897
FXUS63 KAPX 140245
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1045 PM EDT Sat Jul 13 2024

.KEY MESSAGES...

- Thunderstorms return tonight into Sunday morning, including
  the potential for a few strong storms.

- Additional pop-up storms possible Sunday afternoon.

- Hot and humid Monday

- Showers and thunderstorm Chances Monday and Tuesday

&&

.UPDATE...
Issued at 1043 PM EDT Sat Jul 13 2024

Generally zonal flow across the Upper Midwest this evening...save
for a weak shortwave trough axis stretching from near Isle
Royale...down toward the southern end of Lake Michigan. Handful of
even shorter-wave perturbations amid this trough axis...along edge
of broad and capped ridging encompassing the bulk of the central/SW
US. Return flow on the back of departing surface high helping
destabilize the lower-levels over the Upper Midwest/Great
Lakes...though better destabilization of the upper levels is yet
back across the northern Plains...where another subtle shortwave
trough axis (and better cold advection aloft) is digging across
ND/southern Canadian Prairies. Not surprised to see a handful of
different areas of convective activity ongoing...one north of Lake
Superior with energy up there...conglomerating MCS following the
theta-e ridge southwestward across WI...and even some activity
blossoming upstream in the vicinity of MN. Here in northern
Michigan...our environment is, perhaps, slightly less
favorable...downwind of the relatively cooler lakes (compared to
land temps in the 80s today)...with a much drier layer aloft
(surface dewpoints mixed down into the 50s today, and pwat on the 0z
sounding was under an inch...compared to DTX`s 1.36in). Still..we`re
holding onto a few hundred joules of CAPE aloft this evening...which,
in the presence of increasing moisture from upstream convection,
/should/ start to prime things for later in the night. Expectation
is for this first round to move through...and will watch for upstream
development to approach the region late tonight/early Sunday morning.
Still a bit unclear how this will play out...but do think the atmosphere
may have time enough to recover tonight between the current WI convection
and the next line to allow something to continue eastward (or
east-ish -ward) overnight. Will also be curious if we manage to pop
anything ahead of the line...and am somewhat concerned about a zonal-
oriented boundary stalling over the area tonight. Do think there
is a shot, though, to see a couple blobs of convection split
around northern Lower toward morning, but rather unclear
attm...and will still carry pops into NW Lower regardless.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 350 PM EDT Sat Jul 13 2024

Pattern Synopsis:

Subtle shortwave ridging will continue to slide east of the northern
Great Lakes tonight as surface high pressure builds closer to the
Atlantic coast. Meanwhile, a potent shortwave/jet max embedded in
the main mid/upper level flow will punch across the upper Midwest
and over the far northern Great Lakes/southern Ontario by Sunday
morning. Favorable ascent aloft generated by this wave will support
a surface cyclone that looks to trek across northern Ontario and
over south Hudson Bay on Sunday.

Forecast Details:

Thunderstorms return tonight into Sunday morning -- Aside from a few
pop-up showers and storms still possible near Whitefish Bay into
this evening, quiet weather is expected across the rest of the area
into tonight. While there is high confidence in much of northern
Michigan seeing showers and storms tonight and Sunday morning, there
is relatively high uncertainty as to how showers/storms will evolve.
Current confidence is that storms will form across parts of
Wisconsin later this afternoon/evening and move across Lake Michigan
into western portions of northern Michigan tonight. A second round
of storms will be possible late tonight/Sunday morning on the heels
of the first round with a potential MCS moving across the upper
Midwest and into the Great Lakes. Buoyancy on the order of 500-1,500
J/kg MUCAPE looks to be in place ahead of both potential rounds,
with relatively weak deep-layer shear around 25-30 kts. A few
storms/segments may be capable of producing damaging wind gusts --
primarily in closer proximity to the lakeshore -- tonight through
Sunday morning. Should multiple rounds of storms train across
specific locations, locally heavy rainfall of 1-2"+ will be possible
and may create ponding on some area roadways.

