624
FXUS63 KGRB 132337
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
637 PM CDT Tue Aug 13 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- A few showers and storms will continue through early this
  evening, especially near lake breeze boundaries in eastern and
  far northern WI. Severe weather is not expected.

- Areas of fog expected late tonight into early Wednesday. Locally
  dense fog may cause travel concerns for the early morning
  commute.

- Next chances for potentially heavy rainfall will arrive from
  the southwest Wednesday evening and persist through Friday.
  Localized flooding will be possible in low-lying and urban
  areas.

- Conditions hazardous to small craft will be possible on Lake
  Michigan Thursday and Thursday night.

&&

.DISCUSSION...
Issued at 232 PM CDT Tue Aug 13 2024

Short Term...Tonight and Wednesday

A few showers and storms will continue to develop this afternoon
and early evening, as daytime heating has caused MLCAPE to
increase to 300-600 j/kg. The activity should become focused near
weak boundaries, especially the lake breezes over eastern WI (off
Lake Michigan) and far northern WI (off Lake Superior). Other
than locally heavy downpours and brief gusty winds (inverted-V
soundings), no major concerns are expected with the storms due to
weak deep-layer shear and a lack of forcing.

With high pressure lingering through tonight and Wednesday,
expecting mainly dry conditions to prevail. Warmer temperatures
in the mid-levels should prevent a repeat of today`s daytime
isolated convection.

Perhaps of greatest concern during the period will be fog
potential overnight into early Wednesday. Very light winds (5
knots or less) at the surface and aloft should combine with clear
skies to allow areas of fog to develop after midnight. The fog
is expected to become locally dense in river valleys and other
sheltered low-lying areas, and may cause travel concerns for those
with an early morning commute.

Did not make any significant changes to temperatures, other than
lowering min temperatures a few degrees in the typical cool spots
of NC WI.

Long Term...Wednesday Night Through Tuesday

Main focus for the extended revolves around heavy rain potential
Wednesday night through Friday as an organized surface low tracks
from the central Plains through the western Great Lakes. Although
severe potential looks to be low, some embedded storms will be
possible across central Wisconsin on Thursday. Otherwise, main
threat with this system will be localized flooding in urban and
low-lying areas.

Rainfall potential... Expect rain chances to arrive from the
southwest late Wednesday evening ahead of increasing warm air
advection/isentropic lift. Moisture transport will also be on the
rise during this time as shortwave energy propagates across the
northern Plains and saturates the column from the top down. As the
surface low approaches Thursday morning, PWATs will likewise
increase into the 1.75 to 2" range, about 150 percent of normal
for this time of year. Isolated flooding will thus be possible,
especially in urban and low-lying areas. Current thinking is that
flash flood potential will be relatively limited due to a recent
stretch of dry weather and prolonged rainfall duration. This being
said, flash flooding would remain in the realm of possibility
with any convective activity/embedded thunderstorms given slow
storm motion of under 10 knots. The SPC currently highlights
portions of central to east-central Wisconsin under a marginal
risk for severe weather Thursday afternoon given CAPEs approaching
1,000 J/kg; therefore suspect that the main flash flood threat
would be in this area. Regardless, abundant moisture and warm
cloud depths exceeding 12,000 feet suggest the presence of
efficient rain producers on Thursday. Current model guidance shows
rainfall amounts of around 1.25 to 1.5" from central to east-
central Wisconsin through Friday morning.

Rest of the extended... Remnant shortwave energy spinning over
the Great Lakes on Friday should be enough to sustain scattered
showers across the forecast area through Saturday. Otherwise,
conditions look mostly quiet through mid-week as weak high
pressure settles over the Mississippi Valley and northwest mid-
level flow shunts any instability to our south and west.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 637 PM CDT Tue Aug 13 2024

Isolated showers or thunderstorms over northeast Wisconsin
will end a few hours after sunset. Otherwise clear skies are expected
tonight and Wednesday, with areas of ground fog late tonight through
13z Wednesday.

&&

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

&&

$$

DISCUSSION.....Kieckbusch/Goodin
AVIATION.......RDM