Scientific Forecaster Discussion
fxus63 kdtx 121646
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1146 am EST Tue Dec 12 2017
Gusty northwest flow will continue through afternoon before
decreasing in the Evening. Lake effect clouds and snow bands will
continue to dissipate as drier air advects into Southeast Michigan.
Still may see a brief flurry at any taf site but overall expecting
skc-sct skies. Lake effect bands will still be active just to the
west of forecast area and could see them brush at times fnt, yip and
dtw this afternoon and eve with bkn050 and few flurries but overall
should remain VFR. Northwest flow around 15-20kts with gusts 25-30kts will
gradually weaken into the evening. Weak surface high pressure
ridging will bring skc-sct skies for first half of the night.
Lighter winds will gradually back to the SSW by 12z. Clouds will
also be increasing and lowering to 2-3kft after 12z ahead of an
approaching winter storm. Light snow will quickly advect in from the
NW around 15z as winds continue to back to the SSE.
For dtw...strong and gusty NW winds will continue before decreasing
during the evening. Drier air advecting in is dissipating lake
effect clouds and snow showers. Conditions should remain VFR with
mainly sct-bkn clouds around 5kft. Lake effect bands will remain
active just to the west and may brush the Airport briefly later this
afternoon and evening with flurries as winds begin to gradually back
to the west. Skc-sct skies most of tonight as weak high pressure
ridge slides through backing the winds to SSW by 12z. Clouds will
be increasing towards morning ahead of an approaching winter storm.
Ceilings will gradually lower to MVFR after 12z with light snow
moving in from the NW around 15z. Visibilities should remain around
6 miles for a few hours. Conditions should rapidly deteriorate after
18z with several inches of snow accumulations expected along with
low end MVFR ceilings and visibilities around 1sm. Winds will
continue backing to ESE by 00z.
//Dtw threshold probabilities...
* moderate confidence for bkn ceilings at or below 5000 feet at
times this afternoon.
* High confidence in northwest crosswind thresholds continuing
issued at 1135 am EST Tue Dec 12 2017
Wind Advisory for the Huron County shoreline remains in good shape
with peak gusts through the morning right near advisory criteria. The
majority of the County will remain sheltered from higher end wind
gusts. The Winter Storm Watch for lake effect snow pushing onshore in
The Thumb tonight will be cancelled shortly. 12z consensus depicts
typical convergent corridor developing immediately offshore in northwest
flow will keep les over the water for most or all of the night. Hard
to expect anything over an inch at the shoreline...if that.
The afternoon package will contain significant forecast changes for
Wednesday. 00z trends continued through 06z and an improving
conensus has emerged in today's 12z guidance. Confidence is further
improved by the fact that minor variations in wave interactions
amongst the different guidance is resulting in relatively little
change in the surface reflection as forcing remains tied to the much
stronger northern wave. Several inches of snow is expected over most
or all of the area beginning midday Wednesday and lasting into
Wednesday night. 3 to 5 inches for all locations except The Thumb is
expected. A very healthy fgen band will bring potential for 6 inches
or more. The potential placement of this band is expected to be
somewhere between M-59 and the Michigan border with in/OH. A Winter Storm
Watch will be given strong consideration with the 4pm forecast
issuance. Finally - les wrapping in on the back side of the low will
give potential for a few additional inches in portions of The Thumb
making up for what is expected to be lighter daytime accumulations. A
Winter Storm Watch will likely be issued this afternoon.
issued at 1015 am EST Tue Dec 12 2017
as of 1015 am...earlier band of embedded snow squalls impacting
portions of Shiawassee, Genesee, Oakland, Livingston, and Wayne
counties continues to slowly wane in intensity as the morning
progresses. Radar returns from earlier in the morning suggest that
accumulations within the band may have ranged from a coating to half
of an inch. This activity will continue to weaken through the
remainder of the morning hours, with another few tenths possible in
spots. For the rest of the day, snow shower activity will transition
to sporadic flurries across most of Southeast Michigan, with
scattered lake effect snow showers possible along the immediate
nearshore waters of Lake Huron, especially across Huron County where
a Winter Storm Watch remains in effect beginning at 4pm. Will
continue to monitor lake effect development and trajectories, but the
potential still exists for several inches of accumulation at this
time, thus will keep the watch going for now.
The other main weather story today will be the falling temperatures
and gusty northwest winds. Strong cold air advection and tightening
pressure gradient from departing strengthening clipper across the
northeast will lend to gusty winds of 30-40 mph across most areas
throughout the day. The exception will be Huron County, where gusts
closer to 45 mph especially near Lake Huron will be possible with the
more effectively mixed marine boundary layer. Temperatures will fall
throughout the day, into the lower and mid teens by this evening.
