342
FXUS63 KDTX 161413
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1013 AM EDT Wed Jul 16 2025

.KEY MESSAGES...

- Shower and thunderstorm chances increase midday with isolated
strong to severe wind gusts and potential for heavy rainfall
through this evening.

- Areas north of I-69 could see some additional storms late tonight.

- A cold front works through Thursday producing some additional
morning showers/storms, then cooler and less humid air filters in
through Friday.

- Additional storms possible Saturday with temperatures near
seasonal normals.

&&

.UPDATE...

Weak to nil capping of surface based instability will lead to 50-70%
chance of diurnal showers and thunderstorms primarily between 1pm
and 9pm today. At first glance, negligible shear with 0-6km bulk
shear of 15-20 knots limits any strong thunderstorm threats to
isolated damaging wind gusts due to water loading/wet microbursts and
localized heavy rainfall. Note, however, the 3km NAM has been
persistent in resolving a modeled southeast to northwest emanating
gravity wave during the late afternoon. Forward propagating corfidi
vectors would not be in phase/destructive with this if it were to
occur, but could provide some interesting storm mergers and a
different ground relative wind behavior.

Main item for tonight is the eventual track and footprint of the MCV
tracking through northern Iowa. There will be a strong to severe
threat immediately in advance of the vorticity maximum with an
augmented shear profile that is highlighted in the Swody1 by the
Slight Risk upstream across portions of far western Lower Michigan.
Most guidance carries the activity immediately north of the
cwa/Saginaw Bay tonight. Will look at the 12Z guidance.

&&

.PREV DISCUSSION...
Issued at 658 AM EDT Wed Jul 16 2025

AVIATION...

A warm front moving northward from the Ohio border supports pockets
of showers this morning, mainly near DTW. There is also patchy
fog/haze lingering until about mid morning as humidity increases
across the region. Humid air gains traction as the warm front moves
north this afternoon and combines with peak instability for
increasing coverage of showers/storms into this evening. This is
followed by a short break until a potential line of thunderstorms
moves in after midnight and north of PTK. These storms are expected
to be weakening while entering SE Mi along and ahead of a cold front
but still able to bring unsettled aviation weather to the region
through Thursday morning.

For DTW/D21 Convection... Isolated showers or thunderstorms this
morning increase coverage this afternoon into this evening. At least
scattered coverage of slow storms is expected across D21 and at or
near DTW after 18Z.

THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less this afternoon and again later
  tonight.

* Moderate for thunderstorms after 18Z.

PREV DISCUSSION...
Issued at 359 AM EDT Wed Jul 16 2025

DISCUSSION...

Clouds fill in aloft through the morning hours as Southeast Michigan
resides downstream of remnant nocturnal perturbation lifting in from
the Ohio Valley. This releases a stalled frontal boundary near the
MI/OH border, spilling north across the rest of southern Lower
Michigan as a warm front. The elevated portion was on the move as of
06Z as a cluster of showers/storms blossomed on KDTX radar near the
western I-94 corridor, demarcating the 925-850 mb portion of the
frontal slope. Forecast soundings indicate a somewhat unfavorable
column for persistence with this first wave as it outruns necessary
moisture.

Mid-level cooling, albeit limited, coupled with the advection of a
richer ThetaE environment from the south, leads to building
instability through the morning hours. Temperatures quickly rebound
after a mild night while dewpoints spike above 70F within the
expanding warm sector. This quickly translates to +1000 J/kg of
SBCAPE before noon, then ensemble mean SBCAPEs indicate further
rises this afternoon through diurnal heating (1250-1750 J/kg).
Although instability parameters should be more than sufficient for
scattered to perhaps numerous thundershowers, shear will be lacking.
Probabilities for 20+ knots of 0-6 km shear are quite low through
this evening. Severe thunderstorm coverage should therefore remain
more isolated in the absence of substantive dynamic support aloft,
but CAMs highlight broad coverage of single-cell storms through the
day. Heavy water-loading in the more robust updrafts could produce a
few microbursts capable of marginally severe wind gusts. Latest SPC
DY1 outlook maintains Marginal Risk across Southeast Michigan. PWATs
appear to spike over Metro Detroit which exhibits the highest
conditional QPF probabilities and resultant potential for isolated
urban/small-stream flooding (see Hydrology section for more info).

After an evening lull, a more convincing corridor of height falls
translates into Lower Michigan overnight, on the nose of a longer
wavelength trough axis. This shortwave accelerates across Iowa
before shearing into the upper Midwest. This provides meaningful
background ascent while an elevated mixed-layer tries to hold shape,
especially north of I-69. A more substantial wind field accompanies
this wavelet which increases potential for some linear organization
and a low-end nocturnal damaging wind threat, late tonight.

Active pattern continues Thursday morning as a cold front drops
through the Great Lakes, from the northwest. Timing has sped up a
bit which signals renewed convection is now more likely to flare up
within a less favorable environment. Progs indicate the frontal
boundary should clear east as early as 15Z, with weaker post-frontal
activity in-trail. CAMs are extremely bearish regarding storm/QPF
potential in the wake of the front, therefore made significant
revisions to automated NBM PoPs, lowered from Likely to Slight
Chance after 18Z Thursday. A bit breezier during the afternoon as
cooler Canadian air filters in. Comfortable Thursday night with lows
dipping into the 50s, outside of Metro Detroit.

Subjectively pleasant on Friday with highs largely in the 70s and
dewpoints in the 50s as a sub-700 mb anticyclonic gyre works east
across the Great Lakes. Energetic belt of zonal flow aloft persists
through the weekend and into early next week while surface high
pressure eventually moves into the Mid-Atlantic. This leads to a
return flow setup for the local area with rising dewpoints and 2 m
temperatures, although highs should hold near-normal. Potential
exists for showers and storms Saturday as several upstream wave
interactions take place, and MCS remnants flow into the region.

MARINE...

Increasing low level moisture today and daytime instability will
produce numerous showers and thunderstorms in the afternoon. Some of
the thunderstorms could be strong, producing localized wind gusts in
excess of 45 knots. Scattered-numerous showers and thunderstorms
likely persist Wednesday night, as low pressure and associated cold
front race east, passing through the Central Great Lakes Thursday
morning. North-northwest winds behind this system will likely top
out briefly in the 20-25 knot range over Lake Huron, which will
bring a chance of waves of 4 feet or greater to clip the nearshore
waters by Thursday evening. There may be just enough of an offshore
component to prevent small craft advisories however.

Winds veer around to the north-northeast Thursday evening, but
should be 15 knots or less by that time, with light and variable
winds for Friday as a large area of high pressure encompasses the
Great Lakes region.

HYDROLOGY...

Low pressure tracking into the Great Lakes/Ohio Valley brings
chances for scattered showers towards the Ohio border this morning
before scattered to numerous showers and storms develop this
afternoon. An increasingly humid airmass settles over the region
with surface dewpoints in the lower 70s and PWAT values of 1.75 to
2.00 inches. Overall setup is favorable for locally heavy rain with
any thunderstorm given ample moisture and a deep warm cloud layer
increasing precipitation efficiency. Very weak background wind field
will yield slow storm motions during the day with rainfall rates of 1-
2 in/hr expected. Some storms will lead to isolated areas of minor
flooding in low-lying/flood prone areas.

&&

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

$$

UPDATE.......CB
AVIATION.....BT
DISCUSSION...KGK
MARINE.......SF
HYDROLOGY....KDK/KGK


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