Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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401
FXUS63 KDTX 100903
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
403 AM EST Tue Dec 10 2019

.DISCUSSION...

A reinforcing surge of cold air follows the primary cold front
across Lower Michigan during the predawn hours. This takes low level
temperatures downward enough to change precipitation type to snow
and activate Lake Michigan. A west to northwest wind shift on the
leading edge of this colder air helps focus bands of lake effect
snow showers into SE Michigan primarily south of the I-69 corridor
leading up to sunrise and then focused more toward the I-96/94
corridors early to mid morning. The early morning radar presentation
reflects characteristics of respectable lake effect potential shown
in model soundings with the added benefit of enhanced convergence
along the wind shift. Convective depth of 6-7 kft is maintained
within a steep low level lapse rate environment along with deep
supersaturation wrt ice in the cloud layer. Theta-e lapse rate in
the 0-1 km layer of 2 to 3 K/km is maintained inland across Lower
Michigan which is expected to help the wind shift maintain a leading
primary band followed by scattered to numerous filaments of
multiband activity in the NW flow during late morning. The quick
hitting nature of the system keeps accumulation to an inch or less
and again with the greatest concentration south of I-69 before
activity becomes more scattered/cellular with increased boundary
layer mixing during the afternoon.

Lake effect snow showers are diminished by an infusion of dry air
around the 850 mb level that moves over Lake Michigan by early
evening. There is some recovery toward midnight and a slight backing
of the wind field that favors low end scattered coverage of light
snow showers mainly from Flint to the Tri Cities and northern Thumb.
Model soundings indicate a much less favorable profile compared to
today. Convective depth is forced below 5 kft with a shallower cloud
layer although with similar steep lapse rate and high boundary layer
moisture profile wrt ice. These lingering favorable elements support
maintenance of entry level chance POPs tonight to near sunrise
Wednesday.

Additional reinforcement of cold air occurs during Wednesday which
does more to affect temperatures while maintaining a shallower lake
effect profile. Projected high temperatures struggle to reach 20 in
the Saginaw valley and only reach the mid 20s in the Detroit area.
This is the coldest day in the stretch of below normal temperatures
which appears to avoid single digit lows Wednesday night. High
clouds are shown to thicken and lower in model data as warm
advection develops quickly within a short wave ridge moving into the
region. A south surface wind component also quickly develops during
Thursday to help lift temperatures back into the lower and mid 30s.
Readings continue to rebound slightly above normal Friday as low
pressure moves through the northern Great Lakes giving us the
benefit of warmer temperatures and dry weather to finish the week.

The weekend outlook continues to feature a powerful upper level jet
from the Pacific initially forcing zonal flow across U.S. by Friday
which quickly buckles by Saturday. Extended models offer loosely
similar solutions of broad low pressure over the Ohio valley with
relatively mild air over the Great Lakes. This system is subject to
further adjustments due to timing of upper level amplification
during late week but for now presents a chance of rain and snow
showers in our area Saturday into Sunday.

&&

.MARINE...

Ongoing passage of a cold front will produce unsettled weather
across marine areas today. A slight decrease in wind intensity
occurs today, however, continued westerly flow draws in cold air
across the lakes, increasing instability and allowing stronger gusts
and elevated wave heights to persist. Small Craft Advisories remain
in effect and are extended through Wednesday for all nearshore zones
and a Gale Watch is in effect for northern Lake Huron.

In addition to wind, a primary hazard will then transition to snow
squalls starting today for all of Lake Huron reaching south down
into Saginaw Bay. The potential for snow squalls will continue
through Wednesday, thus any snow activity over the lake will have
the potential to quickly and drastically reduce visibilities. In
addition to squall activity, freezing spray will be another
potential hazard across Lake Huron for Wednesday.

&&

.PREV DISCUSSION...
Issued at 1149 PM EST Mon Dec 9 2019

AVIATION...

Cold air advection in wake of passing cold front will maintain gusty
westerly flow overnight. Rain showers will be replaced by widely
scattered snow showers later tonight with coverage increasing to
some extent by Tuesday morning. MVFR to lower VFR cigs will be the
rule with some clearing late in the forecast.

For DTW...A few snow showers will be possible by roughly 12z with
some of this activity persisting on into Tuesday as some degree of
lake effect streamers set up in W/WNW flow from Lake Michigan. Wind
gusts between 25-30 knots overnight will ease to 20 knots or less by
Tuesday afternoon.

DTW THRESHOLD PROBABILITIES...

* High in ceilings below 5000 feet into Tuesday afternoon.

* High in precip being all snow showers Tuesday morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

Lake Huron...Small Craft Advisory until 10 AM EST this morning for LHZ443.

     Small Craft Advisory until 10 PM EST Wednesday for LHZ421-422-441-
     442.

     Gale Watch from Wednesday morning through Wednesday evening for
     LHZ361-362.

Lake St Clair...Small Craft Advisory until 10 AM EST this morning for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 AM EST this morning for LEZ444.

&&

$$

DISCUSSION...BT
MARINE.......AM/BT
AVIATION.....DG


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



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