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000
FXUS63 KGRB 221813
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
113 PM CDT Mon Apr 22 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Elevated fire weather conditions are expected this afternoon and
  early this evening due to relative humidities ranging from 20 to
  30 percent and winds of 15 to 25 mph with some stronger gusts up
  to 30 mph possible.

- Precipitation chances return this evening through Tuesday. A
  few thunderstorms are possible Tuesday afternoon, but severe
  weather is not expected.

&&

.DISCUSSION...
Issued at 408 AM CDT Mon Apr 22 2024

Short Term...Today...Tonight...and Tuesday

Southwest winds will increase today with a tight pressure gradient
ahead of an approaching cold front, which will make its way over
the upper Mississippi Valley by this afternoon, with gusts to 25
to 30 mph at times this afternoon. Mostly sunny skies and warm air
advection will allow daytime temperatures to rise into the 60s
across the region this afternoon. Dry air in place, as evidenced
by the low dew points already in place, will allow for low
relative humidity values (20-30 percent) and elevated fire
weather conditions this afternoon. Although some showers could
make their way into western portions of central and north-central
Wisconsin late this afternoon, the dry air in place should hold
off any precipitation until tonight for most areas.

The aforementioned cold front will sweep through the area tonight,
bringing a swath of rain showers as it moves through Wisconsin
this evening. Subsidence behind the departing cold front will then
end the showers from west to east later this evening, with dry
conditions expected during the overnight hours.

Another more powerful cold front will sink south on Tuesday, which
will be accompanied by a strong mid-level PV anomaly, strong low
to mid-level frontogenesis, a mid-level trough, and a substantial
push of cold air. The push of cold air will be so strong that
temperatures will fall during the afternoon hours with the most
precipitous drop across north-central Wisconsin given an earlier
FROPA. Thunderstorms will be possible on Tuesday as MUCAPE values
rise to 300 to 600 J/kg; however, severe weather is not expected
as instability will be fairly meager with mostly unidirectional
wind profiles and falling 0-6 km shear values as the thunderstorms
develop. The falling temperatures and earlier FROPA could lead to
some snow mixing in and even changing over to all snow across far
north-central Wisconsin late Tuesday afternoon. Despite the snow
across the far north, accumulations are not expected as the snow
will fall during the day.

Long Term...Tuesday Night Through Sunday

Precipitation...Ongoing rain and some thunderstorms will linger in
east-central WI into Tuesday evening, as the strong cold front
mentioned in the Short Term discussion continues to drop south
across the forecast area. The precip will exit the forecast area
quickly and make way for a high pressure system.

Dry conditions will prevail on Wednesday with the high pressure
overhead. Thursday will also be dry as the surface high gradually
shifts eastward and is replaced with upper-level ridging.

Attention turns to Friday and the weekend as two southern stream
systems look to impact the region with rain and thunderstorms. The
first low pressure system originates from the central Plains and
tracks northeastward across the Upper Mississippi Valley Friday into
Saturday. Although some uncertainty remains with the timing and
placement, a consensus has the precip onset sometime Friday morning,
with the heaviest rain occurring Friday afternoon into Friday night,
when PWATs are highest (between 1.25-1.5 inches). Scattered rain
showers will continue on Saturday, with the highest rain amounts in
northern WI due to the proximity to the surface low center as it
moves across northwest WI. Due to the low`s location, a portion of
the forecast area has the potential to be in the warm sector on
Saturday, raising the potential for thunderstorms as the system`s
cold front sweeps across the forecast area. However, since the exact
timing and placement of the surface low is still uncertain, it is
too early to determine if any of these storms will be severe.

Following Saturday`s system, a break in the precip is possible
Saturday evening into early Sunday before the next southern stream
system tracks northeast across the central Plains. This system looks
to bring another round of healthy rainfall amounts and possible
thunderstorms sometime between Sunday and Monday. Since there is
still uncertainty with the first system, predictability for this
system is even lower.

Winds and Temperatures...As the strong cold front drops south across
the forecast area Tuesday evening, westerly winds will quickly turn
north, possibly gusting up to 35 mph, and temperatures will drop
quickly. This will result in low temperatures on Tuesday night with
readings mainly in the 20s. The colder air will prevail on Wednesday
leaving highs only in the upper 40s to low 50s. Temperatures will
gradually increase to slightly above normal on Thursday (highs in
the upper 50s to low 60s), as low-level winds turn southerly.
Temperatures for the remainder of the extended will be tricky to
nail down due to the anticipated periods of rain and clouds, but
if the forecast area can get into the warm sector on Saturday,
some locations could see highs in the low 70s.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 113 PM CDT Mon Apr 22 2024

VFR flight conditions are expected for the afternoon but winds
will remain fairly gusty, with gusts up to 20 to 25 knots. An
approaching cold front could bring a change in categories to MVFR
or possibly even IFR in the evening, along with some showers.
Rain coverage is expected to be relatively scattered and will only
last a couple hours in each site, so included these in a TEMPO
group for now. The passage of the cold front will also bring some
in some LLWS for the evening to early overnight hours.

Better flight conditions arrive later in the night as LLWS departs
the region, but occasional gusts at the surface will still be
possible through the end of the TAF period.

&&

.FIRE WEATHER...
Issued at 408 AM CDT Mon Apr 22 2024

Milder temperatures in the 60s, gustier southwest winds of 15 to
25 mph with gusts up to 30 mph, and low relative humidity values
of 20 to 30 percent will cause elevated fire weather conditions
across the region this afternoon and early this evening until
showers advect into the area from the west.

Another period of elevated fire weather conditions is possible
Wednesday and Thursday, as a dry airmass moves into the region.
Afternoon RH values of 25 to 30 percent are possible on Wednesday,
but cooler temps are anticipated in the low 50s. On Thursday, RH
values will be slightly higher between 25 to 35 percent, and
temps will also be slightly higher in the mid 50s to low 60s. But,
due to the proximity of the prevailing high pressure system, winds
will be below critical levels on both days.

&&

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

&&

$$

DISCUSSION.....Kurimski/Kruk
AVIATION.......Uhlmann
FIRE WEATHER...Kurimski/Kruk