Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 280029
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
829 PM EDT Thu Jul 27 2017


.AVIATION...

Increasing high pressure has led to deep column subsidence in the
7.5 to 20 kft agl layer early this evening. Midlevel moisture progs
suggest this midlevel subsidence is significantly compromising the
structural integrity of the 700mb cold front. With the loss of this
frontal forcing and loss of daytime heating, the potential for any
stray showers has now ended. Question now becomes what sort of
potential exists for stratus development tonight in a low level cold
air advection regime. Models show some saturation potential in the
2.5 to 5.0 kft agl layer overnight, but with largely dry ambient
conditions at the near surface and no rainfall to speak of,
confidence is low for stratus development. Boundary layer gradient
flow will increase from the northeast late, which also dampens any
shot at fog. Interesting PV anomaly is shown to dig right across
Lower Michigan Friday which is almost always a cause for concern.
However, in this particular case, limitations on moisture will keep
a lid on ascent.


//DTW THRESHOLD PROBABILITIES...

* Low for cigs at 5kft after 09z Friday morning.

&&

.PREV DISCUSSION...
Issued at 310 PM EDT Thu Jul 27 2017

DISCUSSION...

Diurnal destabilization is allowing some convective redevelopment
across the area. As of 18Z, most of this is occuring along a remnant
mid level moist axis across the I-69 corridor. The mid level moist
axis will slowly sink south across the area late this afternoon and
evening, suggesting convective chances will decrease from north to
the south. Mid level lapse rates across the region are not terribly
steep. This and ongoing weak low level dry air advection will limit
the strength of any late day convection. High pressure anchored to
the northwest of the Great Lakes tonight will sustain northeast winds
across Se Mi. The rate of low level dry air advection will remain
weak. Model soundings suggest there will be enough remnant low level
moisture to actually support some late night stratus development over
portions of the area. Some lingering fog/low stratus over srn Lake
Huron is lending support to this idea.

The northeasterly gradient will strengthen across the ern Great
Lakes on Friday as high pressure builds in from the northwest and
sfc troughing holds across Lower Mi. The deepening daytime mixed
layer will lead to breezy conditions, especially downwind of Lake
Huron and Saginaw Bay. There is strong support from the 12Z model
suite in showing amplification of the mid level short wave impulse
now over nrn Minnesota into a compact upper low as it tracks across
Se Mi (15-21Z) on Friday. Although there will be ongoing dry air
advection, model soundings suggest there will be enough moisture to
generate weak to moderate instability as the mid level cold pool
(and associated steep mid level lapse rates) traverses Se Mi. These
factors will support a chance of showers/thunderstorms, with the
exception of the northern thumb which looks to remain displaced from
the colder mid level temps. Assuming instability will be able to
achieve deep convection, the degree of mid level dry air suggests
gusty winds and hail would be possible with the strongest storms.
Subsidence in the wake of this feature and building mid level
heights across the northern Great Lakes will allow the sfc high to
expand across Lower Mi on Saturday, with dry and relatively cool
conditions to start the weekend.

High pressure will remain stationary over the Great Lakes region for
the beginning of next week allowing for dry weather and clear skies.
A cold front will then pass through the area during the middle of
the week, bringing the next chance for showers and thunderstorms.
High temperatures will be in the low to mid-80s and low
temperatures in the 60s.

MARINE...

Moderate northeast flow will become fresh Friday into Friday night
as high pressure builds into the area. Persistent onshore fetch will
build significant wave heights up to five feet and maximum wave
heights near seven feet. Small craft advisories are in effect for
the duration of Friday. Saturday through the remainder of the
forecast period will feature moderate winds gradually backing and
diminishing as high pressure settles overhead.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 8 AM Friday to 4 AM EDT Saturday for
     LHZ421-422-441>443.

Lake St Clair...Small Craft Advisory from noon Friday to midnight EDT Friday night
     for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from noon Friday to 4 AM EDT Saturday for
     LEZ444.

&&

$$

AVIATION.....CB
DISCUSSION...SC/MV
MARINE.......JVC


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