675
FXUS63 KDTX 201953
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
353 PM EDT Thu Jun 20 2024

.KEY MESSAGES...

- Isolated strong to severe thunderstorms are possible through 10
  PM this evening. Damaging wind gusts to 60 mph and highly localized
  storm total rainfall in excess of 2 inches will be possible.

- Additional chances for thunderstorms exist Friday and this weekend
  with organized thunderstorms possible Saturday night-Sunday along a
  cold front.

- Hot and humid conditions persist through Saturday with heat indices
  in the low to mid 90s Friday and the mid 90s on Saturday.

&&

.DISCUSSION...

Strong to severe thunderstorms are ongoing along a line from roughly
Marine City to Dearborn with a slow eastward trajectory at around 25
mph. Deep reflectivity cores of 60+ dbz have prompted severe
warnings already, with additional activity upstream in the presence
of a theta-e pool and plentiful instability. Lack of deep layer shear
has resulted in storm organization that is reliant on cold pool
interactions, so while organized convection will not be widespread
there is potential as we have already seen over Oakland/Macomb/St.
Clair. The second concern with these storms is heavy rainfall and
flooding, as hourly rates have exceeded one inch in these storms per
MRMS with additional convective potential through the evening. Please
refer to the Hydrology section for more information. Expectation is
for storms to lose strength after 9pm- 10pm with the loss of daytime
heating.

Friday will once again be hot and humid, but heat indices in the low
90s preclude the issuance of any heat headlines. Otherwise, chances
exist for pulse convection Friday afternoon-evening, even with
temperatures/humidity slightly tempered in comparison to the past
few days. Forcing mechanisms again remain in the form of shallow
surface boundaries and/or weak shortwave impulses aloft. Similar
hazards and timing as today are expected for tomorrow, with strong
precipitation cores likely to develop and resulting in downburst
potential with damaging winds up to 60 mph.

Broad high pressure center will continue to retrograde toward
central CONUS and flatten through the weekend, contributing to mid-
level height falls over lower Michigan and transition to zonal flow
aloft. The ridge has been effective at steering any stronger
synoptic disturbances northwest of SE Michigan, but this will change
over the weekend as a Pacific wave accelerates across northern
CONUS. Locally, this will drive a cold front through the region on
Sunday and draw in a cooler/drier airmass for early next week.

Until then, hot and humid conditions will persist and even be
reinforced on Saturday as theta-e advection wraps from the central
Plains into the Great Lakes invof a ~40 knot low level jet.
Strengthening mid-level flow and approaching upper level trough
should result in more organized thunderstorm potential than what we
have seen the past few days, although frontal timing overnight
Saturday-early Sunday raises question as to if storms will be
surface-based. Nonetheless, the late Saturday-Sunday system will be
one to watch for strong-severe convective potential and additional
heavy rainfall.

Seasonably warm conditions may return briefly middle of next week,
ahead of a strong low pressure system and cold front that looks to
bring in a more permanent Canadian high pressure/cooler weather.

&&

.MARINE...

The southern Great Lakes becomes positioned between surface high
pressure building across the northern Great Lakes and Ontario and
the persistent ridge across much of the eastern conus for the end of
the week. Hot and humid conditions will persist across much of the
area south of Lake Huron keeping chances of pop up thunderstorms
possible each day. The warm temperatures will also add stability
over the waters helping keep wave heights minimized overall. Though
winds should remain generally light and out of the north, any
location in the vicinity of a stronger storm will have higher gusts
potential with it.  A stronger cold front looks to be on track for
the second half of the weekend however, and wind speeds then could
reach or exceed 25 knots with waves building to around 4 feet. Small
craft advisories may be needed.

&&

.HYDROLOGY...

A moist and unstable airmass holds in place through the end of the
week. Thunderstorms this afternoon have already resulted in rainfall
totals in excess of 1 inch in a 30-60 minute period, prompting urban
flood advisories. While there is not a strong signal for training
storms, there is a chance for localized areas to see more than one
thunderstorm which could result in highly localized rainfall amounts
in excess of 2 inches by late evening. Additional thunderstorms are
possible again Friday and this weekend with heavy downpours
possible.

&&

.PREV DISCUSSION...
Issued at 208 PM EDT Thu Jun 20 2024

AVIATION...

Convergence along various shallow boundaries will bring scattered
showers and thunderstorms across Southeast Michigan this afternoon.
Storm motion is expected to be slow with cell movement perhaps at 20
knots or less. Main aviation concern will be obstructed visibilities
due to brief heavy rainfall rates. The potential does exist for wind
gusts to reach 50 knots in thunderstorm activity, but the likely of
occurrence is too low to include in the TEMPO. A main synoptic
dewpoint gradient augmented by outflow should push south of the
Southeast Michigan between 00-06Z. Very weak flow and moist surface
conditions will support br/hz at daybreak Friday morning.

For DTW/D21 Convection...Scattered thunderstorm activity is expected
to develop near DTW in the 18-21Z timeframe. Low confidence in when
thunderstorms will push southward and storm motion may become
variable and slow moving.

 DTW THRESHOLD PROBABILITIES...

* Moderate in thunderstorms this afternoon and evening.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 10 PM EDT this evening for MIZ068>070-075-076-
     082-083.

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

$$

DISCUSSION...MV
MARINE.......DRK
HYDROLOGY....MV
AVIATION.....CB


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