Area Forecast Discussion
Issued by NWS Gaylord, MI

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337
FXUS63 KAPX 181525
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1025 AM EST Sat Jan 18 2020

.UPDATE...
Issued at 1015 AM EST Sat Jan 18 2020

Snow event unfolding about as expected this morning as initial
surge of elevated warm/moist advection drives bands of moderate to
heavy snow across northern Michigan. Surface low responsible for
this snow cutting east across central Lake Michigan, with its
parent sharp shortwave trough rotating a bit further to the
northwest. Expect surface low to continue to move east across
northern lower Michigan this afternoon. Snow should continue to
fill in as mid level forcing increases, with transit pockets of
inch per hour snowfall rates likely. Given increasingly detached
warm conveyor belt to our southeast, not expecting these heavier
snow rates to be particularly organized, but still thinking
several more inches of snow is likely by evening, especially
across eastern upper and the north half of northern lower
Michigan. Approach of narrow (and shrinking) mid level dry slot
across southern areas will bring a mix of light snow/freezing
drizzle into early this afternoon, transitioning back to all snow
during the afternoon as main mid level support arrives. Gusty east
and southeast winds will bring more blowing and drifting snow,
only exacerbating the already hazardous driving conditions.

&&

.NEAR TERM...(Today through Tonight)
Issued at 328 AM EST Sat Jan 18 2020

...Snow, heavy at times today...

High Impact Weather Potential: Moderate to at times heavy snow.
Gusty winds, blowing and drifting snow.

1007mb surface low is in western IA. Warm/moist advection ahead
of the low is resulting in a broad shield of precip well to its
east. This is advancing into northern lower MI early this morning,
in the form of light snow. Radar returns are less than 25dBz in
most places, and vsbys are generally 1-3SM where the snow has
started. The low will move quickly east today, crossing northern
lower MI this afternoon. More widespread and heavier precip will
occur today, especially in the 1st half of the day, with some
potential for lake enhancement in se low-level flow. Once the low
departs, lake-enhanced to lake-effect snow will continue tonight.

Our first push of precip into the area has run out of steam a bit;
the leading edge of snow is making only slow northward progress.
That will change as we approach sunrise, as much more substantial
500mb height falls displace the ridging that is still holding on
aloft. This corresponds with a potent shortwave, rotating around
the parent 500mb closed low in nw MN, taking on a negative tilt as
it swings toward Lake MI this morning. This will provide a much
stronger burst of dynamics and forcing. Widespread, heavier precip
covers much of IL, and it is this that will work northward and
translate into heavier QPF in northern MI. Moderate to heavy snow
will overspread most or all of northern MI this morning, with the
St Marys Valley taking the longest.

Though a slug of healthy snow is inbound, one thing that will hold
accums back is relatively low snow-liquid ratios. A deep isothermal
layer is present in Nam Bufr soundings today, but it is warmer than
desired, between -5 and -10C. Even in eastern upper MI, this leads
to a rather narrow DGZ thru much of today, and a deep warmer layer
beneath. By perhaps mid and especially late afternoon, the DGZ
becomes much deeper in eastern upper MI, and this process plays
out in northern lower MI this evening. Snow-liquid ratios will be
much higher tonight as we transition to lake effect.

A back edge of heavier precip will make some inroads into northern
lower MI by midday, indicative of some temporarily drier mid-level
air. No good surface low passage is complete without a little
freezing drizzle mixing in in the middle of the event, and places
near/south of M-72 have the best chance for seeing it. This should
not be high-impact, as roads should be snow-covered and not prone to
developing a glaze of ice. Deeper moisture will fill back in behind
the intial drier wedge, before mid-level drying starts work back
into the sw beginning late today.

Se winds, and 850mb temps of around -8C over northern Lake Huron,
will generate lake enhancement into far se portions of upper MI.
(Lesser enhancement is expected further south into the APN/Rogers
area of northern lower, where 850mb temps upstream are warmer.)
Thus, despite the somewhat later arrival time for snow up there, the
heaviest snowfall looks to occur in se Chippewa and eastern Mackinac
Cos. Near-term numeric guidance is emphatic on this scenario,
favoring 7 to 9" of snow. Given wind and blowing/drifting snow
concerns, feel reasonably confident in upgrading that area to a
winter storm warning. This has already been done.

For tonight, the upstream mid-level dry punch stalls out, aided by
the close passage of the closed 500mb over Superior and north of
Georgian Bay. Colder air gradually wraps back into the region,
mainly overnight, reaching the mid minus teens at 850mb. In northern
lower MI, an initial wnw fetch become nnw with time, with snow
showers remaining widespread in those associated snowbelts. Eastern
upper MI starts with light winds, before a north to even (very
unfavorable) nne fetch develops. This will suppress lake
effect/enhancement there tonight, and perhaps snow shower activity
will wane over far eastern upper MI overnight. More in the way of
accums is expected in nw lower MI, with the caveat that initial
delta Ts are a little marginal, and the winds will be veering with
time. Have some general 2-4" accums tonight near-west of I-75 in nw
lower MI, highest in Kalkaska Co and environs.

Max temps today mid 20s to mid 30s. Min temps tonight teens to lower
20s.

&&

.SHORT TERM...(Sunday through Monday)
Issued at 328 AM EST Sat Jan 18 2020

...Lake Effect, Does It End?...

