Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
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 will settle over far Southern Lake Huron
tonight...strengthening in the process...which will allow for
expanding snow shower activity through tomorrow. Winds will be light
tonight...but gusting up to 20 knots across far Western Lake Huron.
As the low slowly pulls away tomorrow and cold air rushes into the
central Great Lakes...northwest winds look to be ramping up to 25 to
30 knots across much of Lake Huron Tuesday night...and persisting
Wednesday...with just a small decrease on Thursday. With the amount
of cold air coming in...freezing spray is expected...and may be
heavy. A renewed surge of Arctic air arrives by Saturday...allowing
for another round of stronger winds and likely freezing spray.
Aviation...issued 1148 PM EST Monday Feb 8 2016
Area of light snow continues to gradually increase in coverage and
pivot southward into area around developing low pressure center near
the southern tip of Lake Huron. While west-northwest flow around this low will
act to dry out low levels to some extent...still expect enough low
level moisture to work around this low into area and bring MVFR ceilings
and also visibilities as shsns become increasingly prevalent...first for
kmbs/kfnt/kptk and eventually south into the I-94 corridor. With the
low basically stationary during this forecast period...MVFR to lower
VFR conditions should prevail into Tuesday evening. Shsns will be
possible area-wide...but most persistent kmbs/kfnt where intervals
of IFR will also be possible.
For dtw...a gradual transition to MVFR ceilings...and at times visibilities...
is expected late tonight into the day time as periodic shsns
increase. Flow will remain largely west-northwest...with gusts approaching 25
knots during afternoon as the pressure gradient tightens.
//Dtw threshold probabilities...
* medium in ceilings at or below 5kft overnight...high during day.
* High confidence in precipitation type being snow overnight
through the day.
* Low confidence in northwest crosswind during afternoon.
Michigan...Winter Weather Advisory until 9 PM EST this evening for miz049-054-
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 from 7 PM this evening to 4 PM EST Thursday
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).