Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 220719
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
319 AM EDT Fri Mar 22 2024

.KEY MESSAGES...

- Snow begins in time for disruption of the morning commute across
  the bulk of the area today.

- A Winter Weather Advisory remains in effect Friday for all of SE MI
  except for Lenawee and Monroe counties. Total snowfall
  accumulations ranging between 2-6 inches will be possible for
  counties within the advisory, with the higher end totals favored
  along and north of M-59. Highly localized totals in excess of 6
  inches will be possible with any snow banding.

- Dry weather but below average temperatures return this weekend.

- Warmer temperatures and rain showers return for early next week.

&&

.DISCUSSION...

Lead arm of elevated warm advection tied to a partially sheared
Plains shortwave is on the doorstep of SE MI at time of discussion.
Upstream observations have shown a cellular/convective component to
associated snow showers with this expected to continue as it works
into our area as elevated instability (between 500-700mb) creeps in
from the south. Forecast soundings nearly all advertise impressive
strengthening frontogenetic forcing/ascent along the ~700-550mb
frontal slope as snow expands between the I-69 to I-94 corridors
this morning, which also coincides with the region of the column
where the DGZ is residing. Combination of these factors is
increasing concern for an area of overachievement in snow rates
exceeding 1 inch per hour somewhere across the southern advisory
counties (Livingston, Oakland, Macomb) as well as the northernmost
portions of Washtenaw/Wayne counties. While the more mesoscale
nature of this potential band carries low spatial predictability,
there is enough confidence/concern that we have added the I-94
corridor counties into the advisory given the window for enhanced
rates occurs at least partially within the morning rush hour period.
Overall, areas south of I-69 have the potential to pick up a quick 2-
4" this morning, though if higher rates are realized, can`t
completely rule out a localized area approaching 5". For areas north
of I-69, the higher active frontal slope, aoa 500mb, both prevents a
convective component like areas to the south as well as places best
saturation/ascent above the DGZ limiting potential accumulations to
the 1-3" range through the morning.

Warm frontal slope slides further north by midday as the arrival of
the main mid-level shortwave over the western Great Lakes results in
its reorientation towards SW-NE over the Thumb/Saginaw Valley. Shift
allows a modest 800-900mb dry slot to expand over areas south of I-
96/696 (and potentially as far north as M-59) during the afternoon
leading to a lull in precip. Conversely, the northern CWA not only
continues to see persistent snow but likely increasing intensities
as a jet streak develops over Lake Huron/Ontario increasing the fgen
response as the right entrance region sets up directly overhead.
Additionally with the aforementioned northerly trend in the front,
the active frontal slope shifts lower towards the 600-700mb layer.
Soundings hint at weak elevated instability being available within
this region of the column further strengthening the frontogenetic
forcing. Similar to the morning activity over the southern CWA,
result is that areas along/north of the I-69 could see a quick 2-4"
through this afternoon-early evening.

Attendant mid-level cold front works across the region this evening
into the first half of tonight as the parent shortwave pushes into
southern Ontario. This brings snow back into the southern portions
of the CWA as the lingering fgen band is pulled southeast. Some
weakening of this banding is possible as it works into the Metro
area due to the accompanying jet streak looking to likewise shift
further southeast toward Ohio, however CAM guidance remains in
disagreement wrt the speed this occurs at. Should this trend occur
slow enough, there will be a secondary window for areas south of I-
69 to see a brief heavier burst of snow with rates between 0.5-1"/hr
late evening-early tonight (~22-04Z). Potential accumulations will
be limited by the bands residence time as it rapidly moves east with
0.5-2" currently expected- lowest amounts towards the state line.

High pressure dropping out of the Canadian Prairie expands over the
central Great Lakes for Saturday ushering in colder but drier air
for the weekend. 850mb temps fall to around -10C for both days
resulting in another period of highs holding below normal in the
30s. Active weather looks to make its return early next work week as
a potent Pacific mid-upper trough ejects out of the Desert Southwest
and into the Midwest/Great Lakes.

&&

.MARINE...

Southeast to east wind increases to between 15 and 20 knots today
with some gusts to 25 knots as low pressure tracks from the Plains
into the Ohio Valley tonight. This low brings widespread snow across
the central Great Lakes with some rain and wintry mix possible
across western Lake Erie and Lake St. Clair. Small Craft Advisories
are in effect along the Lake Huron shoreline from Port Austin to
Port Sanilac where wave heights will build to around 4 to 5 feet
today. The system departs late tonight with winds shifting to
north/northwest by Saturday morning. Colder air works back into the
area with winds becoming gusty to around 20 to 25 knots Saturday. A
ridge of high pressure then builds in Saturday night into Sunday
with weaker winds expected. The next low pressure system lifting out
of the Plains will force a warm front across the region Monday into
Tuesday with increasing southeast winds during this period.

&&

.PREV DISCUSSION...
Issued at 1158 PM EDT Thu Mar 21 2024

AVIATION...

A significant early spring snow is delivered to southern Lower Mi
late tonight and through today as central Plains low pressure moves
into the Ohio valley. VFR under thickening high clouds late tonight
gradually lowers while surface wind becomes more consistently SE.
Virga will be evident on radar while initial SE wind maintains dry
air in the low levels but then snow begins with a quick drop to IFR
toward sunrise. A further drop into LIFR is expected not long after
12Z and a slight southward trend on location, now mainly from PTK to
FNT at onset. Persistence of greater coverage and intensity shifts
north of PTK to affect FNT and MBS for the afternoon. Even longer
breaks of improvement are likely toward the DTW corridor where the
south edge of MVFR/VFR clouds lingers until snow moves back in late
in the day. The back edge of the snow pattern then migrates NW to SE
across Lower Mi during Friday evening.

For DTW... VFR under broken high clouds gradually fills in and
lowers below 5000 ft late tonight and down to MVFR in the morning.
MVFR/IFR snow showers brush the terminal for a few hours early to
mid morning until the pattern shifts north for the afternoon.

DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 feet or less toward sunrise through the day.

* High for snow as precipitation type but low on duration time
  impacting the terminal.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until midnight EDT tonight for MIZ047>049-
     053>055-060>063-068>070.

     Winter Weather Advisory until 2 PM EDT this afternoon for MIZ075-
     076.

Lake Huron...Small Craft Advisory from 10 AM this morning to 7 PM EDT this
     evening for LHZ441-442.

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

$$

DISCUSSION...KDK
MARINE.......TF
AVIATION.....BT


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