183
FXUS63 KDTX 180457
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1157 PM EST Mon Nov 17 2025

.KEY MESSAGES...

- Predominately rain and snow chances expected in the morning and
  south of the M-59 corridor. Snow accumulations less than an inch.

- The exception is for a morning light wintry mix mainly across
  Lenawee and parts of adjacent counties.

- Dry and seasonably cool conditions Wednesday.

&&

.AVIATION...

High clouds increase coverage and lower to mid levels during the
late night on departure of surface high pressure and ahead of the
Plains to mid MS valley low pressure system. The system only reaches
the lower OH valley by morning but extends mid to upper level
moisture well north into the Great Lakes. Dry air below 700 mb
remains a formidable obstacle for precip advancement and supports
mid morning onset timing along the DTW corridor and a struggle to
reach PTK. Later timing means a better chance of above freezing
temperatures for a light snow to rain/snow mix and then a transition
to all rain by early to mid afternoon. Both ceiling and visibility
drop into the MVFR range during the most favored time window for
SN/RA while stopping short of FNT on the northward fringe of the
system. Rain showers then linger along the DTW corridor late in the
day and this keeps ceiling at low end of MVFR while the low pressure
system settles into the TN valley and mid Atlantic Tuesday night.

For DTW... Dry air remains a factor in slower onset timing of snow
or rain/snow mix in the morning. Mid to late morning onset improves
the chance of above freezing temperatures in light easterly wind and
a transition to all rain early in the afternoon.

DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 feet or less after 14z Tuesday.

* High for precipitation type of snow after 11z with rain snow mix
  after 14z, and then all rain in the afternoon into Tuesday
  evening.

&&

.PREV DISCUSSION...
Issued at 957 PM EST Mon Nov 17 2025

UPDATE...

Temperature trends and precipitation onset timing/type/northward
extent are the weather elements being monitored for refinements to
the forecast for late tonight and early in the morning. Evening
observations and available 00Z hi-res and regional model data
suggest a mix of snow and snow pellets move in from the west and
make it into Lenawee and Monroe counties by sunrise but remain south
of the I-94 corridor through the bulk of the morning commute.

A deep layer of dry air in place over southern Lower Mi remains a
formidable obstacle for precip advancement as shown in the 00Z DTX
sounding but also balanced by higher precip intensity indicated by
radar to the west across the MN/IA/WI/IL border region. Given the
wet bulb cooling potential within the existing profile, higher
precip rate is expected to maintain a snow sounding at onset toward
Lenawee and Monroe counties then mix with pellets as strong warm
advection moves the thermal profile closer to 0 C after saturation.
There is a chance for a brief period of freezing rain west of US-23
and south of I-94 as the sounding transitions to more of liquid
profile while surface temperatures battle wet bulb cooling and then
rise above freezing. A later onset for points north improve the
chance for temperatures to rise above freezing for a snow/pellet to
rain transition mid to late morning.

PREV DISCUSSION...
Issued at 343 PM EST Mon Nov 17 2025

DISCUSSION...

Main focus for this forecast will be late tonight and tomorrow as
the closed mid level low over the central plains moves east while
becoming an open wave as it reaches the southern Great Lakes towards
Tuesday evening. The surface reflection is forecast to move across
the mid Mississippi River and weaken into the Ohio River Valley.
Solid ascent is expected along and ahead of this system aided by
left exit/right entrance region upper level jet dyanmics and PV
advection triggering strong FGEN over lower Michigan starting early
tomorrow morning. The nose of the LLJ will drive increasing moisture
into the elevated portion of the front during the early morning
hours as specific humidity values at 850-700 mb reach up to 4 g/kg.
Forecast soundings show a top down saturation with a lot of dry air
in the lowest 5-6kft through much of the morning hours. This dry air
provides one challenge bringing some uncertainty with how quickly
this top down saturation occurs allowing precipitation to reach the
ground. Some remaining guidance suggests this dry air could be
overcome in the 4am-7am time frame, though trends have been moving
towards a much later start time towards mid-late morning (7-9 am or
later) into the afternoon.

If any precipitation should make it to the surface before 9am,
favored p-type for most of southeast Michigan would be snow given
soundings showing saturation in the DGZ, wet bulb cooling, and/or
sub zero 0C thermal profiles. The exception would be towards Lenawee
county and along the southern border where a soundings nudge a warm
layer into the southwest CWA. This opens the door for a brief window
for potential wintry mix (including freezing drizzle/rain), mainly
across Lenawee County and portions of adjacent counties possibly
into Livingston County. Surface temperatures trends suggest surface
temperatures into the upper 20s prior to 7am before climbing to
freezing to or above in the 8-10am window and into the mostly above
32 by 10am and after. This puts the lower probability outcome for
wintry mix before 9 am contingent on precipitation that is heavy
enough to overcome the dry air while lows are in the upper 20s/low
30s. Either way, signs point to limited to no impacts with such
light QPF. Will continue to monitor thermal trends and any freezing
rain/drizzle/sleet potential that may bring isolated slick spots
mainly elevated surfaces.

Once surface temperatures climb above freezing, Light rain/drizzle
and or rain/snow mix become the favored precipitation type as FGEN
continues to produce light precipitation through much of the
afternoon. Highest PoPs remain focused along and south of a Howell
to Detroit line with chance PoPs up to around the I-69 corridor.
The drying of mid levels is what may lead to loss of ice in the
clouds towards the afternoon and evening which favors the light
rain/drizzle for much of the area. Expectation is for precipitation
to have largely come to an end before surface temperatures reach
freezing or below Tuesday evening. Overall any snow accumulations by
the end of this event should see most locations with less than an
inch with up to an inch possible and confined mostly to grassy
surfaces.

The arrival of a mid level ridge and surface high pressure will
taper off precipitation chances between 7pm-11pm Tuesday evening
with dry conditions prevailing through Wednesday and likely much of
Thursday. Temperatures mid week will see daytime highs in the 40s
with morning low mostly below freezing. Troughing returns late week,
bringing the next chance of precipitation towards Thursday night
into Friday.

MARINE...

High pressure continues to gain influence across the eastern Great
Lakes tonight, allowing further relaxation to the pressure gradient
in response. Small Craft Advisories will expire on schedule, as 25+
gusts and elevated wave action are now confined to the open waters.
Only other marine item of note is the existence of a few lake effect
streamers over the central open waters. A quieter and drier pattern
emerges for Lake Huron by Tuesday as high pressure gains traction,
while Lake Erie and Lake St. Clair are more likely to be in the
precipitation shield of an Ohio Valley low. While the low level jet
max slides south of the Great Lakes, there is potential for a wintry
mix at onset transitioning to rain during the day. Quiet pattern
then returns for mid-week with the next weather system on track to
reach the Great Lakes Friday.

&&

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

$$

AVIATION.....BT
UPDATE.......BT
DISCUSSION...AA
MARINE.......MV


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