Area Forecast Discussion
Issued by NWS Gaylord, MI

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609
FXUS63 KAPX 052102
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
402 PM EST Mon Dec 5 2016

.NEAR TERM...(Tonight and Tuesday)
Issued at 400 PM EST Mon Dec 5 2016

High impact weather potential: Some dense fog possible in the
higher terrain of interior northern lower Michigan.

Pattern synopsis and forecast:

Mid level ridging in increasing over nrn Michigan, as upper
troughing in the nrn plains sharpens/deepens with sfc low pressure
becoming more organized in SD. A warm front extended from this low
pressure into Iowa, and the max low to mid level WAA was along the
H8 warm front in the srn half of MN and across SW Wisconsin where
there were some light returns on radar. Just some light rain in
spots, but reflectivities were expanding and increasing due to
increased DPVA from a shortwave trough lifting into that region. Of
more concern is the widespread stratus and fog across srn Wisconsin
and nrn Il, back through far srn lower Michigan. There, low level
WAA over the top of a new and wet snowpack was the perfect setup. In
nrn Michigan skies were clearing out in all but the lingering
westerly lake effect in far nrn lower. Low level winds were backing
more SW ahead of the developing low pressure out west, and the
stratus and low level warmer air were starting to lift toward us.

Forecast concerns: Will we get stratus and fog tonight? What are the
chances for seeing precipitation through tomorrow?

The sharpening upper trough develops into a closed low tonight and
slowly lifts into far SW Ontario and becomes a stacked system. The
aforementioned H8 warm front sort of loses definition, as it
occludes, but a convergent zone of wind and low to mid level WAA
does sweep into nrn Michigan overnight. The occluded front then
arrives Tuesday afternoon. The warm front may be able to squeeze out
some light mixed rain/snow tonight into Tuesday morning in eastern
upper, but that may even stay aloft due to some lower atmospheric
drier air. That drier air will continue to be advected in through
tonight across mainly nrn lower. So, skies will initially continue
to clear into evening. However, remember that shallow stratus and
fog seen in WI/IL/far srn lower? Well, many things can happen
through the night. First, BL cooling in clearer skies this evening
may result in a quick drop in temperature to minimal T/TD
depressions, and the subsequent development of fog. Second, stratus
west of us does seem to have a bit of an eastward push to it, like
it wants to near the GTV Bay region and develop through evening.
Potential problem with that is, winds do turn more out of the south
through the night, and most of this is likely to be advected north
through Wisconsin and Lake Michigan. Third, and probably the more
likely scenario, there is a combination of both. Low level warming
over our cold ground and fresh remnant snow, combined with
radiational cooling leading to some fog, and the southerly winds
drawing the far srn lower stratus our way. Stratus could also
develop under a shallow inversion. Fog would be more prone to the
higher elevations of nrn lower.

Finally, the approach of the occluded front tomorrow will bring
temperatures down in the western CWA by late afternoon, low enough
for returning the lake response. The moisture depth/inversion height
appears too low to get any lake effect development. Will just have
low chances for seeing precipitation for south flow regimes late.
This will mainly impact eastern upper.

&&

.SHORT TERM...(Tuesday night through Thursday)
Issued at 400 PM EST Mon Dec 5 2016

...Colder with increasing lake effect snow...

The change in the pattern looks like it will begin to come together
during the middle and end of the week as a trough gets carved out
across central Canada into the Great Lakes. Progressively colder air
in association with waves moving through the flow will increase lake
effect activity. Although the details of this are a bit fuzzy due to
likely shifting winds, some spots could end up seeing significant
lake effect snow over the next week or so. The main short term
forecast concerns revolve around the details of lake effect snow
showers and resultant snow accumulations.

Tuesday night into Wednesday...The first in a series of short waves
veers winds from south/southwest to southwest Tuesday evening with
winds remaining nearly steady through this time. Mean 850-700 mb
relative humidity is a only 40 to 50 percent. So it looks like
chance pops for rain or snow showers with the trough Tuesday evening
then slowly increasing coverage of snow showers overnight Tuesday
into Wednesday. The relative lack of moisture should limit snow
accumulations to an inch or two.

