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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
429 PM EDT Thursday Sep 3 2015

Short term...this afternoon and tonight

Regional reflectivity mosaic and satellite imagery trends support
the mesoscale convective system remnants are in the process of stalling out this afternoon
with a center of the circulation somewhere over the eastern County Warning Area. A
second pv anomaly now dropping southward across northern
Wisconsin...and afternoon/evening convection over Ontario/southern
Michigan will provide an additional stalling component to the
innocuous and very weak upper level forcing aloft. The main focus
for tonight is the overall potential for a long duration
thunderstorm and excessive rainfall event given the sluggish upper
level dynamics.

Focus for tstorm development the past couple of hours has occurred
over portions of central lower Michigan eastward into the Tri Cities
region. This thunderstorm activity has been firing along the
northern flank of a west to east 850-700mb Theta-E axis. The line
of thunderstorms and low level convergent streamlines (most specifically
the one over Midland and Saginaw counties) has been slow to sag
southward and has been providing additional heavy rainfall. Highest
measured rainfall amounts have been over the Tri Cities where a wide
band of 2 to 4 inches has fallen. The environment over southeastern
Michigan will remain conducive for heavy rainfall this afternoon and
tonight with weak 850-300mb mean flow and precipitable waters in excess of 1.8
inches. The favored corridor for additional thunderstorm will remain
within along this northern flank of the higher instability axis.
With the overall potential for both stalling and training of
convection remaining relatively high with the innocuous cva
forcing...a Flash Flood Watch has been issued for those counties
along and to the north of the I 69 corridor including Oakland and
Macomb counties. Uncertainty remains extremely high with the evening
and tonight forecast...with recent model performance very poor. The
most favored timing for excessive rainfall potential will be between

The low end risk for damaging windgusts is expected to persist
across southeastern Michigan through Sundown.


Long term...

Confidence is high that the upper circulation will remain over lower
Michigan during Friday but with lingering uncertainty on the
position of greatest shower and thunderstorm coverage. The state of
convection early Friday morning should be tied to deformation within
the upper circulation and within the middle level Theta-E ridge. The
12z synoptic scale models place these larger scale features over the
Saginaw Valley and thumb region with a reasonably positioned quantitative precipitation forecast maximum
on the north and east flank of the circulation. Expect coverage to
be on the scattered side coming off the diurnal heating minimum
although even weak elevated instability can overachieve in terms of
both coverage and intensity. Plan to allow short term trends to
guide the early part of the day and then focus likely probability of precipitation for the
afternoon with surface heating becomes more of a factor. Greatest
coverage then will be focused along and north of the surface trough
again positioned near the north of the I-69 corridor. Convective
Mode will remain multicellular within the weak wind profile with the
primary hazard remaining locally heavy rainfall due to slow storm
motion. Precipitation loaded downburst wind gusts will also be a concern
much like today but likely not with as much organization.

The tendency for development of nocturnal instability within the
upper circulation keeps chance probability of precipitation in the forecast Friday night
into Saturday. Expect the wave to dampen gradually with time...
especially Saturday...which will make placement problematic for
anything more than chance probability of precipitation before the system exits Saturday

The high pressure ridge to our east will persist through the
beginning of the work week. This will keep hot...humid days and
sticky nights over the County Warning Area through Monday and most of Tuesday. Middle
and upper level wave on Sunday afternoon will help Garner enough
instability to generate scattered rain showers and thunderstorms
during the afternoon/evening. Next front begins working its way
toward Southeast Michigan early Monday morning...bringing in widespread
showers and thunderstorms by Monday afternoon. Chances for showers
and thunderstorms will linger through the week. Once the slow moving
cold front pushes through the area Wednesday afternoon...high
temperatures should drop back near or slightly below normal.



Scattered to numerous showers and thunderstorms will be the main
concern for marine interests tonight into Saturday. This will be the
result of an upper level disturbance moving slowly over the area
before exiting into Canada by Saturday night. The corresponding
surface wind will remain light and variable before gradually
becoming more from the south during the weekend which will continue
to support warm and humid conditions through the Holiday weekend.


Aviation...issued 217 PM EDT Thursday Sep 3 2015

Deeper moisture axis and thermal advection support occurring on
the southeast forward flank of mesoscale convective system is leading to widespread rain
and thunderstorm activity this afternoon. Confidence is high in
continued activity for the next 3-6 hours with increasing
uncertainty for tonight. A stalling out of parent forcing aloft does
support the potential that shower and thunderstorms could affect
the area through much of tonight. High low level moisture content
and wet soil conditions supports fog development late.
Possibility exists for one or more terminals to drop into LIFR
during the early morning period...confidence too low yet to
include but will highlight with IFR visibility restrictions.

For dtw...greatest potential for thunderstorms centered within the
18z-00z window...uncertainty is high with regards to thunderstorm
potential 00-12z.

//Dtw threshold probabilities...

* medium for ceiling at or below 5kft this afternoon and evening

* high for thunderstorms this afternoon and evening


DTX watches/warnings/advisories...
Michigan...Flash Flood Watch until 4 am EDT Friday for miz047>049-053>055-

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


Short term...cumulonimbus

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