Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 141049
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
649 AM EDT Mon Aug 14 2017


.AVIATION...

The approach of an upper wave into the region today will sustain
periodic mid and high level clouds. Some degree of higher based VFR
afternoon cu is expected. The coverage will be limited by lingering
low level dry air associated with departing sfc high pressure. Light
south-southeast winds can be expected through the day, the speeds of
which will be limited by the overall weak sfc gradient

//DTW THRESHOLD PROBABILITIES...

* Low in ceilings below 5000 ft this afternoon. Moderate Tuesday
  morning.

* Low in thunderstorms Tuesday morning.

&&

.PREV DISCUSSION...
Issued at 338 AM EDT Mon Aug 14 2017

DISCUSSION...

Longwave trough will hold over the region through Tuesday with a few
weak impulses and fronts before a more notable southern stream
system targets SE MI Wednesday night and Thursday bringing the best
chance of precipitation.

For today, mid level moisture will continue to stream in off a
shortwave over the Midwest while it slowly drifts eastward. A second
wave diving south out of the Hudson Bay upper low will merge with
the first system as it traverses lower MI early Tuesday. Appears
that an elevated warm frontal surface will lift through early today
in advance of the developing surface low. Also, entrance region of
the upper level jet will be working over the area later today and
tonight. Most of the support will be focused over mid MI with
surface ridge trying to keep a grip over far SE MI. Looking at
current radar imagery we can see some elevated returns already, but
mostly over 10kft. This still shows the moisture is there and won`t
take too much to get a brief shower to develop. HIRES models showing
some instability developing with the diurnal cycle which should be
capable of initiating isolated to scattered coverage of showers.
Most of the activity will be over the Saginaw Valley but some
showers could stray southward. Thunderstorms will be possible with
the few hundred J/kg of CAPE being supported by the models and good
low level lapse rates.

The trough axis will swing through later tonight into Tuesday
morning. Moisture pooling and forcing along the trough axis will
support showers and thunderstorms working southeast through the area
from mid MI. Again, not the greatest setup but a jet streak and
trough axis with a ribbon of higher theta e air sweeping through
should be worth at least a chance pop.

High pressure will slide down from Canada Tuesday night while a mid
level ridge amplifies in advance of the aforementioned southern
stream wave. This will present a brief dry stretch before
precipitation moves back in advance of the next system. This system
will be very moist with models showing PWATs of 2 inches. Elevated
front will lift into the region late Wednesday on the nose of an
upper level jet streak. Low level jet will kick in overnight but may
stay to the west of the area supporting better coverage closer to
Lake MI. Showers and thunderstorms will continue through Thursday
with a cold front sweeping through Thursday night. Mid/upper level
trough will look to linger over the region as it has tended to do
this summer as the surface low lifts away from SE MI. High pressure
will try to build back over lower MI but there are hints of a
shortwave trying to work across the area at least in the GFS.
Upcoming weekend looks mostly dry, but will have to watch for any
shortwave activity through the trough.

MARINE...

Departing high pressure to the east will be replaced by a low
pressure system and frontal boundary moving into the area from the
west today and tonight. The gradient with these systems will be
quite weak, so overall winds will remain light and variable for the
next couple of days. Easterly winds will be on the increase Tues
night into Wed night as high pressure slides into the eastern Great
Lakes from northern Ontario and a deepening low pressure system and
associated warm front approaches from the west. This low is forecast
to move into western Lake Superior on Thursday, with the warm front
lifting across Lake Huron Thursday night. Strengthening south-
southeasterly winds ahead of this front will support rather rough
boating conditions on Thursday, with gusts likely topping 20 knots at
times. In addition, this system will bring a good chance for
thunderstorms to the region. The passage of this system Thurs night
will result in a veering of the winds to the west by Friday.

HYDROLOGY...

Tropical moisture and instability will be transported into Southeast
Michigan Wed night through Thursday along a northeast advancing warm
front. Widespread rainfall totals of a quarter to three quarters of
an inch are highly probable. Locally higher totals are expected in
thunderstorms considering the high level of moisture that will
be present over a considerable depth of the atmosphere.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....SC
DISCUSSION...DRK
MARINE.......SC
HYDROLOGY....SC


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