Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
330 PM EDT sun Oct 4 2015
Short term...this evening and tonight
Elongated deformation axis and associated moisture plume- connecting
a healthy wave over James Bay to the closed low ravaging the
Carolinas- is anchored over the Central Lakes region today. The
moisture rich ribbon aloft in concert with the cool near surface
airmass has served to maintain a strongly stable environment near
the surface...capable of trapping and holding ample moisture for
stratus production. Once last weak wavelet is expected to ripple
through the plume early tonight- responsible for the light showers
over far southwest lower Michigan. There appears to be enough
forcing to maintain a low chance for light showers and possibly some
drizzle across the Saginaw Bay region. The weak moisture convergence
will also be sufficient for nocturnal re-enforcement of the existing
stratus and possible light fog formation again tonight.
Winds will remain light easterly as surface high pressure settles
into the region. Temperatures will only drop a few degrees under low
overcast and a nearly saturated boundary layer.
Long term... Monday through Saturday
The evolution of the upper levels into the semblance of a broader
wavelength upper level ridge will be ongoing Monday over the eastern
and southeastern contiguous United States. However...not much change
with the sensible weather for southeastern Michigan as the interface
between the Pacific and Atlantic airmasses will be in place
overhead. This delineator will be the frontal boundary in place over
the northern County Warning Area at the start of the period. Kinematics to be
lacking over the Great Lakes region along with none advection
points solidly towards a persistance forecast. Net result...is
plenty of overcast with a slight/very low chance of a sprinkle or
light rain shower north of M 59...primarily during the morning
hours. Forecast soundings suggest a fairly significant weakening of
the frontal structure by midday or the early afternoon. Temperatures
are tricky...almost an all or nothing dependent on opacity of
clouds. Sided on the cooler side...by taking a couple of degrees off
of the MOS guidance with low 60s north to around 70 south. There is
some bust potential though...as the forecast could be too warm yet
for the northern County Warning Area and if clouds break across the south...could be
The persistence of surface high pressure will keep the weather quiet
again Tuesday and Tuesday night. Forecast sounding analysis
doesn/T point to alot of active subsidence in the
column...however...there appears to be a very good mix of
subsaturation for a deep layer along with high stability in the
midlevels. A return of some sunshine later on Tuesday should allow
temperatures to respond to near 70 degrees.
After a dry day on Wednesday...another shot of precipitation looks
to move back in by Thursday night. A low pressure system is
expected to move across the northern Great Lakes region Thursday
into Friday...pulling a cold front across Southeast Michigan overnight on
Thursday. Normal temperatures at the beginning of the week will slowly
cool off behind the front as northwest flow takes over on Friday
lasting through the weekend.
Prevailing easterlies will weaken further tonight as the area of
strong high pressure over eastern Canada pulls away and fades. A
light flow pattern will then take hold over the central Great Lakes
with a stalled frontal boundary overhead on Monday before organized
westerlies finally build back in Tuesday and Wednesday.
Aviation...issued 1244 PM EDT sun Oct 4 2015
Only modest gains in ceilings and visibility are yet to be attained
this afternoon as the stagnated deformation forcing over southern
Michigan continues to slowly drift northward. Scattered light
showers and areas of drizzle remain the compliment to the IFR
ceilings. The proximity of the orphaned moisture band over central
lower Michigan tonight will likely aid in the continued formation of
light fog and stratus with the most degraded conditions persisting
at mbs and fnt.
Resident high pressure will ensure winds will remain light through
the course of the forecast period.
For dtw...low ceilings are struggling to scour out from the
southeast and are only expected to slowly improve through the
balance of the day. Enough low-level moisture convergence should
remain to establish additional light fog and status formation
tonight. The restrictive ceilings will likely continue through much
//Dtw threshold probabilities...
* high confidence in ceiling at or below 5kft.
* Low confidence in visibilities below 3sm in fog/haze tonight.
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).