Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1001 am EDT Monday Aug 3 2015
Post frontal cold air advection will lead to deep mixing...strong ll lapse
rates... and a few hundred j/kg of SBCAPE this afternoon ahead of
an approaching middle level shortwave. The shortwave currently over
the Upper Peninsula will reach Southeast Michigan this afternoon during peak
heating. Though moisture parameters are not too impressive...precipitable waters
just under an inch...the aforementioned instability should be
enough to spark a few showers/thunderstorms across the area.
Latest hires models all concur and advertise spotty coverage
across southern Michigan. Main update was to add isolated
showers/thunderstorms across the area this afternoon and into this
Aviation...issued 558 am EDT Monday Aug 3 2015
The onset of low level cold air advection acting upon residual
moisture has led to the development of IFR/MVFR stratus over much of
southeastern Michigan. Transient nature in the coverage and shallow
depth forecasted in model data supports a rapid lifting trend with
growth of boundary layer. Clouds are then forecasted to lift today
before mixing out by this evening. Tight gradient within cyclonic
flow will support west winds ranging between 10 and 20 knots.
//Dtw threshold probabilities...
* high for ceilings below 5000 feet above ground level this morning.
Previous discussion...issued 406 am EDT Monday Aug 3 2015
Short term...today and tonight
Deep cyclonic flow is overspreading southeastern Michigan this
morning as a closed low height anomaly quickly amplifies over much
of eastern Canada. Nwp and satellite imagery supports a lack of any
significant shortwave energy or cyclonic vorticity advection for
today underpinning what will be a lack of synoptic scale forcing for
ascent. Rather overall dynamics appear to be governed by isentropic
downglide. An exception for a completely dry forecast will be over
portions of northern lower...Northern Lake Huron...and down into the
northern thumb where a low chance of a showers will exist. A steep
lapse rate 800-700mb layer is forecasted to stream into these areas
during the late afternoon and evening hours. Modest deformation and
fgen forcing will be possible ahead of low to midlevel temperature
gradient with the shallow nature of the high based instability
limiting the overall potential. Daytime temperatures will range in
the upper 70s over much of the area with some sneaky low to possibly
middle 80 degree readings for the higher surface pressure areas/heat
island south and east of the terrain.
Very large upper level low/circulation encompassing central/eastern
Canada early this week. Several upper level disturbances pinwheeling
around the circulation. One such upper wave descending from western
Hudson Bay early this morning is expected to swing through the
northern Great Lakes on Tuesday...tightening up the 500 mb
temperature gradient across the central Great Lakes. However...with
drier low level air (surface dew points in the 50s) in place...lifted indice's
look to remain positive. However...good 850-700 mb lapse rates should
support a substantial cumulus up during the day with convective available potential energy around 100 j/kg
and will maintain low chance probability of precipitation across the north for light
showers...especially across the northern thumb region...where added
moisture boost from Saginaw Bay may come into play. 850 mb temperatures
ranging from upper single numbers north to lower teens near the Ohio
border...translating to highs in the middle 70s to around 80 degrees.
Continued modest cooling Wednesday and Thursday as high pressure
building over lower Michigan promotes less daytime
mixing...resulting in highs in the 70s. Favorable radiating nights
translating to mins in the 50s. Will have to watch upper wave
coming out of The Four Corners region...as 00z Euro tracks the 500
mb trough through the Ohio Valley during Thursday...and it is
possible a few showers could sneak to the southern Michigan border
or just north....depending on strength and exact location of this
middle level circulation.
Cold front has cleared the central Great Lakes this morning...and
looking at west to northwest winds of 10 to 20 knots through the
day. All small crafts advisories have been allowed to expire. A
secondary front and cooler air arriving for Tuesday will increase
winds over Northern Lake Huron into the 20 to 25 knot range
however...slowly decreasing as we head into Wednesday. High pressure
in control for Thursday will then provide and light and variable
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).