Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 182104
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
404 PM EST Sun Feb 18 2018

.NEAR TERM...(Tonight through Monday)
Issued at 404 PM EST Sun Feb 18 2018

...Some light snow across the UP tonight...then increasing chances
of mixed precip and rain on Monday...

High Impact Weather Potential...Increasing chances of mixed
precip...especially across Eastern Upper Michigan...possibly causing
some difficult travel.

Pattern Synopsis/Forecast...Strong surface high is pushing east out
of the Ohio Valley toward the Mid Atlantic coast this afternoon...
with the surface ridge axis now located just east of Michigan.
Complex area of low pressure continues to develop to the lee of the
Rockies over the Northern and Central Plains. Elongated area of
synoptic snow continues to develop north and east of this
system...the eastern edge of which is now entering northern sections
of our CWA as expected. The rest of our CWA remains dry but mainly
cloudy with temps in the low to mid 30s.

As we head into tonight...all precip chances will remain confined to
the Upper Peninsula in the vcnty of the warm front and associated
area of enhanced moisture/lift. New snow amounts will be minor given
limited QPF...with only an inch or two of accumulation expected and
mainly for NW Chippewa county closer to the better moisture and
lift. Still appears virtually all of Northern Lower Michigan will
remain dry all night as dry low level air remains the rule.
Strengthening low level winds and mainly cloudy skies should hold
temps mainly in the lower 30s tonight.

Upstream inverted trough axis will lean into our CWA on Monday.
Better low level moisture will surge into Michigan along this
feature...resulting in increasing low level clouds and increasing
chances of precip. Still appears precip will be relatively light
during the morning hours...i.e. drizzle/freezing drizzle/light snow
as the low level moistening process takes place. Some locations
across the northern half of our CWA may see a few slick spots during
the morning where freezing drizzle occurs. However...chances of
measurable freezing rain will increase during the afternoon across
Eastern Upper Michigan as deeper moisture arrives...the warm nose
become more pronounced and surface temps hold right around freezing
or so. In coordination with MQT...will issue a Winter Wx Advisory
for Eastern Upper Michigan beginning at 21Z for the potential of
some light ice accumulations across Chippewa and Mackinac counties.
The rest of our CWA will see the development of primarily
widespread rain during the afternoon as temps warm into the upper
30s to lower 40s.

&&

.SHORT TERM...(Monday night through Wednesday)
Issued at 404 PM EST Sun Feb 18 2018

...Freezing rain with significant icing possible in some areas...

High Impact Weather Potential...Significant icing possible along
north of M-32, especially across eastern Upper.

Pattern Synopsis/Forecast...A very tight thermal gradient will set
up over northern Michigan Monday night through Tuesday night, with a
quasi-stationary front laid out along the boundary within an
inverted surface trough. A strong warm conveyor belt will interact
with an open Gulf of Mexico to transport a rich supply of moisture
up into the Great Lakes region. Ensembles continue to indicate very
high PWATs of 3 to 5 standard deviations above the mean for late
February here in northern Michigan, perhaps even approaching +6
sigma down near Saginaw Bay. Deterministic guidance continues to
suggest PWs in excess of 1 inch across most of northern Lower
heading into Tuesday, which would be a very rare occurrence for us
given APX`s sounding climatology shows only one other historical
instance of PWs >= 1 inch here in February. Northern Michigan will
see strong isentropic lift along with occasional rounds of fgen and
a glancing blow from the nose of a robust low level jet. Eventually
a bonefide surface low looks to eject from the lee of the Rockies,
riding northeast along the frontal boundary into the Upper Great
Lakes by Tuesday afternoon. Precipitation throughout this entire
event looks to come in waves, with some lulls possible at times
across mainly the northern half of the forecast area. But with
northeast winds supplying a feed of colder air near the surface
north of the boundary, there could be some impactful wintry
precipitation across our north with significant rainfall across our
south. The system looks to depart quickly Tuesday night with high
pressure and a much drier airmass in its wake for Wednesday.

Primary Forecast Concerns...QPF trends, precipitation types, and
ice amounts.

Deterministic and ensemble guidance seems to be trending towards
somewhat of a drier lull developing north of M-68 late Monday night
through Tuesday morning with more prolonged, steadier precipitation
farther south over northern Lower. This could impact potential ice
amounts across our north, especially since models suggest the lull
would begin during some of the prime overnight ice accretion hours.
Ice accretion would not be so efficient during the daytime hours
given a stronger late-February sun angle and temperatures gradually
climbing above freezing from south to north. Regardless, storm total
QPF from Monday afternoon through Tuesday night looks to run around
1 to 1.75 inches south of M-72 (highest near Saginaw Bay) with
decreasing amounts farther north to around 0.4 to 0.5 inches across
eastern Upper.

