Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
719 PM EDT Wednesday Mar 12 2014
A gusty northerly wind will steadily decrease in both magnitude and
gust frequency through the early portion of the night. Sustained
speeds settle into the 10 knot range overnight. Thin pockets of
MVFR stratus carrying a brief snow shower/flurry may persist for
another hour or two before a drying low level environment takes a
firm hold. Dry/stable conditions as high pressure slip through will
then provide an extended period of clear sky into Wednesday.
//Dtw threshold threats...
Previous discussion...issued 409 PM EDT Wednesday Mar 12 2014
Short term... this evening and tonight
The main bullet point for the afternoon package remains the strong
northerly winds that are in place over southeastern Michigan. A
strong pressure gradient and deeply mixed boundary layer will
support wind gusts in the 30 to 40 miles per hour range for inland areas
through the remainder of the daylight hours. The immediate shoreline
areas of Lake Huron will see higher wind gusts...exceeding 45 miles per hour
for a few more hours. A Wind Advisory is in effect for
Huron...Sanilac...and St Clair counties. Given the freshly fallen
snow...winds...and significantly reduced visibilities observed
earlier went ahead and issued a Winter Weather Advisory for blowing
snow until 00z.
A density discontinuity/boundary has become established over
sections of the central part of the County Warning Area along a surface trough.
Observed wind trajectories along with msas analysis of mslp gives a
signal that this boundary is a result of frictional effects
(convergence) of lower Michigan in comparison to the lake basins.
Surface dewpoints have differed by as much as 10 degrees across this
feature. The feature is important because it has been responsible
for the generation of snow showers. Have included a chance of snow
showers until 00z. Extremely difficult to say what any additional
accumulations could be...but would not be at all surprised to see
the snow showers or banding linger a little beyond 8pm. These weak
inverted surface troughs can have some staying power.
The last forecast bullet point is what will temperatures bottom out
at. Current surface temperatures over Huron County and degree of
near surface cold air advection has been impressive for some areas.
Expecting the Theta-E distribution to eventually flip late
overnight. This suggests coldest locations will be over western
sections of the County Warning Area...with slightly warmer values over the east.
Current forecasted lows are near records.
After a good night of radiating and a cold airmass firmly entrenched
across Southeast Michigan, temperature recovery will struggle on
Thursday. 925mb temperatures around -17c to begin the day will
slowly modify as upper ridging presently over the West Coast
deamplifies and sheds east. Slight rebounding of the thermal field
will be accompanied by the associated eastward progression of the
surface ridge axis. This will in turn allow for columnar warming
along with a general warm advective contribution by the afternoon.
Though likely arriving too late to force temperatures any higher
than the low 20s, the southwest gradient will continue to ramp up
overnight as a wave shears off the alaskan vortex and digs toward
the Great Lakes region. Temperatures will fall off no more than a
degree or two after sunset Thursday night and will proceed to rise
for the remainder of the night. Complete displacement of the
resident airmass can be expected by Friday morning when 925mb
temperatures are prognosticated by the 12z NAM to push 10c. High
temperatures will have little trouble reaching or exceeding 40
degrees. The model consensus depicts the surface wave passing along
the northern extent of Lake Huron, keeping the better isentropic
ascent well to the north. Cold frontal passage late Friday will,
however, mark an end to the brief one day warm spell as Canadian air
rotates back into the lower peninsula while a dry column precludes
any mention of probability of precipitation along with frontal passage at this time. Northwest flow sustained
by the ever-present western U.S. Ridge will maintain falling
temperatures behind the front through the weekend. Highs will fall
into the 30s for Saturday and back into the 20s for Sunday. Lows
will likely return to the single digits for Sunday night. For
climatological perspective, record lows by the second half of March
are generally in the positive single digits.
Strong north northeast gales over Southern Lake Huron today will
quickly subside overnight as the center of a high pressure builds
into the Great Lakes. Winds will then remain light through most of
Thursday before sustained fresh to strong southwest winds ramp up
ahead of a weak low passing north of Lake Huron Thursday night into
Friday. Gusty winds will develop as cold air fills in behind the
passage of the associated cold front on Friday evening.
Michigan...Winter Weather Advisory...miz049-miz055-miz060-miz061-miz062-miz063-
miz068-miz069-miz070-miz075-miz076-miz082-miz083...until 8 PM
Wind Advisory...miz049-miz055-miz063...until 8 PM Wednesday.
lhz463-lhz464...until 8 PM Wednesday.
Lake St Clair...
Gale Warning...until 8 PM Wednesday.
Michigan waters of Lake Erie...
Gale Warning...until 8 PM Wednesday.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).