Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Gaylord Michigan
1003 am EST Friday Dec 13 2013
issued at 429 am EST Friday Dec 13 2013
Lingering light lake effect snow showers today into this evening
will give way to a more widespread snowfall later tonight through
Saturday evening as weak low pressure moves across the area. Cold
weather... along with a few snow showers...will continue across
northern Michigan to end the weekend into the start of next work
week. A slow moderating trend is expected through the middle and end
portions of next week.
issued at 949 am EST Friday Dec 13 2013
Snow, at the moment, is diminishing as the dry air from Ontario is
draining into east upper and NE lower as the winds are turning NE.
The lake bands in northwest lower are coming to an end. The only thing
left is the snow along the surface trough axis that runs roughly from
about Leland to htl to bax. Snow is expected to be light and
periodic through the day with on minor accumulations. This seems
to be working out so haven't tweaked much in the grids.
Update issued at 556 am EST Friday Dec 13 2013
No changes needed yet...convergent snow band over the tip of the
mitt dropping south...with multi-band lake convection south of
that and synoptic snowfall over southwest third of the forecast
area. Pretty much as expected thus far.
Short term...(today through tonight)
issued at 429 am EST Friday Dec 13 2013
Synopsis...midnight surface/composite analysis shows several low
pressure troughs across the Midwest/Great Lakes...with Arctic high
pressure ridge nosing southeast out of central Canada...and another
high centered over the Tennessee Valley. Northwest-southeast
oriented 150+kt jet streak axis runs from Eastern Lake Superior
across Northern Lake Huron and into the lower Great Lakes...
elongated latent potential vorticity anomaly along the cyclonic
shear side of this axis (where it should be dynamically).
Combination of entrance region forcing within this jet...low/mid
level warm advection/isentropic ascent...and perhaps some
frontogenetic response resulting an band of light snow from
northeast North Dakota...southwest across northern Minnesota and
into northern Wisconsin with some of these radar returns spreading
across Lake Michigan.
Meanwhile...lake snow showers continue off lakes Superior and
Michigan with continued unseasonable chill across the upper lakes.
00z apx sounding 850mb temperature was -19c which was right around
where the inversion base was located. Strong low level
frontogenetic axis extending southeast from Eastern Lake Superior
helping focus a band of heavy snow off Lake Superior and into
Chippewa County...but winds already starting to veer over Lake
Superior. Thus earlier west-northwest oriented bands are getting
shoved south en masse...included the dominant band over Chippewa
County which has now pushed south of ery-ciu. Winds at anj have
already flipped around hard to the northeast. Multiple west-
northwest flow bands off Lake Michigan into northwest lower not
particularly intense though increasing synoptic moisture has allowed
an increase in cover since midnight. Increasing synoptic moisture
in the form of aforementioned radar returns out of Wisconsin not
having much noticeable impact on lake convection south of the
Surface front/trough running east-west across the Upper Peninsula
getting pushed south by 2-3mb/3h pressure rises to its north...and
is forecast to cross northern lower Michigan through the morning
hours. High pressure ridge to the north then builds east/southeast
across northern Ontario and the adjacent Great Lakes...while low
pressure begins to organize over the Southern Plains. Between these
two features low/middle level deformation axis will become better
defined across Wisconsin/lower Michigan this afternoon into
tonight...with increasing warm advection into this deformation/
baroclinic zone over the Ohio Valley and Southern Lower Michigan
tonight. Forecast concerns for the short term will deal with
ongoing lake convection and impacts of passing frontal zone this
morning...then synoptic contribution to precipitation across lower
Michigan with strengthening deformation axis/isentropic ascent and
right entrance region jet forcing.
Today/tonight...eastern upper: current snow shower activity is
expected to get shunted quickly to the south and west this morning
with surface winds veering around to a more easterly component.
Only remaining snow shower activity today may be found around
Whitefish Point...perhaps some flurries getting into far western
Mackinac County. Otherwise extensive middle/high clouds upstream will
spread across Upper Michigan this morning and hang on through the
daytime...but should thin tonight with a cold easterly drainage wind
expected to develop
Northern lower: couple things to consider for northern lower today
between lingering lake effect and synoptic component to snowfall.
First...southward sinking convergence axis should light up with
snowfall as it crosses Lake Huron/far Northern Lake Michigan over
the next 3 hours or so and pushes into far northern lower and brings
a quick burst of snow...which should transition to more pure
north-northeast flow lake effect by middle morning. This will continue
into early afternoon but with colder/drier air off the Ontario
plateau filtering into Northern Lake Huron expect snow showers to
taper of flurries as the afternoon wears on. Farther south...band
of synoptic snowfall already setting up from roughly acb-osc.
Periods of snow expected within this corridor pretty much through
today and into tonight...perhaps enhanced a little if any snowfall
attached to the southward dropping convergence axis is still intact
by the time is pushes south of M-72 during the middle/late morning.
