Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211954
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
354 PM EDT Tue Mar 21 2017

.DISCUSSION...

A strong arctic cold front has begun its push southward through
lower Michigan today. Temperatures ahead of the front were able to
quickly reach into the 50s across nearly all of SE MI with mid/upper
50s from the Ohio border up through Detroit. The front is currently
draped across mid MI, about to enter the Saginaw Valley. The front
is lacking the moisture needed to precipitation, although has forced
a thick strato-cu field which was not well depicted by any computer
models. Went ahead and increased sky cover from about Flint
northward this evening to account for this likely spreading into the
area before scouring out with the loss of diurnal heating. In
addition to clouds, the front will bring a period of gusty
northwesterly winds as the unstable arctic air surges into the area.
Judging from models and current upstream observations, gust should
peak around 25 knots for a period this evening before relaxing
overnight. The only other feature of note for this evening and
tonight is a shortwave tracking across southern MI ahead of the
front. This will bring some high clouds to southern lower but that`s
it.

To continue the mention of lake effect snow brought up by previous
forecasters, risk is still there but minimal for the eastern Thumb.
Forecast soundings over Lake Huron show favorable low level lapse
rates developing as the thermal trough swings through at around -15
to -20C but lacks in convective depth (around 5kft) and favorable
fetch (northerly flow peaks after the thermal trough exits). Lake
effect cloud bands over Lake Superior are showing their current
struggles. So some light snow showers could occur but not expecting
much if any accumulation.

An arctic high will settle in over the Great Lakes tonight bringing
in much colder and drier air which will allow temps to drop off into
the teens. This will also help bring an end to any lingering lake
effect bands over Lake Huron. This high will move little from
Wednesday and Wednesday night bringing plenty of sunshine but cold
temps with highs only in the mid 30s. Conditions begin to change
Thursday as the ridge axis slides through allowing warm air return
into the Great Lakes. Most of the day should stay dry with only
increasing cloud cover, but rain will likely move in overnight as
isentropic ascent ahead of a warm front spreads precipitation into
the area.

A warm front extending northeastward from low pressure over the
Central Plains on Friday will remain over Southeast Michigan through
the weekend. As the low slowly approaches the Great Lakes region the
frontal boundary will remain nearly stationary. This boundary will
act as a focal point for rain showers Friday through the weekend.
North of the boundary temperatures will remain in the 40s across the
Saginaw Valley and Thumb while further south temperatures will
remain in the 50s to near 60 along the Ohio border. Rain chances
will continue through late Sunday when the low pressure passes to
the east of Southeast Michigan and drier air filters back into the
region early next week.

&&

.MARINE...

An arctic front sliding south through the Great Lakes will bring a
period of gale force winds across Lake Huron as strong cold air
advection and unstable airmass moves in behind the front. Though
confidence is high on gales right behind the front this evening into
the overnight as per current observations upstream, questions remain
as to how long into the overnight they will persist as guidance
suggests winds will stabilize around 30 knots after the initial
surge. Small craft advisories for Lakes St Clair and Erie will also
remain as winds appear to stay a bit weaker down further south. Much
quieter marine weather is forecasted for both Wednesday and the
beginning of Thursday with sprawling arctic high pressure parked
overhead.

&&

.PREV DISCUSSION...
Issued at 103 PM EDT Tue Mar 21 2017

AVIATION...

Surface ridge centered over southern Manitoba will make a strong
push southeastward into the Great Lakes later tonight and set up
shop for Wednesday. A few areas of concern ahead of this push
include upgrade in wind speeds starting this afternoon as low level
cold advection plows southward. Winds already gusting over 25 knots
in northern lower Michigan in shallow mixing. Expect high
probability of gusts exceeding 20 knots by mid and late afternoon
and gusts exceeding 25 knots buy early evening.  Winds should taper
off gradually later tonight as the boundary later decouples after
sunset and surface high moves further southeast. Some cloud concerns
first in low stratocu over northern lower MI moving southward with
cold advection later this afternoon and evening. Models are bearish
on these clouds surviving southward this evening, but would not be
surprised to sse some sct-bkn bases around 3kft for a few hours in
the evening. Other area of concern is mid and high clouds over
northern Illinois and south wisconsin.  Models are consistent in
moving this area over southern lower MI later afternoon and early
evening hours with bases probably no lower than 10kft at worst. By
Wednesday expect deep dry layer over the Great Lakes as surface
ridge builds over the region. Skies to be mostly clear and winds
relatively light.

For DTW...High confidence in NW winds with gusts 20-25 knots
developing around 20 or 21Z. Moderate probability of crosswind
thresholds being met by early this evening. Gustiest winds will
start to diminish after midnight and drop below 10 kts around
sunrise and continue less than 10 knots throughout the day.

//DTW THRESHOLD PROBABILITIES...

*  Moderate in crosswind thresholds being exceeded late afternoon
   and evening.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 4 AM EDT Wednesday for LHZ362-363-441>443-
     462>464.

     Small Craft Advisory until 10 AM EDT Wednesday for LHZ421.

     Small Craft Advisory from 4 AM to 10 AM EDT Wednesday for
     LHZ441>443.

     Gale Warning until 10 PM EDT this evening for LHZ361.

Lake St Clair...Small Craft Advisory until 10 AM EDT Wednesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 AM EDT Wednesday for LEZ444.

&&

$$

DISCUSSION...DRK/JD
MARINE......DRK
AVIATION.....05


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