Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211940

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
340 PM EDT Wed Mar 21 2018


Closed geopotential height anomaly over the Ohio Valley and Mid-
Atlantic has maintained an influence on the wind field over the
Central Great Lakes today as north northeasterly flow of 20 to 25
knots has been commonplace. Trailing shortwave and jet energy into
the rear portions of the upper level low, resulted in a relatively
strong inverted trough back into portions of western Ohio earlier.
All forecast information supports this surface trough stripping out
this evening.

For tonight, low level dry air will become increasingly entrenched
across the region with sustained northeasterly flow in place. More
quiet weather. There is probably some question of high and mid cloud
potential for tonight with modeled RH showing a corridor of some
saturation advection west to east the latter half of the night.
However, integrity and transparency of ac/high cloud is very much in
doubt gauging from upstream cloud this afternoon.

Sustained northeasterly flow behind the large east coast low
pressure system will allow for deep column cold air advection over
southeastern Michigan on Thursday. Not necessarily colder near the
surface, but degree of cooling in the midlevels will support very
stable conditions. Differential height rises locally will support
some increased surface ridging over the state by late Thursday but
not enough to dissipate the northerly gradient flow. Generally
preferred MOS with a cooler blend given good amount of insolation.
Slowly evolving pattern over North America the latter half of the
week brings a virtual persistence forecast on Friday. Only real
question is how far the surface high will move eastward. With
dominant northern Canada surface high staying still, preference is
for below normal temperatures again on Friday.

Temperatures on the cool side remain through the weekend. Highs in
the 30s and lower 40s with overnight lows in the 20s. Strong high
pressure over Canada will continue to dominant the weather pattern
with northeast to easterly flow at the surface. A low pressure
system will move out of the plains and into the Ohio Valley on
Saturday, but current path keep the precip south of the Michigan
border. So things look to remain dry for the weekend with the high
pressure in control and a mid/upper level ridge passing over.

A long wave trough begins to set up across the western US next week
and will bring the next shot of precipitation to southeast Michigan.
Precipitation is forecast to arrive Tuesday afternoon. Temperatures
will also be on the increase to starting Monday and continuing
through midweek. High temperatures will begin to increase into the
50s for much of the area by midweek.



Moderate northeast winds will continue through the afternoon hours
as low pressure departs to the southeast. Gusts 25-30 knots will be
possible at times, especially across southern Lake Huron. These
winds will continue to lead to elevated waves and hazardous
conditions for small craft along the nearshore waters of Lake Huron
and outer Saginaw Bay into tonight. High pressure will begin to
build across the region from the upper Midwest tonight allowing for
the flow to slacken and back more to the north and northwest heading
into Thursday. Light to moderate northerly flow will continue into
Friday before veering to the northeast this weekend as low pressure
passes by to the south.


Issued at 125 PM EDT Wed Mar 21 2018


VFR flying conditions will prevail through the TAF period as high
pressure and upper-level ridging build into the region from the
upper Midwest. Cloud cover will mainly be in the form of lingering
mid and high clouds associated with departing low pressure to the
southeast, which should linger through much of the night. Cannot
rule out few to perhaps scattered pockets of stratocu developing
this afternoon with peak of daytime heating, with KMBS the only
threat at seeing possible MVFR deck of stratocu aided by moisture
off Saginaw Bay. Will continue to monitor trends for renewed
stratocu deck off Lake Huron tonight, but with flow more
north/northwesterly and amount of dry air working in, the threat
appears minimal at this time. Northeasterly winds will gradually
back more northerly heading into the evening hours, with gusts of 20-
25 knots. Winds back further to more of a northwesterly direction
and diminish overnight to less than 10 knots as high pressure builds
in. After 12z Thursday, SKC with light northwesterly winds around 10

For DTW...Main concern through the TAF period will be favored
northeast flow operations through 06z, with winds becoming more
favorable for southwest flow operations afterwards. N/NE winds
gradually back more N/NW with time, with gusts of 20-25 knots
possible through 03z before decreasing to around 10 knots the
remainder of the period. Mid and high clouds linger through much of
the night with SKC expected after 12z Thursday.


* None.


Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ422.

     Small Craft Advisory until 2 AM EDT Thursday for LHZ421-441>443.

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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