Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 180145
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
945 PM EDT Sat Jun 17 2017

.UPDATE...

Arcing axis of convection remains fixated along the periphery of a
prevalant mid level warm layer left in the wake of the early day
MCV. Enhanced lapse rate environment along this thermal gradient
lodged within some semblence of convergence will sustain convective
development through portions of the I-69 and thumb corridor for
several additional hours. Southern edge of this forcing may
eventually wash into the M-59 corridor during the early morning
period. Also monitoring the convective evolution over northern
IL/southern WI as stronger deep layer ascent begins to fill eastward
in advance of the an inbound cold front and main height fall center.
Latest upstream trends would suggest the greater convective response
will tend to congeal and propagate into a more favorable
thermodynamic environment residing to our south. Northern flank of
any consolidated MCS may still yield an increasing coverage of
convective showers/thunder for portions of SE Michigan late
tonight/Sunday morning - 08z-12z. The underlying bulk wind parameters
leave the door open for the possibility of greater convective
organization, but an arrival at the diurnal minimum may prove the
ultimate limiting factor in sustaining a greater severe risk with any
morning activity.

&&

.PREV DISCUSSION...
Issued at 729 PM EDT Sat Jun 17 2017

AVIATION...

Adequate mid level stability will continue to largely limit
thunderstorm potential early tonight from PTK south into DTW/YIP,
particularly as diurnally enhanced low level destabilization fades
with sunset.  Greatest potential will remain focused across FNT/MBS,
within a region of greater convergence anchored along the edge of
the existing mid level cap.  Episodic showers/thunderstorms
most likely across this corridor throughout the overnight period.
Upstream radar trends in conjunction with recent model guidance
suggest the best potential for a more expansive coverage of TSRA
reaching into Pontiac and Detroit occurs late tonight through early
Sunday, via the downstream propagation of a more organized
convective complex and/or renewed development along the cold frontal
passage.

For DTW...Thunderstorm potential remains very low early tonight,
given continued stability within the mid levels.  There remains the
possibility for a more organized thunderstorm complex to expand out
of northern Illinois overnight, reaching the airspace closer to
daybreak.  Potential currently highlighted as VCTS, but a more
impactful mention may be required should subsequent radar trends
support this scenario.  In addition, window for thunderstorm
development will exist 15z-18z Sunday with a cold frontal passage.

//DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms tonight.  Medium between 14z-18z Sunday.

* Low for cigs below 5000 ft tonight.  Medium Sunday morning.

PREV DISCUSSION...
Issued at 312 PM EDT Sat Jun 17 2017

DISCUSSION...

Large thunderstorm complex over Missouri early this morning,
generated a lot of latent heat release, with some of the warming in
the mid levels pushing into southeast Michigan this afternoon, as
500 mb temps rise above -7 C south of M-59. Thus, thinking we are
looking at bulk of shower/thunderstorms late this afternoon/early
this evening north of M-59 where remnant MCV is tracking. Cloud
cover from this morning activity delayed the warming up north, but
MLCAPES have now reached 1000-1500 J/KG up to I-69 corridor. With
mid level jet coming in, helping to boost 0-6 KM Bulk shear to
around 40 knots, storms bear watching for isolated severe threat.

500 MB height falls to accelerate tonight as strong upper
wave/digging trough ejects out of Eastern Montana/Dakotas, reaching
Lake Michigan around 12z Sunday, which looks to be the highest
probability of showers and thunderstorms, and will carry likely pops
with the good large scale forcing late tonight into early Sunday
morning. There is concern possible MCS developing over Western Ohio
Valley early this evening will disrupt our moisture
return/transport, or again lead to a lot of latent heat release and
warming of the mid levels, preventing instability/capes from even
exceeding a 1000 J/KG. None-the-less, 17Z Rap13 indicating 850 MB
computed cape around 1000 J/kg which poses a low chance of severe
with 45+ knot low level jet overhead. Favoring the instability/low
level theta-e ridge axis to be east of the CWA by around 16Z, with
dry conditions expected for the afternoon hours. Deep boundary
layer mixing looks to promote wind gusts at least around 25 knots as
temps recover into the lower 80s with weak post frontal cold
advection.

Cooler/cyclonic northwest flow for Monday as large 500 MB Low tracks
off toward James Bay. 500 MB temps lowering to between -16 to -18 C
over Lower Michigan. Enough surface based instability expected to
generate scattered showers and isolated thunderstorms during the
afternoon, as NAM indicating surface capes up to 1000 J/KG. That may
be a little high as surface dew pts mix down in afternoon as high
temps rise in the 70s, but with low freezing levels, small hail will
be possible, along with gusty winds with the deep/dry sub cloud
layer.

Upper-level troughing will persist Tuesday into early Wednesday
across the Great Lakes, bringing west to northwesterly winds
throughout the day. As a result, daytime high temperatures will
remain capped in the low to mid 70s for both Tuesday and Wednesday,
which is just below seasonal normals for this time of year.
Additionally, embedded shortwaves will bring the chance for spotty
showers throughout Tuesday, before high pressure moves in on
Wednesday, minimizing rain chances. Otherwise, zonal flow will set
up across Michigan Thursday into early next week, which will act to
keep temperatures in the upper 70s to lower 80s for a daytime high.
Uncertainty remains very high regarding rain chances late in the
week into the weekend as poor convergence is seen between long range
model runs. The best chances for both rain and thunder will enter on
Thursday as a weak warm front enters southern Michigan. PoP values
will then remain sub-30 through the weekend at this time as the GFS,
ECMWF and GEM runs are all suggestive of precipitation chances,
however, timing and location vary greatly between model runs.

MARINE...

Moderately strong storm system for early summer will traverse the
central Great Lakes region on Sunday. In advance of this system, a
couple of rounds of showers and thunderstorms are possible, with the
best chances during the first half of Sunday as the cold front
crosses the region. Winds are expected to approach small craft
gusts, but the flow will be predominantly offshore - so waves will
should remain somewhat tempered. The exception will be Saginaw Bay
where longer fetch conditions will become establish behind the front.

HYDROLOGY...

A very moist atmospheric column will support heavy downpours with
thunderstorm activity through midday Sunday. While coverage will be
somewhat limited, those areas that experience thunderstorms could
see rainfall totals exceeding an inch. This will result in localized
ponding of water and possible short duration flooding in favorable
drainage basins.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 10 AM to 8 PM EDT Sunday for LHZ421-422.

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

$$

UPDATE.......MR
AVIATION.....MR
DISCUSSION...SF/AM
MARINE.......Mann
HYDROLOGY....Mann


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