Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 260353
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1153 PM EDT THU AUG 25 2016
Post frontal westerly flow will bring slightly cooler and less humid
air into SE Michigan during the night. The main effect of this will
be mitigation of fog and low clouds to support VFR through the
night and upcoming day. Some lingering high clouds will follow
the departing entrance region of the upper jet into the northern
Great Lakes before high based cumulus develops during afternoon
into Friday evening. Dry conditions will continue through Friday
night as high clouds thicken while weak surface high pressure
builds over the northern Great Lakes.
//DTW Threshold Probabilities...
Issued at 351 PM EDT Thu AUG 25 2016
We continue to monitor convective activity ongoing in advance of a
weak cold front that will sweep through SE MI through the afternoon.
The cold front now extends from Huron County, southwest through
Kalamazoo, and should pass southeast of Metro Detroit around 22-23Z.
Convection began early this afternoon along a differential heating
boundary laid out by morning MCV that worked across Saginaw Valley
and the Thumb. These storms struggled to achieve much depth as 40dbz
only reach 14kft. Still haven`t even got a single lightning strike
out of it as of 19Z. There remains enough instability ahead of the
cold front in the channel of deep moisture (PWATS are near 2 inches
with surface dewpoints around 70F) that activity should continue into
the early evening. There are no strong forcing mechanisms evident in
models or SPC mesoanalysis. There is weak low level fgen, weak
isentropic ascent around 300-305K, MLCAPE just north of 500j/kg, and
favorable lapse rates only up to about 800mb. Having said that,
there is just enough of several of the parameters in a very moist
(low LCL), moderate shear (bulk shear around 35-40 knots)
environment ahead of a cold front with ongoing convection to keep
the mention of strong storms possible through into the evening. The
continued surface heating southeast of the front will encourage
scattered convection through the duration of the frontal passage.
Main threat continues to be strong damaging wind gusts to 60 mph and
torrential rainfall. The low LCLs and small scale features inducing
backed flow at the surface will continue to warrant keeping the
mention of a brief weak tornado being possible. Would not be out of
the question to see low level rotation on radar in a low topped cell
with no thunder.
Once the front passes, high pressure will bring a drier airmass with
dewpoints down around 60F. This will limit the amount of nocturnal
cooling we`ll achieve the next few nights, even with clearing skies
tonight. Friday will be a dry day with the ridge tracking through
the central Great Lakes. We will not see too much relief in daytime
high temps as flow stays more westerly behind the weak front and
keeps the thermal profile moderated. Look for highs in the low 80s
Friday. The ridge then drifts eastward enough to allow the return of
southwesterly flow and warm air advection. The next trough should
set up far enough west over the Midwest on Saturday to prevent much
precipitation from trickling into SE MI during the day. Pops will
increase later that day and into the overnight as a warm front lifts
through southern MI and a few pieces of energy possibly eject out of
the trough with the entrance region of the jet just to our north.
Will continue chance pops for thunderstorms Saturday night.
On Sunday, a weakening lower-tropospheric front is progged to track
through Southeast Michigan. Despite a warm and relatively moist
atmosphere and likely some instability, lack of good forcing should
limit activity along the weak front, so have opted to undercut
blended PoPs slightly. Little to suggest much in the way of
organized precipitation early to mid-next week with weak surface
high pressure building in beneath quasi-zonal upper flow with
strongest flow remaining north of the international border.
Temperatures look to remain above normal to close out August.
Light to moderate NW wind will become firmly moderate as it veers to
the SE this weekend as a weak low lifts toward the straits.
Thunderstorms will be possible from the southern waters of Lake
Huron to the Michigan waters of Lake Erie this afternoon and then
again over northern Lake Huron late Saturday into Saturday night.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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