Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 171938

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
338 PM EDT Fri Aug 17 2018


Extensive cloud cover remains in place over the area as the upper
low near Chicago slowly makes its way east. Clearing over northern
IN and southwest Lower MI has fostered modest destabilization and
subsequently allowed showers and thunderstorms to develop in that
area. This activity will spread into the the Detroit Metro area and
points south and west into the evening as renewed warm and moist
advection lifts into the area and larger scale dynamic forcing
increases. In the meantime, mediocre convection will likely continue
to flare up at times within areas of enhanced boundary layer
convergence. Further north, more organized mesoscale forcing will
still pose a threat for locally persistent heavy rain. However, the
lack of destabilization to this point, HRRR analysis indicates just
a few hundred J/KG MLCAPE, suggests the outcomes indicated by the
12z suite are highly unlikely. Instead, maintained likely to
categorical pops and will simply highlight a locally heavy rain
threat potentially leading to poor drainage or urban flooding.

Little in the way of airmass change between now and Sunday as H850
temps hover in the mid teens within mean troughing regime. Scouring
out of today`s moisture will limit convective potential,
particularly as mid-level temperatures warm, favoring just diurnal
cu-up Sat and Sun aftn as high temps settle in the low 80s with a
decent coverage of upper atmosphere smoke worthy of an upward nudge
in the sky grid.

Midlevel ridging will remain in place on Monday as surface high
pressure drifts northeast into New England, allowing for a dry
Monday morning and afternoon for our area. Highs near normal in the
lower 80s and light southeasterly winds expected. A shortwave
currently moving over the Pacific Northwest will make its way into
the central Plains by this weekend and interact with additional
upper energy dropping in from the Canadian Prairie provinces on
Tuesday, resulting in a strengthening mid-latitude cyclone moving
into the Great Lakes by late Monday night. Long range guidance has
begun to converge on a solution suggesting the center will track
through lower Michigan during the day Tuesday. Chance for showers
and thunderstorms increases Monday evening and lasts through the day

A broad area of high pressure will build back in on Wednesday and
maintain influence over the area through the rest of the work week,
allowing quiet weather to prevail. The early week system will pull a
good amount of cooler and drier air southward from Canada, leading
to highs in the mid to upper 70s Tuesday through the end of the week.



A weak secondary area of low pressure tracking across Lower Michigan
will maintain showers and thunderstorms this evening before exiting
the region tonight. In its wake, weak high pressure will build
across the Great Lakes bring dry weather for the weekend. Light to
moderate northerly flow will prevail through the weekend, with peak
gusts limited to around 15 knots.



A secondary low pressure system moving across Lower Michigan will
bring scattered to numerous showers and thunderstorms through this
evening. Rainfall amounts will generally range from a quarter to a
half of an inch, with locally higher amounts associated with
thunderstorms. The flooding threat will be minimal, with ponding of
water on roadways and localized minor poor drainage flooding briefly
possible where the heaviest rainfall occurs. Outside of an isolated
shower Saturday afternoon, the weekend will feature dry weather with
weak high pressure building across the region.


Issued at 124 PM EDT Fri Aug 17 2018


Plentiful moisture remains in place across SE Michigan ahead of low
pressure slowly moving from southern Lake Michigan into Lower
Michigan this afternoon. A nearly stationary frontal boundary draped
across the northern TAF sites will slowly drift south through the
afternoon. Various high-res model solutions have come into good
agreement that this boundary will act as a focal point for shower
and thunderstorm development by mid afternoon with the highest
coverage slowly shifting south from MBS to FNT to PTK. More isolated
showers and thunderstorms are expected for the Metro Detroit
terminals this afternoon with highest coverage expected during the
20-22Z time window coincident with peak daytime heating. Ceilings
are expected to remain variable through the afternoon with a general
lifting trend from MVFR to VFR by early evening. As the low departs
the region tonight, drier air filtering into the region from the
northwest will end shower chances as VFR ceilings scatter out. Winds
will remain light through the TAF period while backing to the north
this evening.

For DTW...Ceilings will continue gradually lifting from MVFR to low
VFR through the afternoon before lifting to VFR this evening. High-
res model guidance has continued indicating showers and
thunderstorms will develop through mid afternoon with highest
coverage during the 20-22Z time window. Light variable wind will
continue through the afternoon before slowly backing from northwest
to northeast tonight.


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

* Low confidence in thunderstorm occurrence and timing this


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



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