Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/09/24

Area Forecast Discussion

National Weather Service Detroit/Pontiac MI

 923 PM EST Mon Jan 8 2024

.KEY MESSAGES...

* A Winter Weather Advisory is in effect for most of SE Michigan on
  Tuesday as a strong low pressure system lifts into the area. The
  Tuesday morning commute will likely be impacted by snow covered
  and slick roads with lowered visibilities.

* A rapid accumulation of heavy, wet snow is expected between 4 AM
  and noon Tuesday for areas south of I-69. Total snow accumulations
  of 2 to 4 inches are expected with locally higher amounts possible
  mainly across the Irish Hills. Temperatures rising above freezing
  will cause snow to change over to rain from south to north from
  late morning into the afternoon.

* Longer duration of snow in the Tri-Cities will bring snow totals
  of 3 to 5 inches there. Lower confidence exists in timing the
  transition to rain here, and a low chance (10%) does exist for
  higher snow totals if snow remains the predominant precip type
  through Tuesday evening.

* The combination of heavy wet snow with southeast winds of around
  30 mph may lead to some isolated downed tree limbs and sporadic
  power outages. Onshore winds will be higher in the Thumb with
  gusts up to 40 mph.

* Strong west winds area expected to develop Wednesday in the wake
  of the storm system. Wind gusts of 30 to 40 mph will be possible
  with the strongest winds from Metro Detroit southward to the
  Indiana and Ohio border.

* A quick hitting clipper will bring the potential for a widespread
  inch of snow Thursday morning.

* Confidence is increasing for another major winter storm late
  Friday and Saturday. The potential exists for significant snow
  accumulations across Southeast Michigan. Strong winds, below
  average temperatures, and lake effect snow appear likely next
  weekend.

&&

.UPDATE...

The region of light snow expanding across central Illinois is
associated with excellent mid level isentropic ascent which will
advance across Se Mi (particularly south of the I-69 corridor) late
tonight, affecting the area through the morning rush hour. There is
some concern the ascent may acheive 2 to 4, locally 5 inch type
totals across Lapeer and portions of St Clair County. Opted to hold
off expanding the advisory into those counties and let the mid crew
evaluate latest trends, concern being a slightly more aggresive push
to the warm layer into Se Mi Tues morning and/or a little more an
brief interval of good ascent. Otherwise, the going forecast and
headlines will remain unchanged this evening.



&&

.PREV DISCUSSION...
Issued at 615 PM EST Mon Jan 8 2024

AVIATION...

Light snow is expected to arrive across the Se Mi terminals between
08Z and 10Z per recent hi res model solutions. This will occur as
the moist plume associated with the warm conveyor of the approaching
storm system advances across Se Mi. Peak snowfall is expected in the
11 to 14Z time period, where snowfall rates of 1/2 to 1 inch per
hour are possible. Snowfall rates are expected to decrease markedly
after 14Z as the initial burst of ascent wanes and warmer air gets
advected into Se Mi, transitioning the snow to drizzle. MBS being
closer to the colder air may however see a second period of light
snow during the late afternoon, while the remainder of the terminals
will see precip in the form of rain. The extend of low level
moisture advection will support widespread IFR conditions, possibly
through the entire day. Despite strengthening winds aloft, strong
low level stability through the day Tuesday will keep peak wind
speeds in check; with gusts largely below 25 knots.

For DTW...Light snow is forecast to arrive in the 08 to 09Z time
period with the peak snowfall expected in the 10-13Z time period.
There is some degree of uncertainty as to how quickly the snow will
transition to rain in the 13-15Z time frame. This will be a wet snow
as temperatures hold mainly in the lower 30s. Around 2 inches is
expected with this morning snowfall.

DTW THRESHOLD PROBABILITIES...

* High in precipitation becoming as snow Tuesday morning with a
  transition to rain by Tuesday afternoon.

* High in ceilings at or below 5000 feet through the TAF period.

PREV DISCUSSION...
Issued at 356 PM EST Mon Jan 8 2024

DISCUSSION...

