Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 060153
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
853 PM EST Tue Dec 5 2017

.UPDATE...

Steady deep layer cold air advection continues throughout southeast
Michigan this evening. This process maintaining enough turbulent
mixing despite the loss of diurnal support to sustain gusty southwest
conditions, albeit at a diminishing magnitude. Gusts now below
advisory criteria, but occasional gusts into the 35 to 40 mph will
remain a possibility over the next few hours. 850 mb moisture plume
embedded within the advective process and augmented by modest lake
moisture flux will continue to wash across the region through 06z.
Observational and radar trends suggest nothing more than a few wind
blown flurries. Insufficient overlake moisture depth under increasing
dry air advection will then subsequently squash additional
downstream penetration of lake moisture heading into the morning
period. This will bring increasing potential for a period of open sky
or very low coverage of stratus to start the day Wednesday. Lows of
mid-upper 20s seems reasonable given the progged low level thermal
profile of this inbound air mass, with a moderately mixed southwest
gradient limiting the radiational cooling potential.

Forecast in good shape going forward tonight, simply some minor
tweaks for the update based on latest near term trends.

&&

.PREV DISCUSSION...
Issued at 615 PM EST Tue Dec 5 2017

AVIATION...

Gusty southwest winds will remain in place through the night. The
overall gust magnitude with gradually ease with time, but with gusts
of 30 to 35 knots persisting over the next several hours
/00z-03z/. Expansion of higher based lake augmented stratus may
provide a few flurries, with a period of bkn/ovc cigs near or just
above 5000 ft prior to midnight. Deeper post-frontal drying will
then commence overnight, supporting a decrease in the overall
coverage of stratus lasting through the morning period.  Daytime
mixing will promote an increase in southwesterly gusts /25 to 30
knots/ and potentially VFR cloud cover Wednesday afternoon.

For DTW...Southwesterly gusts near 30 knots will persist for another
couple of hours /thru 02z/, before gust magnitude gradually
diminishes. Upstream observations suggest the inbound cloud deck
will carry ceiling heights within the 5 to 6 kft level.  This will
maintain at least a low potential for 5000 ft cigs early tonight,
before drier air brings dimininishing coverage.

//DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less tonight and Wednesday morning,
  medium Wednesday afternoon.

PREV DISCUSSION...
Issued at 322 PM EST Tue Dec 5 2017

DISCUSSION...

Strong PGF and and a well-mixed environment courtesy of ongoing cold
advection has supported sustained winds of 20 to 30 mph and wind
gusts of 35 to 45 mph this afternoon. A peak gust of 54 mph was
observed at MBS at 1754z. Most locations have fallen short of
achieving advisory criteria, so the 4pm forecast package will
contain of most of the headline based upon the latest obs. Even as
the parent low over Ontario lifts away, energy embedded within the
broad cyclonic flow regime will sustain the the existing pressure
gradient through tonight. Winds of 15 to 20 kts will persist with
mechanical mixing sufficient to maintain an element of gustiness
through the tonight. The relatively warm NAM12 was strongly weighted
in tonight`s low temperature forecast of 25 to 28 degrees areawide
as its radiation scheme tends to handle mixed nocturnal boundary
layers well.

Prolonged stretch of quiet weather in store for the foreseeable
future as deep longwave trough axis stays positioned near the Great
Lakes. Flow will be predominantly confluent and NW to occasionally
WNWLy leaving little room for embedded disturbances to amplify over
the Great Lakes region. As a result, expect episodic light snow
showers and occasional low-impact lake effect over the next several
days. To drive home the point, 10-Day run-total snow accum on the
12z ECMWF averages about 2 inches over the CWA. Most noteworthy
snowfall may be Thursday, when slightly better moisture pivots
across the Great Lakes allowing for some eastward extension of LES
and possibly widespread flurries/snow showers during the day. There
is some concern for the potential of an inch or two of accumulation
in a portion of Lenawee County, but there is still noteworthy spread
in model depictions of moisture quality with no clear answer. Given
background forcing, went with chc pops everywhere, with borderline
likely in Lenawee. Left any accums under 0.5 inches for now.
Persistent troughing will keep temperatures suppressed below through
mid-December.

MARINE...

We are in the midst of a long duration gale event across the Great
Lakes as a strong low pressure system lifts toward James Bay. The
low is just about at it`s forecast deepest pressure, and should
begin to fill back in after 00Z. In spite of this, winds currently
across Lake Huron range from 35 to 45 knots with some potential for
gusts approaching 50 knots over a portion of central Lake Huron for
the next few hours. These gales will persist through Wednesday as
continued cold air advection within a tight westerly pressure
gradient keeps unstable conditions over the waters. Slightly lower
wind speeds across Lake St Clair and Lake Erie being farther removed
from the low thus a small craft is in effect for Lake Erie along
with a low water advisory. Current gale warning for Lake St Clair
should drop off this evening, but will likely need a small craft in
it`s place for the rest of the night through Wednesday. Colder air
moving in mid to late week will also increasing coverage of lake
effect snow squalls to further hinder marine conditions.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 4 PM EST Wednesday for LHZ361-362-421-422-
     441>443-462>464.

     Storm Warning until 10 PM EST this evening for LHZ363.

     Gale Warning until 4 PM EST Wednesday for LHZ363.

Lake St Clair...Gale Warning until 10 PM EST this evening for LCZ460.

Michigan waters of Lake Erie...Low Water Advisory until 4 AM EST Wednesday for LEZ444.

     Small Craft Advisory until 4 PM EST Wednesday for LEZ444.

&&

$$

UPDATE.......MR
AVIATION.....MR
DISCUSSION...JVC
MARINE.......DRK


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