Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 200942

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
442 AM EST Fri Jan 20 2017


Low-level easterly flow has maintained widespread fog and patchy
dense fog across the area this morning, especially in the Detroit
area. Conditions will hover near airport minimums until arrival of
rain from the south which will bring improvements in vsby. Cigs will
be slow to recover given ongoing moisture advection and added
moisture from rainfall. Potential for improvement to IFR during peak
heating before LIFR cigs/vsby return tonight.

For DTW...Easterly flow likely to force NE operations as LIFR holds
firm through at least early aftn. Gradient diminishes and shifts to
southerly late, any improvement to IFR shortlived. Upstream
observations of widespread dense fog over the midwest this morning
portend a high liklihood of a return to LIFR tonight.

//DTW Threshold Probabilities...

* High for cigs aob 5kft

* High for cig/vsby aob 200ft/1/2sm late tonight


Issued at 353 AM EST Fri Jan 20 2017


Monitoring coverage and density of fog during the early morning
prior to the cold rain set to move through lower Michigan during the
day. The latest observational trends continue to suggest the Thumb
region having the best potential for dense fog where visibility
hovered mostly around 3/4sm at press time. Recovery indicated in the
Detroit metro area is partly due to increased surface gradient which
is expected to develop northward through sunrise and help lift fog
into a low stratus layer. This may be just enough to keep visibility
above headline criteria but which will be monitored through the

The rain pattern will be driven by the well organized low pressure
system centered over the mid Mississippi valley that has a strong
upper trough extension into the Tennessee and Ohio valleys. This is
producing a broad area of isentropic ascent into Lower Michigan that
will gradually evolve into a shearing deformation pattern through
the afternoon. The system has access to a plentiful supply of Gulf
moisture as surface observations indicate upper 50s to lower 60s
dewpoint in the warm sector as far north as western Tennessee.
Expect the ongoing band of rain to gradually develop into SE
Michigan from the Ohio border northward through the morning. The
relatively slow northward pace will be part of the deformation
transition as the upper trough extension slides into Ohio and
associated surface pressure falls help back the flow through the mid
levels over Lower Michigan. This will give surface temperatures a
chance to struggle farther above freezing before precipitation
onset, especially in the northern Thumb region. Easterly boundary
layer flow will have temperatures in no big hurry to make a rebound
until later in the day when the filling surface reflection/trough
moves into the region. Surface wind will shift southwest trailing
this feature and help readings make a run into the lower 40s late in
the day, mainly Detroit to the Ohio border.

The next in a series of short waves moving through the broad upper
trough out west will arrive in the central Plains tonight. This
system will kick up a slight ridge aloft between systems over lower
Michigan during the evening before quickly resuming weak moisture
transport overnight into Saturday. Weak warm frontogenesis will make
good use of the already near saturated boundary layer and produce a
mix of drizzle and light rain. Another round of fog is also likely
which will last into Saturday morning before some improvement during
the afternoon. The low track through the Midwest will move the warm
sector over Lower Michigan and boost temps into the lower and mid
50s most locations. The mild and moist theme will then continue into
Sunday as yet another low pressure system moves into the Gulf coast
to Tennessee valley. This will maintain a chance of showers into
Monday before a larger scale ridge arrives to dry things out more
convincingly toward the middle of next week.


Broad low pressure encompassing the Great Lakes region will cause
weak gradient conditions through the weekend and very quiet marine
conditions for late January. By late Sunday, strengthening low
pressure over the Deep South will bring gusty easterlies to around
25 knots. Winds will diminish by late Monday.


A narrow ribbon of deep layer moisture associated with a mid-level
trough axis will lift from south to north across the area early this
morning into this afternoon. Rainfall totals will be around 0.25
inches. There are no flooding concerns.


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



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