Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
546 PM EST Thursday Feb 11 2016
Some downstream expansion of existing lake stratus will be plausible
tonight as low level flow backs to west/southwest. This moisture
working into an otherwise very dry low level environment will ensure
conditions remain VFR as transient fragments of scattered/broken lake cloud
drift through at times overnight. Attention Friday on the strong
Arctic front expected to move through during the early-middle afternoon
period. Attendant period of light snow with the initial frontal
passage will bring potential IFR conditions...with light accums.
Increasing northwest winds with the frontal passage. Gusts peaking
into the 30 knot range late afternoon and evening. This environment
may support some heavier but more localized snow showers/squalls
through the evening. Low confidence scenario at this stage given the
difficulty in defining both timing and duration...but quick/brief
disruptions of visibility /LIFR-IFR/ will be possible.
For dtw...VFR through the morning with the occasional ceiling below
5000 feet possible as pockets of lake stratus funnel through. Period
of light snow Friday afternoon as a strong cold front slips through.
Accumulation currently at a half inch or less. Strong northwest
winds behind this front late afternoon and evening...gusts to 30
knots during this time. Possible heavier snow showers/squalls could
bring abrumpt visibility reductions down to IFR-LIFR.
//Dtw threshold probabilities...
* low for ceiling at or below 5kft through Friday morning...high Friday
* low for crosswind thresholds Friday afternoon and evening.
* High for ptype as snow Friday.
Previous discussion...issued 405 PM EST Thursday Feb 11 2016
A number of factors has allowed surface ridging to finally expand
out of the Great Plains and across the Great Lakes region. Some very
weak lake aggregate troughing has been able to hold on today but the
effects to sensible weather have been negligible. The surface
reflection/trough is more of a testament to the degree of warmth
still exhibited by the Great Lakes...rather than the degree of
this first cold air surge. In fact...temperatures today have been
relegated to the teens which is around 10 to 15 degrees below
early/middle February averages. So cold...but certainly nothing
Low level flow will back from the northwest this afternoon to the
west southwest by this evening in response to the mean anticyclone
centroid building from northern Illinois to the Ohio River. This
should eventually result in the low level convergence maximum over
far southwestern lower Michigan/southern basin of Lake Michigan to
break away from the shoreline and eject across/north of the Michigan/in/OH
statelines. Model data suggests this remnant convergance to pass over
the Detroit metropolitan area and points southward...possibly resulting in
flurries in that location until midnight.
The first item of significant forecast interest is the detail of the
frontal passage that is forecasted to occur between 18-00z Friday.
From this Vantage Point...various solutions within the solution
space are suggesting a split cold frontal feature of sorts with a
relatively broad swath of southwesterly flow confluence becoming
organized along a prefrontal trough type structure. This increased
gradient would mark the first cold front...while the second and
main surface gradient will drop almost due southerly into
southeastern Michigan between 21- 02z. The better precipitation
chances from a more widespread/measuring potential will likely
occur ahead of the first front...during the middle portion of the
day. Deeper moisture advection will advance out of
Wisconsin...providing some lake enhancement into the
aforementioned zone of low level convergence. Deeper saturation
will be present...with model soundings suggesting upwards of 8 kft
of deep saturation within a layer of low static stability and
convective instability. Midday should also have a linkage to the
dgz...so it is plausible that many areas could see a dusting to
snow accumulations of less than an inch between 15-21z. Winds
during this time will be relatively managable...up to 25 miles per hour.
The 850 mb and surface cold fronts are then forecasted to plunge
directly through southeastern Michigan after 21z. For some hi-res
models this is just coming within the time horizon. The solutions
are suggesting a potential for snow-squall activity directly along
and behind the front. The quality and pristine nature of the inbound
airmass is Top Notch with the forecasted 12z Saturday 850mb
temperatures of -27c comfortably breaking the minimum record in the
kdtx/fnt upper air climatologically. A cross-section analysis and
inspection of downglide on isentropic surfaces doesnt really
suggest anything jaw dropping with respect to the frontal
organization...but forecaster recognition remains these Arctic
fronts always surprise and pack more of a punch due to the
contributions from frontal scale circulations. The feeling right
now is that chances for heavy precipitation rates will exist but
be very brief for any one area. Surface winds will then increase
markedly under the strong cold advection...with latest indications
are winspeeds to easily reach 30 miles per hour. The strongest of the winds
will be out over Lake Huron...with wind gusts of up to 45 miles per hour
possible for the shoreline areas of Lake Huron. It is appearing
increasingly likely that a Wind Advisory may be needed for Huron
County Friday evening.
The second item of significant interest this forecast period is
how cold temperatures and windchills will get in the wake of the
Arctic front. The 11.12z model trend came in with a farther
southward displacement/positioning of the upper level jet axis.
This results in a farther south and west tumbling/equaterward push of
the low height anomaly and upper level pv feature. Confidence
remains very high that windchill headlines will be required for at
least a significant chunk of the County Warning Area both Saturday and Sunday
mornings. At this time...it appears areas south and east of the
terrain...including the Detroit metropolitan area may be excluded as
forecasted wind chills remain less than 15 degrees below zero.
The coldest of the morning will be Sunday morning with The Heart
of the 1035 mb surface anticyclone directly overhead. Went a
little conservative with lows in the single digits below
zero...but it is probable that northern outlying areas will see
temperatures colder than 10 degrees below zero.
Frigid Arctic airmass associated with a strong surface high is
expected to shift east by early Monday. This will change the wind
flow from northwest to south allowing temperatures to rebound
noticeably by Monday afternoon. Current anticipated high temperatures for
Monday and Tuesday are ranging from the low to middle 30s. This will
likely feel like a heat wave in the wake of the weekends single
digit lows and subzero windchills. Chances of snow showers remain in
the forecast for most of the extended period as a combination of
weak surface low pressure and upper level waves rotate through the
Low pressure tracking across northern Michigan will bring an
increase in westerly winds tonight. Wind speeds will be highest over
Lake Huron...where speeds will reach 20 to 25 knots with gusts to 30
knots overnight. A strong Arctic cold front will then slide through
the central Great Lakes Friday afternoon and evening. Strong winds
aloft and frigid air gliding over the warmer lake waters will create
unstable conditions...allowing gale force winds to develop over the
open waters of Lake Huron. High-end gale force gusts to 45 knots are
expected by evening...lasting into the early overnight hours. Winds
will subside below gale force Saturday morning...then decrease
further through the day and finally become light Saturday night as
high pressure settles into the area.
The gale force winds combined with large waves and frigid air will
also create areas of heavy freezing spray. A heavy freezing spray
warning is in effect for all of Lake Huron late Friday afternoon
through Friday night...lasting through Saturday for the southern
basin of the lake.
Lake Huron...heavy freezing spray warning from 1 PM Friday to 10 PM EST Saturday
Gale Warning from 1 PM Friday to 10 am EST Saturday for lhz363-421-
Heavy freezing spray warning from 1 PM Friday to 10 am EST Saturday
Heavy freezing spray warning from 1 PM Friday to 4 am EST Saturday
Gale Warning from 1 PM Friday to 4 am EST Saturday for lhz361-362.
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).