Coupled with the winds, wind chill values will generally range from 5
above to 5 below zero.
issued at 252 am EST Tue Dec 12 2017
Arctic air surging into to the Great Lakes region this morning, as
northern stream upper level trough axis arrives over the central
Great Lakes, with 500 mb low (510 dam) tracking across Northern Lake
Huron today. 00z raob out of Pickle Lake Ontario revealed an 850 mb
temp of -24 c. Some modification of the airmass will take place as it
crosses the northern Great Lakes, but 850 mb temps settling down in
the -18 to -20 c range over Southeast Michigan seems reasonable,
which should hold temperatures in the upper teens to around 20
degrees during the day. The phasing/rapid deepening of the low
tracking into the eastern Great Lakes has been a bit slower to
occur, and think peak wind gusts topping out in the 35 to 40 mph
should hold, with the exception of the northern thumb region as
winds/deeper mixing from Saginaw Bay comes into play, supportive of
winds 45+ miles per hour. With water temperatures over much of Lake Huron still
in the mid 40s, still have concerns for heavy snow showers impacting
the northern tip of The Thumb region (grindstone city-Harbor Beach-
richmondville). Once low pressure releases from Georgian Bay, there
is a meso-high/pressure rise occuring late in the day, which should
help push the lake band(s) over Lake Huron toward The Thumb region,
with snow showers likely scrapping the eastern shoreline of Huron
County this evening. Right now, the best support is from the 00z
hires-arw, which is indicating almost two tenths of an inch of quantitative precipitation forecast
00-06z Wednesday. And unfortunately, it indicates this band will
stay uncomfortable close to the shoreline right into Wednesday
morning. Expectations at this time is for localized 2 to 4 inches,
but there is enough concern to issue Winter Storm Watch for
potentially higher amounts. Obviously with lake effect, the majority
of the County will see little to no accumulation, with highly
localized higher amounts right near the shoreline. Outside of the
eastern thumb region, looking for skies to become mostly
clear/partly cloudy with the northwest flow. Any streamers from the
Lake Superior-Michigan connection likely very narrow and struggling
to make it into Southeast Michigan. Thus, favoring lows in the
single numbers to around ten degrees tonight, and with modest
surface wind (5 knots) by Wednesday morning, wind chills of zero to
-10 f are expected.
A bit of a surprise for Wednesday, although the lead upper wave
tracks into the western Ohio Valley as expected, an even stronger pv
anomaly races down from northern reaches of northwest territories,
and it is this feature and moisture flux/lower static stability over
Lake Michigan which will help draw the clipper and fgen band farther
north, now progged to be stretched across Southern Lower Michigan
(along/south of I-69). With what looks to be ideal thermal profiles
to work with, 850-700 mb average temp in the negative low/mid teens,
coupled with 2-2.5 g/kg of specific humidity, it appears 2 to 5
inches will fall across the south half of the County Warning Area Wednesday
afternoon-evening. If the system is a little slower to exit
Wednesday night, could even see a little bit more. This solution has
unanimous support from NAM/GFS/Canadian and European, but exact
placement of highest snow/fgen band varies a little bit.
Additional upper level energy embedded within the northwest flow to
bring another chance of snow Friday-Saturday, with some semblance of
another clipper tracking through, but the upper level flow trending
more confluent leading to a weakening low pressure. The baroclinic
zone/low track is also uncertain, with big differences in the
solutions by Saturday between Euro/GFS. Very low confidence in the
Strong northwest gales will persist today with gusts approaching
storm force over the exposed nearshore waters of The Thumb and the
open waters of central and Southern Lake Huron. Gale warnings
will remain in effect into tonight before winds subside by early
Wednesday morning. Heavy freezing spray warning will remain in place
as well as temperatures fall into the teens and significant wave
heights range between 10 to 15 feet. Maximum wave heights will
exceed 20 feet.
Michigan...Wind Advisory until 4 PM EST this afternoon for miz049.
Winter Storm Watch from late tonight through Wednesday morning for
Lake Huron...heavy freezing spray warning until 4 am EST Wednesday for
Gale Warning until 5 am EST Wednesday for lhz362-363-462>464.
Gale Warning until 4 PM EST this afternoon for lhz422.
Gale Warning until 4 am EST Wednesday for lhz421-441>443.
Gale Warning until 11 PM EST this evening for lhz361.
Lake St Clair...Gale Warning until midnight EST tonight for lcz460.
Michigan waters of Lake Erie...Gale Warning until 4 PM EST this afternoon for lez444.