Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
340 PM EST Sat Feb 13 2016
Deep middle/upper level troughing that moved into the Great Lakes last
night will slowly drift eastward through the overnight. In
addition...a strong 1040mb surface Canadian surface high has begun to build
into the area. The center of the high will pass right over Southeast Michigan
tonight providing calm winds and clear skies. A corridor of snow
showers developed this afternoon as winds backed slightly more
westerly and advected a decent amount of lake moisture under the
5kft inversion. It took the diurnal instability to ignite any
showers but light snow showers filled in quickly this afternoon
mainly south of M59. These showers will last through the daylight
hours before loss of diurnal forcing...and strengthening surface high
quickly scour out any lingering showers and clouds eventually.
This is all setting US up for another cold night. 850mb temperatures have
only slightly recovered from the -25c recorded with the 12z DTX radiosonde observation
as the coldest air drifts eastward...and models only show
improvements to around -22c by Sunday morning. The healthy snowpack
over most of the area will allow for another night of good
radiational cooling. Forecast lows are below all guidance as they
usually perform quite poorly with these setups. Taking last nights
lows into account...minimal heating through the day...skies clearing
pretty quick tonight...and high pressure squarely overhead...lows
should drop to temperatures similar to Friday night. Look for The
Thumb to drop to -5f to -10f and the Detroit area to drop to near
0f. This leads US into the next issue of potential wind chills. Wind
speeds themselves will be down to less than 5 knots as the center of
the high drifts over. That will lead to wind chills falling to -10
to -15f by morning...just below advisory criteria. Would not be
surprised to see a few observations come in below -15f but should
be spotty at best and not enough to warrant a headline.
Dry conditions on Sunday will quickly give way to the next
accumulating snowfall overnight into Monday morning. As the upper
level trough pushes further east away from the Great Lakes...more
progressive longwave pattern sets up. A shortwave trough will swing
through the southern Great Lakes bringing a period of light snow. A
compact vorticity maximum...clipper...rounding the base of the trough will
lift NE through lower Michigan starting 00z Monday. Main forcing looks to
be a band of isentropic ascent as decent middle level warm advection
takes place ahead of the approaching ridge. Coverage looks to be
quite widespread due to the nature of the forcing. Models in fair
agreement with between 0.05 and 0.10 inches of quantitative precipitation forecast for the event
which seems fair giving its Pacific origin. Snowfall should range
from 1 to 2 inches across the area by Monday evening.
A brief break in snow chances will occur on Tuesday as a ridge of
high pressure builds into the region. A clipper system is then
forecasted to track from the northern plains and move southeastward
Tuesday night and into Wednesday. Current model runs show the bulk
of the system tracking south of the County Warning Area...with the extreme northern
fringe clipping the extreme southern counties. While this track is
still a bit uncertain...at this time accumulations for Lenawee and
Monroe counties could total between an inch and two inches between
Tuesday and Tuesday night. As one travels north...less accumulation
will be experienced. Beginning Wednesday...Arctic high pressure
builds into the Great Lakes region...bringing another shot at colder
temperatures to Southeast Michigan. The next precipitation system
arrives next weekend...however...it is much too early to anticipate
precipitation type or track of the system.
High pressure will expand across the Great Lakes tonight. While this
will support decreasing winds and waves...a persistent trough over
Lake Huron will make this diminishing trend a very gradual one. The
departure of the surface high to the east on Sunday will allow southerly
winds to develop...backing southeast Monday morning with the
approach of a low pressure system. Residual Arctic air over the lake
will support unstable conditions which will allow wind gusts to
reach 20 knots over the Open Lake Sun night and Monday. Winds will
then diminish into Tuesday as high pressure builds across the region
in the wake of mondays low pressure system.
Aviation...issued 1157 am EST Sat Feb 13 2016
Despite the dry Arctic air...enough Lake Michigan moisture has funneled
into Southeast Michigan to support the development of a broken diurnal VFR cumulus field.
While there remains some mfr strato cumulus from early this
morning...daytime heating and increased mixing depths will lift
these bases to VFR by taf issuance. There will in turn be some
enhancement to the flurries and light snow showers. The intensity of
which should be less than yesterday. Localized increase in surface
high pressure across NE lower Michigan and the Saginaw Valley should focus
the stronger west-northwest winds south of fnt this afternoon /gusting up to
20 knots at times/. The loss of daytime heating this evening and
increased low level diffluent flow resulting from expanding surface high
pressure will allow skies to clear around or shortly before sunset.
Winds will in turn become light.
For dtw...there will be enough of a westerly component to the low
level wind field over Southern Lake Michigan to enhance the degree of low level
moisture into metropolitan Detroit. This should support ceiling heights
during the afternoon below 5000 feet.
//Dtw threshold probabilities...
* medium in ceilings below 5000 feet this afternoon and early this
Lake Huron...heavy freezing spray warning until 10 PM EST this evening for
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).