784
FXUS63 KGRB 181955
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
255 PM CDT Sat May 18 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Thunderstorms are likely late this afternoon across central and
  north-central Wisconsin. There is a slight chance that some of
  these storms may become severe with damaging winds and large
  hail. Scattered thunderstorms are expected in east-central and
  far northeast Wisconsin this evening, but will be weakening as
  daytime heating wanes.

- Active weather expected Monday through Tuesday night, with potential
  for a couple periods of heavy rainfall, and possibly a severe
  threat.

&&

.DISCUSSION...
Issued at 255 PM CDT Sat May 18 2024

Short Term...Tonight and Sunday

Main forecast concern remains on the severe potential late this
afternoon into early evening as a cold front moves across the
area.

The 19Z MSAS surface analysis showed this cold front stretch from
the MN Arrowhead south to far western WI to central IA. Ahead of
the front, very warm temperatures (in the 80s away from the lake)
were in place with dew points climbing into the 50s.

A broken line of showers and thunderstorms is forecast to sweep
across northeast WI this evening as the cold front moves across
the badger state. Strong to locally severe storms are still
possible with the greater potential over central WI where MLCAPES
reach between 700 and 1000 J/KG. Bulk shear to range from 30 to 40
knots with higher values over northern WI. Mid-level lapse rates
reside between 6.5 and 7.5 C/KM late in the afternoon into early
evening. Hail and gusty winds would be the main threats. This
convective activity is expected to lose some punch as it moves
into eastern WI as we lose daytime heating and instability wanes.
Behind the cold front, high pressure is forecast to build into the
western Great Lakes after midnight, thus skies will become mostly
clear. Min temperatures to range from the middle to upper 40s
north-central WI, to the middle 50s across east-central WI.

This high pressure moves into the center of the Great Lakes on
Sunday with a sunny start to the day. As the high pressure shifts
to our east in the afternoon, expect middle and high clouds begin
to overspread the area as moisture begins to pool around the now-
stalled cold front (turning into a warm front) over the Midwest.
Temperatures on Sunday to be cooler with readings in the upper 60s
to lower 70s near Lake MI, middle to upper 70s inland.

Long Term...Sunday Night Through Saturday

Main concerns revolve around a couple potent systems moving
through the region Monday through Tuesday night, and associated
heavy rainfall and thunderstorm potential.

After a dry start to Sunday night, showers and thunderstorms
will return by early Monday as a potent short-wave trough
approaches from the Plains. Widespread showers and embedded
storms will move through during the day on Monday, then depart
during the late afternoon and evening. With PWATs around 1.5
inches, expect pockets of heavy rainfall to occur. Abundant
cloud cover and widespread shower activity should limit
instability, so the severe threat appears marginal at best.

After a brief lull in the precipitation Monday night, an even
stronger system is expected to approach the region Tuesday.
Models show around a 990 MB low tracking west of the forecast
area in the afternoon and evening. This system will be quite
dynamic, with a 50 knot LLJ and negatively-tilted short-wave
trough. Heavy rainfall looks like a good bet in the afternoon
and evening. The severe threat will depend on whether or not
a warm front can make it into C/EC WI Tuesday afternoon and
evening. Deep layer shear looks pretty impressive, so this bears
watching. SPC has outlined the southern half of the forecast area
on the day 4 outlook, and WPC has the entire area in a marginal
risk for excessive rainfall.

The rest of the extended forecast looks quiet in comparison.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1237 PM CDT Sat May 18 2024

A broken line of thunderstorms are expected to move
across the region during the late afternoon and evening hours
ahead of a cold front. The activity should be along a line from
RHI to ISW around 22z, IMT to DLL around 01z, and ESC to OSH by
02z. The activity will like weaken as it moves towards Lake
Michigan. Strong wind gusts, hail and brief IFR conditions may
accompany the stronger thunderstorms. VFR conditions are expected
outside of the thunderstorm activity. After the convective
activity exits the area by late evening, there will be clearing
overnight and good flying weather Sunday.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION.....Kallas/Kieckbusch
AVIATION.......Kallas