Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 220950
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
550 AM EDT Sat Sep 22 2018


.AVIATION...

Stratus has set up across most of the area and should linger through
the afternoon as northeast flow advects moisture under the
subsidence inversion. Sometime later this afternoon/evening the
clouds should scatter out as dry and and high pressure build farther
east. This will favor clear skies tonight with some potential for
shallow fog by morning. Will hold off on including in tafs until we
can get better data from hires models. Winds should stay below 10
knots today while they veer from N to NE.

For DTW...Ceilings below 5kft should carry us into the afternoon
hours before some scattering can occur. Clear skies look likely
tonight with some potential for shallow fog by morning. Winds will
decrease while veering from N to NE today becoming calm tonight.

.DTW THRESHOLD PROBABILITIES...

*  Moderate for ceilings 5000 ft through this afternoon. Low this
   evening.

&&

.PREV DISCUSSION...
Issued at 357 AM EDT Sat Sep 22 2018

DISCUSSION...

Steady expansion of high pressure into the great lakes will provide
a stretch of tranquil conditions throughout the upcoming weekend.
Retention of low level north-northeast flow as the high builds into
northern lower MI will sustain the resident cooler and drier
environment today. A modestly mixed boundary layer into a 850 mb
layer characterized by temperatures of 2 to 4C will support afternoon
readings of lower and middle 60s. Overall cloud trends may
effectively govern the diurnal temperatures response as well, but
certainly carries some uncertainty within this setup. Some degree of
stratus may exist post-daybreak, but the the overall coverage looks
to become increasingly sparse with time as drying continues to
shrink the existing moist layer tucked beneath the inversion.
Prevailing flow of cooler air off the warmer lake Huron waters will
then allow for some inland penetration of lake moisture. This will
be working against a deepening/mixed boundary layer condition. This
points to the possibility for a brief increase in coverage of
diurnal stratocu during the afternoon period.

Surface high drifts across southeast Michigan tonight. The loss of
diurnal support and removal of onshore flow will favor a progressive
extinction of lingering cloud cover this evening. The combination of
open sky, decreasing wind speed and extensive depth to the existing
dry layer will subsequently support favorable radiational cooling
conditions. Lows generally distributed in the 40s, but with an
environment that could allow the coldest locations to bottom out in
the upper 30s.

Surface ridging will maintain a strong influence through the latter
half of the weekend. Dry and stable conditions will yield nearly
full insolation on Sunday. General airmass modification under the
late September sun, with no real signal to suggest any meaningful
low level advection given the light low level easterly gradient.
Highs 65 to 70 degree range. Another night of favorable radiational
cooling conditions Sunday night, perhaps influenced slightly by the
persistent of light easterly winds. This will leave lows ranging from
mid 40s to near 50 degrees by Monday morning.

Upper wave currently meandering across the southern Plains will
eventually eject northeast early next week. This process at least
partially in response to the strong upstream height falls underway
throughout the western U.S., driven by the inland penetration of a
higher amplitude trough and attendant upper jet. This lead wave
remains projected to draw a plume of deeper gulf moisture northward
and toward the region sometime Monday night into early Tuesday.
Pleasant conditions in advance of this moisture advection on Monday,
with simply a steady increase in high cloud likely by the latter half
of the day. A noted increase in humidity as low level flow veers to
southeasterly allowing dewpoints to creep upward, but with relatively
seasonable temperatures expected.

Warm front will accompany the aforementioned upper wave into the
region Monday night. Increasing rainfall potential results, enhanced
by a period of stronger moisture advection and diminishing mid level
stability. The area will briefly settle within a moist and milder
environment on Tuesday, immediately downstream of the inbound higher
amplitude trough axis and attendant cold front. Potential warm
sector destabilization carries a high degree of uncertainty at this
stage, with strong dependence on the exit rate of the early day
clouds/rain. The current projection for a late day or evening cold
frontal passage could provide an opportunity for organized
convective development should greater instability ultimately
materialize.

MARINE...

Area of high pressure building in from the west will bring drier and
cooler air to the Great Lakes this weekend. The weaker pressure
gradient has allowed winds to relax early tonight, a trend that will
continue through morning. Winds will largely remain below 15 knots
today through Sunday afternoon until a cold front drops south
through the region. Westerly winds will flip to the northeast while
increasing into the 20 to 25 knot range.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until noon EDT today for LHZ421-441>443.

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

$$

AVIATION.....DRK
DISCUSSION...MR
MARINE.......DRK


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