Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
710 am EDT sun Mar 9 2014
Stray patches of stratus near mbs will be all that has a chance to
disrupt a VFR clear start to the day. A shortwave passing to our
north and east will then lift a warm front into the area this
afternoon. This combined with diurnal effects will increase wind
speed to 10-15 knots...possibly gusting to 20 knots at mbs/fnt.
Leaning more pessimistic with ceilings as it looks like ample moisture
will be trapped under the strengthening/lowering inversion which
will result in scattered 2500ft cloud layer late this afternoon with
pockets of broken not out of the question. The trend looks to
continue into the overnight lowering further to around 1500ft or
less while filling in more. There is a low chance of some drizzle
by Monday morning but confidence is too low to include in the tafs
at this time.
//Dtw threshold threats...
* medium confidence that ceilings will fall below 5000ft around 04z.
Previous discussion...issued 403 am EDT sun Mar 9 2014
Short term...today and tonight
Middle/upper level trough will work east of the area today which will
position a northwest to southeast oriented baroclinic zone across the state. This
will prevent too much of a warm up from occurring until later
tonight when a shortwave drops through Ontario pulling a warm front
up into the region which opens the door for increasing heights over
the state. The elevated front will lift through in the afternoon
allowing a nice warmup aloft between about 950-700mb...temperatures above
0c...with the aide of a 50kt westerly ll jet around 900mb. With high
pressure keeping a deep layer of dry air over the region today...the
main issue with this forecast is dealing with the potential for
dz/fzdz late tonight when isentropic ascent with the warm front
modifies/moistens the boundary layer. Model consensus shows a strong
inversion developing around 925mb leaving the surface layer near the
freezing mark with temperatures up to 2-3c aloft. Though there is little
moisture in the warm layer where relative humidity values maximum out near
60%...remnants of the very dry surface ridge in place...the bl becomes
saturated by 04-06z. The depth and location of the moisture leads
to a dz scenario at best. The surface temperatures over The Thumb will
hold just below freezing through the night which opens the door
for a period of fzdz. Temperatures will be above freezing for fnt
and points south and west by the time saturation occurs preventing
any freezing. Regardless of where the freezing line sets up...it
will be a short duration event with little to no impacts to the
A small but potent upper circulation over the Pacific coast of
Canada will be kicked inland today and will reach central Manitoba
by Monday morning. The reinforcing warm front associated with this
wave will maintain a favorable environment for drizzle during Monday
morning before the warm sector arrives during Monday afternoon. The
low level thermal ridge will set up more over the Ohio Valley based
on majority model 850 mb temperature and 1000-850 mb thickness, but
expect enough warming for maximum temperatures in the middle 40s. This
leans the forecast toward the warmer NAM/met MOS guidance which
should counter the cold bias in model skin temperature during strong
warm advection patterns over snow cover. Even when accounting for
the cold bias, model soundings still exhibit limited boundary layer
mixing due to the strong inversion shown centered around 850 mb. At
the same time, there will be a window during the afternoon for March
sun to contribute as low clouds exit and before high clouds thicken.
A complex forecast, no doubt.
The complexity in the forecast continues Monday night into Tuesday
as a weak cold front, at the surface, settles over lower Michigan
and connects with the Lee cyclone developing over the Central
Plains. The surface temperature gradient is on the diffuse side as
the true polar air mass remains bottled up over northern Ontario,
but the character of the front from a Theta-E perspective is shown
in model data to be rather sharp in the 850-700 mb layer. This is
especially true over the plains where Pacific moisture and upper
level height falls will Foster continued surface cyclogenesis and
deepening through Tuesday. Prefer the deeper GFS and European model (ecmwf) solutions
on the system evolution after that as both phasing of energy from
the Gulf system and cold air surging southward through the Midwest
and plains states will contribute to strengthening. The European model (ecmwf) did
make a slight northward adjustment on the low track through the Ohio
Valley which illustrates future track refinement is still likely.
For now, the long wave pattern appears progressive enough to keep
the system moving to the middle Atlantic coast during Wednesday leaving
Southeast Michigan subject to rain and snow associated with middle level
frontal forcing initially and then possibly off the north flank of
the low Wednesday morning. Precipitation probability is pushed up to likely
for Tuesday night in this forecast package, south of I-69, but with
manageable amounts for now.
The trailing surge of polar air will take up residence for Thursday
but model trends continue to indicate a quick departure by Friday. A
fairly large northwest flow short wave is timed with good agreement in the
global models to reach Lake Superior by Friday. Unfortunately, this
system appears to be associated with a round of larger scale height
falls and long wave amplification during the weekend that is all too
familiar for cold air in the Great Lakes this season.
Southwest winds will increase today through Monday ahead of low
pressure moving through northern Ontario, however, the combination
of ice covered lakes and milder air streaming into the area will
support a stable near surface profile and limited gust potential.
That being said, southwest gusts around 30 knots will be possible
over the central axis of Lake Huron including outer Saginaw Bay
during the afternoon and tonight.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).