Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 130357

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1157 PM EDT Sat Jun 12 2021


A weak surface pressure trough exits into Ohio and southern Ontario
during the late night and takes the remaining showers and ordinary
thunderstorms along with it. The slow eastward drift of this feature
shifts low level wind from the north helping to carry areas of MVFR
stratus from northern Lower MI into SE MI leading up to sunrise.
These clouds are already showing up in satellite and surface
observations to the north of MBS. Broken coverage is expected to
develop and slide across the region during the morning before mixing
upward and exiting eastward toward noon. A broad area of high
pressure builds in from the Midwest during afternoon helping to
maintain northerly wind and mostly clear sky into Sunday evening.

For DTW...A few showers remain possible, with an outside shot for a
rumble of thunder, through about 08Z as the last activity moves west
to east near the terminal. A light northward wind shift helps bring
MVFR stratus into the area which brushes eastward during the


* Low for a thunderstorm 06z-08z tonight.

* Medium for ceiling at or below 5000 ft late tonight through


Issued at 337 PM EDT Sat Jun 12 2021


Short-Term (Previous Afternoon Update with Minor Additional

Arrival of a shortwave trough carving through the greater ridging
pattern across the Great Lakes in conjunction with the passage of a
surface cold front will be the main forcing mechanism for late
afternoon and early evening convective initiation across Southeast
Michigan, specifically for the Tri-Cities area and locations across
the western periphery of the cwa. Low-level convergence from weaker
lake breezes off of Saginaw Bay/Lake Huron may also aid in initial
CI across the Tri-Cities region before further expanding south-
southeast through the evening. Effective bulk shear values around 30
knots with MLCAPE values ranging between 1000 - 1500 J/kg will
support widely scattered thunderstorms. Storm relative hodographs
are also supportive of marginal supercell development within the
lake shadow, mainly across central Michigan (& Tri-Cities), given
some weak low-level shear and better streamwise mid-level shear.
There is additional supportive evidence from the 2-5 km updraft
helicity tracks in the latest hi-res ensemble suite showing rotating
updrafts are possible.

Stronger storm development will be capable of producing isolated
damaging wind gusts up to 60 mph given steep low-level lapse rates
around 8C/km with additional aid from dry air entrainment(12Z DTX
RAOB shows a very dry column of air wedged between 700-400 MB).
SPC`s updated Day 1 outlook has also included portions of Southeast
Michigan (along and west of I-75) in a marginal risk for severe
weather for wind gust concerns. Given the near-severe wind gusts
between 40-50 mph along yesterday`s convective outflow & better
thermodynamic fields in place today, the marginal risk for isolated
strong wind gusts are warranted. The greater Metro region and
northern Thumb will also maintain their chance mention (30-40
percent) of precipitation given any outflow and marine boundaries
that will materialize, but severe weather chances will wane as any
potential precipitation makes its way by the late evening and early
night period.

Sunday Through Midweek Period:

A very modest drop in temperatures will be noted on Sunday behind
the passage of the front with temperature highs pushing into the low
to mid-80s, however, a markedly notable change in humidity will be
felt as drier air filters in throughout Sunday morning. Dew points
will drop into the 50s by Sunday afternoon. Otherwise, breakdown of
the subtle ridging over the Great Lakes will occur throughout Sunday
as a jet max and elongated shortwave feature carves south into the
northern Plains and Midwest. This shortwave combined with support
from left exit dynamics from the jet streak and low-level support
from an advancing cold front will bring shower and low-end
thunderstorm chances on Monday as the upper-level trough sets up
across the Great Lakes and continental northeast.

A weak thermal trough will hold through the midweek period as high
pressure drops into the Midwest and Great Lakes region Tuesday into
early Thursday. Anticyclonic flow will draw down very dry air late
Tuesday into early Thursday with PW values ranging between .30 to
50. This will bring an extended period of dry weather and pleasant
conditions marked by temperature highs in the mid to upper 70s and
dew points in the 40s.


Light northeasterly winds backing more northerly tonight will
prevail over the local waters as broad, weak low pressure remains in
place amidst a very warm and humid airmass. Widely scattered showers
and thunderstorms will be possible late this afternoon through this
evening, particularly across Saginaw Bay, southern Lake Huron, and
possibly into Lake St. Clair and western Lake Erie. Drier air will
filter in for Sunday with fresh moderate wind developing over the
northern Lake Huron basin. Showers will again be possible Sunday
night and into Monday as a cold front sags southeast across the
region. High pressure will then build across the central Great Lakes
heading into the midweek period with moderate northerly flow, which
may lead to periods of choppy waves in portions of the Lake Huron
nearshore waters as gusts reach around 20 knots at times.



Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.




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