Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
302 am EDT sun Aug 30 2015
Short term... today and tonight
Moist airmass in place over Southeast Michigan early this
morning...as 00z DTX sounding revealed a 700 mb dew pt of 4
c...850 mb dew pt of 12 c...along with a precipitable water value of 1.6 inches.
Sheared out shortwave/pv will slowly be exiting the central Great
Lakes...but last vestige of 850-700 mb Theta-E axis still prove
sufficient for isolated-scattered light showers this morning before
drier air attempts to slowly filter into Southern Lower Michigan
through the day...but uncertain we will be able to scour out the low
level moisture...as 00z NAM maintains higher relative humidity values in the 925-
850 mb layer. With 500 mb temperatures falling up to 2 c degrees...surface
based instability/cape is prognosticated to rise to around 750 j/g...per
00z GFS...but 1000-2000 j/kg per 00z NAM...as surface dew points remain
solidly in the 60s. However...700 mb temperatures will be rising to around
9 c north of I-69...which should ultimately provide a sufficient
cap. South of I-69 is where cooler middle levels persist longer and
where a slight/low chance of showers/thunderstorms will be carried
for the afternoon hours. Minimal concerns for severe weather with
weak wind fields...if in fact a cell is even able to go up.
Based on pesky clouds expected today...will hold maxes around 80
degrees...but potential for warmer temperatures is there with 850 mb temperatures
of 16 c. Low level moisture/elevated dew points holding in the lower
60s tonight should set the stage for some fog as skies become mainly
clear with light/calm winds in place.
Long term...Monday through Saturday
Southern Plains upper ridge will undergo steady downstream
amplification over the next 48 hours...in response to substantial
height falls working into the western Continental U.S.. this process will
effectively center an upper level anticyclone over Southeast Michigan by
Monday. A high degree of stability under the attendant minimum in
Theta-E and an elevated middle level temperature profile will yield
plenty of sunshine...and no real opportunity for convective
development. The increase in thicknesses and generally light
southwest flow will provide a noted uptick in temperatures relative
to today...with daytime readings reaching the middle 80s.
Upper ridging to remain the primary governing feature through the
remainder of the upcoming work week. This will translate into a
relatively benign stretch of weather conditions...with above normal
warmth and limited /if any/ potential for convection. The ridge
axis may lose some definition by midweek as a weak height fall
center drifts through the Ohio Valley...with a corresponding gradual
increase in Theta-E during this time. Plausible scenario that weak
cva working through along the north end of this feature provides a
localized/brief window for ascent...medium range guidance still
centering on Wednesday. Low end potential at this stage given an
otherwise lackluster looking forcing/wind field.
Benign marine weather will continue across the Great Lakes region
through much of the upcoming week. A strong ridge of upper level
high pressure will maintain light flow and a general southwest wind
Aviation...issued 1144 PM EDT Sat Aug 29 2015
Conditions still expected to steadily deteriorate through tonight
into early Sunday morning by which time all locations will be low
MVFR at best with a good coverage of IFR expected northwest of Detroit
metropolitan. Lowest ceilings/visibilities will be found along the surface low track
in vicinity of kmbs/kfnt where conditions will take longer to recover during
the morning. By late morning, concerted trend toward MVFR lifting to
VFR ceiling should be underway. Winds will remain light through the
For dtw...conditions will improve most quickly in the Detroit area
further from the low and where moisture quality is slightly less.
Confidence in IFR ceiling is not high here...but should one develop,
would expect improvement to MVFR before noon.
//Dtw threshold probabilities...
* high for ceiling at or below 5kft after 08z.
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).