Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 242336
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
636 PM CDT Thu May 24 2018

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Friday
Issued at 344 PM CDT Thu May 24 2018

Convective trends and potential for severe weather are the main
forecast concerns through Friday.

Isolated convection was developing over north central and far
northeast WI, where a surface boundary was evident, and SBCAPE was
1000-2000 j/kg. A strong storm in Taylor county appeared to be
producing hail as it moved toward Lincoln county. Fairly weak deep
layer shear of 15-20 kts is expected to be a limiting factor for
widespread severe weather development, through isolated large
hail will be possible for the next several hours. Convection
should decrease in activity by sunset.

Expect convection to increase again across north central WI toward
midnight, as a 35 kt low-level jet and weak short-wave trof impact
the region. Though the weakening convection will likely edge east
overnight, most should remain northwest of the Fox Valley and
lakeshore areas through daybreak. Lows tonight should be in the
low to mid 60s, except 50s near Lake Michigan.

On Friday, daytime heating (Max temps in the 80s) and increasing
low-level moisture (dew points in the low to mid 60s) will allow
instability to increase during the late morning and afternoon.
Models were indicating CAPE as high as 4-5K J/KG, but appeared to
be biased high due to high dew points (lower 70s). The ECMWF and
modified forecast soundings off the GFS model indicated that more
reasonable values would be 1500-2500 J/KG, which is still plenty.
Deep layer shear of 20 to 25 kts is not impressive, but the
marginal/slight risks on the SPC Day 2 Convective Outlook seem
reasonable. Timing is a bit uncertain, as models hint at a couple
weak short-waves arriving during the late morning and afternoon.
The best bet for severe would appear to be over the northwest
half of the CWA during the mid to late afternoon.

.LONG TERM...Friday Night Through Thursday
Issued at 344 PM CDT Thu May 24 2018

Thunderstorm chances are the main concern in the long term.

Thunderstorms remain possible across the area into Friday evening
as instability starts to wane and a mid level trough axis passes
east of Wisconsin. SPC day 2 outlook has a slight risk for severe
storms 12Z Friday through 12Z Saturday, so severe storms cannot be
ruled out. The atmosphere will start to destabilize again on
Saturday ahead of an approaching surface boundary and another mid
level trough. A mid level ridge and surface high pressure should
bring mainly dry weather to the area for the rest of the weekend
into early next week. Another approaching surface system will
bring some rain chances at times into the middle part of next week
and a better chance for showers and storms Wednesday night
through Thursday.

Much warmer than normal temperatures are expected throughout this
part of the forecast. Highs should be mainly in the 80s, except
near Lake Michigan, and lows will be in the 60s.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 635 PM CDT Thu May 24 2018

Scattered thunderstorms are expected across north central Wisconsin
tonight. Areas that receive rain and then have clearing could get
some ground fog around daybreak. The remainder of the region should
have VFR conditions overnight.

An upper level disturbance will move across the area Friday and
produce scattered thunderstorms, mainly in the afternoon. Some of
the storms could produce hail and gusty winds.
&&

.MARINE...
Issued at 344 PM CDT Thu May 24 2018

Moist air flowing over the cool waters of Lake Michigan may
produce areas of marine fog tonight into Friday. Nothing is
occurring at this time, so will hold off on any mention until
late evening.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....Kieckbusch
LONG TERM......MG
AVIATION.......RDM
MARINE.........Kieckbusch


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