Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
722 PM EDT Sat Oct 22 2016
Corridor of extensive altostratus is pushing through western and
central lower Michigan at press time. The saturation and cloud is
supported by warm air advection off of a initial geopotential
height rise push. Just weaker synoptic scale lift and shallow
saturation will maintain dry weather. Given the trajectory of the
flow and the orientation of the geopotential gradient, suspect the
midcloud will be around awhile. Looking for overcast to broken through 06z
with skies likely scattering out after 09z tonight. No lower
tropospheric cloud is expected through the first 2/3rds of Sunday
but very respectable shortwave energy will push down into
southeastern Michigan for the late afternoon. While the jet
forcing and cva will be adequate, fgen and isentropic ascent is
lacking and will be a major limitation for shower generation. Will
leave the tafs dry for Sunday in this issuance.
For dtw...extensive altostratus canopy set to push across dtw this
evening then persisting into the early morning hours. Scattered high
cloud for the first half of Sunday before shortwave pushes into the
terminal during the late afternoon. Will monitor trends for
potential of rain showers late Sunday afternoon and evening.
//Dtw threshold probabilities...
* low for cigs aob 5kft tonight. Medium to high for cigs aob 5kft
agl late Sunday afternoon.
issued at 333 PM EDT Sat Oct 22 2016
Low level cyclonic flow associated with the deep low pressure system
over New England is finally loosening its grip across se mi. A
surface ridge axis now sliding across wrn lower mi is forcing the
low level flow across se mi toward more anti cyclonic. This and the
very shallow nature of the cloud cover today has resulted in a rapid
clearing trend. There are however some mid clouds now over Lake
Michigan. These have developed within a narrow ribbon of mid level
warm air advection. This axis of warm air advection/isentropic
ascent will track across the forecast area this evening and during
the first half of the overnight, providing some degree of mid clouds
tonight. The gradient will be much weaker tonight and there will be
at least some periods of clear skies. This will support min temps
down into the mid 30s to low 40s.
A low amplitude mid level trough axis over the Montana/Canadian
border this afternoon will move into upper mi on Sunday, then
advance into the eastern Great Lakes/upstate New York Sun night. The
associated mid level height falls will force weak sfc low pressure
and an associated cold front from Wisconsin to srn lower mi Sun
afternoon. The 12z model suite all indicate a plume of mid level
moisture advecting into lower mi Sun afternoon ahead of the upper
wave. Strengthening frontogenesis in the 925-850mb layer will
interact with this moisture plume to provide a chance of showers,
mainly sun evening. The expected brevity of the forcing and lack of
appreciable depth to the moisture suggest low chance pops and
minimal quantitative precipitation forecast with any showers. Low level warming ahead of the sfc
wave is expected to push 925mb temps up to +10 to +13c, which will
support afternoon highs into the 60s over much of the area (outside
the thumb) on Sunday.
A broadening of an upper low over ern Canada and an amplification
of a long wave ridge over central North America on Monday will
lead to fairly strong mid level confluent flow across the region
during the first half of the week. As a result, sfc high pressure
will expand across the wrn Great Lakes, forcing low level
northwesterly flow across the region. This will bring cooler air
back into se mi Sunday night into Monday, where it will persist
into mid week. Lake aggregate troughing should become firmly
established across the region within this airmass and will likely
support a fair amount of cloud cover, especially on Monday.
High pressure building into the area on Tuesday will keep US dry as
we see a mixture of clouds and sunshine throughout the day. The next
chance for precipitation will come Wednesday afternoon into Thursday
as low pressure from the Central Plains pushes ENE, settling over
michgan on Thursday. With unimpressive instability parametes, rain
showers will be the main concern with the low, along with slightly
breezy conditions. Additional chances for precipitation will be
possible Friday into the weekend as a second low pushes east across
Gusty fresh northwest wind will diminish late tonight which will
allow waves to subside and for expiry of small craft advisories.
Marine weather will then remain on the quiet side through most of
Sunday before a passing clipper brings renewed surge in northwest
wind causing widespread gusts to near-gales Sunday night into Monday
night. Small craft advisories will once again be needed for
nearshore zones during this time.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for lhz421-
Lake St Clair...none.
Michigan waters of Lake Erie...none.
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