723
FXUS63 KGRB 170522
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1222 AM CDT Sun May 17 2026

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Near critical fire weather conditions expected across northern
  WI this afternoon. Elevated fire weather conditions elsewhere
  with very warm temperatures, gusty winds, and low RH values.

- Strong to severe storms and locally heavy rainfall from Sunday
  afternoon through Monday night. There is low confidence on the
  timing and coverage of severe storms.

- A return to drier and cooler weather is expected for the mid to
  late part of the next work week. Some nights could need frost or freeze
  headlines.

&&

.DISCUSSION...
Issued at 306 PM CDT Sat May 16 2026

Near term through Sunday...Another dry afternoon with RH values
less than 20% over most of the area. Temperatures have risen into
the mid 70s north, but have reached the lower to middle 80s over
eastern WI. Readings have even cracked the mid 70s on Door County
and Washington Island. Next 24hr will be changeable. Backdoor cold
front charges in from the north this evening, switching winds to
northeast overnight through Sunday as surface warm front will only
be slow to move north. Progress will be further hampered with the
cooler flow off Lake Michigan. Temperatures on Sunday will show a
large range due to the onshore flow and clouds. Coolest readings
in the 50s will be over eastern WI, perhaps as far west as the Fox
Valley. Meanwhile in the far south due to approaching warm sector
and north along the Upper Michigan border, highs will reach well
into the 60s.

As the warm front approaches Sunday, a few showers will begin to
develop with warm advection aloft. Steadier showers and some
thunder develops on Sunday afternoon. Steeper mid-level lapse
rates over 8.5C/km pushing in from the south could aid in a few
stronger storms late in the afternoon closer to low-level jet axis
40-50 kt over western WI. Overall though the thunder on Sunday
looks more embedded as the main period of showers shift north
across the area late morning through mid afternoon. Soundings
over southern WI where the sfc warm front makes it through point
to very strong capping and hostile environment for convection.
This theme continues into Sunday night.

Chances for showers and thunderstorms Sunday night through early
Tuesday...Capping that shows up late Sunday continues to persist
on Sunday night. Also by this time, main convergence at nose of
500mb and 850mb jets looked to be displaced northwest and north of
most cwa. Exception could be over northwest cwa where influences
from upstream convection/possible MCVs and weak sfc waves could
help trigger scattered showers and storms. Forecast effective
(2-8km) shear and MUCAPE would suggest severe storms could sneak
into those areas at times Sunday evening into Monday morning. A
few CAMS (including the 12z HRRR and RRFS) point to a line of
storms making a run into western WI later Sunday night. A lot of
questions in mode, coverage for severe potential Sunday night into
Monday morning.

Rest of Monday into Monday evening, majority of WI will be in the
warm sector ahead of approaching low pressure and cold front. Sfc
based instability (highs in the 80s with dewpoints in the 60s) and
effective shear will be more than sufficient for strong to severe
storms, but soundings in the warm sector still show residual capping
800-700mb layer and there is limited convergence. Think pops in
our forecast may be a bit too widespread and high, but some showers
and storms could occur at times, so will refrain from lowering them
for now. Cold front slowly approaches late Monday night, so like
the categorical pops by that time. MUCAPEs still in the 1500-2500J/kg
with stronger 500mb and 850mb jets sliding overhead and hint of pre-
frontal sfc trough ahead of the cold front support severe risk deep
into Monday evening, if not even into the early overnight hours.
SPC Day3 (12z Mon through 12z Tue) highlights majority of area in
Slight Risk which seems appropriate even though uncertainty in
details is still pretty high.

Cold front shifts through early Tuesday but some showers and embedded
thunder could hang on through Tuesday morning. One last warmish day
with highs well into the 70s eastern WI and in the mid to upper 60s
northern WI. Rest of the forecast looks as it has for a while with
temperatures at or below average midweek and warming into next weekend.
Overall it looks to remain dry until later in the weekend. Only main
impact could be the need for Frost/Freeze headlines midweek over northern
WI.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1222 AM CDT Sun May 17 2026

VFR flying conditions will persist overnight, with some mid and
high clouds gradually moving in from the south. A surface boundary
continues to drop south tonight, bringing a wind shift to the
northeast along with occasional wind gusts up to 30 kts as it
moves through.

By Sunday morning, skies will be broken to overcast, with low
clouds and MVFR cigs moving in during the late morning and early
afternoon, then dropping to IFR from mid to late afternoon. These
low clouds will be accompanied by scattered to widespread rain
showers, along with lowering vsbys. There could be thunder at
times, but confidence in exact timing is still low. Included
PROB30 groups for most likely hours to see any thunderstorms at
each TAF location.

Easterly winds on Sunday will gusts up to around 25 knots.

&&

.FIRE WEATHER...
Issued at 306 PM CDT Sat May 16 2026

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

Rain fell across northern WI last night, with some locations
receiving 0.25-0.40 inch in northwest Oneida, southeast Vilas and
the northern portions of Forest and Florence counties. Although
sunshine, low relative humidity (15-20%) and west winds gusting
to 25 to 35 mph will result in drying this afternoon, suspect that
the areas that received higher rainfall amounts may not become
critically dry. SPS continues in northern WI until 7p this
evening for elevated to near-critical fire weather conditions
this afternoon.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion