999
FXUS63 KGRB 122306
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
606 PM CDT Wed Jun 12 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- There is a chance of strong to severe thunderstorms across all
   of north-central and northeast Wisconsin after 9 pm tonight.
   Overall confidence in the severe weather threat is medium-low,
   but a few of the strongest storms may produce strong to
   damaging winds and hail.

 - Well above normal temperatures are forecast from Sunday into
   the middle of next week. Heat indices may surpass 90 degrees at
   times.

 - The next chance for widespread rainfall arrives Saturday, with
   the best coverage Saturday evening through the overnight. It is
   uncertain if these storms would become severe, but locally
   heavy rainfall will be possible.

&&

.DISCUSSION...
Issued at 242 PM CDT Wed Jun 12 2024

Short Term...Tonight and Thursday

The latest RAP analysis and satellite/radar imagery show
relatively fast zonal flow in the mid and upper levels across the
US-Canadian border with embedded shortwaves within said flow. In
fact, the 200mb and 500mb flow is upwards of the 97.5 percentile.
This flow is above a warm front lifting northeast across Minnesota
and a trailing cold front across North Dakota. An area of showers
ahead of these features is slowly decaying over northern WI,
while more intense thunderstorm activity resides across southern
Minnesota and southwest Wisconsin. These thunderstorms are
expected to continue to move southeast and bypass central
Wisconsin. The area behind these showers and storms over northern
Minnesota is where greater concern lies as this area has seen
strong solar insolation and destabilization this afternoon. Storm
initiation is expected in the 3-4 pm timeframe in this area.
Evolution of these storms and the severe storm potential are the
focus of this forecast.

Precipitation Trends and Severe Thunderstorm Potential: While
it`s possible that some additional shower and storm activity could
redevelop behind the ongoing convection over central and southern
Minnesota, odds appear considerably reduced as the atmosphere
will have little time to destabilize prior to peak heating. If
storms redevelop, the airmass over central Wisconsin is
considerably more stable and likely to keep the severe threat very
low.

A considerably higher potential for severe weather is likely to
arrive from the storms that initiate over northern Minnesota.
These storms are forecast to track southeast towards north-central
WI in the 9 pm to 11 pm time frame. The airmass will be more
stable over northern WI than upstream by this time, and the storms
will likely be in the weakening process. Despite this, most
unstable capes upwards of 1000 j/kg will likely lead to a severe
threat continuing as storms arrive into north-central WI,
especially with deep layer shear from 40-50 kts. With such strong
wind fields aloft, strong to damaging winds will be the primary
threat tonight, but updrafts may be strong enough for large hail
to remain possible, at least over north-central WI. The threat of
damaging winds will likely persist, however, as forward
propagating vectors indicate a storm motion of 55-70 kts. The
chance of storms will end towards the middle of the overnight.

Thunderstorm Potential and Gusty Winds on Thursday: Thunderstorm
activity will likely push the cold front into southern Wisconsin
or northern Illinois by Thursday morning. However, ahead of a
secondary front and shortwave trough, models indicate 1000-1500
j/kg of cape developing over central and east-central WI by late
morning to early afternoon. Think widely scattered showers or
storms could develop in this unstable airmass and have added a
small chance to the forecast. Strong wind fields aloft could lead
to a gusty wind threat if storms develop.

Deep mixing through 6-8k feet should tap into strong winds aloft,
resulting in west winds gusting to around 30 mph in most areas.
Gusts should not be as strong over Lake Michigan, due to more
stable conditions over the relatively cool waters. Thus, expecting
gusts to remain below the 25 knot threshold for a Small Craft
Advisory.

Long Term...Thursday Night Through Wednesday

The two concerns in the extended period will be the potential for
another round of impactful weather moving through the region
Saturday and the much warmer weather anticipated by the end of the
weekend into early next week.

Saturday...
After a quiet start to the extended, active weather returns to the
region as southerly flow picks up again. As warm air advection
increases, showers are expected to develop across the region
Saturday afternoon. Although initial rain will only have a minimal
chance for thunder, the overall potential for stronger storms
increases as we get into the overnight hours. A strong low level
jet is expected to develop in the evening hours, helping to
sustain and strengthen any ongoing showers. With lingering MLCAPE
around 1000-1250 and strengthening shear, wouldn`t be surprised to
see an increase in elevated thunderstorm coverage. Whether
instability and shear remains sufficient for severe weather
remains uncertain. PWATs during this time will also push to
around 1.8-2.0, which will make heavy rainfall a concern,
especially if these storms start training along the warm front. A
few showers and storms may linger on to start off Sunday, which
may skew the high temperatures expected in the region.

Temperatures...
The push of the warm front from Saturday will bring with it some
well above normal temperatures. Highs could be well into the 80s
by Sunday, although this may change slightly depending on how
quickly clouds and active weather move out of the region Sunday
morning. Dewpoints during this time are also expected to push
towards the upper 60s which may make for one of the muggier days
so far this year.

Behind the Sunday system, temperatures early next week will remain
well above normal, with highs into the upper 80s both Monday and
Tuesday. A few of the warmer spots may even hit 90 during this
timeframe. With several days of very warm temperatures in the
forecast, make sure you have a way to beat the heat!.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 552 PM CDT Wed Jun 12 2024

Showers and thunderstorms developing upstream across Minnesota are
expected to congeal into a squall line and track through the area
from northwest to southeast late this evening and into the
overnight hours. Strong straight line winds and IFR vsbys will
impact flight operations if thunderstorms hold together as
planned. Confidence in these thunderstorms tracking through the
area is medium (around 50 percent) with a lower confidence in the
storms still being strong to severe when they track through (5
percent).

In the wake of the storms, IFR low clouds may stick around for a
time over far northern WI, including RHI, but then clear for a
time on Thursday morning. Convective clouds are then expected to
build over east-central WI by late morning, which could lead to
scattered showers developing.

Gusty west winds to 25 kts are possible at the taf sites on
Thursday.

&&

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

&&

$$

DISCUSSION.....MPC/Uhlmann
AVIATION.......Kurimski