Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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633
FXUS63 KDTX 192318
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
618 PM EST Thu Jan 19 2017


.AVIATION...

Decent pocket of dry low level air remains in place early this
evening, but northern edge of stratus to the south bumps right up to
I-94, so those terminals will be in/out of IFR cigs early. Approach
of disturbance from the south will allow low level moisture to edge
up tonight, with any periods of VFR this evening transitioning back
to IFR overnight into Friday morning. This system will bring light
rain late tonight into mid morning Friday with drizzle/fog probably
hanging on a bit longer even as deeper moisture with the system
shifts north as axis of system moves through the area. Will improve
cigs to lower MVFR into the 18z-00z period.

For DTW...Terminal will be along border of 1000 foot ceiling early
in the forecast. This area of stratus will increase and lower later
this evening/overnight as additional low level moisture edges north
into area with approach of weak low. This system will bring -RA by
early Friday morning, but transition to -DZ by late morning as
deeper moisture strips away to north. At best, expect a period of
MVFR cigs beyond 18z, which should trend back to IFR by end of
forecast around 06z Friday night.

//DTW Threshold Probabilities...

* Moderate for ceilings below 5000 ft this and evening, high
  for the rest of the forecast.

* Low for ceilings and/or vsbys aob 200 feet and/or 1/2SM roughly
  10z-14z Friday morning.

&&

.PREV DISCUSSION...
Issued at 345 PM EST Thu Jan 19 2017

DISCUSSION...

Cutoff upper level low over the central plains remains somewhat in
between the split flow longwave pattern but has begun to get picked
up by the energetic southern stream. This as a very strong jet
continues to take aim at southern California for the weekend. This
jet and its lead trough are acting to displace the cutoff low
eastward across the country through the end of the week. The cutoff
low is currently embedded within a broad upper level ridge expanded
across much of the central and eastern conus. This ridge, and
resultant deep layer southerly flow, is responsible for the warmer
than average temperatures through the weekend.

The upper low is currently slowly lifting northeast toward the
Midwest. Water vapor imagery shows an impressive plume of moisture
extending from the Pacific, across Mexico, and northeastward along
the Mississippi. Strong southern stream jet max is causing the
trough axis to become negatively tilted as the deformation region
advances north to the Great Lakes. Models in good agreement with
this scenario, bringing in pwats around 1 inch with a
deformation/fgen band shearing out e/w across the area as it lifts
north. Timing of the onset of precip tonight has been pushed back a
few hours as dry air between the surface and around 650mb will take
some time to saturate. Precip should move into Lenawee and Monroe
Counties around 06-09Z, possibly reaching DTW around 12Z, and may
not reach MBS/BAX til closer to 18Z. The later onset brings into
question ptype issues. We`ve been advertising light freezing
rain/drizzle for a couple forecast cycles now assuming precip would
begin during the nocturnal minimum overnight which is around 30-35F
with dewpoints around 30 as well across the north. This would lead
to wetbulbing and possibly a short period of freezing rain/drizzle
at the onset. With a later start time and precip only across the
warmer southern areas at night, current thinking is that the event
will be all rain. By the time the precip lifts north of I69, surface
temps should be warm enough to mitigate freezing at the surface.

After the lead band lifts through, a second lobe of vorticity
rounding the low will quickly follow Friday night. With broad
cyclonic support and this forcing, could see a resurgence of drizzle
or light rain overnight. This pattern will persist through the
weekend with broad synoptic support and upper level troughs rotating
through the region.

An active weather period is in store for the extended forecast
period beginning on Sunday and going into next week.  A series of
waves will move across the Great Lakes region as longwave troughing
holds.  Chances for precipitation remain during much of this time
with a brief dry period possible Tuesday into Tuesday night as weak
ridging builds in briefly.  Temperatures on Sunday will be the
warmest for the remainder of the forecast as warmer air from
southerly winds is brought up into the area.  After that, temps drop
slightly with highs in the 40s for next week.

MARINE...

Weak surface ridging will persist over the central and northern
Great Lakes through tonight. A surface trough will then lift
from the Ohio Valley tonight across Lower Mi on Friday. This trough
is forecast to weaken, sustaining an overall weak gradient across the
lakes. This along with strong over-lake instability due to warm air
across the region will support relatively light east-southeast winds
on Friday. Light easterly winds will persist through the weekend. The
east winds will increase Monday as deepening low pressure is forecast
to lift up the east coast.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....DG
DISCUSSION...DRK/SS
MARINE.......CB


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