Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
335 PM EDT Tuesday Oct 13 2015
Short term...through tonight
Cool cyclonic flow remains in place over the Great Lakes as low
pressure tracks east across Quebec. The cooler air streaming over
the Great Lakes has also added a lake effect component this
afternoon as mean low-level flow has been out of a westerly
direction today and daytime heating steepened lapse rates. Expect
the lake effect activity over land to begin tapering off this
evening as we lose the heating component...winds veer to a less
favorable northwesterly direction...and a little drier air works in.
High pressure building in over the southern/Central Plains/Tennessee
Valley tonight will also expand up into the area...weakening flow and
lowering inversion heights. Expect mainly sprinkles overnight this
far east...with the exception of the northern thumb which will start
to become more vulnerable to lake effect rain showers off Lake Huron.
Cloud cover remains the most challenging aspect of the forecast
tonight. Cooler air arriving aloft will start to weaken the
inversion while drier air filters in at the low and middle levels. This
will have to fight continued flow across Lake Michigan however...and
given current satellite presentation would prefer to stick with a
persistence forecast with regard to the stratus. Models are
historically not so great with handling low-level moisture...which
was also taken into consideration. Will maintain the mostly cloudy
forecast...but we may see some breaks after about 2 am. Surface
pressure gradient will also relax late as high pressure builds to
our south and west.
Clouds and some lingering wind overnight will hold mins in the 40s
despite the cold dome of air in place.
Long term...Wednesday through Friday
Upper ridging along western U.S. With broad troughing across the
rest of the U.S. Will gradually amplify through the end of the week.
Wednesday morning will start off with thermal trough over the area
and lingering lake effects clouds. As the thermal trough moves east
warm air advection along with weak surface high pressure ridging and
drier air will lead to a fair amount of sunshine as the day GOES on.
A series of shortwaves embedded in the strong polar jet will dive
into the Great Lakes late Thursday through Friday. This will bring
a push of warmer air for the first part of Thursday before a cold
front sweeps through the area in the afternoon. This front will
come through mainly dry as the deeper moisture will remain across
the northern lakes. The second wave will dive a bit further south
bringing another front through Friday. This will bring stronger
cold air advection and deeper moisture leading to a better chance
for showers across the whole area.
For the most part...dry conditions will persist across Southeast
Michigan through the extended period. A few lingering rain showers
are possible mainly across The Thumb region on Friday night and into
Saturday as a weak low pressure system slides across Ontario. Cloudy
conditions and cooler air filtering in from Canada will keep high
temperatures in the upper 40s on Saturday. High pressure builds back
into the region by Saturday night resulting in drier but continued
cooler conditions. Temperatures will top off in the middle to upper 50s
for Sunday and Monday. Low temperatures for Friday night through
Sunday night will drop down into the low 30s before rising slightly
Monday night into the middle 40s. The cooler overnight temperatures
will likely result in frost across much of Southeast Michigan for
Friday night through Sunday night. Advisories may be needed for this
timeframe as the weekend approaches.
A Gale Warning remains in effect for Northern Lake Huron and small
craft advisories remain in effect for the nearshore waters of Lake
Huron...Lake St Clair...and the Michigan waters of Lake Erie. Deep
cold air advection late today and early tonight will continue to
support gusty west to northwest winds area wide. A modest westerly
wind field is forecasted for Wednesday as a weak surface ridge
bubble works across the region. The next cold front is expected to
push rapidly through the central Great Lakes Thursday afternoon. It
appears that conditions could be aligning to support a non-
convective wind event that will likely require marine headlines for
Aviation...issued 112 PM EDT Tuesday Oct 13 2015
Drier air will mix into the lower levels early this afternoon as
winds increase slightly in speed and moisture associated with low
pressure pulls away from the area. This will allow ceilings to
slowly rise several hundred feet...but still remain bkn-ovc.
Prevailing ceilings will most likely remain MVFR...but there is
small potential to see heights rise to low-end VFR near the Detroit
area terminals. Winds will turn more northeasterly and decrease in
speed overnight. This will allow additional dry air to infiltrate
into the area and we could see some breaks in the stratus after 06z
as flow decreases across Lake Michigan. Winds will remain gusty
through early evening from the west-northwest before decreasing in
speed around 00z.
//Dtw threshold probabilities...
* medium confidence for ceilings below 5000 feet through 06z.
Lake Huron...Small Craft Advisory until 11 PM EDT this evening for lhz422.
Small Craft Advisory until 6 am EDT Wednesday for lhz421-441>443.
Gale Warning until 11 PM EDT this evening for lhz361-362.
Lake St Clair...Small Craft Advisory until 11 PM EDT this evening for lcz460.
Michigan waters of Lake Erie...Small Craft Advisory until 11 PM EDT this evening for lez444.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).