through the CWA late
this evening into tonight, but will take several hours to complete
crossing the CWA. This will leave a few more hours of fair weather
for southern and eastern areas of the CWA. Instability has
begun to gradually decline with the shutdown of daytime heating,
and these storms are expected to gradually weaken on approach,
but an isolated severe storm or two cannot be completely ruled
out tonight. Damaging wind gusts would be a threat along any
bowing segments in the line of storms (early tonight only). Hail
cannot be ruled out overnight, though MUCAPE < 1000 joules and
freezing levels > 10 kft make for only a marginal threat.

Sheppard

&&

.SHORT TERM...
Issued 255 PM CDT Thu Jul 4 2024

Tonight through Friday night:

Scattered slow moving thunderstorms have developed along a weak
warm front west of Madison, while isolated showers and storms
are developing over se WI. MLCAPE ranges from 500-1000 J/KG
this afternoon with a vorticity maximum moving across srn WI.
SVR storms are not anticipated with this activity but urban and
small stream flooding will be possible mainly west to nw of
Madison.

For tnt the upper low currently over the ern 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 south central MN into north
central 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

&&

.LONG TERM...
Issued 255 PM CDT Thu Jul 4 2024

Saturday through Thursday:

A brief period of high pressure and shortwave ridging aloft will
take hold for Sat. Afterward, a series of shortwave troughs will
support mean upper troughing over the Upper MS River Valley and
wrn Great Lakes. Thus chances for showers and storms will be
forecast each day. Temps during the extended will be near
normal with above normal relative humidity.

Gehring

&&

.AVIATION...
Issued 935 PM CDT Thu Jul 4 2024

A cold front currently spanning from east-central Iowa to
central Wisconsin will gradually drift eastward tonight, with a
broken line of thunderstorms along it. Though cumulonimbus cloud
bases are generally > 3000 ft AGL, a few pockets of MVFR and
Fuel Alt cloud ceilings have been reported underneath the
leading edge of storms, and even lower cloud ceilings will be
possible late overnight into Friday morning (currently expecting
IFR at KMSN / KJVL and Fuel Alt MVFR further east). Cloud
ceilings gradually lift throughout the day Friday, though
continued shower / storm chances are present until late Friday
evening. Models indicate popcorn-style convection, with
scattered shower and weak storm cells present until daytime
heating shuts off.

As low pressure tracks eastward through central WI on Friday,
southwest winds will develop in the morning, veering northwest
gradually throughout the day.

Sheppard

&&

.MARINE...
Issued 255 PM CDT Thu Jul 4 2024

Weak high pressure around 29.9 inches over Lake MI this afternoon
will slide eastward this afternoon and evening, as a couple weak
low pressure areas develop east across MN and from IL into IN
during the afternoon and early evening. Light and variable winds
are expected over Lake MI.

More organized south to southeast winds will develop over the
south half tonight into Friday morning, with east northeasterly
winds over the north half as low pressure around 29.7 inches moves
from MN across central WI. This low pressure area will gradually
track eastward across the middle of Lake Michigan early Friday
afternoon. Modest southwest winds will prevail over central and
southern Lake MI at this time with northeasterly winds to the
north. The winds will then trend to north northwest Friday night
into Saturday morning as the low moves away across Lake Huron and
southern Ontario. The winds will then back to southwest during the
afternoon and evening, and southerly for Sunday as high pressure
around 30.0 inches moves across Lake MI and tracks to the lower
Great Lakes.

Gehring

&&

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

$$

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