Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 172310
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
710 PM EDT Thu May 17 2018

.AVIATION...

High pressure over northern Ontario and low pressure moving into the
Ohio Valley is supporting northeast surface over SE Michigan.
Moderate gustiness will diminish with sunset but remain steady
around 10 knots through the night. Gustiness toward 25 knots then
returns Friday morning as surface heating commences. Otherwise, just
VFR under gradually thickening high clouds through Friday.

For DTW... Gusty northeast wind diminishes to an average around 10
knots through tonight. Gust around 20 knots return during Friday
morning with a slightly more easterly component. Northeast traffic
flow operations will likely be needed through the period.

.DTW THRESHOLD PROBABILITIES...

* None.

&&

.PREV DISCUSSION...
Issued at 329 PM EDT Thu May 17 2018

DISCUSSION...

Back door cold front has essentially washed out over the southern
Great Lakes/northern Ohio Valley as main push of cool air is east
southeast across eastern Canada/northeast CONUS as high pressure
builds into Quebec. This has set up quite the temperature gradient
across the area with upper 70s over far southeast lower Michigan and
50s further north (40s in the immediate vicinity of the Lake Huron
shore) thanks to the northeast flow off the cool lake waters.

East to northeast flow off this high will maintain dry weather into
Friday. Tonight`s low temperatures will be rather cool, especially
north of the M-59 corridor where mainly clear skies will allow for
decent radiational cooling and widespread temperatures in the lower
to mid 40s. Some increase in upper level clouds drawn north around
upper trough positioned over the Southeast CONUS will begin to
impact the southern forecast area and bring slightly milder readings
in the lower 50s overnight.

This system will continue to edge northward towards the area Friday
and lead to a steady increase/thickening of clouds as moisture is
pulled north from the Gulf of Mexico region. This will be conversely
lead to cooler readings over the southern forecast area on Friday as
mostly cloudy conditions hold temperatures in the mid/upper 60s. To
the north, temperatures may reach 70 in some locations where a bit
more sunshine occurs. However, locations along Lake Huron will once
again by much cooler as east/northeast flow persists.

Eventually, this influx of moisture with the northward progression
of upper trough and associated surface low pressure will bring rain
chances to the area. Model timing suggests that rain chances will
increase Friday evening over the southern forecast area and spread
north through the remainder of the region overnight as a vorticity
lobe rotates north in advance of main upper system to the south and
provide some degree of upper support.

Rain chances persist into Saturday (and a smaller degree Saturday
night) as this southern system opens and is pulled around fringe of
upper ridging along the eastern seaboard. Current track would skirt
Southeast Michigan. As suggested by previous shift, main plume of
moisture remains off to the east of the area throughout this period
so shower coverage will likely be somewhat limited at any given
time. In fact, will maintain only chance pops (40-50%) for much of
the area and limit likely (60%) to the far east/southeast forecast
area.

This system will bring a modest increase in humidity levels on into
the weekend. This will lead to milder nighttime temperatures in the
lower/mid 50s Friday night and mid/upper 50 Saturday night. While
temperatures will continue to range in the 60s/70s (depending on
degree of cloud cover Saturday), conditions should be noticeably more
humid.

A mid level wave and associated surface low pressure lifting out of
the Central Plains will bring a renewed surge of moisture and
instability to the region late Sunday into Monday. This will support
an increasing chance for showers and thunderstorms by late Sunday
that will continue into Monday as the wave slowly tracks east across
the region. Showers and thunderstorms could linger into Tuesday as
the GFS and CMC favor a slower, more northward track for the wave
while the ECMWF kicks the wave out of the region on Tuesday.
Regardless, dry and pleasant conditions look to return by midweek as
confluent upper level flow will support surface high pressure
building into the region. Temperatures will remain near to slightly
above average next week with highs in the upper 60s to lower 70s and
lows in the upper 40s to mid 50s.

MARINE...

Northeast wind at 20 to 25 kt is leading to enhanced wave action
along the Thumb shoreline and Saginaw Bay this afternoon. This is
expected to continue into the evening before weakening, with 4 to 6
ft waves across southern Lake Huron during this period. Wave action
paired with already high undisturbed Lake Huron water level
increases the potential for minor beach erosion and damage to any
unprotected watercraft or boating structures along the shore. Small
Craft Advisories and a Lakeshore Flood Advisory remain in effect
through 10pm tonight for the Lake Huron shoreline. Winds will veer
to easterly by Friday morning with conditions over Lake Huron
remaining below Small Craft Advisory criteria. Western Lake Erie,
however, will see higher gusts tomorrow afternoon and evening with
long easterly fetch. A Small Craft Advisory will be issued for this
period with winds gusting to 30 kt and wave heights reaching 4 to 5
ft.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...Lakeshore Flood Advisory until 10 PM EDT this evening for MIZ048-
     049-055-063.

     Lakeshore Flood Advisory from 6 AM Friday to midnight EDT Friday
     night for MIZ083.

Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-
     441>443.

Lake St Clair...NONE.

Michigan waters of Lake Erie...Small Craft Advisory from 6 AM Friday to midnight EDT Friday night
     for LEZ444.

&&

$$

AVIATION.....BT
DISCUSSION...DG/JD
MARINE.......TF


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