Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 091901
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
301 PM EDT Wed Aug 9 2017

.DISCUSSION...
Area still under the influence of departing high pressure sprawled
across the Ohio Valley. Slight increase in low level moisture from
yesterday is producing a bit more cu development this afternoon but
warm mid levels will keep a cap on any shower development. Skies
tonight for the most part will be mostly clear with just patches of
some mid and high level clouds, especially across the northern
portion. Weak warm air and moisture advection will keep lows more
seasonable in the upper 50s to around 60.

Thursday will start off fairly sunny with a bit more increase in
afternoon cu and an increase in mid and higher level clouds later in
the day ahead of approaching system. Light southerly flow will help
temps reach the low to mid 80s.

Thursday night and Friday a shortwave dropping out of the upper
Midwest will slowly move across the Great Lakes.  A weak surface low
will move slowly across northern Lower Michigan with an accompanying
weak cold front. A psuedo warm front will develop southeastward
across southeastern Michigan ahead of the low Thursday night. Weak
forcing along with weak theta-e advection may produce a few light
showers.

Friday will see a gradual increase in shower coverage along with
some thunderstorms from daytime heating combined with the very slow
moving surface front along with the mid level wave.  Highs around 80
combined with dewpoints in the mid 60s will yield around 1k joules
of cape but severe weather is not expected as lapse rates remain
weak along with the wind shear. Do not expect a lot of qpf but
activity will be slow moving so areas where any thunderstorms develop
could see up to a half inch or so.

Some shower activity may linger into early Friday night along the
eastern portion of the forecast area as system continues to slowly
exit east. After will see slow partial clearing as low level weak
gradient limits dry air advection. Any clearing could result in some
fog development.

The weekend will unfold with a broad upper level trough over eastern
Canada extending into the Great Lakes as part of a maturing omega
block over North America. The primary short wave, responsible for
the Friday low pressure system, is projected to be east of Lower
Michigan by Saturday and will allow weak high pressure to build into
the region. This will ensure dry conditions holding through Sunday
with temperatures dropping back into the mid 70s to around 80,
slightly below normal for early to mid August.

The large scale blocking pattern in the upper level flow will hold
through the first half of next week with good predictability. More
difficult to time short waves embedded in this pattern will provide
the source of forecast variability over the Great Lakes, which will
mainly affect precipitation coverage while temperatures hold around
normal. Solution spread on the smaller scale low pressure features
among the global models is primarily responsible for POP averaging
20 percent or less Monday through next Wednesday.

&&

.MARINE...

High pressure shifting from the Ohio Valley towards the East Coast
will keep quiet weather and fairly light winds over the Great Lakes
through tonight. Low pressure moving into the region will shift
winds to the south on Thursday, but speeds look to remain sustained
around 15 knots or less with gusts not much higher than that. The
low will slowly pull a cold front through the region late Thursday
through Friday, triggering scattered to numerous showers and
thunderstorms. Winds will turn to the northwest on the backside of
the system late Friday as dry weather moves back in, but sustained
speeds should stay at 15 knots or less.

&&

.PREV DISCUSSION...
Issued at 1258 PM EDT Wed Aug 9 2017

AVIATION...

VFR conditions are expected to prevail through the TAF period as
high pressure over the Ohio Valley shifts towards the East Coast.
Low-level moisture will support a modest SCT-BKN cue field this
afternoon before it dissipates with loss of daytime heating. Winds
will be fairly light and from the south-southwest. There is some
potential for the lake breeze to reach DET and DTW late this
afternoon, but westerly gradient will fight it and may keep it out
of DTW.

//DTW THRESHOLD PROBABILITIES...

* None.


&&

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

$$

DISCUSSION...DRC/BT
MARINE.......HLO
AVIATION.....HLO


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at www.weather.gov/detroit.



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