Satellite view across the central CONUS shows the ongoing
significant winter storm progressing across the Plains and into the
Mississippi Valley. Local effects through this evening will just be
thickening high cloud as the expansive baroclinic leaf folds over
the region in the upper levels. Regional observed ACARS soundings
illustrate the drying that has occurred in the mid-levels this
afternoon, keeping conditions quiet through the night as well as
setting the stage for appreciable wet bulb potential as we start to
see snow move in early Tuesday morning.

Strong column PVA commences after 06z tonight with an abrupt arrival
of higher 925-850mb theta-e after 09z as the 60-70 kt LLJ over the
Ohio Valley directs a stream of Gulf moisture directly toward SE
Michigan. This paired with a wave of focused 800-700mb WAA/fgen will
trigger the onset of snowfall early Tuesday morning with a band of
heavy, wet snow arcing in from southwest to northeast between 09z
and 16z, mainly focused south of I-69. Rapid wet bulbing of the
relatively mild 925-850mb layer and heavy precip rates will hold
temperatures in the column below freezing at least until mid-morning
when rates wind down and the continued feed of warm/moist air begins
to win out and facilitate a changeover to rain from south to north.

Latest hi-res guidance offers a slightly earlier changeover which
lowers the ceiling on accumulation potential, but still expect a
quick 2 to 4 inches of heavy, wet snow to impact the morning
commute. Some areas along the elevated terrain of the Irish Hills
that see slightly better snow ratios remain a target for isolated
totals as high as 5 inches. Farther north, the more coherent surge
of moisture will be absent and rates will be lighter, resulting in
lower accumulations more in the 1 to 3 inch range through the mid-
afternoon before the rain begins. SE to ESE winds will become quite
strong across the forecast area as the low approaches - gusts
increasing to 30-35 mph. The Thumb will see locally higher gusts of
around 40 mph, especially near the lakeshore. A Winter Weather
Advisory has been issued for the majority of the CWA, where that
morning burst of snow will cause the most issue for the morning
commute. The Thumb was left out with this package as the lighter
rates should keep impacts lower and totals below criteria.

Another surge of moisture arrives midday as the backed LLJ slides
off to the east, bringing steady rainfall as the surface low begins
to lift into SW Lower MI. Midland and Bay Counties remain a focus
for this period as they will remain very near the rain/snow line.
Favorable localized isentropic ascent boosted by fgen during this
midday window suggests some slightly higher precip rates there which
would keep snow more likely into the early afternoon before rain
then becomes favored by the early evening. This longer duration of
snow brings potential for total accumulations of 3 to 5 inches. Have
low confidence in higher totals than this, but potential does remain
that the low center tracks slightly farther south and results in
accumulations of 6+ inches. Latest NBM ensemble statistics gives
this scenario only about a 10% chance of occurrence.

Precip rates taper off Tuesday evening as the dry slot works in,
with cooler air wrapping around the system and bringing another
ptype change back to light snow Tuesday night. Surface temps will
remain very mild in the mid 30s overnight, so accumulations are not
expected. Some minor accumulations then become possible Wednesday
morning as temps settle near freezing and lingering wrap-around snow
continues with a slight boost from the lakes. Shortwave ridging
builds in quickly on Wednesday and will bring an end to most of the
light snow. The arrival of this ridge and the departure of the
strong low will cause west winds to ramp up on Wednesday with gusts
of 30 to 40 mph likely.

A lower amplitude wave tracking across the northern Plains then
brings a round of light snow Thursday morning. Left exit region of a
130 kt jet streak over the Ohio Valley induces a corridor of system
relative upglide locally. Moisture is much less plentiful with this
clipper and the modified air mass, but models do show at least a
brief period of saturation up to around 500mb. A couple hours of
omega within the DGZ is shown as well, which may bring some larger
flake sizes. With surface temps sitting just below freezing, end
result should be about 1 inch of new snow Thursday morning with dry
air advection bringing an end to the accumulating snowfall by early
afternoon.

