Area Forecast Discussion
Issued by NWS Gaylord, MI

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000
FXUS63 KAPX 170202
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
902 PM EST Thu Nov 16 2017

.UPDATE...
Issued at 902 PM EST Thu Nov 16 2017

Late in the day, a hole opened up in the lake-induced stratocu
deck over far northern lower and extreme eastern upper MI. That
hole has been very slow to expand this evening, but finally in the
past hour a bit more of ne lower MI has opened up. Meanwhile,
surface high pressure is edging into western sections of the
forecast area. As that moves east, it will not be long before
southerly sub-850mb winds on the back side of the high drag push
thicker low clouds back north. And to some degree, that`s all
academic anyway, as mid- and high- clouds will be thickening from
the west overnight as warm advection aloft increases.

However, one impact of the above is that min temps in most places
seem unlikely to get as cool as earlier progged. There are some
exceptions (Kinross in eastern upper already down to 21f), but min
temps will be boosted in nw lower MI.

&&

.NEAR TERM...(Tonight through Friday)
Issued at 318 PM EST Thu Nov 16 2017

...Another round of precipitation arrives on Friday...

High Impact Weather Potential...Minimal, though a few wind gusts on
Friday may marginally approach gale force over a portion of Lake
Michigan and Whitefish Bay.

Pattern Synopsis/Forecast...Pronounced push of drier air evident on
water vapor imagery continues to advect into northern Michigan this
afternoon as a surface Canadian high slides eastward across the
region. This was bringing an end to lingering lake effect showers as
the column gradually dries out from top down and winds become more
northerly. Heading into this evening and overnight, that surface
high will slide overhead as will associated ridging aloft, leading
to warm air and moisture advection on Friday as southerly return
flow develops. Strengthening isentropic lift and some mid level
energy will gradually spread showers across the northern and western
portions of the forecast area through the day on Friday.

Primary Forecast Concerns...Low temperatures tonight and time of
arrival of precipitation on Friday.

Low stratocu across the Great Lakes has been holding on rather
stubbornly this afternoon, even though models are more optimistic at
scouring the clouds out some as ridging and drier air move overhead.
Tonight`s cloud cover will have a big impact on how low temperatures
drop, so will have to monitor trends closely. As of now, thinking
there will be at least partial clearing, mainly east of the I-75
corridor, especially as the high moves overhead. Any clearing will
support efficient radiational cooling, especially over those areas
that saw a bit of lake effect snow accumulation since last night.
Forecast calls for lows on either side of 20 degrees for most of
eastern Upper and interior northern Lower, slightly warmer along the
coasts. If clouds hold together more than currently expected, may
need to nudge forecast lows up a bit higher.

Low level jet will slide across northern Michigan on Friday, with
warm air advection allowing for another somewhat gusty day and
leading to a progressive increase in deep layer moisture. PWATs will
climb from around 0.25" initially to around 0.8" by Friday evening.
Increasing isentropic ascent will spread northeast across the area
late tonight into early Friday, bringing an increase in mid/high
level clouds and triggering some showers just upstream. Those
showers are expected to begin overspreading eastern Upper around or
shortly after daybreak, staying focused generally north of the
Straits through the morning hours. That may light up the radar with
plenty of echoes, but forecast soundings show a pronounced dry layer
just above the boundary layer that will take some time to saturate
from top down before precipitation can eventually make it to the
surface. Showers look to hold off across most of northern Lower
until mid to late afternoon as the LLJ and better mid level support
slide into the area.

Despite that initial dry layer and lack of ice in lower clouds,
seeder-feeder processes are expected to compensate, allowing for a
chance of snow initially as showers overspread eastern Upper and the
higher elevations of interior northern Lower. As warm air advection
ramps up during the day, low level thermal profiles will support a
transition to mainly rain or perhaps a rain/snow mix in some colder
spots. Up to an inch of snow accumulation possible across eastern
Upper. Highs Friday will range from the mid 30s across eastern Upper
and interior northern Lower, closer to 40 along the shores.

&&

.SHORT TERM...(Friday night through Sunday)
Issued at 318 PM EST Thu Nov 16 2017

...Rain transitions to snow this weekend...

High Impact Weather Potential: Gusty winds will develop Saturday and
persist through Sunday night. Rain will transition to snow Saturday,
with a round of lake effect snow Sunday.

