Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 201939
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
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.
Issued at 123 PM EDT Thu OCT 20 2016
Rain and showers will continue through the afternoon before tapering
off overnight as the trough swings across the area. Until then,
ceilings and visibilities will remain on the lower end of VFR with a
few patches of MVFR mixed with some higher end IFR. The IFR
visibilities have been with the heavier bands of rain over FNT and
DTW during the early afternoon. Lower visibilities will start
improving after 03Z but clouds still hang around into Friday. As the
trough axis pivots through the area overnight, there will be a
continued chance for lake effect rain showers to make it into the
For DTW...North/northwest flow and residual moisture will
keep clouds around through Friday. Challenge resides in whether any
lake effect moisture can make it in tonight after the main rain
shield moves off to the east during the overnight period.
//DTW Threshold Probabilities...
* High confidence in ceilings aob 5000 feet before 00Z, low
* High confidence in visibilities falling into the IFR range for
short periods through at least 00Z.
Lake Huron...Small Craft Advisory until 10 PM EDT Saturday FOR LHZ442-443.
Small Craft Advisory until 10 PM EDT Saturday FOR LHZ421-441.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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