712
FXUS63 KDTX 291920
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
320 PM EDT Sun Jun 29 2025

.KEY MESSAGES...

- Warm and humid conditions today and tomorrow. Afternoon heat index
each day will be near 90 degrees.

- Showers and thunderstorms are likely Monday afternoon and evening.
Isolated severe storms are possible as well as isolated instances of
flooding due to heavy rain.

- Classic summer weather pattern during the middle to end of the
week with daytime temperatures well into the 80s.

&&

.DISCUSSION...

A warm front marked by temps in the upper 80s and dew points near 70
degrees is on the doorstep this afternoon with additional northward
progress expected into this evening. A boundary layer cap evidenced
by the shallow cu field remains in place as departing high pressure
maintains a weakly subsident profile to inhibit convective
initiation. However, will continue to monitor a weak outflow
boundary approaching the Tri-Cities this afternoon which may be
enough to trigger an isolated shower or thunderstorm. Warm and muggy
conditions building in will persist through the night but rain
chances remain very low with a lack of ascent in the column.

An upper level trough amplifying over the upper Midwest today
arrives across the Great Lakes on Monday to provide synoptic lift to
engage with the humid, unstable air mass and produce scattered to
numerous showers and thunderstorms during the latter half of the
day. This trough will drive a weak/slow-moving cold front across the
area Monday night but convective initiation will likely precede this
feature as a convectively enhanced shortwave and attendant upper
jetlet arrive from the mid-Mississippi Valley during the afternoon.
Mid-level lapse rates during this time will be relatively modest at
around 6 C/km but SBCAPE generally between 1000 and 2000 J/kg
supports deep convection and some stronger updrafts. Unidirectional
wind shear within the effective storm layer at 30 kt or less will be
the limiting factor for better storm organization - this favors
relatively brief lifespan of individual cells but plenty of
opportunity for additional multicell clusters to trigger from
outflow. Any stronger cells will be capable of producing precip-
loaded downbursts with a localized damaging wind threat.

Heavy rain will be a concern with convection tomorrow given tall,
skinny CAPE profiles with deep layer moisture characterized by PWAT
between 1.75 and 2.00 inches. Warm cloud depth over 11 kft and slow
disorganized storm motion offer additional confidence for torrential
downpours where storms occur. Rainfall rates in excess of 1 inch per
hour will be possible which may produce localized instances of
flooding, especially if boundary interaction causes storms to stall
over a particular location. Confidence in occurrence is not quite
high enough for a Flood Watch at this time. Depiction of convective
evolution among CAMs carries a great deal of variance both between
model suites and from run to run, indicating high sensitivity to
initial conditions. Several MCSs are expected to progress across the
Midwest and Plains this evening into tonight which will alter the
thermal gradient and subsequent upper jet structure/placement. For
now timing and coverage of thunderstorms continues to carry a fair
amount of uncertainty, but the main threat window for any severe
weather and heavy rain will be between 2pm and 10pm. There will be a
secondary window for additional rain overnight along and behind the
cold front. SPC and WPC day 2 outlooks highlight portions of SE MI
within a marginal risk for severe weather and excessive rainfall,
indicating an isolated threat for each.

Northwest flow dominates the upper air pattern from Tuesday morning
through much of the rest of the week as a longwave ridge slowly
advances from the Rockies and eventually across the Plains. This
maintains a seasonable air mass with 850mb temps around 13 to 15 C,
supportive of highs in the 80s. Weak daytime instability and minimal
capping will bring a low probability for unorganized convection each
afternoon. An upper low dropping into the trough over eastern Canada
on Thursday draws a cold front across the Great Lakes which may
bring a higher chance for showers and storms depending on diurnal
timing. Warmer conditions are increasingly likely to return by next
weekend as a mid-level ridge builds across the SE CONUS.

&&

.MARINE...

Light southerly winds through tomorrow, but a few brief gusts
topping out 15-20 knots over the open waters of Lake Huron. A cold
front will trigger showers and thunderstorms tomorrow afternoon into
tomorrow night, with a embedded strong storms around. Westerly post-
frontal winds on Tuesday look to top out around 20 knots, but with
offshore flow, small craft advisory does not seem warranted.

High pressure over the Midwest for the mid week period, with weak
northwest gradient in place over the Great Lakes region looks to
support light winds and waves, right into Friday as the center of
the high pressure arrives.

&&

.HYDROLOGY...

Scattered to numerous showers and thunderstorms are forecast Monday
afternoon and evening. Storms will be relatively disorganized, but
with humid conditions and slow storm motions they will be capable of
producing torrential downpours. Localized areas may receive over 1
inch per hour, which may lead to flooding of urban areas, small
streams, and otherwise poorly drained areas. The main threat for
flooding will be between 2pm and 10pm.

&&

.PREV DISCUSSION...
Issued at 204 PM EDT Sun Jun 29 2025

AVIATION...

High degree of afternoon stability within the atmospheric column
ensures a dry forecast for the rest of today and tonight as surface
high pressure migrates further east, into upstate New York. Diurnal
cumulus response continues to wane as mixing depths increase,
eventually leading to a period of SKC conditions by this evening and
into the early overnight hours. High cirrus spills in tonight as
upstream convection vents into Lower Michigan. Lower column moisture
will advect into the region Monday morning with increasing dewpoint
temperatures yielding unstable conditions behind a lifting warm
front. This will trigger scattered thunderstorm development as early
as 16Z. Did include a PROB30 for this activity, although location
specifics are still murky. Ceilings also fill in, but should remain
VFR on Monday while visibility reductions to IFR cannot be ruled out
due to high rainfall rates with any storms that pass over the
terminals. Light surface flow generally holds within a SSW pattern.

For DTW/D21 Convection...Potential exists for scattered
thunderstorms after 16Z Monday. Enough evidence to support a PROB30
and a TEMPO after 18Z as coverage increases.

THRESHOLD PROBABILITIES...

* Low for thunderstorms after 16Z Monday, then medium after 18Z.

* Medium for ceiling at or below 5000 ft Monday afternoon.


&&

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

$$

DISCUSSION...TF
MARINE.......SF
HYDROLOGY....TF
AVIATION.....KGK


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