Area Forecast Discussion
Issued by NWS Gaylord, MI

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103
FXUS63 KAPX 220242
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
942 PM EST Tue Feb 21 2017

.UPDATE...
Issued at 941 PM EST Tue Feb 21 2017

Mainly clear skies are giving way to increasing mid/high clouds
across the Western Great Lakes as weak troughing becomes better
established ahead of low pressure developing over the Northern
Plains. A few obs over Eastern Upper and NE Lower Michigan have
periodically reported moderate to dense fog already trying to
develop around/shortly after sunset as the boundary layer cools
and winds become light/variable. However...increasing mid/high
clouds have begun to limit fog development...with much of our CWA
still reporting unlimited vsbys attm. Latest NAM suggests the
maintenance of this rather thick mid/high cloud deck during the
balance of the night. Certainly think we will see some fog
development overnight...but at this point do not expect widespread
dense fog development. Overall...expected partly to mostly cloudy
skies with patchy/areas of fog developing. Temps should remain
generally steady in the 30s.

&&

.NEAR TERM...(Tonight and Wednesday)
Issued at 323 PM EST Tue Feb 21 2017

High impact weather potential: Possible dense fog.

Pattern synopsis and forecast:

The passage of a shortwave trough aloft has turned the upper air
pattern to more zonal and progressive. Additional troughing off the
pacific coast was throwing weak vorticity across the nrn states,
over the top of sfc troughing, and within steepening lapse rates
aloft. Water vapor imagery not showing too much in the way of deep
moisture, and precipitable water was running roughly at 0.50-0.65".
Radar showing some weak reflectivity pushing through eastern Montana
and the Dakotas, with sfc reports of only sprinkles attm. While
skies were clearing across nrn Michigan, mid and upper level clouds
were spreading east through the zonal flow, with the next round of
WAA already working it`s way across MN. Temperatures have responded
in nrn Michigan after the sun came out, with many low to mid 50s
across nrn lower and mid 40s in eastern upper.

The weak vorticity will cross through nrn Michigan tonight while the
sfc troughing tries to expand/lay out across Lake Superior/eastern
upper. Lapse rates aloft continue to steepen to 6.5C/km while a
small H8 LLJ feeds the WAA into the region. Moisture and forcing are
nothing to write home about, but would not be surprised to see those
weak reflectivities upstream develop over eastern upper after
midnight. Maybe a brief very light rain/sprinkles in this area.

The next impulse/shortwave arrives Wednesday later afternoon while
lapse rates aloft reach 7C/km. Forcing is better, as we are
projected to see maybe a little upper divergence, while the sfc
troughing also becomes more defined as low pressure enters the
western Great Lakes. Moisture is still a problem, remaining scant,
not increasing from current values out west (0.65"). Conditions for
rain are a little bit better than tonight, but still likely not more
than maybe a little light rain across eastern upper and far nrn
lower. More clouds and cooler air along and north of the sfc
troughing for highs in the middle 40s for eastern upper. South of
the troughing and where the low level air mass will be much warmer
(H8 temps 8C-10C), temps will have the potential to hit the middle
50s, to maybe even lower 60s nearer to Saginaw Bay. This is provided
that fog is able to burn off for some good afternoon sun (see
below).

Fog: Decent afternoon warming has allowed the temp/dew point spread
to increase across most of the region, but there were some areas
still stuck in low clouds and fog and very little mixing. Either
way, the sfc air mass hasn`t changed too much with sfc dew points
expected to stay in the lower half of the 30s in eastern upper, and
in the middle and upper 30s in nrn lower. The clearing skies and
arrival of a weaker pressure gradient/light winds, will allow for
good radiational cooling to shrink those temp/dew point spreads. Can
really see the redevelopment of fog across much of nrn Michigan,
starting first for those areas that took longest to clear out
(Straits region to Drummond Island and areas closer to Saginaw Bay).
Areas of dense fog are expected, but there is definitely some
uncertainty, especially considering winds just above the sfc
increase late tonight, which may help try and slightly churn up the
BL. Any fog would likely last into a good chunk of Wednesday
morning.

&&

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

...Wintry mix leading into Accumulating snow...

High Impact Weather Potential...Heavy wet snow and freezing rain in
E Upper and portions of N Lower on Thursday night and into Friday.

