Pontiac, Michigan 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

026
FXUS63 KDTX 191525
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1125 AM EDT Sat Jul 19 2025

.KEY MESSAGES...

- Scattered to numerous showers and thunderstorms developing late
  today into this evening. Isolated to scattered severe thunderstorms
  are possible in the 4 PM to 10 PM window.

- The main hazard with any severe thunderstorm will be damaging
winds gusts of 60+ mph. Secondary hazards will be large hail to an
inch and/or isolated tornadoes.

- Dry conditions Sunday through Tuesday.

- Heat and a low chance of thunderstorms return mid week, with heat
indices approaching 100 degrees possible on Thursday.

&&

.UPDATE...

The environment this afternoon and evening will be characterized by
nebulous forcing under modest instability and decent kinematics. The
immediate area of interest is the mcv/mcs feature now located over
Illinois. The mcs continues to drive southeast along the better cape
gradient which should remain confined to and south of the Ohio
Valley region. Embedded within the northern edge of this larger
system is a mcv complex which will sustain a more deviant west-east
motion and will attempt to target the southern Great Lakes late this
afternoon and evening. An additional source for shower and
thunderstorm late tonight will be ahead of and along a cold front
that will sweep from northwest to southeast across SE MI between 23Z-
06Z tonight, under the favorable right entrance region of the upper-
level jet. This will bring higher end PoP chances (50-80%) to SE MI
today, with these higher end probabilities favored across the Tri-
Cities and Thumb, tied to the frontal forcing.

Kinematically, the shear profiles are good, noting the stronger wind
profiles in the mid-levels which elevate slightly this afternoon and
evening. 1-6km bulk shear will range between 25 to 35 knots, the
highest found over the northern-third of the cwa. This will be a
positive for organized convection as instability slowly builds in
through the afternoon. The major caveat continues to be the degree of
instability that can pull in ahead of any storm development. Cloud
top storm motion vectors will usher in a large swath of near opaque
cirrostratus from upstream activity through the early afternoon,
limiting the degree of afternoon heating, also taking into
consideration the ongoing stratus in place outside of the Metro area.
Dew points have risen through the morning into the mid-60s, but
local maximums are found on the west side of the state, aligning with
where the better instability will line up. For SE MI, latest hi-res
output have SBCAPE values rising between 500-1000 J/kg across SE MI
in the late afternoon and evening hours, the highest of which will be
found across the Tri-Cities as better moisture arcs through central
Michigan ahead of the cold front.

Overall, this setup still warrants the continued mention for
isolated severe weather development, but severe trends have trended
downward. Shower and storms will be favored between the 4PM-10PM
time frame. Storm mode will likely range between isolated to
multicell cluster with isolated damaging gusts from wet microbursts
the primary hazard. Large hail and an isolated tornado are secondary
hazards, but cannot be ruled out under any organized updrafts. Any
sort of rotating updrafts would be favored more over central
Michigan into the Tri-Cities, aligning with the strongest cape
density and noting better curvature in the mid-levels of sr-
hodographs with a very slight elongation to the 0-1km segment.

&&

.PREV DISCUSSION...
Issued at 701 AM EDT Sat Jul 19 2025

AVIATION...

VFR conditions with light winds will start this TAF period as lower
VFR and high clouds spread across the state this morning. Expect
predominately VFR conditions to last into the early afternoon. Rain
and thunderstorms should then spread across the state with activity
reaching MBS around 19Z and then the southern metro terminals around
21-22Z. MVFR conditions will accompany thunderstorm activity with
bulk of widespread precipitation tapering off toward 06Z tonight.
Post cold front northwest wind will support MVFR to IFR ceilings by
early tomorrow morning.

For DTW/D21 Convection...Favored time period for thunderstorms to
impact DTW airspace will be between 21Z and 01Z. Upstream convective
development should bring a period of numerous thunderstorm coverage
across the airspace. Isolated strong to severe thunderstorms will be
possible.

THRESHOLD PROBABILITIES...

* Medium for ceilings at or below 5000-ft this afternoon and
  evening. High tonight.

* Medium for thunderstorms late this afternoon and evening. Low
  tonight, after midnight.

PREV DISCUSSION...
Issued at 245 AM EDT Sat Jul 19 2025

DISCUSSION...

