NWS Forecast Discussion

FXUS63 KDTX 160805

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
405 AM EDT Sat Oct 16 2021


Ongoing area of light rain will slide east and depart by mid-
morning as midlevel height falls and CVA exit to the eastern Great
Lakes. This process is being governed by an amplified longwave trough
pivoting across the Great Lakes which finally ushers out the active
baroclinic zone that led to several days of wet weather. Strong
negative thickness advection ensuing through the day with 850mb temps
tumbling from 10C last evening to around 0C by later this afternoon.
This cold advection will activate the lake effect response with a
healthy stratocumulus field enveloping the region this afternoon and
possibly producing some isolated sprinkles. Additionally, steepening
low-level lapse rates will aid in breezy conditions with gusts around
20 to 25 mph. Highs in the mid to upper 50s today which for most
areas will be the first day with highs below 60 since September 23.

The loss of daytime heating promotes scattering of clouds this
evening which leads into a night of favorable cooling conditions.
Lows in the 40s tonight may feel cool given the stretch of recent
warm weather, but will be right around normal for mid-October. An
active westerly gradient will keep winds from completely decoupling
and prevent further cratering of temps. Meanwhile, the resident
longwave trough will begin its departure by Sunday morning.

Confluent upper flow spills over the Great Lakes through the day
Sunday as the upper jet moves in on the backside of the trough.
Shortwaves within the energetic northwest flow with some lingering
cold advection may be sufficient to trigger some showers mainly over
the eastern Thumb on Sunday. Otherwise, dry weather and mostly sunny
skies prevail with temperatures beginning a rebound with the exit of
the thermal trough. Still breezy on Sunday with a relatively deep
mixed layer developing within the dry ambient environment with a
persistent northwest gradient.

Benign conditions dominate the early and mid week as tropospheric
ridging expands eastward. The ridge axis itself is progged to stall
just to our west on Monday and slowly dampen in response to a strong
Pacific low tracking across the intermountain west. Northwest winds
then back to the southwest by Tuesday and Wednesday which allows for
a shift to a warm advective regime. This brings the return of warmer
conditions with highs in the upper 60s both days. Active weather
returns Wednesday night into Thursday as the aforementioned Pacific
low reaches the Great Lakes bringing our next chance of rain. This
system is advertised to bring the return of more seasonable
conditions for Friday into the weekend.



Mainly showers through early today as the main upper trough axis and
stronger cold front moves across the western and central Great
Lakes. There will be a much greater lake response behind this front
as much cooler air filters into the region. The cold air moving over
the relatively warmer waters will bring a chance for waterspouts
over the weekend. Winds will also increase with sustained winds of
20 to 25 knots likely across Lake Huron Saturday. Gusts will be
around 25 to 30 knots. A Small Craft Advisory remains in effect
for all marine zones through today. Lingering precipitation with a
chance for waterspouts continues across central and northern Lake
Huron tonight before activity clears out during the day Sunday. High
pressure then brings quieter marine conditions during the early week,
though the cooler air keeps some elevated wind gusts to around 20
knots across Lake Huron on Monday.


Issued at 1145 PM EDT Fri Oct 15 2021


A large area of rain is currently lifting northward out of the Ohio
River Valley towards Southeast Michigan. The rain is associated with
organized differential cyclonic vorticity advection occurring ahead
of a strong PV anomaly. A lot is happening to the thermodynamic
environment as a good amount of cold advection is occurred between 2.0
and 10.0 kft agl. Lapse rates have steepened considerably in the
lower troposphere which has knocked out the low column inversion.
Ceilings have temporarily improved this evening with the loss of the
strong static stability. Rain activity will overspread the area again
as a strong ageostrophic response to dcva steepens the cold frontal
slope. Bulk of data supports VFR rain shower activity tonight with
differential near surface cold advection supporting some shallow
convective instability and MVFR to potential pockets of IFR after
09Z. Post frontal northwest flow will support a well mixed boundary
layer and VFR clouds Saturday.


* High in ceilings at or below 5000 feet late tonight and Saturday.
  Low confidence during the mid to late evening.


Lake Huron...Small Craft Advisory from 10 AM this morning to 4 AM EDT Sunday for

Lake St Clair...Small Craft Advisory from 10 AM this morning to 4 AM EDT Sunday for

Michigan waters of Lake Erie...Small Craft Advisory from 10 AM this morning to 4 AM EDT Sunday for




You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.

NWS DTX Office Area Forecast Discussion