Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KDTX 100754
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
254 AM EST Sun Dec 10 2017

.Discussion...

A strong lobe of vorticity rotating around base of mean upper low
centered over/east of James Bay will brush the northern lakes area
and push a weak surface trough into the region late today. Hires
models, including hrrr/ruc13, all support the idea of a decent
convergence region setting up south of this feature this afternoon
over the northern forecast area. West-southwest flow trajectory will
most likely allow a lake effect plume to funnel into area along and
norther of the I-69 corridor. Models suggest low level inversion in
the 5-6kft range by late in the day in the 5-6kft area, which should
support cloud depths sufficient for decent snow showers activity in
this banding. Previous forecast addressed this well, and still feel
that local snow amounts up to an inch will be possible before the
aforementioned surface trough works through and breaks up the better
snow bands into an area of flurries/scattered light snow showers.

Broadening out across the rest of NOAM, water vapor imagery shows
our next system of interest coming onshore in northern British
Columbia early this morning. This shortwave, while somewhat compact,
looks to be rather vigorous in its satellite representation. This
feature will top the western NOAM upper ridge, dig into the midwest
early Monday and then lift across the Ohio Valley into Monday night.
as it is overtaken by much larger PV anomaly that drops quickly SSE
from Nunavut.

Hires models suggest there will be an interesting interplay between
these features as they phase over/just east of the region. For our
purposes, the quicker this phasing begins, the more influence the
Gulf/Alaska shortwave will have on parts of the area, namely in the
form of additional light snowfall as some form of a deformation zone
precipitation follows the initial light snow. It is very difficult
to interpret the Arctic shortwave(s) given current the satellite
representation that far north, but model trends suggest potential of
this system exceeds our recent light snowfall.

If nothing else, the track of this shortwave from the Gulf/Alaska is
allowing for a plume a slightly better moisture from the Pacific (H7
specific humidities of 2 g/kg, pushing 3 g/kg in H85-H7 layer) which
should support several inches of snow (capped by how quickly the
lift translates east through the area). It will also be interesting
how the lake aggregate modulates low level features as the influence
of the main Arctic wave begins to influence the overall scenario.
This mesoscale influence from the Great Lakes seemed piece meal in
respect to yesterday`s system, but perhaps another couple of days in
this cold airmass will allow for a more organized response. Would
guess this will have a neutral to slightly positive influence on the
strength of low level forcing with this system attm.

Cold airmass of the past week deepens further as colder air of the
season spills in the north in the wake of Monday`s system thanks to
the strong influence of the Arctic stream. Highs Tuesday/Wednesday
will only reach the low/mid 20s-upper teens/low 20s respectively.
Low temperatures in the single digits Tuesday night will also allow
wind chills to dip below zero.

While some moderation in this pattern still seems plausible into
next weekend, it comes as a result of significant jet stream energy
from the Pacific region flattening the western NOAM upper ridge and
allowing for a broader NOAM trough. So, any milder temperatures back
into the 30s to 40ish? will come at the price of unsettled weather
as a series of shortwaves ride through the region within this active
northwest storm track. Meanwhile, the cold air remains poised rather
near the Canadian/US border.

&&

.MARINE...

Westerly flow, mostly in the 20 to 25 knot range over Lake Huron
today will shift to the northwest by this evening as a cold front
slides through. Winds will weaken tonight into Monday as low
pressure advances pushes into the region from the west. Deepening of
the surface low to the east of the Great Lake Monday Night and
Tuesday and an influx of arctic air will lead to a high probability
of northwest gales on Tuesday. In fact, gusts of 40 knots or
slightly greater are possible early Tuesday morning.  In addition,
the degree of cold air will also support high probabilities of
freezing spray and snow squalls. Winds willundergo a gradual
weakening trend Wednesday as high pressure attempts to expand into
the area from the west.

&&

.PREV DISCUSSION...
Issued at 1151 PM EST Sat Dec 9 2017

AVIATION...

Short lived period of clearing will attempt to work through the
region early this morning, before stratus expands eastward off lake
Michigan under emerging westerly low level flow.  Upstream
observations indicate an initial period of lower VFR with this
inbound lake moisture, but with a lower potential for a period of
MVFR and even some flurries yet this morning. There remains a signal
for a more focused region of convergence to settle in the vicinity
of MBS/FNT. This will introduce the possibility for brief disruption
to visibility within an locally heavier snow showers this afternoon,
with some minor accumulations of less than an inch. PTK and the
Detroit corridor largely appear removed from this localized forcing,
but could eventually witness some light snow showers/flurries within
a period of MVFR by late Sunday into Sunday evening.

For DTW...Periodic cigs below 5000 ft expected through Sunday, as
flow turns to westerly and lake Michigan moisture funnels
downstream.  Occasional flurries a possibility through the period,
with best shot for snow showers awaiting the arrival of a frontal
boundary Sunday evening.

//DTW THRESHOLD PROBABILITIES...

* Medium confidence for ceilings at or below 5000 feet tonight and
  Sunday.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Watch from late Monday night through Tuesday evening for
     LHZ361>363-421-441>443-462>464.

     Small Craft Advisory until 4 AM EST Monday for LHZ441.

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

$$

DISCUSSION...DG
MARINE.......SF
AVIATION.....MR


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.