Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
113 PM EDT Tuesday Jul 28 2015
High pressure over the central Great Lakes will continue to provide
light winds and VFR conditions through Wednesday morning. An
approaching cold front will bring an increase in clouds around 6000
feet and southerly winds to 10 knots by about 15-16z Wednesday. Showers
and thunderstorms will be possible during the afternoon and evening
with the passage of the cold front.
//Dtw threshold probabilities...
* medium confidence in thunderstorms between 20z and 24z Wednesday.
Previous discussion...issued 352 am EDT Tuesday Jul 28 2015
Short term...today and tonight
Little change in the overall conditions for today...Southeast Michigan
firmly under the influence of upper ridging as this feature
progresses across the region. The deep layer subsidence and high
degree of sunshine will augment the elevated upper heights to again
support highs of upper 80s/around 90 degrees. It will feel a touch
more humid this afternoon...as dewpoints creep up into the lower and
middle 60s. This will translate into heat indices of lower 90s for
the late day period. Low temperatures will be that of persistence
under this pattern...readings mainly bottoming out in the middle and
upper 60s. Some increase in high cloud late tonight as middle level
moisture advection strengthens immediately downstream of the inbound
front that will be shifting into the Lake Michigan corridor by middle
Long term... Wednesday through next Monday
Forecast continues to be in good shape through the extended as
models seem to have a good handle on the large scale pattern with
minimal small scale features to try to resolve. Only minor
adjustments to the frontal timing on Wednesday as models have slowed
its forward progress for the second straight run.
Overall longwave pattern will undergo modification this week from
coastal troughs/central Continental U.S. Ridge...to a western ridge/eastern
trough. This occurs as the deep wave over the northern rockies
continues to flatten the amplified ridge while working its way east.
The expansive ridge over much of the southern/southeastern Continental U.S.
Will begin to slide west as the trough digs deeper later in the
week. The thermal trough will slide through behind the cold front
but will not affect temperatures all that much as flow remains
largely westerly keeping warm air advection out of the rebuilding ridge.
As for the cold front...still expecting a chance of showers and
thunderstorms across the area as it sweeps through Southeast Michigan in the
evening hours on Wednesday. Not entirely sold on coverage or
intensity of convection as there are several parameters going
against it such as the 250mb jet forcing located well north of the
state...weakening frontal forcing as the parent low lifts NE through
Ontario away from Southeast Michigan...warm air advection in the middle levels...and decent ll
lapse rates but not much to speak of in the middle levels. Conversely a
good ribbon of moisture in advance of the front with dewpoints
climbing to around 70f and model forecast precipitable waters in excess of 2
inches...MLCAPE looking to reach 1000 j/kg with the aide of peak
diurnal heating...and shear around 20-25 knots. So there is enough
to support a chance of thunderstorms with low end severe storms still
possible but not favored. Primary concern of any organized storm
would be strong winds and heavy rainfall. The hires suite will begin
to get a better hold of the front soon which will help with future
High pressure and dry air will quickly fill in behind the exiting
front Wednesday night...holding through the end of the week. Looks
like another stretch of normal Summer weather with temperatures in the 80s
and plenty of sunshine. Next opportunity for precipitation looks be the end
of the weekend as a shortwave dives toward the Great Lakes in the northwest
flow feeding into the trough.
Favorable marine conditions once again today as high pressure at the
surface remains in place. These light winds will increase slightly
out of the southwest on Wednesday ahead of an approaching cold front
on Wednesday. Those modestly strong winds will turn to the west for
Thursday behind the cold front.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).