367
FXUS63 KGRB 151919
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
219 PM CDT Fri May 15 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Scattered showers and a few thunderstorms develop this evening
  into tonight. An isolated strong to marginally severe storm is
  possible in central WI late this evening.

- Near critical to critical fire weather conditions in far north
  central WI (Vilas County) this afternoon through early evening,
  and across much of northern WI on Saturday. A Red Flag Warning
  is in effect for Vilas County through 9 pm this evening.

- Strong to severe storms and heavy rainfall are possible Sunday
  night through Monday night. Uncertainty is still high on timing
  and coverage of severe storms.

&&

.DISCUSSION...
Issued at 218 PM CDT Fri May 15 2026

Near term through Saturday...Clear skies along with warm and
breezy conditions this afternoon. 12z MPX sounding showed high
dewpoint depressions in low-levels and expect sfc dewpoints to mix
out this afternoon. This is already happening north-central WI.
Weak front, more of a wind shift, approaches late today but the
dry air and low dewpoints leads to less instability/MUCAPEs than
what was projected earlier. Thus, like the CAMs that are more
muted with convection late today into early this evening. Most
showers and a few storms likely will not occur until after 8p.
Given effective shear of 40kts, stronger storm could occur, but
less likely given lower MUCAPE mainly below 500J/kg through the
evening. Decaying showers and storms shift into eastern WI
overnight. All areas should be clear of rain by 7a on Saturday.
Rest of Saturday will be warm, breezy and mostly sunny.

Chances for showers and storms Sunday through Monday night...Warm
front lifts across the area late Sunday through Sunday night.
WI being on the northern edge of building instability from
plains, increasing low-level jet and hint of wave aloft generated
out of convection to the southwest Saturday night will bring
showers and some stronger storms late Sunday morning through
Sunday afternoon. Small risk of marginally severe hail, but
greater chances will be farther south/southwest into higher
instability. Sunday night will bring another round of elevated
storms and with greater elevated instability a better potential
for severe storms.

Monday in terms of dynamics and instability is the most favorable
day for severe weather as western Great Lakes region is ahead of
deeper trough and sfc pre-frontal trough and sharper cold front.
Sfc MUCAPEs increase to 1500-3000 J/kg as temperatures reach the
lower 80s and dewpoints make it into the 60s area-wide. As this
occurs, effective shear peaks at 40-60 kts late Monday afternoon
into Monday evening. Despite this, models are not completely on
board with high-end severe signal yet. Some models keep conditions
mainly dry until later Monday evening when initial trough arrives.
ML projections show mixed signals too. Thankfully, there is time
to further hone in on these details. Currently SPC has highlighted
much of our area in a Day 4 30% which would typically equate to
at least an enhanced risk once we get closer to the event. Given
the CAPE and shear, there is a potential for all hazards.

There is also a potential for locally heavy rainfall this weekend
through Monday night due to increasingly moist airmass (PWATs of
1.2 to 1.6 inches). LREF shows a 60-80% chance of seeing over 1
inch of rain Saturday night through Monday night, but less than a
20% chance of over 2 inches. Greatest probabilities are over
central to north- central WI.

Cooler and not as active rest of next week...Cold front moves
through late Monday night into 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 rest of next week.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1227 PM CDT Fri May 15 2026

Developing instability and the approach of a weak frontal
boundary will trigger scattered showers and thunderstorms across
NC/C WI this evening. Greatest chances for a few strong to
marginally severe storms will be over central WI, but likely west
and southwest of the CWA/AUW. Showers and storms will gradually
weaken as they drift east late this evening and overnight, but a
short-wave trough may trigger additional convection across our
far southern and southeast counties overnight. All rain will end
by 12z on Saturday. Continued Prob30 for TSRA at CWA/AUW/RHI from
02z-05z. Before that, capping and dry air (see 12z sounding from
Minneapolis) should allow most showers and storms to hold off.
Still kept a prob30 for rest of TAF sites, but only mentioned
showers. Models have now backed off of low clouds, except along
the lakeshore. Still have maintained prevailing VFR. Clear skies
Saturday morning, but high based cu may develop in the afternoon
over northern WI.

South to southwest winds gust 20-25 knots through late afternoon.
LLWS returns this evening, then taper off late tonight. Winds
Saturday more from the west, but could gust to 25 kts again late
morning through the afternoon.

&&

.FIRE WEATHER...
Issued at 218 PM 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 near-critical fire weather conditions
through Saturday.

A Red Flag Warning continues through 9 pm this evening over Vilas
County. Weather conditions should reach critical levels, with
highs into the 80s, RHs around 20% and southwest winds around 15
mph gusting to 25-35 mph.

Have to watch tonight as coverage and intensity of developing
showers and storms will have impact on whether Saturday is
another fire weather day. As it stands now, there is a chance for
scattered showers and storms over northern WI which could impact
dryness of fuels if coverage is high enough. If this doesn`t
occur though, dry air remains across northern WI on Saturday, with
RHs dropping to 17-22% along with west winds around 15 mph with
gusts to 20 to 25 mph. At this point an SPS will be issued for
much of the Northwoods region Saturday afternoon.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM CDT this evening for WIZ005.
&&

$$

DISCUSSION.....JLA
AVIATION.......JLA
FIRE WEATHER...JLA

NWS GRB Office Area Forecast Discussion