Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 220732
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
332 AM EDT Sat Apr 22 2017

.DISCUSSION...

The right entrance region to the +110 knot upper level jet streak
over Quebec persists over southeastern Michigan this morning. The
combination of this upper level forcing with some decent enough
cyclonic vorticity advection supported a very fleeting duration of
sprinkles overnight across the eastern half of the cwa. CVA will now
remain neutral during the remainder of the morning. The center of a
sprawling surface ridge has been slow to expand into southeastern
Michigan due to the location of the entrance region to the
jetstreak. In fact, northerly gradient flow has been reported
areawide of at least 5 knots. Large scale dynamics will be very
supportive for deep column subsidence. This includes both confluence
aloft but also an internal subsidence bubble rolling southeastward
from the the upper Mississippi River Valley while being compressed
over lower Michigan later today. Expect very stable conditions with
rapid evolution to lowering subsidence actually capping mixing
heights today. The only real uncertainty to the today forecast is
that high cloud could be a nuisance across the southern forecast
area due to the tail of absolute vorticity that will be sluggish to
strip out eastward. With the heart of the ridge not truly building
in until the late afternoon, expect northerly flow to be a modest
surprise south and east of the terrain in the higher surface
pressure areas. Northeast wind gusts of 20 to 25 mph will be
possible early afternoon for the Detroit Metro. The narrative will
be one of picture perfect spring time weather with bright skies,
coolish for those in shaded areas. Additionally, conditions will
likely get cool for the shoreline areas of Lake Huron and Lake St
Clair late in the day as models are showing a clean release of cold
lake origin air mass.

Impressive signal in forecast soundings tonight showing subsidence
inversion collapsing down into the surface. Any other time of the
year and one would expect high fog potential tonight. Instead,
looking at a dry boundary layer. Nil wind, clear skies tonight sets
perfect radiative cooling environment. Lows tonight are expected to
fall into the lower to middle 30s. Will defer any frost headline
decision to the day shift.

While not so much for southeastern Michigan specifically, Sunday is
shaping up to be a curious day for those interested in subtle,
mesoscale, Great Lakes weather. A strong midlevel trough will push
north of Lake Superior Saturday night laying out a cold front west
to east over the Lake Superior, U.P. border by 12Z Sunday. In sum
total it will be a very strong cold front or stationary front with a
incredibly tight 850mb temperature gradient. In fact, 850mb
temperatures will range from 4 to 5 C over central Wisconsin to as
cold as -17C immediately north of Lake Superior at 12Z. All
indications are that residual high stability in the lower
troposphere and surface ridging across southern Wisconsin and lower
Michigan will stall out the southward drift of the surface cold
front. Models show with varying degree the cold front being slow to
move south during the day. Some higher lower column theta e content
pooled ahead of the boundary will allow a good moderating bump to
temperatures for southeastern Michigan. Highs are expected to climb
into the middle 60s areawide under full insolation. The nam suggests
it will struggle, but the ECMWF shows there will be enough internal
lake scale dynamics from a diabatic heating, mesohigh response over
Lake Huron to push the cold front south, particularly during the
evening. Some uncertainty exists whether a true Pnuemonia Front
response will develop off of Lake Huron, but the potential exists.
Much higher confidence in one on the western shore of Lake Michigan.

Larger wavelength geopotential height rises will occur along with
shortwave ridging on Monday. Southeasterly anticyclonic flow
trajectories will persist with residual drainage flow off of
retreating surface high. This will limit the overall warming response
but keep high confidence in dry weather. High temperatures are
expected to rise into the middle 60s.

Latest trend off of latest ECMWF run was to shift the axis of the
high amplitude ridging to the west for the middle and end of the
week. The result of this is to keep southeastern Michigan tucked
more within the ridge and push back the timing of the next potential
for precipitation. Uncertainty exists on timing.

&&

.MARINE...

High pressure building into the region will result in favorable
marine conditions through the weekend. Light northwesterly winds
today will switch to southwesterly on Sunday while remaining below
20 knots. Increased flow out of the east will emerge late Sunday
night when a cold front drops into the region.

&&

.PREV DISCUSSION...
Issued at 1156 PM EDT Fri Apr 21 2017

AVIATION...

High pressure nudging into Lower Mi, forcing dry air advection from
the north, will continue to erode the strato cu from north to south
over the next two to four hours. Other than some cirrus, clear skies
will then prevail through daybreak.

For DTW...Extrapolation from satellite brings the clearing through
metro around or shortly after 07Z. The onset of daytime heating will
support an increase in northeast winds around 10 knots between 14
and 15Z.

//DTW THRESHOLD PROBABILITIES...

* Moderate in ceilings below 5000 ft through 07 or 08Z.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

DISCUSSION...CB
MARINE.......DRK
AVIATION.....SC


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at www.weather.gov/detroit.



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