326
FXUS63 KGRB 081741
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1241 PM CDT Mon Jul 8 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Thunderstorms are possible through early this evening with heavy
  rain and localized urban flooding being the primary hazard.
  Severe weather is not currently expected.

- On and off chances for showers and thunderstorms will continue
  through Thursday. Although the severe weather threat remains
  low, locally heavy rainfall will be possible.

- Some rivers, creeks, and streams across east-central Wisconsin
  will continue to run above bankfull due to recent rainfall.

- A warmer/drier period may be in store toward the end of the week
  and into the weekend.

&&

.DISCUSSION...
Issued at 403 AM CDT Mon Jul 8 2024

Short Term...Today...Tonight...and Tuesday

Thunderstorm timing and coverage through tonight are the main
concerns. Heavy rain will remain a potential given PWATs 1.25 to
1.5 inches and slower moving storm motions. Isolated stronger
storm with gusty winds and small hail could occur this afternoon,
but severe weather is not expected.

Slow moving positive tilted mid-level trough trudges across the
upper Great Lakes today. Weak front with wind shift but little
temp change shifts through late this afternoon into this evening.
Ahead of these features though, modest low-level jet and warm
front is helping to generate clusters of thunderstorms south of
highway 10 early this morning. Elevated MUCAPE up to 500J/kg
feeding this activity and higher PWATs and warm cloud depths with
minimal individual cell motion results in a concern for heavy rain
through 11-12z before low- level jet weakens and veers WSW.
Storms are showing some movement but training cells could offset
this. Will continue to monitor the heavy rain potential through
daybreak.

After this activity diminishes, majority of showers and storms
this afternoon will develop closer to weak front over north-
central also where MLCAPEs build fastest into far northeast WI.
Likely pops only used over north-central with closer proximity to
front and approaching mid-level trough. Eventually chance of
showers and storms will make it to the Fox Valley and Lakeshore
but this may not be until very late afternoon or even early
evening hours. Similar H85 temps to yesterday and mix of sun and
clouds supports highs back into the lower 80s, with upper 70s far
north.

Weak front moves through this evening with sfc winds eventually
shifting to the W-NW. Small chances for a shower or storm through
late evening, then dry overnight. Temps will cool into the low to
mid 50s north-central which is where best chance of fog resides,
especially since those areas see rain today.

Bit of a different pattern on Tuesday. Mid-level trough axis will
be flattening and shifting to our east. General sfc high pressure
will be building into the region in its wake. Meanwhile, the remnants
of TC Beryl will be lifting to the mid Mississippi River valley
and we`ll start to see some cirrus well to its north here in WI.
The day will begin with W-NW flow behind the weak front, but by
midday winds weaken to allow lake and bay breeze circulations to
develop as temperatures just inland reach back into the lower 80s.
Some showers and storms will develop during peak heating though
MLCAPEs remaining under 750J/kg and weak large scale forcing
should limit coverage. Severe weather potential low yet again, but
with the weak wind fields aloft, any storms will be slow moving.
Storms will drift from north to south though.

Long Term...Tuesday Night Through Sunday

Some spotty shower/storm activity is still possible Tuesday
evening through Thursday as shortwave energy dives down from
Manitoba and skims northwest Wisconsin. However, with models
agreeing to a more southerly track for Beryl through the Ohio
River Valley mid-week, expect the axis of highest QPF to remain
well off to our south and east. Otherwise, quasi-zonal flow/weak
ridging should keep any meaningful rainfall out of the forecast
through the end of the work week.

Tuesday evening through Thursday... A combination of partial
clearing and decent low-level moisture will result in slightly
elevated instability (~1,000 J/kg) Tuesday through Thursday. This
may be enough to generate some pulse storms during peak heating,
although meager forcing and weak dynamics indicate that any storm
activity would be short-lived and sparse in coverage. Any westward
shift in Beryl`s track would likely paint a different picture,
although there is currently a strong signal that it will miss us
to the southeast.

Rest of the extended... As the current troughing regime breaks
down and the western heat ridge edges into the central CONUS,
anticipate that Friday into the first half of Saturday will be
mostly warm and dry. Potential for rain/storms then returns
Saturday afternoon into Sunday as ridge riders track through the
western Great Lakes and interact with a warm, moist airmass.
Speaking of warm airmasses: this weekend has the potential to be
rather unpleasant as temperatures climb into the upper 80s to low
90s and a surge of low-level moisture brings dewpoints up into the
low 70s. If temperatures in the low 90s are realized, the
combination of heat and humidity would result in heat indices
flirting with advisory criteria on Sunday. It is too soon to say
anything for certain this far out, but definitely worth keeping an
eye on.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1228 PM CDT Mon Jul 8 2024

A line of strong thunderstorms associated with an MCV was pulling
out of far NE WI at issuance time. Additional scattered showers
and isolated storms were ongoing across the forecast area. Showers
and storms should be most numerous in north central WI this
afternoon, as a weak boundary and upper trough impact the region
during peak heating. Expect convection to weaken after sunset,
with the loss of daytime heating/instability.

Light winds, low-level moisture, recent rain and partly cloudy
skies should set the stage for fog development overnight,
especially in the Wisconsin River valley of NC/C WI. The fog
should mix out rapidly by around 13z/Tuesday. Scattered cumulus
development is expected to occur later in the morning, but any
daytime convection should hold off until afternoon.

&&

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

&&

$$

DISCUSSION.....JLA/Goodin
AVIATION.......Kieckbusch