NWS Forecast Discussion

000
FXUS63 KDTX 231744
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1244 PM EST Sat Jan 23 2021


.AVIATION...

High pressure continues to move across the northern Ohio Valley
early this afternoon, with northern extent reaching into the
airspace and allowing for mainly clear skies with the exception of
lingering stratocu at KMBS and KFNT, which has occasionally dipped
MVFR at times. Sky attempts to stay mainly clear into the early
evening hours before mid/high clouds fill in from the southwest
ahead of approaching upper wave that will bring a round of periodic
light snow late in the TAF period Sunday after 12z. West/northwest
winds 5-10 knots will trend variable overnight for a time before
reorienting out of the southeast Sunday.

For DTW...Light snow looks to hold off until after 12z Sunday as
southern wing of moisture ascent will take some time to overcome
near-surface dry air. Potential will exist for some intervals of
MVFR snow towards the end of the period, but confidence not there to
include mention at this time.

DTW THRESHOLD PROBABILITIES...

* Low in ceilings below 5000 feet after 12z Sunday.

* High in ptype as snow after 12z Sunday

&&

.PREV DISCUSSION...
Issued at 358 AM EST Sat Jan 23 2021

DISCUSSION...

Overnight stratus has held on nicely through the early parts of the
morning, with rapid erosion of cloud cover now noted via infrared
across the Grand Rapids region as mid-level subsidence ahead of
surface high pressure currently located over the Midwest. Expecting
the continued erosion of stratus to take place (south of the thumb)
as high pressure continues to work east into the Ohio Valley by this
afternoon. After a very cold start to the morning marked by overnight
lows in the teens and wind chills in the single digits, a modest
warm up into the mid to upper 20s is expected later today along with
some sunshine. As the high pressure tracks east through the evening,
low-level flow will back from northwest to southwest. This will usher
in low and mid level clouds across the state and will keep overnight
lows slightly warmer, holding in the upper teens to lower 20s.

The next chance for light accumulating snowfall will then expand
across Michigan throughout Sunday morning (after 6 AM EST) as weak
system relative isentropic ascent takes place behind the departing
high pressure system. Saturation will initially occur in the mid-
levels on the 296-203K surfaces and will have to overcome some
initial low level dry air. As the column saturates, expecting light
snow to fill on across the state, with slightly better forcing noted
across Flint up into the Tri Cities, where likely PoPs hold.
Expecting around an inch of accumulation through the early afternoon
in and around the Tri Cities, with totals holding under an inch
elsewhere (half inch or under for northern Metro region south). Area
of best isentropic ascent will then slide into the Thumb during the
later part of the afternoon, with snow chances diminishing by the
late evening.

Water vapor imagery shows one of the main features of interest for
this forecast package, a pv feature just off the coast of
California, set to pivot south across Baja California late in the
day before ejecting east into TX/OK by early Monday morning. This
will result in the development of a low pressure system interacting
with a baroclinic zone, set to track north into the Ohio Valley
between 00Z Tue - 12Z Tue. Plentiful moisture will eject north
across the Ohio Valley and into the Great Lakes ahead of the low
pressure system and will bring the likely chance to see accumulating
snowfall for portions of SE MI starting late Monday evening into
Tuesday morning. Predictability of where the heaviest axis of
snowfall (potential for 4+ inches) will fall remains low given it
will remain sensitive to both the track of the low and
trowal/deformation dynamics. WPC cluster phase space analysis shows
the most likely location the axis will fall will be somewhere across
southern lower Michigan or south into the northern Ohio Valley. As a
result, preliminary forecasted snowfall totals of 3-5 inches will
hold over the Metro region down to the Ohio border, with gradually
decreasing totals north of this heavier forecasted area. Additional
adjustments will be needed as the PV feature comes onshore and is
better sampled by the NWS upper-air stations in the coming days.

Last, snow chances are expected to taper off later in the day on
Tuesday with high pressure filling in from north to south through
the midweek period. This will minimize precipitation chances to end
the week while temperature trends remain seasonable.

MARINE...

Northwest winds still gusting up around 25 knots over Lake Huron
will gradually diminish today, along with the snow showers. Still,
the larger waves over the southern Lake Huron will lag with the
unstable near surface profiles. Small craft advisories continue
through 11 am for the northern/eastern tip of the Thumb region.

Light and variable winds set up this evening as a ridge of high
pressure slides through tonight.

Light southerly flow expected on Sunday as weak low pressure tracks
through the northern Great Lakes through Sunday night. A period of
light warm advection snow likely in this time frame, but visibility`s
probably remaining at or above 2 miles.

A much stronger low will lift into the Ohio Valley late Monday, and
will lead to increasing east-northeast/onshore flow (up around 25
knots), and small craft advisories may be needed by Monday evening
and continued into Tuesday. Snow will likely overspread Lake Erie
and Lake St. Clair, and possibly as far north as southern third of
lake Huron.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....IRL
DISCUSSION...AM
MARINE.......SC


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NWS DTX Office Area Forecast Discussion