Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 230757
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
357 AM EDT Fri Jun 23 2017

.DISCUSSION...

Deep layer moisture of tropical origin firmly entrenched across
southeast Michigan early this morning.  Moistening process augmented
by the earlier strong northward expansion of high mid-level theta-e
content.  This theta-e gradient providing the southern flank of a
well defined convergence axis also marked by the slow southeastward
sag of an elongated frontal boundary that now stretches from Saginaw
Bay to southern Wisconsin.  Forced ascent anchored on this frontal
slope maintaining a heavy concentration of convection throughout
this corridor.   Advancement of the front into a moisture laden
resident airmass should subsequently support a shift of convective
activity into southeast Michigan through the mid-late morning hours.
Instability limited by both the earlier convective overturning and
an arrival near the nocturnal minimum, so attaining greater
convective organization will be a struggle.  Given precipitable
water values near 2 inches, heavy rainfall will remain the primary
issue.

Actual frontal passage will lag the exit of the deepest moisture
axis by several hours.  This will leave a short window early this
afternoon for some degree of pre-frontal airmass recovery, mainly
southeast of a Howell to Port Huron line as dewpoints hover in the
upper 60s.  Assuming sufficient instability emerges, renewed
development of shallow line of convection could yield a quick shot
of rain/thunder for a few locales before the front sweeps southeast.
Highs today in the vicinity of 80 degrees most locations.  Turning
notably drier from northwest to southeast with the frontal passage,
as dewpoints eventually drop into the 50s all locations by this
evening.

Gradual reduction in mid level heights through the weekend period,
as broad upper troughing expands over the region.  This will leave
weekend conditions defined as cooler and less humid.  Steady
downward spiral of the thermal structure throughout the weekend,
with 850 mb temperatures bottoming out in the middle single digits
by Sunday.  This will leave afternoon temperatures in the low-mid
70s Saturday, then potentially struggle to even reach 70F by Sunday
/Depending on cloud cover/.  The arrival of a weak pertubation timed
coincident with peak heating may support isolated to scattered
coverage of showers /rumble of thunder?/ Saturday afternoon.  The
corridor along and north of I-69 will be more favorably positioned
to witness some development.   A stronger wave pivots across
north/central lower MI Saturday night into Sunday morning.  Given
the lack of a diurnal contribution to augment any uptick in forcing,
precipitation potential appears slim during this time.

&&

.MARINE...

Showers and thunderstorms will continue to impact much of the area
early today ahead of a cold front. Quieter weather is then expected
late today and tonight. West to northwest flow will develop behind
the front this afternoon and evening, and persist through the
weekend as broad low pressure remains in place over the Great Lakes.
Speeds are expected to remain modest, but gusts may just top 20
knots over western Lake Erie both Saturday and Sunday afternoons.

&&

.HYDROLOGY...

Heavy rainfall that occurred from late yesterday evening through
early this morning has caused widespread flooding across Midland
county, and across a portion of Bay and Huron counties. This
flooding will be aggravated by additional rainfall through about
8AM, as an additional one to two inches of rain falls. For the
remainder of Southeast Michigan, showers and thunderstorms over
central Michigan will slide southward through the morning and early
afternoon as a cold front drops through the area. Less training of
storms is expected than what occurred over central Michigan
overnight. Rainfall may be heavy at times, however, with rainfall
exceeding one inch in some areas. Dry weather is expected late today
and tonight.

&&

.PREV DISCUSSION...
Issued at 1220 AM EDT Fri Jun 23 2017

AVIATION...

Thunderstorm activity has become increasingly focused north of the I
69 corridor in response to theta e transport up against a synoptic
scale frontal boundary. Consensus of model data continues to suggest
this thunderstorm activity will impact northern portions of the
forecast area through 09Z tonight. Synoptic scale convergence and
frontal forcing will become progressive after 09z sinking down
throughout much of southeastern Michigan by 15Z. Torrential rainfall
rates will be common with thunderstorm activity tonight.

Model data advertises a broad surface trough in place throughout
much of southeastern Michigan through Friday. This will limit the
pressure gradient and keep wind speeds relatively subdued throughout
much of the day.

//DTW THRESHOLD PROBABILITIES...

* Low confidence in timing of thunderstorms for much of tonight,
  becoming medium confidence for 09-13Z Friday.

* High confidence in ceilings aob 5kft tonight into Friday Morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Flood Watch until 6 AM EDT early this morning for MIZ047>049-
     053>055-060>062.

Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

DISCUSSION...MR
MARINE.......HLO
HYDROLOGY....HLO
AVIATION.....HLO


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at www.weather.gov/detroit.



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