612
FXUS63 KGRB 020332
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1032 PM CDT Mon Jul 1 2024

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

 - Periods of heavy rain will be possible early Tuesday morning
   through Tuesday night. In general, 0.5 to 1.5 inches of rain
   will be possible across the entire area, highest in central
   Wisconsin, which could lead to minor river and stream
   flooding, along with urban flooding.

 - There is a high risk of rip currents on Lake Michigan beaches
   on Tuesday and Tuesday night due to high wave action. Beach
   goers are advised to remain out of the water when waves are
   high.

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

&&

.DISCUSSION...
Issued at 352 PM CDT Mon Jul 1 2024

Short Term...Tonight and Tuesday

20Z surface analysis shows the high pressure center over northern
Lake Michigan. The region will remain dry through this evening as
the high departs, however, with the tightening pressure gradient
on the backside of the high southerly winds will increase with
gusts reaching 20-25 mph across central and northern WI tonight.

A pattern shift then comes Tuesday as an upper-level trough and
surface low pressure system are forecast to track north of the
region. Expecting rain to push into central and northern WI just
after midnight and into the Fox Valley early Tuesday morning.
There may be periods moderate to heavy rainfall through Tuesday
morning, especially across central WI where the isentropic ascent
and vorticity advection is expected to be maximized, along with
PWATS approaching 2 inches. Not expected any severe weather with
this first round of rain, however, won`t rule out a few rumbles
of thunder late Tuesday morning. In addition to the rain,
southerly winds will be breezy Tuesday morning with gusts
reaching 25-35 mph. Most of the hi-res models are showing a lull
in the precipitation Tuesday afternoon ahead of a second short-
wave progged to bring another round of rain Tuesday evening (see
long-term discussion). Total QPF amounts have come down a touch
from earlier forecast with much of the region now looking at
around 0.5-1 inch of rain, with locally higher amounts of 1.5-
2 inches possible across central WI. Even with the lower QPF
amounts several area rivers will likely return to or near
bankfull, and low laying areas may see minor flooding.
Temperatures Tuesday will continue to be a few degrees below
normal with highs forecast to reach the upper 60s to middle 70s
across the region.

Long Term...Tuesday Night Through Monday

Main focus from this forecast period revolves around another round
of potentially heavy rainfall Tuesday evening/night, thunderstorm
potential for the Fourth of July, and additional rain chances for
the weekend.

Tuesday night through Wednesday morning...Rain chances will increase
into Tuesday evening/night as a cold front, supported by the RRQ of
an upper-level jet, moves across the region. With the Gulf open,
impressive PWATs of 1.75 to 2 inches will lift into the area and
support moderate to heavy rainfall at times. Rainfall amounts have
decreased some due to deterministic guidance indicating the
convective axis being further south of the forecast area. However,
ensemble guidance is still showing signs of higher amounts across
central and east-central WI with probabilities of 1 inch or more
between 10-20%. Given the uncertainty of the convective axis,
decided to lower rainfall amounts slightly during this time frame,
with most locations seeing at least a couple tenths of a inch in far
north-central WI to about 0.50" in far eastern WI. Isolated higher
amounts are expected if the convective axis shifts slightly further
north. Severe weather is not expected with this frontal passage due
to limited instability around 200 J/kg, but non-severe thunderstorms
will be possible at times.

Independence Day through Friday...A low pressure system will track
across the Northern Plains into MN on Thursday, across WI on Friday,
and exit the region Saturday morning. The onset of the precip has
changed very little, leading to portions of central and north-
central WI seeing the greatest chance for thunderstorms late
Thursday evening, when firework displays are likely to occur. The
remainder of the forecast area would see the arrival of shower and
thunderstorm chances early Friday. Rain and thunderstorms will
continue across the region for the remainder of Friday through early
Saturday morning. Will continue to monitor the timing of this system
given the holiday festivities on Thursday and busy holiday
weekend.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1024 PM CDT Mon Jul 1 2024

Rain is expected to arrive at the western TAF sites around
07z-08z/Tue and eastern TAF sites 10z-11z/Tue. The steadier/heavier
rain is expected to taper off from west to east during the late
morning and early afternoon on Tuesday, but patchy drizzle or
light showers may continue during the afternoon. Another round of
more significant rain is expected to arrive during the late
afternoon and evening hours as a short-wave trough and resurgent
low-level jet impact the region. There may be a small chance of
thunderstorms during the late afternoon and evening, but
confidence is not high enough to mention any storms in the TAFs.

Flight conditions will deteriorate to MVFR/IFR at RHI/AUW/CWA
late tonight into early Tuesday, and to MVFR at GRB/ATW/MTW in the
late morning and afternoon.

Have continued the mention of LLWS at RHI/AUW/CWA late tonight
into Tuesday morning, but current models suggest the threat will
remain northwest of GRB/ATW/MTW. SE-S surface winds will prevail
through the TAF period, with winds becoming quite gusty during the
day on Tuesday.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement from 7 AM CDT Tuesday through Wednesday
morning for WIZ022-040-050.
&&

$$

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