182
FXUS63 KGRB 040340
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1040 PM CDT Mon Jun 3 2024

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Showers and thunderstorms late this afternoon into this evening.
  Isolated severe storms are possible mainly south of Highway 10.
  Gusty winds, small hail and torrential downpours will be the
  main threats.

- Locally heavy rainfall is possible late this afternoon into
  tonight with isolated amounts of 1 to 2 inches. This may lead to
  minor flooding in urban and low-lying areas.

- More strong storms are possible late Tuesday into Tuesday
  night. Gusty winds, small hail, and heavy rain will be the
  primary hazards.

- Conditions hazardous to small craft will be possible at times
  from Wednesday through Saturday.

&&

.DISCUSSION...
Issued at 332 PM CDT Mon Jun 3 2024

Short Term...Tonight and Tuesday

Several concerns to focus on from potentially strong storms into
this evening, locally heavy rainfall that may lead to minor
flooding and timing of next precipitation event Tuesday afternoon.

The 19Z MSAS surface analysis showed one area of low pressure over
the MN Arrowhead with a warm front extended southeast through Lake
Superior. A second area of low pressure was over southeast SD with
a second warm front extended southeast through central IA.
Finally, a cold front connected the two areas of low pressure.
Radar mosaic indicated one band of thunderstorms across eastern
WI with more storms developing over western/southern WI, eastern
IA and northern IL.

Ongoing showers and thunderstorms will continue this evening (more
so over eastern WI) as a remnant MCV moves northeast across
southern WI and interacts with moderate instability (MLCAPES 1000-
1500 J/KG). Shear is rather weak (25-35 knots) and focused more
over southern WI. A few of these storms could become locally
strong with gusty winds and small hail, but the bigger threat
could be heavy rain with PW values around 1.5 inches and the
potential for training cells to create a minor flood situation,
especially in urban or low-lying areas. Have held off on any flood
watches since we have only received one report of one inch rain
totals so far today. Once the MCV exits the area, the weather
should calm down but with lingering low-level moisture in place,
low clouds and fog are expected overnight. Min temperatures to be
in the upper 50s near Lake MI, around 60 degrees north and middle
60s south.

The start of Tuesday looks relatively quiet with a lack of trigger
evident. Attention turns to the Upper MS Valley where a cold front
and mid-level shortwave trough to be co-located. Instability will
be on the rise across WI through the day and expect the next round
of showers and thunderstorms to push toward/into central WI late
in the afternoon. MUCAPES could surpass 2K J/KG, however shear is
practically non-existent (< 20 knots), thus pulse-type storms are
expected with a minimal threat of severe. Heavy rain threat will
continue with dew points in the 60s and PW values still around 1.5
inches. It will feel like summer on Tuesday as max temperatures
reach the lower to middle 70s near Lake MI, upper 70s to lower 80s
inland and humid conditions to exist.

Long Term...Tuesday Night Through Monday

A cold front will sweep through the area Tuesday night into
Wednesday morning, bringing showers and thunderstorms along with
the possibility for moderate to heavy rain. The best chance for
heavier rain will be Tuesday evening across central Wisconsin;
however, there are some indications some moderate rain could make
its way to the east late Tuesday night into Wednesday morning.

Some storms Tuesday evening could be strong to severe as MUCAPEs
rise to 1000 to 2000 J/kg; however, bulk shear values will only be
around 20 knots. The main threat for any severe weather would be
damaging winds, as wet bulb zero heights will be 10k ft along
with fairly narrow CAPE profiles in the hail growth zone. The area
of concern is mainly central and portions of north-central
Wisconsin as the storms will move through before the instability
diminishes later in the evening and overnight.

Once this cold front pushes east of the area, the weather will be
dominated by cooler weather and periods of light showers and a few
thunderstorms through the weekend. The main driver of the weather
during this period will be a closed upper low situated across
south-central Canada that will spin off other closed lows that
will track southeast from southern Canada through the Great Lakes
region at times. The first of these lows to spin off will occur
later Wednesday into Wednesday night and slowly track towards the
eastern Great Lakes by the end of the week. The second low to spin
off will be on the heels of the previous one, as it spins off
during the weekend towards the Great Lakes and eventually
establishes itself across southeastern Canada early next week.
Meanwhile, the original low will continue to meander across
southern Canada and spin off shortwaves that will track through
the Great Lakes when the spin off lows aren`t affecting the
region.

What this boils down to is these mid level lows and shortwaves
will bring several periods of light rain showers and isolated
thunderstorms at times from late this week through the weekend and
into early next week. There will also be dry periods at times,
especially at night and in the morning when instability will be at
its lowest. Holistically, the forecast looks more dry than wet
during this period with the periods of rain difficult to pinpoint
given the light nature of the precipitation and weak forcing.
Temperatures will start out above normal for Wednesday, then fall
to around normal for this time of year through early next week.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1039 PM CDT Mon Jun 3 2024

Conditions will gradually begin to dry out tonight as showers/storms
exit to the east. However, lingering low-level moisture and
relatively light winds should allow for some low clouds and fog to
stick around north and west of the Fox Valley, with cigs and
vsbys dropping down into the MVFR to IFR range. Locally LIFR
conditions will be possible across central to north-central
Wisconsin.

Tuesday is expected to start out mostly dry with IFR and MVFR
cigs gradually lifting to VFR across the region by mid-afternoon.
GRB, ATW, and MTW may briefly meet the LLWS threshold early
Tuesday morning as 925 to 850 mb winds increase in the wake of a
shallow, transient shortwave. A cold front is then expected to
arrive late Tuesday, bringing additional chances for showers and
thunderstorms to the forecast area Tuesday evening. MVFR to IFR
cigs are expected to return from west to east during this time.
Some thunder may be possible at the end of the TAF period,
although opted not to include due to low confidence given timing
and a stabilizing effect from a lake breeze.

&&

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

&&

$$

DISCUSSION.....Kallas/Kurimski
AVIATION.......Goodin