Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 271112
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
712 AM EDT Thu Apr 27 2017
Very localized shortwave ridging will get squeezed out of
southeastern Michigan at the start of the period. In fact, model
signal supports a very abrupt transition from localized subsidence
to synoptic scale ascent with significant gradient of potential
vorticity set to lift into the area. The main aviation item is the
strong south to southwest winds that will develop momentarily.
Latest HRRR, RAP, and Nam data suggests a high likelihood for wind
gusts reaching/exceeding 35 knots. Will be watching the 17-20Z
timeframe for the development of shower and thunderstorm activity.
Greater wind gusts will be likely in/around convective activity.
Latest model data suggests a lower probability.
//DTW THRESHOLD PROBABILITIES...
* Moderate for ceiling 5000 ft or less Thursday afternoon.
* Low for thunderstorms tonight. Moderate along the front Thursday.
Issued at 342 AM EDT Thu Apr 27 2017
Active stretch of weather begins today and will take us through the
weekend. We`ll start off today with gusts winds through the
afternoon and strong (possibly severe) storms this afternoon as a
cold front lifts through the area. Friday may actually stay dry as
an active warm from remains south of the area but then a low
pressure system will lift through the region this weekend bringing
chances of showers Saturday through Monday with thunderstorms
For today the main concerns will be strong gradient flow through the
afternoon and severe potential. First we`ll look at winds. The
gradient flow will be strong both ahead of, and behind the cold
front that will traverse the area around 18Z. A strong low level jet
will be lifting out of the region as the mixing depths increase so
will likely miss out on strongest winds early. Soundings show a deep
layer of winds around 30 knots but increasing rapidly above the
inversion. Momentum transfer supports capping gusts around 30 knots
this morning in the prefrontal airmass. The front will sweep
through around 18Z veering winds from south to southwest. Cold air
advection behind the front will produce a strong inversion through
the evening. the again will cap gust potential around 30-35 knots.
Strong winds should be north of I69 close to the low pressure center
lifting through northern lower, but a broad area of gusts to 30
knots may persist a few hours. Not enough of a signal in the models
to warrant higher gusts or a wind advisory.
Having said that, winds aloft will be strong. In the morning we
could be looking at 60 knots down to around 7kft and 70 knots around
10kft. This strongest core lifts north but we`re still left with 60-
80 knots in the mid levels. Afternoon convection will possibly bring
down these stronger winds if we can get some stronger cores along
the front. Convection potential remains but is not overly
impressive. Still looking at a high shear (50 knots), tall skinny
CAPE (~500 J/kg) environment. The low will be tracking nearly north
through the western Great Lakes while strong jet energy though the
base of the longwave trough surge the base of the trough axis
further east, creating new area of height falls to our south. Also
noted in the previous discussion the upper level difluent flow will
displace further north bringing confluence over southern MI working
against the potential for widespread organized convective bands.
best chance for convection will be in the 16-20Z window working from
southwest to northeast through that time as the prefrontal trough
lifts through. Any storm that goes up will have the potential to tap
into the strong winds in the mid levels making winds the primary
threat today. SPC continues to highlight a marginal risk area over
SE lower MI which is reasonable.
Friday could see a lull in activity as a warm front redevelops south
of the state and high pressure builds in from the west. This will be
short lived as the next low pressure system will be developing over
the southern plains, which will push the front back north over lower
MI Saturday. Then several waves could eject out of the low into the
region providing more support for periods of showers through the
weekend. The low itself will then lift through the western Great
Lakes Monday and Tuesday providing additional support for showers
into next week.
Moderate pre-frontal southeast wind will remain in place through
this morning. Existing higher degree of stability will continue to
limit higher gust potential, with gusts capped at or below 25 knots
during this time. Winds will turn to southwesterly this afternoon
as a cold front slips through the region. The combination of
increasingly gusty conditions and a period of wave heights above 3
feet will lead to a marginal small craft condition today across
Saginaw Bay, the lake Huron nearshore waters, Lake St Clair and Lake
Erie. There will be a low probability for thunderstorms with the
cold frontal passage this afternoon. Winds and waves will diminish
this evening as high pressure builds into the region. Lower southwest
winds speeds expected Friday as this high sustains a weaker
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-
Lake St Clair...Small Craft Advisory until 10 PM EDT this evening for LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EDT this evening for LEZ444.
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