Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 241912
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
312 PM EDT WED AUG 24 2016
Decent MCV exiting Northern IL will track across far Southern Lower
MI through this evening. The hi-res models continue to have a robust
response to this feature, especially south of I 69. Will continue to
let the forecast work a few more hours despite radar trends and have
the likely POPs for the south half of the forecast region.
Thoughts on severe weather and flooding from earlier discussion
still largely on target. Severe threat, and even generic
thunderstorm threat is rather minimal. ML CAPEs were around 500 J/kg
with a 30kt low level jet feeding on the back side of the MCV. The
low level jet will also continue to advect some good moisture as
precipitable waters get to around 2 inches. While the storms should
continue to move to the northeast around 30 mph, the high water
content with the forcing on the back side of the MCV continuing to
feed the system could lead to a couple of rounds of showers and
storms with heavy rainfall for a few isolated locations, espcially
from Detroit on south. Subsidence behind this MCV will end most of
the shower and storm threat after about 02z until the next
convective system moves into the state from the west and southwest
around 12z Thursday.
The Thursday system is associated with a good shortwave and a
surface low riding along the cold front. Lower MI will be in the
right rear entrance region of a good jet over the northern Great
Lakes. 500 mb winds get up to 50 kts with 0-6 km shear from 30-40
kts. Question will be the amount of instability. Both the NAM and
GFS keep the best instability south of the border, but with that
type of forcing would just need to squeeze a little instability into
Southeast Michigan to have a decent threat of severe winds with the
storms. Enough forcing to have likely POPs for areas south of a OZW
to PHN line.
Drier air works into the forecast area from 21z to 03z Thursday
evening for a mostly clear night. That dry air holds in place for
Friday morning, but then a return in moisture will bring broken
cumulus and cirrus by the afternoon for partly sunny skies. The mid
and high level moisture continues to advect on good and deep
southwest flow Friday night into Saturday with plenty of cloud cover
expected. Saturday will stay dry as all of the instability and
forcing stays west of the forecast area.
Medium-range model consensus supports a deamplifying wave transiting
Lake Superior Saturday night. Best precip chances for now over the
Saginaw Valley closest to the best forcing/moisture advection. Weak
frontal boundary tracks through Sunday, but this will warrant only
low chance PoPs as there is little upper support. Dry forecast
favored for early next week with surface high attempting to build
into the Great Lakes. Above-normal temperatures are forecast Sunday
into early next week.
Moderate southerly flow in advance of a slowly approaching front
will be accompanied by showers an an occasional thunderstorm through
this evening. Another round of thunderstorms will sweep across the
southern waters on Thursday before winds veer to light to moderate
west northwest for the remainder of the week.
Issued at 1255 PM EDT Wed AUG 24 2016
700-500mb forcing has given rise to a narrow band of showers that
will approach the TAF sites at or shortly before valid time.
Additional development behind this line and an increase in weak
echoes warrants carrying TEMPO -SHRA through the early and mid
aftn hours. Encroaching cloud deck presents a forecast issue as
cigs will no doubt lower, but MVFR is slowly eroding with diurnal
heating. Prefer to reserve MVFR mention until arrival of deepest
moisture w/ rain this evening. MCV over NE Illinois will bring a
high probability of rain with embedded TS to the Detroit area this
evening. Environment in the wake of this wave will be favorable
for fog or some low stratus.
//DTW Threshold Probabilities...
* High for cig aob 5kft
* Medium for tstorms impacting KDTW airspace
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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