Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 180522
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1222 AM EST Mon Dec 18 2017


.AVIATION...

Difficult forecast continues as low level moisture advection begins
to increase as surface wave lifts toward lower Michigan. Main trend
this evening is to be much more bullish with light precipitation in
the 09-13Z timeframe on northern periphery of cyclonic circulation. A
fairly consistent consensus has developed with more coverage of
light qpf at less than 0.05inch. Taking the model soundings at face
value for depth of saturation. As a result, carrying a prevailing
group for light snow at MBS while including -FZRASN at FNT. With
surface temperature lifting above the freezing mark, and outside of
better deformation forcing will only be carrying a DZ mention for
the southern TAF sites. Unidirectional southwest flow with little
advections will keep low cloud over the area.

For DTW...given observation trends, rolled back on the LIFR/IFR
vsby/cig forecast. Did include prevailing drizzle with surface
temperatures above zero.

//DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less tonight.

* Moderate for rain precip type tonight.

* Low for 200 ft ceiling and/or 1/2 sm visibility tonight and Monday
  morning.

&&

.PREV DISCUSSION...
Issued at 346 PM EST Sun Dec 17 2017

DISCUSSION...

Stationary boundary that was draped generally west to east just south
of the OH/IN/MI border this morning will eventually lift north as a
warm front this evening in response to a shearing wave entering the
western Great Lakes and associated surface reflection. Cloudy
conditions will remain in place through today as stratus associated
with the wave continue to stream in from the southwest. Winds will
gradually veer from easterly flow influenced by the high pressure
over the Ontario/Quebec border to a more south-southwesterly flow
later today as the surface low nears. This southwest flow is also
resulting in a period of warm air advection and some more deeper
moisture, though the better dynamical forcing for precipitation has
remained to the south for the most of the afternoon. Still do not
see a signal in the ensemble probabilistic guidance for any freezing
drizzle the rest of the afternoon and evening as the front as we are
struggling to get any appreciable precipitation.

The front is forecast to stall out around the Tri-Cities area this
evening. This will provide a better opportunity to see light
precipitation fall in the later part of tonight and tomorrow morning
period with the increased moisture and weak ascent over the
boundary. The trailing surface pressure will begin to enter Michigan
and ride along this boundary. Some weak low-mid level ascent should
be enough to produce some light precipitation/drizzle conditions.
Expect most of what falls to be in the form of liquid since thermal
profiles should be warm enough over the majority of the area. This
should prevent any ice from being introduced into the column. The
one exception will be areas north of I-69 where the boundary will
reside. It still may be cold enough to get some mix of
drizzle/flurries/freezing drizzle near the vicinity and north of the
boundary. However, no impacts are expected with little if any
accumulation in the forecast. The saturated low levels under these
conditions will also lead to fog potential overnight. Have
introduced patchy fog, which will need to be monitored for any dense
fog development late tonight.

Rather benign weather expected by tomorrow afternoon as low end
precipitation chances may linger around as low amplitude wave
passing to the north of the Great Lakes draws in some weak forcing.
Southwesterly flow will help push some of the cold air out and allow
temperatures to increase toward 40 degrees near the MI/OH border.
Mid to upper 30s expected elsewhere. By Tuesday morning, 850 mb
temps are expected to increase to 2-3C. This will help temperatures
reach into the 40s across the entire area before cold air advection
is pushed southward from another low amplitude wave moving across
the northern Great Lakes.

Surface high pressure building into the region on Wednesday will
bring dry, calm conditions as a slightly cooler air mass keeps highs
in the low to mid 30s. An upper wave digging into the Southwest US
will induce lee cyclogenesis over the Central Plains on Thursday.
This low pressure system will bring the next chance for widespread
precipitation to Southeast Michigan during the late week period.
Latest model guidance suggests an initial period of warm advection
snowfall develops along and north of a frontal boundary draped
across Southeast Michigan on Thursday. Better chances for snowfall
currently look to remain across the Saginaw Valley to Thumb region
and points northward.

The low pressure is then progged to lift northeastward west of
Southeast Michigan on Friday as increasing warm advection boosts
temperatures into the 40s. This current solution would favor mainly
rainfall as better moisture overspreads the region on Friday.
However, a slight southward deviation in the track of the low could
bring a snowier solution to the region. After the passage of the
low, colder conditions will return to the region next weekend as
highs fall back into the low to mid 30s on Saturday.

MARINE...

Light wind and low waves will continue over all marine areas tonight
and Monday as a weak low and warm front move through the central
Great Lakes. A light rain and snow mix will be possible, along with
some fog, as the only marine weather concerns before these features
dissipate Monday in favor of a larger and stronger low over central
Canada. This system and the associated cold front are projected to
be strong enough for wind gusts reaching gale force first late
Monday night in southwest flow and then Tuesday and Tuesday night in
the colder west to northwest flow. High pressure will then quickly
settle over marine areas Wednesday into Thursday.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Watch from late tonight through late Tuesday night for
     LHZ361>363-421-441-462.

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

$$

AVIATION.....MR
DISCUSSION...AA/JD
MARINE.......BT


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