159
FXUS63 KAPX 050345
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1145 PM EDT Fri Oct 4 2024

.KEY MESSAGES...

- Frost potential tonight across interior northern Lower.

- Gusty winds developing Saturday.

- Cold frontal passage brings an increase in winds accompanied by
  shower and thunderstorm chances Saturday night into Sunday.
  Some thunderstorms may contain locally stronger wind gusts.

- Lingering lake effect rain showers Sunday through Tuesday before
  dry conditions return, along with abnormal warmth later in
  the week.

&&

.UPDATE...
Issued at 951 PM EDT Fri Oct 4 2024

Mostly clear skies and light/calm winds remain the rule across
our entire CWA late this evening as strong high pressure holds
over the Western Great Lakes. Temps are falling thru the 40s on
their way down to the 30s across much of our area. Will
certainly maintain all Frost Advisory headlines across most of
Northern Lower Michigan where low temps in the low to mid 30s
will be the rule.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 312 PM EDT Fri Oct 4 2024

Pattern Synopsis/Forecast: Clouds have thinned nicely this afternoon
across most of northern Michigan as drier air gets mixed into the
boundary layer.  Still some more persistent Sc along the St. Mary`s
River and around the Lake Huron shoreline counties of northern Lower
Michigan.

High pressure centered over northern Wisconsin at 18z will slide
into Lower Michigan this evening...accompanied by mid level short
wave ridging...the axis of which will lie across the upper Lakes by
Saturday morning.  A strong short wave trough moving onshore over
the Pacific Northwest this afternoon will move quickly across the
northern Rockies overnight and through the northern Plains Saturday.
Surface high will give way Saturday afternoon as height falls
associated with the short wave trough reach Lower Michigan.

Primary Forecast Concerns:

Frost potential tonight across interior northern Lower: Mostly
clear skies (outside of a bit of Ci this evening)...light winds
with a flat pressure gradient...and dew points coming down into
the 30s allowing for some "room" expected to result in a good
radiational cooling night. Usual cold spots (Manistee/Au Sable
River valleys...the Pellston ice box) will see temperatures fall
into the lower-mid 30s). Used a blend of NBM 50th percentile
minimum temperatures (which are a good bit colder than the
actual minimum temperature forecast). Have covered the resulting
frost threat with a Frost Advisory along most of the M-55
corridor and the northeast toward Presque Isle county.

Gusty winds developing Saturday: Pressure gradient tightens up
Saturday afternoon between departing surface high and the
approaching cold front as it works its way across the upper
Mississippi Valley. 20-30kts southerly flow into the mixed layer
during the afternoon should bring about gusts in the 25-30mph
range across eastern Upper and along/west of the US-27 corridor
in northern Lower.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 312 PM EDT Fri Oct 4 2024

Pattern Synopsis / Forecast:

Sharp shortwave trough will pass through the region Saturday night
into Sunday, forcing attendant cold frontal boundary through the
region. Impressive 850mb jet will provide moisture intrusion aloft,
and with modestly steep lapse rates, likely leads to some elevated
showers and storms Saturday night. In the wake of this frontal
boundary, this shortwave will largely phase with a much deeper
trough over Quebec, resulting in a longwave trough developing over
the northeastern CONUS and into Atlantic Canada, while ridging
amplifies over the western and central CONUS. This leaves northern
Michigan in between these features, and with non-zero synoptic
moisture in the wake of the cold frontal passage, any embedded
shortwaves pivoting around the longwave may be just enough to spark
some minor shower activity into early next week before
aforementioned ridging regime builds eastward into the area,
returning drier weather and above normal warmth to the region.

