Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 181653
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1253 PM EDT TUE OCT 18 2016
Strong SW wind continues with gust potential near 35 knots ahead of
the cold front on track to move through SE Michigan during the
afternoon. Borderline MVFR/VFR ceiling set up in the warm/moist
prefrontal air mass will continue to mix more into VFR and leave any
additional restriction confined to spotty showers of greater
intensity. Shower coverage will be higher in the DTW corridor as the
front moves through there during peak heating. The wind will then
drop off considerably behind the front with a decreasing cloud
trend, especially toward early evening and through tonight as cooler
air is carried into the region. The air is cooler and less humid but
upstream observations of surface dewpoint in the 50s over the
Midwest supports guidance suggesting a short period of shallow MVFR
fog around sunrise. High pressure building into lower Michigan will
help the sky remain otherwise clear. Morning sun will dissipate fog
quickly on light west wind becoming variable again through
For DTW...While SW wind gusting to near 35 knots will continue, the
main concern will be borderline MVFR/VFR ceiling persisting into the
evening traffic push. Coverage of showers will also increase but
thunderstorm potential appears very low in the latest data. Rapid
improvement is then expected during early to mid evening leaving
clear sky and light wind to persist through tonight. A short
interval of shallow fog is also possible around sunrise.
//DTW Threshold Probabilities...
* High for ceiling 5000 feet or less through late afternoon.
Issued at 259 AM EDT Tue OCT 18 2016
Surface low pressure will lift from eastern Lake Superior into
Quebec today the axis of an upper trough moves from the Dakotas into
the Great Lakes. The low will continue deepening as it lifts
northward, helping to sustain a tight surface pressure gradient
early this morning and into the afternoon as strong high pressure
remains anchored off the East Coast. Atmosphere will remain warm and
well-mixed ahead of a cold front trailing the low. This boundary is
expected to drop across Southeast Michigan during the afternoon and
very early evening.
Plume of higher theta-e combined with steeper lapse rates below 6000
feet may allow a few showers or maybe a thunderstorm to develop in
advance of and along the front as it sweeps through. Dry and warmer
air above 750mb will limit coverage however, and will keep chances
for rain/thunder low. CAPE values look to be limited to 500 J/kg
(barely supporting thunder...showalter indices near -1) or less, but
strong unidirectional wind field and inverted-v type soundings could
allow gusts to 50 mph to mix to the surface in any thunderstorms or
even stronger showers that develop.
Biggest question for early this morning and today is how strong
winds will get. There may be a few hours this morning and into the
early afternoon where we see gusts up to 45 mph as mixing deepens
within the warm sector and we tap into stronger winds aloft. This is
suggested by GFS/NAM/HRRR forecast soundings. Cannot rule out a few
wind-advisory strength gusts of 45 mph or more, but confidence is
not high and duration may be too short-lived to justify a headline.
Gusts upstream in the Chicago-area now just topping 40 mph, as they
mix into the core of H925 winds of about 50 knots. NAM/GFS show this
core weakening as it lifts across Lower Michigan, but expect
boundary layer to also deepen as low-level lapse-rates steepen with
daytime heating. Good isentropic descent shown on Nam 294K surface
supports gusty winds as they turn west with the frontal passage this
afternoon before post-frontal winds quickly decrease, but not
expecting anything above 40 mph.
Good mixing within the warm sector will provide another day with
well-above normal temperatures. Temperatures across far southeast
Michigan will be similar to yesterday, near 80, with later frontal
passage allowing more time for heating. The remainder of the area
will see max temps in the 70s.
Low pressure will exit into Quebec this evening allowing the
pressure gradient to relax as high pressure over the Central Plains
begins to expand into the area. This will bring light winds and dry
weather. Temperatures tonight will run much cooler, but still well
above normal, in the mid 40s to low 50s.
Approach of the next upper trough will send an elevated warm front
northward into at least a portion of Lower Michigan Wednesday night
and Thursday. Differences with how amplified this trough becomes
leads to uncertainty with the position/track of low pressure as it
lifts northward through the Tennessee Valley and possibly clips the
Ohio Valley. Expect rain to occur within deformation on the
northwest flank of the low track and along the elevated front, with
westward extent of rain shield into Southeast Michigan still
uncertain. Best potential for rain remains east of US 23. Cooler air
will be pulled into the Central Great Lakes behind this system,
cooling temperatures dramatically Friday through Sunday. Only
expecting max temps to reach into the 50s, with lows Friday and
Saturday night dropping into the 30s for most locations.
Low pressure will continue to deepen as it lifts from eastern Lake
Superior to James Bay this morning. South to southwest flow will
increase early this morning within tightening pressure gradient.
While gust potential will be limited due to the stable conditions
created by this warm southerly flow riding over cooler lake waters,
still expect wind speeds into the 25 to 30 knot range with slightly
Will maintain the ongoing Gale Warning over northern Lake Huron and
Small Craft Advisories for all of the nearshore waters. A cold front
will wrap around the exiting low pressure and cross the Straits and
northern portions of Lake Huron this morning. This will enhance gust
potential, especially within showers or thunderstorms along this
front. So, gale force gusts to 35 knots will remain possible. Gusts
over the nearshore waters will range closer to 25 knots, although 30
knot gusts may be more common for a time this morning over Saginaw
Bay as southwest flow funnels up the bay.
Winds will decrease quickly tonight as the low pressure races to the
northeast through Quebec and a ridge of high pressure builds into
the central Great Lakes.
Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon FOR LHZ421-422-
Gale Warning until 4 PM EDT this afternoon FOR LHZ361-362.
Lake St Clair...Small Craft Advisory until 4 PM EDT this afternoon FOR LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EDT this afternoon FOR LEZ444.
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