Pattern Synopsis/Forecast...Wednesday evening, a 500 mb shortwave
trough pushes into Upper Michigan by 06z. Models have above 0c 850
mb temperatures in E Upper and N Lower and sfc temperatures look to
remain above freezing through the night. So the mix may be more of a
rain/snow mix before changing to all rain Thursday morning and then
ending. It`s the next system which is moving up out of C Plains
Thursday night. There`s as decent baroclinic zone along the warm
front that is in S Lower by 06z. The above freezing sfc temperatures
remain south of M-32  through 06z as the warm advection keeps the
temperatures flat, but the temperatures north of M-32 will slowly
fall to below freezing so that the rain falling along the baroclinic
zone have a chance for freezing rain to fall, north of M-32. E Upper
looks to rain all snow while the interior highlands of N Lower and
portions of NE Lower remain the battleground for the rain/freezing
rain. However, once the sun rises Friday morning with the warm
advection, the warmer air moves a little more north pushing the
likelihood of freezing rain into E Upper and out of N Lower through
the afternoon. This interface between above and below freezing sfc
temperatures sets up mainly over Mackinac and eastern Chippewa
Counties for several hours, however it looks like a decent mix of
snow, freezing rain and sleet as the baroclinic zone stalls as the
sfc low moves into the Upper Great Lakes.

One other thing to talk about, while the icing and snow issues are
taking place around the Straits, the showalter index drops to -1c
along M-72. With the impending sfc low moving into the region and
the good dynamics ahead of the 500 mb cutoff low have continued the
mention of thunder for areas along and south of M-32/M-72 through
the day.

Primary Forecast Concerns...The main concern is the track of the sfc
low Friday. the GFS/nam solution takes the low out of Iowa and into
southern Minnesota, while the sfc trough swings east into the
Straits. This would push the warmer air farther north and make this
just plain rain with little mix. The Canadian solution take things
farther south and puts the mix in N lower/C Lower while the ECMWF
solution is a middle of the road solution. Kept things middle of the
road for now, in keeping with WPC`s idea of the freezing rain/snow
idea for Friday.

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

The extended period looks active to say the least.  It begins Friday
night/Saturday morning...with a strong closed low pulling through
the great lakes. Models seem to be congealing on a more northern
track...with the low passing through the straits of Mackinac. That
means, we`re picking up right about the time we have the best chance
for thunder...and in the transition of p-type from liquid to
eventually all snow on Saturday.  During this transition time...a
wintry mix is certainly a risk...but I don`t have the confidence to
pin point locale or timing at this point.

Wrap around moisture on the back side of the low should provide
mainly snow for Saturday...but I would keep an eye out for the dry
slot...which might set us up for a little -FZDZ and cut down the
accumulation opportunities a bit. We then transition into a lake
effect regime for Sunday into Monday...as 850mb air of -16c
traverses the area.  The winds lock in for only a brief
period...while aligning with sufficient moisture to give us a chance
at some accumulating LES...the best time looking like 00Z-06Z Sunday.

The latest run of the Euro shows us a bit dryer...with a chance for
a respite the later half of Monday into Tuesday...before the next
swath of moisture arrives in advance of the next weather maker.
However the GFS and blended solutions do not...and would favor a
wetter solution.  Grids will reflect this latter option...and we`ll
keep an eye on later runs as we get closer.  Regardless...a return
to a more seasonal situation is certainly in the offing, as we all
knew it would be...and quite frankly, is preferred/needed for
forestry, agriculture and local commerce.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 613 PM EST Tue Feb 21 2017

Areas of fog will develop tonight across most of Northern Lower
Michigan...dropping vsbys to MVFR and eventually IFR in many
locations. The fog will mix out shortly after sunrise on
Wednesday...returning VFR conditions to all TAF sites for the
remainder of the day. Light/variable winds tonight will become SW
AOB 10 kts on Wednesday.

&&

.MARINE...
Issued at 323 PM EST Tue Feb 21 2017

Winds will continue to weaken heading into the evening, before winds
back more southerly overnight and increase in speed. While some low
end advisory gusts will be possible, believe the stability will
largely keep winds in check. Winds drop off again later tomorrow
afternoon and evening, while also becoming more variable, as weak
low pressure and a few possible showers cross the nrn nearshores. A
stronger storm system arrives late Thursday night into Friday with a
good chance for at least advisory level winds, with generally
snow in eastern upper and rain over nrn lower.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...NONE.
LM...NONE.
LS...NONE.
&&

$$

UPDATE...MLR
NEAR TERM...SMD
SHORT TERM...JSL
LONG TERM...KAB
AVIATION...MLR
MARINE...SMD



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