Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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367
FXUS63 KDTX 211001
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
601 AM EDT Sun May 21 2017


.AVIATION...

Chaotic skies in the wake of overnight convection. CIGS range from
400ft to 6000ft across lower MI but models and trends suggest
IFR/MVFR CIGS will spread across the whole area this morning for
several hours as moisture is locked under the sinking inversion. A
few scattered showers will likely be present through the first half
of the day but coverage will be low enough to leave out of this
forecast. A cold front will pass through SE MI this afternoon
bringing a renewed chance of thunderstorms. Window of opportunity
will be around 18-22Z though any one location will more likely see 1-
2 hours of activity. CIGS will rise in the wake of the front but
cold advection will ensure stratus lingers through the remainder of
the forecast. Winds will shift from SE to SW behind the cold front.

For DTW...Low clouds, most likely MVFR, will plague the area through
the morning.  A cold front will bring a chance of thunderstorms
between about 18-21Z this afternoon.


//DTW THRESHOLD PROBABILITIES...

* High for ceiling aob 5000 feet through this afternoon. Medium
  tonight.

* Low for thunderstorms between 18-21Z this afternoon.

&&

.PREV DISCUSSION...
Issued at 350 AM EDT Sun May 21 2017

DISCUSSION...

Southeast Michigan currently lodged within the deep mid level
southwest flow along the outer periphery of the pending height falls
emanating from closed mid level circulation now lifting into
Minnesota.  This favorable positioning yielding a solid waa/moisture
advection driven region of rain/elevated thunder early this morning,
the overall process backed by sustained convergence/ascent across
the existing warm frontal slope.  Surface warm front still anchored
well south, mitigating a risk for this activity to become surface
based going forward this morning.  Heavy rainfall the only concern
given the existing high pwat environment.

Brief subsidence in the wake of this activity may a leave a lull by
late morning/early afternoon.  This will allow for some air mass
recovery in advance of the inbound cold front, now forecast to sweep
west to east mid-late afternoon. The degree of potential
destabilization still carries some uncertainty, particularly given
the muddled picture this morning. There will be an infusion of a
higher near surface dewpoints with time /upper 50s -lower 60s/ as low
level flow briefly veers to southerly. A period of partial sunshine
immediately in advance of the front will certainly help the cause,
with model consensus pointing to afternoon temperatures lifting into
the lower and middle 70s. Given the expected timeline, enough of a
window seemingly exists to generate a weakly unstable pre-frontal
profile, particularly with eastward extent. This will favor the
development of a broken linear coverage of convection at the cold
frontal interface mid-late afternoon. Given the likely brevity of
this activity for any one location /less than 30 minutes/, will
maintain simply a chance mention. Severe risk limited by a lack of
greater lapse rates and generally modest instability overall, but
worth acknowledging roughly 40 knots of bulk shear will exist during
this time. This may prove sufficient in organizing a few robust
updrafts during peak heating, should the instability ultimately
materialize as currently projected.

Steady deep layer post-frontal drying commences tonight, with an
accompanying weaker component of cold air advection.  This will
leave a relatively dry and stable profile to begin the work week,
with the local area just outside the influence of a lead shortwave
rotating through the broader cyclonic flow of the closed low parked
over northern MN. An increase in the gradient in response to this
system translating through the upper peninsula will result in breezy
conditions. Otherwise, rather seasonable looking day with
temperatures just a shade below normal.

Conditions look more unsettled during the Tue-Wed periods, as the
closed low fractures with a sizable piece of this energy then
digging southeast into the region.  Reasonable model consensus in
the pattern evolution, but with differences in timing/details yet to
resolve.  A general increase in cva should lead to periodic showers,
with some renewed moisture advection and increasing mid level lapse
rates also yielding weak instability and the possibility of embedded
thunder /particularly Tuesday/.  Temperature trends remain somewhat
flat, with any advective process largely holding neutral.  This will
retain a temperature profile is simply defined as seasonable for
late May.

MARINE...

Waves remain excited across Lake Huron with southeast flow in the 20
to 25 knot range. This direction keeps the bulk of the waves off
shore, but waves in the 3 to 5 foot range continue to clip a couple
nearshore zones along the Thumb thus small crafts will be issued
through this afternoon. A cold front then sweeps through the region
this evening bringing an abrupt wind shift to the southwest. This
may necessitate additional small craft advisories for Saginaw Bay
and/or the nearshore zones of Lake Huron as winds approach criteria.
Unsettled weather will remain over the region through midweek as
general troughing remains overhead with possible low pressure
systems developing within it.

HYDROLOGY...

Showers will taper off through the morning hours but additional
showers and thunderstorms will be possible this afternoon as a cold
front sweeps across the area. Rainfall amounts around a quarter inch
can be expected this afternoon, with higher amounts possible for
those locations impacted by thunderstorms.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ441-442.

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

$$

AVIATION.....DRK
DISCUSSION...MR
MARINE.......DRK
HYDROLOGY....DRK


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at www.weather.gov/detroit.



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