Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
321 am EDT Sat Nov 1 2014
Short term...today and tonight
Early morning observations reveal widespread temperatures in the low
to middle 30s beneath an extensive lake enhanced stratocu deck. Winds
within the well-mixed boundary layer continue gusting 30 to 35 miles per hour
producing wind chills in the upper teens to low 20s. In addition,
moderate instability within northerly flow over Lake Huron is
supporting lake effect rain and snow showers, with far eastern areas
still struggling to change over due to warm advection off the lake.
This morning's water vapor imagery reveals a significant disruption
to stratocu coverage over western lower due to subsidence trailing
the passing middle-level trough axis. This band of subsidence will work
across the area between now and about 13z, which will likely lead to
some compromising of the integrity of the cloud shield, but
increasing diurnal instability and continued Theta-E flux off the
lake will be an offsetting factor and will help sustain mostly
cloudy to cloudy conditions for all but the westernmost areas well
into the afternoon. Dissipation of clouds over most of Southeast Michigan will
have to wait until deep layer anticyclonic flow builds in from west
to east 18z-00z behind the departing thermal trough this afternoon,
leading most areas to remain solidly beneath extensive cloud cover
for most of the day. Temperatures will struggle to recover at all
from early morning lows spelling highs ranging from 36 to
40...lowest along the glacial ridge. Wind chills will be 25-30f for
the balance of the daylight hours.
Building heights will force surface high pressure to translate into
the region tonight. Assuming complete erosion of lake clouds by
sunset, overnight lows will fall well into the 20s areawide. Any
locations that haven't yet had a hard freeze will get it tonight.
Thermal troughing along the shoreline will keep the gradient up a
bit and support slightly warmer lows of 25-28. West of US-23, lows
may fall to 20 degrees...perhaps an isolated upper teens
reading...before high clouds presently over North Dakota spread into
the area during the predawn hours.
Long term...Sunday through Friday
After a cold start to the day Sunday...afternoon highs should rise
into the 40s as the low level flow backs toward the west marking the
onset of low level warm air advection. This warm air advection
regime will persist into Monday night. A progressive long wave trough
advancing across the western US will force a high amplitude middle level
ridge across the Great Lakes sun into Monday...maintaining dry
conditions across the forecast area. Despite lingering dry air in
the low-middle levels on Sunday...model plan views suggest a good
degree of high level moisture spilling overtop the approaching middle
level ridge and cascading across lower Michigan /suggesting opaque skies
at times/. Low to middle level moisture will then advance into lower Michigan
Monday and Monday night withing strengthening west-SW flow ahead of the long
wave trough pushing into the central US. While this will increase
cloud cover on Monday...the degree of low level warming still suggests
daytime highs will rise into the 50s.
The medium range model suite suggest the southern branch of the long
wave trough will evolve into a cut off circulation over northern Mexico
Tuesday into Wednesday...while the northern branch remains progressive and
rotates into the Great Lakes. Persistent deep layer moisture
advection and isentropic ascent along with increasing frontogenesis
along the associated cold front will support a good chance of
showers in the Monday night to Tuesday time frame. Although model
solutions diverge with respect to the timing of additional northern
stream waves rotating into the region toward the end of the week...a
general consensus remains that some semblance of large scale trough
amplification will occur across the Great Lakes Thursday into Friday. This
will support a cooling trend during the later half of the work week.
Marine...marine observations still suggest gale force winds are
ongoing across Southern Lake Huron and Western Lake Erie. The winds
and waves will steadily decrease during the morning and afternoon as
high pressure builds in from the west and weakens the gradient over
the eastern Great Lakes. This high will then influence the region
through the end of the weekend providing relatively light winds in
comparison to the last couple of days. S-SW winds will increase
Monday into Tuesday. Warmer air will also filter into the region
will will boost the stability over the lakes and will suppress the
magnitude of the winds.
Record low high temperatures for 11/1:
Detroit area (dtw).....30f (1879)
Flint area (fnt).......36f (1996)
Tri-Cities (mbs).......38f (2002)
Record low temperatures for 11/2:
Detroit area (dtw).....22f (1951)
Flint area (fnt).......20f (1951)
Tri-Cities (mbs).......18f (1951)
Aviation...issued 1207 am EDT Sat Nov 1 2014
MVFR in ceiling and snow showers will continue through sunrise...
especially in the dtw corridor...while finally moving east of fnt.
Thanks to the strong northerly flow downslope from northern
lower...mbs will have low end VFR ceiling most of the time until
ceiling begins to break up entirely by middle afternoon as high
pressure builds over the western Great Lakes. Daytime boundary layer
growth will maintain MVFR ceiling and gusty north wind elsewhere
through at least middle afternoon.
For dtw... north wind gusts near 30 knots will continue to drive
enough cold air into the metropolitan area for mostly snow to fall during
the rest of the night. No accumulation is expected as snowfall rates
will remain too light to overwhelm warm ground surfaces.
//Dtw threshold threats...
* high confidence in ceiling below 5000 feet through middle afternoon.
* High confidence in northerly wind gusts 25-30 knots.
* High confidence in snow during the night.
Michigan...Wind Advisory until 4 am EDT early this morning for miz049-055-063.
Lake Huron...Gale Warning until noon EDT today for lhz363-441>443-462>464.
Gale Warning until 8 am EDT this morning for lhz421-422.
Lake St Clair...none.
Michigan waters of Lake Erie...Gale Warning until 8 am EDT this morning for lez444.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).