Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
645 PM EDT Thursday Mar 26 2015
A general MVFR to lower VFR deck in the 3-5kft range will be common
this forecast within cold...cyclonic northwest flow. Ceilings will tend
to be lowest from kptk northward during this forecast period. While
a few scattered -shsn will be possible with a surface trough passage
on Friday...these should not impact the terminals in any notable
way. West to northwest flow will veer to the north with this trough
For dtw...ceilings will be near 5kft much of the forecast period with
just a few breaks possible overnight. True clearing will occur late
in the forecast period...Post 00z Friday...as high pressure begins
to nose into the area. West-northwest winds will veer to north then north-northeast...and
remain near 10 knots much of the time.
//Dtw threshold probabilities...
* high in ceilings at or below 5000 feet through much of the forecast period.
Previous discussion...issued 356 PM EDT Thursday Mar 26 2015
Short term...through tonight
Low/middle level cold advection continues to support an extensive
stratocu deck across the western Great Lakes. This began as the
strong upper jet and associated low level baroclinic zone shifted
eastward this morning. Upstream cloud coverage appears solid on
visible satellite this afternoon despite slightly more cellular
appearance over far southern Michigan lately. As such...expect cloudy/mostly
cloudy conditions to persist into the evening with temperatures holding
steady or falling.
Secondary cold front at 19z aligned from Georgian Bay through the
far northeastern u.P. And into Lake Superior. This front will
progress through northern Michigan and Lake Huron
overnight...approaching The Thumb/Saginaw Valley regions by around
09z. NAM forecast soundings for bax paint a favorable picture for
lake effect snow over The Thumb after 06z. Low-level wind
trajectories become north/northeasterly with lapse rates increasing
and supersaturation with respect to ice up to about 750 hpa. 0-1 km Theta-E
lapse rates increase to 1-3 k/km by 12z as 925/850 mb temperatures fall to
-9/-14c. Character of the lake effect snow is still somewhat
uncertain. Some hi-res guidance depicts more disorganized light snow
pushing into The Thumb initially after 06-09z as lapse rates and
moisture increase...possibly evolving into more of a dominant band
09-12z as low-level winds become more unidirectional out of the
north-northeast...at least before daytime heating commences. This
scenario seems plausible...especially if low-level convergence can
occur. Snow accums through 12z generally 0.5-1 inch for Huron County
with a half inch or less elsewhere in The Thumb...but this will need
to be refined if it looks like a more dominant localized band will
Elsewhere...mostly cloudy skies with continued cold advection
allowing lows to drop to the low/middle 20s. Best chance of cloud deck
scattering out for a time will be across the south...but confidence
is not high.
Northern stream trough over Ontario will rotate through the central
Great Lakes tomorrow. 12z soundings out of International Falls and
Pickle Lake Ontario revealed 850 mb temperatures of -14 c and -20 c
respectively...with an almost true north wind. This cold
airmass...albeit modified slightly...is expected to lead to some
lake effect snow showers tomorrow with the northeast to north flow
developing...as even 925 mb temperatures are expected to fall to around -13
c over Lake Huron.
12z NAM showing good 925 mb positive Omega signal pushing through
the northern thumb region and extending southwest through the rest
of Southeast Michigan during the day. With the commencement of
daytime/surface heating...probably going to become disorganized
activity...with steep low level lapse rates and rather deep layer of
supersaturation with respect to ice to support scattered snow
showers across much of the area. With the transient and disorganized
nature expected...will keep accumulations below 1 inch.
North-northeast flow gradually weakening Friday night as surface
high attempts to build eastward...but with The Heart of the low
level cold airmass in place (850 mb temperatures as cold as -18
c)...additional light lake effect snow showers are expected across
The Thumb region. Extend of cloud cover beyond The Thumb region
becomes challenging as much drier air and anticylonic flow begins to
push in. Regardless...expecting mins in the low to middle teens.
Center of high building and general subsidence over lower Michigan
on Saturday should lead to mostly sunny skies...but cold airmass
(850 mb temperatures in the negative middle teens to start the day...rising to
-10 to -11 c by day's end)...points to low to middle 30s even with full
Brief ridging on Sunday quickly gives way to another trough as a low
pressure system slides across the Hudson Bay area Sunday night into
Monday. A cold front associated with the low will transverse across
the Great Lakes region later on Sunday. Exact timing of the frontal
passage across the County Warning Area has yet to be pinned down due to differences
currently laid out in the latest model runs. This puts in to
question precipitation type that will accompany the front depending
on when it does push through the area. Next week looks to stay
somewhat active as more shortwaves move across the Great Lakes
region. Warmer air does finally start to make inroads into the area
next week...as temperatures get back to near normal readings.
A very cold airmass will be ushered into the central Great Lakes
tonight into tomorrow...as northerly winds gust up to 30 knots over
Lake Huron. Airmass will even be cold enough to generate snow
showers...but mostly over Southeast Michigan. Winds will gradually
diminish Friday night...as high pressure settles over the
region...leading to light winds on Saturday. Southwest wind will
ramp up Saturday night into Sunday as we get into return flow around
the high and a cold front approaches. Expecting winds of at least 25
knots over much of Lake Huron.
Lake Huron...Small Craft Advisory from midnight tonight to midnight EDT Friday
night for lhz421-441-442.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
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at www.Weather.Gov/Detroit (all lower case).