Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Gaylord Michigan
335 PM EST sun Dec 28 2014
Near term...(this evening through tonight)
issued at 332 PM EST sun Dec 28 2014
Well the break from the cold weather was nice for some of US...but
it is definitely now in the rear view mirror. The pattern over the
next week to ten days looks more like what you would typically
expect in late December/early January. As far as tonight
GOES...convergence along a surface trough moving through the region
in combination with good over lake instability will lead to a period
of light snow and flurries. This activity will move across northern
lower from north to south through this evening. Overnight...winds
shift into the northwest and it is plenty cold enough for lake
effect (lake/850 mb Delta ts of around 20) but moisture is rather
limited (mean 850-700 mb relative humidity only a paltry 30 to 40 percent at best).
This should only lead to scattered snow showers across northern
lower (with widespread activity across eastern upper where moisture
is just a tick higher). Accumulations will be light on the order of
an inch or less (except for perhaps a couple of inches from Paradise
to Whitefish point). Colder with lows ranging from the upper single
digits above zero north to the middle and upper teens south.
Short term...(monday through wednesday)
issued at 332 PM EST sun Dec 28 2014
High impact weather potential: moderate lake effect snow Monday
through Wednesday. Very chilly temperatures
Forecast challenges: snow amounts with the lake effect as we go
through some dry periods during the 48 hour period.
Overview(analysis and forecast)...broad trough in the western Continental U.S.
Is beginning to dig as the pattern is about to split with a cut off
500 mb low in the west and broad trough in the middle of the country
with lots of smaller waves running through it. The issue though is
the moisture in the 700-500 mb layer with several dry slots
associated with some of these waves. As things Ebb and flow this
week, it makes the lake effect a little more challenging as the lack
of synoptic moisture will keep things light, and a plethora of
moisture briefly moving through will bring a period or two of
moderate snow into the middle of the week.
(12/29)monday...this forecast period starts out with a few things
that seem to be no brainers. First, the wind direction in the 1000-
850 mb layer is pretty consistent over the 24 hour period (12z-12z)
with the 850 mb temperatures falling from -16c to -20c at the same
time. The only problems that occur during the period are the
aformentioned dry air that seems to move in and out of the area
enough to keep the snow amounts light, and also the inversion
heights lower and rise above and below 3000 feet. So during the day,
kept the same probability of precipitation in the northwest flow area, and also kept the snow
amounts as the moisture in the 850-700 mb layer dries out and the
inversion stays below 3000 feet. Will expect light snow
accumulations through this time. Monday night, the inversion height
rises to around 4000 ft, and the moisture in the 850-700 mb layer
looks to be slowly increasing as a wave 500 mb trough axis moves
into North Lake Superior and adds some extra kick by 12z, especially in
west Chippewa County, near Paradise and Whitefish Point. There could be
moderate amounts in east upper near those locations, while in northwest lower,
will expect that the snow amounts continue to be light.
(12/30)tuesday...all of the models have 850-700 mb synoptic moisture
with -21c or colder air. The models are in good agreement on the
timing of the moisture now, and the winds are roughly west-northwest through
the 12 hours of the day (12z-00z). Continue with a light to moderate
accumulations in east upper as the snow moves from Whitefish toward anj.
The inversion height continue to be around 4000 feet, so will
continue with light amounts for now, but am wondering if the European model (ecmwf)
is right, there could be some moderate amounts even in northwest lower.
Tuesday night...the winds will shift through the night, from west-northwest at
00z, to west at 06z and then west-southwest at 12z, so tried to shift the snow
patterns over the 12 hour pattern. This seems a little more straight
forward as the changing wind direction will spread the snow amounts
around with some bursts as some of the snow bands get pushed
together. So will continue with the light snow accumulations.
(12/31)wednesday...another 500 mb shortwave trough moves into the
upper Great Lakes and brings moisture with it, but not until the
afternoon. The morning starts with the 850-700 mb layer relative humidity <50% with
the winds west to WSW, by 18z the winds shift to the west-southwest as the
trough approaches with dry air still streaming into the region, but
as the trough descends into the upper Great Lakes, the moisture
comes with it, and the 850-700 mb layer relative humidity rise to above 60% with
winds still west-southwest. With the 850 mb temperatures holding around
-17c-ish, the will expect that minor snow turns to possibly moderate
snow at the end of the day. Think that the accumulations will be
light however, as it would be a slow start.
Long term...(wednesday night through sunday)
issued at 332 PM EST sun Dec 28 2014
Wednesday night through Thursday night: broad upper-level longwave
troughing over the eastern half of the Continental U.S. Will be the dominating
feature during the period. A couple of weak shortwaves are expected
to rotate through the upper Midwest and Great Lakes...each
reinforcing the already entrenched cold air and providing subtle
synoptic support to any ongoing lake effect snow showers. While over
the lake instability will continue to support lake effect snow
throughout (850 mb temperatures of -12c to -18c)...am expecting the most
widespread snow and the majority of any light accumulations to occur
during the periods of synoptic support from the aforementioned
Friday through sunday: on Friday...weak high pressure diving into
the northern Great Lakes in combination with a brief decrease in
moisture and lake effect steering winds becoming more
transient...should gradually diminish coverage of any lingering lake
Quite a few differences lie in terms of the overall evolution and
track of an upstream cutoff low over the southwestern Continental U.S. That
ejects east late in the week. Clearly two quite different scenarios
could come to fruition this far out. Scenario 1...with the surface
low tracking from southern Illinois/Kentucky to the mid-Atlantic. This would
lead to a continuation of cold temperatures but turn the area much
drier (not even much lake effect to note) as moisture really begins
to lack with Canadian high pressure over the northern plains helping
to suppress any interaction with the northern stream and keeps the
majority of any notable synoptic precipitation well south of the area.
Scenario 2...with the surface low tracking over southern Michigan/Northern
Ohio...would certainly lead to a rather snowy solution over the
majority of the County Warning Area during the Friday night-Sunday timeframe as
southwest flow...warm air advection and an increase in moisture
could bring a leading wave of isentropically driven precipitation as early
as Friday night and continue in some fashion on Saturday.
Of course other solutions aside from the two extremes mentioned
above are possible...primarily something in between. At this
point...will somewhat split the middle as several of the 12z
ensemble and operational members continue to support less
interaction with the northern wave and the approach of Canadian high
pressure aiding to suppress the system over the Ohio Valley. With
low confidence and many factors at play...it at least warrants
keeping an eye on as we go through the work week.
Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1236 PM EST sun Dec 28 2014
Light lake effect snow showers will gradually increase in
frequency as colder air filters into the region through tonight.
Overall visibilities are expected to remain VFR...with mainly MVFR ceilings
through tonight...expect low end VFR at apn. West winds around 10
kts with higher gusts this afternoon will shift into the
LH...Small Craft Advisory until 10 PM EST this evening for lhz345>348.
Lm...Small Craft Advisory until 10 PM EST this evening for lmz342-344.
Ls...Small Craft Advisory until 10 PM EST this evening for lsz321-322.