Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 091802
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
202 PM EDT Sun Aug 9 2020


.AVIATION...

Precipitation stayed north and/or east of the terminals today
followed by a thickening of the diurnal cumulus field early this
afternoon, including some brief MVFR ceilings. Current dryness will
persist into the overnight period ahead of a slowly traversing cold
front. FROPA timing has shifted later and the previously anticipated
warm front appears to washout well southwest of the terminals. This
diminishes the potential for overnight activity leaving Monday
precipitation largely tied to pre-frontal showers/storms during the
afternoon and evening hours. Introduced a PROB30 for MBS to the
highlight the higher potential toward the end of the TAF period, but
timing remains uncertain. Winds backed southwesterly in time for the
18Z forecast and expect this to continue with slightly higher speeds
midday Monday with high-based VFR afternoon cu.

For DTW...SCT-BKN 4 kft cumulus ceiling with southwesterly flow
continues, unless the Lake Erie breeze front makes far enough
inroads to back winds south/southeasterly late this afternoon. Some
degree of shower/thunderstorm activity is expected on Monday, mainly
beginning late afternoon/evening. Included a PROB30 for SHRA after
21Z.

.DTW THRESHOLD PROBABILITIES...

* High for ceiling at or below 5000 ft today and medium on Monday.

* Low for lake-breeze to shift winds from southwest to southeast
  after 20z this afternoon.

* Low for thunderstorms on Monday.

&&

.PREV DISCUSSION...
Issued at 407 AM EDT Sun Aug 9 2020

DISCUSSION...

The return of mid summer heat and humidity is on schedule for today
as early morning surface observations show mid to upper 60s dewpoint
making eastward progress from the Midwest into lower MI. Expect this
air mass to wash over the entire area as the day unfolds and as high
temperatures make a run toward 90 this afternoon for heat index in
the mid 90s. The increased humidity comes in with limited potential
for thunderstorms with the best chance for activity actually
occurring during the morning. Model analysis fields indicate a
diffuse mid level theta-e ridge overhead in which elevated
convection will percolate leading up to sunrise. A generous
scattered coverage is possible mainly north of the I-69 corridor
until about mid morning before dissipating as elevated instability
fades. After that, the short wave ridge aloft reinforces mid level
warm air and effectively caps surface based convection around the
800 mb level according to model soundings. It is possible that an
isolated storm occurs around the Tri Cities to northern Thumb region
either near the shoreline or moving in from higher terrain areas of
northern lower MI. A low POP remains in the forecast for that area
late afternoon through this evening.

Warm and humid conditions become firmly entrenched across SE MI
tonight as light SW surface wind reinforces higher dewpoint from the
central Plains and Midwest. This occurs under clear to partly cloudy
sky through the night depending on the extent of cloud debris from
daytime thunderstorms. The scenario for convection remains complex
beginning with the ongoing central/northern Plains MCS and resulting
MCV that is projected to move over the U.P. tonight. Activity tied
to this wave remains well to our north but is followed by a new
round of surface based convection along the northern Plains to upper
Midwest cold front. These storms are shown to grow upscale enough
for a chance of survival into Lower MI Monday morning and into SE MI
by Monday afternoon. Larger scale support is limited to minor height
falls shown in model data preceding the main short wave still over
central Canada and the northern Plains. Mid chance POPs in the
guidance package look reasonable for a weakening pattern of
convective remnants.

Scattered remnant showers and cloud debris keep afternoon
temperatures in check with highs in the mid to upper 80s accompanied
by continued humid conditions. Boundary layer moisture stands ready
to fuel another round of convection that organizes along the cold
front moving into Lower MI Monday night. The front is driven into
the central Great Lakes by the southern extent of the Canadian upper
level trough. It provides substantial larger scale forcing that
leads to a stronger low to mid level wind field and sharpening
moisture axis ahead of the front. There is some concern about
recovery of instability as a limiting factor for convective
intensity but this should not have much affect on coverage which is
worthy of likely POPs Monday night into Tuesday morning.

Assuming the strength of the upper level trough holds into Tuesday,
then its passage should bring enough subsidence to push the cold
front south of the Ohio border Tuesday afternoon. The post front air
mass settles in with cooler and less humid conditions for the mid
week period. The front itself remains active to our south and could
brush the Ohio border region with some showers depending on the
actual character of any waves in the zonal flow aloft. These carry
low predictability for minimal POPs during late week and into
next weekend.

MARINE...

Broad high pressure will continue slowly drifting eastward toward
the Mid-Atlantic region today as return southwest flow continues to
bring an increasingly warm and humid airmass across the region that
will become firmly established today and Monday. Widely scattered
showers and thunderstorms will be possible this morning associated
with a pocket of elevated instability moving into northern Lower
Michigan and possibly Saginaw Bay/portions of central Lake Huron. The
better potential for showers and thunderstorms, however, will
accompany the arrival of a cold front Monday. Ahead of the cold
front, southwest winds will ramp up with gusts in nearshore waters
likely approaching 20-25 knots. Drier weather and lighter, northerly
flow behind the cold front passage will then prevail for the middle
of next week.

&&

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

$$

AVIATION.....KK
DISCUSSION...BT
MARINE.......IRL


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