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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
605 am EST Friday Nov 28 2014



Aviation...

//discussion...

Some lingering lake effect clouds between 3500-4000 feet will stream
over the area this morning. These will primarily be scattered in
nature...but a terminal site could see some periods of broken skies.
VFR conditions are expected to prevail this afternoon as drier air
arrives from the west. A warm front will then lift through Southeast
Michigan late today and tonight...spreading snow and MVFR ceilings
into Southeast Michigan starting between 20-23z. The best snowfall
and lowest visibilities (ifr to mvfr) will be this evening as an
upper level disturbance rides over the front...enhancing lift. There
is some uncertainty to where the heaviest snow will fall...and how
long into the night it will last. Further refinements to the tafs
are likely as this event begins to unfold. At this time...it appears
the terminals will receive between 1.0 and 2.0 inches. Low-level dry
air will work into the area Saturday morning behind the
front...allowing ceilings to rise back up to VFR.

For dtw...snow and MVFR ceilings/visible look to spread into the area
around 22z. A period of IFR visibilities could develop if a heavier
band of snow settles in over the terminal this evening.

//Dtw threshold threats...

* high confidence in ceilings below 5000 feet late Friday afternoon
through early Saturday morning.

* High confidence precipitation type will be all snow through 12z
Saturday.

&&

Previous discussion...issued 342 am EST Friday Nov 28 2014

Short term...today and tonight

Drier air and a ridge of surface high pressure extending up into
lower Michigan has allowed lake effect showers to taper off...even
allowing for some breaks in the clouds. The trend for lower clouds
to break should continue through the early morning hours as a very
dry airmass arrives (per 00z grb raob) and inversion heights
continue to lower over the lake...tempering the lake effect
response. Higher clouds will however begin to arrive ahead of the
next system.

Models are a little divided with how a small snow event will unfold
from late this afternoon into tonight. Upper energy off the West
Coast and over British Columbia will continue to drop south and east
into the Pacific northwest and northern rockies today and
tonight...allowing a large area of surface low pressure to develop
over The Rockies and plains. This will push the ridge over the area
east...and send an elevated warm front northward into lower Michigan
late this afternoon and tonight. Lead shortwave energy ejecting out
of the system over the west will meanwhile track across
Michigan...over the top of the frontal boundary. Isentropic
ascent...and a little upright forcing from fgen...look to overcome
dry air in the boundary layer by evening allowing light snow to
spread into the area. Forcing should be aided by steepening middle-
level lapse rates this evening and overnight as cooler air aloft
slides in with the upper wave. This is when the best snowfall should
occur.

Models are a little divided on where over Southeast Michigan the
shortwave will meet up with the front...and further adjustments to
the forecast remain possible as the day unfolds. NAM solution
currently looks to be the furthest north (and most aggressive with
qpf)...while the operational GFS has trended the furthest
south...now focusing better precipitation south of the M-59
corridor. Gem/Euro/parallel GFS/and Storm Prediction Center WRF solutions all lie
somewhere in the middle...and preference is given to this consensus.
Did expand higher band of probability of precipitation and snow from previous forecast
slightly southward...on account of 00z model trends and considering
radar returns further south into Iowa/Illinois than previously
anticipated this morning. Expecting to see between 0.5-1.5 inches of
snow across most of Southeast Michigan...mostly between 4 PM and
midnight...with some light snow showers then continuing overnight as
the 850-925mb frontal boundary continues to lift through Southeast
Michigan. Precipitation type is expected to remain all snow...with
00z forecast soundings and thermal profiles now keeping the layer of
above-freezing air aloft to our southwest by sunrise.

Maximum temperatures will run lower today in the wake of some cooler air
that pushed in yesterday. Highs are only expected to reach the middle
20s to near 30. Warm air advection overnight will limit
cooling...allowing min temperatures to fall very little from daytime
highs...cooling only into the middle 20s.

Long term...Saturday through Thursday

Warm air advection will work its way to the surface on Saturday as a
surface warm front lifts north through the central Great Lakes as
middle level heights continue to rise across the region. 850 mb
temperatures are forecast to rise to around +10 celsius across the
southern Great Lakes. Despite the passage of the surface warm front
daytime temperatures are only expected to get to around 40 degrees
as a strong inversion traps low level moisture in the lowest few
thousand feet of the column. This will lead to an extended period of
light rain or drizzle during the weekend. Low temperatures on
Saturday night will be close to saturdays highs with abundant cloud
cover and continued drizzle preventing much in the way of
radiational cooling. Temperatures on Sunday will range from the middle
40s across the north to the middle 50s towards the Ohio border ahead of
an approaching cold front prognosticated to track through the area late
Sunday afternoon into Sunday evening. Although this front will
bring a strong push of cold air through the area...it will not have
much in the way of precipitation as the low will be of Pacific
origins and unable to tap into deeper Gulf moisture well to the
south.

Behind the cold front daytime highs will come back down into the 30s
during the early part of the work week as strong high pressure of
1040+ mb tracks through the Great Lakes region. Modest warm air
advection will boost temperatures a few degrees Wednesday and
Thursday on the back side of the high as a middle level trough with a
weak surface reflection brings a slight chance for snow showers to
the area during the middle part of next week.

Marine...

Although surface winds have dropped well below headline
criteria...elevated wave heights continue across Southern Lake
Huron...clipping the nearshore zones around The Thumb. Therefore
will continue the small craft advisories early this morning for
these areas. A warm front will lift north into the region today
which will flip the winds to the southwest/south by this evening.
Wind gusts of 25 knots are expected over much of Lake Huron before
warmer and more stable air works into the region Saturday night.

&&

DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...Small Craft Advisory until 7 am EST this morning for lhz421-441.

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

$$

Aviation.....Hlo
short term...hlo
long term....kurimski
marine.......kurimski



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