Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
626 am EST Tuesday Dec 10 2013
Pockets of lake stratus based within the 2500 to 3500 feet layer will
intermittently drift through Southeast Michigan through the latter
half of the morning. An area of deeper moisture will work back into
Southeast Michigan during the afternoon and evening hours as low
pressure tracks through the region. This will result in an
expansion in snow shower coverage...especially from ptk northward
where conditions will tend to fluctuate within MVFR/IFR. Westerly
winds will turn gusty middle afternoon through the evening as mixing
For dtw...terminal on the southern periphery of the main moisture
plume tied to the trough passage. Some intermittent MVFR
restrictions in light snow showers centered in the 20z-00z
period...minimal if any accumulation. Westerly winds gusting in
excess of 25 knots after 20z...plausible a few peak gusts to approach
35 knots early evening before winds ease.
//Dtw threshold threats...
* low confidence in ceilings remaining below 5000 feet through 18z...
high confidence in ceilings below 5000 feet from middle afternoon into
Previous discussion...issued 358 am EST Tuesday Dec 10 2013
Short term...today and tonight
High amplitude upper troughing anchored off the nearly stagnant
polar vortex centered over Hudson Bay fully entrenched across the
Great Lakes...a significantly lower height field attendant to the
main trough axis now arcing into the region. This adjustment the
driving force behind a renewed intrusion of Arctic air into
Southeast Michigan overnight...a weak cold air advective component
likely still in play through the duration of the morning. Flurries
or very light snow showers remain possible yet this morning with
this process...although the eastern reaches of the lake supported
low level moisture plume will temporarily be trending drier with
Focus into the afternoon period turns to the compact clipper system
now noted on water vapor working through the broader cyclonic flow
over eastern Minnesota. This wave will sweep across the lower
peninsula during the middle-late afternoon hours...the main vorticity
center aligned across northern/central sections of lower Michigan.
This will provide a spike in middle level ascent largely tied to DPVA.
Nice little region of light snow at present attendant to this
wave...despite the seemingly inherent modest synoptic moisture field
tied to the Arctic air. Suspect this wave will receive a healthy
lake moisture contribution as it centers over Lake Michigan late
this morning...with 00z model guidance presenting a moderate degree
of Overlake instability in the lowest 1 km at that time. Main area
of saturation...or supersaturation at times...with respect to ice
will again align in that favored -10 to -13c range. This
points toward seeing a steady increase in snow shower coverage
downstream this afternoon and evening...greatest across central and
northern sections of the area. Growing Overlake instability within
a persistent westerly flow immediately in the wake of this system
will continue to direct lake moisture downstream heading into
tonight. This will perpetuate the development of additional light
snow shower or flurry activity. All told...looking at an
accumulation potential generally of a dusting to locally half an
inch through tonight.
Temperatures will recover little today in this environment...highs
arriving largely in the lower 20s. Westerly gradient will tighten
immediately behind the clipper...while a period of renewed cold air
advection erodes the existing stable layer and provides some added
depth to the mixed layer. This will again lead to a gusty latter
portion of the day. Gust potential slightly higher today...
certainly plausible to see the strongest gusts exceed 35 miles per hour. This
will ensure wind chill readings hold in the single digits through
the day. Lows tonight in the teens...wind chills dipping below
Long term...Wednesday through Monday
The next dry clipper system will slide out of the northern plains
tonight tracking through the southern County Warning Area between 12-18z Wednesday.
Difficult to gauge progress of the shortwave at this point with the
responsible shortwave energy still hung up over portions of northern
British Columbia and Alberta. All signs point to a well developed
shortwave residing within entrance region of a middle to upper level
jetlet that will become ingested in the back end of the consolidated
eastern United States polar jet. Shearing deformation in the 800-700
mb layer projects to be outstanding residing immediately north of a
+50 knot midlevel jet streak. Static stability remains high
throughout the column with very little in the way of frontal
forcing. Midlevel cva shapes up to be best immediately south of the
County Warning Area. Therefore...a small qpe event the first half of the day with
high snow ratios. For these dry clippers prefer to lean on precise
shortwave track for the relatively higher amounts. With this event
like the look of the midlevel jet/shearing deformation forcing to
allow for a fluffy one half to 1 inch of snowfall for the southern
two tiers...perhaps 3 tiers. High efficiency due to cold
temperatures should allow many other areas to check in with a few
tenths. Cold air advection will occur behind this wave causing highs
to be during the morning...falling temperatures during the
afternoon. Wind chills will be in the single digits above
zero...falling below zero with the setting sun Wednesday evening.
Fresh subsidence is forecasted to flash across Lake Michigan and
take hold of lower Michigan Wednesday night. Nwp is showing an
inversion set to build in with this subsidence which causes some
heartburn for clearing. However...the airmass will be incredibly dry
as precipitable waters crash by more than half of the morning values. Will call
for lower sky cover which will support a very cold night. Undercut
guidance with lower to middle single digits above zero. Wind chills
are expected to bottom out between 10 and 15 degrees below zero.
Geopotential heights will begin to rebound on Thursday with flow
turning west southwesterly. Don/T think this will matter much for
temperatures as readings will move off of a cold start. With a very
short day here in middle December temperatures will remain stuck in the
teens...wind chills creeping upward between 0 and 5 degrees above
zero. With the arrival of the more westerly flow trajectories models
hint at a convergence streamer off of Lake Michigan penetrating
central portions of lower Michigan. This is good for increasing
clouds and a mention of flurries Thursday.
A weak surface low feature will pass over the Great Lakes this
afternoon ahead of another surge in fresh Arctic air. The
combination of the very cold temperatures with a tightened pressure
gradient will bring another round of westerly gales for the open
waters of Lake Huron from late this afternoon through tonight. A
heavy freezing spray warning has also been issued to accompany the
Gale Warning. A weak surface ridge will try to push through the
Great Lakes on Thursday. However...this high is expected to be
squeezed southward which will keep relatively higher gradient in
flow over the Great Lakes well into Friday.
heavy freezing spray warning...lhz361...from 10 PM Tuesday to 10 am
Gale Warning...lhz361...from 10 PM Tuesday to 10 am Wednesday.
Heavy freezing spray warning...lhz362-lhz363-lhz421-lhz441-lhz462-
lhz463-lhz464...from 4 PM Tuesday to 10 am Wednesday.
lhz464...from 4 PM Tuesday to 10 am Wednesday.
Small Craft Advisory...lhz422-lhz442-lhz443...until 10 am Wednesday.
Lake St Clair...
Small Craft Advisory...until 4 am Wednesday.
Michigan waters of Lake Erie...
Small Craft Advisory...until 4 am Wednesday.
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