942
FXUS63 KDTX 191021
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
521 AM EST Sun Jan 19 2025

.KEY MESSAGES...

- Arctic air gains ground across the Great Lakes with nearly steady
temperatures in the teens today and single digit lows tonight.

- The coldest temperatures of the winter thus far then arrive Monday
through Wednesday. Air temperature struggles to remain above zero
during the day and easily reaches below zero lows at night.

- Hazardous wind chill of -15 to -25 F is also expected late at
night and early in the morning with little relief for the
afternoon.

- A period of greater lake effect snow organization is possible
later Monday into early Tuesday.

- A modest warming trend begins Thursday into next weekend.

&&

.AVIATION...

Strong cold air advection and passage of an upper-level wave will
support advancement and sustainment of lake effect stratus to strato-
cu off of Lake Michigan, with the chance for flurries to light snow
showers. Low-end vfr cigs expected, but some periodic mvfr may be
possible this afternoon and evening with the snow shower potential.
Confidence is low regarding how well cloud coverage holds up after
sunset given the battle of a very dry airmass vs the persistent
advection of low-level moisture off of Lake Michigan.

DTW THRESHOLD PROBABILITIES...

*   Moderate for ceiling aob 5000 feet this afternoon and evening.
    Low late tonight and overnight.

*   High for ptype of snow for any light activity this afternoon and
    evening.

&&

.PREV DISCUSSION...
Issued at 357 AM EST Sun Jan 19 2025

DISCUSSION...

Early morning observations and model analysis fields lay out the
large scale scenario that brings arctic air on schedule into the
Great Lakes through the mid week period. The full latitude 500 mb
trough covering all of North America east of the Rockies drives deep
NW flow into the Great Lakes helping the intrusion of arctic air
gain traction throughout today. This is reflected in temperature
guidance that calls for readings to hold in the teens this afternoon
after just a few degrees of recovery from morning lows. The trend is
solidly down from there given observations this morning of surface
temperatures already in the teens below zero across the upper
Midwest. Some initial buffering by the Great Lakes aggregate is
evident while the low level wind field still has a NW component and
this holds air temperature in the single digits above zero tonight
but does little to help readings climb out of the single digits
Monday, especially toward the Ohio border where a SW wind component
is first to develop and help arctic air wrap around the south end of
Lake Michigan. Additional forecast refinements to surface wind speed
and direction continue in this forecast cycle with respect to wind
chill. Monday morning low temperatures near zero toward the Ohio
border have wind chill touching -15 F briefly with the diurnal
uptick in wind speed before recovering toward single digits below
zero. Concerns increase for Advisory level wind chill Monday night
as air temperature drops to lows in the single digits below zero and
wind chill becomes more widespread with longer duration in the -15
to -20 F range during the night into Tuesday morning.

The cloud pattern and any associated lake enhanced or pure lake
effect snow across the Great Lakes are additional factors to assess
on temperature impacts throughout this arctic air outbreak,
especially at night. Consideration today arises with the mid level
wave tracking across the Ohio valley with a substantial mid and high
cloud pattern covering Lower Mi and a component of virga on radar.
Patches of stratocu do support flurries across Lower Mi while system
snow is well south of the Ohio border, and as NNW low level wind
holds Lake Michigan lake effect snow showers closer to the lake.
Passage of the mid level wave strips out system clouds tonight as
low level wind backs more westerly to bring lake effect clouds and
flurries farther east. Broken coverage is expected mainly south of
the I-69 corridor tonight into Monday morning leaving more open sky
toward the Tri Cities and northern Thumb for low temperatures at the
colder end of the range. Lake effect clouds and snow showers then
have potential to gain organization during Monday and Monday night
as the next NW flow mid level wave reinforces the long wave trough
and lake effect seeding over the Great Lakes. The surface reflection
of the short wave nicely augments the lee side trough off the south
end of Lake Michigan which typically supports a dominant lake effect
snow band, or at least a high concentration of multiple bands that
extend well into SE Mi. This time around arctic air produces extreme
lake instability and convective depth is around 7.7 kft, but the
surface based DGZ still raises enough concern about disruptive cloud
microphysics for a conservative approach at this time range. For
now, a scattered to numerous coverage expectation fits best which
may eventually trend to some light accumulation centered on Monday
night.

Passage of the Monday night mid level wave brings surface high
pressure into the Ohio valley and the core of arctic air into the
Great Lakes Tuesday night into Wednesday. Guidance low temperatures
are advertised in the single digits below zero by sunrise Wednesday
accompanied by another round of wind chill around -15 F until south
wind begins a cold air displacement during the day. Warmer air
inbound ahead of the next low pressure system is still below normal
but returns to the 20s during the day and teens at night into next
weekend.

MARINE...

Cold northwest flow continues to filter an arctic mass into the
region today with wind speeds on the order of 10 to 15 knots. Lake
effect snow will increase in coverage and intensity over Lake Huron
this afternoon as a corridor of localized convergence develops in
response to strengthening lake aggregate troughing. As this snow
band shifts southward across the lake through the afternoon, wind
will veer to the north/northeast behind it. Flow then shifts to the
west and west-southwest on Monday and strengthens to the 20 to 25
knot range as even colder air works in. This uptick in wind
magnitude brings freezing spray across parts of Lake Huron Monday
through Wednesday as the coldest air holds in place. Milder air then
works back into the area Thursday into Friday amidst moderate
southwest flow.

&&

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

$$

AVIATION.....AM
DISCUSSION...BT
MARINE.......TF


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