126
FXUS63 KGRB 162354
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
654 PM CDT Fri Aug 16 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Isolated severe storms possible into this evening over central,
  east-central, and far northeast Wisconsin. Strong wind gusts,
  small hail and torrential rainfall are the main hazards.

- Locally heavy rainfall in excess of an inch possible will
  accompany any slow moving thunderstorms. The heavy rain could
  produce localized flooding in urban, low-lying, and poor
  drainage areas.

- Additional showers and storms on Saturday, especially eastern
  WI, then quiet weather conditions and near-normal temperatures
  in the mid 70s to low 80s are expected Sunday into much of next
  week.

&&

.DISCUSSION...
Issued at 251 PM CDT Fri Aug 16 2024

Short Term...Tonight and Saturday

Forecast concerns include precipitation trends, and potential for
severe weather and heavy rainfall.

Numerous showers and scattered thunderstorms were ongoing over
much of the forecast area this afternoon, as forcing associated
with a western WI short-wave encountered a moist (PWATs around 1.5
inches) and unstable (SBCAPE of 1500-2500 j/kg) air mass. So far,
thunderstorms have remained below severe limits, as deep layer
shear was only 10-25 knots (strongest southeast) and wet-bulb zero
heights were high (10.5-11.5k ft AGL). Pockets of heavy rainfall
have been reported, and the threat of continued heavy rainfall and
localized urban flooding will remain the primary concern through
this evening. An isolated severe storm with damaging winds is
still possible through about sunset.

There will be a decrease in convection as the short-wave shifts
east this evening, but showers and isolated storms will likely
persist over far NE WI; especially Door County, through the night.
Low clouds and patchy fog are expected overnight, though surface
and boundary layer winds should increase enough to prevent dense
fog formation. Lows will be in the lower to middle 60s.

On Saturday, the upper low will shift east of the region, but
short-wave energy will continue to wrap around its western
periphery. This will combine with cyclonic north flow and
modest daytime instability of 500-1000 j/kg to support showers
and a few thunderstorms, especially during the afternoon.
Shower coverage will be less over the far west; farther removed
from the upper low. Highs will in the 70s.

Long Term...Saturday Night Through Friday

Low pressure crossing northern WI this evening will only shift
across lower Michigan by Saturday evening. Some showers and
thunderstorms over eastern WI will diminish by late evening. Fog
on Saturday night probably ends up limited due to steady north
winds developing in wake of the low. Still looks like Small Craft
Advisories may be needed late Saturday night into Sunday Night.
However, the north wind direction will result in an offshore flow
and minimal wave action so will not need any Beach Hazards
Statements.

Thereafter, northwest flow will be present over the western Great
Lakes through the middle of next week before the upstream ridge
moves overhead late in the week. Still some hints a cold front may
try to drop across late in the week. Overall though precip chances
look low (staying less than 20 percent for any time frame). Temps
will not be too far from normal with highs upper 70s to lower
80s. Lows will start out 40s north to mid 50s south, then gradually
increase into the 50s to lower 60s by late in the week.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 654 PM CDT Fri Aug 16 2024

Precip...Scattered rain showers were occurring across the area at
00Z/Sat with thunderstorm coverage starting to become more
isolated. Kept mention of TSRA in the TAFs for another 2-3 hours,
then trends indicate coverage of showers and thunderstorms will be
very limited. Removed any precip from the TAFs for the rest of
the night and Saturday morning as likelihood at any one location
is too low. However, with cyclonic flow aloft, it is possible for
a brief shower during this time frame. Saturday afternoon, shower
and thunderstorm coverage will increase as instability builds.
Coverage will be similar to or a little less than this afternoon.

Cigs and Vsbys...Flight conditions were primarily in the VFR
range at 00Z/Sat. Expect lowering cigs and some patchy fog
overnight which will bring conditions into a mix of MVFR/IFR, with
localized LIFR conditions possible with cigs < 500 ft (primarily
in central and north-central WI).

Winds...Winds will veer to the N/NW this evening and remain steady
around 4 to 10 kts. Higher gusts are possible within any showers
or thunderstorms.

&&

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

&&

$$

DISCUSSION.....Kieckbusch/JLA
AVIATION.......KLJ