Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
557 am EDT Friday Oct 9 2015
Higher ambient moisture preceding the surface cold front was
adequate in generating MVFR ceilings with some patches of IFR ceilings this
morning. Cold air advection now kicking into gear...and the
increased mixing potential will erode any remaining IFR. Looking at
a solid setup for MVFR ceilings this morning which will then steadily
lift this afternoon. The amount of dry air that is forecasted to
advect into the region today and the loss of daytime heating...will
allow skies to clear quickly this evening. A favorable radiative
cooling environment will exist which will bring the potential for
some shallow radiation fog. At this time...not looking at anything other
than some potential MVFR visibility restrictions as the modeled
thermodynamic profile is extremely shallow with saturation.
For dtw...a solid setup for MVFR ceilings today in Post cold front
stratus. Ceilings to steadily lift this afternoon into MVFR but less
than 5000 feet. High confidence that any remaining ceilings will fall
apart quickly near Sundown. A chance for some very shallow ground
fog Saturday morning.
//Dtw threshold probabilities...
* high in ceilings below 5000 feet this morning and afternoon.
Previous discussion...issued 345 am EDT Friday Oct 9 2015
Short term...today and tonight
As of 2 am...a cold front is overhead of southeastern Michigan with
the associated surface wind shift near and along a line from Saginaw
Bay to Holland. Winds behind the front have been shifting to the
northwest with wind speeds in the 10 to 15 miles per hour range. The front will
progressively push south and eastward...expected to clear the far
southeastern sections of the County Warning Area shortly before 12z. The measurable
rain activity has been ahead of nwp projections...and has been ahead
of the surface front by as much as 75 to 100 miles. Additional rain
chances are expected to end across much if not all of the area by
09z this morning.
Low level cold air advection will limit mixing heights for a good
portion of the day...which will put a fairly Stout lid on the
overall temperature response potential. Forecast soundings do show
steadily lifting cloud bases after 11am/noon with saturation
becoming razor thin by the late afternoon. With model performance
poor recently in underestimating the amount of saturation at the top
of the boundary layer will err on the pessimistic side for clouds.
Will carry cloudy to overcast throughout much of the day. Do expect
some sunshine late. Cams are suggesting some light simulated
reflectivity...particularly between the 21-00z time window. Just
cant see it...however...given limited amount of saturation. If
anything...this adds some confidence to an overcast cloud mention
throughout the afternoon. Cold air advection will promote
northwesterly surface winds with northwest winds of 10 to 20 miles per hour
Surface high pressure will expand aggressively into lower Michigan
during the evening hours. This will set the stage for some favorable
radiative cooling late tonight. A fairly strong consensus exists
within the guidance with respect to lows tonight. Readings are
expected to dip into the lower 40s....propped up by surface
dewpoints supported by recent rainfall. Pattern recognition and time
of year supports a patchy radiation fog potential right around
daybreak Saturday morning. Model relative humidity profile supports nothing more
than a very shallow ground based fog.
High amplitude West Coast ridge forced by expansive goa low will
flatten and release east over the weekend as a powerful jet maximum
snakes into British Columbia and Alberta. Deep layer subsidence will
scour much of the column of clouds while transient surface high
pressure provides a gradual increase in southwesterly return flow by later in
the day Saturday. Passage of today's thermal trough will allow 850 mb
temperatures to rebound into the middle single digits supporting just a modest
recovery in high temperatures to the middle 60s. Only clouds of note will be
cirrus and some patches of middle-level clouds zipping along in the
fast-moving zonal regime.
Pattern persists through Sunday as a potent Pacific shortwave ejects
into the Front Range, amplifying the local ridge and further
increasing the southwesterly gradient through the layer. 850 mb temperatures are
prognosticated to rise markedly into the middle teens supporting highs solidly
in the low to middle 70s under mostly sunny skies. Gradient will be
strong enough to maintain mixed conditions overnight into Monday
morning guaranteeing rather warm low temperatures in the middle to
upper 50s. Kept lows on the warm side of guidance here.
Small craft advisories remain in effect as fresh northwest winds
build in behind a cold front early this morning. Significant wave
heights are forecast to peak near 8 feet over the southern open
waters and exposed nearshore waters of The Thumb before subsiding
late tonight. After a brief reprieve late tonight into Saturday...an
approaching low pressure system this weekend will cause fresh SW
winds to ramp back up again by late Saturday evening through Sunday.
The axis of strongest winds will align from Saginaw Bay into Central
Lake Huron with the highest waves remaining far from the coast due
to the prolonged offshore fetch.
Lake Huron...Small Craft Advisory until 4 am EDT Saturday for lhz421-441>443.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
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