450
FXUS63 KGRB 110907
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
407 AM CDT Tue Jun 11 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Showers and a few thunderstorms expected, especially this
  afternoon and evening. No severe weather is anticipated.

- There is a Slight/Marginal Risk of severe thunderstorms late
  Wednesday afternoon and Wednesday night. One or more complexes
  of storms could impact the region, but confidence is low where
  the complexes would have the biggest impact.

- Warm Wednesday and Thursday, then cooler Friday and Saturday
  before temperatures turn well above normal late in the weekend
  into the middle of next week.

- Gusty west to northwest winds are expected on Thursday which
  could create hazardous conditions for small craft. A Small Craft
  Advisory may be needed which could linger into early Thursday
  evening.

&&

.DISCUSSION...
Issued at 406 AM CDT Tue Jun 11 2024

Short Term...Today...Tonight...and Wednesday

Precipitation trends today into tonight, and potential for strong
thunderstorms late Wednesday afternoon, will be the main forecast
concerns.

High pressure was departing eastern WI as a cold front moved from
the eastern Dakotas into western MN. A band of light rain was
moving through MN, ahead of the cold front, and in association
with a short-wave trough.

This morning will start off with some sunshine, as high clouds
gradually increase. Models generally agree that light showers will
reach NC/C WI late this morning, but the best chance of measurable
rain should occur as a more potent short-wave trough and a 30-35
knot low-level jet move through during the late afternoon and
evening. This wave will have better moisture to work with, as
PWATs increase to 1.0-1.3 inches. It will also have a little bit
of instability, with mid-level lapse rates of 6.5 to 7 C/km, and
H8 LI`s of 0 to -2 C. Will carry high end chance to low-end likely
pops during the more favorable period, along with a slight chance
of embedded thunderstorms. These showers should taper off from
west to east during the early to mid evening. Dry conditions
should prevail overnight, and for most of the day on Wednesday.
Late in the day, a developing 35-45 knot low-level jet will
develop over the western half of the forecast area, and could
generate a few strong storms in a moist (PWATs increasing to 1.5
inches) and marginally unstable (CAPE 750-1250 j/kg) air mass.
However, the best instability is expected to develop to our west
(closer to the approaching cold front), and models are suggesting
that storms may split north and south of the forecast area
Wednesday evening, with the stronger complex possibly clipping
central WI.

High temperatures will be dependent on the extent of clouds and
precipitation today, but there should be enough sunshine for a
quick recovery this morning, and there likely be breaks in the
rain. Will forecast highs from the middle 60s to the lower 70s.
Partial clearing late tonight should allow lows to drop into the
50s regionwide, though some upper 40s may occur in the typical
cold spots. Patchy fog may also occur, but will hold off on any
mention at this time. On Wednesday, plenty of sunshine is expected
through much of the day, with increasing S-SW winds and WAA
helping to boost highs into the upper 70s to middle 80s, but a
little cooler lakeside.

Long Term...Wednesday Night Through Monday

Zonal pattern at 500mb expected through much of the work week,
then building 500mb heights suggest above normal temperatures
early next week. This is a typical summer time pattern which will
mean for periodic chances of thunderstorms into early next week.

The first chance of thunderstorms arrives Wednesday evening. The
Storm Prediction Center Day 2 Outlook has a Marginal Risk across
much of the area, with the only exception across our western
counties where there is a Slight Risk. Looking at some of the
severe parameters indicated most unstable cape values around
1,000 J/KG and 0-6 km shear values around 35 knots. The problem
tonight is where to focus the strongest convection. The ECMWF
model was significantly different with the focus for the strongest
convection across the far northern counties. However, the GFS-
Canadian-NAM was focusing strong or severe storms across southeast
Minnesota and west-central Wisconsin and then dives the complex
south/southeast with our western counties being clipped by the
strongest storms. Have trended the highest chances of rain across
the north and across central Wisconsin with the lowest chances
towards Door County. Most of the shower and storm activity should
come to an end overnight, with a few lingering showers possible
into Thursday morning. One thing to watch is convection is
expected to fire again Thursday afternoon across northern
Minnesota. Will need to watch to see if any of this activity would
sneak into the far north Thursday evening. High pressure builds
into the area Friday and lingers across the region into Saturday
morning. Lowered minimum temperatures across the north with the
slower arrival of the rain on Saturday.

The weekend will be interesting as there could be the potential
for several rounds of showers and thunderstorms. The showers and
storms should arrive sometime Saturday afternoon and continue
Saturday night into Sunday morning. Could not rule out some
stronger storms with this round. For Sunday, confidence is lower
on the high temperatures as the area will be drying out from the
first round of storms. There have been events where temperatures
struggle to climb to forecast values due to how quick the
rain and ends and how quick the clouds break up. More uncertainty
exists Sunday afternoon as the ECMWF is more robust with
convection breaking across the area. The Canadian and GFS model
were not as bullish in the QPF totals which support the previous
convection may have not allowed the atmosphere to destabilize as
much. With all the uncertainties in the forecast at this point,
there are a lot of uncertainties in the frontal position for
Monday which would impact precipitation chances and the expected
high temperatures.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1040 PM CDT Mon Jun 10 2024

Mostly clear skies and VFR conditions will prevail over the TAF
sites overnight as high pressure tracks through the western Great
Lakes region. A cold front will bring increasing clouds and shift
winds to the south-southwest on Tuesday. Showers will then track
through the TAF sites Tuesday afternoon from west to east as
conditions fall to MVFR and even IFR at times, especially across
central and north-central Wisconsin. There will be a small chance
for a few thunderstorms, but not high enough to include in the
TAFs. Showers will exit the region from west to east Tuesday
evening as conditions return to VFR.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Frost Advisory until 7 AM CDT this morning for WIZ005-010>013-
018.
&&

$$

DISCUSSION.....Kieckbusch/Eckberg
AVIATION.......Kurimski