Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 211043
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
543 AM EST Mon Jan 21 2019


.AVIATION...

Divergent low level winds and extremely dry arctic air across Lower
Mi will keep lake clouds well away from the Se Mi TAFS today. A sfc
ridge axis will pass overhead this afternoon. This will result in a
slow but steady drop in the northwest winds this morning, with winds
becoming light and variable this afternoon.

.DTW THRESHOLD PROBABILITIES...

* None.

&&

.PREV DISCUSSION...
Issued at 250 AM EST Mon Jan 21 2019

DISCUSSION...

Frigid airmass in place, as the 00z DTX sounding came in with an 850
MB temp of -25 C. Surface temperatures have already fallen into the
zero to -10 F range at press time, with just enough wind to easily
support wind chills in the -20 to -25 F range. Wind chill advisory
will continue through Noon for all of southeast Michigan, with a few
locations even briefly colder than -25 F. Meanwhile,
multiple/disorganized bands of lake effect snow continues over
southern Lake Huron, with NAM/RAP still indicating modest 925 MB
lift/positive omega through the morning hours impacting the eastern
shoreline, and seems prudent just to extend the winter weather
advisory to Noon to match the wind chill expiration. Building
heights/warming mid levels and anticyclonic flow pushing eastward
will certainly cause activity to gradually diminish and push bands
offshore as the day wears on.

Meanwhile, the center of the arctic high should be over Northwest
Ohio this evening, setting up areas right near the southern michigan
border with the deeper snow cover to have a good drop, below zero
this evening, with temps rising a bit overnight as we begin to get
in return flow behind the high and warm advection mid/high clouds
work through the area. These dry arctic air masses tend to be
stubborn to dislodge right near the surface (and this is evident
with the dew pts lagging), and actually think a snow to wintry mix
(sleet/freezing rain) is in store Tuesday evening as low pressure
tracks into the Western Great Lakes, with the night time setting not
doing any favors helping to accelerate the transition to rain.
Still, the low level jet is so strong (70 knots), transporting 5
g/kg of specific humidity within the 850-700 MB layer, warm air
should win out fairly quickly, at least up through I-69 corridor,
with areas north having a bit longer of a period of frozen
precipitation as they will be closer to the low track on Wednesday.
Even so, local SREF weighted probabilistic guidance suggests just 1-
3 inches of snow accumulation, with ice accumulations less than a
tenth up that way for Tri-Cities and northern Thumb region, with
amounts quickly tapering off as one heads south with the quicker
transition to rain.

Enjoy the milder Wednesday, as the next arctic plunge is on track to
arrive Thursday evening/night, sending 850 MB temps back down into
the negative low-mid 20s on Friday (blend of FV3-GFS/Euro), with a
reinforcing shot coming for Saturday as clipper tracks through
Friday night. Light snow accumulations are possible with this
moisture starved system due to the pristine thermal profiles/high
snow to liquid ratios. Although the latest Euro has trended farther
south with the track and is almost too far south, and many GFS
ensemble members provide support to the Euro solution.

Bitter cold airmass, with temps 10-15 degrees below normal appear
locked in for the Weekend in the clipper`s wake, as amplified North
American trough sets up along and east of the Mississippi river.

MARINE...

Winds and waves will decrease during the course of the day as arctic
high pressure expands across Lower Michigan. This will lower the
risk of freezing spray as the day wears on. The high will advance
east to the east coast by Tuesday morning. Strengthening southerly
return flow will develop across Lake Huron tonight in its wake. The
high will hold over the east coast into Wednesday morning while low
pressure lifts across the northern Great Lakes Tuesday night.
Strengthening southerly winds will result tonight into Tuesday. The
strong winds will persist into early Wednesday before the low exits
to the northeast of the region. The onset of the winds will occur as
remnant arctic air resides across the lakes. Even as strong low
level warming gets underway Tuesday night, the corresponding
strengthening of the southerly gradient will sustain strong winds
despite decreasing over lake stability. While the probability of
wind gusts over 40 knots Tues and Tues night is low, the probability
of gusts to 35 knot gales is high, prompting the issuance of a gale
watch.

Another intrusion of arctic air is forecast to overspread the Great
Lakes Thurs night into Friday. This will bring another round of
gusty winds (possibly gale force) and high probabilities of heavy
freezing spray.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Wind Chill Advisory until noon EST today for MIZ047>049-053>055-
     060>063-068>070-075-076-082-083.

     Winter Weather Advisory until noon EST today for MIZ049-055.

Lake Huron...Heavy Freezing Spray Warning until 4 PM EST this afternoon for
     LHZ363-462>464.

     Gale Watch from Tuesday morning through Tuesday evening for
     LHZ361>363-462>464.

     Heavy Freezing Spray Warning until 10 AM EST this morning for
     LHZ421-441>443.

     Small Craft Advisory until 4 PM EST this afternoon for LHZ421-
     441>443.

Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....SC
DISCUSSION...SF
MARINE.......SC


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