907
FXUS63 KGRB 160328
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1028 PM CDT Wed May 15 2024

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- There is a chance of thunderstorms on Thursday, especially
  during the afternoon. A few of these storms may become strong
  with small hail and gusty winds.

- Additional thunderstorms are possible Saturday afternoon into
  Saturday evening and again early next week.

&&

.DISCUSSION...
Issued at 237 PM CDT Wed May 15 2024

Short Term...Tonight and Thursday

Main forecast issues to include: timing of precipitation late
tonight/Thursday and whether any thunderstorms could become
locally strong Thursday afternoon.

The 19Z MSAS surface analysis showed a ridge of high pressure that
extended from eastern Ontario southwest through the western Great
Lakes. An area of low pressure was located over eastern SD with a
cold front stretched southward through the central Plains. Visible
satellite imagery indicated mostly sunny skies over most of WI,
however clouds were quickly spreading across the Upper MS Valley.

The ridge of high pressure slips toward eastern sections of the
Great Lakes tonight, allowing for the low pressure/cold front and
mid-level shortwave trough to move into the Upper MS Valley after
midnight. Look for clouds to steadily be on the increase through
the night and reach eastern WI toward daybreak. An increase in
moisture ahead of the cold front could already bring rain chances
into central WI by 12Z Thursday. More clouds will translate to
temperatures not falling as far as previous nights. Min
temperatures to range from the upper 30s far northeast WI, to the
upper 40s over central WI.

As this system pushes into the western Great Lakes region on
Thursday, showers will spread across the rest of central WI in the
morning and reach eastern WI late morning to midday. Sufficient
moisture (PW values around 1"), combined with modest lift from the
cold front and mid-level Q-G forcing to bring these showers across
the forecast area. Instability is marginal (MUCAPES of 200-700
J/KG), but moderate shear (30-40 kts) will support at least a
chance of thunderstorms, especially in the afternoon under peak
heating. A few of these storms could become strong, thus SPC has
placed parts of northeast WI under a marginal risk of severe
storms. Max temperatures on Thursday to be in the lower 60s near
Lake MI, lower to middle 60s north and upper 60s to around 70
degrees south.

Long Term...Thursday Night Through Wednesday

Attention in the extended period will mainly focus on a couple of
active weather chances before attention then turns to the
potential for a larger weather system in the middle of next week.

Thursday evening into Friday...The occluding low will be on its
way out of the region Thursday evening through the overnight
hours. Any stronger storms are expected to rapidly decrease in
strength during this time period as quieter conditions return to
the region overnight. Friday then continues to remain largely dry,
with the system to our south holding off and the other remaining
west, so kept the pops out of the forecast for now.

The weekend... A strong surge of warmer air will push into the
region during the weekend, bringing temperatures into the upper
70s and lower 80s across the region. As dewpoints also push
towards the middle to upper 50s, we will begin to hit convective
temperatures across the region. This coupled with some weak CAA
around 850mb should help get some scattered precipitation across
the area. Shear will be minimal for this timeframe and little
upper support will be present so organized severe weather is not
expected, but a few pulse thunderstorms aren`t out of the
question. Any active weather will again depart fairly quickly in
the overnight hours as drier air continues to push in aloft and
surface instability diminishes after sunset.

Next week...Finally, attention turns towards the middle of next
week as another low pressure system ejects from the Central Plains
and heads towards the region. The track and strength of this
system remain variable at this time however and will largely
depend on how quickly weak high pressure breaks down ahead of this
system earlier in the week.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1011 PM CDT Wed May 15 2024

VFR conditions will continue through 12z, then CIGS may drop into
the MVFR and possibly the IFR category across central into north-
central and far northeast Wisconsin by 18z. The first round of
rain should reach KRHI/KAUW/KCWA between 12z and 15z, and to
KGRB/KATW/KMTW between 15z and 18z. Additional showers and storms
are expected Thursday afternoon and early evening, especially
across central and east-central Wisconsin which will be closer to
the surface front and better instability for storms to form.
Stronger storms are possible Thursday afternoon with hail and
gusty winds over 30 knots. Showers and storms will come to an end
from west to east Thursday evening.

&&

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

&&

$$

DISCUSSION.....Kallas/Uhlmann
AVIATION.......Eckberg