168
FXUS63 KAPX 211848
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
248 PM EDT Fri Jun 21 2024

.KEY MESSAGES...

- Widespread showers and thunderstorms with heavy rainfall
  likely later tonight and especially into Saturday. Isolated
  areas of flooding will be possible.

- Heavy rain threat continues into Saturday evening.

- Additional shower chances at times next week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 245 PM EDT Fri Jun 21 2024

Pattern Synopsis and Forecast:

Energy aloft quickly moves into the area tonight with
lingering/additional shower & storm development. The main story will
be a short wave trough riding the north periphery of a ridge thus
facilitating sfc low development across the Plains, Midwest, then
Great Lakes later tonight through later Saturday. Additionally, warm
front/stationary boundary will drape across northern Michigan. All
the while, an anomalously moist environment will remain in place,
and even increase into Saturday, facilitating the potential for
heavy, efficient rainfall. Along with other aspects, this pattern
described above takes after the classic "Upper Level Ridge" Maddox
Flash Flood Pattern/Conceptual Model and is definitely food for
thought in regards to this upcoming event.

Primary Forecast Concerns:

Real intriguing pattern upcoming from a heavy rain perspective.
Anomalous moisture is already in place, as both sampled from this
mornings 12Z sounding (1.71" PWs) in addition to anecdotal evidence
via on/off-duty meteorologist observing very efficient, warm rain
processes with this mornings rain in the vicinity of Gaylord and
north. Thus, with the threat for increased showers and storms this
afternoon/evening, especially if portions of the area clear out and
some instability is able to manifest, very heavy rainfall will be
possible, mainly south of M-32 and east of I-75 (where the best
moisture/clearing will likely be). Quick 1 to 2 inches of rain
cannot be ruled out.

Pattern late tonight into Saturday night emulates classic "Upper
Level Ridge" Maddox Flash Flood Pattern/Conceptual Model. Short wave
rides the upper level ridge with stationary boundary and anomalous
moisture in place. Plenty of lift, minor but long skinny CAPE, PWs
in the vicinity of all time/top 10-20 or whatever values, and some
pretty ridiculous warm cloud layer heights (11-13kft) for this
region of the world. Conceptual model suggests the heaviest rainfall
will be just to the north of the boundary on the "cool" side, which
would put the heaviest rainfall across the northern half of northern
lower, tip of mitt and vicinity generally. All of this considered,
CAMs and global models suggest 2-4", some 6"+, especially north of M-
32. Pretty significant signal for efficient, very heavy rainfall
especially in locations that have training storms/cells.
Additionally, region from Torch Lake and East Jordan east to Alpena
has seen 1 to 3 inches of rain the last 48 hours, so this region may
be slightly more prone to flooding with this event. Thus, at this
time, we think at least isolated instances of flooding will be
possible Sat-Sat night, especially across flood prone regions and
urban areas. This rich environment with heavy rain potential will
continue into the overnight hours on Saturday, visit the long term
discussion for more details.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 245 PM EDT Fri Jun 21 2024

Pattern Synopsis/Pattern Forecast:

A period of transition as sub-tropical ridge slow retrogrades west
into early next week, taking up it more familiar summer location
across the Desert Southwest by the middle of next week. This
forces/allows more northern stream influences into the northern
Conus...including the Great Lakes...next week. Per the usual, such
transitions often bring about some of our more active weather, and
this one is no exception with periods of heavy rain and perhaps some
severe weather to kick off this weekend.

Primary Forecast Concerns/Challenges:

Addressing heavy rain and severe thunderstorms concerns Saturday
night. Secondary focus on additional shower chances and temperature
trends through next week.

Details:

Heavy rain threat will continue as we head through Saturday night.
Pattern recognition strongly suggests such, with a stalled
baroclinic axis serving as a source of forced deep layer convergence
within an exceptionally moisture rich vertical profile of the
atmosphere (precipitable water values up and over 2 inches across
parts of northern lower Michigan...nearing max potential for
northern Michigan). Persistent low level jet forcing along primary
baroclinic axis/stall warm front will only enhance deep layer
convergence into Saturday evening as weak area of low pressure rides
along the stalled frontal boundary. Efficient warm cloud processes
will enhance rainfall rates, which could easily exceed an inch per
hour a times...with pattern recognition again supporting potential
for training of these heavier rainfall rates. While nearly all of
northern Michigan remains within the slight risk category per latest
WPC excessive rain outlook, current primary target areas based off
deep layer convergence signature suggests areas between M-72 and the
Straits remains the primary focal point. Combine this with the
expected heavy rain on Saturday (see short term section above for
all those good details) and very likely some areas will exceed 2
inches of rain by sunrise Sunday. Wouldn`t be terrible surprised to
see some local areas exceed this amount be quite a bit given
expectations set above.

Secondary concern remains severe potential. While moist adiabatic
lapse rates through nearly the entirety of the column, increased
cyclonic curvature along and south of stalled frontal boundary 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+. Combine this with low lifting
condensation levels and the potential for precipitation loading,
and the stage is set for a low end tornado and gusty wind threat.
Again, this remains a secondary concern...taking a back seat to the
heavy rain potential.

Honestly speaking...not a lot of time devoted to the rest of the
extended forecast. More northern stream influence for sure, voiding
our area of any more periods of prolonged heat. Passing waves within
what looks to be a rather energetic/active flow regime should brings
the threat for showers and thunderstorms at times. Exact timing of
any individual waves subject to change of course.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 146 PM EDT Fri Jun 21 2024

MVFR to IFR CIGs remain in place this afternoon for portions of
the area, which will likely linger into this afternoon for
some. Chance for TSRA/SHRA this afternoon and evening generally
along and south of M-32, and mainly east of I-75. More RA/TSRA
approaches tonight after about 03Z with MVFR-IFR CIGs and VIS
likely in any steadier precipitation. Main hazards will be very
heavy rainfall, but isolated instances of gusty sfc winds
possible as well.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...Flood Watch from 2 AM EDT Saturday through Sunday morning for
     MIZ016>018-020>030-099.
MARINE...None.

&&

$$

SHORT TERM...JLD
LONG TERM...MSB
AVIATION...JLD