252
FXUS63 KGRB 080337
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1037 PM CDT Sun Jul 7 2024

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Slow moving thunderstorms with heavy rain are possible tonight.

- On and off chances for showers and thunderstorms will continue
  Monday through Wednesday. 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 and drier summer pattern may be in store toward the
  end of next week and into next weekend.

&&

.DISCUSSION...
Issued at 232 PM CDT Sun Jul 7 2024

Short Term...Tonight and Monday

The latest RAP analysis and satellite/radar imagery show several
shortwaves spinning over the northern Plains and northern
Mississippi Valley. Northeast Wisconsin is positioned on the
eastern periphery of these systems with moisture advection
occurring in the low levels, and difficult to resolve impulses
embedded with southwest flow aloft. These impulses have
supplemented the 1000-2000 j/kg of surface based instability
analyzed across the region to generate scattered showers and
storms. Coverage has been highest over northwest Wisconsin, but
think coverage will continue to increase over north-central and
northeast Wisconsin as we approach peak heating late this
afternoon. A strong to near severe storm is possible given the
deep layer shear of 25-30 kts. Focus of this forecast is storm
trends and heavy precip potential.

Storm trends: After a period of storms over north-central WI this
afternoon, convective allowing models indicate that a broken line
of storms will move into north-central Wisconsin around mid to
late evening along a weak cold front advancing eastward. These
storms should be weakening as diurnal instability is lost. There
may be sufficient instability leftover for a strong storm to
occur, but severe weather is not expected.

A second area of showers and embedded storms remains expected to
move into central and east-central Wisconsin after around 3 am
associated with a shortwave out of the central plains and
augmented by a modest 25 kt low level jet. While there is up to
1000 j/kg of elevated instability, severe thunderstorms are not
expected as effective shears are only around 20 kts. Probabilities
remain low (10-30%) for rainfall amounts of 1/2" or greater, but
slow storm motion around 10 kts and precipitable water values
around 1.6 inches indicate some potential for heavy rainfall if
convection is more widespread/potent than what it indicated in
models.

Shortwave troughing will be overhead for the rest of Monday. While
precip early in the day will likely exit in the morning,
instability of 1000-2000 j/kg will lead to redevelopment of
showers and storms in the afternoon. Higher chances appear
northwest of the Fox Valley where the heating curve will be less
impacted by morning precip.

Fog potential: Besides precipitation, guidance is also showing
potential for dense fog over north-central Wisconsin late tonight.
This makes sense with the precip that has occurred today. Will add
to the HWO.

Long Term...Monday Night Through Sunday

Moisture, instability, and a weak shortwave will keep the chance
for pulse showers and thunderstorms in the forecast through
Tuesday. The lack of better dynamics and lift should keep coverage
fairly low across the region during this period, with the best
chances during the afternoon with peak heating.

The next feature of interest is where Beryl ends up during the
middle part of the week. NWP models seem to agree that our area
will largely miss out on this feature; however, the region will
still see rain as a mid level shortwave and associated positively
tilted trough dive southeast from Canada through the western Great
Lakes region.

Instability showers and/or thunderstorms will be possible Thursday
afternoon; however, with a lack of any significant dynamics or
forcing coverage is expected to be isolated at best. Some weak
ridging is expected to keep Friday dry, with isolated to scattered
showers and thunderstorms possible next weekend as some shortwave
ridge riders track through the western Great Lakes on the
periphery of a larger scale ridge in place across the central
CONUS.

Temperatures during the week will be right around normal through
Thursday. Temperatures will then warm to a few degrees normal on
Friday and several degrees above normal by next weekend as the
upper level ridge builds in across the central CONUS.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1036 PM CDT Sun Jul 7 2024

An upper level trough will produce scattered showers and thunderstorms
as it moves slowly across Wisconsin tonight and Monday. The activity
will be most abundant during the daytime and evening hours and decrease
overnight. There may also be some patchy ground fog late tonight where
significant rain falls.

Outside of any convective activity and ground fog, VFR conditions
are expected.

&&

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

&&

$$

DISCUSSION.....MPC/Kurimski
AVIATION.......RDM