NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 300730
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
230 AM CDT Sun Jun 30 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Conditions hazardous to small craft will continue early this
   morning due to gusty north winds.

 - The cold spots over north-central Wisconsin could see low
   temperatures in the 30s tonight. Widespread frost is not
   expected, but protecting cold sensitive plants are encouraged.

 - Periods of heavy rain will be possible from late Monday night
   through Tuesday night. There is a 40 to 70 percent chance of
   rainfall greater than 1 inch over central to east-central
   Wisconsin.

 - The next chance of widespread rain will arrive late on July 4
   into July 5.

&&

.DISCUSSION...
Issued at 229 AM CDT Sun Jun 30 2024

Short Term...Today...Tonight...and Monday

Cold air advection into the region will setup a fairly robust area
of high pressure over the western Great Lakes for the latter half
of the weekend through Monday. As result, expect clear skies and
cooler temperatures for both today and Monday. High temperatures
will run below normal as well, with highs in the upper 60s to
middle 70s today, and in the lower to middle 70s on Monday. The
only concern weather- wise for this early week period will be
temperatures tonight, as a few of the colder spots may drop into
the middle to upper 30s tonight. While this is unlikely to support
any widespread frost, cold sensitive plants may need some
additional protection.

Long Term...Monday Night Through Saturday



Focus of this forecast continues to revolve around the thunderstorm
and heavy rainfall potential from Monday night through Tuesday
night.  Secondary focus is weather for the Independance Day holiday.

Monday night through Tuesday night...As a large high pressure system
shifts from the eastern Great Lakes to the northeast coast on Monday
night, return flow will rapidly increase including a 35 to 45 kt low
level jet that will lead to surge of elevated moisture into the
region from the west. The strong moisture advection and convergence
will lead to a large area of rain spreading across the region from
west to east. Instability is lacking and less than 200 j/kg, so
severe weather is not expected despite decent wind fields.  But
probabilities appear to have increased (30-50%) over central to east-
central Wisconsin for 1+ inches of rainfall by midday Tuesday.
Isolated amounts to 1.5 inches appear possible over central WI.

After the first push of precip exits across the area on Tuesday
morning, indications continue to suggest a relative lull in the
precip on later Tuesday morning or Tuesday afternoon.  This is a
little slower than guidance was showing yesterday. Then precip
chances ramp up again on Tuesday evening along the cold front.  The
ensemble means continue to show precipitable water values (pwats)
approaching their daily high and in excess of 2 inches.   Like the
previous shift mentioned, chances of heavy rain have shifted south
somewhat over the past 24 hours closer to the higher instability.
Chances of an additional 0.50 inches of rain lie around 20 to 30%
over central Wisconsin.

To summarize, probabilistic data continues to show potential for 1-2
inches of rain over central to east-central Wisconsin from late
Monday night through Tuesday night.  Given the marginal instability,
the severe weather risk remains lower than heavy rainfall.

Thursday thru Friday (July 4-5)...Low pressure will be moving into
the northern Mississippi Valley on Thursday and into the western
Great Lakes on Friday. The latest data suggest timing of rain will
hold off until late on Thursday night, and heavy rain will be
possible again on Friday.  Considering the timeframe, details could
certainly change.  Temperatures are forecast to be near normal on
Independence Day.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1028 PM CDT Sat Jun 29 2024

MVFR ceilings over northern WI should erode early in the TAF
period, followed by VFR conditions through Sunday evening.
Gusty NW-N winds will subside overnight, then veer NE-E near lake
Michigan Sunday afternoon.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION.....Uhlmann/MPC
AVIATION.......Kieckbusch