Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 251655
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1255 PM EDT SUN SEP 25 2016
VFR conditions will transition to MVFR late tonight into Monday as
shras/stratus spread into area with cold front. Pulled the onset of
shras forward to 08z for I-94 terminals given morning guidance. Will
not mention thunder ATTM given limited instability and expectation
of isolated tsra at best. Gusty WSW flow (gusts near 25 knots during
best afternoon mixing) after FROPA on Monday as area of subsidence
overspreads area. While this subsidence may also bring period of SCT
clouds, generally expect BKN strato-cu bordering on MVFR-VFR.
For DTW...Rough timing for shras in advance/along cold front will be
~08z-14z with at least periods of MVFR conditions. Post-frontal flow
on Monday should be gusty after 18z, perhaps touching 25 knots.
//DTW Threshold Probabilities...
* Low confidence in ceilings below 5000 ft this morning, High Monday
morning (12-15 Z).
* Low confidence in thunderstorms Monday morning.
Issued at 1011 AM EDT Sun SEP 25 2016
Forecast largely on target. Had a quick update for a slightly
quicker cloud trend. Decent deck of altocumulus across western
Lower and Lake Michigan around 800-700 mbs. 12z DTX sounding was
very dry except in that particular layer. Latest RAP indicates
that moisture will be able to sufficiently move over the forecast
area between 18z and 22z.
Issued at 404 AM EDT Sun SEP 25 2016
Extreme anticyclonic flow trajectories will remain in place today
over the central Great Lakes. Plan view charts show that a high
amount of localized anticyclonic vorticity advection will occur
today as an absolute vorticity structure is expected to fold before
rolling through the state. Soundings show a bulk of the subsidence
response to be confined to the 3 to 6 kft agl layer. Persistence of
dry easterly flow underneath squatty mixing heights should keep
temperatures in the lower 70s today despite the top-end subsidence
dynamics. Really a picture perfect early autumn day with high clouds
moving in during the late afternoon.
Highly amplified upper level trough and surface low pressure
reflection will push out of the northern Plains today and position
over portions of western Ontario and the upper Mississippi River
Valley by this evening. Despite some fairly wild oscillations
regarding this system in recent model runs, the guidance has
remained steadfast in the depictions for the upper level trough to
take on an extreme negative tilt here over the Great Lakes. The
tilting of the trough will turn sharply negative in response to an
upper level jet streak making the cyclonic turn an lifting
northward on the eastern flank of the trough and a stout PV maximum
or filament maintaining surprisingly very good cohesion within the
trough. Forcing for precipitation across southeastern Michigan will
come in the form of mature frontal dynamics and lower tropospheric -
div axis along the lead edge of meridional moisture transport. All
in all, the upper level synoptic scale dynamics with this system are
really not that great for southeastern Michigan. There is very poor
upper level jet support, what could be outstanding PV advection is
actually lagged off of the frontal forcing that gets shoved out
ahead of it.
The poor synoptic scale dynamics should be a major limiting factor
for the tonight and Monday morning period. High resolution guidance
is advertising a band of widespread showers and embedded
thunderstorms pushing inland into western Lower Michigan.
Thereafter, there is a strong consensus that shows convective
strength falling apart as it moves across the remainder of Lower
Michigan. Will keep thunder in the forecast due to some weak
instability - moist adiabatic lapse rates but confidence in
thunderstorms is very low. Timing for the band of showers is set
between 06-14Z beginning first across the Tri Cities. It will likely
take a some time before precipitation moves into the Detroit Metro as
the 4km Nam waits until 09-10z. Kept likely to categorical pops with
a short duration limiting QPF. No severe weather expected with
stable lower troposphere.
A decent westerly wind response is expected during the late morning
on Monday with a combination of increased postfrontal mixing and
increase lapse rates from diurnal heating. This diurnal heating will
be aided by a textbook dry slot that will be in place over Lower
Michigan for the late morning and afternoon. The data continues to
support a breezy mention with wind gusts of 30 mph supported.
A complete transition to a cutoff low is forecasted for Tuesday.
There is definitely uncertainty with exactly where the center of the
vertically stacked low pressure will be owing to the exact evolution
of the PV maximums. Expectations are low level diabatic
contributions will draw it either of Lake Superior, Lake Huron or
Lake Michigan. Latest solutions suggest a track from Lake Superior
to Lake Michigan, but this very well could flip again. With
pronounced cyclonic flow have gone away from modeled QPF and have
introduced a general chance pops for showers all areas from Monday
night through Wednesday. Persistent cloud cover and nil temperature
advections will limit the daily heating response to the 60s
certainly through midweek.
Southeast winds increasing to 10 to 20 knots today as high pressure
exits East. The strongest winds will focus over the northern half of
Lake Huron. Winds will increase further Tonight as the pressure
gradient strengthens in advance of an approaching cold front. Expect
wind gusts topping out around 30 knots over the open waters of Lake
Huron. Wind gusts over nearshore waters look to be reaching around
25 knots. This cold front will bring showers to the area late
Tonight into Monday morning. In its wake, strong southwest flow with
gusts approaching gale force over central Lake Huron tomorrow and
tomorrow evening. Strong southwest winds will persist on Tuesday, if
not increase slightly more, as much colder air filters into the
Central Great Lakes.
Low pressure lifting into Northwest Ontario Today will swing a cold
front through Lower Michigan Monday morning. Showers are likely late
Tonight into Monday, with rainfall totals of a quarter to half an
inch. The progressive nature of the front and lack of heavy rain
producing thunderstorms will be a limiting factor, thus no flooding
Lake Huron...Small Craft Advisory from 10 PM this evening to 10 PM EDT Tuesday
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
You can obtain your latest National Weather Service forecasts online