159
FXUS63 KGRB 010339
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1039 PM CDT Sun Jun 30 2024

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

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

 - Periods of heavy rain will be possible from late Monday night
   through Tuesday night. There is a 50 to 75 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 352 PM CDT Sun Jun 30 2024

Short Term...Tonight and Monday

Quite weather conditions this afternoon as the 19Z surface analysis
shows a high pressure centered over the Twin Cities metro.
Temperatures this afternoon are running about 8 to 10 degrees normal
for the end of June with most of the region ranging from the middle
60s to low 70s. As the high shifts over the region tonight it will
create favorable radiative cooling conditions with low temperatures
overnight forecast to drop into the 40s at most locations. The
typical cold spots across northern WI may even see temperatures drip
into the middle to upper 30s. With isolated pockets of frost
possible sensitive plants should be covered or brought indoors.
Additionally, with the rapid overnight cooling patchy areas of fog
may develop early Monday morning, but should produce minimal
impacts.

With return flow setting up on the back side of the departing high
Monday morning cloud clover will start to increase from southwest to
northeast throughout the day, but the chance for showers and
thunderstorms should hold off until later Monday evening. With the
help of increasing southerly winds temperatures and dew points will
be on the rise Monday with afternoon highs forecast to reach the low
to middle 70s.

Long Term...Monday Night Through Sunday

Main focus throughout this forecast period revolves around the
potential for heavy rainfall late Monday through early Wednesday,
and the potential for showers and thunderstorms on the Fourth of
July.

Monday night through Wednesday morning...High pressure will give way
to strong moisture advection via an increasing southerly LLJ (35-50
kts) late Monday night. As a result, rain will spread/lift over the
area from the west. While thunderstorms are possible, instability
will be limited during this time, leading to a very low possibility
of severe weather. The bigger concern will be the heavy rainfall and
potential for flooding given PWATs of 1.75 to near 2 inches. By
Tuesday afternoon, probabilities for 1 inch or more are highlighting
central to east-central WI with 30-50%. A small lull in precip is
possible late Tuesday afternoon before the next chance for showers
and thunderstorms arrives with the passage of a cold front Tuesday
evening through early Wednesday morning. PWATs will still be in the
1.75 to 2 inch range during this time, raising concern for
additional heavy rainfall. Probabilities for an additional 1 inch or
more of rain are not as high as the first round of rain with values
between 15-35% across central and east-central WI. Additionally, due
to the timing of the frontal passage occurring Tuesday evening/night
and the better instability focused across southern WI, it will
become less favorable for surface based thunderstorms. But, elevated
thunderstorms will still be possible with the potential for a few
marginally severe storms. Overall, anticipate total rainfall amounts
of 1-2 inches across central and east-central WI, with lesser
amounts further north.

Independence Day through Friday...A low pressure system will track
across the Northern Plains into MN on Thursday, moving over WI on
Friday, and exiting over the central Great Lakes on Saturday.
Depending on the timing of this system, portions of central and
north-central WI may see impacts late in the evening on the 4th with
showers and thunderstorms. The remainder of the forecast area would
see the chances for showers and thunderstorms Friday through Friday
night. Will continue to monitor the timing of this system given the
busy holiday weekend.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1028 PM CDT Sun Jun 30 2024

VFR conditions will prevail through the TAF period, with the
possible exception of patchy MVFR/IFR fog overnight. Temp/Dew
point spreads are already getting low in parts of NC WI and near
the lakeshore, so may add a TEMPO group for fog at RHI and MTW.
Mostly clear skies are expected, with an increase in mid-level
clouds Monday evening. Showers and storms are not expected to
arrive until after 06z/Tuesday.

Light and variable winds tonight will become SE-S and increase on
Monday. Some LLWS is expected to develop after 06z/Tuesday.

&&

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

&&

$$

DISCUSSION.....GK/Kruk
AVIATION.......Kieckbusch