Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 030455
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1155 PM EST Fri Dec 2 2016
Despite the deep inversion shown on the 00Z sounding, fairly large
breaks in the overcast have occurred this evening. This started
around MBS where a little downslope coupled with the large scale
subsidence. The moisture under this inversion is very shallow, so
clearing has rippled all the way down into metro Detroit. The
inversion will persist through the morning and actually through Sat
afternoon. Given the extent of stratus still in place upstream, it
is expected that these clouds will filter back into the terminals
during the morning. Wide variability in cloud cover is likely for at
least the first couple hours of the TAF period. The height of the
inversion will hold nearly steady through the rest of the morning,
if not lowering just a little more under the subsidence. This will
keep cloud bases in the MVFR category (2k to 3k feet).
//DTW Threshold Probabilities...
* High in ceilings below 5000 ft tonight and Saturday.
Issued at 908 PM EST Fri Dec 2 2016
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.
Issued at 357 PM EST Fri Dec 2 2016
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
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.
Lake Huron...Small Craft Advisory until 4 AM EST Saturday FOR LHZ421-441.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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