Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 251450
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1050 AM EDT Thu May 25 2017

.UPDATE...

Radar composite indicates a large area of showers over southern
Ontario, Lake Erie, down into Ohio and Pennsylvania during the
morning. This is part of a distinct smaller scale circulation within
the upper level trough, along with another pivoting through the Ohio
valley. The interaction of these two features, along with the
accelerating progression of the larger scale trough will cause the
resulting deformation pattern to set up over SE Michigan, mainly with
a western edge running from the Thumb region through metro Detroit.
Shower coverage will be lower into central sections of lower Michigan
while wet and damp conditions will be ensured by drizzle forced
within the inverted surface trough that will remain in place as the
surface low slides from Ohio through central Lake Erie. The update
maintains the wet and gloomy message already in the forecast along
with cool temps nearly steady through the day from the mid 50s to
lower 60s.

&&

.PREV DISCUSSION...
Issued at 525 AM EDT Thu May 25 2017

AVIATION...

Expansive region of low level moisture positioned north of low
pressure over Ohio will maintain a broad canopy of low stratus
through tonight.  A predominant IFR condition during this time, with
just the possibility of brief improvement to lower MVFR as diurnal
heating peaks.  A greater component of visibility restrictions yet
to materialize, but the potential does exist for some disruptions to
emerge particularly within any pockets of drizzle and/or heavier
showers.  Existing modest northeast wind will shift to north-
northwest by late today.  Low clouds persist through Friday morning.

For DTW...Extensive low stratus holds firm through Friday morning.
Some minor fluctuation to CIGS will be possible, but prevailing IFR
to low MVFR is expected.  Periodic showers/drizzle may provide an
additional disruption to vsby.  Modest northeast flow into early
afternoon, favoring NE operations.  Winds may tend to back to N-NW
by mid or late afternoon, given consideration to SW operations.

//DTW THRESHOLD PROBABILITIES...

* High for cigs below 5000 ft through Friday morning.

PREV DISCUSSION...
Issued at 251 AM EDT Thu May 25 2017

DISCUSSION...

Upper low was spinning over southwest OH with the best
TROWAL/deformation axis over eastern IN.  Pieces of the old TROWAL
were slowly weakening from DTX to OEB as it moved northwestward. The
other residual deformation axis was pivoting away from the Tri
Cities area early this morning. New activity was developing along
the state line, right on the edge of the mid layer dry slot. Expect
this overall pattern to continue through the morning with some
additional development on the edge of the dry slot and generally a
diminishing trend as the showers move into southeast Lower MI. However
between showers, there is plenty of moisture below the mid layer dry
slot with low level cyclonic flow and convergence. Suspect there
will be areas of drizzle or light rain between the showers. Will
have a high likely pops to cover the morning.

Models in agreement with the showers across PA rotating far enough
back to the northwest this afternoon to carry categorical pops for
areas east of a BAX to DTW line and perhaps even a little farther
west than that. That low level convergence with the cyclonic flow
continues all day. Then southeast Lower MI is on the edge of good
500 mb Fgen and deformation along with good upper jet support, that
is mainly across southwest Ontario. All of those low clouds and
showers will only allow a few degree diurnal temperature swing. Kept
the idea of highs a degree or two below the lowest guidance values.

As both the surface and upper low peel away this evening, so does
the support and deep moisture. Will carry chance pops for the
evening hours.  Then will be left with lots of low clouds for the
rest of the night into Friday morning. This low level moisture
slowly erodes away Friday afternoon, but the high and mid clouds
will already be streaming ahead of the next weak wave. May still
have enough peaks of sunshine Friday afternoon to call it partly
sunny. With the expected clouds around though, will lean toward the
cooler side of guidance temps.

The NAM has finally gone with a weaker solution for that Friday
night wave, but remains the farthest north. Canadian is also too far
north and too strong with that wave. Will be leaning toward the
flatter solutions of the 00z GFS and ECMWF which should keep
southeast MI dry Friday night and Saturday morning.

On Saturday, low level moisture returns for some broken cumulus to
develop. Model soundings indicate enough warm air from 5k to 15k to
provide the necessary cap to any convection that might want to try
to develop. With partly sunny skies all day on Saturday, rising
heights and warm air advection...Saturday will be the warmest of the
forecast and actually above average.

Saturday night and Sunday will see the lead wave ahead of the main
upper trough, push a cold front through the region with some showers
and storms. Can`t go any higher than chance pops with the best
moisture and instability stuck to the south along I 70. After that,
it looks like the waves rotating around the upper low will be timed
fairly well with the diurnal cycle to produce a chance of showers
during the daylight hours of each day from Memorial Day through
Wednesday.

MARINE...

Moderate northeast winds will persist today as the area remains
north of strong low pressure centered over western Ohio.  Continued
onshore flow will also maintain higher wave activity, particularly
near the tip of the thumb.  Small craft advisory conditions will
exist from the tip of the thumb into Saginaw Bay through the
evening.  Northeast winds ease tonight as the low weakens and lifts
east.  Modest north to northwest then take hold into Friday.  A weak
gradient will keep wind and wave activity on the lower side to start
the holiday weekend.  Potentially more unsettled conditions return
by Sunday and Monday, as low pressure tracks toward the region.

HYDROLOGY...

Periodic showers will continue to lift across southeast Michigan
today, north of strong low pressure slowly lifting across Ohio.
Highest rainfall amounts will tend to align from Port Huron down
through Detroit and Monroe, where upwards of .3 to .4" of additional
rainfall will be possible.  Elsewhere, rainfall will generally
remain at a quarter inch or less.  This long duration event is not
expected to produce any flooding other then some minor ponding on
roadways and low lying areas.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-
     441.

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.

&&

$$

UPDATE.......BT
AVIATION.....MR
DISCUSSION...RBP
MARINE.......MR
HYDROLOGY....MR


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