Troy, Michigan Weather Forecast Discussion

824
FXUS63 KDTX 201958
AFDDTX
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
358 PM EDT Sat Sep 20 2025
.KEY MESSAGES...
- Pleasant this evening, then a chance of showers late tonight.
- Scattered to numerous showers and thunderstorms Sunday. Greater
  coverage and intensity from mid afternoon through evening.
- There is a Marginal Risk of severe thunderstorms Sunday afternoon
  and evening. Damaging wind is the primary hazard.
- Scattered showers continue Monday and Tuesday.
&&
.DISCUSSION...
Sun filtered through thin cirrus and temperatures near 80 make up an
outstanding mid/late September Saturday across SE Mi. Conditions
settle into a comfortable evening as Quebec high pressure supplies
cool easterly wind into the Great Lakes. However, not far to the
west, showers and a few thunderstorms are ongoing across western
Lower Mi which extend into WI/IL and associated with the next low
pressure system. This convection is within the stronger southerly
flow that supports the low to mid level moisture axis north of the
Ohio valley to Midwest surface front. Scattered to numerous coverage
this late in the day is a sign that elevated instability will remain
adequate for support of additional showers/ordinary storms tonight.
The larger scale system sustains the convection but is just slowly
progressive on a pace that grazes the Tri Cities late tonight with a
stray shower possible farther south and east toward sunrise.
Late night activity lingers into the morning in scattered coverage
just on the inertia of nocturnal moisture transport. The mid level
theta-e ridge also holds plentiful cloud cover able to disrupt
daytime surface heating, especially during the morning. After that,
the SPC Marginal Risk hinges on how much instability can recover as
diffuse warm sector builds into Lower Mi under an otherwise weakly
supportive larger scale configuration aloft. HREF mean surface based
CAPE fails to exceed 1000 J/kg even with an advective component
evident in the hourly projections. Otherwise, 0-6 km bulk shear
gradually strengthens into the 20 kt range with near 30 knot speed
at 500 mb. There is also some weak directional curvature for an
overall not bad sounding, again depending on a shaky recovery of
enough instability to support a multicell convective mode. Precip
loaded downburst wind is the primary hazard in this scenario.
There is uncertainty on storm intensity and severe potential, but
with greater confidence in numerous to widespread showers and
ordinary storms. Coverage peaks Sunday evening under difluent and
weak DCVA short wave support aloft acting on the eventual outcome of
boundary layer instability within the low to mid level theta-e ridge.
This moisture axis slides eastward later in the night leading to
decreasing coverage toward Monday morning. Scattered coverage in the
morning builds back toward numerous with a boost of daytime
instability Monday afternoon. Showers/storms are further boosted by a
lingering favorable environment downstream of the 500 mb trough
axis, although the surface pressure structure is not well defined
until the Tuesday period. Model projections show central Rockies
height falls elongating the 500 mb trough which sharpens up the
surface front from the central Plains into the Great Lakes for the
mid week period.
&&
.MARINE...
High pressure drifts from southern Quebec to New England by Sunday
morning. Meanwhile, an occluded low pressure system meanders over
the Upper Midwest. This maintains a tightened pressure gradient over
the Great Lakes through tonight, with breezy east to east-southeast
wind of 10 to 20 kt. Locally higher wind with gusts up to around 25
kt will focus within longer fetch regions of northern Lake Huron and
western Lake Erie through this evening before subsiding tonight.
Probability for showers and thunderstorms increases tonight and
especially Sunday as the aforementioned low pressure system sends
its warm front across the region. Any isolated stronger storm
development will be capable of producing localized wind gusts in
excess of 34 knots and waterspouts. Wind will prevail out of the
southeast around 10 kt through Sunday before shifting to southwest
Monday. An unsettled showery/stormy pattern continues through Monday
into Tuesday as multiple disturbances pass over the region along
with a slow moving frontal boundary.
&&
.PREV DISCUSSION...
Issued at 118 PM EDT Sat Sep 20 2025
AVIATION...
VFR conditions today as high pressure continues to hold off the
advancement of the warm front positioned to our west. Wind remain
out of the east-southeast and largely below 10 knots. High clouds
will continue to stream in on the elevated portions of the front
today and tonight before the front releases northeastward through
lower MI. CIGS lower and rain chances begin after midnight tonight
for MBS and FNT as the deeper moisture pushed up through western
lower MI and Mid MI first. Then chances remain through the afternoon
as the upper level trough lingers over the region. Deeper layer of
dry air in the boundary layer for the Detroit area taf sites should
hold off most of the early showers, but chances do increase through
the daylight hours. Mainly showers for all locations but embedded
thunderstorms will be possible.
For DTW/D21 Convection... No thunderstorms expected tonight and but
chances for showers increases through the late morning and afternoon
as the front inches closer to the state line. Dry air in the
boundary layer will keep CIGS mainly above 5kft Sunday and that dry
air layer will lead to potential wind gusts with any thunderstorm
that develops.
DTW THRESHOLD PROBABILITIES...
* Low for ceilings at or below 5,000 feet through tonight, medium
  for Sunday.
* Low for thunderstorms to impact DTW on Sunday, but the best chance
  would be 18-00Z.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...Small Craft Advisory until 2 AM EDT Sunday for LEZ444.
&&
$$
DISCUSSION...BT
MARINE.......TF
AVIATION.....DRK
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.

NWS DTX Office Area Forecast Discussion