Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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509
FXUS63 KDTX 181007
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
607 AM EDT Sat Aug 18 2018

.AVIATION...

Fog is the first concern for aviation interests this morning with
the possible exception of MBS where NW wind has managed to remain
above 5 knots. The combination of surface observations and satellite
imagery indicates the fog expanding toward the southeast as mid/high
clouds exit eastward, and with enough depth to usually last a while
after sunrise. The combination of daylight and increased northerly
wind will work to dissipate the fog on a faster pace than surface
heating alone, or will lift the moisture into a low stratus layer
through mid morning. Either way, borderline LIFR/IFR will be in
place through mid morning from FNT southward. After that, expect VFR
under gradual development of cumulus through afternoon. Showers
and/or thunderstorms are possible by mid afternoon but with only
isolated coverage into early evening.

FOR DTW... DTW is close to the edge of LIFR/IFR fog and stratus
during early to mid morning, eventually breaking up into VFR
ceiling. The main concern after that is light northwest wind veering
to northeast and increasing to around 10 knots which may require NE
traffic flow operations.

.DTW THRESHOLD PROBABILITIES...

* Low for ceiling/visibility down to 200ft and/or 1/2 mile.

* Moderate for ceiling 5 kft or less today.

&&

.PREV DISCUSSION...
Issued at 342 AM EDT Sat Aug 18 2018

DISCUSSION...

Rather typical mid August conditions will exist across the region
through the upcoming weekend. Pattern governed by lower amplitude
mid level nw flow and weak high pressure to the north will
effectively retain the resident environment, charactered by a
seasonable thermal profile and moist low level conditions. Standard
diurnal mixing potential under a high degree of insolation will tap
into 15C at 850 mb. This will translate into highs of lower to
middle 80s each day. The exception will be across the northern
thumb, where onshore flow will tend to mute the response slightly.
Humidity levels slightly below that noted on Friday, but still
noteworthy as dewpoints hover in the mid 60s. Large scale pattern
void of meaningful forced ascent, but potential does exist for a
localized region of low level convergence to emerge with the aid of
lake breeze activity. Given weak airmass destabilization - MLCAPE
less than 500 J/KG - isolated potential for a shower or thundershower
to develop mid-late afternoon today.

Dry conditions under a high degree of stability on Monday, as upper
ridging lifts across the region. Despite the increase in upper
heights, low level flow maintains an easterly component. This will
limit the prospects for a modest warming trend from readings noted
this weekend. Highs again low to mid 80s.

Upper level wave currently lifting across the pacific northwest
remain projected to strengthen as it digs into the plains over the
weekend. This system will then eject northeast early next week,
tracking through lower Michigan on Tuesday. Increasing mid level
southwest flow along the immediate downstream flank of this system
will draw deeper moisture northward in advance of the inbound height
fall center. This will likely establish a blossoming region of
showers and thunderstorms under increasing mid level warm air
advection and dcva. Precipitation chances will increase
incrementally locally Monday night in response, with rain becoming
likely overnight into early Tuesday as the surface low lifts
through. Passage of the trailing upper wave will be timed more
favorably with the diurnal heating cycle, maintaining a chance for
additional development throughout the day. Slightly cooler and
notably less humid conditions arrive in the wake of this system for
the latter half of the week.

MARINE...

High pressure building into the northern Great Lakes is producing a
moderate northeast wind pattern across Lake Huron to start the day.
A quick wave response exceeding Small Craft Advisory is expected as
wind speed reaches 20-25 knots at times across the long fetch of
central Lake Huron into Saginaw Bay. A diminishing trend is then
expected during the afternoon as the pressure gradient weakens. High
pressure settling over the central Great Lakes tonight brings ideal
marine conditions that last through Sunday, and even into Monday
before the next low pressure system moves into the Midwest. This
system arrives around the south end of Lake Michigan by Tuesday
morning with early indications of not much wind but generous
coverage of showers and thunderstorms.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...Beach Hazards Statement until 4 PM EDT this afternoon for MIZ049.

Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-441.

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.

&&

$$

AVIATION.....BT
DISCUSSION...MR
MARINE.......BT


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