Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 130137

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
937 PM EDT Mon Mar 12 2018


Heavy snow showers developed during late afternoon peak heating as
mid level clouds exited SE Michigan with the cold front. This allowed
surface heating to generate impressive instability within the
boundary layer. The 00Z DTX sounding depicts the profile nicely and
suggests it should be no surprise that the resulting convection
eventually developed upscale enough for mesolow formation. This of
course further intensified the ongoing pattern of snow showers and
helped with impressive longevity past sunset. The mesoscale feature
is now expected to make it into the Detroit to Ann Arbor area before
weakening and/or exiting SE Michigan by midnight. Outside of this
area, a marked decrease in coverage and intensity of snow showers has
occurred since sunset. The forecast update mainly covers the area
affected by the organized snow showers with higher POPs for the rest
of the evening. Accumulation will remain less than 1 inch but with
some accumulation now possible on area roads as temperatures fall
into the mid and upper 20s.


Issued at 707 PM EDT Mon Mar 12 2018


Late afternoon surface heating, permitted by a decrease in mid level
clouds, will fuel snow showers over SE Michigan through the evening.
The snow showers will weaken after sunset but instability is high
enough for this process to be slower than normal. Until then, expect
a wide range of ceiling and visibility conditions ranging from VFR
outside of snow showers to brief LIFR in the heaviest activity.
There will be a modest increase in northwest wind as the cold front
exits the eastern Great Lakes overnight. The cooler incoming air and
lingering convergent low level flow will allow MVFR ceiling to
increase as snow showers diminish. These clouds will persist through
Tuesday morning as another round of snow showers develops first at
MBS and then spreading southward through the day. The snow showers
will become heavy again during Tuesday afternoon as daytime surface
heating adds to instability.

For DTW... Snow showers will diminish during the evening as
scattered coverage and warm ground temperatures minimize
accumulation potential, and likely leave paved surfaces only wet.
MVFR ceiling will gradually return during the night with increased
northwest wind. Snow showers will increase coverage again during
late Tuesday morning and then increase intensity during the
afternoon in a similar scenario as today.


* Moderate for ceiling 5000 ft or less tonight and Tuesday.

* High for snow as precipitation type.

* Very low for northwest crosswind

Issued at 305 PM EDT Mon Mar 12 2018


Closed mid level circulation now anchored just north-northeast of
lake Superior, with the southern expanse of the associated height
falls now encompassing southeast MI. Trailing shear axis contained
within the back end of the exiting mid level trough axis will
maintain residence locally into the evening. This in combination
with a diurnally supported steep lapse rate environment and
sufficient moisture quality will maintain the potential for snow
shower development through early evening. A noted decrease in both
large scale ascent and thermodynamic support will then subsequently
diminish snow shower chances overnight. Some repositioning of the
pressure fields as the parent circulation digs southeast into the
lake Huron basin tonight may establish a smaller scale region of
enhanced low level convergence. Greater potential for a localized
response will focus over the Saginaw Bay/thumb region, where the
nocturnal timing could prove more efficient at generating some

Center of the closed low pivots from Lake Huron to western NY on
Tuesday. This movement will draw the western flank of the pronounced
mid level cold pool /-40C at 500 mb/ across the area during the day.
This process will capitalize on favorable diurnal timing to
establish an environment characterized by steep low-mid lapse rates
and convective depth nearing 7-8 kft. Passage of an attendant lake
aggregate surface trough will supplement this background ascent. A
corresponding increase in snow shower coverage expected from north
to south, possibly originating off from any ongoing activity that
fixates over the thumb tonight. Potential will exist for brief but
intense bursts of snow to emerge given the convective component,
leading to a quick accumulation and abrupt drop in visibility. As
noted today, a stronger mid March sun angle requires higher snowfall
rates to carry longer residence time to provide any meaningful
accumulation on pavement. Greater potential will lie across the
thumb should a more pronounced convergence band materialize,
particularly during the morning period. Accompanying weak cold air
advection will translate into slightly cooler readings relative to
Monday. Highs low-mid 30s.

Departure of the mid level trough axis and associated cold pool
timed coincident with the loss of diurnal support results in a quick
decrease in snow shower potential by late Tuesday evening.  A
trailing pv feature pivoting through the mean trough will lift
through Tuesday night/early Wednesday, but seemingly lacks the
moisture depth or favorable diurnal timing to support a secondary
window for snow shower development. Otherwise, high amplitude mid
level troughing maintains residence through the midweek period.
Retention of a deep layer northwest flow ensures temperatures remain
on the cooler side of average Wednesday.

Northwest flow in conjunction with mid-level shortwaves aloft will
help produce the slight chance for lake effect snow showers across
the thumb, closer to the Lake Huron shoreline for both Thursday and
Friday. The bulk of SE MI, however, is expected to remain dry as a
dry airmass resides across the state through the weekend. Lake
effect snow chances across the thumb will taper off early Saturday
as flow turn from the northwest to the southwest, cutting off the
moisture source from Lake Huron. Otherwise, mid-level ridging and a
surface high pressure will help keep conditions dry for all of SE MI
through the weekend as temperatures push into the low to mid-40s on
Friday and lower 50s on Saturday. The next chance for precipitation
will move in Tuesday morning as low pressure tracks east from the
Central Plains into the Ohio Valley.


Northwest winds over the central Great Lake will increase tonight,
reaching into the 15 to 20 knot range over Lake Huron. Colder air
streaming in tomorrow will support a further increase, but more out
of the north direction, with winds peaking between 25 to 30 knots
over Lake Huron. Waves of 5 to 10 feet will build over the southern
Lake Huron basin by Tuesday evening. Small craft advisories have
been issued. Winds will then gradually weaken Tuesday night through
Wednesday as they slowly back toward the northwest as the gradient




Lake Huron...Small Craft Advisory from 11 AM Tuesday to 4 PM EDT Wednesday for

     Small Craft Advisory from 5 AM Tuesday to 4 PM EDT Wednesday for

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.




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