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afdapx

Area forecast discussion
National Weather Service Gaylord Michigan
955 PM EST sun Dec 17 2017

Update...
issued at 955 PM EST sun Dec 17 2017

Weak low pressure was in far srn Lake Michigan this evening, on
top of a frontal boundary that stretches nearly west-east. Coupled
with high pressure off to our ENE, this has resulted in weak east-southeast
winds trying to turn more south. This has allowed some deeper low
level moisture to advect into nrn Michigan, seen increasing from
the 12z to 00z apx observed soundings. This has led to solid
overcast conditions, with the thought that some freezing drizzle
would be possible. This has not been seen or noticed on any
observation around the region. Since the greatest chance for it in
most areas was through this evening, before the weak low passes
to our east and the moisture Shallows out, feel comfortable to
take it out of the forecast in all but areas near Saginaw Bay.
These areas will be closer to the low while waiting on deeper
moisture associated with a weak upper trough that passes Monday
morning. For most of the region, we will rather be dealing with
light fog, thicker in the higher terrain of interior nrn lower,
while temperatures are below freezing. This freezing fog is not
likely not pose any difficulties, except maybe later tonight and
into Monday morning in the higher terrain.

Meanwhile in eastern upper, there are reports of some light snow,
out ahead of another weak positively sheared upper trough that
passes overnight. Still not expecting any more than a dusting at
best.

Just rather grungy out there (and to continue into much/all of
monday).

&&

Near term...(tonight through monday)
issued at 246 PM EST sun Dec 17 2017

High impact weather potential: a period of light snow/mix from The
Straits into part of eastern upper tonight. Patchy freezing
drizzle possible parts of northern lower.

Primary forecast concerns/challenges: weakish forcing and p-type
questions tonight.

Much of northern Michigan caught between weather systems tonight,
with a weakish system sliding across eastern upper and another
moving well to our south. Mid level f-gen increases this evening
over The Straits and eastern upper associated with a weak
shortwave/trough sliding through the northern lakes. Forcing is
not that impressive overall but forecast soundings certainly
point to a period of mainly light snow through the first half of
tonight with minor accumulations. As deeper moisture departs,
precipitation may transition to freezing drizzle. South of the
bridge, forcing is weaker and moisture not quite as impressive,
with a few light snow showers/patchy freezing drizzle possible.

Later tonight, the far southeast parts of the area will be
brushed with deeper moisture associated with an area of low
pressure moving south of the area. Areas closer to Saginaw Bay
could see a period of light snow or a mix of light snow/freezing
drizzle. Tough call on how far north this moisture will push, but
given the potential for a little freezing rain, it will bear
watching. Areas of fog are likely to develop overnight with
increasing low level moisture and weak boundary layer flow. This
could become locally dense in spots, especially closer to the M-55
corridor in northern lower.

Milder temperatures on Monday as 800 mb thermal ridge pushes into the
Great Lakes. High temperatures at or above freezing across the
entire area, with a few locations likely near 40. Not much
happening weatherwise. Clouds/fog in the morning will give way to
some "brightening" of the skies as the day progresses. A few
flurries/sprinkles possible but overall it will be a dry day for
most areas.

&&

Short term...(monday night through wednesday)
issued at 246 PM EST sun Dec 17 2017

High impact weather potential...minimal. Chances of rain and
or/snow...with some light snow accumulation for northern sections
of our County Warning Area.

Pattern synopsis/forecast...broad cyclonic flow will remain over the
upper Midwest and the Great Lakes region thru mid week. Our brief
"warm-up" early this week will give way to cold air advection Tuesday night as a
cold front sweeps thru the region. The front and associated short
wave and deeper moisture will increase pops to likely Monday night.
Precip type Monday night into Tuesday will be a mix rain and/or snow
per model sounding temp profiles. Cold air advection Tuesday night and Wednesday
will switch all precip over to all snow...with the primary forcing
mechanism transitioning to lake processes. Overall synoptic lift
along and ahead of the front as well as increasing over-lake
instability in the wake of the front are both rather modest...and
expected quantitative precipitation forecast thru this forecast period is relatively minor
(sub-advisory).

Temps will only drop a few degrees Monday night...with overnight
lows mainly in the lower 30s. Tuesday will bring US one more
relatively mild day...with highs in the mid 30s to around 40
degrees. Cold air advection Tuesday night will drop low temps back into the low to
mid 20s...with highs on Wednesday only warming into the mid to upper
20s.

Long term...(wednesday night through sunday)
issued at 246 PM EST sun Dec 17 2017

High impact weather: deepening low pressure over the Great Lakes
region Friday...mixed precipitation possible...then lake effect
behind the departing system.

Long range guidance have come into agreement with a developing low
pressure system over the Great Lakes region tracking through
northern lower Michigan Friday. Still can (and probably will) change
a bit before then, so too far out to say exactly what type of
precipitation, how much accumulations we will see, and where
different precip types will be...could definitely bring some Holiday
travel headaches though. Behind this departing system very cold air
filters back into the forecast area producing More Lake effect
accumulations beyond this forecast period. Highs will be in the mid
20s to low 30s Thursday. Depending on the exact track of the
aforementioned storm system...highs could drastically change Friday,
for now, mid to upper 20s over eastern upper to near 40 over the
southwest County Warning Area. Highs then cool behind the departing system...only
reaching into the 20s Saturday and then only the teens to low 20s
Sunday. Lows will generally be in the teens to low 20s until
temperatures drop Sunday...dropping into the single digits over
eastern upper and low teens over northern lower.

&&

Aviation...(for the 00z tafs through 00z Monday evening)
issued at 701 PM EST sun Dec 17 2017

Widespread MVFR cigs dropping to IFR with reduced visibilities in light
fog this evening and much of the overnight, as low level moisture
deepens across nrn Michigan. Periods of freezing drizzle is also
possible. The low level moisture does thin out with the passage of
a sfc trough overnight, and there should be some fog improvement
into Monday, but doubt the MVFR ceilings will scour out much. Moisture
thickens from aloft Monday night, out ahead of a weak warm front,
resulting in a chance for a mix of light rain/snow mainly around
pln. Fog is a little unclear right now, but temperatures will be
rising above freezing, as well as dewpoints, and this air over
snowpack could lead to some reduced visibilities.

Winds just above the ground increase decently Monday night. May
have to consider low level wind shear in the next taf issuance.



&&

Marine...
issued at 246 PM EST sun Dec 17 2017

Winds veer to the southwest tonight and will increase
considerably on Monday/Monday night ahead of a cold front.
Widespread small craft conditions developing on Monday, continuing
through the day on Tuesday as a cold front sweeps across the
area.



&&

Apx watches/warnings/advisories...
Michigan...none.
LH...Small Craft Advisory from 9 PM Monday to 6 am EST Wednesday for
lhz345>349.
Lm...Small Craft Advisory from 2 PM Monday to 6 am EST Wednesday for
lmz323-341-342-344>346.
Ls...Small Craft Advisory from 9 PM Monday to 6 am EST Wednesday for
lsz321-322.
&&

$$

Update...smd

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