306
FXUS63 KGRB 062340
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
540 PM CST Fri Mar 6 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Areas of dense fog will impact travel at times into tonight.
  Most persistent fog will be near the lakeshore.

- Rain comes in waves this afternoon, then again later this
  evening into the overnight hours. Greatest chance for
  thunderstorms will be from 10p this evening through 4a Saturday
  morning. Primary hazards with storms late tonight are heavy
  rainfall, gusty winds and small hail. Localized flooding
  possible.

- Wintry mix far north-central WI late tonight into Saturday
  morning. Minor snow and ice accumulations could impact travel.

- In addition to minor flooding tonight with thunderstorms, the
  rain and warmer temperatures will result in ice shifting and
  breakup on rivers, leading to a localized ice jam flooding
  threat into the weekend. Ice floes could also be a concern
  Sunday into Monday.

- Very warm and breezy Sunday and Monday. Highs reaching the 60s
  in some areas. Turning cooler by midweek with potential for rain
  and snow.

&&

.DISCUSSION...
Issued at 1249 PM CST Fri Mar 6 2026

Near term through early evening...
Showers and isolated storms over southern WI into lower Michigan
with light rain into especially east-central WI at present supported
by 700-500mb speed max moving into lower Michigan. Additional
showers and storms over central IA into far southwest WI are on
nose of 850mb jet, though still north of the warm front. Two areas
of elevated instability are noted, one feeding into the initial
cluster of showers and storms that mainly stayed south, the other
with activity moving into far southwest WI. Expect these showers
and a few storms to have better chance of making it into southern
areas this afternoon, though veering low-level jet likely will
keep the bulk of higher elevated instability to the south. Between
both rounds of rain today, expect total rainfall amounts mainly
0.50 inch or less, greatest amounts south of highway 10.

Other concern into this evening will be dense fog near the lakeshore
as flow remains onshore. The rain will likely cause the fog to
diminish briefly, but when steadier rain ends, expect it to expand
again as low-levels across Lake Michigan remain very saturated to
the north of approaching warm front.

Active weather tonight...
Late this evening through most of the overnight strong low-mid
level jet energy on leading edge of strong trough over the plains
arrives over WI. At the sfc, warm front lifting into southern WI
early this evening makes it to east-central WI by around midnight.
50 kt low-level jet will be aimed toward Fox Valley/lakeshore
which along the warm front present should allow blossoming of
showers and thunder given elevated instability (1-6km MUCAPE
500-1000J/kg). Appears that initiation of the showers and storms
occurs over western IA, so that will be area to watch by early
this evening. Latest forecast soundings back across our area
show inversion based at 1-2kft northern Fox Valley to lakeshore
and points west/northwest. Hint still there inversion could try to
diminish briefly southern tier of forecast area as warmest low-
level temps/dewpoints arrive from the south with the warm front.
Expect one primarily slug of moderate to heavy rain, gusty winds
40+ mph and possible small hail as wet-bulb zero heights are
5-7kft. Main concern is if stronger winds just aloft (50kt 850mb
and 60kt at 700mb, can be brought down to the sfc. Seems that sfc
based instability is too low and remains to the south, but if the
orientation of the line of storms ends up perpendicular to the
axis of low-level jet, chances of seeing stronger sfc gusts could
increase.

Hydro concerns are still present as rain tonight falls on at least
partially frozen ground, saturated from the rain that occurs today.
As we have mentioned in discussions recently, many of our rivers remain
ice covered, so the moderate to heavy rain falling on this could
cause at least localized flooding issues once the increasing flow
begins to break up and shift the ice. Given the strong winds aloft,
storm motion and motion of the overall cluster of showers and
storms will be fast. Thus, flooding issues should overall be minor
unless training of convective elements can occur. The wild card
is the ice on the rivers as runoff off this could lead to minor
localized flooding. At this point, appears the heaviest swath of
rain tonight occurs in parts of our forecast area that have no
snow on the ground, versus far north-central where 10-20" of snow
depth remains. Rates with the rainfall tonight should be high
given the elevated instability interacting with PWATs over 1"
which is near or above the maximum for the date. Rainfall that
occurs from late this evening to 6 am on Saturday could at least
locally exceed 1" and the reality is most of that will occur in a
2-3 hour time frame. Last issue tonight will be the lingering
areas of fog that could be dense, especially when rain is not as
steady. This fog really will not abate until cold front and
primary cluster of showers and storms sweep through late tonight.
The last locations to lose the fog will be near the lakeshore due
to flow off Lake Michigan.