High Impact Weather Potential...Lake Effect continues into Sunday.

Pattern Synopsis/Forecast...Sunday, models show that the LES should
be plentiful, except that the wind direction will be North to NNE
This takes E upper out of the LES for the day, with maybe some snow
near Whitefish Point. otherwise, as the lake aggregate trough sinks
south, then the winds over Lake Michigan begin to veer to the NE,
before backing to the North and possibly NNW by 00z/Mon. Almost all
of the models, including some of the CAMS models are beginning to
show that the snow diminishes to flurries, and then dry air moves in
overnight, and warmer 850 mb temperatures. The models show flurries
in Upper Michigan at 12z/Mon, and the dry air is moving into the N
Lower and N Lake Michigan by 18z/Mon. Any Light snow amounts in the
morning will probably be followed by minor amounts or flurries by
the afternoon. Between 00z/Tue and 06z/Tue, the 850 mb temperatures
warm above -10c which begins to lower the delta Ts to <13c,
especially by 12z/Tue when both the GFS and the ECMWF  are around
-8C, which would put the delta Ts around 12c or lower.

Primary Forecast Concerns...Several days ago, the models showed that
the LES would last for several days. As we have gotten closer to
this time frame, the models have backed off on that idea, with dry
air and eventually, warmer 850 temperatures to end the snow by
Monday some time. As tough as LES is, the diminishing snow is
looking more likely with the expected dry air to push into the
region starting Sunday night. That`s not to say that an
overachieving band isn`t possible, but the likelihood decreases with
time before the next system is expected to get going (Wednesday
night? see below).

.LONG TERM...(Monday night through Friday)
Issued at 328 AM EST Sat Jan 18 2020

High Impact Weather Potential...Maybe a storm by the end of the
week?

Extended (Tuesday through Friday)...The winds remain favorable
Tuesday morning with a favorable temperature profile on the GFS. The
ECMWF is slightly warming lowering the delta TS to around 13C.
However, by Tuesday evening, the high is moving through the Ohio
Valley, and puts the Upper Great Lakes in the return flow, and thus
with warmer and drier air. So the LES looks to end by the Tuesday
afternoon/evening.  The next system looks to affect the region on
Wednesday. The ECMWF has a mix on during Wednesday afternoon
changing to snow (The amounts look minor at this point). While the
GFS start snow until early Thursday morning. Both models slow the
precipitation down during Thursday. Friday morning the models begin
to diverge quite a bit. The ECMWF is dry as the 500 mb low digs into
the Lower Ohio Valley and develops a much weaker sfc low that drifts
up the valley and keeps the precipitation our of N Lower. While the
GFS lifts the 500 mb low out of the Southern Plains, and up into the
mid-Mississippi Valley rain or a mix up into N Lower which would
then change back over to all snow by 12z/Sat, as the 500 mb low
moves over Lower Michigan. This means low chance pops as the
National Blend averages out the pop from the two models.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 652 AM EST Sat Jan 18 2020

Light snow has been falling in much of northern lower MI for the
overnight hours. Vsbys in the 1-3SM range have been common. The
first round of heavier snow is now pushing into nw lower MI, with
vsbys around 1/2SM at MBL and FKS, and 1/4SM at Big Rapids. These
lower vsbys/heavier snow will gradually push across northern lower
MI today, with only lighter snow lingering past late afternoon.
Not impossible for MBL/TVC to see a touch of FZDZ mix in for a
short while today. Lake effect snow showers will return behind
departing low pressure for tonight, resulting in more variable
conditions, but nw lower MI (including TVC) will get the worst of
it.

Snow-liquid ratios will be in the lower teens this morning, the
middle teens this afternoon, and the upper teens to around 20
tonight.

Se winds will be gusty this morning, with diminishing and variable
winds this afternoon and early evening as the low moves overhead.
W to n winds will be established tonight, and will be gusty again
late.


&&

.MARINE...
Issued at 328 AM EST Sat Jan 18 2020

Se gales will continue on our Lake Huron waters early today,
before slackening somewhat. Low pressure will eventually cross
central/northern Lakes MI and Huron this afternoon, with a period
of quite variable winds. Eventually will settle back in with gusty
northerly winds by late tonight.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY until 7 PM EST Sunday for MIZ020-021-
     025>027-031>033.
     WINTER STORM WARNING until 5 AM EST Sunday for MIZ088-096.
     LAKESHORE FLOOD ADVISORY until 1 PM EST this afternoon for
     MIZ018-020-024-030-035-036-042-088-095>098.
     WINTER WEATHER ADVISORY until 1 PM EST Sunday for MIZ016-022-028-
     086-087-095-098-099.
     WINTER WEATHER ADVISORY until 7 AM EST Sunday for MIZ017-018-023-
     024-029-030-097.
     WINTER WEATHER ADVISORY until 1 AM EST Sunday for MIZ034>036-041-
     042.
LH...GALE WARNING until 1 PM EST this afternoon for LHZ345>349.
LM...SMALL CRAFT ADVISORY until 1 PM EST this afternoon for LMZ323-
     341-342-344>346.
LS...NONE.
&&

$$

UPDATE...MB
NEAR TERM...JZ
SHORT TERM...JL
LONG TERM...JL
AVIATION...JZ
MARINE...JZ



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