Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 202338
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
738 PM EDT THU OCT 20 2016
Observational data including regional Z mosaic and satellite imagery
supports that bulk of the warm advection support and higher theta e
isentropic ascent is well east of southeastern Michigan. The gap in
the Z mosaic over portions of Ohio and Lake Erie suggests that
some orphaning of the midlevel fgen has occurred. Thus, the
midlevel forcing is expected to persist for awhile over
southeastern Michigan this evening before the stretching
deformation runs its course. Enough dry air entrainment likely
points to the conclusion of heavier rain activity, but the
thinking is that drizzle will remain possible for longer duration
tonight. Hi-resolution output and plan view of RH data suggests
drizzle may remain possible until as late as 09z across the
eastern areas. Therefore, went decidedly more pessimistic with
duration of drizzle and also more pessimistic with low level cloud
Friday. Good structure to the subsidence inversion base at
approximately 5000 ft agl suggests that moisture, saturation, and
cloud will remain trapped below this feature. Probably will take
until late afternoon to scatter clouds out.
For DTW...Went decidedly more pessimistic with drizzle through 09Z
with MVFR cig heights right into Friday.
//DTW Threshold Probabilities...
* Medium to high confidence in ceilings aob 5000 feet tonight.
Medium confidence Friday.
Issued at 339 PM EDT Thu OCT 20 2016
Deep tropospheric frontal zone extends from Ohio/Pennsylvania at the
surface to northwest Lower Michigan at jet level. Ongoing isentropic
ascent and deep frontogenesis have fueled persistent stratiform rain
for the balance of today. Embedded shower component has also been
noted streaming in from the northeast off of Lake Huron, a testament
to moderate lake instability. A sharp northern edge to the rain has
also been observed as forcing becomes increasingly elevated and
hydrometeors evaporate in deep sub-front dry layer.
Trough featuring a robust PV anomaly over Missouri at 19z will
gradually evolve a neutral tilt this evening. Eastward migration of
the upper jet will force the current batch of rain east by around
00z or shortly thereafter. However, lighter/less organized showers
will likely persist as the secondary cold front works through the
area at the surface. There then exist potential for a renewal in
coverage and intensity as the upstream PV anomaly and attendant
height falls pivot through the Ohio Valley 06-12z. All said, pops
have been given a generous increase through tonight, particularly
across the south and east. In addition, lake effect will continue in
some capacity well into Friday morning as NNE to NE flow persists
off of Lake Huron within an environment characterized by 0-1km theta-
e lapse rates falling to an impressive -6 to -8C overnight. Given
the favorable background of deep cyclonic flow and mid-level forcing
as the upper trough pivots through, felt likely pops in the northern
and eastern Thumb were prudent through at least late tonight.
Gradually backing flow in advance of building high pressure will end
the lake effect threat altogether by Friday afternoon. Beneath lake
enhanced clouds reinforced by a thermal trough of -4C at 850mb,
highs will struggle to 50 degrees on Friday...perhaps just upper 40s
along the glacial ridge. Cold advection will support a wind gust
component of 20-25kts adding a chill to the air that will likely
make it the coldest day of the young Autumn season so far.
Gradient will remain on the stronger side through Friday night as
low pressure deepens off the New England coast. Bumped lows up a few
degrees given the expectation for both a nocturnal mixed layer and
developing lake effect clouds. Highs rebound slightly into the low
50s on Saturday beneath increasing heights aloft, but little
difference from Friday overall as a healthy stratocu component is
likely to persist beneath generally cyclonic flow in the low levels
and continued gustiness with moderate wind field.
A warmer day expected Sunday as warm air advection boosts
temperatures back above normal values. The warm-up looks to be short-
lived, however, as a quick-moving shortwave tracks through Sunday
night. It appears to be a mostly dry event with a lack of moisture
and low-level wind trajectories favoring lake-effect precipitation
remaining over Canada, but any light precipitation that could occur
would appear to favor the Thumb. Cooler and dry once again for
Monday and Tuesday as Canadian high pressure noses into the region.
Possibility for additional precipitation mid-late week with warm
advection ahead of a wave moving in from the Plains.
Gusty northerly winds will continue into the evening as low pressure
lifts through the Ohio River Valley into the eastern Great Lakes.
Moderate winds will stay around through Saturday as colder air
filters into the region. The persistent northerly flow over such a
long fetch of Lake Huron will build waves to hazardous levels in the
nearshore zones by evening with a prolonged period of elevated winds
and waves then continuing into Saturday as the aforementioned low
pressure system undergoes significant deepening over the New England
states heading into the weekend.
A Small Craft Advisory remains in effect during this time frame for
the Lake Huron nearshore waters. The strongest wind gusts will occur
from early Friday into Saturday as much colder air in pulled across
the area into the low pressure system. At this time, it appears that
wind gusts should remain below gale force, averaging 25 to 30 knots
over the Lake Huron open waters.
Light to moderate rain will continue into the evening as low
pressure lifts through the Ohio River Valley on its way to the
eastern Great Lakes tonight. The main shield of rain has been
situated along and south of a line from Harbor Beach down through
Lansing with areas north and west staying mainly dry. The highest
rainfall totals will be in southeast portions of the county warning
area where the rain will stick around longer as the system slowly
shifts off to the east. Expected rainfall totals in the half to
eight tenths of an inch range will be common in this area.
Lake Huron...Small Craft Advisory until 10 PM EDT Saturday FOR LHZ421-441>443.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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