Expert Forecast Opinion

705
FXUS63 KDTX 170750
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
350 AM EDT Wed Jun 17 2026

.KEY MESSAGES...

- Widespread rain and thunderstorms are expected this evening. Heavy
rainfall is likely which may lead to localized flooding,
especially in urban areas. A Flood Watch is in effect for areas
south of M-59. The potential also exists for severe weather in the
same area tonight, with damaging wind gusts, large hail, and
isolated tornadoes possible.

- Breezy on Thursday with westerly wind gusts of up to 35 mph.

- Slightly below normal temperatures are expected through the week
and this weekend.

&&

.DISCUSSION...

A seasonably strong shortwave will ride into the Great Lakes today
at the nose of a 130+ kt upper jet streak. Remarkable deep layer
ascent will spread in ahead of this wave, producing a deep surface
low that swings across the Midwest this afternoon and Lower MI
tonight. Model progs continue to advertise a sub-990mb low which is
4 to 5 standard deviations below normal for mid June, and if it
verifies will challenge low MSLP records for the month. Ahead of
this system a powerful 60+ kt LLJ will spread east across the
southern Great Lakes, rapidly advecting in deep moisture and strong
isentropic ascent into the elevated warm frontal boundary taking
shape through the day. The result will be widespread rain from late
this afternoon into the late evening hours, with a threat for flash
flooding and severe weather.

Elevated showers and storms will move in late afternoon with heavier
activity culminating during the late evening as the strongest ascent
drives a line of convection through ahead of the cold front. Model
soundings continue to showcase deep saturation and warm cloud layer
with PWAT rising to the 1.50 to 1.75 range during the evening. This
will allow for efficient, heavy rainfall processes in any convection
and instantaneous rates within the strongest cores will likely
exceed 1"/hr. The bulk of the rainfall is expected in a relatively
brief window between 8pm and 2am and brings a heightened threat for
flash flooding especially across urban areas including Metro
Detroit. Bulk of ensemble QPF output supports widespread 1 to 2 inch
amounts, and 30 to 40% probability for 2+ inches exists in the
latest HREF, REFS, and NBM ensemble suites. Placement of the axis of
highest QPF continues to carry uncertainty, but signal appears to be
most focused along the eventual track of convection near the triple
point. Confidence is high enough to issue a Flood Watch for areas
along and south of M-59. Will note there is a subset of hi-res
guidance that bifurcates the convection and actually places the
higher QPF north of the current watch. This remains a possible
outcome but carries less probability than the farther southern
solution.

The late evening period also brings concern for severe weather as we
sit near an upstream environment supportive of supercells and bowing
structures given high amounts of low-level shear and SRH.
Instability remains the limiting factor locally as we sit north of
the CAPE gradient until a brief window during the late evening where
the occlusion/surface warm sector attempts to nudge in from the
south as the low begins to pivot off to the north. Afternoon/evening
convection is likely to ride ESE along the CAPE gradient from
northern IN into OH which should prevent the higher surface based
instability from advancing north, but trends show the dynamic system
still capable of advecting in a narrow axis of marginal instability
just as the LLJ begins to depart during the late evening. Hi-res
reflectivity hints at potential for bowing and/or supercellular
structures to survive into the local area with perturbed MSLP fields
indicating capability to produce severe wind gusts even if tenuous
amounts of CIN otherwise suggest instability remains elevated. The
environment also support a QLCS tornado threat. The cold front
quickly passes through shortly after midnight which brings an end to
the severe threat. SPC expanded the slight risk farther north to
include Metro Detroit to account for the trend in guidance.

Low-level wind veers around to westerly Thursday morning as the
system departs, with a secondary LLJ keeping windy conditions in
place through the morning as the system departs. Gusts of 30 to 35
mph will be common early with wind gradually subsiding through the
afternoon. Lighter and more scattered showers will continue behind
the cold front early Thursday morning and lead into a slight
increase in coverage mid Thursday morning as a weak secondary cold
front tracks through. Seasonably cool conditions continue Thursday
and Friday with just a 15% chance of showers on Friday as cool,
cyclonic flow aloft maintains weak diurnal instability.

