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000
FXUS63 KGRB 060849
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
349 AM CDT Thu May 6 2021

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 345 AM CDT Thu May 6 2021

Chilly temperatures continuing into early next week, necessitating
the protection of cold-sensitive plants on most nights. Light
precipitation at times, some of which could even fall as wet snow.

A large scale upper trough will remain centered in the James Bay/
Great Lakes region throughout the forecast period. Amplification
of the upstream pattern will cause the trough to expand/deepen
into the southeastern CONUS the next few days. That will result in
a strengthening northwesterly upper jet across the Plains and a
persistent feed of cold polar air into the forecast area. The
pattern across Canada will become blocky next week, resulting in
undercutting of the upstream ridge and allowing for the
development of a southern stream across the southern CONUS.

Temperatures will be seasonably cold throughout most of the
period, with readings 8-15F degrees below normal into early next
week before some moderation occurs late in the period. There will
be a few rounds of light precipitation, some of which could fall
as wet snow or a rain/snow mix. But the 7-day total is expected to
end up below normal as the significant precipitation producing
systems in the developing southern stream pass south of the region.
&&

.SHORT TERM...Today...Tonight...and Friday
Issued at 345 AM CDT Thu May 6 2021

Precipitation with the baroclinic leaf feature shifting through
the area has been confined to areas south of a line from MFI-ATW-
MTW. It may edge a little farther north in the east during the
next couple hours before it begins to pull off to the southeast.
WV satellite imagery indicated a couple disturbances back to the
NW across MN that did not seem to be handled well by the models.
These were generating some light precip earlier in the night, but
now seem to be just related to some mid-clouds. Adjusted skycon to
account for the clouds. Left the morning dry in the wake of the
departing system, but will continue to monitor for possible SHRA
with the arrival of the MN disturbances.

Low-level convergence combined with diurnal destabilization may
allow isold-sct SHRA to develop in the east this afternoon. More
substantial forcing in the form of a stronger shortwave and LFQ of
an upper speed max will likely result in another round of sct-
nmrs showers spreading SE across the area tonight. A weak surface
boundary dropping south through the region will add some low-
level convergence. Temperatures tonight may cool enough across the
north to allow for the precipitation to fall as snow and for a
minor accumulation on grassy surfaces.

The precipitation with the more organized forcing will pull off to
the east late tonight or early Friday. But the forecast area will
remain on the cyclonic side of an impressive upper jet throughout
the day. Diurnal destabilization should again be sufficient to
generate some showers during the afternoon, especially in the
east.

Generally stayed close to a broad based blend of guidance
products for temperatures, shading a bit toward the recent top
performers.

Will not be posting any frost/freeze headlines with this
issuance. Some frost is possible across the far west toward
daybreak Friday, but if clearing occurs any slower than currently
forecast frost formation won`t happen. Given the uncertainty, will
allow the day shift to make the final call on any headlines for
tonight. As a reminder, we are starting Frost/Freeze headlines
across the remainder of the area Friday.

.LONG TERM...Friday Night Through Wednesday
Issued at 345 AM CDT Thu May 6 2021

Models continue to advertise that northeast WI to remain between a
closed upper low over southeast Canada and an active southern
stream that will take a pair of systems south of WI. A mainly
northwest flow should keep temperatures below normal with
precipitation amounts also below normal. This cool regime will
likely lead to several frost/freeze headlines into early next
week.

Friday night and Saturday...High pressure to extend from south-
central Canada southeast through the western Great Lakes to the OH
Valley Friday night. Mainly clear skies, light winds and a cool
air mass aloft will be a recipe for a frosty night across
northeast WI. Min temperatures to drop into the lower to middle
20s north- central WI, lower to middle 30s east-central WI.
Frost/freeze headlines will become necessary. This high pressure
to remain over the Great Lakes through Saturday and other than the
development of fair weather cumulus clouds in the late morning
through the afternoon, expect a good deal of sunshine with max
temperatures in the lower 50s near Lake MI, lower to middle 50s
north and middle 50s to around 60 degrees south.

Saturday night and Sunday...We continue to watch a mid-level
shortwave trough move across the Rockies Saturday night and enter
the central Plains on Sunday. Lee-side cyclogenesis over the
central High Plains with the surface low moving due east into the
mid-MS Valley by 00Z Monday. Other than the GFS which takes the
northern periphery of precipitation into southern WI, the rest of
the deterministic models keep precipitation in northern IL, thus
prefer to keep the forecast dry for Mother`s Day. Assuming sky
cover becomes at least partly cloudy Saturday night, more frost/
freeze headlines would become necessary, especially over northern
WI where min temperatures fall below freezing. Max temperatures on
Sunday to range from around 50 degrees far north/near Lake MI,
to the upper 50s west of the Fox Valley.

Sunday night and Monday...The next area of high pressure is
forecast to drop south out of east-central Canada into the western
Great Lakes region Sunday night into Monday. Frost/freeze
concerns return for Sunday night, although there may be enough of
a pressure gradient between the incoming high pressure and low
pressure over the OH Valley to limit the amount of frost.
Anticipate fair weather cumulus on Monday, thus skies will become
partly cloudy by the afternoon. Max temperatures for Monday to be
in the lower 50s near Lake MI, lower to middle 50s north and
middle 50s to around 60 degrees south.

Monday night and Tuesday...This high pressure settles over the
Great Lakes Monday night and with clear skies/light winds,
anticipate the need for more frost/ freeze headlines. Plenty of
sun with fair weather cumulus for Tuesday with max temperatures
warming into the middle 50s lakeside, mainly 60-65 degree range
inland.

Tuesday night and Wednesday...High pressure to remain over the
Great Lakes through Wednesday, therefore keeping dry conditions
ongoing with temperatures slowly moderating. We could still see
some patchy frost over northern WI Tuesday night, but more
sunshine for Wednesday will lead to max temperatures in the middle
to upper 50s near Lake MI, lower to middle 60s inland.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 345 AM CDT Thu May 6 2021

Some MVFR conditions are possible early today across the far
southern part of the area, otherwise generally good flight
conditions are expected today into tonight. Convective clouds
will form again and should have greater coverage than yesterday
but bases should be high enough to result in VFR conditions even
where a ceiling develops.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Kallas
AVIATION.......Skowronski