Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1223 am EDT Tuesday Apr 28 2015
Another feed of moisture advection from the northeast is leading to
some expanding cloud cover across portions of Southeast Michigan. The 00z DTX
sounding shows a very deep inversion based near 5500 feet...which is
causing this moisture advection to spread out into a scattered-broken cloud
deck based between 5k and 6k feet. The inversion is expected to lower
a little during the course of the morning under slight warming above
the inversion base. This will cause the cloud bases to settle into
the 4k to 5k feet range by daybreak. Indications in the available 00z
model data is for these clouds to sustain themselves under the
diurnal heating cycle and thus persist well into the afternoon.
For dtw...recent satellite data is showing the better feed of
moisture occurring northwest of metropolitan. It is becoming increasingly
uncertain whether or not a cloud deck based below 5000 feet will
expand into metropolitan prior to daybreak. In light of recent observations
and available 00z model data...a 4-5k feet ceiling will become more
likely at metropolitan once the diurnal heating cycle kicks in late this
//Dtw threshold probabilities...
* low in ceilings at or below 5000 feet this morning. Medium this
Previous discussion...issued 332 PM EDT Monday Apr 27 2015
Short term...this evening and tonight
Southeast Michigan still under the influence of expansive middle level
low pressure now centered off the New England coast. The effective
maintenance of a deep northerly flow within the western cyclonic
periphery providing yet another day of cool/cloudy conditions
locally. Strong diurnal component to the existing cloud
field...increasing subsidence and daytime mixing beginning to lift
and gradually scatter this deck now across the north. This process
will continue into this evening. Latest sounding data and relative humidity Fields
Point toward seeing at least partial clearing by evening...if not a
more agressive clearing trend...as diurnal enhancement fades. Cloud
trends into the overnight period less certain. There is the
potential for an additional period of low level moisture advection
to commence during the early morning hours as the flow veers
slightly to northeasterly...drawing in that higher moisture
Reservoir still residing over eastern Ontario/western Quebec. Will
hold the line with a partly cloudy mention for now...allowing
subsequent near term trends dictate further adjustment in sky
condition. Lows a touch warmer tonight...still largely in the middle
and upper 30s.
Long term...Tuesday through Sunday
A more comfortable stretch of Spring weather is expected Tuesday and
Wednesday with predominately dry conditions and moderating
Persistent stratocumulus should let up briefly at the start of the
period Tuesday with two good surges of subsidence and a fairly rapid
loss in deep cyclonic flow. This loss in low cloud should only be
temprorary as a good signal exists that low level residual moisture
will then Blossom into a fairly robust diurnal cumulus response. Highs on
Tuesday are expected to climb a couple of degrees above
60...although areas hugging the Lakeshore will be a few degrees
Muddy middle to upper level ridging and lack of flow in the column will
lead to persistence for Wednesday. The low levels are forecasted to
be marginally drier while there is some signal for some midlevel
moisture to pool over lower Michigan ahead of the next shortwave.
Still expecting some midcloud...but better low level lapse rates
should support highs in the middle 60s on Wednesday.
Model data is aggresive with an upper level energy/vorticity maximum
dropping straight southward into the Lake Michigan vicinity
Wednesday night and Thursday. The book hasnt been written yet on
specifics with models trending westerly with the quantitative precipitation forecast axis.
Regardless...fairly robust shortwave and inbound trajectory of air
parcels support an increasingly good potential for a cool down and
rain showers Wednesday night and Thursday. Bumped probability of precipitation upward from
the offered gridded guidance. Temperatures Thursday could struggle
to climb into the 50s...especially across the northern County Warning Area.
Rain chances continue through Thursday as a middle level disturbance
drifts southward across the Great Lakes. High pressure then quickly
builds into the region by Thursday night...bringing dry conditions
through Saturday morning. Beyond Saturday...models disagree on
timing of the next rain maker...with a couple models not even
showing any chance of rain for the weekend. For now...due to the
uncertainty...have only included slight chance probability of precipitation for the late
Saturday night through Sunday timeframe. A better chance for precipitation
arrives early next week as a cold front tracks across lower
Favorable marine conditions tomorrow as surface high pressure will
reside across the central Great Lakes...providing light winds and
low waves. Weakening high pressure will be replaced by weak surface
troughing late tomorrow/tomorrow night...but winds are still
expected to remain below 20 knots. However...winds will be
northerly...and there could be onshore component to support
slightly higher waves along the nearshore waters.
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).