Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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882
FXUS63 KDTX 030234 CCA
AFDDTX

Area Forecast Discussion...CORRECTED
National Weather Service Detroit/Pontiac MI
908 PM EST Fri Dec 2 2016

.UPDATE...

The 00Z DTX sounding showed a very deep inversion based around 3k
ft. The moisture within the inversion was quite shallow. Shallow
enough to where the subtle downslope into the Saginaw Valley under
the west northwest flow opened up a large clearing. The persistence
of this inversion through the night and extent of stratus across the
entire Great Lakes and upper Midwest suggests a good chance that
clouds will fill back in across the area during the overnight. So
there will not be an update to the forecast to deviate from the
mostly cloudy skies attm.

&&

.PREV DISCUSSION...
Issued at 604 PM EST Fri Dec 2 2016

AVIATION...

Ceiling heights within the stratus have been slowly inching downward
since late this afternoon. This is the result of ongoing mid level
subsidence. A 22Z AMDAR sounding out of DTW showed the inversion at
3200 ft, deeper and lower than suggested by all model solutions.
Persistent mid level subsidence through the night should continue to
support some slight downward trend in the ceiling heights. The
extent of stratus across the entire Upper Midwest and Great Lakes,
with weak cyclonic flow persisting in the low levels, will hold the
stratus in through the night and likely into Sat evening.
Considering the slight downward trend in ceilings, a persistence
forecast looks in order, indicating MVFR cigs persisting through
the TAF period.

For DTW...

The stratus should sustain some degree of mixing in the boundary
layer. Thus, WNW winds should hold around 10 to 12 knots, with a few
higher gusts, through the night.

//DTW Threshold Probabilities...

* High in ceilings below 5000 ft tonight and Saturday.

PREV DISCUSSION...
Issued at 357 PM EST Fri Dec 2 2016

DISCUSSION...

The lake effect driven precipitation pattern has diminished during
the day as larger scale subsidence begins to limit convective depth
more convincingly compared to last night. This is a trend that will
continue through tonight but not much else will change with the low
level thermal profile and this will help stratus remain abundant
within the lingering low level cyclonic flow. Localized lake
aggregate induced filaments of low level convergence within the
large scale pressure pattern could give sprinkles or flurries a
chance to make it down/over from Lake Michigan during the evening
and overnight, especially with a minor boost of conditioning from
Lake Superior. Plan to monitor these trends for now as mesoscale
model solutions are running high on coverage and intensity over
the northern Great Lakes during late afternoon and likely
projecting too much coverage in our area considering the
increasingly less favorable larger scale environment.

Afternoon observations also indicate a broad expanse of stratus from
the Ohio Valley all the way back into the northern Plains and
central Canada. This is plenty of evidence to maintain a pessimistic
sky forecast through Saturday, especially as the surface ridge axis
remains to our west through the day. The clouds will keep low
temperatures from falling below 30 tonight but then prevent much of
a warm up Saturday afternoon with 40 being a struggle.

The benign weather pattern will continue through Saturday night as
the next low pressure system moves in from the Plains Sunday. Low
clouds will eventually be exchanged for high clouds thickening and
lowering ahead of this system and as the surface high passes to our
east. The window for precipitation remains firmly in the time window
from late Sunday afternoon through about midnight Sunday night.
Considering the good agreement between models and over the last few
cycles, some temporal resolution is added to POPs in this forecast
package along with a bump to categorical. A standard isentropic lift
scenario is projected ahead of the wave with a plentiful Gulf
moisture supply represented by specific humidity around 3 g/kg.
Stability will be low enough through the mid levels, judging by
visual inspection of theta-e cross sections, while daytime onset
will probably limit ratio to single digits before trending toward
climo after sunset Sunday evening. The 1 to 2 inch forecast
inherited from the early morning package is maintained with lower
end in the Detroit area and higher end Tri Cities and northern
Thumb before the system exits by midnight.

Models showing little change in course from yesterday though timing
is somewhat shifted. Brief ridge of high pressure is on track to
build over the region on Monday which will yield drier, slightly
warmer conditions. Low pressure developing over Texas is still
expected to surge northeastward, but now looks to arrive over
southern Michigan Tuesday afternoon vs Tuesday morning. North
Pacific low tracks into western Ontario late Tuesday afternoon and
the two lows merge by Tuesday evening. Chances of rain or rain and
snow are expected to persist in the forecast through most of the
extended period with precipitation likely to change over to all snow
on Thursday. Still too early for the forecast to be set in stone.
Updates to timing will remain possible as systems develop. Stay
tuned!

MARINE...
Cold cyclonic flow will be diminishing overnight. Weak surface
pressure gradient will produce relatively light winds through the
weekend into next week. A front will bring the chance for rain or
rain snow mix late Sunday and Sunday night. Diminishing wind
tonight will allow advisories to run as scheduled with no
additional headlines for winds or waves expected through the
remaining forecast period.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 4 AM EST Saturday FOR LHZ421-
441.

Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

UPDATE.......SC
AVIATION.....SC
DISCUSSION...BT/DE
MARINE.......DRC


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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