But otherwise expecting light accumulations through tonight...though
as boundary layer flow continues to veer more easterly...may see
some enhanced snowfall develop downwind of Lake Huron (with easterly
flow lake bands developing farther north toward apn/pzq overnight).
Long term...(saturday through thursday)
issued at 429 am EST Friday Dec 13 2013
Nowhere to go but up...right (talk about stating the obvious)?
Indeed...that is the general trend we look to be heading as current
anomalous cold pattern begins to relax some. Subtle shift to a more
progressive North Pacific flow pattern to be thanked for such...with
downstream affects of forcing a relaxation of deep Great Lakes
troughing. This...in turn...directs primary cores of reinforcing
shots of Arctic air to glance by to our north into early next week.
However...simple magnitude of current cold anomalies suggests below
normal temperatures will continue right through this coming weekend.
Increasing temperature gradient supports a continuation of the
ongoing snowy pattern...with a combination of system and lake
responses given plenty of opportunity to add to the deepening
snow pack. Trends since end of the October support growing Middle Range
guidance of another downward spiral in the epo...with quick east
Pacific Ridge amplification leading to a cold air dump/western
trough development heading toward the middle and end portions of
next week. This would result in a quick hitting surge of much milder
air into the North Woods via eastern ridge development...with strong
middle/upper level support and tight pressure gradient raising the
potential for significant low pressure development. Of course...
uncertainty at this early hour remains exceedingly high...and would
suspect this to remain so for the next several days. Unlike recent
Winters gone by...coldest temperatures continue to reload on this
side of the Globe...strongly supporting another significant cold
outbreak heading into Christmas week. Plenty to talk about...with
forecast concerns centered on additional snow chances right through
Kinda an interesting snow event to kick off the extended as current
Arizona centered southern stream shortwave rockets east into the middle
Mississippi Valley Saturday morning...all the while northern stream
energy dives into the northern plains. Deepest moisture no doubt
looks to remain tied to southern energy across the lower lakes into
the Ohio Valley. Development of inverted surface trough between the
two waves should draw moisture north...and combined with weak
isentropic upglide and hints of fgen (especially south) should be
enough to drum up a rather widespread light snow event Saturday.
Limited moisture and Omega displaced high up in the column should
keep most snow amounts light...on the order of an inch or two.
Couple wild cards in the mix...however. Pre-frontal air mass remains
plenty cold enough to entice some Lake Huron component to the
snowfall across northeast lower in east to northeast flow regime.
Could see this adding another inch or two..if not locally more...in
favored areas. Pattern recognition of these east flow patterns hints
at often observed standing wave phenomena...supporting additional
lift across the sunrise side...while forcing a downward response and
less snowfall over northwest lower. Should not be too big of a
deal...but something interesting to monitor. By and large...
inherited forecast already well trended toward this general theme...
with few changes needed on Saturday. Southern stream component to
snowfall exits quickly Saturday evening...with northern stream wave
and attendant lake effect potential taking center stage later
Saturday night into Sunday. Still plenty of uncertainty on how all
important wind fields will manifest themselves...with lake aggregate
troughing and northern wave attendant surface low determining such.
Focused convergence and what looks to be an ideal fluff producing
thermal regime (h8 temperatures in the negative middle and high teens)
could produce decent snowfall for some of the traditional snow
belts. Time will tell. A relative break in the active weather
expected Sunday night into at least the start of Monday as high
pressure slips overhead.
Next clipper system dives southeast along tightening western lakes
thermal gradient...with attendant warm air advection Wing kicking off another round
of light snow later Monday and Monday night...followed yet again by
lake effect snow showers Tuesday. What happens there-on-after
subject to much debate in the guidance world. As mentioned...simple
late fall/early winter trends and rapid development of -epo suggest
rapid and deep trough development into the intermountain west as
strong shortwave dives out of the Gulf of Alaska. This would support
Central Plains low development and good surge of milder air north
into the Great Lakes towards the end of next work week. Definitely
something to monitor in the coming days...with even the potential we
get on the rainy side of things by Thursday and Friday.
Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 556 am EST Friday Dec 13 2013
Periods of MVFR conditions expected through tonight at mbl/tvc
with snow...brief period of IFR at apn this morning with mostly
MVFR into this evening. Pln conditions to improve to VFR by late
issued at 429 am EST Friday Dec 13 2013
Cold front dropping across the forecast area from the north/
northeast this morning will shift winds around to a more of an
easterly component with time this morning and early afternoon
(within Lake Michigan nearshore zones)...along with a dropping off
of wind speeds as pressure gradient relaxes. Any remaining small
craft advisories this morning will be due to lingering wind/wave
effects. East/Northeast Boundary layer flow will continue
tonight...with winds picking up on lakes Michigan/Huron by Saturday
and may usher in a new round of small craft advisories especially
within Lake Huron nearshore zones.
LH...Small Craft Advisory until 11 am EST this morning for lhz345-
Lm...Small Craft Advisory until 11 am EST this morning for lmz323-342-