The jet stream lifts northward and introduces some upper confluence
on Saturday, though additional PVA may still support a diurnal flare-
up of weak convection. The next notable wave in the flow arrives
from the Midwest Sunday evening with another relatively deep low for
June standards somewhere in the vicinity of the Great Lakes. Local
impacts are uncertain as there are still many moving parts, but
something to monitor through the late week.

&&

.MARINE...

A brief break in convective activity is underway this morning as
ridging aloft quickly passes through. A strong low pressure system
follows in quick succession leading to evening and overnight
thunderstorms capable of damaging winds, and to a lesser extent,
waterspouts. Prevailing southeasterly gradient flow accompanying the
low climbs above 25 knots across the southern waterways, after the
center approaches Lake Huron tonight. Gusts to gales remain
possible, mainly for Lake St. Clair and western Lake Erie, as the
strongest LLJ winds of 40-50 knots pass through the lowest 3 kft.
Shallow mixing profiles appear to exhibit only meager growth,
maintaining uncertainty with the potential/duration of gales. Opted
out of gale headlines for Lake St. Clair and western Erie given the
anticipated sporadic nature of the gale-force gusts. A Small Craft
Advisory was issued for all nearshore zones with high confidence in
wind and wave criteria being met. Post-frontal winds decline a bit
and organize out of the west-northwest on Thursday, remaining so
through at least Saturday. Additional chances exist for periods of
showers and thunderstorms through the rest of the workweek and over
the weekend.

&&

.HYDROLOGY...

A strong low pressure system will arrive this evening, producing
widespread rainfall with numerous heavy thunderstorms through late
tonight. Rainfall totals ranging between 1 and 2 inches are likely
for much of SE MI, and isolated areas may receive over 3 inches.
Most of this rainfall is expected to occur in 4 hours or less,
currently centered between 8pm and 2am, and rainfall rates will
likely exceed 1"/hr at times. This rainfall may pose a flash
flooding threat, mainly in urban areas, and rises on rivers and
streams can be expected. A Flood Watch is in effect for areas along
and south of M-59. Additional scattered showers are possible
overnight and into Thursday, but these will be much lighter.

&&

.PREV DISCUSSION...
Issued at 130 AM EDT Wed Jun 17 2026

AVIATION...

Dry weather expected overnight in the wake of a cold front. Residual
moisture from prior day rainfall combined with clearing trends will
likely support periodic stratus development through the night.
Current observations have held cloud bases ranging between ranging
between 5-8kft which will likely hold as the minimum base height.
Models have trended away towards the possibility towards mvfr/ifr
stratus, however, there still remains a lower confidence window to
see this more pessimistic potential during the mid to late morning
hours, with the strongest signal favored across northern lower and
south into KMBS. Cig heights to improve after sunrise with stronger
diurnal heating.

For the evening... A very strong low pressure system coupled with
impressive low and upper-level jet support brings high confidence
for widespread rain along with embedded thunderstorms. Moderate to
heavy rainfall will be likely at times which may lead to some
localized flooding concerns, pending where the stronger storm
development lines up. Additionally, isolated severe weather will be
possible, most favorable across KPTK down to the Metro terminals.

D21/DTW Convection...Widespread rainfall moves in by the late
afternoon to evening, with isolated to scattered thunderstorms
possible around or after 00Z.

DTW THRESHOLD PROBABILITIES...

* Low for ceilings aob 5kft this morning.

* Moderate for thunderstorms this evening.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Flood Watch from this afternoon through late tonight for MIZ068>070-
075-076-082-083.

Lake Huron...Small Craft Advisory from 8 PM this evening to 8 PM EDT Thursday
for LHZ421-422-441>443.

Lake St Clair...Small Craft Advisory from 8 PM this evening to 8 PM EDT Thursday
for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 8 PM this evening to 8 PM EDT Thursday
for LEZ444.

&&

$$

DISCUSSION...TF
MARINE.......KGK
HYDROLOGY....TF
AVIATION.....AM


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