Wintry Precip Saturday North-Central...
Still have to watch far north-central late tonight through first
thing on Saturday morning. As widespread precipitation diminishes
that area will be on southern fringe of deformation over western
Lake Superior/western Upper Michigan and within right entrance of
departing jet streak. Steady precip starts off as rain, but soundings
show warmth aloft being undercut by cold air advection, suggesting
a brief period of freezing rain/sleet before a switch to snow occurs.
QPF for the entire duration of wintry precip is less than 0.10,
looking at minor impacts given marginal sfc temps even when wintry
mix to snow occurs. High-end of NBM not suggesting any more than
1-2" of snow in far northern Vilas County late tonight through
midday Saturday. This idea is roundly supported by deterministic
model snowfall output as well. At this point, do not foresee need
for an advisory, but more of a nowcast/SPS type event. Away from
north-central, a few rain showers may swing through the rest of
the area as last of mid-level jet wind max slides through as the
cold front finishes crossing the area. No thunder is expected as
elevated instability will be east of the area. High temperatures
Saturday reach upper 30s north and probably the low to mid 50s
east-central. Northwest winds behind the front may reach 25-30 mph
Fox Valley to the lakeshore.

Warm, Breezy on Sunday...
Strong cyclone with MSLP less than 985mb crosses central Canada.
Dry with this system, but warm and windy. If not for the rain into
tonight, would be more of a fire weather issue where no more snow
is on the ground. NBM probabilities of seeing wind gusts over 30
mph are 40-60% with little change in last 24 hrs. Chances of seeing
highs 60+ 50-90%, with again little change. Adjusted winds/gusts
upward on Sunday given deep mixed profile and stronger pressure
gradient.

Next System Tuesday/Wednesday...
Main trend continues with shifting primary track of the low
southeast, thus heaviest QPF into the system also stays mainly
southeast. Ptype becomes more of an issue, especially northern
forecast area. NBM mean/50th percentile for 24hr snow ending 12z
Wed nothing too noteworthy, but reasonable high-end (90th percentile)
shows potential for several inches over northern WI. Diving into latest
model output there is decent spread noted in how far south could see
snow. Upshot is this will be a period to watch for trends as we move
into early next week.

Ice Jam/Ice Floe Potential...In addition to the previously
mentioned potential for runoff flooding from heavy rainfall
tonight, at least a low threat of ice jam flooding will carry into
the weekend, and continued mild temperatures will further increase
the threat of ice break-up into early next week. Lower river
levels initially do lead to a lesser threat, though this may
change after the expected heavy rainfall occurs tonight. Given the
gusty southwest winds expected Sunday and potentially into Monday
as well, an increased threat of ice floes on Green Bay may also occur.
Already saw in local media that ice shoves occurred during stronger
winds yesterday (Thu) near Washington Island and we could be in
for more of this type of activity later this weekend into Monday
with the stronger winds and deteriorating ice conditions.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 540 PM CST Fri Mar 6 2026

Poor flying conditions blanket the region late this afternoon as
LIFR status based 200-300ft AGL has develop along with areas of fog
reduce visibility down to 1/4-1/2SM at most terminals. These poor
flying conditions will persist through the evening before a round of
showers and thunderstorms move across the region tonight between
about 04-09Z. Main concern with any storms that develop will be
lightning and small hail. Also included a mention of wind gusts up
to 30kts as storms move through at ATW, GRB, and MTW was those sites
will likely reside just south of a warm front lifting into east-
central WI this evening. LLWS is also a concern this evening as
southerly winds just above a shallow inversion will strengthen to 35-
45kts.

Once widespread showers and storms end late tonight, a few widely
scattered showers will linger into Saturday as cigs begin to lift to
IFR/MVFR. More widespread precip in the form of fzra/sleet switching
to snow will occur over far north-central WI, eventually making it
to RHI by mid morning Saturday. Most of the accumulating snow will
remain north of RHI though.

Behind the departing showers Saturday winds will shift to the
northwest as cold front moves through, with gusts of 20+ kts across
the area by afternoon.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 6 AM CST Saturday for WIZ022-040-050.
&&

$$

DISCUSSION.....JLA
AVIATION.......GK

NWS GRB Office Area Forecast Discussion