FXUS63 KDTX 172046
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
346 PM EST Sun Dec 17 2017
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.
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.
Issued at 1247 PM EST Sun Dec 17 2017
Poor aviation conditions will continue across the area today and
tonight as a warm front struggles to move northward through lower
Michigan. The boundary is now expected to stall in the MBS area as a
weak wave of low pressure slides more eastward through the southern
Great Lakes. A more northward track was needed to pull the front
completely through the terminal corridor. Precipitation potential
with this system remains low and of the sprinkle/flurry variety as
the pattern over IL/IN/OH weakens while moving northward. Borderline
MVFR/IFR ceiling and visibility is then expected to lower down into
IFR/LIFR on the downside of the diurnal cycle and as relatively mild
boundary layer air continues to increase across the snow cover. The
persistence of IFR/LIFR conditions will then be further supported by
a southward return of the front early Monday before conditions
improve as the boundary dissipates during Monday afternoon.
For DTW... The morning pattern of light rain over IL/IN/OH is
expected to weaken before reaching DTW during the afternoon. That
will allow time for temperatures to rise above freezing before any
new development tonight, which is also expected to be very light
rain or drizzle. Otherwise, IFR ceiling mixed with fog will break
intermittently after the front moves north during late afternoon
into early evening. If clearing is substantial after sunset, then
fog could become more widespread and dense during late evening and
before milder air and increase wind renews stratus coverage
//DTW THRESHOLD PROBABILITIES...
* High for ceiling 5000 ft or less today and tonight.
* Moderate for rain precip type tonight.
* Low for 200 ft ceiling and/or 1/2 sm visibility tonight.
Lake Huron...Gale Watch from late Monday night through late Tuesday night for
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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