Pretty much just rain expected for the duration of the event roughly
south of M-32 where temperatures will largely remain above freezing.
Between M-32 and the Straits, freezing rain is expected to be the
predominant ptype through Tuesday morning, perhaps mixed with a bit
of sleet at times. By afternoon, surface temperatures will climb
above freezing, heading for highs across the Tip of the Mitt in the
40s. By the time temperatures fall below freezing there Tuesday
night, precip will be rapidly tapering off with perhaps a brief
period of light drizzle or freezing drizzle. And across eastern
Upper, freezing rain looks to also be the predominant ptype, mixed
with a bit of snow and sleet at times. The aforementioned lull in
precip up there may be a period of freezing drizzle late Mon night
into Tue morning. Eastern portions of Chip/Mack counties may warm
into the mid 30s by Tue evening, perhaps leading to mainly rain
there for a few hours before transitioning back to a period of
freezing rain overnight.

Ice amounts are still far from certain, depending on how the low
level thermal profiles play out and the possible lull in
precipitation across the north. Gridded forecast reflects the
possibility of 0.1 to 0.2" of ice between M-32 and the Bridge with
up to 0.3" or more possible across eastern Upper. However, it is
/VERY/ important to stress that those are storm total ice
accumulations, and we are expecting to see a couple rounds of
freezing rain with the potential for some melting in between on
Tuesday. Considering the warming daytime temperatures, stronger sun
angle, and possible lull in precip across the north, not expecting
eastern Upper to see 0.3" or more of ice accumulation all at once.
Hopefully the first round will melt a good amount before the second
round develops. At any rate, do anticipate potential damage to trees
and power lines leading to power outages, especially across eastern
Upper.

Strictly considering storm total ice accumulations would suggest the
need for perhaps an ice storm warning across eastern Upper, but
because of the reasoning above and the fact that the ice accretion
will be spread out over a prolonged period of time, have decided to
just issue a winter weather advisory to get the word out. Also
included Charlevoix, Emmet, Cheboygan, and Presque Isle counties.
Could see the need to perhaps expand another tier of counties
farther south, but will leave that to later shifts to determine.

Finally, not to be overlooked is the potential for significant
rainfall south of M-72, especially towards Saginaw Bay where storm
totals could easily reach in excess of 1.5 inches. More of a light
to moderate steady rainfall over a prolonged period of time, so not
necessarily worried about significant flooding potential at this
time. There will be rises on area streams and creeks, though.

&&

.LONG TERM...(Wednesday night through Sunday)
Issued at 404 PM EST Sun Feb 18 2018

High pressure and quiet weather is expected to start the extended,
with things a bit more muddled going into the weekend. Temperatures
will remain above normal as deep troughing persists in the west and
somewhat low amplitude ridging remains over the eastern CONUS.
Expect temperatures to warm slowly through the period, with low 30s
Thursday warming into the upper 30s and low 40s by the weekend.
There will be a couple of systems to watch for weekend precip
potential, though currently the better forcing and moisture look to
remain to our south. Expect some adjustments to the track in the
coming days, and it won`t take much of a northward shift to affect
our forecast area.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1217 PM EST Sun Feb 18 2018

Mainly VFR conditions are expected at all Northern Lower Michigan
TAF sites this afternoon and much of tonight. Conditions will
deteriorate to MVFR/possibly IFR very late tonight into Monday as
ample low level moisture surges northward into Michigan ahead of
a complex area of low pressure developing over the Central Plains
and Mid Mississippi Valley. There is a chance of a mixture of
light drizzle/freezing drizzle/snow after 12Z Monday...which will
handle with VCSH for now. Southerly surface winds will strengthen
to 15 to 25 kts by this evening...with LLWS also developing. South
winds will weaken to 10 kts or less on Monday.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY from 4 PM Monday to 1 AM EST Wednesday
for MIZ008-015.

WINTER WEATHER ADVISORY from 7 PM Monday to 1 PM EST Tuesday for
MIZ016>019.

&&

$$

NEAR TERM...MR
SHORT TERM...MK
LONG TERM...AM
AVIATION...MR


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