561
FXUS63 KGRB 102002
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
302 PM CDT Mon Jun 10 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Chilly again for northern Wisconsin with another frost advisory
  issued for late tonight into early Tuesday.

- Light showers spreading west to east on Tuesday afternoon
  through Tuesday evening. Rain amounts less than 0.25 inch and
  minimal chance of thunder.

- There is a risk of strong thunderstorms Wednesday night as one
  or more complexes of storms impact the region, but confidence is
  low in exact tracks of these complexes. Threat for severe
  weather needs to be monitored.

- Warm up begins Wednesday with well above normal highs late this
  weekend into early next week.

&&

.DISCUSSION...
Issued at 301 PM CDT Mon Jun 10 2024

Sunsplashed day this afternoon with high pressure overhead. This
will transition to another quiet and chilly night. High clouds
thin and fleeting do increase late but this will not impact temps
much. PWAT still well below normal and light winds will result in
good radiational cooling. Continued to favor MOS guidance which
has another round of low to mid 30s for northern WI toward the
Upper Michigan border. Issued another Frost Advisory. Only
difference tonight is northern Marinette County is included. Temps
elsewhere will bottom out in the low to mid 40s.

No big changes to the forecast for Tuesday and Tuesday night.
Narrow ribbon of deeper moisture and lift within that higher RH
ahead of an cold front and mid-level trough will be efficient in
squeezing out some pretty light rainfall as instability over
central and eastern WI is less compared to what builds up by late
in the day MN/IA to western WI. Initial showers will be ahead of
that instability axis but eventually diminishing instability
working east could support some rumbles of thunder over much of
the area. Showers and any rumbles will end around midnight over
east-central WI. Warmer ahead of the front across the board with
readings in the low to mid 50s.

Wednesday and Wednesday night are in focus for the potential for
strong to severe storms. Ahead of this, cold front washes out it
is lifts east/northeast of our area. This results in decent surge
of warm air aloft working in from the west/southwest. H85 temps by
late day are 18-19c over the area which supports highs into the
low if not mid 80s. A touch humid too as dewpoints near 60 Fox
Valley to the southeast. Late Wednesday heading into this airmass
will be strong mid-level jet across the Dakotas with increasing
low-level jet aimed into the upper Mississippi River valley. This
forcing will be interacting on MLCAPES over 2000J/kg banked from
central MN into southwest WI. Decent agreement from models of more
sfc based complex of storms developing late afternoon over MN and
shifting southeast, mainly staying south of our area. However,
there is also a signal that additional storms will develop farther
north, closer to the nose of the H5 jet from northern MN into
northwest WI and western Upper Michigan. Strong effective shear
(50+ kts) and sufficient instability (500-1000J/kg CAPE) that if
these storms develop they would swing southeast across much of
our forecast area. Main issue by time they reach central, north-
central and northeast WI would be strong to damaging winds. SPC
has the Day3 slight risk just clipping far west with marginal risk
elsewhere. That idea fits the forcing/instability pattern
forecasted, but there is still a LOT of uncertainty with the
details that result in lower confidence at this point for the
Wednesday night forecast.

In wake of whatever occurs on Wednesday night, seems the primary
axis of instability and what generally will be the effective
frontal boundary will be shoved to the south of most of our cwa.
Thus, pops have trended down on Thursday/Thursday night which is
very reasonable. Other thing to watch Thursday is there is still
decent warm air around aloft and stronger winds aloft and really
not a lot of low clouds shown in wake of the convection. Thus,
could end up being a warm and breezy day. Friday appears quiet
with temps a bit cooler (mid to upper 70s) with high pressure
briefly settling across.

Plan on increasingly unsettled, warmer and humid conditions next
weekend into early next week. A warm front lifting across will
focus multiple chances of showers and thunderstorms. Temps
probably remain only upper 70s/near 80 on Saturday, but by Sunday
and Monday will be heading upward with good chance of at least
low to mid 80s and even a chance of seeing readings near 90 by
early next week. Currently NBM shows just over a 50 percent
chance of the high reaching 90 over at least southern half of the
area next Monday (upward trend from previous run). However, one
thing to note is NBM temp spread is pretty high by then with
warmer guidance suggesting lower or even mid 90s while cooler
tail of guidance is mainly lower 80s. Plenty of time to sort out
the details as we get later into this week.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1234 PM CDT Mon Jun 10 2024

Wide open VFR conditions this afternoon through tonight. North
winds will gust to 15-20 kts early this afternoon at GRB/ATW/MTW
but winds diminish by late afternoon.

Cold front moving in from the west on Tuesday will bring thickening
and lowering mid clouds, but conditions through end of TAF period
will remain VFR. Showers will then shift west to east across the
region Tuesday afternoon through Tuesday evening. Only a small
chance of thunder with this system for the TAF sites as higher
instability remains over Minnesota and west to southwest Wisconsin.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 1 AM to 7 AM CDT Tuesday for WIZ005-010>013-
018.
&&

$$

DISCUSSION.....JLA
AVIATION.......JLA