Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 230748
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
348 AM EDT SUN OCT 23 2016
Compact shortwave currently lifting out of the northern plains will
accelerate east-southeast over the next 24 hours, placing this wave
near central Lake Erie by early Monday morning. This late
afternoon/evening timing locally will leave southeast Michigan
within a moderating pre-frontal environment for a good portion of
the daylight period, as a prevailing low level southwest gradient
works the ongoing weak mid level warm air advection down through the
lowest levels. A high degree of early day insolation will augment
this advective process, promoting a solid albeit brief warming trend
for today. Highs of lower to middle 60s, just a touch cooler in the
thumb /upper 50s/.
Dynamic wave transits the local area within the 21z-04z time window.
Defined cold front marking the edge of the inbound height falls
enters the Tri-Cities as early as mid afternoon, before sweeping
southeast in conjunction with the mid level feature through the
evening period. Overall looking at a healthy amount of low-mid
level forcing, most pronounced once trailing upper jet forcing/cva
works across the existing frontal boundary already positioned
locally. This will leave a window for a respectable fgen response
across a sliver of the forecast area. The degree of forcing
certainly provides a chance for shower development /mainly I-94
northward/ this evening, but limited moisture quality still
seemingly working against seeing a more widespread/higher coverage
of rainfall emerge with this system.
Early week period defined as cool and dry, conditions dictated by
gradually expanding high pressure tucked beneath confluent mid level
northwest flow. Deep column northwesterly flow for Monday, ongoing
cold air advection shifting 850 mb temperatures below freezing by
mid morning. Substantial component of low level moisture advection/
lake enhancement accompanies the advective process, favoring a more
pessimistic/cloudy forecast for the daylight period. A muted
diurnal temperature response given the environment, with highs back
down around 50 degrees. Similar profile heading into Tuesday,
little evidence for temperatures to really moderate despite the
increase in mid level heights.
Attention through the midweek period focuses on the evolution and
eventual downstream projection of a deepening wave that ejects
into the Plains by Wednesday. Setup exists for a solid low level
response with this system, leaving a classic mid latitude cyclone
evolution featuring a lead corridor of mid level moist isentropic
ascent/waa followed by strong cold frontal dynamics/convergence as
the surface low ejects into the Great Lakes. High end moisture
quality accompanies this system, with the level of dynamics
certainly pointing to a solid rainfall event within the late
Wednesday through Thursday period. Cool east flow with plenty of
cloud and eventually precipitation maintains below normal
temperatures through this time.
West to northwest winds will ease today, lowering to 15 knots or
less. A renewed surge of cold advection under northwest flow will
return Tonight into Monday however, as low pressure tracks across
southern Lower Michigan this evening. Frequent wind gusts of 25 to
30 knots can be expected over the open waters of Lake Huron. Small
Craft Advisories have been issued for nearshore zones of Lake Huron
during this time, as gusts hover near 25 knots and waves increase
above 4 feet. Winds will slowly diminish on Tuesday, but will be
coming from a northerly direction, which may help to sustain higher
waves along the nearshore waters a bit longer.
Issued at 1157 PM EDT Sat OCT 22 2016
Warm advection altostratus is directly overhead of southeastern
Michigan. Trajectory of the flow aloft and orientation of the
thermal gradients supports keeping the cloud in over the terminals
through approximately 09Z. Actually could see the cloud line push in
towards the Detroit terminals first. Low sky fraction is then
expected for much of Sunday before a shortwave and well developed
midlevel trough pushes across the central Great Lakes late Sunday
afternoon and Sunday evening. 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 is in place over DTW.
Expect it to persist 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.
Lake Huron...Small Craft Advisory from 1 AM to 10 PM EDT Monday FOR LHZ421-
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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