Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 261901
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
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.

&&

.PREV DISCUSSION...
Issued at 1241 PM EDT Fri May 26 2017

AVIATION...

Stratocu maintaining its integrity while slowly lifting in response
to diurnal heating. Expect all sites to improve to low MVFR during
the afternoon, approaching 4.5kft once NW flow diminishes after
about 21z. Further scattering expected upon onset of nocturnal
stabilization. MCV originating from tstorm activity over eastern
IA/western IL will track through Southern Lower roughly 04-07z
bringing a chance of higher based showers carrying minimal vsby
restriction. Just a brief MVFR period of cig possible with this
activity. Several hours of clearing in the wake of the MCV followed
by return of sub-5kft cigs during Sat morning in response to renewed
diurnal heating.

//DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5kft through 00z. Low 00z-15z. High after 15z
  Saturday.


&&

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

$$

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


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at www.weather.gov/detroit.



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