Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 281646
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1246 PM EDT SUN AUG 28 2016
Convective initiation underway along convergent band of cu that
has set early this afternoon along the instability axis. Extremely
high dewpoints in the upper 70s along and south of this line are
contributing to 0-1km MLCAPE of 1500 to 2000 j/kg despite
temperatures only being in the low to mid 80s. Ambient wind field
is quite weak, but deep layer shear pushing 30 knots may support
lose organization. Latest RAP/HRRR soundings indicate plenty of
dry air in the column that could support brief a brief downburst
containing a 60 mph gust as storm cores collapse while instability
may support hail approaching one inch in diameter. The threat will
be confined to the Monroe County, far southeast Wayne county, and
the Southeast half of Lenawee County. Gradual supression of the
instability axis should push activity south of the MI/Oh border by
mid to late aftn.
Issued at 641 AM EDT Sun AUG 28 2016
Fog and low clouds early this morning will lift and dissipate,
transitioning to low VFR CU deck this afternoon. An isolated
thunderstorm is possible, best chance across southern taf sites, but
coverage too low to include in tafs. Drier air will work into
southeast Michigan late in the day and this evening, which will help
limit fog potential, but would still expect some light MVFR Fog.
Light southwest winds becoming westerly, mainly below 10 knots
during the day. Isolated showers and thunderstorm activity looks to
be predominately near the Ohio border this afternoon.
//DTW Threshold Probabilities...
* Medium for ceiling aob 5000 feet today.
* Low for ceiling/visibility below 200 ft or 1/2 sm late tonight.
Issued at 303 AM EDT Sun AUG 28 2016
A corridor of fast low to mid level west-southwest flow has resided
across Lower Mi during the overnight period. Moist isentropic ascent
along the nose of the low level jet, tied to the entrance region of
an upper jet max within the base of the upper trough now rotating
across wrn Lake Superior, resulted in the development of a cluster
of thunderstorms over central Lower Mi overnight. This localized
forcing will continue on a northeast track across Saginaw Bay during
the pre dawn hours.
The upper trough will continue on an eastward track across Lake
Superior/nrn Ontario today. The entrance region of the upper jet
will linger over srn Mi throughout the day and will force a narrow
region of mid level frontogenesis. This frontal forcing, now
extending from srn Lake Mi into cntl Lake Huron, will gradually
slide south across the forecast area during the course of the day.
Mid level dry air and subsidence will follow in its wake. This
forcing will generally provide a slight chance of morning convection
across the northern half of the forecast area. The chances being
limited substantially be weak available instability. Daytime
destabilization will provide a little better chance for some
afternoon convection as the forcing slides south of a KPHN to KOWZ
line this afternoon. Meanwhile, daytime heating will erode morning
fog and low clouds and will support afternoon highs into the 80s.
The deepening daytime mixed layer and low-mid level dry air
advection will result in a slight drop in sfc dewpoints across the
Saginaw Valley early this afternoon, spreading south into Metro
Detroit during the evening.
Mid level confluent flow and building heights following the
departure of the mid level wave to the east of Lake Superior tonight
will force sfc high pressure to expand into the area from the west.
North-northeast low level flow across Lake Huron into Se Mi will
occur in advance of this high. The latest NAM, HRRR, and ARW all
suggest marine stratus will have a difficult time eroding today.
This moisture will then advect across Se Mi tonight with the onshore
flow. Fog and/or low stratus will result and will likely persist
through the Mon morning rush hour. Once the low level moisture mixes
out lat Mon morning, a warm and dry afternoon can be expected on as
the sfc high continues to influence the region.
Model trends have been a little slower bringing a sfc cold front
into the area from the north next week. The latest model suite do
not bring the sfc cold front across Se Mi until Tues night. The
front will be driven south by a mid level wave forecast to track
from nrn Manitoba into nrn Quebec. Limited forcing and instability
along the front as it tracks across the area will support very low
chances for convection. The passage of the front will however mark a
substantial airmass change. Long wave trough amplification across
ern Canada during the latter half of the week will drive much cooler
air into the Great Lakes (850mb temps forecast to drop into the
single digits by Thursday). Thus cool temps (highs in the 70s and
lows in the 50s) can be expected the latter half of the work week.
Westerly winds today will be predominantly in the 5 to 15 knot range,
except across northern lake huron will sustained winds look to be
closer to 20 knots. Winds will shift to the north tonight as high
pressure continues to build in, allowing for light and variable
winds on monday. Modest southwest winds expected on Tuesday
ahead of a weak cold front tracking through.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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