The next more potent Pacific wave arrives over the Pacific NW late
Wednesday, digging into the Four Corners region on Thursday before
inducing lee cyclogenesis over the southern Plains Thursday night
into Friday. This system shows lots of similarity to tomorrow`s
system as it then sends a surface low from the OK/TX Panhandle
directly into the central Great Lakes. The difference exhibited in
ensemble data is that the better warm/moist tongue looks to be
shoved farther east which brings higher confidence in an all-snow
scenario for most of the CWA. Main impacts will be late Friday into
Saturday when moderate to heavy snow and strong winds will be
possible. There continues to be fairly low spread among the medium
range solutions at this point, so this system carries relatively
high confidence and will continue to be monitored. Latest NBM
probabilities show a 50-70% chance of exceeding 4 inches across much
of the CWA. Temperatures in the wake of the system are likely to
fall below normal for the late weekend into early next week. This
pattern favors a period of lake effect snow showers during this
period as well.

MARINE...

Influence of high pressure now located across the Appalachia will
maintain lighter winds heading into the evening. This will rapidly
change as high pressure drifts into the Atlantic while a strong low
pressure system, derived from the Panhandle of Texas, fills in
across the southern Great Lakes by tomorrow evening. This will
result in the development of a strong pressure gradient over the
Great Lakes and will reinforce southeast flow through tomorrow
evening. Wind speeds will rapidly increase between 20 to 30 knots
through tomorrow morning which will rapidly increase wave heights
across the Lake Huron shoreline. A very strong low-level wind field
will also set up over the Great Lakes during this time frame,
however, this will coincide with warm air advection which will
prevent mixing of these stronger winds aloft. Despite shallow mixing
depths, the overall gradient winds will occasional mixing into the
stronger winds aloft will support gust to gales tomorrow morning and
afternoon across Lake Huron. The Gale Watch has been upgraded to a
Gale Warning for Lake Huron, which now includes northern Lake Huron.
Some occasional gust to gales will be possible across the Saginaw
Bay into Lake St. Clair and Lake Erie, however, better stability is
expected to mostly cap gust potential below 34 knots. Small Craft
Advisories are in place for these locations.

The strong low pressure system will bring bring widespread snow to
start, with a transition over to rain across the greater portion of
the Great Lakes through the afternoon. Northern Lake Huron will have
the best chances to hold onto mainly snow through the event. A flip
back over to all snow is then possible late tomorrow evening into
Wednesday morning as a cold front moves through. The passage of this
front will flip wind direction to the west-Northwest.

Last, enhanced mixing depths from the cold front will maintain
breezy conditions across the Great Lakes on Wednesday. The strong
low-level jet will have shifted away from Lake Huron at this time,
so renewed gales are unlikely for Lake Huron, however renewed Small
Craft Advisories will be possible for portions of the lakeshores.
Some stronger winds aloft do linger on across Lake St. Clair and
Lake Erie, coinciding with the better mixing depths, so there
remains a low chance (30%) to briefly see gales for these locations.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 4 AM Tuesday to 4 AM EST Wednesday for
     MIZ047-048.

     Winter Weather Advisory from 4 AM to 4 PM EST Tuesday for MIZ053-
     060-061.

     Winter Weather Advisory from 4 AM to 11 AM EST Tuesday for
     MIZ068>070-075-076-082-083.

Lake Huron...Gale Warning from 1 PM to 10 PM EST Tuesday for LHZ361>363.

     Small Craft Advisory from 7 AM to 10 PM EST Tuesday for LHZ421-422.

     Gale Warning from 8 AM to 10 PM EST Tuesday for LHZ441>443-462>464.

Lake St Clair...Small Craft Advisory from 7 AM to 7 PM EST Tuesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 7 AM to 7 PM EST Tuesday for LEZ444.

&&

$$

UPDATE.......SC
AVIATION.....SC
DISCUSSION...TF
MARINE.......AM


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