Primary Forecast Concerns:

Saturday Night Cold Frontal Passage: Certainly an impressive cold
frontal passage from a dynamics standpoint is on the docket for
Saturday night. Weakening 990-995mb surface low over Ontario will
still be interacting with a 1020mb high pressure in the
Appalachians, bringing quite the pinched pressure gradient over
northern Michigan. Result will be increasing SW to SSW winds
Saturday evening into the overnight hours... and a surge of warm and
moist air aloft. Fortunately, this should bring about a pretty steep
inversion in the low levels, which should prevent most of, if not,
all of the absolutely rippin` flow aloft from mixing to the surface.
Impressive wind parameters nonetheless, with 925mb and 850mb flow
progged at 50kts and 70kts respectively right ahead of the cold
frontal boundary. This should translate to a steadier wind at the
surface, probably in the order of 20-25mph sustained winds, and a
few 35-40mph gusts (highest in both NW lower MI and western Mackinac
county near Lake Michigan thanks to that long overlake fetch).
Instability will be heavily dependent on how much moisture can be
transported at 850mb, and how steep lapse rates aloft remain. Latest
trends on guidance showcase enough cooperation between these two
features to drum up anywhere from 500-1,000 J/kg of instability
aloft, which would be more than enough to support convective shower
development, along with some storms. Coverage will spread from west
to east, with a quick SSW to NNE storm motion. Concerns do arise
with the potential for some stronger gusts to materialize in any
convection given the aforementioned rippin` flow aloft, but given
the expected continuity of the inversion, this potential may too be
limited. Will have to watch closely, as the difference between
mostly sub-severe gusts happening and potentially severe (50kt+)
gusts is pretty thin. In addition, with the ample 850mb winds
stretching out shear profiles, it wouldn`t be overly surprising to
see any robust updrafts produce some hail. At this time, the Storm
Prediction Center`s Day 2 outlook keeps a Marginal Risk (1/5) west
of our area, but that may change in future outlooks.

Sunday into Next Week: Post-frontal airmass will be slightly cooler,
and with some lingering synoptic moisture and vort maxima pivoting
around the longwave trough to the east, windows for some isolated
shower activity may arise Sunday through Tuesday, particularly in
the eastern Yoop where the colder 850mb temps (-1C) and better
synoptic moisture will reside to contribute to lake effect
instability. As such, slight chance and chance PoPs remain in order,
with the highest values across the eastern Yoop. Sunday will be on
the breezy side, with sustained W to NW winds probably peaking 15-
20mph, with some 30-35mph gusts as cold air advection materializes.
Winds will taper some as we progress through the week. Otherwise,
conditions turn dry CWA-wide as ridging / surface high pressure
builds in Wednesday and beyond. Highs Sunday in the 60s and 70s
before the colder air really settles in, knocking highs back into
the mid 50s to mid 60s Monday and Tuesday. More well above normal
warmth builds later in the week as ridging returns, with highs
possibly reaching back into the 70s by the end of the forecast
period. Lows Saturday night in the 50s, possibly near 60 near Lake
Michigan, falling to the 30s and 40s for much of the remainder of
the forecast period, with some additional potential for frost.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1145 PM EDT Fri Oct 4 2024

Large area of strong high pressure currently centered over the
Western Great Lakes will slowly drift eastward into the Eastern
Great Lakes over the next 24 hours. Aside from some patchy fog
overnight...prevailing conditions will remain VFR thru early
Saturday evening thanks to strong subsidence and dry air thru
the column. Wx will change quickly by late Saturday evening as a
line of convection begins to impact Northern Michigan along and
ahead of a strong cold front. Conditions will begin to
deteriorate to MVFR during late evening as this convection
begins to impact Eastern Upper and NW/North Central Lower
Michigan by around 03Z. LLWS will develop ahead of the
approaching cold front Saturday night. Light/calm surface winds
overnight will become SE and strengthen to 10 to 20 kts by
Saturday afternoon with some higher gusts possible...and then
further strengthen to 15 to 25 kts with higher gusts by late
Saturday evening.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...Frost Advisory until 8 AM EDT Saturday for MIZ017-018-022>024-
     027>036-041.
MARINE...Gale Watch from Saturday evening through late Saturday night
     for LHZ345.
     Gale Watch from Saturday evening through Sunday morning for
     LHZ346.
     Gale Watch from Saturday evening through Sunday morning for
     LHZ347>349.
     Gale Watch from Saturday evening through late Saturday night
     for LMZ323-341-342-344>346.
     Gale Watch from Saturday evening through late Saturday night
     for LSZ321.
     Gale Watch from Saturday evening through Sunday morning for
     LSZ322.

&&

$$

UPDATE...MLR
SHORT TERM...JPB
LONG TERM...HAD
AVIATION...MLR