Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 242313
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
713 PM EDT TUE MAY 24 2016


.AVIATION...

Sufficiently dry/stable low level environment will sustain a clear
sky within the lowest 5000 ft tonight and early Wednesday. Modest
southwesterly flow during this time as dominant high pressure of
recent days gradually pulls east.  Weakening frontal boundary will
slide into central lower MI during the early morning period. This
may support some widely scattered high based showers in the vicnity
of MBS. Gradual increase in moisture Wednesday may allow for a low
coverage of late day VFR cumulus.  Prospects for thunderstorm
development through Wednesday evening remain too low to include at
this time.

//DTW Threshold Probabilities...

* None

&&

.PREV DISCUSSION...
Issued at 412 PM EDT Tue May 24 2016

DISCUSSION...

Afternoon surface observations across southeastern Michigan show
that lower to middle 80s temperatures are in place areawide clear up
to the Lake Huron shoreline. The surface dewpoint evolution has been
enlightening and not at all surprising as dewpoints have been
struggling to climb out of the lower to middle 40s. There was some
lowering behavior as the atmosphere mixed out, but there has been no
tanking. This contrasts some of the surface skin forecasts of
dewpoints in the middle 50s by 18z and 60 degrees by 00z this
evening. Buyer beware in this pattern for forecasted precipitation.
The question comes down to what degree of shower and thunderstorm
potential exists later on this evening. The setup discussion was
provided in the earlier update. Latest data observed in a Theta t
framework offers a few ideas. The first is that shower and
thunderstorm activity over portions of Wisconsin and the U.P.
of Michigan is being supported more by thermodynamics with
instability development due to the introduction of saturation,
rather than from any synoptic scale warm advection processes. Moving
forward this evening, nwp forecasts the 310-320K axis of moisture to
narrow and shrink by the time it strings across the northern cwa
after 03z. Instead, the theta t progs suggest any isolated shower or
thunderstorm chance will occur along some secondary shortwave energy
that will settle south southeastward from the vicnity of Lake
Superior and swing down into the cwa between 09-12z. All in all, the
feeling is a low chance for a shower and thunderstorm is sufficient.
Very low instability tonight of a couple hundred J/kg MUCAPE does
not support a strong thunderstorm risk.

Very weak forcing with some lower troposphere confluence will
support organizing a low level frontal boundary in vicinity of, or
just to the north of Saginaw Bay on Wednesday. The mid to upper
level ridge axis will directly overhead of the region which will
suppress and severely limit precipitation and convection. The latest
progs support the low level frontal boundary north of the area which
will allow the warm sector to remain in place all areas. Highs
tomorrow solidly in the lower 80s look good, as tomorrow will be
missing the strong midlevel subsidence and compressional warming
contribution. Explicity convection hires solutions suggest that lake
breeze and lake convergence boundaries may support a thunderstorm
late Wednesday afternoon otherwise banking on some high cloud of
varying opacity and transparency. Convective vigor potential should
remain low again Wednesay. There remains serious reservations on
exactly what the surface dewpoints or quality of near surface
moisture will be in this pattern. Additionally, there is a residual
subsidence artifact in the 5 to 11 kft agl layer that will limit
midlevel lapse rates and amount of instability. MUCAPE tomorrow
appear to remain less than 1000 J/kg.

A spoke of midlevel vorticity adection in and around a deeper
midlevel trough feature will break away from northern plains upper
level low late Wednesday. This inflection point of the flow will
delineate greater cyclonic trajectories and return of a possible
nose to a veered low level jet axis late Wedesday night. It depends
on the details of what sort of mixed layer can survive and not be
turned over by prior convection, but the model data suggests that
best chance for organized thunderstorms will occur with the remnants
of a MCS through lower Michigan 09-12z. It is certainly possible
that instability and MUCAPES could be above 1250 J/kg which bears
watching. However, there is a strong signal a stable lower
troposphere in the lowest 5000 ft agl, which will limit the high
wind threat, not to mention the nocturnal near surface inversion.

The upcoming Memorial Day weekend will continue to advertise chances
for rain and thunderstorms as highs remain in the lower 80s.  The
area will remain in between high pressure off the east coast and
toughing over the central plains.  This will allow multiple
shortwaves to traverse across the area bringing continual chances
for precip and storms to the area.  With the area situated on the
northern side of the high, southerly flow will continue to work in
over the area resulting in warmer temps through the weekend.  Highs
for the Memorial Day weekend will rise into the lower to middle 80s
with lows in the middle to upper 60s.

MARINE...
A weak cold front will slowly settle southward across Lake Huron
tonight and Wednesday morning before lifting back north as a warm
front Wednesday night. Not much in the way of shower activity is
expected with this front.  Winds will veer to a northerly direction
behind the front then veer back to southerly flow as it lifts back.
The Great Lakes will remain in a warm moist southerly flow through
the weekend.  There will be periodic shower and thunderstorm
activity also during this time frame.  Winds overall will be
relatively light, generally below 20kts except during any storm
activity.

HYDROLOGY...

Warm air with increasing humidity will produce a chance of rain over
SE Michigan tonight far north but mainly Wednesday night through
Memorial Weekend.   The greatest coverage and intensity of showers
and thunderstorms is expected Wednesday night as a cold front
settles into the region, stalls, and then returns northward Thursday.
Rainfall amounts are expected to vary widely depending on
thunderstorm coverage but should average 0.25 to 0.5 inch for the
Wednesday night-Thursday period with locally higher totals near 1
inch possible in thunderstorms. Warm and humid air will then remain
in place to support shower and thunderstorm potential into the
weekend with lower probability until arrival of the next front
possibly by Saturday.

&&

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

$$

AVIATION.....MR
DISCUSSION...CB/SS
MARINE.......DRC
HYDROLOGY....DRC


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