Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 171820
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
220 PM EDT Fri Mar 17 2017

.UPDATE...
Issued at 1148 AM EDT Fri Mar 17 2017

12Z surface/composite analysis shows a couple of low pressure
centers upstream of the Great Lakes region...a more prominent
1006mb low over far northwest Ontario with a trailing cold front
back into northwest Minnesota...and a weaker 1012mb wave over
eastern Iowa. Broad zone of warm advection between these lows and
a ridge of high pressure over the mid Atlantic/lower Great Lakes
is pushing a broken band of radar returns across western Upper and
the southwest half of the Lower Peninsula. Initial radar returns
not reaching the ground with plenty of dry air still evident on
12z APX sounding (dew point depressions at or above 10C below
500mb). Sounding was mostly below freezing...with a surface based
warm layer developing with some early heating especially east of
the M-37 corridor with some filtered sunshine through cirrus
bands. Precipitation has started to reach the surface at MBL with
a rain/snow mix...while LDM started as rain bug has switched to
snow.

Warm boundary layer temperatures will be running into evaporative
cooling...with surface dew points still in the teens across the
forecast area. So it is likely that many areas may end up starting
as rain...then perhaps transitioning to snow or a rain/snow mix
depending on the efficiency of evaporative/melting induced
cooling. Tried to be a little more precise in PoP timing across
the area this afternoon...not likely to see precipitation reach
far eastern Upper/far northeast Lower until after 21z...and more
likely to start as all rain. There could be a brief period of
freezing rain during the transition to more frozen precip types
but lower confidence in these details. Snowfall upstream thus far
this morning not looking overly impressive...a lot of 1-2SM
visibilities...so combined with warm boundary layer temperatures
not expecting much in the way of snow accumulations today. As
mid levels dry out later this afternoon over northwest Lower will
likely see precip taper to drizzle or freezing drizzle depending
on surface temperatures which will likely be hovering near
freezing by that point. Will evaluate potential hazards with
freezing drizzle for the afternoon forecast.

&&

.NEAR TERM...(Today and Tonight)
Issued at 343 AM EDT Fri Mar 17 2017

...Period of wet snow today through this evening...

High Impact Weather Potential...Nuisance. Some wet accumulations
of snow and travel difficulties.

Pattern Synopsis/Forecast...Fairly low amplitude flow pattern
across the CONUS this morning with a Pacific shortwave and
attending surface low pressure slowly diving into the northern
plains and thermal ridge axis folding into the midwest. Shortwave
forcing and isentropic ascent ahead of the wave has/is slowly
pushing a relatively narrow axis of precip toward the western
lakes region. Shortwave trough will dig and deepen over the
western Great Lakes over the next 24 hours or so with the main
shortwave circulation sliding down through southern lower Michigan
overnight into Saturday. Narrow axis of QG-forcing and resulting
precip will slide through the state today/this evening diminishing
with a period of drizzle/freezing drizzle (mainly northern lower)
as deeper moisture strips out aloft.

Primary Forecast Concerns...precip timing and type as axis of
lighter precip slowly slides through the region. Some light icing
possible tonight with freezing drizzle.

Today...Shortwave trough and attending surface low will dip into
the far northwestern Great Lakes region by the end of the day.
Axis of (weakening) warm advection forcing and narrow band of
precip will slowly slide through the CWA through the course of
the day then pivot north/east across upper Michigan tonight.
Precip timing continues to be slower (a few days ago...looked
like precip would already be here by now). Thus the first tweak
to the forecast was to fine-tune timing to slow the onset of
precip. Areas across NE lower Michigan and parts of eastern upper
may not see anything until late in the day.

Once precip does arrive, P-type will once again be tricky.
Forecast wet-bulb temperature profiles aloft remain largely below
freezing across the CWA, even in the far southern areas as main
thermal axis/warmer air folds down through lower Michigan. Thus
precip type will be dominated by surface/boundary layer temps.
It`s cold out there to start...but a slower onset of precip will
allow surface temps to rebound to above freezing for many areas
particularly over the northern/eastern part of the CWA. That said,
warming will be offset by evap cooling given the lower dewpoints
across the region. All told, I do think precip will start as
mainly snow...perhaps mixy in some of the warmer areas...then
trend toward rain or drizzle in the SW counties as deeper moisture
strips out aloft.

