Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 271029
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
629 AM EDT SAT AUG 27 2016
Mainly Mid clouds to start the day, but increasing chance of showers
and possible thunderstorms, with showers and isolated thunderstorms
likely this afternoon. Brief MVFR and even IFR conditions expected
within strongest storms, but duration, location, and exact timing
uncertain. The coverage and intensity of the rainfall this
afternoon/early evening will also play a role in the extent of fog
and/or low stratus tonight as partial clearing takes place with very
light winds overnight, attempting to become light westerly by Sunday
For DTW... VFR above 5000 ft expected to hold this morning before
showers and possible thunderstorm overspreads the terminal late this
afternoon into early this evening. Activity then expected to exit by
mid evening, with partial clearing leading to at least MVFR FOG.
//DTW Threshold Probabilities...
* Moderate confidence in CIGS aob 5000 feet late this afternoon,
otherwise low confidence during rest of the forecast period.
* Low confidence in thunderstorms this afternoon/early this evening.
Issued at 309 AM EDT Sat AUG 27 2016
Ongoing convection extending from the Mid Mississippi Valley into
the western Great Lakes has been growing upscale over the last
couple of hours. This convection is occurring within a broad region
of warm air advection on the nose of the low level jet, which is
coupled with entrance region upper jet dynamics preceding a longer
wavelength trough now rotating across the northern plains.
Observational trends lend support to the bulk of hi res solutions
which indicate a convectively induced mid level short wave impulse
and associated sfc wave evolving out of this convection across the
Midwest early this morning. This wave is then forecast to quickly
lift into the northern Great Lakes by afternoon, exiting the region
to the northeast by evening. The stronger mid level ascent and low
to mid level moisture transport associated with this wave will
largely remain north and west of Southeast Michigan today. Low to
mid level flow across the western Great Lakes will however veer
toward the west during the afternoon as the short wave impulse lifts
northeast. This will advect much deeper moisture into the forecast
area during the course of the day. Remnants of the convective
cluster which impacted wrn Tennessee/Kentucky last evening will
rotate into the Ohio Valley this morning, reducing the mid level
height field across Se Mi. This and the potential for secondary short
wave features lifting into the area from the southwest this
afternoon will support increased chances for convection across
the forecast area this afternoon into the early evening.
Given the presence of respectable deep layer shear values on the
order of 30 to 40 knots, the forecast area is under a marginal risk
for severe weather. The severe weather risk is dependent upon the
degree of daytime destabilization, which given potential early day
convection and cloud debris may be significantly limited.
The potential for higher instability to advect into the area from
the south suggests the southern portions of the forecast area (metro
Detroit/Ann Arbor south) have a bit higher potential for stronger
storms than locals to the north. Assuming the availability of at
least modest instability, deep layer shear and cyclonically curved
hodographs suggest storm structure may be linear/supercellular
hybrid. Moisture quality this afternoon and evening will also be
supportive of efficient rainfall rates in any convection.
Rainfall chances will decrease during the late evening into the
overnight as drier air in the mid levels overspreads the forecast
area. Ample low level moisture in the presence of boundary layer
convergence along a sfc trough will support fog and/or low clouds
overnight into Sun morning. Mid level subsidence will overspread srn
Mi on Sunday as the longer wavelength trough slides east of Lake
Superior. While this will still support a dry forecast, remnant low
level moisture will sustain fairly high humidity. Morning clouds
should break up with afternoon mixing, allowing Sunday high to rise
into the 80s.
Sfc high pressure and mid level ridging will support dry and
continued warm conditions on Monday. The medium range model suite,
particularly the ECMWF, continue to trend toward more long wave
amplification across NOAM next week, featuring a deepening long wave
trough across eastern Canada. The impact across Se Mi will be a
notable cooling trend the latter half of next week, following a cold
frontal passage in the Tues/Tues night time frame.
Light and variable winds early this morning will become southeast at
10 to 15 knots by this afternoon with numerous showers and
thunderstorms developing, as low pressure tracks through the
northern great lakes Tonight. Winds will subsequently increase a
bit more overnight, around 20 knots, shifting to the west-northwest
tomorrow, and still around 20 knots sustained across north half of
Lake Huron. High pressure will then bring a light and somewhat
variable flow for early next week.
Numerous showers and thunderstorms are expected to develop this
afternoon as deep moisture moves in and modest instability develops.
Localized amounts over one inch will be possible, which could lead
to urban and small stream issues, otherwise the areal rainfall
average should be between quarter and half an inch. Dry conditions
are expected to return tomorrow and continue on Monday.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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