453
FXUS63 KDTX 291734
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
134 PM EDT Mon Apr 29 2024

.KEY MESSAGES...

- Potential exists for showers and thunderstorms to develop through the
  evening. There is a marginal risk for storms to become
  severe during this time. Damaging wind gusts will be the main threat.

- Dry and slightly cooler Tuesday.

- Well above normal temperatures remain through the week.

&&

.AVIATION...

Frontal boundary moves through southern Michigan this afternoon
bringing chances for thunderstorms to all TAF sites this afternoon.
VFR conditions are expected outside the storms, with MVFR conditions
or lower possible as storms move overhead. Showers have the
potential to fill in behind the initial band of storms, but
confidence remains low on what the extent or precise timing on those
showers will be. Wherever these showers appear will have chances to
drop to MVFR conditions, with the most likely sites being KDTW and
KDET. Westerly flow will take over after the passage of a cold front
early Tuesday morning. Some light fog is expected before sunrise,
giving way to a 5000 foot cloud deck that will be present through the
day Tuesday.

For DTW/D21 Convection...A scattered to broken line of showers and
thunderstorms moves overhead between 19-22Z this afternoon. Behind
this line further showers are expected to develop and impact the
area between 0-4Z Tuesday. Although unlikely, there is still a
possibility of thunder with these secondary showers.

DTW THRESHOLD PROBABILITIES...

* Moderate in thunderstorms this afternoon, then low this evening.

* High in ceilings at or below 5000 feet this afternoon, moderate
  this evening into early Tuesday morning.

&&

.PREV DISCUSSION...
Issued at 937 AM EDT Mon Apr 29 2024

UPDATE...

Linear band of rain containing isolated thunderstorms easing into
western lower Michigan late this morning. This nocturnal
remnant corridor of saturation maintained along the nose of
persistent 40+ knot 850 mb flow and focused within an east-
northeastward propagating pre-frontal trough. This moist axis on
pace to encounter a gradually destabilizing low level environment
across the local area downstream, particularly southeast of a Howell
to Bad Axe line as periods of greater insolation fuel steeper low
level lapse rates within the modulating warm sector. A frontal zone
currently anchored invof of the I-69 corridor will drift northward
with time. Projected pace of this movement relative to the inbound
precip band suggests the Saginaw valley will maintain a higher degree
of stability. To the east, the existence of the boundary actually
lends increased probability for backed low level flow to exist as the
thumb continues to destabilize. With the underlying bulk shear
magnitude sufficient to offer greater organization, marginal severe
risk in play should instability prove adequate to generate and sustain
meaningful updrafts. In addition to a standard stronger wind gust
threat across the outlooked area, will continue to monitor the
potential for updrafts to rotate as stronger cells engage the
boundary/backed flow still lingering over the thumb region. Main
window for activity from mid afternoon into the early evening
/18z-23z/.

PREV DISCUSSION...
Issued at 404 AM EDT Mon Apr 29 2024

DISCUSSION...

West to east stationary boundary resides across the M-59 corridor
this morning along with a very moist airmass. Dewpoints across much
of southeast Michigan are into the 50s. North of this boundary are
much cooler temperatures, which is supporting areas of patchy fog
along and north of the I-69 corridor. Flow should be just strong
enough to limit dense fog development with the isolated lower
visibility in the half mile to three quarter mile range. A few
isolated to scattered showers have moved northeast across the
forecast area and have cleared to the north at press time.

