Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 262321
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
721 PM EDT Fri May 26 2017

.AVIATION...

Residual stratocu field, associated with the expansive upper low to
the east of the region, is finally stripping out to the east.
However, a multi-layered cloud field is replacing it from the west.
These clouds are an extension of a wave driving the thunderstorm
complex over northern Illinois. The storms are expected to remain
south of the Detroit terminals. However, rain showers falling from a
mid-cloud deck to the north of the main convective activity is
likely for the southern sites. Expectations are for only minimal
reduction in visibility and for ceilings to remain VFR through the
rain episode.

There may be enough surface layer moisture convergence to aid in
some light fog formation around daybreak under light wind
conditions. Otherwise, a diurnal cloud field is expected to build
and increase in coverage during the late morning and persist through
the afternoon on Saturday. Winds will remain light but will favor
the easterly side of the compass as the surface low pressure
assoicated with the thunderstorms move south of the area.

//DTW THRESHOLD PROBABILITIES...

* Low for cigs aob 5kft through 15z Saturday...then High.

&&

.PREV DISCUSSION...
Issued at 301 PM EDT Fri May 26 2017

DISCUSSION...

While several shortwaves and associated low pressure systems will
affect the forecast area over the weekend, expect the overall
weather for Saturday and Sunday to be relatively decent given the
timing of these two systems.

The first shortwave is currently move east towards the Chicago area
this afternoon. The rain shield associated with this system extends
generally from far southern Wisconsin into northern Illinois now
that it is exiting Iowa. The northern part is primarily stratiform
in character while southern portion is characterized by a decent
degree of convection (particularly along/south of surface low).

Models continue to have difficulty in determining just how much of
the stratiform precipitation will survive into tonight as convection
expands into warm sector across Illinois/Indiana/Ohio fed by roughly
1000-1500 J/kg of MLCAPE along/south of warm front.

The northern extend of precipitation is generally rather limited in
such setups as convection along southern portion of eventual MCS
intercept much of the moisture feed. Will refine forecast to trim
out most rain chances north of the M-59 corridor. However, the upper
wave itself is rather well defined and still steering just north of
due east as it traverses mean upper ridging centered over the area.
This suggests that while northern extent of measurable precipitation
will be limited, southern area of the forecast area will still see a
good chance of rain. So, will increase precip chances into the 60/70
percent area late this evening into the overnight Detroit south.
Given hires model runs, it appears the main question left is whether
the best rainfall is able to extend up to about I-696 or whether it
is subdued I-94 south.

This system will work east of the area early Saturday, so expect
rather nice conditions during the day as skies become partly cloudy
and temperatures climb well into the 70s most locations. Even winds
will be on the light side as a bubble of high pressure translates
into area.

The next shortwave, now over the central Rockies, will progress into
the area on Sunday. Timing is a bit slower with this system than
model runs had yesterday at this time. If this trend continues, it
suggests the low pressure and attending warm front would work into
the area generally in the afternoon/early evening. So, while there
are some rain chances in the morning, better coverage of showers or
storms would be 18z-02z or so.

This later timing would also support a better chance of strong
thunderstorms as the atmosphere over the region would theoretically
be allowed to destabilize for a larger part of the day. Either way,
coverage of measurable rain across the forecast area still looks to
be more extensive than tonight`s system. It is mainly the timing of
said activity that remains mostly in question. This later arrival
supports guidance temperatures on Sunday into the 70s once again.

Much of next week will be dominated by an upper low positioned
across the nrn Great Lakes and nrn Ontario. Subtle low level cold
air advection on Memorial Day will be offset by good diurnal mixing
depths. This will support warm (highs in the 70s) and breezy
conditions. An upper level short wave perturbation pivoting around
the upper low combined with cooling temps aloft will however support
a chance of late day convection. The quasi stationary nature of the
upper low Tues into Wed will hold temps on the cool side of normal
to end the Month of May. Diurnal contributions along with the
potential for additional mid level short wave features circulating
around the parent upper low will support continued chances for
diurnally enhanced showers. The medium range model suite generally
suggest the upper low will fill as it lifts into ern Canada during
the end of next week, supporting drier conditions across the Great
Lakes. Lingering low level thermal troughing holding back across the
ern Great Lakes may however support just a slight warming trend
during the end of the forecast period.

MARINE...

Light to moderate winds will oscillate between northwesterly and
southeasterly through Sunday night as a series of weak lows
traverses the region. Deep low pressure is forecast to stall north
of Lake Superior bringing a period of moderate southwest flow Monday
through Tuesday. Winds will gust to around 20 kts during this time,
especially in nearshore areas.

&&

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

$$

AVIATION.....Mann
DISCUSSION...DG/SC
MARINE.......JVC


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