-- Discussion containing changed information from previous version are highlighted. --
659
FXUS63 KAPX 100345
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1145 PM EDT Thu May 9 2024

.KEY MESSAGES...

- Potential for localized instances of frost tonight,
  particularly in the Au Sable River Valley.

- Rain showers & shallow convection Saturday, patchy frost
  possible into the nighttime hours.

- Showers (thunder?) Sunday into early next week, warmer too.

&&

.UPDATE...
Issued at 1001 PM EDT Thu May 9 2024

Remnants of Ontario diurnally-driven cumulus in the process of
dropping south into the area this evening...this as our own
earlier diurnally-driven cu drop south out of the area. Expect
pockets of clouds to continue overnight. Have raised
temperatures a touch, but still thinking some frost is possible
in our traditional ice-box locations.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 300 PM EDT Thu May 9 2024

Pattern Synopsis / Forecast: Current water vapor imagery tells the
tale of the upper pattern: a midlevel shortwave trough moving
through the southern Great Lakes, all the while residual forcing is
slowly advancing through the upper Great Lakes. Surface high
pressure over Hudson Bay has been making an attempt to scour out low
level moisture, but mixing processes have been slow to commence,
resulting in more diurnal cumulus coverage across the region. Enough
lingering moisture will allow for the continuity of diurnally driven
showers near and south of Grand Traverse Bay through 00z before loss
of daytime heating erodes instability. Upper winds flip north
tonight, making an attempt to disperse cloud cover across the
region, but also advecting lingering mid level moisture currently
over Ontario into northern Michigan. As winds decouple and pockets
of clearing move overhead, some efficient diurnal cooling may
materialize overnight.

We find ourselves sandwiched between an approaching shortwave
tomorrow and the departing wave tomorrow. Light winds as the
influences of high pressure remain should allow for lake breezes to
commence owing to differential heating, with enough moisture
potential for some diurnal cumulus to produce an isolated sprinkle
or shower across the eastern U.P. and northeast lower.

Primary Forecast Concerns:

Potential for frost tonight is a murky forecast based off tricky
cloud trends. Decoupling of winds is expected, but current analysis
shows numerous areas continuing to hold dewpoints in the 40s across
northern lower Michigan. Expectation is that clearer skies build
across the region with upper winds flipping north, but returning
cloud cover from Ontario looks to build across the eastern U.P. and
portions of northeast lower. In theory, any local clear spots
tonight should allow for a localized drop in temperatures,
especially across the interior of northern lower Michigan. In
addition, the brief instances of how long temperatures remain below
36F may not allow for frost conditions to fully develop. Lots of
uncertainty and lack of confidence in a widespread frost has kept
the necessity of issuing a frost advisory across northern lower
Michigan at bay for the time being. Will handle this with a Special
Weather Statement mentioning potential for localized instances of
patchy frost across interior northern lower Michigan, with the best
shot of frost favoring the Au Sable River Valley. Low temperatures
tonight in the mid 30s to lower 40s, with perhaps a typical interior
cold spot approaching 32 degrees.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 300 PM EDT Thu May 9 2024

Pattern Synopsis and Forecast:

Vigorous, quick moving upper low will travel to the southeast into
Michigan Friday night into Saturday resulting in rain
showers/shallow convection. Low pressure to the north in Canada will
force a sfc boundary into northern Michigan Sunday into Monday with
more showery activity. Sfc feature will looks to shift to the south
of the region mid next week, and in addition to zonal flow/height
rises mid next week, a brief break in activity looks possible.
Another upper system influences the region in some way late next
week.

Primary Forecast Concerns:

Vigorous upper low and cold pool aloft dives into Michigan Friday
night into Saturday. Consequently, rain showers will be possible
Friday night into Saturday. Will likely be steep enough lapse
rates/minor enough instability in the mid levels to facilitate some
shallow convection/isolated storms, especially Saturday afternoon.
Slightly cooler airmass settles in during the nighttime hours
Saturday night. Winds will largely become light and there is a
chance for skies to be more clear than not, thus temperatures may
drop into the mid 30s, facilitating patchy areas of frost. This will
be for mainly the interior/higher terrain & notoriously cold valley
locations.

Sfc boundary approaches northern Michigan Sunday into Monday as a
low pressure system passes well to the north in Canada. Looks like
there may be some hints of instability hanging around during this
time which would result in some embedded/isolated thunderstorms
within the broader showery region (but a little uncertain at this
time). Depending on exactly how the sfc low/feature progresses,
showers could remain into the afternoon hours as well. Boundary
likely pushes south into mid week resulting in a break in the action
and quiet weather. During this time period (Sunday into next week)
temperatures will rise into the mid 60s to low 70s across interior
northern lower. Looks unsettled thereafter late next week based on
current model guidance.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
-- Changed Discussion --
Issued at 1143 PM EDT Thu May 9 2024

Only concern is MVFR to IFR producing fog/br and low clouds
impacting KMBL early this morning. Otherwise, VFR conditions
will continue under just some passing higher level clouds and
relatively high based cumulus. Light winds will local lake
breeze development expected this afternoon.
-- End Changed Discussion --

&&

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

&&

$$

UPDATE...MSB
SHORT TERM...HAD
LONG TERM...JLD
AVIATION...MSB/HAD