871
FXUS63 KDTX 172358
AFDDTX

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

.KEY MESSAGES...

- Predominately rain and snow expected tomorrow, mainly south of the
  I-69 corridor. Snow accumulations likely less than an inch.

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

- Dry and seasonably cool conditions Wednesday.

&&

.AVIATION...

A brief period of clear sky and light wind is afforded by a ridge of
high pressure sliding across Lower Mi this evening. High clouds then
increase quickly before midnight as the first sign of low pressure
approaching from the Plains. The system only reaches the mid MS
valley by Tuesday morning but extends mid to upper level moisture
well north into the Great Lakes. Dry air below 700 mb remains a
formidable obstacle and supports later onset timing in the going
TAFs along the DTW corridor up to 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 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. Precipitation ends and ceiling improves north to
south as the system weakens while settling into the TN valley to mid
Atlantic Tuesday night.

For DTW... Dry air remains a factor in slower onset timing of snow
or rain/snow mix Tuesday 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.  pattern.

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 Tuesday afternoon.

&&

.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
DISCUSSION...AA
MARINE.......MV


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