584
FXUS63 KGRB 151006
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
506 AM CDT Wed May 15 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Relative humidity is expected to drop into the 25 to 35 percent
  range away from the bay and lake this afternoon which may cause
  increased fire potential.

- Thunderstorms are possible Thursday, and again at times into
  early next week.

&&

.DISCUSSION...
Issued at 339 AM CDT Wed May 15 2024

Short Term...Today...Tonight...and Thursday

The upper ridge over Wisconsin will move slowly off to the east
by the end of the day. Dry air in the low levels will continue to
arrive from the east, thanks to a surface high over James Bay.
This adds up to a mostly sunny and pleasant day with low relative
humidity and seasonable temperatures.

Clouds will increase tonight as an upper trough and surface warm
front approach from Minnesota. There may be some showers in central
and northcentral Wisconsin by daybreak. Low temperatures will be
close to normal.

An area of showers and scattered thunderstorms will move across
the region Thursday in association with the upper trough and
surface warm front. Instability and shear are very modest, so we
do not expect severe storms. High temperatures will be in the 60s
to near 70s, except it will be cooler near Lake Michigan and where
it is raining.

Long Term...Thursday Night Through Tuesday

An active pattern will persist through the duration of the
extended as several transient shortwaves bring multiple rounds of
rain/storms to the forecast area. Forecast for Friday looks to be
trending drier as most models keep the more unsettled airmasses to
our northwest and south; however, maintained low PoPs given the
possibility for some showers or a pop-up storm to make it into
the area. Still decent model spread with precip amounts for a
weekend system, although they seem to be honing in on rain
arriving Saturday evening.

Thursday evening precip... As a vertically stacked surface low
and attendant occlusion approach from the west, models seem to be
honing in on portions of central and north- central Wisconsin to
receive periods of light to moderate rain Thursday evening.
Although mid-level dry air will initially pose a concern, model
soundings eventually saturate enough to warrant PWATs of around 1"
to 1.15" across east-central Wisconsin. Additionally, confidence
in increasing in thunder potential Thursday evening as a corridor
of Gulf moisture drags a swath of 500 to 700 J/kg of surface-
based CAPE across central and east-central Wisconsin. Overall, a
widespread 0.2" to 0.5" of QPF looks likely across the forecast
area, although locally higher amounts of over half an inch will be
possible with stronger cells/storms.

Weekend precip chances... Next chances for rain arrive over the
weekend as closed upper-level energy spins up a surface low over
Manitoba. The most recent suite of model runs seem to be coming
into agreement about precip arriving along a cold front Saturday
evening, although QPF amounts are still variable. With temperatures
in the low 80s across central Wisconsin and windows for partial
clearing during the day, CAPE values in the 400 to 500 J/kg range
would warrant potential for thunderstorms Saturday afternoon and
evening. However, Gulf moisture out ahead of the front will have
to fight with dry air and high pressure building in behind the
departing system. Thus, main thing to look out for will be changes
in precip amounts as additional models come in range. No severe
storms are currently expected.

Rest of the extended... The beginning of the week looks to be
quieter as mid-level flow flattens out and weak high pressure
settles in over the central Plains. Temperatures in central
Wisconsin will plateau in the upper 70s to low 80s Saturday
through Monday before gradually declining through mid-week.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 506 AM CDT Wed May 15 2024

VFR conditions should continue through tonight. Skies will start
out sunny today, with increasing middle and high clouds late in
the day and overnight.

An approaching upper level trough and surface warm front will bring
showers and scattered thunderstorms and MVFR conditions as it moves
across the region Thursday.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Frost Advisory until 7 AM CDT this morning for WIZ005-010>013-
018-019-021.
&&

$$

DISCUSSION.....RDM/Goodin
AVIATION.......RDM