Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 231540
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1140 AM EDT Tue May 23 2017

.UPDATE...

Light rain and showers continue to percolate along the moisture axis
that moved into lower Michigan during the night. Expect this to
continue through early afternoon before increasing in both coverage
and intensity mid to late afternoon as activity moves in from the
Illinois region. Morning satellite imagery and model analysis fields
indicate the incoming pattern is associated with a maturing entrance
region of the upper jet over the Ohio valley and a short wave over
the mid Mississippi valley, both of which are within the deep
southwest flow ahead of the long wave trough digging into the Plains
states. This support combined with daytime heating through filtered
sunshine over lower Michigan will lead to enough coverage increase to
hold the going forecast. The greatest coverage will be focused more
in the Tri Cities and northern Thumb region closer to the stalled
surface boundary over northern lower Michigan then diminishing
progressively toward the Ohio border.

&&

.PREV DISCUSSION...
Issued at 524 AM EDT Tue May 23 2017

AVIATION...

A high coverage of mid level cloud will continue to stream across
the southeast Michigan airspace through the period.  Greater
prospects for some lower ceilings will exist at MBS/FNT given closer
proximity to a stalled mid level frontal boundary, but confidence in
development of MVFR level restrictions remains low. This corridor
will also maintain a higher probability for scattered/intermittent
showers, with isolated embedded thunder possible. Modest south to
southeast winds through the daylight period, becoming light easterly
overnight.

//DTW THRESHOLD PROBABILITIES...

* None.

PREV DISCUSSION...
Issued at 314 AM EDT Tue May 23 2017

DISCUSSION...

Models in decent agreement with the forecast over the next couple of
days, especially for the first 24 to 36 hours. Differences then
noted Wednesday afternoon and evening with the location of the
TROWAL/deformation on the north side of the upper low which leads to
less confidence in this features evolution.

Today will be focused on a wave lifting out of Western WI and
eastern IA as the main upper low over MN dives south. Forcing along
the 850-700 mb front, which will remain nearly stationary over
central lower MI, along with diurnal heating will be the trigger for
likely chances of afternoon showers and storms north and west of a
OZW to Sandusky line. ML CAPEs only reach about 500 J/kg this
afternoon across the northern forecast area, so expect a likely
showers with a chance of thunderstorms afternoon and into the early
evening.

The forecast area is between features for much of the overnight into
Wednesday morning. The shortwave that brings this afternoon`s
convection pushes northeast while any showers around the upper low
stay west and south of the forecast area.

From Wednesday afternoon through Wednesday night will be watching
the development of a TROWAL in a region of strong and deep
deformation and FGen on the northeast flank of the upper low that is
diving southeast into the OH and TN valleys. Also some upper support
with a piece of energy rotating around that upper low and good upper
divergence. There is some disagreement with the placement of these
features with the GFS and ECMWF being the farthest north...the NAM
and Canadian in the farther south camp. Given the position of the
upper low, thinking any errors will be on the north side of the
envelope. Still thinking there will be a good solid rain event for
the southern half of the forecast area, just not widespread 1+ inch
rainfall totals. In addition to the possible error in placement,
precipitable waters only reach 1 to 1.25 inches with modest increase
in theta-e (no theta-e ridging). Suspected the high pops will work
well but that the models are again overdoing the QPF yet again this
spring.

Thursday remains unsettled with cyclonic low level flow with lower
500 mb heights near the upper low. Shortwave ridge with the weak
surface ridge may be enough to keep Friday and Saturday dry (and
warmer on Saturday, closer to average) before the next system moves
through Saturday night and Sunday.

MARINE...

Relatively light winds will exist today throughout the region as
weak surface troughing lingers.  Winds will become northeasterly and
increase tonight and Wednesday as strengthening low pressure lifts
into the Ohio valley.  This long fetch of moderate onshore flow
could result in waves exceeding small craft advisory threshold for
Saginaw Bay and southern Lake Huron late Wednesday and Wednesday
night.  Gradual decrease in wind speed and wave heights as low
pressure exits the region Thursday.

HYDROLOGY...

Low pressure developing over the Ohio valley Wednesday will stall
and intensify through Wednesday night. A band of rain is expected to
develop on the north side of the system and spread into Lower
Michigan late Wednesday and Wednesday night. Rainfall totals
averaging 0.75 inch are likely with locally higher amounts in
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...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.

&&

$$

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


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