Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1243 PM EST Wednesday Feb 10 2016
Persistent cyclonic flow combined with weak stability in the lower
troposphere will maintain the chances for banded snow shower
structures through the afternoon hours. Shortwave energy aloft and
aggregate surface trough will also be in the process of ejecting
through southeastern Michigan which will provide additional support.
Model data suggests localized increases in low level convergence for
areas south of Interstate I 69 during the 20-02z timeframe.
Staggered a tempo IFR visibility mention from north to south. Increasing
cold and dry air advection tonight brings higher potential for
clouds to scatter out overnight...before filling back in Thursday
morning with an increasing diurnal heating contribution.
For dtw... west to northwest wind will continue to gust mostly at 20
knots or less and stay under cross wind threshold. Banded to
occasional cellular snow showers should increase again this
afternoon with increased diurnal support. There is increasing
potential that an enhanced pocket of convergence along with the
residual lake aggregate surface trough will push from northwest to
southeast through the Detroit metropolitan area during the evening
commute/early evening hours. Will monitor trends...but there is
a good signal that IFR visibility restrictions of 1sm will be possible
at dtw between 23-02z.
//Dtw threshold probabilities...
* high for ceiling at or below 5kft today and tonight.
* High for snow as precipitation type.
* Low for exceeding westerly crosswind threshold today.
Previous discussion...issued 358 am EST Wednesday Feb 10 2016
The Great Lakes are active and widespread snow showers linger across
the area as broad moist cyclonic flow in the wake of yesterday's
winter storm persists. 850mb temperatures around -15c at present
will probably be as good as it gets until Monday considering the
baffin island special will not arrive until late Friday into
Saturday when 850 mb temperatures will fall to -25c to -29c and highs into the
single digits Saturday.
In the near term...through late morning, the feature of interest is
the band of light returns stretching from Chicago to northern lower
over top of existing les activity. This is driven by approaching
convergence along the back edge of the upper trough and is easily
identifiable on water vapor imagery. Expecting an areawide half inch
at best as it transits the area through about 15z. Cold advection in
its wake will increase convective depths by an appreciable margin to
around 7kft. In addition, Overlake 0-1km Theta-E lapse rates will
fall to a moderate -4 to -6c/km. Together, these should contribute
to a boost in upstream les. Persistent cyclonic northwest flow will then
have the potential to guide a band or two into the area during the
day if the last couple days of high res solutions are to be
believed. Recent radar trends suggest a lake connection may already
be in play in Shiawassee/Genesee/Oakland counties early this
morning. If that is the case, some persistence and a late morning
boost in intensity will be a possibility. The limiting factor for a
healthy les band of the Superior-Michigan variety extending into the
County Warning Area will be a lack of synoptic scale moisture, the bulk of which
will depart with the upper trough axis. In fact, the lack of
moisture is reflected well in the aforementioned Theta-E lapse rates
which are only moderate in spite of the so-called "delta-t" method
which would suggest greater potential. Nonetheless, radar trends
will warrant monitoring through the day.
Cold advection will continue tonight, the airmass supportive of very
cold low temperatures. However, a Stout gradient and cloud cover
will likely put a floor on low temperature potential. The raw NAM/arw are
usually Superior in these cases and both are rather warm, but fresh
snowcover gives reason for pause. Lows around 10 degrees represent a
compromise between the warm/cold guidance.
Resident airmass will stagnate on Thursday with high temperatures
just a touch colder than today as backing anticyclonic flow around
high pressure over the Ohio Valley will introduce the prospects for
at least partial sun if not better.
Isentropic ascent and modest middle-level Theta-E advection will
increase as the motherlode of cold air approaches the Great Lakes
and New England. Felt a blanked low chance pop was warranted given
slightly improving moisture and ramping up of background large scale
ascent. The cold front itself will swing through late Friday, but
large scale forcing will direct surface low pressure over Georgian
Bay due east. As a result, low-level convergence will rapidly follow
suit and the best prospects for frontal precipitation will therefore reside
over eastern and northeastern portions of the County Warning Area. Lows will fall to
around 0 Friday night in spite of gusty winds. Highs Saturday will
range from 5 to 10. The peak wind period in the wake of the front is
appearing to carry an increasing likelihood of warranting a Wind
Chill Advisory late Friday night through Saturday morning for part
or all of the area. Will make an introductory mention in the severe weather potential statement.
Low pressure over Lake Ontario during the morning will continue to
move into the New England states today. This will leave strong northwest
wind over all marine areas today through tonight. A Gale Warning is
now in effect this afternoon and tonight for the open waters of
central and Southern Lake Huron. Small craft advisories remain in
effect for the nearshore waters of Southern Lake Huron through
Thursday due to the resulting high wave action and wind gusts around
30 knots. Freezing spray remains a concern as Arctic air surges
southward over the region today through tonight. A warning for heavy
freezing spray is in effect tonight when the best combination of
frequent gale force wind gusts and cold air occurs. Lake effect snow
squalls will have greatest coverage around Middle Lake in this wind
configuration through the period.
All of these harsh marine conditions will ease gradually during
Thursday as the wind backs and decreases by late in the day...but
the break will be short lived as another Arctic front approaches
Thursday night into Friday. Some of the coldest air of the season
will Brush Lake Huron and lower Michigan behind this front for the
Lake Huron...heavy freezing spray warning from 7 PM this evening to 7 am EST
Thursday for lhz362-363-462>464.
Gale Warning until 4 am EST Thursday for lhz363-462-463.
Small Craft Advisory until 4 PM EST Thursday for lhz441>443.
Gale Warning until 10 PM EST this evening for lhz362.
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).