119
FXUS63 KDTX 210355
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1155 PM EDT Thu Jun 20 2024

.KEY MESSAGES...

- 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.

&&

.AVIATION...

Convective potential remains minimal overnight as greater nocturnal
stability maintains control. Very moist near surface conditions and
limited wind will provide favorable conditions for some shallow
fog/haze development during the pre-dawn hours. The underlying moist
and unstable environment will again bring potential for diurnal
convective development Friday afternoon and evening. Similar to
recent days, overall coverage and placement of possible development
remains quite ill-defined at this stage.

For DTW/D21 Convection...The overall environment will again be
favorable for some degree of thunderstorm development Friday
afternoon and evening, but with usual uncertainty at this stage on
timing and coverage.

DTW THRESHOLD PROBABILITIES...

* Low in thunderstorms impacting the airspace Friday afternoon and
  evening.

&&

.PREV DISCUSSION...
Issued at 353 PM EDT Thu Jun 20 2024

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.

&&

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

$$

AVIATION.....MR
DISCUSSION...MV
MARINE.......DRK
HYDROLOGY....MV


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