342
FXUS63 KAPX 211556
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1156 AM EDT Tue May 21 2024

.KEY MESSAGES...

- A strong to severe line of storms is expected late this
  evening/tonight. The primary hazard will be damaging winds,
  with large hail and a tornado or two also possible.

- Pleasant temperatures but with occasional rain chances for
  Memorial Day weekend.

&&

.UPDATE...
Issued at 1143 AM EDT Tue May 21 2024

No huge changes to the forecast for this afternoon with the focus
remaining on tonight. Low clouds have inhibited heating thus
far this morning which should ultimately limit afternoon
instability. Convection currently across Wisconsin should remain
to our west through this afternoon. Continued mixed guidance as
to what the strength of convection will be when it reaches
northern Michigan very late this evening into the overnight
hours. This will continue to be assessed over the next couple of
hours.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 414 AM EDT Tue May 21 2024

Pattern Synopsis:

The weak shortwave and associated cyclone that supported strong
thunderstorms this past evening will continue to work east of the
Great Lakes today as subtle ridging temporarily slides overhead. A
second weak shortwave over the Midwest will progress over the
northern Great Lakes this afternoon and evening ahead of the main
wave ejecting from the Great Plains over the Midwest at that time.
This much stronger wave with coupled upper-level jet dynamics will
punch overhead tonight, providing impressive forcing aloft to
support a sub-990mb cyclone that looks to trek across the Upper
Midwest into Wednesday morning. The attendant warm front draped east
of the cyclone is expected to lift into northern Michigan later this
afternoon/evening as the cold front swings across the state late
tonight/early Wednesday morning.

Forecast Details:

Strong/severe storms this evening/tonight -- Lingering showers will
exit the area this morning, leaving rain-free conditions and
clearing skies for most of northern Michigan into this afternoon.
The primary focus will be the anticipated line of strong to severe
storms set to impact northern Michigan late this evening and
tonight. This line looks to begin as storms forming back across the
Midwest near the Nebraska/Iowa state border this afternoon,
eventually congealing into a line and racing northeast towards the
Great Lakes. A few main points on severe potential:

1.) Uncertain instability -- One main uncertainty later this
evening/tonight will be how much instability will be in place for
expected storms to work with. This will likely be the main
"limiting" factor for storms later today. As storms track northeast
across the Midwest and into the Great Lakes, they`ll encounter an
environment characterized by decreasing instability with eastward
extent and time into tonight -- especially surface-based
instability. Storms will likely have elevated instability to work
with (~500-1,000 J/kg MUCAPE) as they reach the Lake Michigan
shoreline, but will move into an increasingly unfavorable
environment and become further displaced from support aloft as they
work east across the area. While confidence is relatively high in
strong/severe storms across our western counties, confidence
decreases with eastward extent. Most high-res/CAM guidance resolves
considerable weakening of storms as they arrive in the forecast
area, but said guidance notoriously struggles handling these
forecast situations and current confidence is that strong/severe
storms will at least maintain themselves as they move into the
CWA. Future guidance later today should bring higher confidence
in how far east strong/severe storms may be supported.

2.) Expected hazards -- The primary threat with the aforementioned
line of storms today will be damaging wind gusts. Forecast soundings
display impressive wind profiles with 50+ kt winds just off the
surface. Strong low-level shear (35-45 kts 0-1km shear, 40-50 kts 0-
3km shear) combined with relatively steep low-level lapse rates and
dry air near the surface will fuel the damaging wind threat,
especially near the Lake Michigan shoreline. Latest Day 1 SPC
Convective Outlook noses the Enhanced Risk (3/5) into Manistee
county, with a Slight Risk (2/5) outlined for most of northern lower
Michigan to highlight this threat. With aforementioned strong wind
shear, a tornado or two cannot be ruled out for western portions of
the area where surface-based instability may linger into the evening
hours as the line moves onshore, supporting this threat for a short
window of time. However, near-surface stability/dry low-level
airmass is expected to limit a higher threat for tornadoes at this
time. Large hail will also be possible, but comes as a secondary
threat to damaging winds. Most likely timing of severe storms will
be between 11 PM and 4 AM tonight. Be sure to plan ahead and have
multiple ways to receive warnings for severe weather, as this is
especially important for severe weather threats after dark.

Low chances for storms this afternoon -- While confidence is low in
this forecast scenario, there are slight chances for storms to form
along the warm front lifting across the area this afternoon.
Forecast soundings display a favorable environment to support
strong, even severe storms should this occur. Low confidence exists
as forcing for initiation will be weak with the shortwave and main
wave well to our west and relatively dry boundary layer in place.
However, a favorable enough environment supportive of low-end
chances for all severe hazards will be in place to at least mention
this potential at this time. Future forecast updates may remove
mention of this potential, or highlight it further with addition of
expanded severe threat timing in more public-facing products should
afternoon storms become more likely.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 414 AM EDT Tue May 21 2024

Pattern Synopsis / Forecast:

Cutoff 500mb low will slowly be forced eastward by a ridging
response ahead of a Canadian prairie wave through the day on
Wednesday. Dry slotting / strong subsidence within the surface
cyclone associated with the 500mb cutoff should suffice in scouring
out deeper moisture across the board through the day across northern
lower, resulting in more of a partly to mostly sunny day filled with
diurnal cumulus and temps in the 60s and 70s. West wind and
downsloping could bump Lake Huron locales near 80. May be just
enough moisture in the eastern Yoop coupled with closer proximity to
forcing for some diurnally driven showers, though even up there, the
day will be far drier than not. Trough axis pivoting around the low
Wednesday night may be enough to generate a widely scattered shower,
but overall confidence in this is quite low outside the eastern
Yoop. Ridging and high pressure should bring about slowly moderating
temperatures into the weekend, with highs holding more seasonable in
the 60s and 70s for Memorial Day weekend as flow turns more zonal.
Long term guidance paints a quick moving wave passing through Friday
night, which could bring the next appreciable shower chance to the
region. On the heels of this wave, a much deeper shortwave ejecting
into the Plains is set to be forced into the region later in the
holiday weekend, bringing more shower chances to the region.

Primary Forecast Concerns:

Holiday Weekend: All important Memorial Day weekend outlook is
within sight, and it looks like temperature wise, things should be
quite pleasant with highs in the 60s and 70s for most, perhaps in
the 80s across the far southern part of the CWA. That all being
said, there will be some rain chances at times through the weekend.
As of now, the best chances for showers and perhaps some thunder
will be Friday night into Saturday as a quick moving wave passes
through, and again Sunday night into Memorial Day as low pressure
moves into the Great Lakes. Overall, the weekend does not look to be
a washout at this juncture, with ample dry time expected to be had.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 659 AM EDT Tue May 21 2024

FG/BR is expected to linger across parts of northern Michigan for a
few hours this morning before lifting to mainly VFR conditions
through the remainder of the day. A line of storms is expected to
move into western portions of the area late this evening/tonight,
bringing the potential for strong wind gusts -- especially at TAF
sites near Lake Michigan. LLWS will also be possible with 50kt winds
just off the surface. CIGs look to lower behind aforementioned
rain/storms late tonight.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from 10 PM this evening to 8 PM EDT
     Wednesday for LMZ323-341-342-344>346.
     Small Craft Advisory from midnight tonight to 8 PM EDT
     Wednesday for LSZ321-322.

&&

$$

UPDATE...AJS
SHORT TERM...DJC
LONG TERM...HAD
AVIATION...DJC