336
FXUS63 KGRB 071954
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
254 PM CDT Tue May 7 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- A few strong storms are possible through early this evening,
  mainly south of a line from Marshfield to Waupaca to Oshkosh.
  The primary hazards will be small hail and gusty winds.

- Areas of dense marine fog are expected through late this evening along
  Lake Michigan to the south of Algoma.

- Areas of frost are expected to develop over parts of central
  and north-central Wisconsin on Thursday night.

- Active pattern to continue into early next week.

&&

.DISCUSSION...
Issued at 253 PM CDT Tue May 7 2024

Short Term...Tonight and Wednesday

Arc of steady rain that swept through earlier driven by mid-level
fgen has given way to scattered showers and a few thunderstorms
into central WI. Thus far the strongest thunderstorms by far are
over southern WI closer to warm front and on edge of MLCAPES up to
1000J/kg. An isolated strong storm remains possible 3-7p as warm
front and instability attempt to shift northward. Easterly flow
off Lake Michigan will slow the progress somewhat. SW/S areas
generally south of a Marshfield to Waupaca to Oshkosh line will
see greatest risk for small hail and gusty winds. Then, will have
to see if another cluster of showers and storms currently
developing ahead of occluded front over western WI can make it
into western area later this evening. Likely these will outrun
greater instability while working eastward, so they should be in a
weakening state. Chances of showers and storms drop off after late
evening. Fog will be an issue right along the Lake Michigan shore
this evening then more areas could see patchy fog overnight with
today`s rain and nighttime low-level inversion setting up.

Wednesday begins mainly dry though a few spot showers or sprinkles
could still occur along the Upper Michigan border closer to
departing H85 low and cyclonic flow to the west of it. Expect a
mix of sun and clouds otherwise into early afternoon. Possible
that a few showers develop mid to late afternoon either from
pop-up showers or storms due to buildup of at least weak
instability farther inland or due to weak H85 trough dropping in
from the north during the afternoon as the Canadian has been
showing for the last couple days. GFS on board now too, so there
may be something to it. Soundings and instability progs would only
support thunder over central WI though. Decent range in temps on
Wednesday from highs only around 60 in the north, to readings well
into the 70s over the southwest forecast area.

Long Term...Wednesday Night Through Tuesday

An active weather pattern to continue over northeast WI into early
next week as a series of systems traverse the region. The first
system to be a weakening upper low into an upper trough with
precipitation chances Wednesday night into Thursday. Mean flow
turns northwest into WI by late week with the passage of two
shortwave troughs (Friday night and Sunday afternoon/night)
bringing additional precipitation chances. Temperatures to
generally be at or below normal through the weekend, then slightly
above normal early next week.

Wednesday night and Thursday...
An elongated shortwave trough stretching from eastern Canada to
the Midwest will swing through northeast WI Wednesday evening into
Thursday morning. Instability looks minimal at best over the
northern half of the state and stronger forcing to be focused to
our south, thus have kept thunder out of the forecast. Anticipate
shower chances to range from slight from Hwy 8 northward, to
likely from Hwy 21 southward. Rainfall amounts over parts of
central and east-central WI will range from one-tenth to one-third
of an inch. Min temperatures Wednesday night to range from 35-40
degrees far north, middle to upper 40s south. High pressure is
forecast to begin building south into the western Great Lakes by
Thursday morning which should start to dry things out. Max
temperatures Thursday to be in the middle 50s to lower 60s.

Thursday night and Friday...
This high pressure will move across the forecast area Thursday
night, allowing for skies to clear as well as bring a cooler air
mass to the region. Min temperatures across north-central WI could
drop to around 30 degrees with lower to middle 30s for central and
far northeast WI. This may bring frost headlines into play if
winds can decouple which is looking more likely. Anyone with
sensitive plants may want to take the appropriate precautions. By
Friday, clouds will be on the increase as a sharp upper trough
digs southeast across the Upper MS Valley. By the afternoon,
enough lift from the left exit region of the upper jet, in concert
with increasing Q-G/FGEN mid-level forcing, could bring a chance
of showers into central WI. Max temperatures on Friday to mainly
be in the lower to middle 60s.

Friday night and Saturday...
This upper trough sweeps southeast across the western Great Lakes
Friday night with a chance of showers and a slight chance of
thunderstorms. Even as this trough departs on Saturday, lingering
cyclonic flow may keep shower chances in the forecast through at
least the morning hours. Limited sunshine and north wind will keep
max temperatures Saturday in the upper 50s to middle 60s.

Saturday night and Sunday...
After a brief lull in the precipitation Saturday night as a weak
surface ridge slides across WI, a weaker upper trough is progged
to move into the western Great Lakes Sunday afternoon. This trough
will be accompanied by a cold front, thus another chance for
showers across northeast WI. A minor uptick to temperatures aloft
will bring max temperatures on Sunday into the lower 60s near Lake
MI, lower to middle 60s north and middle 60s to around 70 degrees
south.

Sunday night and Monday...
The chance for showers will linger into Sunday evening until the
cold front clears the area. The rest of Sunday night should be dry
under partly to mostly cloudy skies. A cool air mass is left
behind over northeast WI on Monday with 8H temperatures of 0 to
+4C. This cooler air and the passage of a mid-level shortwave
could kick off a few showers Monday. If the showers stay away, max
temperatures on Monday could reach the middle 60s lakeside, upper
60s to lower 70s inland.

Monday night and Tuesday...
Models diverge after Monday with the GFS bringing a push of warmer
air toward WI with more rain chances versus the ECMWF which sends
high pressure into WI. Have followed the blended guidance which
does bring a chance of showers to all of northeast WI by Tuesday.
Max temperatures on Tuesday to be in the middle 60s near Lake MI,
upper 60s to middle 70s inland.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 113 PM CDT Tue May 7 2024

Widespread rain impacting north-central WI to far northeast WI.
Scattered showers are developing in wake of swath of rain and
these will impact all the TAF sites the remainder of the
afternoon through 22-24z. Expect isolated thunder to develop
later this afternoon (after 20z) but coverage was too uncertain
to include anything more than VCTS at this point. Another period
of isolated showers and possible thunder will occur after 00z
before showers end after midnight from west to east. Flight
conditions will mainly prevail at IFR/MVFR this afternoon. MVFR
conditions will occur this evening but then will improve to VFR
from west to east as a front slides past the area.

&&

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

&&

$$

DISCUSSION.....JLA/Kallas
AVIATION.......JLA