003
FXUS63 KDTX 042341
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
641 PM EST Wed Dec 4 2024

.KEY MESSAGES...

- An arctic cold front will bring numerous snow showers as it
  crosses the area this evening. Snow squalls are likely within
  this activity. Gusts up to 35 to 40 mph will produce brief but
  near whiteout to whiteout conditions under snow squalls.

- Temperatures will quickly drop below freezing after the frontal
  passage. A flash freeze will be possible on untreated roadways.

- Snowfall accumulations of 2 to 5 inches expected over the Thumb
  with 2 inches or less expected elsewhere.

- Wind chills in the single digits overnight.

&&

.AVIATION...

Area of snowfall on pace to expand across southeast Michigan early
tonight. Upstream radar trends continue to lend confidence for a
brief window of higher intensity snow showers/squalls to emerge
along an advancing arctic front, within a broader region of light
snow during this time. Inbound timing still focused within the 00z-
03z window, with the most intense burst(s) carrying potential for a
rapid reduction of conditions to LIFR and a quick accumulation.
Trailing snow showers to linger within the immediate wake overnight,
with a particular focus at MBS/FNT as consolidated smaller scale
forcing along the northern edge of the moisture axis may offer a
secondary or prolonged window of greater intensity snow. Noted wind
shift to westerly with an increase in gust magnitude as arctic air
surges into the region overnight and early Thursday. Gusty northwest
winds with some potential for intervals of light snow
showers/flurries on Thursday.

For DTW...Brief higher intensity snow showers/squalls will focus
within the 01z-03z window. Lighter intensity snow will exist outside
these bursts early tonight. Snow shower potential rapidly declines
after midnight, as westerly winds strengthen and temperatures
plummet through the early morning hours.

 DTW THRESHOLD PROBABILITIES...

*  High tonight and Thursday.

*  High precipitation type as all snow tonight and Thursday.

*  High to reach crosswinds thresholds tonight.

&&

.PREV DISCUSSION...
Issued at 316 PM EST Wed Dec 4 2024

DISCUSSION...

Rapidly deteriorating conditions are expected this evening as a
strong arctic cold front sweeps through the region as low pressure
passes to the northern of Lake Ontario. For many locations, the
passage of this front will bring a 30 to 60 minute period of snow
showers/squalls within the 7pm-10pm window with rapid reductions of
visibility to white out or near white out conditions. Local snowfall
amounts will range from 1/2" to 1 1/2" during this short time frame
as moisture flux from Lake Michigan will be robust given the strong
cold air advection and convective depths will increase to 10kft or
more as the strong upper level shortwave driving this arctic front
crosses the area.

In addition to this quick burst of snow squall activity along the
front, there is increasing support within the 12z model suite for a
low/mid level mesoscale vorticity center pivoting through northern
lower Michigan and dropping southeast through parts of the Saginaw
Valley into the Thumb late this evening into the early morning hours
as the main upper level shortwave/low pressure works through the
region. This feature will act to enhance snowfall rates within this
quadrant of SE Lower MI and also increase the duration of meaningful
snowfall rates.

Given these model trends this morning/early this afternoon, am
planning on issuing a Winter Weather Advisory for the Thumb where
the potential for 3 to 5 inches of snowfall seems most pronounced.
Will extend this into Thursday given the enhanced wind gusts off
Saginaw Bay and some potential for additional lake effect snow
showers/squalls over portions of the Thumb. Will likely also issue
an advisory from the Saginaw Valley into parts of the I-69 corridor
around the periphery of the main area of focus for marginal snowfall
amounts (around 2 inches).

The most difficult call of the forecast will be whether to extend an
advisory south and west into the M-59/I-96 corridor region as both
the coverage/duration for heavy snow squall activity will be more
questionable and reliant on the location of rapidly developing lake
effect streamers from Lake Michigan in the wake of the arctic
frontal passage. Given the relative lack of coverage/duration for
heavier snow showers/squalls south of the mesoscale vorticity, short-
fused Snow Squall Warnings for the most intense bands may be the
better way to handle the situation as any given burst of heavy snow
will last for less than an hour.

Temperatures will be close to freezing (32F) as the arctic front
reaches the area with temperatures then falling quickly into the mid
to lower 20s from midnight into the overnight as west to northwest
winds increase significantly with gusts into the 40 to 45 mph range.
This will lead to flash freeze conditions on untreated roadways as
the colder air deepens over the area in the mid/late evening period.
So, even after heavier snow squalls shift out of the area, travel
conditions later this evening will be questionable especially as
wind gusts increase to 40 mph or more.

Overall, the lake effect snow shower/squall activity will lessen
overnight into Thursday morning as the low level flow veers to the
northwest with lingering flurries/light snow showers into the
afternoon with only locations in Washtenaw/Lenawee counties as well
as the Lake Huron shoreline still being brushed by squally activity
within this trajectory.

After temperatures fall into the upper teens to around 20 Thursday
morning with wind chill readings in the single digits as wind gusts
to 40 mph or more continue, expect cold conditions to persist
through Friday into early Saturday with lows remaining into the
teens to around 20 and highs in the 20s to around 30 as the modified
arctic high pressure system settles from the northern plains into
the Mississippi Valley. Increasingly mild return southwest flow
around this high pressure will lead to strong moderation into the
weekend and early next week with highs back into the 40s to possibly
50. Any precipitation beyond Saturday will be in the form of rain.

MARINE...

Low pressure, 29.20 inches, will track southeast across south-
central Ontario this evening and overnight delivering a potent cold
front. Stronger gradient winds and gusts to gales briefly diminish
early tonight while under southwest flow, but once the cold front
moves through and winds veer northwesterly overnight, lapse rates
steepen significantly. This allows gusts to gales to quickly settle
back in with coverage expanding across the entire central Great
Lakes with the cold advection. Forecast remains largely on-track,
maintaining the current Gale Warnings in effect late this evening
into Thursday afternoon. The arctic airmass may also favor the
development of snow squalls, especially late this evening before the
colder air lingers into Saturday. Winds remain elevated Friday,
becoming westerly, but should remain below Small Craft Advisory
criteria through Saturday as high pressure eventually builds in on
either side of the central waterways over the weekend.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 4 AM EST Thursday for MIZ047-048-053-
     061>063.

     Winter Weather Advisory until 4 PM EST Thursday for MIZ049-054-055.

Lake Huron...Small Craft Advisory until 10 PM EST this evening for LHZ441>443.

     Gale Warning from 10 PM this evening to 10 PM EST Thursday for
     LHZ361-362-441>443-462>464.

     Gale Warning until 10 PM EST Thursday for LHZ363-421-422.

     Low Water Advisory until 4 PM EST Thursday for LHZ422.

Lake St Clair...Small Craft Advisory until 10 PM EST this evening for LCZ460.

     Gale Warning from 10 PM this evening to 1 PM EST Thursday for
     LCZ460.

Michigan waters of Lake Erie...Low Water Advisory until 1 AM EST Thursday for LEZ444.

     Small Craft Advisory until 7 PM EST this evening for LEZ444.

     Gale Warning until 1 PM EST Thursday for LEZ444.

&&

$$

AVIATION.....MR
DISCUSSION...DG
MARINE.......KGK

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at www.weather.gov/detroit.