649
FXUS63 KDTX 291516
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1116 AM EDT Sat Jun 29 2024

.KEY MESSAGES...

- There is a low chance for an isolated strong to severe
thunderstorm late this afternoon into the late evening.

- Damaging wind gusts and locally heavy rainfall are the main
threats if something develops this afternoon. Hail would be possible
near the Tri-Cities late this evening if stronger cells survive out
of northern lower MI ahead of an approaching cold front.

- High pressure builds in behind a cold frontal passage on Sunday
and brings cooler and drier weather for early next week.

&&

.UPDATE...

Widespread rainfall has cleared SE MI with ongoing surface
destabilization now taking place, aided by breaks in cloud cover. A
subset of hi-res guidance hints at redevelopment of isolated to
scattered shower and thunderstorm coverage across southwest lower
Michigan, but given very subtle forcing within the subtropical
airmass, confidence in exact location and timing of thunderstorm
potential remains low. Will continue to monitor satellite/radar for
development, with best window for development wedged between the
16-21Z (12PM - 5 PM) window.

Upscale growth in thunderstorms will be possible if development is
observed given the favorable thermodynamic and kinematic environment,
with WSW storm motion pathing any sustained development into SE MI.
MUCAPE values rising to 2500-3000 J/kg with DCAPEs nearing 1000 J/kg,
and up to 50 knot winds noted within any potential convective column
will make damaging wind gusts to 60 mph the most probable threat
with any strong to severe thunderstorm development. Effective bulk
shear values are decent around 30 knots. A weak isolated tornado
cannot be totally ruled out given some streamwiseness noted in 0-1 km
storm relative hodographs, but the 1-3 km shear is very poor and
is not favorable for any meso production. Last, any hail threat up
to an inch would be reserved for potential thunderstorms focused
later this evening, confined north of M59, where drier mid-level
humidity will reside.

Overall, given this highly conditional low PoP setup, a marginal
risk for severe weather remains in place across SE MI.

&&

.PREV DISCUSSION...
Issued at 638 AM EDT Sat Jun 29 2024

AVIATION...

Deeper moisture surging into Southeast Michigan will maintain a
chance for showers, with isolated thunderstorms, throughout the
morning period. Observational trends suggest a dip in cloud base to
lower VFR/MVFR within this window. Trailing diurnal stratocumulus
expected lingering into at least a portion of the afternoon period,
but may tend to mix out with time. Prevailing winds from the
southwest turning gusty, nearing 25 knots at times this afternoon.
While conditions appear less favorable for shower and thunderstorm
this afternoon and evening, an isolated cell or two cannot be ruled
out. Standard reduction in wind gust potential with loss of daytime
heating this evening. A cold front brings a wind shift to the
northwest overnight, with some potential for a brief shower or storm
along with renewed increase in cloud.

For DTW/D21 Convection...Main window for possible tsra focused on
this morning, although with coverage likely remaining isolated.
Local heavy downpours will be the main impact of these embedded
thunderstorms.

DTW THRESHOLD PROBABILITIES...

* High for ceiling aob 5000 ft this morning, medium into the
  afternoon.

* Low for thunderstorms this morning.

PREV DISCUSSION...
Issued at 316 AM EDT Sat Jun 29 2024

DISCUSSION...

A mid-level shortwave is in the process of crossing lower MI this
morning coincident with the lead edge of a richer theta-e plume
lifting up the Mississippi. This will support widespread moderate to
heavy showers throughout the morning in addition to a few embedded
thunderstorms as weak elevated instability expands into southern
lower MI. While no severe weather is expected within this activity,
locally heavy rainfall carries a fairly high potential as PW values
exceed 2" (nearing daily climo max) in combination with a deep warm
cloud layer pushing 11-12kft.

