Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 202337
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
637 PM CDT Sun May 20 2018

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Monday
Issued at 335 PM CDT Sun May 20 2018

A dry night is expected across the area as high pressure
pushes into the region from the north. Clouds will continue to
slowly shift south and/or thin out late this afternoon, but may
continue to clip locations from Wisconsin Rapids to Manitowoc. The
clouds (mainly cirrus) will begin to move north again later
tonight ahead of the next low pressure system approaching from the
southwest. Light winds and mostly clear skies will provide ideal
conditions for radiational cooling this evening, especially
across the north, but high clouds are expected to spread across
much of the area later this evening into the overnight hours,
which could slow the cooling. Best performing guidance shows lows
mainly in the middle 30s for most spots across northern WI, with
a few of the typical cold spots dropping into the lower 30s or
even upper 20s for a short period overnight. Opted to not issue a
frost advisory, with more patchy/areas of frost expected (vs
widespread), as the clouds increase overnight plus most locations
will only fall below 35-37 degrees for a short period. That said,
if people have sensitive vegetation, precautions should be made.
Will continue to highlight in the HWO. Farther south, lows will
drop mainly in the 40s.

Majority of models have trended north/wetter for Monday as a weak
surface low / decaying mesoscale convective system (MCS) tracks
from Iowa into southern Lake Michigan by Monday evening. We will
be on the northern fridge of what is left of it. There is always a
chance with an MCS that models are too far north with it, but most
meso models have some rain approaching the Fox Valley / lakeshore
Monday morning. Will have the highest POPs across the far
southeast. Additional weak forcing from a shortwave trough passing
through will keep lower chances for rain for locations across
central WI and across the east in the afternoon. Very little to no
instability shown on the model soundings, so will not mention any
thunder. Northern WI looks to stay dry. High will vary greatly
across the area. With more clouds/precip expected, plus a wind off
of Lake Michigan, lowered forecast highs over the Fox Valley /
lakeshore into the mid 50s to lower 60s. The warmest temps will be
across far northern WI where the lower and middle 70s are
expected.

.LONG TERM...Monday Night Through Sunday
Issued at 335 PM CDT Sun May 20 2018

Some showers may linger across the south Monday night before
ridging builds in on Tuesday, keeping the area dry through
Wednesday. This ridge quickly breaks down Thursday and Friday as a
low pressure system develops over the Plains, then heads east
through the western Great Lakes region Friday and Saturday. There
is quite a bit of uncertainty regarding the timing of this system,
however the models seem to agree there will be a period where
showers and thunderstorms are possible from late Wednesday night
through next weekend.

During this period there is the potential for strong storms Friday
and Friday night as instability increases across the western Great
Lakes region. Although MUCAPEs rise to 2000 to 3000 J/kg during
this period, bulk shear is a fairly paltry 15 to 20 knots. On
Saturday MUCAPEs fall a bit to 1000 to 2000 J/kg with about the
same bulk shear, however wind profiles are fairly unidirectional.
Therefore will continue with the strong storm wording in the HWO
and refrain from mentioning severe given the uncertainty regarding
the timing of the low approaching from the west and the
unfavorable wind profiles.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 636 PM CDT Sun May 20 2018

Good flying weather tonight through midday Monday, then an upper
level disturbance will bring light rain showers and MVFR
conditions mostly south of a Wausau to Green Bay line.
&&

.FIRE WEATHER...
Issued at 335 PM CDT Sun May 20 2018

Rainfall amounts over the next few days are not expected to
alleviate the abnormally dry conditions across the north. Warm
and dry conditions are expected through Wednesday, resulting in
an elevated fire weather conditions and worsening drought
conditions. Relative humidities are expected to be in the middle
teens to lower 20s on Monday, with a slow moderation to 25 to 40
percent by the middle of the week. Some relief is expected by the
end of the week as a low pressure system is slated to bring a
widespread rain to the region.
&&

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

$$

SHORT TERM.....Bersch
LONG TERM......Kurimski
AVIATION.......RDM
FIRE WEATHER...Kurimski



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