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000
FXUS63 KDTX 171044
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
644 AM EDT Wed Apr 17 2024

.KEY MESSAGES...

- Elevated showers and a few thunderstorms are possible this morning
as elevated portions of the warm front lift into the area. Daytime
highs around 70 degrees.

- A cold front tracks west to east through the region between 1 PM
and 7 PM today with a Slight Risk for severe weather generally south
of the I-69 corridor.

- Damaging wind gusts will be the main threat this afternoon and
evening, although isolated large hail or a tornado cannot be ruled
out.

- Drier on Thursday with temperatures in the mid to upper 60s before
another round of rain arrives Thursday night.

&&

.AVIATION...

Remaining scattered showers this morning will be working northeast
of the terminals between 12z-14z. In the wake of this activity, MVFR
cigs begin to shift over the area as warm front encroaches and winds
veer to the southeast and south with time into early afternoon.
Scattered to numerous thunderstorms are still expected along a cold
front from mid to late afternoon with the most likely window holding
in the 19z-21z time frame with some stray showers or storms perhaps
developing a few hours before the main line crosses the area. Heavy
rain and gusty winds can be expected. Winds switch to the southwest
to west after the cold front passes with MVFR cigs predominant in
this flow wrapping around low pressure to the north.

For DTW/D21 Convection...A north to south oriented line of
thunderstorms is anticipated to develop and move through between 19Z
and 21Z. Expect reduced visibility from heavy rainfall and strong
winds from stronger thunderstorm. The environment will bring some
potential for tornadic thunderstorms. Will need to monitor potential
development of discrete cells a few hours prior to 19Z ahead of the
main line and adjustments in timing of the main line remains
possible with upcoming TAFs.

.DTW THRESHOLD PROBABILITIES...

* High for ceiling aob 5000 ft by around 13Z and after.

* Low for thunderstorms impacting terminal 16z-19z, medium 19z-21z.

&&

.PREV DISCUSSION...
Issued at 412 AM EDT Wed Apr 17 2024

DISCUSSION...

Leading wave of showers has just been scattered in coverage so far
this morning, driven by elevated forcing on the nose of the 300mb
jet and leading ribbon of vorticity advection. Minimal instability
has led to limited lightning activity so far. On the heels of this
elevated activity is a prominent mid level dry slot, which will
effectively reduce PoPs significantly through the morning as seen in
upstream observations. The dry slot will also represent the leading
edge of MUCAPE, in which some guidance flares up convection
generally across the Tri Cities and Thumb. Elsewhere, the dry slot
will establish a capping inversion and very dry air aloft.

Meanwhile, northward surge of the surface warm front will accelerate
after 12z as a mid level shortwave begins to catch up to the warm
sector while the parent system takes on a negative tilt. The warm
sector is currently over Illinois with observed dewpoints in the 60s
which have been largely untouched by convection, likely the result
of the aforementioned dry slot and capped atmosphere. Given lack of
convective contamination so far, it is looking increasingly likely
that at least a narrow corridor of these 60+ degree dewpoints will
make it to SE Michigan by around 16z (12pm local). As the warm
sector lifts through, expect temperatures to climb toward 70
degrees.

By late morning, will see a marked erosion of the capping inversion
under broad synoptic ascent, resulting in increasing chances for
surface-based convection by early afternoon. Strongest forcing will
be along a north-south oriented cold front that tracks west-east
across the area between roughly 17z and 23z (1pm-7pm). Majority of
forecast models depict a broken line of thunderstorms along the
front, initially forming over southwest lower MI/northern IN around
mid-day before tracking into southeast MI and growing upscale in the
timeframe outlined above. A more understated possibility in the
guidance is potential for discrete cells to form along or just ahead
of the front, especially if any pockets of sunshine develop that
could accelerate surface destabilization. 500mb winds push 50 knots
invof the shortwave, which combined with a 35-40 knot LLJ contribute
to deep layer shear that is favorable for organized thunderstorms.
Further, veering low level profiles suggest some rotating storms
will be possible as well.

All severe hazards are in play today, as outlined in the SPC Day 1
Slight Risk that extends up to I-69. Strong linear forcing along the
front will take advantage of dry air aloft to support strong
downdraft potential with eventual upscale growth, making damaging
wind the primary threat of the day. With 1000-2000 J/kg MLCAPE and
potential for discrete cells initially, large hail will be possible
as well especially within any rotating updrafts. There is also a low
chance of a tornado both in discrete cells or along the line itself.
While the parameter space is not overly impressive, hodograph
curvature, backed surface winds, and potential for cell mergers are
all characteristics that present a low tornado threat. Finally,
there is a chance for heavy downpours with these storms but an
overall progressive system should combat any significant flooding
concerns. See the hydrology section for more details.

By roughly 00z tonight, the cold front is expected to clear Lake
Huron, marking an end to the severe weather threat. The parent low
will weaken as it tracks across northern lower MI, followed by a
glancing period of mid-level ridging on Thursday. The frontal
passage has minimal effect on daytime highs Thursday, mid to upper
60s, as warm advection quickly returns. This precedes yet another
low pressure system and cold front that will track across lower MI
Thursday night, although nocturnal timing and track of the surface
low should keep any organized storms to our south across the Ohio
Valley. Cannot rule out elevated thunderstorms however, as a few
hundred J/kg of MUCAPE will be present overnight. This system will
be much more effective in drawing in cooler Canadian air to support
highs only in the 50s Friday through this weekend. High pressure
however ensures a quieter pattern.

MARINE...

Low pressure over SE MN this morning tracks ENE into the central
Great Lakes today while gradually weakening. Strong easterly wind
precedes this system with gusts to gale force expected across
northern and parts of central Lake Huron where a Gale Warning
remains in effect through tonight. E to ESE winds of 25 to 30 knots
will be common farther south today and a Small Craft Advisory
remains in effect for Saginaw Bay, the Lake Huron nearshore waters,
and Lake St. Clair. Two main rounds of showers and storms will occur
with the first this morning and the second this afternoon and
evening, when some storms may be strong to severe across the south.
The center of the low passes near Lake Huron after midnight with
winds decreasing and veering to westerly for Thursday. A weak cold
front then moves through the region Friday morning with another
round of showers and possible storms. Westerly winds in the wake of
the front reach 20 to 25 knots Friday afternoon and remain moderate
through the weekend.

HYDROLOGY...

A warm front lifts into the region this morning in advance of a
strong low pressure over the midwest. Scattered showers and a few
rumbles of thunder are possible this morning. A cold front then
tracks west to east through the area between roughly 1 PM and 7 PM
today with numerous thunderstorms along the front. The progressive
nature of this system keeps total rainfall around a half inch for
most locations, although localized higher totals are possible as
thunderstorms will be capable of heavy downpours. Significant
flooding is not anticipated at this time, but minor flooding in prone
urban and poor drainage areas is possible along with notable rises in
area rivers. Another round of rain arrives Thursday night, with total
rainfall amounts expected to hold under a half inch.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Gale Warning until midnight EDT tonight for LHZ361-362.

     Gale Warning until 11 AM EDT this morning for LHZ363.

     Small Craft Advisory until midnight EDT tonight for LHZ421-422-
     441>443.

Lake St Clair...Small Craft Advisory until 11 AM EDT this morning for LCZ460.

Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....DG
DISCUSSION...MV
MARINE.......TF
HYDROLOGY....MV


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