Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 220715
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
315 AM EDT FRI JUL 22 2016

.DISCUSSION...

MCS over northern IL continues to propagate south and southwest away
from Lower MI. Despite most of the models not having a good
initialization of these feature, there is very good agreement with the
evolution of today over Lower MI. There is a surge of high theta-e
air that will take place mainly south of I-96 / I-69 corridor from
forecast time to 12z. Expect elevated showers and storms to
continue to develop early this morning and continue until about 12z
as they push south of the state and weaken as they move away from a
weakening nocturnal low level jet.

After this...not much to support additional storms to develop. There
is a dew point front that moves to about I-69 corridor by 00z this
evening. This front might have just enough convergence to kick off a
storm with 3000-4000 J/kg of ML CAPE.  Model soundings indicate a cap
to overcome and with little forcing, that may be difficult. If a
storm does go, not only does it have that CAPE but also 35 kts of 0-
6 km bulk shear.  Will continue the 20 to 30 pops for the south half
of the forecast area this afternoon and the SPC marginal risk looks
to be about right.

Continue to see warming at 850 mb and 925 mb today with temps
reaching 21C and up to 29C respectively.  This should allow the
temps to get into the mid 90s across the forecast area.  The caveat
is the clouds. Dense debris clouds were over the state early this
morning, along with any clouds that can develop with the showers and
storms along the theta-e surge this morning. Expect these all to
dissipate by 14z and that should be enough time to get some good
insolation. Dew points continue to rise early this morning and that
will continue into the morning with most locations getting into the
lower and mid 70s. That will allow heat indices to get into the mid
and upper 90s along and north of M-46 and above 100 south of that
line. The highest dew points will stay south of the previously
mentioned front over metro Detroit. There is certainly a decent shot
of getting to heat warning criteria with heat indices of 105 or
higher for three hours.  But this is also the area that will likely
have the most clouds and still need dew points to get to 75 which
might be at the top of the expected range. Will hold off at this time
and let any morning updates issue if necessary.

The drier and stable air takes over for tonight, Saturday and most
of Saturday night.  Not sure dew points will fall as low as the NAM
has, but somewhere around 60 to the lower 60s seems reasonable.
Still have the warm air at 925 and 850 mb for Saturday. This should
allow temperatures to warm nicely again especially with the dry air in
place. Mid 90s seem possible again for areas south and west of a
Midland to Flint to Detroit line. With those lower dew points, heat
indices only get into the mid 90s and may not need an advisory to
be extended into Saturday, especially since overnight lows will
fall into the 60s for most areas outside of metro Detroit.
There will be a temperature gradient to the northeast with north to
northeast winds off of Lake Huron for the Thumb region.

The next system moves in late Saturday night, Sunday and Sunday
night. This model run seems to be less stout with the wind field,
struggling to get to 30 knots of 0-6 km shear, and available
instability, maybe ML CAPEs of 1000 to 1500 J/kg.  There are good jet
dynamics for late July, a couple of shortwaves within the trough
structure and a cold frontal passage Sunday night. All that leads
to that SPC Marginal risk of severe weather.

Dry weather for Monday through Wednesday with temperatures slowly
cooling back to average.  Next chance of showers and storms will be
late next week.

&&

.MARINE...

A weak surface trough and cold front will drop southward through the
Central Great Lakes today and this evening. Thunderstorms will again
be possible in a continued warm and humid airmass as this occurs,
with greatest potential over Lake St Clair and Western Lake Erie.
Coverage today is expected to be less than yesterday, with only
scattered storms expected to develop. West to southwest winds today
will remain at or below 15 knots. High pressure will build in
overnight through Saturday night, bringing light winds and quieter
weather. Low pressure tracking across Ontario will push the next
cold front across the area on Sunday, bringing a good chance of
thunderstorms and an increase in southerly winds.

&&

.HYDROLOGY...

Shower and thunderstorm activity today will be much more scattered
in nature, and mainly occur south of the M-59 corridor. While
widespread heavy rainfall is not expected, locations that experience
a thunderstorm may see a quick accumulation of one-quarter of
an inch or more of rain.

The next chance of widespread thunderstorms will come Sunday and
Sunday night as a low pressure system and associated cold front
cross the region. Average rainfall looks to range between 0.25 and
0.5 inches, but isolated locations could see totals up to one inch.

&&

.PREV DISCUSSION...
Issued at 1157 PM EDT Thu Jul 21 2016

AVIATION...

A stray shower or thunderstorm remains possible during the night
into the morning hours. So far, radar is quiet over lower Michigan
and this will be monitored before adding any short term activity
into the TAF. Conditions will also be monitored for MVFR fog and
ceiling overnight through Friday morning. Widespread ground moisture
and recovering surface dewpoint will favor fog development toward
sunrise and there is loose evidence in model data for stratus
development along and ahead of the weak front settling through lower
Michigan. Should this develop, then it will follow a typical diurnal
upward trend through afternoon. This front will be weak but capable
of supporting a few thunderstorms by mid to late afternoon into
Friday evening, however timing and coverage still need refinement.

For DTW... VFR will be in place through late tonight with only
cirrostratus debris from the CHI area MCS. Confidence is moderate
for MVFR fog around sunrise through mid morning after earlier
rainfall and recovering humidity. There could also be some stratus
but southward extent from northern lower is in question at this
forecast issuance.

//DTW Threshold Probabilities...

* Low for ceiling 5000 ft or less during the morning. Moderate
  during afternoon.

* Low for thunderstorm potential during afternoon into Friday
  evening.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 10 PM EDT this evening FOR MIZ047>049-053>055-
     060>063-068>070-075-076-082-083.

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

$$

DISCUSSION...RBP
MARINE.......HLO
HYDROLOGY....HLO
AVIATION.....BT


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