Area Forecast Discussion
Issued by NWS Gaylord, MI

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000
FXUS63 KAPX 220139
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
939 PM EDT Tue Mar 21 2017

.UPDATE...
Issued at 939 PM EDT Tue Mar 21 2017

...Brisk with light snow showers overnight, lots of sunshine for
Wednesday...

Overview: Surface cold front and surge of much colder air dropped
through northern Michigan earlier in the day pushing surface temps
quickly downward this afternoon and dropping H8 temps to a few
degrees either side of -16 C. Cold front is now well south of the
region...now dropping into Ohio. In it`s wake, we managed a
period of more robust lake/surface heating induced cloud cover
along with a some modest snow showers for parts of the CWA into
early evening.

Much of the lake clouds/snow showers have diminished at this
point after losing the diurnal heating component. But...there
remains a narrow corridor of lake clouds and light snow showers
stretching from NW lower Michigan up into eastern Lake Superior on
stout NNW flow...despite some fairly dry air advecting into the
region (surface dewpoints dipping into the single digits and a dry
00Z APX sounding, PW=0.09"). That long fetch and ample over water
instability able to overcome the dry air.

Upstream, large area of high pressure resides across SE Manitoba
this evening, pushing into southwestern Ontario. Strong northerly
dry/cold advection flow will persist across the northern lakes
region for the rest of tonight before the high pressure center
builds overhead for Wednesday. And given the long fetch and cold
airmass, lake clouds and light snow showers will likely persist as
well, although winds will veer more northerly overnight and push
bulk of snow showers/clouds out of eastern upper Michigan and
toward the Lake Michigan shoreline in NW lower Michigan.

Have tweaked pops/sky cover to account for all this pushing clouds
and light snow showers toward Lake Michigan overnight. But given
the dry air, I don`t anticipate much more than light snows and
very minor (if any) accumulations.

Temps should handily dip into the single digits to teens and have
lowered forecast min temps a few degrees from inherited forecast.
And with those gusty winds...it`s quite brisk out there.


&&

.NEAR TERM...(Tonight and Wednesday)
Issued at 323 PM EDT Tue Mar 21 2017

...A few flurries...otherwise quiet and cold...

High Impact Weather Potential...None.

Pattern Synopsis/Forecast...Moisture-starved cold front continues to
push through our CWA this afternoon...serving to reinforce the cold
air across our region and to kick off some scattered snow showers as
well. Latest KMQT and KAPX 88D base ref loops combined with regional
surface obs show indicate some scattered light lake enhanced snow
showers via the cold front and resulting lake enhancement as CAA
kicks in behind the front. Front itself is only providing some weak
lift and very limited moisture...but with lake enhancement...expect
scattered light snow showers will remain the rule into tonight for
NW flow areas despite building subsidence later tonight into
Wednesday as strong Canadian high pressure builds into the Western
Great Lakes region. Expect well under an inch of snow accumulation
for N/NW flow areas thru tonight...as overnight lows fall into the
single digits above zero inland and to the teens along the
lakeshores. Wednesday will be partly to mostly sunny and dry with
temps rebounding into the upper 20s to lower 30s.

&&

.SHORT TERM...(Wednesday night through Friday)
Issued at 323 PM EDT Tue Mar 21 2017

...Freezing rain looking likely Thursday night...

High Impact Weather Potential...There is increasing confidence in a
freezing rain event for most of northern Michigan Thursday night. At
this time, up to a tenth of an inch of ice accumulation is expected.

Pattern Synopsis/Forecast...Strong, sprawling surface high centered
over northern Michigan Wednesday evening will drift southeast
towards the Lower Great Lakes by Thursday morning. Southerly return
flow will lead to developing WAA during the day Thursday, which will
intensify heading into Thursday night as an upper level ridge slides
overhead and a low level jet moves through. Moisture will increase
substantially between Wednesday night and Friday morning, with PWATs
jumping from just over 0.1" initially to near 1" (2 to 4 standard
deviations above the mean) by daybreak Friday. A cold front will
drop southeast from Lake Superior Friday morning as a warm front
downstate creeps further north. This will result in a deformation
zone setting up just south of the APX forecast area, keeping the
warmest air locked up over southern Lower Michigan. As atmospheric
moisture increases, precipitation will develop and spread across the
area Thursday evening in response to increasing isentropic ascent
and frontogenesis, continuing into Friday but focusing more over
northern Lower through the day where the deformation zone sets up.

