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000
FXUS63 KGRB 181926
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
226 PM CDT Thu Apr 18 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Light rain will exit the region late this evening or early
  overnight.

- Gusty west winds of 30 to 40 mph over central to northeast
  Wisconsin will create conditions hazardous to small craft and
  may blow loose objects around on Friday.

- Elevated fire weather conditions are possible on Sunday and
  Monday afternoon due to low relative humidities ranging from 20
  to 30 percent and sustained winds of 10 to 20 mph.

&&

.DISCUSSION...
Issued at 224 PM CDT Thu Apr 18 2024

Short Term...Tonight and Friday

...Breezy on Friday...

Light rain that has been over central WI much of the day has
struggled to make much eastward progress. Main forcing remains
well to the south closer to sfc low pressure wave across the
western Ohio Valley and there was quite a bit of dry air on the
12z GRB sounding. Even so, axis of deeper moisture to the north
of the trough (along a weak cold front/moisture gradient) will
move through 22z-02z so this will represent the best chance for
seeing some spotty *light* rain from the Fox Valley to the
lakeshore. Beyond this, drying and clearing skies takes over the
rest of the night. Low temperatures are expected to range from
around 30 across the north, to the middle 30s across east-central
Wisconsin.

A vigorous mid level shortwave will track through northern
Wisconsin during the day on Friday on the southern edge broader
mid-level low over northwest Ontario. This wave along with
steepening low-level lapse rates will result in chance pops (20-30
percent) for light snow showers over north-central Wisconsin late
Friday morning through the afternoon. Any snowfall will likely
just be in the air instead of accumulating on the ground due to
higher sun angle as we work into later April.

As we have highlighted a while, Friday will be a breezy day for
all areas. A tight pressure gradient and deep boundary layer to
700-750 mb will result in breezy west winds gusting to 30-35 mph
with a few higher gusts around 40 mph possible from central to
east-central WI where there will be more breaks in the clouds. Highs
on Friday are expected to range from the lower 40s across the
north (though these readings could drop back to the mid-upper 30s
once any precip begins), to the lower 50s across east-central
Wisconsin.

Long Term...Friday Night Through Thursday

Fire Weather...As a deep upper trough lifts to the northeast and the
upper flow backs around to the west, temperatures will be moderating
and the airmass will remain quite dry on Sunday and Monday.  Minimum
humidities will be falling into the 20 to 30 percent range each
afternoon.  Winds will be a little stronger on Sunday compared to
Monday with sustained values of 10-20 mph and gusts up to 25 mph
(sustained winds 10-15 mph with gusts to 20 mph on Monday).  While
elevated fire weather conditions will be present each day, concern
is a little higher on Sunday due to stronger winds expected.  Will
therefore add the concern to the HWO.

Precipitation...A compact, yet dynamic shortwave trough is then
expected to impact the region during the Monday evening through
Tuesday afternoon period.  Spread is higher for timing of the
system, but there is also considerable model differences for the
strength of the shortwave and associated surface low.  Regardless,
the ensemble means generally support a further south track like the
ecmwf that brings the highest precip chances to the southern half of
the forecast area.

Ensemble means point towards precipitation of a 0.25 to 0.50 inches
will be possible.  Given the dynamics, mid-level lapse projected to
reach up to 7 C/km, and a potent low level jet up to 40 kts, it`s
not unreasonable to think that some embedded storms will be
possible and will pass concerns to the next shift.

Very cold air for this time of the year will be present over
northern Ontario and Lake Superior by Tuesday. Some of this cold
air will get pushed into northern WI as the precip is ending on
Tuesday morning. Guidance is showing up to around a 20% chance of
light snow mixing in on Tuesday morning across far northern WI.
But given the time of day and year, no accumulations are expected
if snowfall occurs. A small craft advisory may also be possible as
the colder air arrives behind the system on Tuesday.

Temperatures:  Will be on a roller coaster ride over the next week,
but no anomalous cold or heat is expected.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 121 PM CDT Thu Apr 18 2024

VFR conditions will gradually give way to MVFR conditions this
afternoon as a weak low pressure system brings scattered light
rain showers across central and eastern WI. Conditions should
then improve back to VFR this evening as the rain exits the area
to the east and drier air advects into the region. Clouds and a
few snow showers will build into northern WI on Friday. Conditions
should remain VFR. Otherwise, expect just scattered mid clouds
across the area.

W/WSW winds are expected this afternoon with gusts up to 20 knots.
Winds will ease below 10 knots this evening, before becoming 10-15
knots overnight. On Friday, west winds will increase to 15-20 kts
with gusts to around 30 knots. The strongest wind gusts will impact
the central to east-central WI terminals.

&&

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

&&

$$

DISCUSSION.....JLA/MPC
AVIATION.......JLA