912
FXUS63 KDTX 231107
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
607 AM EST Mon Dec 23 2024

.KEY MESSAGES...

- Wintry mix expected from this afternoon into this evening.

- Highest snowfall amounts will be north of M-46, with lighter
  amounts and the increased chance of a period of sleet and/or
  light freezing rain south into parts of the Detroit Metro
  region.

- Warmer weather expected Christmas Day on through the rest of
  the week with increasing rain chances by the weekend.

&&

.AVIATION...

An arc of mid-level ascent and moisture transport resulted in virga
and a slight lowering of mid-level ceilings overnight but conditions
remain VFR this morning. These ceilings may lift again or scatter
for a time through mid-morning, especially across the Metro Detroit
sites as slightly drier air works back in from the south. This gives
way to deteriorating conditions from NW to SE this afternoon and
evening as low pressure from the Midwest arrives. This system will
bring widespread light snow this afternoon and evening with
potential for brief periods of freezing rain and sleet south of I-69
mainly as the precip arrives. VFR conditions drop to IFR in the
snowfall with potential for LIFR conditions especially north of
Metro Detroit where the steadiest snow rates are expected. Precip
will come to an end during the mid to late evening, but saturated
low-levels will favor continued MVFR/IFR ceilings overnight with
potential for additional visibility restriction in pockets of
drizzle.

For DTW...Forecast start time of precip continues to trend later,
and adjusted onset to 20z in the TAF. Brief 1 to 2 hour window of
freezing rain or sleet remains possible near the onset before wet
snow becomes dominant late afternoon into early evening. The bulk of
the precip departs before midnight with potential for a period of
light rain as temps hover in the mid 30s. IFR will be most likely
this evening with potential for improvement to MVFR after the main
area of precip moves out.

DTW THRESHOLD PROBABILITIES...

* High for ceiling at or below 5000 feet after 18Z.

* Low for precipitation type as light freezing rain and/or sleet
  before 21Z, then high for predominantly snow after 22Z. Low for a
  brief transition to rain after 01Z.

&&

.PREV DISCUSSION...
Issued at 312 AM EST Mon Dec 23 2024

DISCUSSION...

Well developed shortwave now working from the Northern Plains into
the Upper Midwest has slowed notably over the past 24 hours with
precipitation associated with this wave now focused from mid/late
afternoon into the evening hours. Model trends of shifting the best
forcing with this system to the north and muting it somewhat have
remained in place for the 00z model cycle. Only minor adjustments
seem necessary in the precip/snow accum/ice accum fields.

Generally expected snow to overspread the northern forecast area
early this afternoon with the progression of lighter precipitation
then working south and east into the mid/late afternoon. Warm wedge
of air overriding the western edge of modified arctic air mass will
lead to a wintry mix at times, especially south of I-69.

Will issue a Winter Weather Advisory for portions of the forecast
area. Areas from the Saginaw Valley into Thumb will receive mainly
snow with 2 to 5 inches expected before precipitation ends with the
passage of the system by around midnight. The I-69 to M-59 corridor
region should receive 1 to 3 inches of snow with more sleet and
possibly patchy light freezing rain mixing in at times. Further
south, higher elevations of Washtenaw County may remain cold enough
for minor ice accumulations mid to late afternoon with light snow
accumulations under an inch into early evening before precipitation
shifts east by mid/late evening. Otherwise, most locations south of
I-96/I-696 will receive only minor snow and/or ice accumulations.

The western edge of this cold high pressure system centered well to
the east holds fast into the middle of the week with highs only edge
up in the mid to upper 30s after reaching the lower/mid 30s later
today. Another weak impulse within west to northwest flow will bring
sporadic rain showers Christmas Day. Otherwise, dry conditions are
expected once today`s system passes east of the area later tonight.

A more pronounced warming trend will ensue later this week into the
weekend as temperatures climb into the 40s (to around 50 in some
locations by the weekend). Plenty of clouds, however, remain in play
through the week with increasing rain chances heading into the
weekend as a series of southern stream shortwaves parade into the
area and eventually break down the western portions of persistent
high pressure anchored from the northeast CONUS back into the Great
Lakes.

MARINE...

Low pressure arrives over the Great Lakes this morning bringing
widespread snow showers that persist into late tonight. In advance,
moderate to strong south winds (25-30kts) are expected across the
bulk of Lake Huron with 20-25kt flow likely over the remainder of
the region. Small Craft Advisories remain in effect around the Thumb
due to 3-5+ ft waves developing in this offshore flow. Low pressure
exits the region by early Tuesday tapering off any lingering snow as
well as shifting winds to the NW. Flow then veers to the NE by late
Tuesday morning as high pressure quickly becomes established. These
northerly winds hold on the lighter side, at or below 15kts, due to
the aforementioned high quickly weakening the local gradient.
Influence of high pressure maintains lighter winds through the
midweek period.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from noon today to 1 AM EST Tuesday for
     MIZ047>049-053>055-060>063-068>070.

     Winter Weather Advisory from 2 PM this afternoon to 10 PM EST this
     evening for MIZ075.

Lake Huron...Small Craft Advisory until 4 PM EST this afternoon for LHZ421-
     441>443.

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

$$

AVIATION.....TF
DISCUSSION...DG
MARINE.......KDK


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