Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 220847
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
347 AM EST Sun Jan 22 2017

.DISCUSSION...

A very weak and broad trough of low pressure is positioned over
Lower Michigan during the early morning and will remain in place for
much of the day. Within this pattern is a mild and moist boundary
layer that is being increasingly exposed to radiational cooling as
mid and high clouds slide eastward or remain to the south with
convection over Indiana/Ohio. The result is widespread dense fog
that will persist through the morning and then struggle to lift
during the afternoon. Mid and high clouds will begin to thicken
again over the fog layer as the day progresses and inhibit already
weak mid January potential for surface heating. Calm to light and
variable wind is projected to increase from the east around mid
afternoon which should help with some improvement. Given this
favorable environment for persistence, the dense fog advisory will
be extended through noon with updates later in the morning possibly
needed to extend the headline later in the day.

Other than the fog, a stray shower is possible as the mid level
moisture increases over the region during the afternoon. This type
of moisture transport is more effective at generating precipitation
during the night as demonstrated by the showers/storms over Indiana
and Ohio early this morning. The mid level wind field will also
weaken and back toward the east as the Gulf Coast low pressure
system progresses into the Tennessee Valley by evening. The northern
fringes of this system will give us a better chance of showers
tonight, and especially Monday. This is when the upper low will
phase more with the northern stream to produce a deep layer of
deformation of moderate intensity over Lower Michigan. The agreement
among the 00Z model solutions on this scenario is quite good with
all showing a vertically stacked low near the mid Atlantic coast and
an inverted trough extending through the Great Lakes to help focus
moisture and contribute to deeper vertical motion. The GFS is most
bullish on QPF, as usual, but has some merit in this pattern while
the other models all still favor a high POP/lower QPF scenario
which was already built into our going forecast. The good news
here is that precipitation will be all rain Monday into Monday
evening before the temperature profile begins a slow cooling
trend. A short period of rain/snow mix will be possible as the
deformation pattern shifts eastward and precipitation ends by
Tuesday morning.

The break in the action will be short as the next low pressure
system arrives in the Great Lakes Tuesday night. This system will
be feeding off the larger scale upper level trough and powerful
upper jet as it progresses through the Rockies during Tuesday.
Once east of the Rockies, lee side cyclogenesis will take place
and will be enhanced by sharp baroclinicity pre-existing from the
Gulf Coast into the southern/central Plains. Strong deepening of
the system is then likely as the system approaches the Great Lakes
Tuesday night. The individual model solutions from the latest 00Z
cycle offer a wide range of tracks and intensities but the larger
scale pattern favors the stronger GFS/ECMWF on a track through the
central Great Lakes through Wednesday. A brief wintry mix would be
possible in this scenario before changing to all rain for SE
Michigan should the track and timing hold in upcoming forecast
cycles. A cooling trend will then get underway for the end of the
week as this system exits the Great Lakes and pulls in an air mass
more typical for the end of January.

&&

.MARINE...

Dense fog advisories remain in effect for marine area through mid-
morning. Winds and waves will remain on the light side through the
forecast period...but easterlies will perk up late tonight through
Monday. Onshore flow may necessitate small craft craft advisories
for ice free areas due to elevated waves on Monday. Marine weather
then remains on the quiet side through midweek.

&&

.PREV DISCUSSION...
Issued at 1150 PM EST Sat Jan 21 2017

AVIATION...

Dense fog has remained anchored at KMBS all evening and has built
back west into KPTK. Otherwise, broader area has just begun to
expand through I-94 corridor. Still expect some expanse of fog,
but advance of 4-7kft SCT-BKN clouds with a weak mid level
disturbance main act to limit widespread dense fog. That said,
locations under these clouds over northern Indiana have still be
able to drop to 1/4-1/2SM, so will maintain some expanse of low
cigs and vsbys into the overnight hours. With low level flow
becoming calm and then light east/northeast Sunday morning in
response to as low pressure begins to take shape, any fog in place
will be slow to dissipate completely.

For DTW...Terminal is slowly being surrounded by LIFR/VLIFR vsbys
and cigs, so will maintain a trend in that direction. It should be
noted that where dense fog has developed, vsbys have dropped very
low (near zero at times), so variability has been quite pronounced
in the immediate area. Improvement on Sunday will be very slow as
low level flow becomes very weak and generally easterly with time.

//DTW Threshold Probabilities...

* High for cigs aob 5kft.

* Medium to high for cig/vsbys aob 200ft and 1/4SM much of time
  over night into Sunday morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...Dense Fog Advisory until noon EST today FOR MIZ047>049-053>055-
     060>063-068>070-075-076-082-083.

Lake Huron...Dense Fog Advisory until noon EST today FOR LHZ361>363-421-422-
     441>443-462>464.

Lake St Clair...Dense Fog Advisory until noon EST today FOR LCZ460.

Michigan waters of Lake Erie...Dense Fog Advisory until noon EST today FOR LEZ444.

&&

$$

DISCUSSION...BT
MARINE.......JVC
AVIATION.....DG


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