Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
628 am EDT Sat Aug 1 2015
West winds will gust to 20 kts by late this morning and will subside
this evening with the loss of diurnal heating. Winds will then back
to the southwest overnight. VFR through the period.
//Dtw threshold probabilities...
Previous discussion...issued 318 am EDT Sat Aug 1 2015
Short term...today and tonight
Modified persistence forecast today as a weak h4 pv anomaly embedded
within cyclonic northwest flow rotates through the area during peak
heating. Lower moisture quality compared to yesterday will limit
prospects for shower coverage, but once again expect best forcing
and lapse rates across The Thumb. Isolated showers, perhaps a clap
or two of thunder, along with another afternoon cumulus up are in store
with greatest coverage of clouds across the north. Slightly cooler
column noted as cooling takes place in the wake of yesterday's
shortwave. 850 mb temperatures around 11-12c at 12z this morning will support
highs topping out near 80 degrees. Diminished gradient will support
westerly afternoon gusts topping out at only 15-20 kts. Limited cooling
potential once again tonight as heights rebound with the passage of
embedded shortwave ridge and light warm advection persists through
the overnight period. Cirrus debris from any convection that
develops upstream this evening will spread into the area by sunrise.
No complaints with 00z guidance offering lows around 60.
The forecast for the second half of the weekend will be influenced
by the upper level energy/wave coming out of the Pacific
northwest...which tracks through the Midwest tonight and through the
Ohio Valley during Sunday. How much moisture will this wave
take/displace to our south and east? And how much Post wave
subsidence will linger...as northern stream upper level trough digs
southeast from central Canada and main cold front moves through
early Monday morning. Good dynamics Sunday evening/night...along
with favorable low level fgen/convergence should support showers and
thunderstorms...even if that lead wave robs much of the
moisture...and still OK forecasting likely probability of precipitation for Sunday
evening/night. 00z NAM indicating surface dew points approaching 70
degrees...which is probably a bit of a stretch...but middle/upper 60s
would still yield convective available potential energy around 1500 j/kg...which could support a few
severe storms with the strong wind fields and steep middle level lapse
rates advertised (7+ c/km between 700-500 mb). Day 2 out of Storm Prediction Center
indicating a slight chance for the majority of Southeast Michigan.
Very large upper level low centered over northern Ontario early next
week...allowing for cooler temperatures over the Great Lakes region
as 850 mb temperatures fall into the upper single numbers by Wednesday.
Spokes of energy/upper level disturbances rotating around the
periphery could trigger isolated/scattered convection...but
uncertainty on timing and exact position of these features.
Westerly winds today are expected to be a bit lighter compared to
yesterday...with stronger winds forecasted to peak out around 20
knots. An approaching cold front will strengthen the southwest
gradient on Sunday however...with gusts around 25 knots likely over
the nearshore waters. The cold front will likely trigger strong to
severe thunderstorms Sunday evening and night before slipping south
through the central Great Lakes Monday morning. Post frontal
northwest flow over Northern Lake Huron looks to be in the 20 to 25
knot range Monday afternoon and Monday night before decreasing
slightly as we head into Tuesday.
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).