Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 011711
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1211 PM EST Thu Dec 1 2016

.AVIATION...

Cold cyclonic flow will continue and is expected to sustain MVFR/Low
VFR ceilings through the TAF period. Southwest winds 10-15 knots
gusting at or above 20 knots at times this afternoon expected to
shift a bit more westerly Tonight into Tomorrow from north to south.
With less of a fetch of Lake Michigan, possible for breaks in the
low clouds to develop, especially across MBS and FNT where
confidence is lowest in ceilings holding. Brief light rain or non-
accumulating snow showers remain possible, but mostly left out of
the TAF forecast as inversion heights lower this evening, limiting
the coverage but narrowing the focus of lake Michigan band (s)
Tonight.

For DTW...Maintaining MVFR Ceilings through the entire TAF PERIOD,
but brief periods of VFR are possible. In addition, there is a low
chance of IFR conditions Tonight if an organized Lake band hits
the terminal, which appears low at this time.

//DTW Threshold Probabilities...

* High in ceilings below 5000 ft through tonight.

* Medium confidence in precipitation type being mostly rain.

&&

.PREV DISCUSSION...
Issued at 1110 AM EST Thu Dec 1 2016

UPDATE...

The short wave rounding the base of the upper level trough will
start the system lifting into eastern Canada during the afternoon.
This will begin a drying trend over SE Michigan by suppressing
lake effect both due to larger scale subsidence and due to the
veering low level wind field left behind the system. These two
elements will combine to limit the eastward extent and coverage of
activity from Lake Michigan and force farther south that which is
able to make it over, other than pockets of drizzle which will be
possible areawide. The trend toward lower chance POPs in the going
forecast look good. Model soundings also indicate healthy enough
boundary layer growth for freezing level to rise from 300 ft
observed in the 12Z DTX sounding to well above 1000 ft through
the afternoon. This will ensure a liquid precip type as surface
temperatures creep into the lower 40s.

PREV DISCUSSION...
Issued at 312 AM EST Thu Dec 1 2016

DISCUSSION...

Modest instability over Lake Michigan is producing an equally modest
shower response that is gradually extending east as shortwave energy
aloft pivots overhead. Deep saturation and lift will continue to
promote showers lifting into areas north of roughly I-69 through the
early morning hours. Subsidence wake will likely cause activity to
retract back closer to the lake for the remainder of the afternoon.
Extensive stratus canopy extending back into the northern Great
Plains is not going anywhere, especially with southwest surface
winds veering to westerly over the lake as the low-level flow
flattens out a bit today. Further, NAM12 forecast soundings indicate
aggressive deepening of the subsidence layer this afternoon into
this evening, but high quality moisture remains in tact below 5kft
well into tonight. Lake enhanced drizzle production overnight will
likely be a consideration for the day shift today. Raised forecast
lows several degrees due to extensive cloud cover and steady
gradient wind.

The energy digging south along the California coast this morning
will cut off over Mexico, opening the door for a weak wave of
Pacific origin to translate along the northern tier on Sunday. Solid
NWP consensus here, so no complaints with likely pops on Sunday.
Ptype will largely depend on timing given marginal temperature
profiles and ongoing warm advection in advance of the wave. Attm,
NWP consensus suggestive of rain in the aftn and mostly snow after
sunset. QPF output of 0.1 to 0.2" is in line with unimpressive 850-
700mb layer specific humidities falling short of 3g/kg. Hard to
envision more than an inch or so of accumulation even if ptype is
all snow. Would expect timing to shift around in the models given
progressive nature of the northern branch and the fact that the
energy of interest is only just making it past the International
Dateline this morning.

Slightly variable temps through the extended as episodes of
progressive shortwave troughing are interrupted by the tendency for
longwave ridging over the Great Lakes due to persistent height falls
out west. No expectation for significant departures from normal with
daytime highs likely remaining +/- 5 degrees of average through day
7.

MARINE...

Extended period of cold cyclonic flow will sustain gusty conditions
today through Friday.  Westerly gusts generally peaking in the 25 to
30 knot range today.  This will maintain small craft conditions for
waves from outer saginaw bay through the tip of thumb.  Winds become
more northwesterly on Friday.  High pressure for the weekend will
allow winds to become light and variable.

&&

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

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

$$

AVIATION.....SF
UPDATE.......BT
DISCUSSION...JVC
MARINE.......MR


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