684
FXUS63 KGRB 160659
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
Issued by National Weather Service Milwaukee/Sullivan WI
159 AM CDT Fri May 16 2025

.KEY MESSAGES...

- Gusty southwest winds are expected today with highest gusts up
  to 40 mph, primarily between Fox Valley and Lake Michigan.

- Scattered showers and thunderstorms are expected this
  afternoon. Damaging wind gusts and small hail may be possible
  with any stronger storms.

&&

.DISCUSSION...
Issued at 1205 AM CDT Fri May 16 2025

A warm and windy day is in store for today. The low will be
over northwest MN at 7AM this morning and should make it to
Duluth around 7PM. A lobe of vorticity is expected to swing up
from IA through eastern WI during the day. Vorticity advection
and also upper divergence from the left exit region of an upper
jet will provide synoptic forcing to allow for showers and
storms.

Forecast soundings show very steep low and mid level lapse
rates during the afternoon, with 500 to 1000 j/kg CAPE. Some
models show a weak cap while others try to mix us all the way up
to 10kft. The winds through the profile are very strong with SW
winds up to 43kt at 5kft and 50 to 60kt at 10kft. There will
probably be a weak cap that will help keep our wind gusts in
check today, but a few gusts over 39kt (wind advisory criteria)
are not out of the question. If gusts begin to over-achieve by
noon today, we will know we need a wind advy for the afternoon.

Despite the weak cap, the overall synoptic forcing should be
enough for scattered thunderstorm development. The CAPE values
and low freezing level of 9 or 10kft support the chance for
small hail, with a report of two of 1 inch hail possible. There
is strong shear. The main threat for any stronger storms that
develop is the damaging wind potential, since the strong winds
aloft will efficiently mix down with momentum transfer.

As the upper low tracks across MN today, another frontal
boundary will push into north central and eastern WI. This will
feature cooler temperatures, low clouds, and rain or drizzle.
Northern WI will be fully engulfed in these damp, brisk
conditions Friday night.

Saturday, expect breaks in the clouds as the upper low starts to
exit the region. With steep low level lapse rates and lingering
low level moisture, scattered showers are expected, although
coverage is still uncertain. In addition, expect gusty west
winds up to 30 mph during peak daytime heating/mixing. Saturday
highs will range from the upper 50s north central to the mid 60s
east.

MRC

Saturday night through next Thursday

Upper trough exits across the eastern Great Lakes Saturday night with
ridging aloft beginning to build from the plains into the western Great
Lakes. Surface high pressure over Manitoba and northern Ontario will ridge
into MN and WI Saturday night with more influence of ridging by Sunday night.
The ridge will bring dry weather and also the risk of frost Saturday night
and/or Sunday night. PWATs lower Sunday night, but with high more off to the
north than the east, the area will keep some wind in lowest 1kft with tighter
pressure gradient on southern edge of high. It still appears that temps could
drop into the mid 30s north Saturday night and/or Sunday night. NBM probabilities
of min temps less than 35 are 30 to 40 percent Saturday night over Vilas County,
but increase and expand to 40-80 percent Sunday night north of highway 29. If and
where winds become light, some frost could occur either of these nights, though
Sunday night looks more favorable at this point.

Troughing over the western CONUS late this weekend shifts east early next
week, bringing the next chance of showers and storms to the area Monday night
into Tuesday. One trend that seems to be emerging though is the dry east flow
out of the high to the north may restrict chances of rain only to the southern
part of the forecast area on into southern WI. Risk of any stronger storms also
is well to the south of the area. Given these trends, its feasible that much of
northern WI could stay dry early this week.  Whatever chances of rain occur will
shift south and east of the western Great Lakes Wed into Thu as broad 850-700mb
low shifts across lower Great Lakes. Cool flow in wake of the low flowing across
the region could lead to more clouds and a small chance of spotty showers by
Thursday. Overall a cooler than normal stretch is expected for the coming week
with highs in the upper 50s to mid 60s.

JLA

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1050 PM CDT Thu May 15 2025

While strong thunderstorms have departed late this evening and a
lull in the weather is expected overnight, expect flight conditions
to deteriorate on Friday as low pressure slowly crosses the region.

South to southwest winds will become strong and gusty by mid to late
Friday morning with gusts of 30 to 35 kts likely.  These gusty winds
will diminish on Friday evening.

Low level wind shear will likely develop across the region late
tonight and continue through Friday morning.

Scattered showers and thunderstorms are forecast to develop on
Friday afternoon.  A few strong storms are possible that could
produce wind gusts in excess of 45 kts.

Ceilings are forecast to fall to MVFR on Friday evening with another
round of showers moving across the region.

MPC

&&

.MARINE...
Issued at 1205 AM CDT Fri May 16 2025

Gusty south-southwest winds are expected today, highest over
land. Cooler lake water should keep wind gusts below gale
force, so a Small Craft Advisory goes into effect mid morning.
We initially set the end time of 7PM this evening, but after a
brief lull in the winds tonight, gusty westerly winds will
develop. Therefore, we extended the end time all the way until
7PM Saturday.

MRC

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WI...None.
MARINE...Small Craft Advisory from 10 AM this morning to 7 PM
CDT Saturday evening for LMZ521-522-541>543.

&&

$$