Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1252 PM EST Tuesday Feb 9 2016
Low pressure over Southern Lake Huron and a very deep layer of moisture
has combined to produce a large swath of snowfall across the area. The
primary band has stalled over the central thumb but a secondary band
has aligned from mbs...to fnt...to ptk. This band will result in IFR
conditions for the next few hours with some drops to LIFR within the
heaviest showers. The Detroit area tafs will primarily be low MVFR but
could dip to high IFR at times as it hover around 3sm in lighter snow
showers. Drier air is working into the area from the west and south
which will bring an end to the heaviest showers. A second area of light
snow showers over Wisconsin is then expected to slide into the area
For dtw... the terminal lies on the southern edge of the precipitation
shield which means it could see some rapid fluctuations in conditions
through the afternoon. Expect mainly MVFR although a few dips to IFR
cannot be ruled out. A few more opportunities for light snow exist
tonight and tomorrow as another weaker disturbance passes overhead and
diurnal showers initiate tomorrow.
//Dtw threshold probabilities...
* high for ceiling at or below 5kft through Wednesday.
* High for snow as precipitation type.
* Low for exceeding northwest crosswind threshold today.
Previous discussion...issued 1101 am EST Tuesday Feb 9 2016
Very persistent band of heavy snow is parked along a Sebewaing to
Port Huron line /per kdtx and Exeter radars/. Snow totals around
7 inches have been reported under this feature across eastern
Tuscola...western Sanilac...and northern St Clair counties.
Expect this band will maintain structural integrity for a couple
more hours...as it appears to be locked in with the surface low
over Southern Lake Huron. Have opted to upgrade to a Winter Storm
Warning for localized totals approaching 10 inches. Rest of the
forecast remains unchanged.
Previous discussion...issued 900 am EST Tuesday Feb 9 2016
Integrity of spiral bands of snow showers across Southeast
Michigan remains rather high. These bands are associated with a
developing lower level circulation over southwest Ontario and
Southern Lake Huron. This feature will continue to develop as
upper level trough maintains a favorable environment. Given the
overachieving nature of the band of snow showers along the
initial surface trough early this morning...and the prospects
conmtinue for periods of moderate snow...especially along and
north of M-59...have opted to expand the Winter Weather Advisory
into the northern reaches of the Detroit metropolitan region.
Expectations are for an additional 1 to 3 inches in the expanded
area with little change over the initially advisory area.
Previous discussion...issued 314 am EST Tuesday Feb 9 2016
A 999mb surface low near Exeter, Ontario will continue to gradually
deepen by another mb or two over the next several hours as embedded
energy pivots around the closed low aloft. Ongoing advisory event is
panning out in reasonable fashion and no changes are needed to the
0730z radar mosaic reveals a band of moderate to heavy snow
translating southward through Southeast Michigan. This band is being
forced by the lead edge of cold air aloft and will likely hold
together for the most part as it continues to track south, reaching
the I-94 corridor by 6am and exiting the area to the southeast middle-
morning. This brief burst of snow will represent the peak of this event
south of the M-59 corridor, as large scale forcing is prognosticated to
remain largely stationary over the NE County Warning Area.
The primary change to the forecast will be an inland adjustment of
snowfall amounts in Huron, Tuscola, and Sanilac counties. Radar
returns and cooling cloud tops on infrared are indicative of a
strengthening vertical motion field. Broad elevated warm air advection/isentropic
ascent is supporting light snow from Ontario to Lake Huron. However,
it appears to be the back edge of the trowal. Far from a classic
trowal, mainly due to the lack of any appreciable deformation, an
elevated moisture feed into this region is evident on regional infrared
and WV. The snow band that has developed is due to convergence and
weak fgen along the trowal's back edge. This feature will most
likely only show a slow cyclonic pivot through the noon hour, and it
is within this axis that the heaviest snow is now forecast.
Unfortunately, distance from the radar, lack of reports, and a void
in surface observation is severely limiting diagnosis of actual snow
intensity. Although the 00z NAM handled the relevant features well,
its quantitative precipitation forecast output has not been useful. That has changed with the 06z
NAM, which appears more reasonable in spatial extent/intensity and
correlation with relevant features. It will represent the primary
quantitative precipitation forecast guidance through today.
As the upper low opens up this afternoon, the trowal, or what
remains of it after the circulation opens, will rapidly pivot
through the area bringing a round of light snow mainly to locations
north of 8 mile. Trailing this activity will be the lake enhanced
surface trough that remains over Lake Huron at the moment. This
feature will come crashing onshore with peak snowfall intensity
falling in the 19-22z time frame. The introduction of colder air
over the lake 12-18z will contribute to more robust, though still
modest, Overlake instability. This will in turn have a chance to
strengthen the lake enhanced trough before it pivots ashore.
Observations will therefore be Worth monitoring during the
afternoon as a brief period of intense snow will be on The Table
for Huron and Sanilac counties. Progressive flow then takes over
as the open wave exits resulting in a rapid diminishing of snow
coverage and intensity by 00z.
The story Wednesday through Thursday will be cold temperatures as
925mb temperatures fall from -2c at present to -15c by Wednesday
night. With the bulk of the first wave of cold advection occurring
tonight, and then continuing in weak fashion through Wednesday,
little in the way of diurnal recovery is expected. Highs will
struggle to 20 degrees in most spots. There will also be a good
chance for snow showers, especially during the first half of the
day, as the dgz will be supersaturated with respect to ice before lingering
moisture exits late. Northwest flow will tend to limit pure les potential,
although the fetch will favor monitoring potential for a Superior-
Michigan band stretching into SW portions of the area. Clouds and
a strong gradient should keep lows easily above modeled values in
most locations...raised lows Wednesday night several degrees into the
low teens. Little change for Thursday in terms of temperatures,
though the exit of deeper moisture and slightly anticyclonic flow
may allow for peeks of sun by afternoon.
Edgewave racing east along the lead edge of a much colder upper low
will bring a chance of light snow to all locations Friday.
Temperatures will plummet into the single digits or lower Friday
night and highs are unlikely to reach 10 degrees on Saturday.
Subzero lows will be possible again Saturday night. Wind chills
around -15 will be common during this time. Unlike last February,
this intrusion of dangerously cold air will be short-lived and long
gone by early next week.
Low pressure over the south end of Lake Huron during the morning
will maintain increasing coverage of snow squalls and increasing
north wind as it drifts toward Lake Ontario today. A wind headline
is not anticipated but the increased wind and long northerly fetch
will build wave action well into criteria for Small Craft Advisory
by tonight and lasting into Thursday. The north wind will also bring
a surge of Arctic air across the lake during this time that will
maintain snow squalls and support increasingly favorable freezing
spray potential by Wednesday morning which will likely become heavy
Wednesday night into Thursday. The wind will diminish later Thursday
through Friday while Arctic air maintains a hold on the region into
Michigan...Winter Weather Advisory until 9 PM EST this evening for miz047-048-
Winter Storm Warning until 9 PM EST this evening for miz049-054-055-
Lake Huron...heavy freezing spray warning from 7 PM Wednesday to 7 am EST
Thursday for lhz362-363-441>443-462>464.
Small Craft Advisory until 4 PM EST Thursday for lhz441>443.
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).