Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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957
FXUS63 KDTX 241419
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1019 AM EDT Sat Jun 24 2017

.UPDATE...

Large upper level cold pool/circulation entering western Minnesota,
with lead upper wave embedded within the negative tilted trough axis
exiting Chicago, which will move through Lower Michigan, sending 500
mb temps toward -20 C during peak heating of the day, with the noted
inversion seen in the 12Z DTX at 700 MB also cooling/weakening. With
surface dew pts somewhat elevated in the 55-58 degree range right
now, looks like surface based CAPES will easily exceed 1000 J/kg,
with MLCAPES exceeding 500 J/kg, and planning on raising pops and max
temps slightly, but overall limited moisture (pw values around 0.75
inches) quality and dry mid levels should limit areal extent. None-
the-less, favorable freezing levels for hail, and there may also be
just enough lingering 0-6 KM wind shear (exiting 60 knot max) to
support single severe/pulse type storm. Will be watching dew pts
closely, as they should mix down in the afternoon.

&&

.PREV DISCUSSION...
Issued at 540 AM EDT Sat Jun 24 2017

AVIATION...

Mostly clear skies will prevail through the morning hours. Daytime
heating and an upper level disturbance working across the area will
then allow for a BKN VFR cu field this afternoon. Isolated to
scattered showers are also expected to develop, with greatest
coverage up towards MBS and FNT. A few thunderstorms will also be
possible across Southeast Michigan, but probability is too low to
include in TAFs. Loss of daytime heating and subsidence behind the
exiting upper wave should allow clouds to scatter out this evening.
Otherwise, westerly winds will gust to 25 knots this afternoon.

For DTW...Potential for showers will exist between 17-00Z, but
coverage should be isolated. The chance for a thunderstorm in the
airspace is low this afternoon/evening, but possible.

//DTW THRESHOLD PROBABILITIES...

* Low confidence in ceilings aob 5kft this afternoon and evening.

* Low confidence in thunderstorms at DTW this afternoon and evening.

PREV DISCUSSION...
Issued at 350 AM EDT Sat Jun 24 2017

DISCUSSION...

Broad mid level troughing will grip the Great Lakes region
throughout the upcoming weekend.  The subsequent suppression of the
mean thickness field under prevailing deep layer west-northwest flow
will maintain a cooler and less humid resident environment during
this time.  The combination of cooler mid level temperatures and
near surface diabatic heating will establish a steep lapse rate
environment for substantial diurnal cu growth today.  This ascent
will be augmented this afternoon by the arrival of a shortwave and
cold pool, as energetic northwest flow directs a series of
perturbations into the base of the mean trough over the next several
days.  Recent model guidance remains supportive of an increase in
shower coverage as weak instability emerges beneath the inbound cold
pool and with the small scale increase in cyclonic flow.   Higher
probability of development with northward extent given favorable
positioning, which should translate into a scattered coverage of
showers with isolated thunderstorms largely impacting the tri-
cities/thumb down through the I-69 corridor.   MLCAPE reaches
upwards of 800 J/KG, perhaps sufficient to generate a deep enough
updraft to support small hail given the lower freezing levels.
Paltry deep layer wind fields will preclude a greater risk of
organized development.

A stronger wave will lift across central lower MI late tonight into
early Sunday.  This will yield a period of greater forced ascent,
potentially capitalizing on sufficient moisture and steep lapse
rates at the mid levels to produce another round of scattered
showers/isolated thunderstorms.  Should the timing prove a touch
slower allowing for greater diurnally driven low level
destabilization, then a localized region of higher coverage will be
plausible.  This wave will lead in a secondary period of cold air
advection for Sunday, as 850 mb temperatures dip into the 5-6C
range.  This will place highs in vicinity of 70 degrees all
locations, or a good 10 degrees below normal.

Timing of any subsequent shortwaves remains too ill-defined to
provide greater detail, but it generally appears SE Michigan will
remain susceptible to additional bouts of heightened cva and cold pool
intrusions through Monday.  A scattered shower/isolated thunder
mention remains highlighted for the Monday period.  Neutral
temperature advection under this relatively static pattern will
again ensure temperatures remain well below normal to begin the work
week.  Airmass modification commences beginning Tuesday as the upper
trough axis eases eastward and upper heights begin to recover.  Warm
air advection then ramps up Wednesday, with temperatures returning
to around average for midweek.

MARINE...

West to northwest flow will be maintained through the weekend
between low pressure over eastern Canada and high pressure building
through the Plains and into Tennessee Valley. The highest speeds
will be over western Lake Erie where the gradient will be a little
tighter, resulting in gusts that will just top 20 knots both this
afternoon and Sunday afternoon. Scattered showers, and possibly a
thunderstorm, are also expected each afternoon. Weak low pressure
tracking through the area will bring scattered to numerous showers
and a few thunderstorms Monday.

&&

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

$$

UPDATE.......SF
AVIATION.....HLO
DISCUSSION...MR
MARINE.......HLO


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