Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 270227

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1027 PM EDT FRI AUG 26 2016


Monitoring convection over Indiana and Illinois that is remnants
of surface based storms combined with developing elevated
activity, especially over Illinois. This is where low to mid level
flow is backing and strengthening the most to establish low level
jet quality moisture transport. Model indicated surface pressure
falls over Iowa should keep the strongest and deepest theta-e
advection focused west of Lake Michigan for much of the night, and
resulting convection moving mostly north. Plan to continue
monitoring weaker isentropic ascent over lower Michigan that could
also produce a few light showers overnight through Saturday
morning. Isolated/slight chance trending to scattered/chance is a
measured approach for now.


Issued at 703 PM EDT Fri AUG 26 2016


High pressure departing from the Great Lakes toward New England will
allow moisture to stream back into lower Michigan late tonight
through Saturday. This will result in mid level cloud development
over the terminal corridor that will also be under higher cirrus
debris from upstream convection. There is potential for the mid
level clouds to produce some light showers toward sunrise through
Saturday morning and this will be monitored for improved
observational and model evidence before inclusion in the forecast.
Should the morning showers materialize, conditions are still
expected to be VFR through Saturday afternoon outside of late day
thunderstorm prospects that could linger into Saturday evening.
Expectations remain for shower coverage to be greater FNT to MBS
while scattered thunderstorms will have a better chance to impact
locations from PTK southward.

For DTW... VFR above 5000 ft tonight will hold through Saturday
morning. Increased surface humidity Saturday afternoon will bring
cumulus bases to around 5000 ft along with a chance of thunderstorms
late in the day into Saturday evening.

//DTW Threshold Probabilities...

* Moderate for ceiling 5000 ft or less Saturday afternoon.

* Low for thunderstorms Saturday afternoon.

Issued at 347 PM EDT Fri AUG 26 2016


High clouds and convective debris originating from convection
embedded within strengthening moist SW flow aloft will continue to
stream across the area tonight. This will inhibit radiative cooling
despite high pressure at the surface and likely land lows solidly in
the 60s, which is in agreement with most 12z guidance.

National radar mosaic and water vapor imagery reveal a few different
foci of precipitation from the central plains into the Lower Ohio
Valley. Energy responsible for this activity will consolidate
tonight as the deepening trough over the northern Intermountain West
forces the SW flow corridor aloft to contract and strengthen
overnight. With assistance from a nocturnally enhanced low-level jet
and quasi-stationary strong right entrance region support over the
Upper MS Valley/Western Great Lakes, expect precipitation to
consolidate/expand and lift northeast, reaching the western Lower
Peninsula by early Saturday morning. The 12z WRF-ARW best
illustrates forecast thinking, though the guidance is all in general
agreement during the next 12-18 hours. Displacement of stronger
forcing to the west will limit the opportunity for early day precip
over most of the CWA. Caveat exists in the form of a potential
convectively enhanced wave emanating from this afternoon`s
convection blowing up near Memphis. General speed of the steering
flow suggests arrival coincident with tomorrow morning`s wave, and
it could feasibly support an eastward expansion of precip along a
weak low/mid-level warm frontal feature.

Veering flow at the surface on Saturday will be symptomatic of
departing high pressure and will support a steady rise in dewpoints
through the afternoon. Although general moisture advection may
support an isolated storm or two during the day, best chance appears
to be late evening into the overnight.

EC/4-km NAM/ARW indicate a similar scenario unfolding late Sat
evening into Sat night. Additional energy embedded within
consolidated SW flow aloft will arrive post-21z. This will also
apparently include a PV streamer, best illustrated on the 0.5 PVU
height plan view, originating in the circulation near Tallahassee at
1930z this afternoon and lifting across Detroit Metro around 00z.
This is only worth noting as multiple members of the NWP suite co-
locate late-day convection with this feature.

This is not to mention ongoing right entrance forcing through about
06z. Very moist environment characterized by PWATs pushing 2 inches
will be weakly capped and the probability of convection focused in
the 21-06z period appears to be increasing. Forecast bumped into
high chc category for SE third of CWA including Detroit Metro area.
Severe weather potential will be limited due to poor/moist adiabatic
lapse rates. However, sufficient shear will exist on the tail end of
peak heating to support loosely organized multicell type clusters
and the potential for an isolated wind gust to 60 mph.

Some question about convective potential on Sunday, given continued
potential for low amplitude forcing within a weakly capped/moist
environment. Forecast soundings still look well-capped, although a
trend toward an increasingly depressed height field is noted. Will
leave Sunday dry for now and allow at least one more model cycle
before considering introduction of pops.

Surface cold front will move through the area on Tuesday and
Wednesday. A fairly moist airmass ahead of the front will allow for
scattered showers and thunderstorms to develop over portions of
southeast Michigan. As the cold front passes through on Wednesday,
above average temperatures should drop to near normal for the
remainder of the period. On Friday, an upper level low is expected
to send another weather front through the Great Lakes region, which
will bring in more chances for showers and thunderstorms through the

High pressure will slide to the east by Saturday afternoon.  Light
and for the most part variable winds will continue over the lakes
through Saturday morning before becoming more southeasterly on the
return flow around the departing high pressure. A surface warm front
will develop Saturday across north-central lower Michigan producing
some shower and thunderstorm activity mainly across Saginaw Bay and
Lake Huron.  As the warm front lifts north Saturday night shower and
thunderstorm activity will shift east across all of the marine
areas. A weak cold front Sunday will bring winds back to a
northwesterly flow.  High pressure will then bring a light and
somewhat variable flow for early next week.



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




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