Scientific Forecaster Discussion
fxus63 kdtx 141713
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1213 PM EST Thu Nov 14 2019
Ongoing mid level subsidence has forced some lowering of the stratus
deck that has been advancing into se mi from the west. This trend
will continue into the afternoon under westerly flow. There has been
some IFR conditions in the fnt and ptk vicinity, downstream of the
better moisture flux off Lake Michigan. There have been some
freezing drizzle reports in the GRR area. Despite some sfc vsby
restrictions farther east, there has yet to be drizzle reports in
the ptk/fnt vicinity, including here at weather forecast office DTX. So unless some
better evidence of fzdz arises, it will continue to be left out of
the tafs. Based on regional observations, the stratus will persist
through the evening and into the overnight. Some differential
thermal advection along the low level inversion may disrupt some of
the clouds after 08z, perhaps supporting brief breaks in the
overcast or improved ceiling heights.
For dtw...the mean low level wind fields will focus the enhanced
Lake Michigan moisture plume and resultant IFR cigs and potential
drizzle north of Metro. As of 17z, the low level stratus is on the
doorstep at Metro and should overspread the Airport by 18z.
Dtw threshold probabilities...
* high in ceilings below 5000 feet today and tonight. Medium on
issued at 948 am EST Thu Nov 14 2019
Bands of light to moderate snow responsible for producing an inch or
so of early morning accumulation over the northern suburbs of Detroit
and vicinity have exited east. Quick update this morning mainly to
clean up that aspect of the forecast with dry wx anticipated going
forward. Highs have also been lowered a couple of degrees given
satellite presentation of extensive stratus and deep low-level
moisture evident on regional observed and forecast soundings.
Aggressive mid level drying in the wake of the departing shortwave is
modeled to scour out moisture down to the -10c layer in short order,
if it hasn't already, and down to -5c or warmer by this afternoon.
Loss of ice nuclei in an otherwise moist profile introduces non-
zero freezing drizzle concerns, particularly as modest flux off of
Lake Michigan advects east within light westerly flow. However,
shearwise forcing in the boundary layer is quite weak and will
further weaken as the diurnal boundary layer overturns during the
next several hours. The same process will also tend to reduce near-
surface moisture quality in the absence of a mitgating factor such as
meaingful flux of Lake Michigan moisture, which will be a variable
Worth monitoring today. Even so, recently treated roads further
reduce concern for any low end impact. Potential too low to warrant
inclusion in the fcst.
issued at 344 am EST Thu Nov 14 2019
Light snow will take US through the early morning hours as a broad
region of isentropic ascent expands southward from the Saginaw
Valley and thumb region. While the best forcing peels off to the
east, a mid level shortwave seen on water vapor imagery near Chicago
will sweep across the southern Michigan border. Models have been hinting
at this for 24 hours and obs are now showing it. Looks like a band
of mid level deformation will sweep across the Metro Detroit area
between 08-12z. A leading batch of moisture acted to pre-saturate
the dry layer below 10kft leading to widespread ceiling heights
around 3-5kft, so although it did not result in snow it should help
precip hit the ground this go around with the mid level forcing
having been primed. Regional radar already shows some returns to the
west so expect this to continue eastward. Not expecting more than a
tenth or two of snow at most so will bump up pops to likely through
the rest of the night.
A cold front will sweep through the state later this afternoon
bringing a reinforcing shot of cooler air to help US keep our streak
of below normal temperatures going. We could see some light lake
effect snow make it over from Lake Michigan this morning as westerly flow
and steep low level lapse rates develop with cool air advection. Not
the best signal with mixing depths sub 5kft across Southeast Michigan and the top
of the saturated layer barely touching -10c, but low level saturation
will be solid and the airmass will be primed with ice crystals
before the ridge compresses the inversion so snowflakes should be the
primary ptype. Otherwise expecting a cloudy day to help keep temps
muted with highs around the freezing mark.
Broad longwave trough will continue to encompass the Great Lakes on
Friday but the bulk of the energy, and next wave, will focus to our
north over Ontario. Though the weather locally will be quiet, this
next system will send a cold front down through the state late
Friday bringing another push of cold air. With high pressure
spreading into the region and a thermal trough, low temps will dip
back into the teens Friday night. Highs will stay cool on Saturday
with upper level zonal flow setting up across the region allowing
for only slow moderation to the airmass.
The next longwave trough and strong shortwave is setting up to sweep
across the Central Plains Sunday and Sunday night reaching the Great
Lakes on Monday. This would present the next chance of precipitation
across the area while also ensuring temps stay on the cool side
through at least the first half of the week.
Small craft advisories will expire early this morning as southwest
flow relaxes. However, a tightening pressure gradient in advance of
the next approaching cold front will require the issuance of another
Small Craft Advisory for tonight into Friday morning as southwest
flow up Saginaw Bay increase again with gusts to 30 knots possible.
Winds will then veer to the northwest and then northeast from Friday
into Friday night. Gusts in the immediate wake of this front may
approach gale force, but generally expect 30 knots to be the rule.
Building waves in this developing flow will lead to additional Small
Craft Advisory conditions by Friday evening as onshore flow pushes
this high wave action into the nearshore waters.
Lake Huron...Small Craft Advisory from 7 PM this evening to 10 am EST Friday for
Lake St Clair...none.
Michigan waters of Lake Erie...none.