Tonight...deep moist axis and remaining light snowfall pivots up
through the upper peninsula leaving most of northern lower
Michigan in low cloud cover and likely some drizzle/freezing
drizzle with fairly deep surface based saturated layer. Light snow
accumulations across eastern upper Michigan, but some light icing
is possible across northern lower Michigan as temps dip back
below freezing.

Headline-wise...none anticipated for today. Warmer temperatures
will make accumulating snow hard to come by and I have less than
an inch in all areas. Some better accumulations tonight as
remaining snowfall pivots up through the tip of the mitt and
eastern upper Michigan, but still and inch or two and sub
advisory. Again, there is potential for freezing drizzle/light
icing across interior northern lower Michigan tonight and perhaps
that will eventually warrant an advisory from the day crew.

&&

.SHORT TERM...(Saturday and Sunday)
Issued at 343 AM EDT Fri Mar 17 2017

...Moderating Temperatures...

High Impact Weather Potential...freezing drizzle to start the day on
Saturday and again on Sunday night.

Pattern Synopsis/Forecast...The 500 mb low moves off to the east out
of SE Lower Saturday morning. The sfc low takes a little longer to
get out of the region with the sfc trough running through the
eastern part of the state and into Ontario east of Lake Superior.
The 850 mb temperatures continue to be running around -5c with the
850 mb moisture around 90%, but above that is dry air that runs up
through -10c level. As the dry air aloft continues to move into the
region with the 500 mb ridge, the sfc trough and the 850 mb moisture
with the -5c temperatures continue to remain over the region through
00z/Sun. This will continue to produce the chance of
drizzle/freezing drizzle into the evening. However, with the sfc
high building into the Upper Great Lakes during the evening, the 850
mb moisture looks to begin to wane, from the building subsidence. So
will continue the dry forecast through the night and into Sunday.
Sunday evening, the chances for precipitation begins to increase as
the 500 mb ridge axis moves east of us, and the warm front/occluded
front dips into the Upper Great Lakes. Then the cold front moves
through around 06z, which will continue the chance for
precipitation. It looks like temperatures will begin to dive
sometimes before 00z/Mon, so will expect that the freezing
temperatures will set up and produce some wintry mix overnight.

Primary Forecast Concerns...The two time we have wintry mix, look to
possibly produce some advisory issues with the wintry mix, mainly in
E Upper, but also in NE Lower as the colder air looks to take some
time to get out, while the drizzle/rain is still around. The model
soundings are right around freezing, so nothing is for sure. It will
only take a degree either way for it to be all snow, or just rain.


.LONG TERM...(Monday through Thursday)
Issued at 343 AM EDT Fri Mar 17 2017

High Impact Weather Potential...minimal for now. Friday may be
interesting.

Extended (Monday through Thursday)...The dry air pushes into the
region pretty quickly post cold front on Monday morning, before the
secondary, arctic front pushes in after 06z/Tue. 850 mb temperatures
fall below -10c in E Upper by 06z, and below -12c in N lower by
12z/Tue. This will bring about the chance for lake effect snow or
rain Tuesday and Tuesday night. Wednesday, the core of the sfc high
moves into W Upper and W Lower this will dry the region and cut off
the LES, except maybe some flurries. Thursday, the sfc high
retreats, but the models disagree on the speed at which the high
retreats. The GFS is much faster and with a much flatter 500 mb
ridge than the ECMWF, The difference is that snow/rain moves into
the region 12 hours sooner on the GFS than the ECMWF. If the models
are right, they phase into agreement, somewhat, and bring about a
decent little spring storm for Friday. One track is north, and the
other is south.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 217 PM EDT Fri Mar 17 2017

Expecting deteriorating flight conditions as the afternoon wears
on as a band of snow/rain overspreads northern Lower Michigan...
followed by IFR ceilings and periods of drizzle/freezing
drizzle/flurries that should continue into the first half of
Saturday. Potential for freezing drizzle will lead to icing
concerns.

&&

.MARINE...
Issued at 616 AM EDT Fri Mar 17 2017

Winds will increase from the SE today ahead of low pressure that
will track down through the state later today and tonight. Some
gusts to around 20 knots are anticipated, although winds/waves
should largely remain sub smallcraft advisory.

Winds veer into the northwest later tonight as the low passes
through with gusts once again around 20 knots. A few marine areas
could see a bit higher gusts and waves...specifically that stretch
from the straits to Presque Isle where a small craft advisory may
be needed.


&&

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

$$

UPDATE...JPB
NEAR TERM...TBA
SHORT TERM...JSL
LONG TERM...JSL
AVIATION...JPB
MARINE...TBA



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