Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 191956
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
356 PM EDT TUE JUL 19 2016

.DISCUSSION...

The eastern edge of a large upper ridge centered over the central
CONUS will gradually expand into Michigan through the mid-week
period. We will have to remain mindful of occasional shortwaves that
ride the periphery of the ridge during this timeframe as they will
provide rounds of convection over the Upper Midwest and Great Lakes.
These rounds, while they may not impact us directly with rain and
thunderstorms, may provide debris clouds and impact temperatures.

Surface high pressure center over Michigan will shift east into
Ontario tonight but still remain the dominant player in our local
weather. Good radiational cooling conditions will set up under
clearing skies and light winds, providing one more cool night before
the heat and humidity start to build. Min temps are expected to run
in the 50s for most locations, with low 60s in the Detroit heat
island.

Surface high center will continue to shift east on Wednesday as an
upper shortwave riding the ridge periphery drops towards the area.
Most model solutions continue to keep this wave far enough to our
southwest to support a dry forecast Wednesday, but cloud debris
potentially spreading into Southeast Michigan from off convective
complexes to our south and west could shave a few degrees off
temperatures from what they would have otherwise been. Forecast
highs remain in the mid/upper 80s, which is pretty close to
guidance. Latest model trends are keeping energy/convection both to
our southwest and north (12Z NAM/GFS/GEM/EURO) for Wednesday night.
Dome of higher theta-e and instability will begin to wash into the
area late Wednesday, but it looks like there will be no trigger for
convection over Southeast Michigan.

Hot conditions look to ramp up on Thursday as the upper ridge builds
eastward and H500 heights rise above 590dm, but there will again be
concern for remnants of nearby convection to keep cloud debris over
the area. Latest forecast soundings keep a weak cap in place over
the area during the day. This would keep storms at bay and allow
heat to build, while increased southerly flow ahead of a trough
working across Canada advects higher dewpoints into the area. Kept
only low chances for tstorms starting in the late afternoon, and
raised temperatures closer to guidance near 90. Dewpoints in the 60s
would yield heat index values from the low to upper 90s. Thursday
night is starting to look like more interesting set-up for
thunderstorms as all models track an upper wave across Ontario.
Confidence in this wave is higher than the others as it breaks off
of upper energy already over the Pacific Northwest as opposed to
being convectively induced/enhanced. As the wave tracks to our
north, it is forecast to push a surface trough/wind shift down
through the area Thursday night. Models show a strong wind field in
place, and keep an axis of good instability and mid-level lapse rates
over us through the night as this boundary drops across. The concern
is for a convective complex to get going to our north where strong
jet dynamics will reside, and ride through Lower Michigan overnight
as it feeds on instability. For now will go with chance pops and
continue to watch the ever-evolving model solutions.

Guidance still points to hot temperatures continuing into the
weekend. 850/925 temps of low 20s/mid-upper 20s C respectively
support extended MOS guidance of highs in the low to mid-90s or
possibly a bit higher. Dewpoints solidly into the 70s F are also
likely given modeled southwesterly winds. Still there is potential
for convective activity to disrupt heating, as Michigan lies on the
periphery of the upper ridge and may be susceptible to ring-of-fire
MCS activity. Convection will likely have to contend with a cap, but
eastward advection of an EML will likely result in high instability
if anything can break through. Still fairly low confidence in
convective potential/timing, so POPs in the 20-40 range remain.
Frontal passage appears to be timed for late Sunday, with slightly
milder and drier conditions projected for Monday.

&&

.MARINE...

Winds will turn light southerly by Wednesday morning, becoming
moderate southwesterly on Friday. Episodes of thunderstorms will be
possible across the waters during this time...particularly Thursday
and Friday.

&&

.PREV DISCUSSION...
Issued at 1219 PM EDT Tue Jul 19 2016

AVIATION...

Areawide VFR through the period as high pressure transiting the
region causes winds to continually veer from westerly early this
morning to NE around 10 kts this aftn to light southerly by
Wednesday morning.

For DTW...Current obs and latest satellite increase confidence in
SCT-BKN cu coverage near 5kft this aftn. Loss of heating will allow
clearing tonight.

//DTW Threshold Probabilities...

* Medium for ceilings at or below 5000 ft today.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

DISCUSSION...HLO/DT
MARINE.......HLO
AVIATION.....JVC


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