Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
101 PM EST Thursday Feb 11 2016
Northwest flow off Lake Michigan will continue to provide lake
effect clouds and even a few flurries today. Ceilings across
Southeast Michigan have mainly settled into low VFR...with some
pockets of high-end MVFR at fnt and ptk...closer to the lake. Flow
across the lake will weaken and turn more westerly this evening.
This will most likely allow ceilings to scatter out as we also
advect some low-level dry air into the area. There is potential
however as the winds shift for clouds releasing off the lake over
southwest Michigan to stream overhead and keep ceilings intact for a
few more hours...particularly from ptk north. Otherwise...additional
low-level moisture arriving ahead of a cold front will drop ceilings
back to MVFR late Friday morning. The cold front will push through
during the afternoon and early evening...bringing a chance for snow
showers. Westerly winds will also gust up to 30 knots tomorrow
afternoon and early evening.
For dtw...VFR ceilings expected to prevail today with pockets of
MVFR expected to remain closer to Lake Michigan and north of dtw.
Fairly good confidence with ceilings below 5000 feet...but there may
be a few breaks as typically consistent with lake effect. A few
flurries are also possible. Loss of daytime heating and a shift in
flow over the lake from northwest to west should allow low clouds to
scatter out this evening. Approaching cold front will then pull
additional moisture back into the area tomorrow morning...dropping
ceilings back to MVFR and providing a chance for snow showers.
//Dtw threshold probabilities...
* medium for ceiling at or below 5kft through 01z tonight.
* Low for crosswind thresholds after 15z Friday.
Previous discussion...issued 330 am EST Thursday Feb 11 2016
Departure of large scale moisture has set the stage for dry cyclonic
flow and a partly cloudy start to the day. Clouds will be limited to
individual lake effect bands which will periodically affect most
areas, particularly the Superior-Huron band presently over the
central County Warning Area. Intensity of the lake response has been insufficient to
generate anything more than flurries in Southeast Michigan and
expect that to be the case through the day. Strongly confluent
northwest flow aloft will drive high pressure from the upper MS
valley into the Ohio Valley during the day, turning the flow
anticyclonic over Lake Michigan. This will release the lake trough
and its remnants will quickly translate across the County Warning Area during the
day. Expecting little more than an increase in cloud cover and a few
flurries as this occurs. Cold airmass featuring 850mb temperatures -20c at
12z this morning will support a slight downward nudge in high temperatures
compared to yesterday...upper teens to around 20.
By tonight, local surface winds will be feeling the effects of the
baffin island express, already dislodged from its origin at press
time this morning. The increasing gradient as surface low pressure
deepens over the northern Great Lakes and increasing clouds from the
plains will limit low temperature potential. However, not expecting
particularly thick cloud cover and the gradient will not be
strengthening until late, so a narrow window for decoupling 00-06z
and subsequent lower temperatures will be a short term issue to monitor.
Friday then gets interesting as large scale ascent and deep layer
convergence in advance of the cold polar low. Modest moisture
advection from the west will raise 850mb specific humidity from 0.3
g/kg over Lake Michigan tonight to around 1.1 g/kg by middle-morning
Friday. This will be sufficient to activate the lake as 0-1km Theta-
east lapse rates fall to -3 to -5c c/km. Lake effect showers will be
enhanced by large scale support and the lake plume will potentially
be entrained into the frontal zone as it works through the area. At
least chance probability of precipitation are warranted, but there is potential for a short-
lived higher intensity snow along the front by Friday afternoon.
Confidence in measurable precipitation is higher over the far eastern thumb
where proximity to the eastward-moving surface low will provide
ample low-level support for snow showers regardless...likely probability of precipitation in
In the wake of the front, winds will ramp up significantly over Lake
Huron in response to developing instability. Although this
instability will not be present over land areas, the onshore fetch
in Huron will have the potential to cause borderline Wind Advisory
level gusts to 45 miles per hour along the immediate shoreline. Updated severe weather potential statement to
mention potential for a wind headline for just Huron County.
Strong cold advection behind the front will force temperature down
to within 5 degrees either side of 0 depending on location. Wind
chills from roughly 10pm Friday night to 7am Saturday morning will
be in the neighborhood of -15f/Wind Chill Advisory criteria.
Advisory-level wind chills likely to hang on a little longer in The
Thumb, particularly in Huron County where continued onshore flow may
drive the wc toward borderline warning criteria. The wind chill will
remain below zero at all locations for all of Saturday. Potential
for a solid radiating scenario on Saturday night. Dusted off Gem
guidance as it tends to Excel when cold potential is maximized by
snowcover, calm wind, et cetera. Trended the forecast colder to around -5f
Saturday night...low single digits in Detroit city.
Arctic air continues to spill into the Great Lakes today on moderate
northwest wind. A heavy freezing spray warning remains in effect
during the morning 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 the day. Bands of snow squalls
will be numerous through central and south sections of the lake
through the day until direction backs toward the west middle to late
afternoon. These harsh marine conditions will ease later today and
tonight before another strong Arctic cold front moves through Lake
Huron and lower Michigan Friday. A gale watch is in effect as this
front will likely bring a round of high end northwest gales and
possibly another round of heavy freezing spray to the open waters of
Lake Huron through Friday night. The wind will drop below gales
Saturday but remain moderate in strength until high pressure arrives
Saturday night and drifts across the area through Sunday.
Lake Huron...gale watch from Friday afternoon through Saturday morning for
Small Craft Advisory until 4 PM EST this afternoon for lhz441>443.
Gale watch from Friday afternoon through late Friday night for
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).