820
FXUS63 KGRB 191742
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1242 PM CDT Wed Jun 19 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Quite a bit cooler today than yesterday, along with a chance of
  showers and thunderstorms.

 -An active pattern is expected to continue through the end of
  this week and into this weekend. Stronger storms and locally
  rainfall will be possible each day, with the greatest risk for
  excessive rainfall coming Friday and Saturday.

&&

.DISCUSSION...
Issued at 413 AM CDT Wed Jun 19 2024

Short Term...Today...Tonight...and Thursday

A cold front will move across the region today and bring scattered
showers and thunderstorms, especially across east central Wisconsin.
Gusty winds and brief heavy rain are possible, but severe storms
are not expected. Highs today will be around 5 degrees above
normal, but about 15 degrees cooler then yesterday.

The front will stall across the southeast part of the state during
the evening hours, which may keep scattered showers going across
east central Wisconsin. Lows tonight will be close to normal.

An upper trough will move across the area Thursday, and produce
scattered showers and isolated thunderstorms. Showers, clouds,
and northeast winds from Lake Michigan will make for a cooler than
normal day, especially south of highway 29.

Long Term...Thursday Night Through Tuesday

A low pressure system developing over the central Plains and
ejecting toward the western Great Lakes Friday and Saturday will
be the dominate feature of the extended period. With abundant
moisture forecast to be available during this time expect a few
rounds of heavy rainfall that may cause area rivers and streams
to rise near or to bankfull.

Thursday night through Sunday...A weak high pressure system
developing over Lake Superior Thursday night into Friday morning
may bring a brief lull in the precipitation. Chance for showers
and thunderstorms will then ramp up Friday afternoon as a surge
of warm moist air lifts over the region ahead of a low pressure
system developing in the Central Plains. PWATs are progged to
range from 1.75 to 2 inches Friday afternoon which is around the
97th percentile for this time of year. The combination of
widespread lift and robust available moisture makes periods of
heavier rain possilbe Friday afternoon and evening. The potential
for severe weather is low as instability looks rather weak (less
than 500 J/kg) and forecast soundings do show a cap over much of
the region Friday afternoon and evening.

The chance for thunderstorms and heavy rain will continue through
Saturday as the main surface low phases with an upper level
shortwave propagating east along the US/Canada boarder. Forecast
soundings Saturday afternoon show PWATs approaching 2-2.25 inches
which is the 99th percentile of climatology. With the strong PV
anomaly associated with the low and robust moisture expect
periods of heavy rain through the day Saturday. The severe
weather potential has trended downward over the last 24 hour
hours as models now show the warm front stalling out over souther
WI and shunting the stronger instability south of the region.
However, won`t rule out some strong thunderstorms late Saturday
as a cold front sweeps across the region. Showers and weak storms
may linger through Sunday as the area remains in the cyclonic
flow. In terms of the flooding concern for Friday and Saturday,
much of the region is in a slight (15% chance) risk for excessive
rainfall both days. Probabilistic guidance is showing about a 15-
30 percent chance for greater than 2 inched of rain over the two
days, highest in central and north- central WI.

Rest of the extended...A developing ridge of high pressure Monday
should bring a reprieve from the showers and storms to start next
week. However, does not look like this dry stretch will last long
as ensemble models show the upper-level pattern flattening out
toward the middle of next week with signs that the round of
thunderstorms may sweep through the region next Tuesday and
Wednesday.

Temperatures...With the chances for rain and widespread cloud
cover temperatures should trend slightly cooler than the
beginning of this week, however, the humidity will stick around
until the cold front comes through Saturday. Does look like heat
and humidity will return during the early to middle part of next
week.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1242 PM CDT Wed Jun 19 2024

MVFR cigs to exist behind a cold front that extends from far
northeast to southwest WI. These lower cigs are expected to rise
into the lower VFR category later this afternoon as the cold
front sags into southern WI. Scattered showers and isolated
thunderstorms are expected to accompany the cold front and impact
mainly east-central WI.

This cold front is forecast to stall near the IL border tonight
and may try to lift back north a bit as a warm front on Thursday.
Meanwhile, an upper-level disturbance is forecast to move into
northern sections of the Great Lakes on Thursday. These two
features will bring additional chances for showers and storms
across northeast WI, especially during the afternoon. MVFR
conditions south of a SUE to AUW line are expected on Thursday
with low clouds along the Lake Michigan shore, with IFR
conditions possible at MTW and SUE.

&&

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

&&

$$

DISCUSSION.....RDM/GK
AVIATION.......Kallas