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FXUS63 KDTX 271642
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1242 PM EDT Thu Apr 27 2017


.AVIATION...

Cold front will pretty much clear all terminals at the beginning of
the forecast period with just a brief window 18z-19z where a shower
or storm will remain possible. MVFR/lower VFR stratus will funnel in
behind the front and persist, at least in a scattered to broken
fashion, into tonight. Wind gusts to 30 knots or more will remain
possible, particularly 18z-21z within strongest surge immediately
behind the front.

//DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling 5000 ft or less this afternoon/evening.

* Low for thunderstorms 18z-19z as cold front passes.

&&

.PREV DISCUSSION...
Issued at 931 AM EDT Thu Apr 27 2017

UPDATE...

Expecting southwest wind gusts in the 40 to 45 mph across southeast
Michigan, based off upstream obs and local probablistic SREF weighted
guidance, as low pressure (990-992 mb) and 6 hr rise fall pressure
couplet (18 MB) lifts northeast through northern lower
Michigan/Central Great Lakes. Best chance for gusts reaching and
exceeded 45 mph will be Tri-Cities region where best low level cold
advection will occur (850 mb temps dropping below zero by 00z), but
with strong wind gusts being short lived (around noon and just after)
and due to localized nature of 45+ MPH gusts, may hold off on wind
advisory and just handle it with an SPS.

PREV DISCUSSION...
Issued at 342 AM EDT Thu Apr 27 2017

DISCUSSION...

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
possible Sunday.

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.

MARINE...

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
gradient.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-
441>443.

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.

&&

$$

AVIATION.....DG
UPDATE.......SF
DISCUSSION...DRK
MARINE.......CB


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