Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221739
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
139 PM EDT Fri Mar 22 2024

.KEY MESSAGES...

- A Winter Weather Advisory remains in effect Friday for a greater
  portion of SE MI. New accumulation totals of 1-4 inches will be
  possible for counties that remain within the Winter Weather
  Advisory, with higher end totals favored along or north of M-59.
  Highly localized snowfall totals 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.

&&

.AVIATION...

A shallow dry slot has temporarily ceased snowfall production across
the Metro terminals while multiple elevated frontal boundaries
continue to produce widely varying snow intensity across the
remaining terminals. The forcing from the elevated boundary across
the Tri-Cities will initially intensify through this afternoon which
will result in periodic heavy snowfall rates which will likely reduce
visibilities down to LIFR at times. This frontal boundary will then
sweep southeast through the evening hours, sustaining snow across
KFNT and KPTK, and bringing the return of snow to the Metro
terminals. Cigs are expected to periodically range between MVFR-IFR
along the front, where visibilities to or below 1SM will be possible.
Snow will abruptly come to an end after the passage of the front,
where MVFR/IFR cigs will likely sustain in the wake of the front.

For DTW... A lull in snowfall is expected to last through the early
evening hours. A cold front will bring a window of snow tonight,
roughly between 01Z to 05Z. There may be a brief hour window within
this time frame with moderate to heavy snowfall that can quickly
produce an inch of snow accumulation.

.DTW THRESHOLD PROBABILITIES...

* High for snow as precipitation type.

* Low in ceilings aob 5000 feet this afternoon, high late tonight
  with snowfall.

&&

.PREV DISCUSSION...
Issued at 319 AM EDT Fri Mar 22 2024

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.

&&

.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 until 7 PM EDT this evening for LHZ441-442.

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

$$

AVIATION.....AM
DISCUSSION...KDK
MARINE.......TF


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