Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
610 am EDT Monday Oct 20 2014
A steady increase in lower level moisture will result in a lowering
ceiling through the daylight period. Recent observations upstream
suggest conditions will remain in VFR as an initial round of light
showers exits the region. MVFR conditions most likely arrive
immediately in advance of and along a cold frontal passage middle-
late afternoon. Potential for ceilings to dip below 2000 feet
overnight as a period of deeper saturation commences. Pre-frontal
southwest winds will shift to northwesterly with the frontal
//Dtw threshold threats...
* low confidence in ceilings below 5000 feet this morning...high
confidence this afternoon.
Previous discussion...issued 353 am EDT Monday Oct 20 2014
Short term...today and tonight
The 00z kdtx radiosonde observation sounding showed a continued dry airmass...however
it was slowly moistening from the top down. This moistening will
continue during the early morning hours as 295k isentropic ascent
moistens up the remaining low levels of the atmosphere. Once this
occurs showers are expected to develop late this morning into the
early afternoon as a cold front pushes through with a decent middle
level shortwave embedded in a middle level trough tracking through the
central Great Lakes.
There appears to be a fairly decent response upstream with the
activity currently off to the north and west. With convective available potential energy of a few
hundred j/kg a few rumbles of thunder are not out of the question.
Given the upstream response and decent dynamics will continue with
the inherited high likely probability of precipitation across much of the area today.
Temperatures ahead of the cold front will get into the middle to
upper 50s today.
Behind the cold front light showers and drizzle will persist during
much of the overnight hours as abundant low level moisture maintains
a low stratus deck behind the cold front. Lows tonight will remain
in the middle 40s underneath the fairly solid overcast deck.
Long term... Tuesday through Sunday
Exiting upper wave anchoring the broader middle level trough
amplification will close off as it settles into the middle Atlantic
region through the middle week period. The extensive trailing moist
cyclonic flow will wash across Southeast Michigan on Tuesday. This
realignment in the pressure gradient will establish a firm
north-northeast flow...effectively placing the existing low level
thermal trough /-2c at 850 mb/ over the region throughout the day.
This environment will sustain an extensive stratocu field...and
likely support some degree of light shower production /particularly
early/. Temperatures will struggle to respond...high temperature
readings capped at around 50 degrees.
Existing 925 mb thermal troughing will be slow to release
eastward...suggesting a very slow clearing process /if at all/
Tuesday night as a favorable mean flow off Lake Huron reinforces the
a moist sub-inversion layer. This will put a lid on the degree of
nocturnal cooling...especially across eastern sections. Greatest
potential for clearing will be over the Tri-Cities. This will
translate into a broader spectrum of low temperatures...middle 30s west
to upper 30s/lower 40s east.
Deeper northerly flow will remain in place through Wednesday...the
region still within the extensive outer periphery of East Coast middle
level circulation. Middle level subsidence will be on the increase...
while a steady drying of the boundary layer commences under
expanding low level anticyclonic flow. This should yield at least
partial sunshine...but otherwise leave the existing airmass with
little reason to moderate more than several degrees relative to
highs on Tuesday /lower 50s/.
Dry/stable environment with the overall airmass making a more
noteworthy upward jump in temperatures starting Thursday as low and
middle level ridging take hold. Weakening shortwave working through
the elevated height field will shear through Thursday
night...providing the only possible wrinkle for the end of the
work week. Little forcing behind this axis to suggest anything
more than perhaps some increase in middle cloud and a few sprinkles
Thursday night/Friday morning. A period of stronger warm air
advection currently appears to center on the Friday and Friday
night period /in the wake of this wave/...850 mb temperatures
making a run toward the lower teens. This points to a brief warmup
into the first half of the weekend.
Modest southwest winds will exist today in advance of a cold front.
This front will result in some shower development through tonight.
Winds will veer to northeast as low pressure continues to move
toward the Atlantic coast and as high pressure builds across
northern Ontario. The combination of a stronger gradient and onshore
flow will bring a period of gusty wind and building waves throughout
central and Southern Lake Huron through Tuesday. The potential for
gusts around 30 knots looks solid with a lower probability for brief
gusts to gales early Tuesday. The colder air over the Warm Lake
water will yield strong instability but may also limit the potential
for gale force gusts by altering the pressure field and limiting the
gradient flow. No gale headlines are planned at this time... small
craft advisories will be issued for all nearshore waters of Lake
Huron including Saginaw Bay.
Small Craft Advisory...outer Saginaw Bay and the nearshore waters
from Port Austin to Harbor Beach...from 5 am Tuesday to 6 am
Small Craft Advisory...nearshore waters from Harbor Beach to Port
Huron...from 8 am Tuesday to 6 am Wednesday.
Small Craft Advisory...inner Saginaw Bay...from 8 am Tuesday to 10
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).