Morning shortwave clears the region by late morning-early afternoon
with SE MI residing firmly within the overall system`s warm sector.
Southwest flow continues to advect an impressive Gulf-originating
theta-e plume into the area through the afternoon resulting in
dewpoints climbing into the lower 70s across the area with mid 70s
possible over the southern portion of the area (Detroit to the Ohio
border). Result is MLCAPEs ranging between 1000-2000J/kg, highest
over the those southern locales. Kinematically, with the mid-upper
trough sagging into the central Great Lakes, overall bulk shear is
favorable for convective organization at 35-45kts. Main question
remains however to what degree convection is above to fire this
afternoon-evening as subsidence in the wake of morning activity will
likely be lingering over the area providing a modest cap. There is
signal amongst a few high res solutions, such as the ARW and to a
lesser extent the HRRR, for a remnant MCV feature to lift out of the
Midwest this afternoon towards northern IN/OH, potentially creeping
into far southern MI, supporting the development of scattered
convection along or south of the stateline this evening. Though
worth noting, at this time, confidence in this scenario is low. In
the absence of this feature, CAM guidance is generally unsupportive
of convective development late this afternoon-evening due to the
aforementioned subsidence. `Best` potential instead looks to occur
along the cold front as is drops out of the northern Great Lakes.
This frontal timing however has slowed compared to prior day`s model
runs, and now appears to cross the area between 02-07Z falling
mostly within the diurnal instability minima. Additionally, system-
relative streamlines are fairly parallel to the frontal boundary
limiting its low level convergence and subsequent coverage of
convective development.

Should a few cells manage to fire this afternoon-evening (which
again carries low confidence in occurrence), there is good setup for
these updrafts to become organized leading to strong to severe
storms with damaging wind gusts and locally heavy rainfall as
primary threats. Hail can`t be ruled out in the strongest updrafts
given the available instability and shear though would be a
secondary threat. While convective potential is a bit better along
the cold front given at least some (albeit weak) forcing mechanism,
late day timing greatly hampers any severe potential. Instability
will have largely waned over areas south/east of the Tri-Cities by
the time it arrives and with the Tri-Cities residing in the edge of
the main moisture axis, MLCAPEs only top out around 1000 J/kg this
evening which will likewise be in the progress of waning by the time
of fropa. With current timing, several hundred J/kg look to still be
available around the Saginaw Valley/western Thumb and combined with
straight, elongated forecast hodographs, can`t completely rule out
an isolated strong storm (hail being main threat)... though chances
aren`t great.

Northerly flow develops Sunday in the wake of the frontal passage as
Canadian high pressure builds in from the upper Midwest. Impressive
thermal troughing also settles over the Great Lakes as 850mb temps
fall to 5-6C (which is below the 10th percentile for the day
climatology). Highs likely struggle to break into the 70s,
particularly in the Thumb, as a result even with the significantly
drier airmass promoting sunnier skies. Surface ridge axis doesn`t
cross the area until Monday night maintaining below average and dry
weather to start the new work week. Temperatures moderate back to at
or above normal by midweek as high pressure shifts east setting up
southwesterly return flow. This however also likely advects Gulf
moisture back into the region ahead of approaching northern Plains
low pressure.

MARINE...

Incoming low pressure system will bring chances for showers and
storms through the day today. Tightening pressure gradient will
allow for strong southerly flow over Lake Huron. Winds veer
southwesterly through the afternoon and evening, aligning flow
direction with the maximum fetch of Saginaw Bay. Low-level flow will
also have little trouble mixing down 30+ knot gusts, leading to a
Small Craft Advisory being issued for Saginaw Bay from 12pm to 10pm
today. Winds veer to the north-northwest on Sunday behind the cold
front, maintaining speeds over 20 knots around the nearshore areas
of the Thumb and over central Lake Huron. Gusts to 25 knots or
greater are also possible. Due to fetch direction and length, the
potential for waves to meet Small Craft Criteria exists on Sunday
despite a lesser concern for gusts mixing down. Behind the low,
drier conditions and gentle winds will take over on Monday.

HYDROLOGY...

Widespread rain, with a chance for embedded thunderstorms, continue
to track across the area this morning before largely clearing by 10-
11AM. Periods of heavy downpours are likely given the warm and humid
airmass in place. Basin averaged mean precipitation amounts are
forecast to vary between a quarter to three-quarters of an inch,
however, highly localized rainfall totals between 1-2 inches will be
possible with heavy downpours, especially with any thunderstorm
activity. Given current radar trends, areas between I-69 and I-94
have the greatest chance to see these higher rainfall totals due to
potential for repeated heavier bursts.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422.

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

$$

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


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