Additional pop-up storms possible Sunday afternoon -- After morning
showers/storms move out, there is expected to be a lull in precip
chances into the early afternoon hours. Additional development is
still uncertain at this time as it will depend on the
arrival/departure time of aforementioned storms and how quickly
breaks in the clouds can form, allowing for destabilization in the
afternoon. Current thought is that this will occur in time for
additional scattered showers/storms to form across parts of northern
Michigan, primarily east of I-75 where ant lingering outflow
boundaries/lake breeze boundaries can interact. A few strong storms
will be possible in the presence of ~1,000 MLCAPE and ~30 kts of
deep-layer shear to support at least some organization.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Issued at 350 PM EDT Sat Jul 13 2024

Pattern Synopsis and Forecast: An anchored upper level ridge over
the western CONUS will continue zonal flow aloft over the northern
Rockies into the northern Plains and Great Lakes region through mid
week. A very warm and wet airmass near the surface currently resides
over the northern plains. This airmass will make its way towards MI,
where surface dewpoints are forecasted to reach into the high 60s
and low 70s for most of the CWA Monday afternoon (some slightly
drier air could be over eastern upper). A cold front will begin to
slide down the Canadian plains along the front range, kicking off
convection over ND/MN Sun afternoon/evening. This will likely induce
shortwaves aloft on the zonal flow, which will help aid convection
Monday afternoon over WI/IL. Some of the northerly winds near the
surface with the initial front could reach the wave and create weak
cyclogenesis as the convection approaches MI. Isolated to scattered
storm chances exist for Monday afternoon and night (due to slight
uncertainty in timing with these features). Best chances for storms
at this time are over northern lower. Skies have a chance for
clearing ahead of storms Monday, which could bump heat indices into
the 90s Monday afternoon. This will be hard to pin down exactly
where will be the hottest due to the uncertainty with cloud cover.

A seasonally deep upper closed low will start to drop south from
eastern Hudson Bay. Clouds and chances for showers will linger
Tuesday. A cold front will move through early Wednesday, brining in
cooler and drier Canadian air. Low to no rain and storm chances for
the end of the work week and next weekend.

Primary Forecast Concerns/Key Messages:  Although the air will feel
heavy and humid Monday afternoon, there is enough uncertainty in
skies that heat indices could remain in the high 80s to low 90s for
most of northern lower. Eastern upper has chances of seeing slightly
drier air Monday, which will keep heat indices lower. Places where
skies can clear could see temperatures quick warm, possibly rising
heat indices into the low to mid 90s. High uncertainty remains on
what Monday`s storm chances will look like. Confident exists in the
environment being capable of producing storms with some severe
attributes (hail and winds) and even higher chances of torrential
rainfall with storms (PW values average around 1.3"  Monday
afternoon). However, forcing that could lead to storm initiation
might be weak by the time they reach northern MI. At this time,
chances for isolate to scattered showers and thunderstorms for
Monday afternoon and night are in the forecast. With these storms a
few could be capable of marginally severe hail and winds. Chances
for storms decreases through the day Tuesday.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 736 PM EDT Sat Jul 13 2024

Upstream TSRA over WI making its way southeast. Think first shot of
any rain/thunder at KTVC, KMBL would be between 3-6z...though some
uncertainty how things will hold together across Lake MI. These
could produce gusty winds and heavy rain (visby reductions upstream
to IFR/LIFR beneath heavier rain). Primary forecast attm is for a
second round of storms to dive across the Upper Midwest
tonight...likely reaching KTVC/KMBL sometime between 9-12z. Gusty
winds again a threat with these as they track west-southeast in the
morning...as well as lower cigs/visbys (IFR/LIFR possible). Gut
feeling we could see additional development ahead of the main line
late tonight...and/or an E-W line of storms develop and slowly lift
north into the morning. Do think a brief break is on tap toward
midday Sunday...with some shot at pop-up storms in the
afternoon.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

UPDATE...FEF
SHORT TERM...DJC
LONG TERM...ELD
AVIATION...FEF