846
FXUS63 KDTX 190753
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
353 AM EDT Tue Aug 19 2025

.KEY MESSAGES...

- Showers and thunderstorms move across SE Michigan during the
  morning and linger into the afternoon south of I-69. Locally heavy
  rainfall is the primary concern with this activity.

- Seasonable temperatures and dry weather move in and hold Wednesday
  through Friday.

&&

.DISCUSSION...

A 500 mb short wave/MCV hybrid is nearly overhead at forecast
issuance and is combining with a deepening surface trough/low to
aggressively draw a pronounced moisture axis across Lower Mi.
Improved organization of the surface system reflects an overall
strengthening of the wind field below 700 mb and thus the surge of
moisture transport that sustained the leading edge of evening
convection from the west into SE Mi since midnight. The more
impressive low level jet response is occurring west of this leading
edge from northern Lower Mi southward across Lake Mi into IL/IN and
is still set to move across central/southern Lower Mi during the
morning. Locally heavy rainfall is the main concern with this
otherwise elevated convection as HREF mean PW is right around 2
inches within the moisture axis. Fortunately, this pattern stays on
the move ahead of the mid level wave and surface low on a pace to
exit SE Mi by early afternoon. HREF mean MSLP projections track the
surface wave roughly along the I-69 corridor from central Lower Mi
near LAN early this afternoon into Ontario east of PHN by 00Z this
evening. The exit of morning activity is early enough to expect a
rebound of surface based instability in the warm sector along and
south of the low track. HREF mean MUCAPE gets into the 1000-1500
J/kg range by 21Z, on the north flank of the Ohio valley instability
axis, however the best wind profile shifts eastward with the
wave/MCV. RAP 0-6 km bulk shear struggles to hold 20 knots during
the 21-03Z time window over Lower Mi this evening. Both skinny CAPE
and weak shear profiles are limiting factors for severe storms,
however a stray precip loaded subsevere wind gust is possible as the
storm environment maintains access to 2 inch PW until the front
exits into Ohio/Ontario by midnight.

The rest of tonight is characterized by a respectable wind shift to
the north on the heels of the low pressure system. Weather is dry
other than a stray shower off Lake Huron and clouds linger into
Wednesday afternoon until low level dry air begins to make progress
ahead of northern Ontario high pressure. The inbound cooler and less
humid air mass advances at a gradual pace judging by model surface
Td projections but most locations show Td < 60 by Wednesday evening.

The long wave ridge centered over the 4 Corners reaches north into
central Canada and then leans eastward into the Great Lakes Thursday
and Friday. The current Gulf of Alaska low is then projected to
reach northern Ontario Friday night on pace to pull a cold front
through Lower Mi Saturday. The 19/00Z consensus of deterministic
models shows a much larger system compared to those of recent days,
but it is cut off from Gulf moisture by high pressure covering
nearly the entire Atlantic and Gulf coasts. A quick round of light
showers is then about all that is expected with the front in SE Mi
along with some reinforcement of cool/dry air into Sunday.

&&

.MARINE...

A low pressure system tracks across Lower MI today before reaching
western Lake Erie this evening. Scattered to numerous showers and
thunderstorms accompany this system through the day and diminish in
coverage tonight. Isolated severe storms will be possible, mainly
near western Lake Erie. East to southeast wind on the order of 15
knots prevails through the day before shifting to northeast tonight
as the system departs into the lower Great Lakes. By Wednesday, wind
speeds increase to around 15 to 20 knots with gusts to 25 knots
across southern Lake Huron. This sends a building wave field across
the nearshore waters around the Thumb which may necessitate a Small
Craft Advisory for Wednesday. High pressure then builds in from the
northern Great Lakes through the late week with northeast wind
becoming light.

&&

.PREV DISCUSSION...
Issued at 1159 PM EDT Mon Aug 18 2025

AVIATION...

Increasing moisture advection brings increasing chances for showers
and thunderstorms across the terminals through the morning hours.
Best thunderstorm potential across southeast Michigan lies within
the 12Z to 16Z time frame this morning, with the stronger
thunderstorm potential focused across the southern metro terminals.
Brief IFR to LIFR conditions will accompany the thunderstorms
bringing potential for heavy rainfall. A more solid low MVFR/IFR
ceiling with scattered LIFR ceilings settle in towards the afternoon
with continued rain chances. Low clouds hold into the evening and
tonight along with a few stray showers in the northerly to northeast
wind off Lake Huron, though focus may hold east of terminal
corridor.

For DTW/D21 Convection...Thunderstorm activity is possible between
12Z and 16Z today. Gusty winds and heavy rainfall will be possible
with strongest thunderstorms.

THRESHOLD PROBABILITIES...

* Medium for thunderstorms between 12Z to 16Z today.


&&

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

$$

DISCUSSION...BT
MARINE.......TF
AVIATION.....AA


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