Surface ridging and 850 MB Theta-E trough still holding on over
southeast Michigan this morning, with surface dew pts in the 50s.
Main moisture axis not progged to reach southeast Michigan until
00-03z Sunday. Still a complicated forecast with multiple upper level
PV filaments/jet streaks triggering convective activity upstream.
The prospects for morning showers/thunderstorms looks highly doubtful,
despite decent moisture advection at the 700 MB level, with rather
steep mid level lapse rates (up around 7 C/km) tracking through. This
is associated with warm air at the 700 MB level, at or slightly
above 9 C. The warm air in the 850-700 MB level looks to provide a
cap and limit instability through at least 18z today. Also the
complex entering Iowa, tracking into western Ohio Valley today may
prevent the better low level moisture (surface dew pts over 70
degrees) from making it into the CWA, or at least delay things.
However, as we head toward early evening, still looks like just
enough low level moisture (upper 60s/near 70 degrees) advecting into
Lower Michigan ahead of the cold front to support MLcapes of 1000
J/kg, with the potential to reach 1500 J/kg, per latest RAP/NAM (but
both look to be a touch too moist). Even with the lower end
instability, isolated-scattered severe storms remain a concern with
the seasonably strong mid level jet tracking through northern Lower
Michigan, as 0-6 KM bulk shear progged to be at or above 70 knots
over northern Lake Huron, decreasing to 30-45 knots over southern
Lower Michigan. Fortunately, mid level lapse rates are weak, another
big negative and making the prospects for severe weather murky. Low
level shear may be just enough (15-20 knots of 0-1 KM bulk shear) to
support possible rotating updrafts, and SPC has continued the slight
risk of severe weather. Main window looks to be after 4 PM till about
10 PM, supported by the 00z HRRR, which looks to be more realistic
with respect to dew pts and still generating some discrete cells.

After storms exit/end after midnight, quiet weather to end the
weekend into Monday with a large area of high pressure tracking
across the Central Great Lakes. It also looks like Tuesday will be
dry as well as latest Euro indicating a pronounced upper level ridge
axis building over the Western Great Lakes. And much like this
morning, surface ridging/dry low level air looks to be holding on for
one more day. Warm front and moisture pushing into the Central Great
Lakes for the mid week period then looks to support a low chance of
showers and strong thunderstorms. Although, so much warm air
streaming in on Thursday may lead to capped environment, with the
potential for a heat advisory with max temps climbing into the 90s
(22 C advertised at 850 MB level) and surface dew pts in the lower
70s. Despite most Euro ensembles indicating these hot temps, the
active frontal boundary does not look to be too far off to the north,
so forecast is subject to change. The strong inversion could also
trap low clouds/moisture from Wednesday`s potential activity,
limiting maxes.

MARINE...

Departing high pressure maintains south wind up to 10 to 15 kt and
predominantly dry conditions through the morning hours. A low
pressure system tracking east from the Midwest then arrives into the
area and crosses Lake Huron later this evening. This system advects
a humid, unstable air mass with scattered to numerous showers and
thunderstorms developing during the latter half of the day. Ambient
wind speeds and wave heights will hold below Small Craft Advisory
criteria but isolated to scattered severe storms will be capable of
producing gusts in excess of 40 kt, hail, and waterspouts. The cold
front clears the area Sunday morning with drier conditions and
moderate north wind to wrap up the weekend. High pressure passing to
the north causes light wind to veer to easterly on Monday. The next
chance of thunderstorms looks to hold off until Tuesday night into
Wednesday along a warm front moving in from the Midwest.

HYDROLOGY...

Numerous showers and thunderstorms are expected to develop across
southeast Michigan late today and this evening. Basin averaged
rainfall totals will range between a quarter-inch to a half- inch,
however, any strong thunderstorm will be capable of quickly producing
localized rainfall totals between 1 to 2 inches. Given faster storm
motions, overall flooding concerns remain low, however, highly
localized flooding remains possible across urban areas and low-lying
flood prone locations.

&&

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

$$

UPDATE.......AM
AVIATION.....AA
DISCUSSION...SF
MARINE.......TF
HYDROLOGY....SF


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at www.weather.gov/detroit.