Cassian, Wisconsin Weather Forecast Discussion

334
FXUS63 KGRB 122359
AFDGRB
Area Forecast Discussion
National Weather Service Green Bay WI
659 PM CDT Fri Sep 12 2025
Updated aviation portion for 00Z TAF issuance
.KEY MESSAGES...
- Showers and scattered thunderstorms this evening through
  Saturday morning. Severe weather is not expected, but an
  isolated strong storm or two is possible.
- Above normal temperatures through next week, with small rain
  chances middle to late part of the week.
&&
.DISCUSSION...
Issued at 259 PM CDT Fri Sep 12 2025
In the near term through Saturday, main issues will be storm trends
and strength, along with fog near Lake Michigan.
Showers and storms...Low pressure and warm front will remain
southwest of the western Great Lakes through Saturday. Elevated
instability will spread from the plains to the Great Lakes on edge
of elevated mixed layer (EML) of steeper mid-level lapse rates.
Shortwaves topping ridge over the southern Plains and mid-level
warm air advection and subtle low-level jet/moisture transport
interacting with MUCAPEs to around 500J/kg will lead to a couple
rounds of showers and storms this evening through daybreak on
Saturday. First round of storms which is extension of storms over
central MN (these caused severe weather earlier southwest of
Duluth where MUCAPE was around 1000j/kg) arrives over central and
north-central WI after 23-24Z/6-7pm. A few showers may even make
it over northern WI before this. Initial storms should weaken per
HREF 40+ dbz paintball trends as they outrun elevated instability
and stronger shear which remain to the west. Based on where stronger
storms have been generating though, possible that isolated strong
storm may make it into central WI this evening. Small hail and
heavy rain would be the primary hazards.
Then, stronger shortwave currently causing the arc of storms from
northeast SD into south central MN then should help develop
another round of storms after midnight over western WI, which will
track across especially central and east-central WI 07z-12z/2-7am.
Stronger low-level jet stays west before veering, so appears
greater risk of severe storms, still a low risk as it stands now,
would be more southwest of our area. Trends in LREF joint
probabilities for MUCAPEs of 500j/kg and effective shear of 25-30
kts have trended more southwest of our cwa as well. Similar to
the evening activity, cannot rule out stronger storm. Appears
primary risk for any showers and storms exits far south and
southeast forecast area 7-9am (12z-14z).
Dealing with convection, so though rain is likely, amounts
showing wide ranges. Not surprisingly. Looking at 25th to 75th
percentile ranges on HREF/NBM, a low-end for most locations will
be around 0.10 inch, but higher end values may end up over 1 inch.
Those amounts likely will be pretty localized though. Right now,
there is decent agreement that stripe of heavier QPF if it
materializes runs from Wausau to Oshkosh and points southwest,
building into greater instability. Rest of Saturday looks dry and
warm with highs reaching the upper 70s. Readings near Lake
Michigan will be held down some due to se winds.
Fog...Areas of fog this morning gave way to mainly marine based
stratus and fog this afternoon. Per satellite and webcams along
the shore (Sheboygan, Manitowoc and Two Rivers), restricted fog
mention to Lake Michigan, but this could also impact locations
very near the shoreline since the winds are light southeast into
Saturday morning. Marine Dense Fog Advisory was issued until 7
am Saturday, but admittedly am not very confident on the timing as
could see it lasting longer. And, on the flip side, the fog could
diminish quickly as it did over most of the area earlier today.
In addition on land, patchy fog may develop late tonight over
far north-central if the main area of showers and storms exit
quicker. Finally, also added patchy fog on Saturday night with
tonight`s rain adding moisture and temps later Saturday night
expected to fall well below the crossover temps with high pressure
overhead.
Precipitation and temperatures Sunday into the upcoming
week...Rain chances are few and far between through midweek as
ridging aloft builds over the region. Late this week, ridging
begins to break down and small chances for showers and storms re-
enter the picture. However, looking at LREF qpf progs, potential
for much precip most of the week is looking low. After the cool
start to the month, temps have rebounded and are expected to be
above normal through the week. Highs reaching the upper 70s to
lower 80s will be common most of the time through midweek. Normal
highs are in the low to mid 70s. Low temperatures will also be on
the warmer side, with readings many nights settling in the 55-60
range. Normal lows are a couple degrees either side of 50.
&&
.AVIATION...for 00Z TAF Issuance
Issued at 659 PM CDT Fri Sep 12 2025
Showers, a few storms and fog will all be aviation concerns this
evening into Saturday morning. Area of showers and isolated storms
continues to move into central and north central WI this evening.
It will bring showers to RHI/AUW/CWA. Opted to keep a TEMPO group
for some thunder at AUW/CWA for this first round of showers, but a
weakening/southward trend has been noted in the lightning, so the
storms may end up missing the TAF sites. Models show another shot
at thunder overnight when another round of showers and storms
spreads east across the region. Mainly VFR conditions are expected
for most of the night though, with MVFR conditions possible in
the heavier rain/storm. Some lower clouds may develop overnight
into Saturday morning as southeast flow prevails. Lingering
showers are possible into Saturday morning, with partial clearing
in the afternoon.
Dense fog will linger across Lake Michigan into Saturday morning.
Some of the fog could make it into MTW at times into the early
morning hours. Additional fog is possible across the rest of the
area after the second area of showers exits.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION.....JLA
AVIATION.......Bersch

NWS GRB Office Area Forecast Discussion