Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211521

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1121 AM EDT WED SEP 21 2016

Forecast update center around the MCS tracking across mid MI this
morning on the lead edge of the 850mb moisture gradient. A
weakening trend has been evident in IR satellite over the last few
hours as cloud tops warmed pretty rapidly as it crossed Lake MI
around 12Z. As the system moves further east into an increasingly
less favorable environment with drier air and less instability,
the weakening trend will continue. As the MCS tracks further east,
it will become further removed by the parent surface low sitting
over the plains and the associated height falls over MN/WI/IA.
This separation is clearly visible in recent radar images over GRR
with upstream convection hold over, and to the west of, Lake MI.
Expectation from here on out is for the MCS to continue eastward
roughly along and north of I69. Convection should continue to wane
with the loss of instability but showers should persist to Lake
Huron. The tail of the convection along I96 is struggling but
looks like it may hold together long enough to give a quick shot
of rain for Livingston Co and possibly into Oakland. Any storm
that does occur may produce a wind gust to around 30 to 40 mph but
severe weather is not expected. Once this system works east by
early this afternoon, most of southeast MI should dry out through
the evening hours before next shortwave approaches for the
overnight period. Will be digging more into that potential moving


Issued at 554 AM EDT Wed SEP 21 2016


Lingering influences of slowly exiting high pressure will maintain a
dry lower level environment today.  This will ensure VFR conditions
through the daylight period, with plenty of clear sky within the
lowest 5000 ft.  High level cloud cover will increase as cirrus
debris works downstream of the convective complex now over eastern
Wisconsin.  This complex will continue to weaken while tracking
toward the east, but may provide a few light high based showers
around midday.  Advancing warm front will bring a low chance for
thunderstorm late today into tonight at FNT and MBS.  Confidence in
development and coverage remains too low to include a mention at
this time.

For DTW...Some increase in high cloud expected today, but skies will
remain clear within the lowest 5000 ft.  Any thunderstorm
development expected to remain north of the airspace.

//DTW Threshold Probabilities...

* None

Issued at 342 AM EDT Wed SEP 21 2016


Upper low dropping through the western U.S. and shortwave energy
lifting out ahead of it into the plains will allow a weak warm front
to lift across Lower Michigan today as large surface low pressure
organizes over the plains. Convective complex organized overnight
over Minnesota/Wisconsin along the leading edge of mid-level theta-e
advection and on the nose of a 30 kt low-level jet. MCV may be
generated from this system, which would then track into mid-Michigan
by this afternoon. For this morning, may see a few showers or light
sprinkles from activity as it moves westward but antecedent dry
conditions shown on 00Z DTX raob should help dissipate most of what
makes it into the eastern half of the state. Chances for showers and
thunderstorms will however increase by this afternoon and evening,
mainly north of the I-69 corridor, as any potential MCV works across
the area and as isentropic ascent and theta-e advection occur with
the front. Steeper mid-level lapse rates will also overspread the
area from the south and west to aid in convective initiation. ML Cape
around 1000 J/kg looks to be in place over the Saginaw Valley by the
afternoon, but weak wind field should mitigate a severe storm
threat. Expecting mostly some pulsy-type activity.

Small shortwaves, some with tropical origins, can be seen on water
vapor lined up through the Desert Southwest and Four Corners Region,
riding the northern periphery of large upper ridge centered over the
southern U.S. These waves should stream into Michigan late tonight
through Thursday night, guided by an upper trough passing through
Manitoba and Ontario as it pivots down around the Hudson Bay low.
This should trigger a wetter pattern over the Great Lakes, with much
of the activity expected to remain over the northern half of
Michigan where the frontal zone will stall, and where right entrance
region forcing will coincide with the nose of the low-level jet
tonight and Thursday. Forecast chances for precipitation have not
changed much over the past few days, with better chances still
remaining north of I-69, and only low pops south of there through
Thursday night.

The front will slowly drop through the area Friday into Friday night
as upper energy pivots through Ontario/Quebec and strong Canadian
high pressure builds into Ontario. The stabilizing influence of
upper ridging building in from the west should allow for less
coverage of convection as the front drops through Southeast
Michigan, with a decrease in instability also favoring showers over
thunderstorms. Timing of the front looks slightly faster in recent
model runs, and have cooled max temps on Friday several degrees. Now
expecting highs to range from the mid 60s over the thumb to the
upper 70s near the Ohio border. Upper portions of the front look to
remain over the area on Saturday. Cannot rule out a shower after the
onset of daytime heating, but 21.00Z soundings from the GFS look too
stable to warrant more than a 20 percent mention. Temperatures over
the weekend will be notably cooler for the first official weekend of
fall, with highs in the mid 60s to low 70s and crisp overnight lows
dipping into the 40s to low 50s.


A warm frontal boundary will setup across northern Lake Huron today
and tonight. Light southeast to southerly winds will exist south of
the boundary.  As low pressure track through the region, this
boundary will settle southward through the end of the week.  Winds
will shift to northeast and increase with the frontal passage.  This
boundary will be a focus for thunderstorms as it moves across the
region.  In addition, onshore flow may bring a period of higher
waves Friday into Friday night.


Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.



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