Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
639 am EDT Thursday Oct 23 2014
A stretch of favorable aviation conditions expected through tonight
as high pressure takes control. Existing shallow fog at mbs/fnt
will quickly burn off with the onset of daytime heating. Otherwise
a mostly clear sky for today...with a steady increase in middle level
cloud anticipated tonight. A light/west wind through the period.
//Dtw threshold threats...
Previous discussion...issued 341 am EDT Thursday Oct 23 2014
Short term...today and tonight
1024 mb surface high tucked beneath a narrow high amplitude upper
ridge will define conditions locally today. Some pesky pockets of
shallow fog will quickly burn off this morning with the onset of
daytime heating...an existing deep dry layer and increasing middle
level subsidence then ensuring plenty of sunshine through the day.
Recent model guidance integrating roughly 2-3 degrees of warming
through the 925-850 mb layer relative to yesterday...accounting for
both the added insolation and general increase in thicknesses via
rising heights. This will center highs in the middle 50s areawide.
Sharp middle level trough axis anchored to a strong wave/closed low
currently translating eastward across south-central Canada will
pinch into the existing ridging...shearing across Southeast Michigan late
tonight/early Friday. With the better forcing tied to the parent
system well to the north...expect little more than a brief period of
weak cva as the trailing shear axis ejects through. A limited
degree of moisture advection will be working against a Stout dry
layer held in place by persistent surface ridging. This points to
simply seeing an increase in middle cloud overnight...perhaps a few
sprinkles emerging very late within an expanding field of virga.
Model evidence does not support the inclusion of a defined pop
mention at this time. Lows tonight ranging from upper 30s to lower
Long term...Friday through Wednesday
Upper wave will exit the area early on Friday with just virga or
perhaps a sprinkle or two. GFS/NAM forecast soundings suggest
lingering moisture behind the system should be enough when combined
with daytime heating to keep some clouds around during the day.
Temperatures should continue to moderate as h850 temperatures rise back up
near 7c...resulting in maximum temperatures in the upper 50s to near 60.
Bigger feature to watch will be upper energy ejecting out of the
Gulf of Alaska and Pacific northwest. Models continue to bring this
energy across Ontario and northern Michigan late Friday night
through Saturday...with the surface reflection tracking across
northern Ontario. Cold front still expected to drop through the area
as this system passes to our north...however model timing has sped
up a little. Consensus is for an early day frontal passage (12-18z
per GFS/nam)...however the past few runs of the Euro have shown a
timing closer to daybreak. Although the frontal passage still looks
dry given limited available moisture...especially in the low
levels...the timing will have a big impact on temperatures for
Saturday. An earlier frontal timing will mean that maximum temperatures are
reached earlier in the day (still forecast in the low 60s)...and if
other models come around to the Euro solution...temperatures may
need to be lowered further. Main issue with the frontal passage will
be a noticeable increase in northwest winds. Boundary layer mixing
should be quite healthy as cold air advection increases lapse
rates...and we should be able to mix down a core of 30-35 knot winds
advertised by both the GFS and NAM. Surface gusts therefore look to
achieve 35 to even 40 miles per hour during the afternoon and early evening.
Upper ridge looks to slide over the area Sunday into Monday
continuing the dry stretch of weather over the area. Maximum
temperatures will cool back into the 50s however on Sunday behind
the front...before moderating slightly for Monday as warm air
advection commences ahead of the next low pressure system. Models
are still divided with regard to the progression of this system east
of The Rockies...with the 00z GFS tracking it across on Tuesday (has
support from the Gem at 144 hours)...and the 12z Euro bringing it
across on Wednesday. Current forecast maintains chances for rain
showers through this period.
A ridge of high pressure will remain centered over the central Great
Lakes today...keeping calm and quiet conditions over the area.
Conditions will then remain fairly quiet Thursday night through
Friday...however a few showers will be possible over Northern Lake
Huron as an upper level disturbance tracks across the area. The next
low pressure system will track across northern Ontario Friday night
and Saturday. Southerly winds will increase late Friday night in
response...before Flipping to the northwest and increasing in speed
behind a cold front Saturday. Colder air spilling over the warmer
lake waters will allow strong wind gusts to mix down to the lake
surface...and these gusts could potentially reach gale force over
portions of Lake Huron. A gale watch may be needed as we draw closer.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
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