Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221043
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
543 AM EST Mon Jan 22 2018

.AVIATION...

Favorable positioning north of a warm front will sustain the
existing widespread low stratus and fog throughout the SE Michigan
airspace during the late morning period. Recent observations
indicate that pockets of rain now entering the region will bring
some improvement to visibility, limiting the potential for
additional dense fog where visibility drops below 1 mile. LIFR
ceilings will remain common through this time. Improvement in
conditions from south to north by early afternoon as the warm front
lifts across the region. Upstream trends and recent model guidance
continue to support a complete removal of low level moisture at
least as far north as FNT.  This will provide a window for VFR
conditions as a mid level dry slot dictates conditions late today
into early tonight. Greater potential for MBS to retain LIFR
conditions throughout the daylight period, with the warm front
struggle to reach this far north. Low level moisture will increase
all locations upon the arrival of a cold front by early Tuesday
morning. This will bring a corresponding reduction in ceiling height
and a renewed increase in precipitation potential.

For DTW...Existing LIFR conditions in low ceiling and dense fog will
see slow improvement during the late morning period as intermittent
rainfall lifts through. Much greater improvement then expected this
afternoon in the wake of warm frontal passage. Window for cigs to
lift above 5000 ft for the latter half of the day.

/DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less this morning. Low this afternoon.

* High for rain as precipitation type today and tonight.

&&

.PREV DISCUSSION...
Issued at 347 AM EST Mon Jan 22 2018

DISCUSSION...

Early morning fog will persist several more hours until a warm front
lifts north and showers fill in across the area. Overall
visibilities have improved over the last few hours with only
sporadic 1/4SM observations being noted across SE MI. Though fog
will remain across the area for several hours, only locally dense
fog is expected here on out, thus the headline will expire at 4am
and we`ll handle any brief pockets of dense fog with SPSs.

Active stretch of weather to start the new work week as a dynamic
and very mature low/mid level low over the plains continues it`s
march toward the Great Lakes. Models in good agreement with the
center of the low tracking through mid MI late tonight into Tuesday
morning. Several rounds of rain showers will pass through the region
associated with this low and the several fronts connected to it.
Timing these periods of showers and possible dry slots seems to be
one of the biggest forecast challenges early on. Model soundings
show temperatures above freezing across all of SE MI up through
about 700mb keeping ptype all liquid through Tuesday morning.

In advance of the low, the lead wings of isentropic ascent along a
warm front, current draped just south of the MI border, will provide
the first round of rain showers this morning. The band of showers
has already come together as seen on regional radar mosaic and
should lift into the state by about 09Z. Strong low level jet
starting to nose into SW lower MI should keep this band progressive
lifting it north of the M59 corridor by 17Z as the warm front itself
pushes north. Good moisture and forcing should allow a quick quarter
inch of qpf with this band as it lifts through.

Models vary with handling the pops during the daytime hours as it
appears there is 2 distinct dry slots rotating about the low. First
one is lifting northward just ahead of the first cold front and
could clip the metro Detroit area this afternoon from about 17-20Z.
Coverage of showers will decrease but still could see some scattered
light showers. The cold front them moves through and is losing its
definition due to occluding processes and distance from the low.
Still should see a second batch of showers pass east through the
area after 20Z. Meanwhile, with the warm front stalling over mid MI
the east west oriented isentropic band could stall across the
Saginaw Valley and Thumb leading to rain through most of the day.

The next dry slot then looks to lift up and through southern MI
between about 00-06Z Tuesday ahead of the secondary cold front
located much closer to the low. Water vapor imagery shows this dry
slot very well so the only question is do showers start bubbling up
and filling back into the dry slot as its sliding though? In terms
of the forecast, will recognize the dry slots with chance pops and
highlight the frontal bands with likely or categorical pops.

The center of the low and mid level PV max will keep at least
scattered showers around through the rest of the night.
Northwesterly winds on the backside of the low will usher in a
colder airmass but still plenty of moisture to work with as the
deformation band passes through on Tuesday. We will be dealing with
a cooling boundary layer which could bring about a mix of rain and
snow later in the day. At this point still expecting any snow
accumulations to be on the light side as change over won`t occur til
waning hours of the event late Tuesday evening.

Event total rainfall amounts should range from around a half inch
near the Ohio border to around 1 inch north of I69. This much
rainfall over frozen ground with recent snow melt could cause some
flooding concerns. Look for area rivers to rise with runoff and
ponding in low lying areas also seems quite probable.

Quiet weather returns through the mid/late week as ridging builds
into the region. Temps will fall back to late January normals with
highs around freezing and lows in the 20s. Models advertising the
next system to arrive over the weekend. Model consensus currently
points toward another warm event across lower MI as the surface low
is north of the area pulling warm air back up through the region.

MARINE...

Low pressure will track toward the central Great Lakes today and
tonight, reaching the central Lake Huron waters by Tuesday morning.
Easterly winds will strengthen today as this system approaching,
leading to a period of gales over the north half of Lake Huron this
afternoon and evening.  The system will also produce widespread
coverage of precipitation, primarily rain from Saginaw Bay southward
and a wintry mix to the north. Wind will diminish as the low moves
through central Lake Huron overnight and Tuesday. Northwest wind
trailing the system could approach gales briefly Tuesday afternoon
and evening.  Winds will ease by Wednesday as weak high pressure
builds into the region.

HYDROLOGY...

Mild and moist conditions across the region will result in periodic
bouts of rainfall through the daylight period.  This environment
will also work to to melt any remaining snow cover while the ground
remains mostly frozen. Efficient runoff from both the melting snow
and rainfall could result in ponding of water on roads and other
prone areas. Rivers, creeks and streams around the region could also
become elevated due to runoff. Total rainfall is expected to be
around 1 inch through Monday night, with most falling during the
day.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning from 10 AM this morning to 10 PM EST this evening for
     LHZ361>363.

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

$$

AVIATION.....MR
DISCUSSION...DRK
MARINE.......MR
HYDROLOGY....MR


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