Forecast Discussion for GRB NWS Office
FXUS63 KGRB 181111

Area Forecast Discussion
National Weather Service Green Bay WI
611 AM CDT Sat Sep 18 2021

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Sunday
Issued at 308 AM CDT Sat Sep 18 2021

After a cool start to the morning, temperatures will rebound to
around normal levels as high pressure drifts off to the east;
allowing surface winds to turn southerly across central and
north- central Wisconsin and southeasterly across east-central and
northeast Wisconsin. Highs today are expected to rise to around
70 across north-central Wisconsin, with lower to middle 70s across
central and east-central Wisconsin away from Lake Michigan where
temperatures will remain in the middle to upper 60s.

The high will continue drifting east tonight and Sunday, as
surface winds become southerly across the entire area. Warm air
advection will allow temperatures to climb to well above normal
levels by Sunday as highs soar to 10 degrees above normal. Upper
level ridging and subsidence will keep the weather dry through the
weekend. Lows tonight are expected to be a bit warmer, ranging
from around 50 across north-central Wisconsin, with lower to
middle 50s across central and east-central Wisconsin. Highs on
Sunday are expected to soar into the lower to middle 80s away from
Lake Michigan, where highs will be limited to the 70s.

.LONG TERM...Sunday Night Through Friday
Issued at 308 AM CDT Sat Sep 18 2021

The focus of this forecast continues to revolve around precip
chances and timing during the Monday to Tuesday time period, then
followed by frost potential on Tuesday and Wednesday nights. No
clear model preference for these time periods, but given the
amplitude of the trough, will give a slight nod to the ecmwf.

Sunday night through Monday night...While low pressure will be
shifting east across the northern Plains, south-southeast winds will
continue to push warm air into the region on Sunday night, creating
a mild and breezy night.  The cold front will move into the northern
Mississippi Valley on Monday with strong forcing remaining west of
the region.  However, signs continue to point towards an influx of
Gulf moisture along with weak shortwave energy swinging northeast in
vicinity of the region that could result in scattered showers.
Suppose an isolated thunderstorm cannot be ruled out with
instability of 200-400 j/kg possible in the afternoon.  The main
period of precip appears to be during the Monday night into Tuesday
morning timeframe.  Instability up to 600 j/kg doesn`t point to
severe weather, but precipitable water values of 2-3 standard
deviations above normal could result in a heavy rain threat if
details work out. Highs could reach into the 80s at most locations
before clouds and showers arrive on Monday.

Rest of the forecast...The front will exit the region on Tuesday
morning, but rain chances in the comma head may linger into the
afternoon over north-central WI.  Otherwise, much colder air will be
filtering into the region behind the front.  Clouds and winds may
prevent a frost on Tuesday night.  But with temps on Wednesday
struggling to rise above 60 across the northwoods, frost looks
possible on Wednesday night.  Will see how timing shakes out in the
coming days.  Warmer air then returns by the end of the next work

.AVIATION...for 12Z TAF Issuance
Issued at 610 AM CDT Sat Sep 18 2021

Morning patchy fog across north-central Wisconsin should
dissipate in the next few hours. Some LIFR conditions are possible
with the fog before it dissipates. Otherwise, clear skies are
anticipated through this TAF issuance. High pressure is expected
to slowly track east of the area today. This will lead to calm
winds and good flying conditions.



SHORT TERM.....Kurimski

NWS GRB Office Area Forecast Discussion