276
FXUS63 KGRB 192353
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
653 PM CDT Wed Jun 19 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Chance of showers and thunderstorms mainly across east-central
  Wisconsin tonight.

- Chance of more showers and storms area-wide on Thursday.

- An active pattern is expected to continue through the end of
  this week and into this weekend. Stronger storms and locally
  rainfall will be possible each day, with the greatest risk for
  excessive rainfall coming Friday and Saturday.

&&

.DISCUSSION...
Issued at 217 PM CDT Wed Jun 19 2024

Short Term...Tonight and Thursday

Main forecast concern remains on precipitation trends over the
next 24 hours as a frontal boundary to linger to our south and a
shortwave moves into northern sections of the Great Lakes.

The 19Z MSAS surface analysis showed a cold front that extended
from roughly MNM-Y50-DBQ. High pressure was situated over northern
sections of the northern Plains/Upper MS Valley. The radar mosaic
indicated scattered showers and thunderstorms across the southeast
half of WI ahead of the cold front where sufficient instability
and shear present.

The cold front is forecast to move across the rest of east-central
Wisconsin this evening and then stall near the IL border later
tonight. The proximity of the front is close enough such that a
chance of showers and thunderstorms will need to be kept in the
forecast across parts of central and east-central WI, mainly south
of Hwy 54. Meanwhile, the high pressure will move into northern
sections of the Great Lakes and keep northern WI dry tonight.
Cooler/less humid air mass to settle over northeast WI tonight
with min temperatures to range from the lower to middle 50s north,
to the upper 50s to lower 60s south.

Models hint at this stalled boundary will begin to slowly lift
back north as a warm front on Thursday, but remain south of the
forecast area. A mid-level shortwave is expected to move northeast
into the western Great Lakes in the afternoon. Between these two
features, the chance for showers and thunderstorms will be on the
increase, mainly during the afternoon. The combination of clouds,
precipitation chances and an east-northeast wind will keep
temperatures below normal on Thursday. Look for readings to only
reach the upper 60s to lower 70s.

Long Term...Thursday Night Through Wednesday

Despite high pressure over the northern Great Lakes region,
isentropic lift north of a warm front over the southern Great
Lakes will bring the chance for showers and thunderstorms to the
region Thursday night. This warm front will then lift north on
Friday into southern Wisconsin, with increased chances for
precipitation across the region. Although there will be modest
instability of a few hundred J/kg of MUCAPE, the best instability
will be well to our south along with the severe weather risk.
However, heavy rainfall and some minor flooding will be a risk
with long skinny CAPE profiles and PWAT values of 1.75 to 2
inches.

The warm front will linger across Wisconsin Friday night and
Saturday, with additional chances for moderate to heavy rainfall.
Instability will remain fairly meager across our area, keeping the
severe weather threat minimal. However, the continued threat for
several rounds of rainfall will increase the flood threat as
repeated rounds of moderate to heavy rain cause rivers and streams
to rise to or near bankfull.

The region is in a slight risk for excessive rainfall Friday and
Saturday. Probabilistic guidance indicates there is a 30 to 40
percent chance of exceeding 2 inches of rain Friday and Saturday,
with the highest chances across central and north-central
Wisconsin.

A cold front will then sweep through the area Saturday night,
which will end the threat for moderate to heavy rain across the
region. Although additional light showers are possible on Sunday,
this activity is not expected to exacerbate the flooding threat
like the previous activity.

Next week will start out dry, with additional chances for rain
Tuesday and next Wednesday as several weak low pressure systems
track through the area. Next week will bring a return to warmer
weather as daytime highs soar into the 80s with a few 90 degree
readings possible, especially across central and east-central
Wisconsin.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 651 PM CDT Wed Jun 19 2024

A cold front continues to settle across east-central WI. Until
this front and a weak disturbance clear the area by late evening,
will have showers and scattered thunderstorms at GRB/ATW and
especially MTW. Additional showers are possible again just to the
north of the departing front late tonight into Thursday at times
over east-central WI. At this point, it does not look like the
showers will be widespread. Meanwhile it will remain mostly dry at
AUW/CWA/RHI until late afternoon on Thursday as a warm front
shifts in from the southwest and an upper disturbance crosses the
northern plains.

Conditions will be mostly VFR this evening, but will trend MVFR
overnight into much of Thursday at east-central WI terminals as a
cooler/moist NE flow develops to the north of the cold front.
Cigs may drop to IFR near the lakeshore at times, including at
MTW. Cigs will improve to VFR late on Thursday.

&&

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

&&

$$

DISCUSSION.....Kallas/Kurimski
AVIATION.......JLA