Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 242044
AFDGRB

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

Forecast discussion for routine afternoon forecast 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 18Z TAF Issuance
Issued at 1236 PM CDT Thu May 24 2018

Scattered showers/thunderstorms have mainly lifted into the Upper
Peninsula of Michigan early this afternoon, but increasing
instability could lead to additional development in north central
WI later in the day. There is a better chance of storms over
north central WI toward midnight, as a low-level jet and weak
upper level disturbance move through. There will also be a brief
periof of LLWS at the RHI TAF site overnight.

More showers and storms will be possible late in the TAF period,
especially northwest of the Fox Valley and lakeshore areas.

Most locations will have VFR flight conditions through the TAF
period, except during thunderstorms. There could be also some fog
near Lake Michigan at times, especially from late evening on.

Gusty south to southwest winds will diminish early this evening,
then pick up again Friday morning.
&&

.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.......Kieckbusch
MARINE.........Kieckbusch



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