Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 211859
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
259 PM EDT FRI OCT 21 2016
Overcast stratus is firmly in place over the area in response to the
intrusion of a seasonably cool airmass today. Temperatures have
responded relatively little, about 5 degrees or less, since this
morning`s lows. Lake effect showers are underway beneath the upper
trough which is currently directly overhead and will persist, along
with the stratus, through the early evening. Deepening low pressure
off the New England coast and high pressure being forced east
downstream of a deepening Aleutian low will force winds to back to
northwesterly prior to midnight. In addition to causing lake showers
to pivot toward the eastern Thumb between about 21-03z, backing wind
will disrupt the northerly fetch likely leading to some breakup of
clouds during the latter half of the night. The gradient alone will
be sufficient to prevent frost except on an isolated basis, but
temperatures will still fall into the low to mid 30s in most areas
per most guidance. Superior-Michigan stratocu may work into the area
by early Saturday morning, but warm advection, backing flow, and
increasingly anticyclonic flow through the boundary layer will
ensure erosion of any lingering lake cloud through the morning
hours. However, steep lapse rates in the presence of sufficient
moisture will still support a partial coverage of diurnal component
through the day. Increased insolation should support at least a 4-5
degree moderation of temps compared to today.
Clipper is progged to sweep across the area on Sunday, the large
upper low over Quebec acting as a wave guide. This compact feature
will be subject to track adjustments, but it does appear that it
will be impressive dynamically. Warm advection ahead of it will
force double digit 850mb temps to lift into the area supportive of
highs in the low 60s on Sunday. Specific humidity of 3-4 g/kg will
be adequate in the presence of such forcing to support showers
within a band of enhanced fgen and quick-hitting deformation on the
back side. Confidence in track will likely increase after the rapid
deepening of downstream low pressure gets underway. Highs fall back
into the 50s in its wake.
The start of the work week will be dry and cool as high pressure
builds over the region through Tuesday. As a shortwave approaches
the region midweek, expect milder conditions and increasing chances
for precipitation. The best chance for precipitation will occur
Wednesday night and Thursday as a warm front lifts slowly through
southern Michigan followed by the trailing cold front on Thursday.
After the passage of the shortwave, northwesterly flow will remain
in place through the end of the period with cooler and unsettled
conditions through the end of the week.
Marine observations indicate northerly winds gusting in the 25 to 30
knot range, supporting small craft advisory conditions across
southern Lake Huron and Saginaw Bay. Low pressure off the East Coast
is forecast to deepen as it lifts into New England tonight into
Saturday. Winds will back toward the northwest tonight, but this
strengthening of the New England low pressure system will support
continued gusty winds across the lakes through Saturday night. Wind
gusts across southern Lake Huron will reach 30 knots at times. Winds
will decrease by Sunday as the gradient finally relaxes across the
region. This will be brief however as another push of cold air will
support a reintesification of the northwest winds by Monday.
Issued at 1250 PM EDT Fri OCT 21 2016
Ongoing low level cold air advection will sustain a deep low level
inversion through the day. The flux of moisture off Lake Huron
within the N-NE flow is supplying ample cloud cover to the region.
Given slightly rising inversion heights, cloud bases will trend
slightly upward during the afternoon and evening. There will however
continue to be areas of MVFR based clouds within more organized lake
bands, impacting mainly FNT and PTK. The low level flow will back
slightly toward the N-NW this evening into the overnight. This will
cut off the lake connection to Central Lower Mi and will allow an
opportunity for clearing to overspread much of SE MI inland from
Lake Huron. There is still uncertainty as to the extent and
timing of this clearing. The ongoing expansion of clouds suggests
perhaps a late evening clearing.
For DTW...Recent observations have shown a trend toward a more
northerly wind direction (350-360 deg). The well mixed boundary
layer will support gusts up around the 20 knot range during the
afternoon. The loss of daytime heating this evening (21-23Z) will
result in a decrease in wind speed and a backing of the wind
toward the NW.
//DTW Threshold Probabilities...
* Moderate in ceilings below 5000 ft this afternoon and evening. Low
overnight and Sat morning. Moderate Saturday afternoon.
Lake Huron...Small Craft Advisory until 4 AM EDT Sunday FOR LHZ441>443.
Small Craft Advisory until 10 PM EDT Saturday FOR LHZ421-422.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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