290
FXUS63 KGRB 062307
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
607 PM CDT Mon May 6 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Relative humidity values in the 20s and 30s will continue for
  the rest of the afternoon into early this evening away from the
  bay and Lake Michigan. Recent rain, lack of strong gusty winds
  and continued green-up will limit fire weather concerns.

- Next round of showers and storms arrives Tuesday morning. Best
  chance for thunderstorms will be Tuesday afternoon and evening.
  There is a marginal risk for severe storms generally south and
  west of a Merrill to Green Bay to Kewaunee line.

- Showers will again be possible Wednesday afternoon through
  Thursday with a few storms possible Wednesday afternoon and
  evening, mainly in central WI.

&&

.DISCUSSION...
Issued at 252 PM CDT Mon May 6 2024

Short Term...Tonight and Tuesday

Mild and dry conditions were noted across the area this
afternoon. Temperatures warmed into the middle 60s to lower 70s
with humidity readings from the middle 20s to the 30s away from
the bay and Lake Michigan.

For tonight, skies will start out mostly clear and then turn
mostly cloudy overnight. The rain should off until after 12z on
Tuesday. Easterly winds shouldn`t allow for temperatures to fall
off as much as light night. Lows should drop into the 40s to
around 50.

On Tuesday, an upper level disturbance will bring the main band
of rain into central and portions of north-central Wisconsin
between 12z and 15z, and then across much of northeast Wisconsin
between 15z and 18z. The progression of the rain may cause high
temperatures across the north to occur during the morning before
temperatures fall back due to the rain. Across the south, high
temperatures should occur during the late afternoon as the
steadier rain shifts to the northeast of the area.

As the first upper level disturbance moves northeast of the area
during the afternoon which should result in subsidence behind it,
a frontal boundary will move into the area resulting in some
lift. There is still a lot of uncertainty in stronger storms
Tuesday afternoon as the models continue to show scattered
activity behind the main line and the main secondary shortwave
doesn`t arrive until 00z. Bufkit soundings not impressive with
respect to the 0-6km shear 10 to 20 knots and CAPE of a few
hundred J/KG. If stronger storms do form, the main risk would be
large hail and damaging winds.

Long Term...Tuesday Night Through Monday

Possible strong storms early Tuesday evening, gusty northeast
winds on Thursday and potential for frost Thursday night are the
primary impacts through the long term.

Not completely sure how things will look on Tuesday evening, but
seems there is loose consensus that secondary shortwave emerging
out of main upper low over the Dakotas will interact with built up
instability in the afternoon to our west will result in area of
decaying thunderstorms shifting into central WI during the evening
before fading out as they move east-northeast across the rest of
the area. Have highest pops early in the evening over the west
tapering to chance pops east. Lingering chance pops through midnight
then drop off late as drying trend takes hold. Did keep mention of
a few showers north-central with deeper moisture and cool/moist
low-level flow off Lake Superior. Marine fog that is expected to
form later Tuesday will linger Tuesday evening south of Algoma
before winds turn offshore/SSW.

Expect much of the region to turn dry Wednesday morning as drier
air filters over the area behind an occluded front. mixed signals
on whether additional showers or storms develop during peak heating
on Wednesday afternoon. Canadian most on board as it drops a secondary
trough in from the north to enhance the potential. For most part
other primary models are dry, but ensembles do hint at some additional
showers. Forecast for now will be dry in the morning with low-end
chances during peak heating. So long as showers don`t end up being
too widespread in the afternoon, temps will reach the upper 60s to
mid 70s most areas, though north-central which will remain on edge
of more clouds and some showers off Lake Superior could stay in
the upper 50s.

Wednesday night into Thursday, decent agreement of another wave of
showers to mainly impact south half of the state as primary sfc
low redevelops across the central and eastern Ohio Valley. Main
impact will be cool and breezy conditions as northeast winds flow
in off Lake Michigan. Many areas Thursday will see temperatures
remain in the 50s.

Rest of the extended....Ensembles are trending toward a mostly
dry Friday as a brief ridge of high pressure develops over the
region. Depending on how much rain falls Thursday and how quickly
clouds clear out Thursday night there is the potential for fog or
frost to develop across northern WI with temperatures forecast to
fall to or near freezing Friday morning. Will start to mention
this in the Hazardous Weather Outlook as we get later into the
week as our frost/freeze program will have started up in all areas
by then. Temperatures should recover back into the 60s by Friday
afternoon.

Models continue to show broad consensus with a quick moving
short-wave passing over the region Friday night into Saturday
that may bring another round of showers and a potential for
thunderstorms. Unsettled weather will continue beyond this with
the risk for at least some spotty showers lingering into Sunday
and Monday as the system through Saturday is followed by another
reinforcing cold front.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 607 PM CDT Mon May 6 2024

VFR conditions will prevail through 12z Tuesday. Wind shear
will develop between 04-07z Tuesday and continue at times through
Tuesday, although wind shear should diminish across central
Wisconsin around 16z. A round of rain will move into central
Wisconsin between 12z and 15z, and across north-central and
northeast Wisconsin between 15z and 18z. CIGS will fall into the
MVFR category and then into the IFR category late Tuesday morning
through Tuesday afternoon. Scattered thunderstorms are possible
Tuesday afternoon, which could produce some gusty winds and small
hail; however, confidence in coverage and timing is too low to
include in this set of TAFs.

&&

.MARINE...
Issued at 252 PM CDT Mon May 6 2024

Southeast winds will increase Tuesday morning, with a few gusts
to 25 kts possible. The cooler waters will create more stable
conditions compared to land, so still some question just how much
of the wind aloft will mix down over the lake. The persist
southeast winds will produce building waves, especially south of
Algoma on Lake Michigan, where waves will climb to around 4 feet
Tuesday morning. Have issued a Small Craft Advisory to cover the
potential. As dewpoints increase Tuesday afternoon, dense fog
will be possible, which could linger into at least Tuesday
evening.

Gusty and persistent northeast winds will bring a period of
hazardous conditions for small craft Wednesday night into
Thursday.

&&

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

&&

$$

DISCUSSION.....Eckberg/JLA
AVIATION.......Kurimski
MARINE.........Eckberg