Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 281903
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
303 PM EDT WED SEP 28 2016
First major vorticity spoke has pivoted north to northwewt into
Southeast Lower Michigan around parent upper level low pressure
system now dropping gradually south through the Ohio Valley. Rain
shield associated with this wave has featured light to occasionally
moderate rain for the most part with isolated thunderstorms also
noted during the day along the northeast periphery of the main area
of rain where solar insolation from the southern tip of Lake Huron
on into Thumb region has led to a pocket of better instability.
While the higher resolation model solutions vary considerably in
the mesoscale details of the anticipated bands of moderate to
locally heavy rainfall, there is a strong consensus of maintaining a
rather persistent arc of rain from western Lake Erie/far southeast
lower Michigan northwestward through a bulk of the 1/2 to 2/3 of the
forecast area. Will increase precipitation chances into the 80-100
percent range along this axis of most persistent rain and taper off
from that, particularly over the northern forecast area. That said,
even locations from parts of the Saginaw Valley back to the Thumb
will have a good chance of showers along with a few thunderstorms,
especially into evening before daytime heating and instability
Forecast thinking has not changed much through the rest of the week
as the upper low settles south to Kentucky and the feed of moisture
back west to northwest into the area remains steady. In fact, as an
increasing levels of moisture from the Atlantic is drawn into the
area within this flow and precipitable water values climb to 1.50
inches or so, periods of rainfall should become more prolific from
tonight into Friday.
The most persistent rain will focuced roughly along/south of M-59
during this time frame, but a gradual expansion north through the
rest of the area should also occur as the overall abundance of
moisture expands. While not all locations will receive heavy
rainfall amounts, several inches of rain can be expected where
the this most persistent banding becomes established.
With the increase in moisture and a more or less persistent shield
of clouds over the area, temperatures will remain rather steady with
highs in the mid/upper 60s for the rest of the week and lows in the
Upper low projected to drift back northward across Lower Michigan
this weekend with unsettled weather continuing. Upper ridging builds
in early next week ahead of deep troughing over the western CONUS,
leaving Southeast Michigan dry with a modest warming trend into
Strong northeast winds will develop over the Central Great Lakes
tonight as high pressure settles in over Ontario and as low pressure
drops into the Ohio Valley and then Kentucky. This pattern will
remain fairly stagnant into Friday, providing a prolonged period of
northeast winds with sustained speeds in the 15 to 25 knot range.
The persistent northeast wind and large fetch over both Lake Huron
and Western Lake Erie will allow large waves to build from tonight
into Friday night. Small craft advisories remain in effect for all
marine areas into late Friday night due to large waves and gusty
winds. The area of low pressure will lift back northward into
Michigan late Friday night into Saturday. This will decrease the
surface pressure gradient and turn winds more to the east, allowing
wind speeds and wave heights to decrease overnight.
Moisture will meanwhile continue to wrap around the area of low
pressure into the weekend, providing numerous showers but only a low
chance for thunderstorms. The cool airmass will provide a chance for
waterspouts tonight and Thursday as the colder air resides over the
warm lake waters.
Issued at 228 PM EDT Wed SEP 28 2016
Moisture will continue to wrap around an area of low pressure as it
drops from south of Lake Michigan and into Indiana late today and
tonight. This will continue to steer moisture into Southeast
Michigan, generating periods of showers. Although showers will be
possible through the entire TAF period (and into the weekend for
that matter), a few periods of more organized activity are expected
and lead to higher confidence with timing SHRA and vis restrictions
in the TAFs. Band of precipitation currently stretched from northern
Ohio through central Michigan is expected to affect DTW through
about 21Z before lifting slightly northward. Drier air in the lower
levels is expected to keep prevailing ceilings at MVFR however. The
arrival of additional moisture and an upper level disturbance after
06Z tonight will lead to a rapid deterioration in conditions, with
ceilings and visibilities expected to fall to MVFR. Some
consideration will have to be given in future TAF packages on
whether to include a potentially lengthy period of IFR conditions
late tonight lasting through much of tomorrow.
For DTW...Larger band of rain should impact the terminal through
about 21Z before heavier rain lifts north. Showers will remain
possible through the remainder of the evening, and through the
entire TAF period, but will be harder to time. Additional moisture
will arrive tonight, bringing higher potential for rain and MVFR or
IFR conditions. While thunderstorms are also possible today and
tonight, the potential to impact DTW is low. East to southeast winds
will also prevail around 10 knots today but are expected to increase
tomorrow to between 15 and 20 knots.
//DTW Threshold Probabilities...
* Medium for ceiling at or below 5000 ft before 02Z. High after 02Z.
* Low for thunderstorms today and tonight.
Lake Huron...Small Craft Advisory from 10 PM this evening to midnight EDT Friday
night FOR LHZ421-422-441>443.
Lake St Clair...Small Craft Advisory from 8 AM Thursday to midnight EDT Friday
night FOR LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory from 8 AM Thursday to midnight EDT Friday
night FOR LEZ444.
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