Primary Forecast Concerns...Precipitation type Thursday night will
be the main forecast concern and is complicated by lingering
differences between the models in low level thermal profiles. By
8pm, a saturated warm nose will start to develop aloft, lifting from
southwest to northeast overnight. The GFS remains the warmest
solution and takes the warm nose well north of eastern Upper by
midnight. Meanwhile the NAM, CMC, and ECMWF are cooler and slower to
advance the warm nose across the area. Models also differ with
regard to time of precip onset, but general consensus would keep
northern Michigan dry until after 8pm. In fact, dry low levels will
take awhile to fully saturate and may further delay the time of
precip onset. Used a blend of model guidance to account for these
subtle differences.

Surface temperatures will be near or below freezing across most of
the area Thursday evening, setting the stage for a freezing rain
event for many. It appears thermal profiles over eastern Upper and
northeast Lower will initially be cold enough for all snow there
until the warm nose arrives early Friday morning. Elsewhere,
freezing rain looks to be the dominant precip type Thursday evening
(with the exception of near Lake Michigan from Leelanau Peninsula
south where surface temps should stay above freezing). Some sleet
may mix in as well where the near surface freezing layer is deeper.
The good news is that as WAA ramps up overnight, surface temps will
start to creep up after midnight, slowly bringing an end to the
threat of freezing rain before daybreak for areas generally south of
M-55 and west of M-66. Across the rest of northern Michigan, surface
temperatures will rapidly jump after daybreak, with precip
transitioning to just rain from south to north for the rest of the
day. At this time, up to a tenth of an inch of ice accumulation
looks plausible across most of northern Michigan (highest across our
southeastern counties), with the exception of areas near Lake
Michigan.

.LONG TERM...(Friday night through Tuesday)
Issued at 323 PM EDT Tue Mar 21 2017

High Impact Weather Potential...Periods of icing potential
this weekend in the interior portion of N Lower and in E Upper.

Warm advection showers will continue through the weekend ahead of an
approaching occluding low. While it will remain liquid through the
day, overnight cooling will still be sufficient to change to a mix
for some and to completely snow for others. There is some concern
with wet surfaces freezing overnight. Similar to last week, there is
some signal for a brief period of freezing rain as well. Model
soundings over some locations Saturday night and into Sunday morning
are certainly supportive of that right now, but it is something
susceptible to very small changes in storm track and just where the
mid level warm air can get set up. This far out, will leave the mix
in the grids, and keep an eye on the thermal profiles in the coming
days.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 900 PM EDT Tue Mar 21 2017

Large area of Canadian high pressure is centered over southern
Manitoba this evening producing cold northerly flow across the
Great Lakes. Earlier cloud cover/lake and heating induced snow
showers have dwindled over the last few hours with the loss of
daytime heating. However, there remains a narrow corridor of lake
cloud cover and overall light snow showers stretching from around
Grand Traverse Bay back up into eastern Lake Superior. This batch
of lake cloud cover and light snow showers will shift westward
toward the Lake Michigan shoreline overnight and low level mean
winds veer more north/northeasterly. So, light snow showers and
BKN-OVC VFR cloud cover will remain a possibility at TVC/MBL for
the next several hours. Clouds/snow showers may ultimately push
offshore toward Wednesday morning. PLN/APN will remain solid VFR
with some SCT-BKN clouds possible at times.

On Wednesday, high pressure/dry air/strong subsidence build right
over the state. This will lead to lots of sunshine/VFR conditions
along with much weaker surface winds.



&&

.MARINE...
Issued at 323 PM EDT Tue Mar 21 2017

Winds and waves will remain at gale warning criteria for Whitefish
Bay and Northern Lake Huron into tonight thanks to strong gusty
N/NW winds in the wake of a cold front pushing thru the region
this afternoon. Winds will diminish later tonight and especially
on Wednesday as strong high pressure builds into the Western Great
Lakes region.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until midnight EDT tonight for LHZ345-346.
     SMALL CRAFT ADVISORY until 6 AM EDT Wednesday for LHZ349.
     GALE WARNING until 6 AM EDT Wednesday for LHZ347-348.
LM...SMALL CRAFT ADVISORY until midnight EDT tonight for LMZ341.
     SMALL CRAFT ADVISORY until 6 AM EDT Wednesday for LMZ323-342-
     344>346.
LS...SMALL CRAFT ADVISORY until midnight EDT tonight for LSZ321-322.
&&

$$

UPDATE...TBA
NEAR TERM...MLR
SHORT TERM...MEK
LONG TERM...ALM
AVIATION...TBA
MARINE...MLR


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