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000
FXUS63 KGRB 251132
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
632 AM CDT Thu Apr 25 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Elevated fire weather conditions are likely today due to
   relative humidities ranging from 20 to 30 percent. However,
   relatively light winds and seasonal temperatures will keep
   conditions from meeting critical fire weather thresholds.
   Humidity readings as low as 30 percent are possible on Friday
   along the Upper Michigan border, combined with increasing
   southeasterly winds with gusts around 25 mph.

 - Two systems will result in rounds of showers and thunderstorms
   from Friday afternoon through Sunday night. There is an
   increasing risk of strong or severe storms on Saturday,
   especially during the afternoon and evening. Large hail and
   damaging winds are the main risk. Storms this weekend could
   also produce locally heavy rain with isolated flash flooding
   possible.

 - Conditions hazardous to small craft will be possible at times
   from Friday through the weekend on the Bay and Lake.

&&

.DISCUSSION...
Issued at 332 AM CDT Thu Apr 25 2024

Short Term...Today...Tonight...and Friday

High pressure originating from Hudson Bay will continue to bring
dry weather today. Generally a persistence forecast works, in
terms of low RH and for the most part light winds though they will
be slightly stronger closer to the lake (10-15 mph). High
temperatures will rebound, reaching upper 50s to lower 60s most
locations west of I-43. Cool exception will be along the Lake
Michigan shore, where readings will struggle through the 40s.

High shifts east tonight placing our region in steadier SE flow.
This will result in a warmer night compared to the chilly start to
this morning. Lowest temps just below freezing over far northeast
WI toward the Upper Michigan border.

On Friday, SE flow increases further as pressure gradient tightens
with advance of deep plains low pressure system tied to sharp
negative tilted mid-level trough. Even the more aggressive models
have come in line with slower solutions the ECMWF/Canadian were
indicating. Net result is showers will gradually spread northeast
into WI, but most of our area likely will not see rain until mid
to late afternoon. SE winds will increase, but soundings show most
of the stronger winds will remain just above the sfc so have
continued to back off of gusts. Plenty of thickening clouds will
keep temps mainly in the mid to upper 50s. Any thunder will hold
off until after early Friday evening.

Long Term...Friday Night Through Wednesday

An active pattern is expected Friday night through the weekend as
two waves of low pressure move across the region. For Friday
night, the slower arrival of the rain will make into far northeast
Wisconsin by mid to late evening. The better instability arrives after
midnight with most unstable CAPE values of at least 200 to 700
J/KG. 0-6km shear values off bufkit soundings were from 30 to 40
kts. Wet bulb zero heights off bufkit soundings were around nine
thousand feet, thus not exceptional high. Model qpf output would
also suggest that discrete cells would be anticipated with the
northward push of the warm front. These types of event would
support storms that would produce hail. With the boundary layer
only in the upper 40s to lower 50s, some of the hail stones could
approach 1 inch.

The models are still insistent that the warm front will push north
across much of the area late Friday night and Saturday morning. Still
worried that portions of northeast Wisconsin from Oconto and Marinette
counties through Door County may not see a true frontal passage into
the warm air due to the southerly wind component and stronger stable
layer off the colder waters of the bay and Lake Michigan. There should
be scattered showers and storms around during the morning, and some
of these storms could be on the stronger side with hail. Attention then
turns to Saturday afternoon and evening as temperatures warm into the
70s. Bufkit soundings would support at least 1,000 to 2,000 J/KG of
surface based CAPE in the warm sector along with 0-6km shear values
of 30 to 45 knots. Strong or severe storms are possible with damaging
winds and large hail as the cold front moves east across the area
Saturday afternoon into Saturday evening. The latest SPC Day3 risk
has outlined much of our area for a slight risk (level 2/5) for
severe weather. Later Saturday night, the frontal boundary is
expected to sag southward due to the movement of the cold front,
and will likely be aided in outflow boundaries and some effects of
the cooler air mass off the bay/lake will likely result in the
boundary sinking further south than what the models indicate.
There will be a lull in rainfall later Saturday evening and
overnight before the next round of showers and storms moves across
the area Sunday.

There is still a lot of uncertainty in the risk of severe weather
on Sunday depending on how far south the front sinks Saturday night.
If the models are correct, the warm front will push north across
the area on Sunday which could lead to another round of strong or
severe storms. Unsettled weather will continue into Monday before
dry conditions return Monday night. Next system arrives Tuesday PM
with a chance of showers and possibly a few storms with another
system arriving on Wednesday.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 630 AM CDT Thu Apr 25 2024

Dry Canadian high pressure will bring VFR conditions to the
forecast area through the TAF period, with only some high clouds
moving through this morning and again late tonight. Light and
variable winds will become SE-S and increase around 10 knots by
this afternoon. SE winds become light again tonight, but will
increase late tonight with some 15-20 kt gusts expected.

&&

.FIRE WEATHER...
Issued at 332 AM CDT Thu Apr 25 2024

Elevated fire weather conditions are likely today as RH values
are expected to drop into the 20 to 30 percent range and fuel
moisture remains fairly low. Concerns are somewhat tempered with
temperatures only forecast to warm into the mid 50s to lower 60s
and southeast winds only increasing to around 10-15 mph this
afternoon, strongest near the lake where temperatures will remain
below 50. Overall, do not expect conditions to meet critical fire
weather thresholds.

On Friday, elevated fire weather conditions are possible, at least
for parts of the area. The arrival of rain with the next system
continues to slow, only reaching central Wisconsin in the afternoon.
Thus, areas from far north-central to northeast Wisconsin closer
to the Upper Michigan border could stay dry all day and may see RH
values as low as 30 percent into mid afternoon with SE winds to
15 mph gusting to 25 mph.

&&

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

&&

$$

DISCUSSION.....JLA/Eckberg
AVIATION.......JLA
FIRE WEATHER...JLA