Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 060848
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
348 AM EST Wed Dec 6 2017

.DISCUSSION...

NEAR TERM / TODAY THROUGH TONIGHT

As of 345 AM EST...Much quieter night across southeast Michigan as
compared to last night`s cold front passage and accompanying strong
wind gusts. Continued mechanical mixing in the boundary layer has
allowed for 10-20 mph winds through the night with occasional gusts
of 25-35 mph. The persistent winds have helped kept low temperatures
from falling too much, but the combination of clearing skies and
continued CAA will still allow low temperatures to fall into the mid
to upper 20s.

Powerful low pressure system stalled near southern Hudson Bay has
begun the occlusion process and will continue to fill throughout the
day. This will allow the gradient flow to slowly weaken as the day
progresses, but diurnal heating and deepening mixed layer in the 4-5
kft range will allow for another day of gusty conditions. Gusts
today will typically range from 25-35 mph, well below advisory
levels. Plentiful stratocu is expected to fill back in across the
region as the low-levels are moistened by lake enhancement below the
boundary layer capping inversion. Very dry airmass in place and well-
mixed boundary layer coupled with southwest flow trajectory will
lead to a generally dry day for most, although as the flow becomes
slightly more westerly this afternoon cannot rule out some flurries
with no accumulation expected. High temperatures will overachieve in
the well-mixed environment, reaching into the mid and upper 30s,
warmest in far southeastern Michigan.

Lake effect activity east of Lake Michigan ramps up tonight, with
continued flurry potential across most areas. A more persistent band
continues to be picked up by high-res guidance and may drift into a
corridor between M-59 and the Ohio border late this evening into
tonight, but should be rather transient and fractured in nature as
mesoscale forcing is frayed far from Lake Michigan. Still, if this
band plays out, a coating to a few tenths of an inch of snow will be
possible given the high snow ratio environment (greater than 20:1)
in place. Low temperatures tonight will range from the low to mid
20s.

SHORT TERM / THURSDAY THROUGH SATURDAY NIGHT

The short term period will be characterized initially by the
southwest/westerly lake effect snow regime, with the significant
activity staying largely out of southeast Michigan. Episodic
flurries and brief light snow showers will be possible continuing
into Thursday, as some better moisture and a trailing shortwave
aloft move over the region. Anticyclonic vorticity advection behind
the departing shortwave will lead to a dry day Friday.

The next potential, more impact-based, weather system to watch will
be a possible clipper system this weekend diving southeast from
Manitoba. Model guidance is showing a clear trend in some sort of a
clipper low forming as additional energy diving south in the
longwave trough spawns cyclogenesis, but there is considerable
uncertainty with the track, which will have big implications on snow
potential this weekend. The NAM is further north and east with the
track, and the deepest solution (995 hPa), leaving southeast
Michigan on the unfavorable side of the clipper low although the
strength of the dynamics would still be enough for scattered light
snow. The ECMWF is weaker (around 1005 hPa) and further south with
the track across northern Indiana/Ohio, putting the area in the
favorable quadrant for accumulating light snow, while the GFS is
taking the middle ground. Still some time to watch how this system
plays out in the short term model guidance, as it will all hinge on
how the embedded pieces of shortwave energy interact with the
longwave trough, but there is some potential for a widespread light
snowfall Saturday into Sunday.

Temperatures will trend below freezing as the thermal trough moves
overhead aloft during the period, with highs around 30 and lows from
the upper teens to lower 20s. It will continue to be brisk with
occasional gusts of 20-25 mph especially during the daytime hours.

LONG TERM / SUNDAY THROUGH TUESDAY

Broad longwave troughing will continue into the long term with the
flow regime becoming more northwesterly. This pattern will continue
to support below normal temperatures and chances for periodic light
snow. Long range guidance diverges significantly on influence of
embedded shortwaves, but overall the pattern will be more favorable
for light snow showers with lake connections from Michigan, Huron,
and Superior all in play depending on the eventual placement of the
upper-level trough axis.

&&

.MARINE...

Gale warnings and small craft advisories remain in effect with no
change in expiration as weakening trends remain intact in this
forecast cycle. A large and deep low pressure system near James Bay
will maintain westerly gales across Lake Huron today. Gusts in the
40 to 45 knot range will be within reach for a few more hours during
the morning before settling toward the 35 knot threshold by
afternoon. The low pressure system will move slowly across James Bay
during the day while filling steadily, which will allow gusts to
drop toward 30 knots by late afternoon and tonight. Another front
will move through overnight and Thursday and bring an additional
surge of cold air into the region. It will produce an uptick in snow
squalls over the lake but will not bring much additional wind
impact. A stronger low pressure system is then due to move through
the central Great Lakes during the weekend.

&&

.PREV DISCUSSION...
Issued at 1157 PM EST Tue Dec 5 2017

AVIATION...

Gusty southwest winds will remain in place through the night. The
overall gust magnitude with gradually ease with time, but with gusts
settling below 25 knots during the early morning hours.  Ensuing
increase in mixing depth accompanying daytime heating will then lead
to some increase to the gustiness on Wednesday /25 to 30 knots/.
Higher based VFR stratus will slide northeast overnight, leaving a
period of limited cloud coverage into the early-mid morning period.
VFR conditions throughout Wednesday, simply some increase in higher
based stratocu again for the afternoon. A deeper plume of moisture
will drop southeast into the region toward evening. This may result
in some reduction of ceiling height and a low potential for light
snow showers or flurries Wednesday night.

For DTW...Winds remain gusty from the southwest through Wednesday.
Gusts peaking during the afternoon period near 25 kts. Very low
potential for cigs at or below 5000 ft through the morning period,
as greater cloud coverage remains to the north. Potential increases
after 15z.

//DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less through Wednesday morning, medium
  Wednesday afternoon.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 4 PM EST this afternoon for LHZ361>363-421-422-
     441>443-462>464.

Lake St Clair...Small Craft Advisory until 4 PM EST this afternoon for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EST this afternoon for LEZ444.

     Low Water Advisory until 4 PM EST this afternoon for LEZ444.

&&

$$

DISCUSSION...IRL
MARINE.......BT
AVIATION.....MR


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