158
FXUS63 KGRB 140918
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
418 AM CDT Sun Jul 14 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Areas of showers and non-severe storms exits early this
  morning. Small chance of storms later today. Additional strong
  to severe storms possible on Monday as a cold front moves across
  the area.

- Heat index values in the 90s are expected over central, east-
  central, and parts of far northeast Wisconsin today and Monday.

- Cooler and drier conditions expected mid-late next week.

&&

.DISCUSSION...
Issued at 418 AM CDT Sun Jul 14 2024

Short Term...Today...Tonight...and Monday

Main forecast concerns remain trying to make sense of the poorly
performing CAMs with regard to MCS/shower/storm timing/placement
and intensity. The heat and humidity will remain in place today
and Monday with heat indices mainly in the 90s. Also watching for
possible fog and smoke impacts.

Convective Trends & Severe/Flooding Potential:

For today and tonight...CAMs were struggling initializing with
the current placement/strength of shower and storm activity early
this morning, but the HRRR seems to finally have a good handle on
it as of its 06z run. Luckily, any shower/storm activity will be
exiting the area this morning, by 12-15z. Can`t rule out some
small hail as mid-level lapse rates across central WI will be
close to 7 C/km and MUCAPE still between 800-1200 J/kg with a push
of higher CAPE trying to advect in from the west. But the more
robust storms will stay to our south/west closer to the
instability gradient and we should mainly see the stratiform rain
on the northern side of the MCS. Heaviest rain will miss the area
as well, but the Wausau and Appleton areas can`t take much rain at
all before flooding would occur again. PWATs still between
1.5-2.0" so any storm could produce some heavy rain. The rest of
the day is looking mainly dry. The lake breeze could touch off
some activity near the MI border in the afternoon or evening. Will
need to watch for another batch of convection to develop in the
late afternoon as well, which the HRRR/FV3 are advertising. Unsure
if this is with an actual shortwave or a phantom one. If
something were to form, it is likely to stay just to our south,
but something to keep an eye on as models likely not exactly
capturing this potential feature well. Plenty of instability and
decent shear to produce some strong to severe storms if activity
were to occur, along with the threat for heavy rain. Most/all of
tonight is looking dry then the uncertainty arrives again early on
Monday, with the next MCS tracking toward the area. Some models
have it over northwest WI at 12z Monday, while others have it over
southern WI. The wait and see method will have to be used as
where it initiates will determine eventual track.

For Monday...could be dealing with the overnight MCS somewhere
across the area early in the day, then expect some partial
clearing later in the morning, allowing for instability to build.
Strong to severe storms will be possible ahead of a cold front and
shortwave in the afternoon and evening, with 30-50 kts of shear
and 2000+ CAPE. Damaging winds and hail will be the primary
threats with organized and fast moving storms, but with 0-1 and
0-3 SRH increasing ahead of the front, a few discrete supercells
could bring the risk of a tornado. Still a chance the morning MCS
could linger into the day and reduce instability and therefore
limit coverage in our area, with the higher instability in
southern WI. But those mesoscale features will be hard to pin
down until a clearer picture emerges in regards to the morning
MCS. Most of the activity looks to have some decent forward speed,
so the overall flooding threat looks to be low. However, any
storms that can align and move over the same location could bring
a flooding threat, especially in areas that saw recent heavy rain.

Temps & Heat Index:

Clouds and smoke aloft may hinder temps reaching their full
potential today and Monday. 925mb temps of 21-25C would support
highs in the upper 80s and low 90s. With some sun expected across
the area this afternoon, won`t cut too much into highs, with most
spots in the mid and upper 80s, with a couple spots possibly hitting
the 90 mark. A little more afternoon clouds on Monday should hold
highs in the low to mid 80s for most spots. While some guidance
wants to bring in some mid or even upper 70s dewpoints, think
lower 70s are more realistic. This will hold heat index values in
the 90s. While short of heat advisory criteria, those that will be
outdoors for an extended period should take precautions from the
heat and humidity.

Fog & Smoke Trends:

Patchy ground fog developed across parts of central and northern
WI early this morning when/where skies cleared out for a time. But
the thicker clouds have spread across the area, so any fog will be
very patchy. Fog is looking more likely early Monday morning,
through around sunrise, as a steep low level inversion forms,
trapping moisture from recent rainfall, and winds will be light.
Clouds approaching from the west could be just enough to keep the
fog from getting too dense. Will continue to monitor for areas of
dense fog on Lake Michigan today as water temps are in the low to
mid 60s and dewpoints increase.

Elevated smoke will remain over the region into Monday. The surface
smoke is forecast to approach Lake Superior late this afternoon and
evening, then possibly spread into northern WI overnight into
Monday. Could have some air quality issues at times, along with
possibly visibility reductions if the thicker/lower smoke makes it
here.

Long Term...Monday Night Through Saturday

Storms may still be pushing through the region at the start of
the extended period as the cold front works its way eastwards, but
quiet conditions are expected to move in fairly quickly. Strong
cold air advection behind the cold front on Monday as northwest
flow arrives aloft. While this will mean predominantly dry
conditions, a few light showers could still work their way into
the region during the middle of the week. While these showers
could include some brief rumbles of thunder, currently would not
expect any severe in the extended forecast. Temperatures will drop
towards highs in the 70s for the middle of the week before
gradually moderating into next weekend.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1043 PM CDT Sat Jul 13 2024

Thunderstorms developing across Minnesota have recently been
progged by the CAMs models to mainly miss the area, and the TAF
sites, tracking through western Wisconsin during the overnight
hours into Sunday morning. Given the drier trend with the CAMs
models, and the atmosphere being worked over across the region,
will pull the precipitation from the TAFs with this issuance. Some
low clouds may linger early in the TAF period behind the departing
precipitation, but should dissipate within a few hours. The rest
of the TAF period later on Sunday should be quiet with VFR
conditions expected as most models focus additional showers and
thunderstorms south of the area Sunday afternoon and evening.

&&

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

&&

$$

DISCUSSION.....Bersch/Uhlmann
AVIATION.......Kurimski