Scientific Forecaster Discussion
fxus63 kdtx 170104
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
904 PM EDT Mon Sep 16 2019
The 00z DTX sounding features a deep inversion based near 800mb and
is relatively moist below the inversion base. The inversion will
lower through the night under ongoing mid level subsidence and subtle
cooling below the inversion base. There is already some stratus
streaming into portions of se mi off Southern Lake Huron underneath
the inversion, a trend that will likely persist into the overnight.
The gradient will also weaken during the night, especially across the
Saginaw Valley region. This weakening gradient along with current
sfc observations suggest that any areas that do not see stratus or
regions were stratus breaks apart will be conducive to fog formation.
So regions of fog and/or low stratus look likely tonight. The
current forecast looks reasonable attm.
issued at 653 PM EDT Mon Sep 16 2019
Remnant clouds have a distinct diurnal appearance to them, with the
exception of the clouds over Southern Lake Huron and The Thumb. So
the terminals will see continued clearing with the loss of daytime
heating this evening. Sfc dewpoints are hovering in the low to mid
60s and there will be a light northeast flow off Lake Huron tonight.
This degree of moisture will support the development of fog and or
stratus underneath a developing nocturnal inversion. The low level
wind fields will be weaker across the Tri Cities and Flint due to the
closer proximity to the center of sfc high pressure. This and a more
direct influence from the moisture flux off Lake Huron/Saginaw Bay
suggest a greater potential for fog development late tonight/early
tues morning at mbs and fnt. A little stronger easterly gradient
farther south suggests stratus will be more prevalent from ptk across
For dtw...the probabilities for fog and IFR/LIFR stratus is higher
in locations north of Metro. A little stronger gradient should favor
stratus development. Latest model soundings suggest cigs around or
just under 2000 ft. If however the gradient relaxes a little more
than expected, IFR or LIFR conditions will be more likely.
Dtw threshold probabilities...
* moderate in ceilings below 5000 ft overnight and Tuesday morning.
* Low in ceiling/visibility falling below 200ft and/or 1/2sm Tuesday
issued at 315 PM EDT Mon Sep 16 2019
Amplified upper level ridge over central North America slowly
building east will lead to an extended period of dry weather.
Morning fog/low stratus is about the only potential impactful
weather over the next several days.
Surface dew pts still in the 60s this afternoon, as mostly cloudy
skies today preventing this moist airmass from mixing out. 12z DTX
sounding indicated a higher based inversion at 760 mb. However, with
heights rising tonight and ridge axis sliding into the western Great
Lakes, subsidence inversion should push down well below 5000 feet,
and looking at fog and/or low stratus development tonight. Winds
will become very light, but may keep just enough of a North/East
component off Lake Huron to support low stratus (see regional gem).
However, the rap soundings and surface cpd's suggest more in the way
of dense fog, which was the case underneath the high over Wisconsin
this morning. As usual, the answer probably lies in between, and will
at least be adding areas of fog to the zones, along with maintaining
the higher sky grids for stratus. Probably take much of tomorrow
morning to increase mixing depths enough to dissipate the low clouds,
but airmass will be supportive of a warm day (80+ degrees
potential), as 850 mb temps reach 15 c. However, with surface flow
still out off the southeast, mixing depths likely coming up short of
850 mb level, and will keep maxes in the upper 70s.
The upper level ridge moves directly overhead of the central Great
Lakes on Wednesday, 587 dam at 500 mb/320 dam at 700 mb. 850 mb
temps increase to between 16-17 c, but still enough off a southeast
component not to fully reach this level, but around 80 (78-82)
degrees per mav/NAM/Euro MOS certainly looks doable.
Even warmer as we end the work week, as surface winds come around to
the south, and then southwest by first half of the weekend. The
strong upper wave/trough currently the West Coast will be moving off
to the northeast, tracking along the Manitoba/Ontario border on
Wednesday. Thus, tracking too far north to breakdown the upper level
ridge in place over Southern Lower Michigan, with the Summer-like
ridge center (590 dam at 500 mb) holding strong close to/just to the east
of the central Mississippi River valley. The ridge will slide east
over the weekend, with next chance of rain showers arriving on
Sunday with decent cold front tracking through (per 12z euro).
Weak instability axis with the front worthy of a slight chance of
thunderstorms. Cooler Post frontal airmass sending temps back to
normal values for Monday, lower 70s.
High pressure will drift across the northern Great Lakes through mid
week resulting in light winds and waves. Winds will veer from
northeasterly today to southeast by Tuesday. An approaching trough
will then bring a slight increase to southerly winds to around 20
Lake St Clair...none.
Michigan waters of Lake Erie...none.