304
FXUS63 KAPX 161343
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
943 AM EDT Fri Aug 16 2024

.KEY MESSAGES...

- Showers and a few thunderstorms today and tonight. A few
  strong storms with locally heavy rain are possible.

- Showers and thunderstorms through the weekend, locally heavy
  rain the primary concern.

&&

.UPDATE...
Issued at 943 AM EDT Fri Aug 16 2024

1005mb surface low in central MN. An occluded/cold front is
progressing east across central/southern Lake MI. A secondary
boundary is back in sw WI and ne/central IA. Return flow is
supporting showers/storms in MI, with one cluster in eastern
upper MI, and a larger one in central lower. A small but growing
cluster is over central Lake MI, with increasing deep convection
w of MKG. Skies are overcast here, but partial sunshine is
upstream in parts of central/eastern WI.

We will continue to support spotty showers/storms into tonight.
The stacked low will continue to head our direction, which will
help steepen lapse rates tonight even after today`s diurnal
heating is gone.

Our ability to see strong/severe convection is dependent on the
sun coming out and aiding surface destabilization. That is far
from certain here. Mesoscale models (recent HRRR/Rap runs) allow
for more than 1500j/kg to develop today...but with a bullseye
in w central lower MI, just south of this forecast area. The
ongoing activity w of MKG will reinforce cloud cover and rain-
cooled surface air, with some development northward into nw
lower MI expect late this morning and even early afternoon. Can
the sun blast thru behind that? If so, then yes a severe threat
can be realized later on. It`s easier to see that threat in
eastern WI today than is it here...at least so far.

But guidance max temps have if anything trended cooler for
today, and have lowered a tiny bit.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 220 AM EDT Fri Aug 16 2024

Pattern Synopsis/Pattern Forecast:

A period of change across the Northwoods early this morning, driven
by exit of sharp mid level ridge and approach of rather vigorous
shortwave trough/mid level low pressure. Intial surge of isentropic
upglide/deep layer moisture advection on heels of modest low level
jet spreading northeast across the region, kicking off a band of
mostly light showers in the process. Deeper buoyancy plume and axis
of more respectable lapse rates lurking just upstream, as evident by
deeper convection and even some thunder working into the western
Great Lakes.

Story over the next several days will be the approach and slow
passage of that upstream wave and attendant weak surface low.
Increasing mid level support/gradually cooling mid level
temperatures and pockets of enhanced deep layer convergence...all
within a respectable moisture rich vertical environment...sets the
stage for some periods of wet, and potentially stormy, weather today
through the weekend.

Primary Forecast Concerns:

Shower and storm evolution through tonight. Low end severe storm
potential and localized heavy rain threat will also need to be
addressed.

Details:

Definitely a bit of a challenging forecast with regards to shower
evolution both today and tonight. Using simple extrapolation and
pattern recognition as a starting point, would expect additional
showers and a few embedded non-severe storms to rotate northeast
across the area early this morning along leading edge of buoyancy
and elevated lapse rate gradient. Forcing becomes much more
negligible for a period thereafter, supporting just some scattered
activity for most of the day as low level instability materializes
(if we can scatter out some of the cloud cover). Better threat for
showers and storms returns tonight as low level convergence
increases with slow passage of surface low.

Severe Threat: Limited at best as better shear for more organized
storms now looks to pass off to our south. However, the chance is a
non-zero one, especially if we can muster some decent clearing later
this morning and afternoon. Perusal of convective allowing guidance
soundings do at least support this potential, with some advertising
in excess of 1.0K Joules/kg of mixed layer cape this afternoon. If
that does indeed occur, could definitely see a bit more upscale
convective growth/storm organization and the potential for some
isolated severe wind gusts (perhaps wet micro-burst potential?).
Latest SPC Day One Convective Outlook continues the southward
adjustment on marginal severe storm potential...now focused
primarily south of M-55.

Heavy Rain: Precipitable water values near and in excess of 1.50
inches definitely supports some heavy rain concerns...while expected
lack of better storm organization and more persistent areas of
focused low level convergence argues otherwise. Expect we will
see some localized areas of heavy rain...likely well in excess
of an inch...where storms repeat and along any yet to be
determined areas of enhanced low level convergence. Pattern
definitely does not support any widespread heavy rain
concerns...as evident in the utilization of just marginal
excessive rain wording in the latest WPC outlook.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 220 AM EDT Fri Aug 16 2024

Pattern Synopsis and Forecast:

Upper low dives across central Michigan on Saturday, with 850 mb low
following suit. Lots of lift expected throughout Saturday, with a
corridor favoring the south-southeast portions of the northern lower
(in the vicinity/to the north of the 500/850 mb low) although a good
chunk of the area will have a pretty good chance to see showers and
storms. Meanwhile, sfc and column remains very moist as PWs in the
vicinity of ~1.5"+. Long, skinny, weak CAPEs on Saturday coupled
with the lift from the upper low will kick off plenty of showers,
and embedded convection. Will likely be some very efficient
rainfall, and potentially heavy if any more robust thunderstorms
develop given the column saturation. No severe threat as winds aloft
will be erratic and weak, and instability will be weak. Thus, the
main concern will be locally heavy rainfall. Will be lingering
showers on Sunday as moisture and perhaps a bit of meager
instability remains, as the upper low takes its time to depart to
the east. That being said, by the end of the day and into the
overnight, sfc moisture will be on the decrease, a sign of more
pleasant conditions.

High and dry by the early to middle portions of next week as a
refreshing airmass settles into the region. Dewpoints tank amidst
deep north to northwesterly flow reinforced by troughing in Quebec,
with picture perfect weather expected (Monday-Tuesday will be in the
low 70s with no humidity). No signs of any significant weather
systems for the end of next week with temperatures remaining in the
70s.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 612 AM EDT Fri Aug 16 2024

MVFR to IFR cigs/visibilities this morning, with some
improvement possible this afternoon as diurnal trends attempt to
raise cig heights some. Another round of lower cigs and fog/mist
expected to spread back into the area tonight. Scattered showers
and perhaps a rumble of thunder will impact the region through
tonight, with any showers bringing the potential for brief
periods of heavy rain and some gusty winds. Otherwise, no
significant wind concerns through the period.

&&

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

&&

$$

UPDATE...JZ
SHORT TERM...MSB
LONG TERM...JLD
AVIATION...MSB