Pattern Forecast: A weak cold front attendant to low pressure in
Hudson Bay and low pressure passing through southern Michigan will
move through the region Saturday. A large area of high pressure
spanning from the Plains into southern Canada will be following
close behind, helping to reinforce the cold northwesterly flow
behind the departing low. This cold, northern airmass will push
the high pressure south, with the northern periphery passing
through the region Sunday night/Monday. This will bring another
brief period of warm advection early next week.

Primary Forecast Concerns/Challenges: Timing of changeover from rain
to snow Saturday. Magnitude of lake effect Sunday, especially
concerning persistence of flow and collocation of lift with the DGZ.

Saturday looks to start off rainy, with strong moisture advection
ahead of the approaching low, with currently progged PWATS around
0.8", a bit anomalous for this time of year and above the 90th
percentile. Higher values can be found from central Michigan south,
so a northward shift of this low could bring more moisture.
Transition from rain to snow looks to begin in the afternoon for
areas in the U.P. and higher elevations in northern lower, changing
over for the rest of the area throughout the night. This changeover
will take place after the bulk of the enhanced moisture has moved
off, with some of the earlier transitioning areas possibly picking
up a few inches of snow. Will need to keep an eye on the possibility
of some freezing drizzle Saturday night as the deep moisture strips
out, and ice nucleation could be lost. Will keep with rain/snow in
the grids for now and see how model soundings evolve tomorrow. With
high pressure close behind the departing low, a tightening pressure
gradient and a cold advection regime will bring some gusty winds
Saturday afternoon. Expect to see winds lowering through the day
Sunday as the gradient relaxes, but small craft criteria could
remain over the waters into the overnight hours Sunday.

Attention will then turn to the lake effect potential Sunday. Delta
Ts in the neighborhood of 20C will  be over Lake Michigan through
most of the day Sunday. So instability will certainly be sufficient.
Still some questions with persistence in the flow. There is pretty
good agreement in the guidance that the flow will slowly back from
Northerly to Westerly from 0Z Sun to 0Z Mon. This will be
detrimental to large accumulations, but if the winds get locked in a
bit more than currently progged those totals could increase. Should
see this lake effect come to an end over night Sunday into early
morning Monday and warm advection again takes over, albeit briefly,
as high pressure slides through the Tennessee Valley.

.LONG TERM...(Sunday night through Thursday)
Issued at 318 PM EST Thu Nov 16 2017

...Another Storm Expected Tuesday...

Sunday night lake effect snow showers will end as an upper ridge
moves into the Great Lakes and surface high pressure sets up across
the SE U.S.  Then a period of rising heights starts Sunday night
through early Tuesday as warm advection on the west side of the high
overspreads MI.

An upper trough moves out of SW Canada then strengthens as it moves
into the northern U.S. Monday night and becomes closed over the
western Great Lakes on Tuesday. The strengthening low will force a
cold front through the region Tuesday with cold advection and lake
effect snow showers on the backside for Wednesday.

Right now, for Thanksgiving it looks like there could be some
scattered precipitation especially on the west side of the area with
temperatures in the 30s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 630 PM EST Thu Nov 16 2017

MVFR cigs lifting this evening.

Lake-induced stratocu is slowly eroding from n to s, as high
pressure moves across Lake MI. This erosion will continue,
resulting in improving cigs this evening. Mid cloud will be
increase overnight into Friday, ahead of our next system. Light
rain and snow is expected to develop in the PLN area Friday
afternoon.

North winds becoming light this evening. Gusty se to s winds
developing Friday.


&&

.MARINE...
Issued at 318 PM EST Thu Nov 16 2017

High pressure building into the region will cause gusty winds
to subside late this afternoon and evening, but it will take a
few additional hours for waves to diminish. Will therefore leave
current small craft advisory untouched for Lake Michigan,
Whitefish Bay, and the St. Marys. Gale force gusts have subsided
over Lake Huron nearshores, so will replace the warning there with
a small craft advisory through later this evening. Otherwise the
high will drift overhead tonight with quiet conditions and
northerly winds shifting to the SE by daybreak. Winds will become
gusty again during the day with some gusts perhaps marginally
approaching gale force over portions of Lake Michigan and
Whitefish Bay. Considered another gale warning, but due to low
confidence in magnitude of wind gusts will leave decision up to
later shift. More rain/snow showers overspreading the area during
the day on Friday.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until 10 PM EST this evening for LHZ347>349.
LM...NONE.
LS...NONE.
&&

$$

UPDATE...JZ
NEAR TERM...MK
SHORT TERM...AM
LONG TERM...KF
AVIATION...JZ
MARINE...MK


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