029
FXUS63 KAPX 210753
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
353 AM EDT Fri Jun 21 2024

.KEY MESSAGES...

- Shower and Thunderstorm Chances continue today and tonight

- Heavy rainfall with amounts of 2-4"+ possible Saturday into
Saturday night.

- Isolated severe storms also possible Saturday into Saturday night.

- Less active, cooler weather possible next week.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 336 AM EDT Fri Jun 21 2024

Pattern Synopsis and Forecast: Current satellite and obs depict
light and generally east to northeast winds around northern MI this
morning. Low clouds are around the region with some areas of
haze/fog likely (although obs show this at the moment). This
overrunning of moisture over the cooler airmass near the surface
will continue into the morning hours. CAM guidance is mixed on
suggesting how long clouds and light rain will linger. Confidence is
in it taking most of the morning to exit northern lower, and
possibly lingering over eastern upper through the afternoon hours.
Southerly winds will form over the southern and central part of the
state, possibly creating an area of convergence late this afternoon.
Some CAMs are showing isolated convection sprouting from this
boundary and around ~700 j/kg of SBCAPE in the environment. The main
hazards with any storms that do form later this afternoon will be
heavy downpours, lightning, and possibly small hail and locally
gusty winds. Mild overnight temperatures with chances for fog
formation again as anomalous moisture hangs around.

Primary Forecast Concerns/Key Messages: Guidance shows the
uncertainty in the morning, more for what will happen to the upper
level moisture overrunning a slightly cooler airmass near the
surface. 00z KAPX sounding had 1.67 PWAT, which is near the daily
max. The environment is very moist, and nothing really scours it
out. Clouds will likely persist over eastern upper and near the tip
of the mitt today as convection upstream will continue to bubble and
throw clouds overhead. Areas closer to the central part of the state
will get a good shot at clearing. If this happens and they warm into
the low 80s, there is a good chance a few isolated non-severe storms
will form along a low level convergence zone.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 336 AM EDT Fri Jun 21 2024

Pattern Synopsis: Low-amplitude ridging will depart east of the
Great Lakes as troughing slides overhead this weekend. A lead
shortwave looks to punch across the region Saturday with a much
stronger, more prominent shortwave set to dig across the Great
Lakes Sunday/Sunday night. Forcing provided by these features
aloft will support a seasonably-strong cyclone that is expected
to trek across northern Michigan Saturday into Sunday.
Subsidence on the backside of this system as it moves out will
likely build surface high pressure into the region on Monday
before another wave enters the picture closer to the middle of
next week.

Forecast Details: Heavy rainfall possible Saturday into
Saturday night -- Scattered showers and embedded thunder is
expected to be ongoing at the start of the period as warm, moist
advection will already be underway ahead of the approaching
system. Strongest advections tied to 35- 45kt 850-700mb flow
will arrive later on Saturday, helping to pump PWAT values to 2"
or higher -- an impressive number for northern Michigan. This
would far exceed the max moving average for any time of year
(~1.8") and could possibly be sampled as a top-25 all time PWAT
value at the 00Z Sunday 6/23 launch based on SPC sounding
climatology. To no surprise, forecast soundings display moist
adiabatic profiles through the depth of the troposphere with
500- 1,500 J/kg MLCAPE in place into the evening hours. With the
warm front draped west-east across the lower peninsula, mean
cloud-layer flow oriented parallel to the boundary, and
aforementioned buoyancy in place, ingredients appear to be
aligning themselves to support a heavy convective rainfall event
across northern Michigan.

Very efficient rainfall is expected over a several hour stretch for
most locations -- and perhaps over the bulk of an 8-12 hour period
for a swath of northern Michigan Saturday afternoon into Saturday
night. Training convection will lead to the potential for some areas
to see several inches of rain by Sunday morning. Based on latest
guidance, parts of northern Michigan have high chances (70+ percent)
to see at least 1" of rain, medium chances (40-60 percent) to see at
least 2" of rain, and even low chances (10-30 percent) to see at
least 4" of rain. Exact locations of heaviest rainfall are still
uncertain, but current confidence has shifted further south than
previous thought -- with best chances for heaviest rainfall lying
between M-72 and the bridge. Flood potential will be monitored
closely with this system given how favorable the environment in
place will be to support efficient heavy rainfall over an extended
period of time.

Isolated severe storms possible Saturday into Saturday night --
While the primary, highest-confidence threat is heavy rainfall
Saturday into Saturday night, isolated severe storms will also be
possible during that time. Buoyancy will support convection, but
aforementioned moist adiabatic profiles with buoyancy struggling to
extend much past freezing aloft will hinder hail potential. Best
chances for any severe storms may be late afternoon/evening as the
wind field strengthens with the cyclone working into the region.
This will enlarge already cyclonically-curved low-level hodographs
in an environment characterized by 0-1km shear of 35+ kts, 0-3km
shear of 40+ kts, and effective SRH of 200+. While a largely
unfavorable convective mode is expected at this time -- and will
limit overall severe threat -- aforementioned shear magnitudes,
if/when combined with any partial clearing to foster elevated low-
level CAPE, will support both a damaging wind and low-end tornado
threat across northern lower Michigan.

Less active, cooler weather next week -- Rain/thunder chances look
to wind down through the second half of the weekend as high pressure
builds in to start the week, bringing about a reprieve from rain
chances on Monday. Rain chances look to return closer to the middle
of the week, but the overall pattern appears to be less active for
the Great Lakes through the end of the period. High temperatures in
the upper 70s/low 80s to start the week look to cool back closer to
70 through back half of the period.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1142 PM EDT Thu Jun 20 2024

Mixed VFR/MVFR conditions.

Weak high pressure over Lk Superior has pushed cooler air into
the region. That will be temporary, as the high weakens, and a
warm front pushes north into the southern and central lakes on
Friday. There are good chances for showers thru the period,
especially late tonight, and again on Fri afternoon. MVFR will
be most prevalent late tonight and Sat morning, otherwise a mix
of VFR and MVFR conditions are expected.

Light winds.

&&

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

&&

$$

SHORT TERM...ELD
LONG TERM...DJC
AVIATION...JZ