Southeast Michigan should remain mostly rain shower free through the
morning with the exception of a few scattered showers streaming
across the Tri-Cities. To the west will be a nearly stacked low
pressure system lifting across the western Great Lakes states and
eventually into Ontario by tomorrow morning. Downstream will be
increasing south-southwest flow starting to pick up around 12Z with
gusts to 20-25 knots during the afternoon. Winds will drive the
stalled boundary northward before the morning ends, which will also
help improve visibilities after sunrise. Greater large scale ascent
and height falls arrive today ahead of an advancing cold front. The
lead wave of activity ahead of the cold front associated with a
developing surface wave moving our of Illinois will move through
mainly between 12 pm to 5 pm. The favorable diurnal timing will
allow for the very moist airmass to destabilize helped by some
breaks in clouds ahead of activity. MLCAPE up 250-500 J/kg looks
achievable with the RAP offering MLCAPEs approaching 800 J/kg. The
30-40 knot 850 mb LLJ will be well positioned over southeast
Michigan during the afternoon yielding 0-6 km bulk shear values to
35-45 knots. This environment would support at least some potential
for isolated thunderstorms approaching severe levels. One of the
limiting factors for robust convection today will be the meager mid
level lapse rates at around 5.5 C/km. One area of interest to keep
an eye on during the afternoon will be across the Tri-Cities and
northern Thumb if the frontal boundary hangs around here. This would
lead to a more southeasterly surface wind increasing low level shear
as activity arrives and could lead to better thunderstorm
organization for a 2-4 hour period.

Will maintain PoPs through the evening and overnight period as the
main cold front moves through supporting mainly scattered showers.
Dry air is eventually ushered in under west winds bringing an end to
precipitation shortly before 8 am tomorrow morning across eastern
portions of the CWA. The cooler airmass for Tuesday will yield
daytime highs in the upper 60s to low 70s aside from some cooler
spots along the Thumb lakeshores. Mostly clear skies will help
temperatures fall into the 40s for tonight.

Some uncertainty in the mid-week, but the outgoing forecast is
currently dry for Wednesday as a broad trough gets hung up over the
northern US Rockies and northern plains. The northern jet turns more
poleward and bring upper level diffluence over the region as deep
south-southwest flow ushers in higher moisture back into Michigan.
This brings the next appreciable chance for precipitation in the
Thursday to Friday time frame. High confidence exists in the mid to
late week for above normal temperatures with daytime highs generally
in the 70s and overnight lows in the 50s.

MARINE...

A low pressure system will continue to push northeast from southern
Minnesota, settling over western Lake Superior by tonight. This will
push the stalled frontal boundary across central Michigan north into
the northern Great Lakes. Widespread rain showers and possibly a
rumble of thunder is expected along and north of this front, across
central and northern Lake Huron. Additionally, the position of the
low will also reinforce northeast flow across the Great Lakes
through tomorrow morning, with wind direction veering to the
southeast by the afternoon. This will help maintain elevated wave
heights across the outer Saginaw Bay to Harbor Beach, where Small
Craft Advisories are in effect.

A very shallow mixing layer has developed over north to north-
central Lake Huron, which will produce localized higher wind gusts
now until 18Z. Gusts around 30 to 35 knots will be likely over the
open waters from Mackinac Bridge to Sturgeon Point. Will preclude
the issuance of a Gale Warning as confidence remains low whether
gale potential will persist in any given three hour window,
especially considering the stability of the marine layer. However,
sporadic gusts to gales are likely through the morning and early
afternoon hours. A short fused Gale Warning cannot be ruled out if
early observational trends support it.

Otherwise, shower and storm potential will increase for all
locations during the afternoon and evening, ahead of a cold front.
Any strong thunderstorm development will have the potential to
produce isolated gusts to or above 30 knots.

HYDROLOGY...

Scattered showers and thunderstorms ahead of and along a cold front
today. Additional rainfall amounts averaging a quarter inch to a
half inch is expected today. The higher isolated totals up to a half
inch or slightly more will be reserved for any more organized
thunderstorms and favored more towards the Tri-Cities and Thumb
region. No major flood concerns are expected through today.
Precipitation will come to an end by around 8 am tomorrow.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-441.

     Dense Fog Advisory until 2 PM EDT this afternoon for LHZ441>443-
     462>464.

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

$$

AVIATION.....BC
UPDATE.......MR
DISCUSSION...AA
MARINE.......AM
HYDROLOGY....AA


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