Wednesday night into Thursday...Another short wave trough moves
slowly into the region. This will veer southwest winds Wednesday
night into the west Thursday morning then the northwest northwest
Thursday afternoon. We get an influx of moisture as well with mean
rh increasing to a robust 80 to 90 percent. In addition...lake/850
mb delta ts are right around 20. Model soundings look very
impressive with inversion heights through the roof (at least to
20,000 feet). This all should add up to intensifying lake effect
snow bands, especially for the normal snowbelts. These bands should
be shifting around though because of the veering winds, so despite
very favorable parameters, snow accumulations may be tempered some
(although still could see a few spots getting up to around 6 inches
during this time period). Daytime temperatures will be closer to the
normal upper 20s to lower 30s while lows remain a little above
normal in the middle and upper 20s.

&&

.LONG TERM...(Thursday night through Monday)
Issued at 400 PM EST Mon Dec 5 2016

High Impact Weather Potential: Lake effect potential greatest
Thursday night through Friday, with some significant
accumulations possible west of I-75.

Primary concern through the extended remains lake effect snow
possibilities, especially Thursday night through Friday. Cold H8 air
will move overhead behind a mid-week system, getting progressively
colder going into the weekend. Flow continues to remain
predominantly NW with this, and the favored snow belts could see
some significant accumulations by Saturday morning. While the cold
air remains overhead going into the weekend, the environment will be
a bit more hostile for lake effect with weakening winds and warm
advection as subtle ridging moves in. This will result in lowering
PoPs through the day Saturday. Signals for another system
Sunday/Sunday night could bring some more accumulating snow, but
with considerable divergence in the guidance details will have to
get hammered out in the coming days.

With the arrival of the cold airmass, temperatures will run below
normal from mid-week through the weekend, something we haven`t
seen much of so far this winter.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1243 PM EST Mon Dec 5 2016

Remnant westerly flow lake effect will keep clouds in across PLN
for a few more hours, while skies have been thinning with more
holes for sunshine across much of nrn lower. Maybe there can be a
handful of hours of VFR, but looking upstream across Wisconsin and
srn Lake Michigan, more widespread stratus was seen. The nrn edge
of this clouds was also thinning due to a bit of afternoon mixing,
but can foresee these clouds expanding north and east into tonight
as night falls and the BL cools with the presence of an inversion
just above the ground. This would lead to IFR/MVFR CIGS.
Confidence is not too high right now with the whole cloud scenario
though.

Winds will back around to out of the south, then SE and increase
into Tuesday.


&&

.MARINE...
Issued at 400 PM EST Mon Dec 5 2016

Developing low pressure lifts into SW Ontario tonight, then drifts
into Quebec by Thursday. A cold front will arrive tomorrow, and will
be followed by increasingly colder air and a tighter pressure
gradient through the end of the week. Not only will lake effect
snows becoming more prevalent over time, starting Tuesday night,
snows will become more intense, especially Thursday.

Winds will increase late tonight and even strengthen further through
Thursday. Veering from SW to NW over that span. Will just put
advisories out everywhere for now, but gales certainly remain
possible.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY from 1 AM Tuesday to 7 PM EST Wednesday for
     LHZ345>349.
     SMALL CRAFT ADVISORY until 5 PM EST this afternoon for
     LHZ345>347.
LM...SMALL CRAFT ADVISORY from 1 AM Tuesday to 7 PM EST Wednesday for
     LMZ323-341-342-344>346.
     SMALL CRAFT ADVISORY until 5 PM EST this afternoon for LMZ341-
     342.
LS...SMALL CRAFT ADVISORY from 1 AM Tuesday to 7 PM EST Wednesday for
     LSZ321-322.
&&

$$

NEAR TERM...SMD
SHORT TERM...AJS
LONG TERM...ALM
AVIATION...SMD
MARINE...SMD



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