Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 240935
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
535 AM EDT Wed May 24 2017

.AVIATION...

Moisture will increase through the day as low pressure lifts toward
the region.  Simply a substantial component of mid-high cloud will
define conditions through the morning period.  Exception at MBS,
where the southern periphery of LIFR stratus will linger into the
mid morning period before lifting. Defined axis of higher moisture
and instability will then pivot northwest across the southeast
Michigan airspace through the afternoon hours. While the exact
coverage of thunderstorms remains somewhat uncertain yet, the most
likely window for TSRA to be in the vicinity is now highlighted for
all terminals. Intermittent VFR/MVFR likely during this time, with
dependence on heavier showers/storms to disrupt visibility. Low
level moisture will increase more substantially in the wake of this
instability axis toward evening, resulting a greater deterioration
of conditions. IFR restrictions now appear possible within periodic
bouts of showers for portions of the region tonight.  Modest
easterly winds today, becoming northeasterly tonight.

For DTW...Greatest window for TSRA to lift across the airspace
remains centered 17z-21z.  Movement from southeast to northwest
today.  Existing northeast flow settles to east-southeast by midday,
then back to northeast again tonight.

//DTW THRESHOLD PROBABILITIES...

* Low for cigs aob 5kft thru 18z, then high mid afternoon onward.

* Moderate for tstorms to impact the airspace 17-21z.

&&

.PREV DISCUSSION...
Issued at 257 AM EDT Wed May 24 2017

DISCUSSION...

Large upper low continues to churn south-southeast across IA and
will move into the OH and TN valleys by tonight.  Then it slowly
moves to the mid Atlantic sea board by Friday.  A surface low will
develop this afternoon over northern KY/southwest OH in response to
wave rotating around the east side of the upper low and the 150+ kt
jet streak. These features will be the main forecast issues over the
next two days.  While the models do exhibit some differences, the
overall flavor is the same for southeast MI.

Southeast MI is in a region of weak forcing this morning with weak
moisture advection. This will keep the scattered high based showers
or sprinkles around this morning. Enough indication of thin spots in
the high clouds that there will be a few filtered rays of sun around
daybreak before a thicker cloud shield develops. Modest Fgen and
deformation will accompany a better theta-e advection pattern from
the southeast over much of the forecast area this afternoon. Model
soundings indicate possibly around 500 J/kg of ML CAPE this
afternoon. This should be good enough for high likely or low
categorical pops for this afternoon with showers and a few storms.
With the clouds and showers around, will go toward the cooler MET
numbers for highs.

The best response with the strongest Fgen, deformation and jet
forcing occurs this afternoon and early evening well south of the
forecast area in Ohio and east central IN. This area will pivot into
the forecast area from southeast to northwest during the overnight
hours. While it will be weakening as it does move into southeast MI,
enough confidence of at least light QPF to have mostly categorical
pops tonight. Instability wanes tonight and will take out any
thunder mention.

Weak deformation axis and surface troughing remain over southeast MI
on Thursday with the upper low centered over OH.  With a little
diurnal boost, expect scattered showers to develop quickly on
Thursday. Again will leave out any thunder mention with modest lapse
rates and little if any CAPE. Like Wednesday, clouds and showers
should keep high temps close to the cooler MET numbers.

Think we can squeeze a dry day on Friday as surface ridge builds
over Lower MI with rising 500 mb heights. Sun will be slow to return
with plenty of low clouds in the morning and mid and high clouds
already returning ahead of the next weak wave in the afternoon.
Speaking of that next weak wave, the NAM and Canadian appear to be
having some convective feedback issues. Meanwhile the GFS and ECMWF
keep the wave weaker and much further to the south.  Will have just
a chance of showers for the far south late Friday night into
Saturday morning. Saturday afternoon is expected to be dry and
warmer ahead of the next cold front. That front and the next wave
still look to move through late Saturday night and Sunday as another
upper low settles over the Great Lakes bringing more cool and
unsettled weather for the beginning of next week.

MARINE...

Low pressure developing over the Ohio valley today will lift north
and near southeast Michigan tonight.  This low will remain in the
vicinity through Thursday before exiting to east by Thursday night.
This will produce a stretch of unsettled weather, resulting in
episodic showers and a few thunderstorms during this time. A period
of moderate northeasterly winds will develop beginning today.
Despite the higher degree of stability over the waters, this
favorable trajectory may generate stronger gusts over Saginaw Bay.
This will warrant a small craft advisory today over the bay. The
steady onshore flow will then result in waves exceeding small craft
conditions for all lake Huron nearshore waters by this evening.  The
long duration will then maintain small craft advisory conditions
through Thursday.  Eastward exit of this low will bring improving
conditions by Friday.

HYDROLOGY...

Low pressure developing over the Ohio valley today will lift north
and near southeast Michigan tonight.  This low will remain in the
vicinity through Thursday before exiting to east by Thursday night.
Periods of showers and thunderstorms will develop during this time,
producing rainfall averages ranging from less than half inch north
of I-69 to almost one inch towards the Ohio border.  There may be
locally higher amounts in areas that experience thunderstorms.
Ponding of water on area roads and in other prone areas is likely,
especially considering the widespread activity over the weekend that
left the ground saturated in most areas.

&&

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

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

$$

AVIATION.....MR
DISCUSSION...RBP
MARINE.......MR
HYDROLOGY....MR

You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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