Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 200451
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1151 PM EST Thu Jan 19 2017


.AVIATION...

IFR/LIFR ceilings continue to slowly expand back across the area
late this evening. This trend is expected to continue as low level
moisture slowly increases from the south with approach of weak low
pressure. IFR fog can also be expected with pockets of 1SM or lower
vsby also possible at times. Light rain will spread into area with
the low pressure in the 12z-15z time frame with either -RA or -DZ
persisting into the afternoon hours. Ceilings may lift to lower MVFR
with passage of this system at end of the period.

For DTW...IFR/LIFR ceilings will persist through Friday morning at
least with areas of fog being replaced by light rain by 12z or so
and -RA/-DZ into the 18z time frame. At best, expect lower MVFR cigs
by 22z-24z with a likely return to IFR/LIFR overnight Friday night.

//DTW Threshold Probabilities...

* High for ceilings below 5000 feet this forecast.

* Low for ceilings and/or vsbys aob 200 feet and/or 1/2SM
  into early Friday morning.

* High in precipitation falling as all rain/drizzle Friday.

&&

.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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