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000
FXUS63 KDTX 171725
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
125 PM EDT Wed Apr 17 2024

.KEY MESSAGES...

- Severe storms exit by 7 PM.

- Another round of showers moves through Thursday night.

- Drier and cooler weather Friday and into the Weekend.

&&

.AVIATION...

Broken line of convection evident on radar attendant to an advancing
frontal boundary on pace to move across the southeast Michigan
airspace late this afternoon. Downstream extrapolation of the
movement brings this activity through between 19z and 21z,
highlighted by potential for brief strong to severe thunderstorm
intensity featuring strong winds and a rapid reduction of visibility
in heavy rain. Existing south/SE wind shifts to southwest in the
wake of the convection and trailing boundary heading into early
evening. Infusion of colder air will promote some degree of lower
stratus development lasting through tonight. Forecast will continue
to outlook a transition from low VFR to MVFR restrictions associated
with a steady increase in low level moisture.

For DTW/D21 Convection...Inbound broken convective line set to
arrive within the 19z-21z window. Expect reduced visibility from
heavy rainfall and strong winds from any stronger thunderstorm.

.DTW THRESHOLD PROBABILITIES...

* High for ceiling aob 5000 ft through Thursday morning.

* High for thunderstorms impacting terminal between 19z and 21z.

&&

.PREV DISCUSSION...
Issued at 1000 AM EDT Wed Apr 17 2024

UPDATE...

Mid level dry slot sliding through southeast Michigan this morning,
with low level moisture on the increase, as lower 60 dew pts noted
over Northern Indiana attempt to move into the CWA this afternoon.
Meanwhile, 12Z DTX sounding indicated a warm 850 MB temp of 12 C,
which will provide a cap through the early afternoon hours,
eventually eroding late in the afternoon as temps push aoa 70
degrees and occlusion/triple pt lifts through southeast Michigan,
which is expected to prove sufficient to generate a line of showers
and thunderstorms, with MLcapes on the order of 1000-1500 J/kg, per
latest RAP. Sufficient 850-700 MB flow (30-40 knots) to support
potential of organized convection, despite 0-6 KM bulk shear
lowering under 25 knots. 0-1 KM bulk shear on the order of 20-30
knots will also bring risk of low level rotation/isolated tornadoes.
A slight risk of severe thunderstorms exists for all of southeast
Michigan (both hail/wind), mainly in the 3-6 PM time frame. The line
looks to remain progressive/quick hitter, thus flooding is not
expected.

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.

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

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

$$

AVIATION.....MR
UPDATE.......SF
DISCUSSION...MV
MARINE.......TF
HYDROLOGY....MV


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