097
FXUS63 KGRB 271738
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1238 PM CDT Thu Jun 27 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Showers and thunderstorms may bring locally heavy rainfall to
   the region Friday and Friday night. Small hail is possible with
   some storms on Friday night, but the severe weather threat is
   low.

 - Small Craft Advisory may be needed from Friday morning through
   Friday night on Lake Michigan.

 - Some rivers and streams will remain above bankfull and near flood
   stage into the middle of the week.

&&

.DISCUSSION...
Issued at 312 AM CDT Thu Jun 27 2024

Short Term...Today...Tonight...and Friday

Cool weather will continue across northeast Wisconsin today as
high pressure drifts off to the east. A deck of mid clouds will
persist across central and north-central Wisconsin early this
morning before giving way to mostly sunny skies later this
morning. Later in the day clouds will increase from the west as a
low pressure system develops across the northern Plains. Highs
today are expected to mainly be in the upper 60s to lower 70s.

Clouds will continue to thicken and lower tonight as the
aforementioned low pressure system tracks east towards the upper
Mississippi Valley tonight. While much of the area will remain dry
for most of tonight, some precipitation could make it into central
and north-central Wisconsin late tonight. Lows tonight will be a
bit warmer given the abundant cloud cover; with temperatures
mainly in the 50s.

The main surface low slows down and stalls across Minnesota on
Friday as two mid level PV anomalies track through northern
Wisconsin and Illinois. These shortwaves and some modest warm air
advection will bring widespread light rain showers and isolated
thunderstorms on Friday, with the best chance for thunder on
Friday afternoon due to the increased instability. Model soundings
indicate thunderstorms will mainly be elevated, with MUCAPEs of
only 300 to 600 J/kg Friday afternoon. Therefore, severe weather
is not expected during the day on Friday. Highs on Friday are
expected to range from the upper 60s across north-central
Wisconsin, to the middle 70s across east-central Wisconsin away
from the lake. Given the fairly meager forcing, heavy rainfall is
not expected on Friday as QPF amounts should generally be one half
of an inch or less. The probability for greater than one half of
an inch of rain is fairly low and at most 20-30 percent across
far western central and north-central Wisconsin.

Long Term...Friday Night Through Wednesday



Focus of this forecast continues to revolve around the thunderstorm
and severe potential for Friday night.

Friday night into Saturday...

A relatively potent shortwave trough will push a cold front across
the region on late Friday night into early Saturday morning.  Strong
to severe thunderstorms will likely be ongoing upstream and along
the front over Minnesota within a instability axis of 1500-2500
j/kg.  As the front moves east, most unstable capes within the
instability axis weaken to 600-1000 j/kg by the time it moves into
north-central Wisconsin around 1 am Saturday.  Forecast soundings
indicate storms will be elevated by this time with a stout inversion
present around 850-800mb.  While surface to 6 km shear will be
increasing with the approaching front, effective bulk shear values
are only around 20 kts due to the inversion present.  Therefore
think there will be an elevated hail threat with storms, and perhaps
an isolated large hail threat should a storm acquire a rotating
updraft.

Despite precipitable water values upwards of 1.75 inches, the threat
of excessive rainfall appears low on Friday night.  The percent
chance of greater than 0.25 inches of rainfall is only around 10%
from 7 pm Fri to 7 am Sat.  Therefore dont think there is a
significant risk of flooding with storms on Friday night.

The chance of showers and a few storms will continue on Saturday
morning until the front clears.  Behind the front, the boundary
layer remains modestly moist beneath troughing aloft.  Forecast
soundings indicate deep mixing over north-central WI with skinny
cape values up to around 700 j/kg.  Could see additional shower and
isolated storm development on Saturday afternoon that could bring a
gusty wind threat.

Rest of the forecast...After quiet weather on Sunday and Monday,
strong warm advection will bring a widespread thunderstorm chance to
the region on Monday night into Tuesday.  Wind fields are fairly
robust, so will need to monitor for a severe thunderstorm chance.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1237 PM CDT Thu Jun 27 2024

Mostly sunny skies and VFR conditions are expected to persist
through the late afternoon as a daytime cu field continues to
develop throughout the day. Cloud cover will then build back in
from the west this evening out ahead of an approaching warm
front. Ceilings will continue to lower as cloud cover thickens
during this time, with MVFR to IFR cigs arriving to the western
TAF sites by around 16Z Friday. Light rain will likely be ongoing
across portions of central to north-central Wisconsin at the end
of the TAF period. LLWS will likewise be a concern for RHI, AUW,
and CWA early Friday morning through early afternoon as a
nocturnal LLJ of 50 to 60 knots builds in across western
Wisconsin.

&&

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

&&

$$

DISCUSSION.....Kurimski/MPC
AVIATION.......Goodin