746
FXUS63 KGRB 150732
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
232 AM CDT Fri May 15 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Showers exit eastern WI early this morning, with scattered
  showers and thunderstorms redeveloping late this afternoon into
  tonight. A few strong to marginally severe storms are possible
  in central WI during the late afternoon and evening.

- Near critical to critical fire weather conditions expected in
  far north central WI (Vilas County) this afternoon and early
  evening, and across much of northern WI on Saturday. A Red Flag
  Warning has been issued for Vilas County from noon to 9 pm
  today.

- Periods of heavy rainfall and strong to severe storms are possible
  Sunday night through Monday night.

&&

.DISCUSSION...
Issued at 232 AM CDT Fri May 15 2026

Main forecast changes include increased pops for showers and
thunderstorms late this afternoon into tonight, potential for
a few strong to marginally severe storms in central WI late
this afternoon and evening, and concern for additional fire
weather headlines over northern WI on Saturday afternoon.

The main band of showers was rapidly shifting east this morning.
This band dropped a tenth to three-tenths of an inch of rain in
central WI. Only light amounts have occurred in north central WI,
but a narrow secondary band of showers associated with a short-
wave trough will move through that area over the next couple
hours. The showers will move out of eastern WI early Friday
morning, followed by clearing skies and warm temperatures. Highs
will reach the upper 70s to lower 80s away from Lake Michigan.
Cooler readings in the lower to middle 60s are expected along the
Lake Michigan shoreline due to SSE winds. Southwest winds will
gust to 20 to 30 mph at inland locations.

Models have trended more moist and unstable late this afternoon
and tonight, with an axis of MUCAPE now expected to reach
500-1250 j/kg from northeast into central WI late in the afternoon
and early evening. The approach of a weak boundary should trigger
late day convection (after 22z/Fri) over parts of NC WI, which
should spread southeast into the evening. A few strong to
marginally severe storms are possible in central WI, where the
greatest instability will exist. With strong deep layer shear of
40-60 knots, very favorable wet-bulb zero heights of 7-9k feet
and inverted-V soundings, cannot rule out a few reports of large
hail and damaging winds. Though the daytime convection should tend
to weaken later this evening, lingering moisture (PWATs of 1-1.5
inches), short-wave energy and frontogenetic forcing should bring
at least scattered showers and storms to the far south/southeast
parts of the forecast area between 06z-12z/Saturday. Overall, have
trended pops higher through this period, but have capped them at
chance category for now.

Generally dry conditions are expected Saturday into Saturday night.
Very deep mixing will support highs in the upper 70s to middle 80s
on Saturday, along with gusty west winds and very low relative
humidity.

Southwest flow aloft will bring an increasingly moist and
unstable air mass to the region later in the weekend, with the
leading surge arriving on Sunday, resulting in an uptick in
shower and thunderstorms activity. Low pressure developing in the
Central Plains on Sunday will lift northeast along a slow moving
cold front Sunday night through Monday night. This system will
generate periods of showers and storms, and locally heavy
rainfall, in an increasingly moist (PWATs of 1.2 to 1.6 inches)
and unstable air mass. Probabilistic forecasts show a 20-80%
chance (highest over NC/C WI) of 1+ inch of rain from Sunday
through Monday night, with a 10-50% chance (highest in NC/C WI) of
2+ inches. Potential for severe thunderstorms increases Sunday
night, as increasing elevated instability (mid-level lapse rates
of 7.5-8.5 C/km and MUCAPE of 750-1500 j/kg) and deep layer shear
of 30-40 knots support a threat of large hail. Surface based
instability increases to 1500-3000 j/kg Monday afternoon and early
evening, leading to potential for a significant round of severe
storms as the cold front approaches the forecast area.
Temperatures should remain above normal during this period.

Models suggest the frontal boundary will move through the region
Monday night or Tuesday, followed by a decreasing threat of
showers and storms. Once the front clears the area, drier weather
and a return to near normal temperatures is expected through the
middle of next week.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 946 PM CDT Thu May 14 2026

Mid and high clouds continue to increase and thicken late this
evening ahead of approaching low pressure. Scattered showers make
it to RHI, AUW, and CWA by 06Z, decreasing in coverage by the time
they arrive to the east-central sites by around 10Z. Have opted
to represent this via PROB30 groups for -SHRA across the east-
central sites. Cigs are then forecast to lower to MVFR mainly
across the western TAF sites in the vicinity of a cold front early
Friday morning, after any lingering showers have departed the
area. However, lower cigs will likely be short- lived as
scattering occurs from west to east, with conditions eventually
lifting to VFR by mid-afternoon Friday.

South/southeast winds will increase and shift to southwesterly by
early Friday afternoon, with gusts between 20 and 25 knots
possible during this time. LLWS will become a concern late
tonight as winds at 2 to 3k ft AGL increase to around 40 to
45 knots, departing the area from southwest to northeast by mid-
morning Friday.

&&

.FIRE WEATHER...
Issued at 232 AM CDT Fri May 15 2026

Pine fuels have reached their peak volatility and fine fuels have
still not greened up over northern WI, so periods of dry and
windy weather will bring elevated to near-critical fire weather
conditions through Saturday.

A Red Flag Warning has been posted for Vilas County this
afternoon and early evening. Rainfall in north central WI has
been on the light side early this morning, so fine fuels should
have an opportunity to dry out by afternoon. Weather conditions
should reach critical levels, with highs near 80, RHs around 25%
and southwest winds around 15 mph gusting to 25-30 mph.

Dry air remains across northern WI on Saturday, with RHs dropping
to 18-25% along with west winds around 15 mph with gusts to 20 to
25 mph. Suspect we will need additional fire weather headlines
across much of the Northwoods region Saturday afternoon.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 9 PM CDT this evening for
WIZ005.
&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......Goodin
FIRE WEATHER...Kieckbusch

NWS GRB Office Area Forecast Discussion