Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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280
FXUS63 KDTX 181627
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1227 PM EDT Fri Aug 18 2017


.AVIATION...

Ceilings will vary bkn-sct 3-5kft through the afternoon. Tight low
level gradient will produce a moderate westerly flow with mechanical
mixing bringing wind gusts up to 25kts. clouds and wind will
dissipate/decrease towards sunset leading to vfr conditions for most
of the night. Another disturbance and frontal boundary will move
through the area 09-15z bringing mainly a mid level cloud deck across
the north and more towards low end vfr south. Deeper moisture south
will bring a small chance for some light shower activity south so
included a prob30 there. There may also be a brief dip to mvfr with
any shower. Winds will lighten up tonight and continue into Saturday
from a westerly component.


For DTW...moderate and gusty westerly wind along with 3-5kft
ceilings bkn-sct will decrease/dissipate towards sunset. Vfr
conditions over night.  There may be enough instability this
afternoon yet to produce a brief light shower/sprinkle but not
significant enough to include in taf.   Increasing low vfr ceiling
starting around 09z Sat as another mid level wave and surface front
swing though 09-15z.  There maybe enough moisture and lift to
produce a few light showers so included a prob30. Any shower
Saturday morning could produce a brief mvfr ceiling.  Winds will
remain light westerly through Saturday.

//DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5kft

* Low for reaching crosswind threshold from 270-280 degrees roughly
  19-22z.

&&

.PREV DISCUSSION...
Issued at 343 AM EDT Fri Aug 18 2017

DISCUSSION...

Low pressure centered over eastern Lake Superior is sweeping a cold
front through Lower Michigan during the early morning. The front and
associated clusters of showers will be east of the region shortly
after sunrise leaving cloudy but dry conditions in place across SE
Michigan during the remainder of the morning. The passage of the
front will bring cooler and less humid air into the region as
surface dewpoint settles into the 60-65 degree range compared to
lower 70s yesterday. Most of the postfrontal low level cold
advection will be complete by late morning which, along with
lingering cyclonic low level flow, will support broad coverage of
stratus/stratocu into early afternoon. Decreasing clouds mid to late
afternoon is expected to occur first in the Detroit area as the low
level thermal trough follows the low pressure center to the north
and east. Highs around 80 will then be possible with a late boost of
sun while readings linger in the mid 70s for the Tri Cities and
northern Thumb. The gradient trailing the low pressure system will
also support breezy conditions with gusts approaching 30 mph as
boundary layer mixing builds through the day.

The decreasing cloud trend will continue into the evening but will
be short lived as the next upper wave approaches from the Midwest.
This system is observed over the Plains states this morning and
appears plenty strong enough to support model solutions that
indicate the wave sharpening as it enters the long wave trough over
the Great Lakes tonight. The surface pressure reflection is shown to
be weak and well south of the Ohio border compared to the upper
level features. The farther south position looks Ok but the surface
wave could end up deeper as it interacts with the remnant baroclinic
zone in the Ohio Valley. Backed and slightly stronger low level flow
will then begin northward moisture transport that will be greatest
closer to the surface wave. This is where convective potential will
be better while higher based theta-e advection spreads clouds over
Lower Michigan with a chance of showers after midnight through
Saturday morning.

The upper level short wave exiting Saturday morning will propel the
long wave trough axis into the eastern Great Lakes Saturday
afternoon. Subsident northwest flow aloft and building surface high
pressure will produce dry conditions Saturday night through Sunday.
This will be part of a quick transition into a more zonal large
scale upper air configuration heading into next week. Expect
temperatures to return well into the mid and upper 80s by Monday as
surface high pressure shifts toward the Atlantic coast. Global model
solutions then project the next wave aloft already developing over
the Great Lakes by Tuesday. The low pressure system and associated
front will bring the greatest probability of rain Tuesday into
Tuesday night followed by a modest cooling trend for the second half
of next week.

MARINE...

A fresh southwest breeze is developing over the waters this morning
as cooler air moves into the area. Cold air in the wake of the cold
front is boosting the over-lake instability profile and will support
wind gusts around 25 knots. Elevated wind gusts to 30 knots are
possible in as the flow funnels through Saginaw Bay. Maximum wave
heights around 7 feet are likely in outer Saginaw Bay and the tip of
the Thumb. Otherwise the offshore fetch will contain the highest
waves to central and northern Lake Huron. Wind and waves will then
decrease over the weekend as high pressure builds into the Great
Lakes region.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 8 PM EDT this evening for MIZ049.

Lake Huron...Small Craft Advisory until 8 PM EDT this evening for LHZ421-422-
     441>443.

Lake St Clair...Small Craft Advisory until 8 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 8 PM EDT this evening for LEZ444.

&&

$$

AVIATION.....DRC
DISCUSSION...BT
MARINE.......JVC


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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