Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
356 am EDT Thursday Jul 2 2015
Short term...today and tonight
The center of surface high pressure will lake hop
today...dropping southward to Northern Lake Michigan this
afternoon before centering over the Central Basin of Lake Huron
tonight. Northerly flow will persist in advance of this surface
feature...preserving relatively higher boundary layer Theta-E
content over the Mainland of Southern Lower Michigan. Thus far...
the moisture has presented itself as a low cloud stratus deck. The
cloud has been drifting to the southwest...aided by a component of
the Evening Lake Huron/St Clair aggregate marine layer release.
Forecasts generally allow it to push southwestward across the southern
peninsula this morning before diabatic heating/planetary boundary layer growth occurs.
The overall sounding structure today will be a stable one with a
Stout subsidence inversion based at approximately 4500 feet above ground level. The
belief is the stratus deck will hold on this morning...evolving
into a stratocumulus deck under daytime heating. Soundings do not
show a steep lapse rate pocket at the top of the mixed layer...but
the feeling is that cloud may prove stubborn to burn off.
Preference is for a partly-mostly cloudy forecast this morning
before skies totally clear out for tonight. Cool low to midlevel
temperatures will support below average highs for today. A blend
of persistence with afternoon sunshine suggets highs today will
push the lower to middle 70s.
The forecast item of note tonight is the cool temperatures. The
hourly temperature trace suggests a rapid cool down in The Thumb by
01-02z...with mins ranging Friday morning in the upper 40s to
Quiet weather is expected on Friday as a surface ridge axis remains
stretched across lower Michigan. Little moisture available through
the column should allow for mostly sunny skies. Flow off the lakes
will weaken...allowing the sunshine to help boost temperatures well
into the 70s. Lake breezes are still expected to work inland
however...which will shift winds and cool areas near the lakeshores
during the day...and then pretty far inland by evening.
The last in a series of shortwave troughs will then migrate through
the longwave that has been established over the Great Lakes and New
England for much of the past week. This wave...currently seen on
water vapor dropping into northern Saskatchewan...is forecast to
drop across the northern Great Lakes late Friday into Saturday. This
will push a weak cold front down into northern and central lower
Michigan on Friday...before this boundary loses upper support and
becomes parallel to mean low-level flow over the region. The front
is currently forecast by NAM/GFS/Euro to reach into central Michigan
before it washes out...providing just a small amount of lift. Cooler
air arriving aloft and surface heating look to steepen lapse rates
(surface through 600mb) enough over the Saginaw and northern thumb
to warrant chance probability of precipitation for showers/thunderstorms during the afternoon and
through the evening. Ribbon of Theta-E advection spreading in ahead
of the front and steeper lapse rates look confined to areas north of
I-69. Surface ridging axis near the Ohio border will also hold some
influence over stability over the southern 2/3 of the forecast area.
Any storms that do build should dissipate with the loss of daytime
The upper wave will lift through east-central Canada by Sunday
morning...allowing ridging to rebuild aloft in advance of a larger
area of low pressure tracking across western Canada. Latest round of
models support pretty good upper height recovery in the 586-588dm
range. This should provide large-scale subsidence as surface high
pressure builds underneath it. Dry forecast prevails with model
forecast soundings exhibiting warmth through the middle-levels and lots
of cin...despite model output occasionally spitting out spotty quantitative precipitation forecast.
Strong upper low over central Canada then looks to cast a cold front
our way Tuesday into Tuesday night. Models have come to a better
consensus with this...and prefer the slower timing given the
amplitude of the system.
Temperatures will remain below normal with maximum temperatures in the 70s to
end the work week...but warm gradually warm near 80 with sunshine
and less flow off the lakes over the weekend. Warm air advection and
increased mixing in advance of the approaching trough and cold front
should help boost temperatures on Monday into the low/middle 80s.
A surface ridge axis will settle into Michigan today and remain
overhead through Friday. This will bring fairly light winds for most
of the area...but sustain winds at 10 to 15 knots over Western Lake
Erie today and Friday as it remains located around the periphery of
the high. A weak trough and cold front will drop through Lake Huron
Friday night and Saturday...bringing a chance for showers and
thunderstorms. High pressure will then rebuild on Sunday yielding a
return to quieter weather.
Aviation...issued 1158 PM EDT Wednesday Jul 1 2015
00z upper air soundings from apx and DTX indicate strong potential
for low clouds to fill back in over Southeast Michigan during the night.
The apx sounding was launched with clouds in place while the DTX
sounding shows an extension of the subsidence inversion around 850
mb that will provide a duct for low level moisture and MVFR clouds
to return during the night. This will occur as low level winds
continue to veer from northwest to northeast over the region as a
broad area of high pressure builds over the central Great Lakes.
Except for a brief shower off Saginaw Bay in the mbs area...the high
will maintain dry conditions but low level wind pattern will help
spread MVFR ceiling from northeast to southwest over the terminal
corridor while being boosted by an infusion of moisture from Lake
Huron. Dry air will then make a stronger push into the area from the
surface high and bring some improvement during the afternoon and
then promote a clearing trend into Thursday evening.
For dtw... MVFR ceiling will reach dtw later than the other terminal
sites and the wind trajectory could provide more of a glancing shot
of coverage. Observed clouds at phn combined with the DTX sounding
supports a more pessimistic forecast for now.
//Dtw threshold probabilities...
* moderate for ceiling 5000 feet or less late tonight through the
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).