Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
713 PM EDT sun Jul 5 2015
A few streamers of cirrus will be mixed with high altitude smoke
coverage tonight. This will be the only sky cover making it through
weak but expansive high pressure surface and aloft over the eastern
Great Lakes. Borderline MVFR haze restriction remains a concern
around sunrise as a persistence element of the resident air mass at
the surface. Light and variable wind will then increase slightly
from the southwest ahead of the next frontal system during Monday
under a mix of shallow cumulus and increasing mixed high clouds into
//Dtw threshold probabilities...
Previous discussion...issued 309 PM EDT sun Jul 5 2015
Low and middle level ridging fully encompassing Southeast Michigan this
afternoon...with the corresponding deep layer subsidence and
elevated mean thickness field maintaining a stable/cloud free sky
and supporting an uptick in surface temperatures. Despite the lack
of cloud...steady stream of smoke emanating from wildfires across
northwest Canada sustaining an extremely hazy middle level condition...
magnified by the lack of steering flow within the upper ridge dome.
Little variation in conditions heading into tonight...ridge axis
tending to ease eastward with time. This will sustain a light
southerly gradient into the early morning period...with a nudge
upward in low level moisture quality. This will effectively contain
low temperatures in the 60s areawide.
National WV imagery reveals well-defined trough anchored by a closed
circulation lifting from northern Manitoba to Hudson Bay this
afternoon. Southern extent is defined by consolidating shortwave
energy pivoting across Montana. Increasing southwesterly flow beneath remnant
dry air and subsidence will support another day of nearly cloudless
skies and temperatures warming into at least the middle 80s as 850 mb
temperatures rise into the middle teens. Some concern that, similar to today,
unexpectedly high albedo due to smoke will inhibit warming potential
a bit, but evolving deep layer SW cyclonic flow should help scour
out suspended aerosols through the day...though a decent coverage of
smoke may linger yet during the morning before ridge shifts further
east. No changes to middle/upper 80s for highs as guidance will
typically underperform under full sun. Overnight lows will remain
warm as southwesterly gradient persists and moisture advection in advance of
the front increases. Lows of 70 still look reasonable.
Model cross-sections indicate upstream front will enter lower
Michigan with healthy deep layer dynamics courtesy of the jet streak
over the northern Great Lakes. However, as dynamic forcing lifts
northeast, forcing will be gradually stripped away leaving Southeast
Michigan with a weakening front and subsequent diminishing trend in
of overall precipitation coverage. Further, late morning/early afternoon timing
will be unsupportive of severe potential, though modest middle-level
instability is still forecast to be sufficient to maintain a
coverage of showers/tstorms. Slightly better severe potential across
the far southeast where marginal MLCAPE < 1000 j/kg will exist
during later afternoon frontal passage. Progressive nature of the wave limits
any heavy rain/flooding concern despite very high precipitable waters approaching
2 inches. Inherited 60-70 probability of precipitation still appropriate.
12z consensus supports a dry day Wednesday in the wake of the cold
front...however the front is prognosticated to stall just south of the
border so it bears watching. Probability of precipitation return Wednesday night/Thursday for the south
portion of the region as models suggest a wave riding along the
front. Temperatures on Wednesday/Thursday start out below normal with a warming trend
thereafter as models hint at upper ridge expanding into the Great
Light wind will transition to a moderate southeast breeze Monday
into early Tuesday with warm stable flow limiting wind gusts. Winds
will veer to the northwest and become moderate to fresh...strongest
over Northern Lake Huron...in the wake of a passing cold front on
Tuesday. The front will bring a chance of thunderstorms to area
waters. Winds and waves will diminish Tuesday night as the surface
pressure gradient weakens.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
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