Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 240113

Area Forecast Discussion
National Weather Service Gaylord MI
913 PM EDT Sun Jul 23 2017

Issued at 910 PM EDT Sun Jul 23 2017

Low pressure has slid east of nrn Michigan and has allowed for
winds to turn northerly everywhere, while also increasing, as the
pressure gradient has tightened up decently (MCD gusting to
29 mph). A corridor of deeper lower level moisture was settled in
over eastern upper and nrn lower roughly along and north of M-32.
Even deeper moisture, working with DPVA, cyclonic flow, weakish
WAA and upslope flow, was resulting in light rains across mainly
eastern Chip/Mack counties and far nrn/NE lower. For the balance
of the night, the sfc low moves quite slow, but these forcing
mechanisms and deeper moisture will gradually drift into mainly
just NE lower by daybreak, while slow clearing develops from the
NW due to invading higher pressure and drier air. The cool
advection sliding in overnight will get lows down to the lower
half of the 50s in eastern upper, to the lower 60s closer to
Saginaw Bay.


.NEAR TERM...(Tonight through Monday)
Issued at 300 PM EDT Sun Jul 23 2017

...Thunderstorms...possibly severe...into early evening...

High Impact Weather Potential...Marginal chance of severe storms
south of the Straits with a slight risk SE of a line from APN to

Pattern Synopsis/Forecast...Surface low is centered over the Straits
area...with the upper level low close behind. Deep cyclonic flow and
strong upper level divergence just ahead of the upper low continue
to generate widespread convection over Eastern Upper Michigan and
the tip of the Mitt. Radar estimates that rainfall amounts of 2 to
2.5 inches have fallen over portions of Mackinac county throughout
the day...which fall short of 6 hr FFG by over an inch. Rainfall
intensities have dropped over the past couple of hours...and overall
trend of echoes is slowly eastward out of that area. Attention now
turns to the south over Northern Lower Michigan and the potential
for stronger/severe storms later this afternoon and evening as the
upper level trough axis pivots thru the area during peak heating/

So cover across our CWA has been fairly extensive
throughout the day...which has limited destabilization. Per latest
SPC mesoanalysis...MUCAPES across our area attm are around 1000
J/kg...with the instability axis now over NE Lower Michigan...which
lines up well with the latest SPC Day 1 outlook for slight risk over
our SE CWA. 0-3 km bulk shear values remain around 30 kts and NAM is
still projecting MUCAPES reaching near 2000 J/kg in our SE CWA by
late afternoon. Expect ongoing storms will increase in areal
coverage and intensity as they reach our SE CWA over the next few
hours...with a few storms possibly reaching severe limits. Damaging
winds and large hail will be the primary threats.

Thunder threat should end across our entire CWA by late  evening...
but lingering low level moisture and deep cyclonic flow will keep
precip chances in the forecast overnight into Monday morning.
Highest POPs will be across our eastern CWA and taper off to the
west. Strong high pressure and dry low level air will build into the
region Monday...resulting in decreasing clouds from NW to SE...
decreasing humidities and cooler temps.

Low temps tonight will cool into the mid 50s to around 60 degrees.
High temps on Monday will warm mainly into the lower 70s across our
entire CWA thanks to CAA behind this system.


.SHORT TERM...(Monday night through Wednesday)
Issued at 300 PM EDT Sun Jul 23 2017

...High and dry through Tuesday; thunderstorms return midweek...

High Impact Weather Potential...Thunderstorms possible late Tuesday
night into Wednesday.

Pattern Synopsis/Forecast...High pressure at the surface and aloft
along with a dry airmass sitting over the Upper Great Lakes will
slide off to the east by Tuesday night. Southerly return flow
developing Tuesday night will draw increasing moisture into the
region, aided by a modest 30-40 knot low level jet. PWATs will climb
above 1.5 inches on Wednesday, perhaps approaching 2 inches in some
areas. Increasing isentropic lift and some mid level energy ahead of
an approaching cold front will overspread northern Michigan late
Tuesday night through Wednesday, bringing the next chance of showers
and thunderstorms.

Primary Forecast Concerns...Thunderstorm potential late Tuesday
night into Wednesday will be the main forecast concern. Moisture and
lift will be sufficient, but instability currently looks to be a
limiting factor due to weak low/mid level lapse rates from ongoing
low level warm air advection. Better instability will be found over
WI, with around 500 J/kg or less of MLCAPE over northern MI. Despite
the meager instability, deep layer shear is looking favorable over
our area, especially across eastern Upper. Forecast soundings show
nice low-level clockwise curvature suggestive of good storm
organization and possible rotation...again, conditional on storm
development/intensity given meager instability. SPC is currently
highlighting all of northern Michigan in its Day 4 outlook.
Something to monitor over the next couple quiet-weather days.

.LONG TERM...(Wednesday night through Sunday)
Issued at 300 PM EDT Sun Jul 23 2017

Models continue to be in good agreement with rain ending Thursday
morning as a cold front associated with a low pressure system to the
east of Hudson Bay moves off to the east. High pressure then
builds in behind the departing system. Said high pressure will
provide northern Michigan with rain free weather and mostly sunny to
partly cloudy skies through the weekend. Daytime highs will be in
the upper 70s to low 80s, while lows will drop down into the mid to
upper 50s.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 741 PM EDT Sun Jul 23 2017

Low pressure will slowly work into the eastern Great Lakes over
the TAF period. This low pressure will continue to drag IFR/MVFR
CIGS into all of nrn lower Michigan, which will persist into early
Monday morning. Scattered light showers on the backside of the low
will continue to periodically impact mainly APN. Maybe some brief
VSBY restrictions, but nothing too low is expected. Skies will be
clearing Monday morning across NW lower, then APN/NE lower later
in the day as high pressure and drier air overtake the region.

Winds will be northerly through the period, generally 5 to 15
knots. There may be a little gustiness through this evening as the
pressure gradient tightens up.


Issued at 300 PM EDT Sun Jul 23 2017

Winds and waves will continue to strengthen to SCA criteria for much
of our nearshore area tonight into early Monday as deep low pressure
slowly moves thru Northern Michigan. Showers and thunderstorms will
impact most of our nearshore areas late this afternoon and
tonight...with a few stronger storms possible south of Thunder Bay
thru early evening. High pressure will build in by Monday
afternoon...bringing an end to any linger precip chances.


LH...SMALL CRAFT ADVISORY until 8 AM EDT Monday for LHZ345>347.
     SMALL CRAFT ADVISORY from midnight tonight to 11 AM EDT Monday
     for LHZ348-349.
LM...SMALL CRAFT ADVISORY until 8 AM EDT Monday for LMZ341-342.
LS...SMALL CRAFT ADVISORY until 8 AM EDT Monday for LSZ322.


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