Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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561
FXUS63 KDTX 201045
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
645 AM EDT Fri Sep 20 2019


.AVIATION...

A slow moving upper level short wave across northern Lower Michigan
today will sustain intervals of mid and high clouds (based above 8k
ft) through the day. There has been an ongoing influx of low level
moisture into Se Mi early this morning, resulting from a weak low
level south-southwest flow. This has already translated to some
clouds in the 4k to 6k ft layer. Diurnal heating on this moist layer
will likely support scattered to perhaps briefly broken clouds
today.

For DTW...With the bulk of the high clouds north of metro,
radiational cooling has been efficient enough in developing some
shallow fog. This will erode within a couple hours after sunrise.

DTW THRESHOLD PROBABILITIES...

* Low in ceilings at or below 5000 ft.

&&

.PREV DISCUSSION...
Issued at 336 AM EDT Fri Sep 20 2019

DISCUSSION...

Recent warming trend continues again today as dominate ridge of high
pressure remains in control of the area while sinking farther south
down the east coast. A lead shortwave ejected from the deepening
longwave trough over the Rockies has folded the amplifying ridge
over the central Plains into the Great Lakes. This and the
southwesterly flow moderating the airmass for yet another day, will
lead to highs in the low/mid 80s. A weak mid level shortwave will be
drifting over northern MI this afternoon but should do little other
than provide a bit of afternoon cloud as a warm layer between about
5-9kft caps any attempts of shower development.

Notable change come Saturday as the leading flank of mid level
moisture and isentropic ascent with a pseudo elevated warm front
gets forced into Lower MI. A developing low level jet in advance of
the slowly moving cold front extending from the UP down trough WI
will force this boundary into the region and provide energy needed
for possible showers to develop on the leading moisture gradient in
the afternoon. With the jet axis and front located farther west,
expecting only some scattered showers over SE MI. Not expecting
severe storms with this activity as the cap is still present and
instability and shear are both weak in the approaching airmass. Most
of Saturday looks to be dry outside of the period of scattered
afternoon showers.

Much attention remains on Sunday and Sunday night as the positively
tilted long wave trough draws nearer. The already moisture laden,
humid airmass with PWATs around 1.5 inches will increase from there
as the axis of highest moisture just ahead of the cold front lifts
into the area with PWATS at or above 2 inches. Could even be some
remnants of Tropical Storm Imelda feeding moisture into the
prefrontal airmass. How exactly the day plays out with prefrontal
boundaries and the cold front is still in question but models have
been pretty consistent with an afternoon/evening fropa. With flow
vectors aligned parallel to the front we could get training waves of
showers along this slow moving front leading to heavy rainfall
across the area. Can`t rule out some thunderstorm activity but
soundings are not looking very favorable with warm air in the mid
levels, poor lapse rates, little in the way of instability, but
decent shear owning to the strong low level jet around 45 knots.
Decent boundary layer mixing in the warm sector will lead to a gusty
day with NAM and GFS showing mixing depths to about 875mb tapping
into winds around 30-35 knots.

The longwave trough will then lift through the region Sunday night
into Monday producing some lingering showers before high pressure
builds back in and shuts it down. Bulk of the activity may occur
across northern Lower as the core of the cold pool sweeps across.
Otherwise look for mainly a dry week ahead with troughing
leading to cooler temperatures with highs in the lower 70s.

MARINE...

Light south-southeast winds will prevail through the day today as
high pressure remains anchored across the eastern Great Lakes.
Southerly winds will steadily increase during the day Saturday into
Sunday in advance of a slow moving cold front approaching from the
northwest. Probabilities for wind gusts to reach 20 knots are
relatively high, however probabilities for gusts to reach 25 knots
drop off markedly. The exception is across Saginaw Bay out into the
middle portion of Lake Huron where gust around 25 knots are much
more likely. There are even chances for gusts to reach 30 knots.
This slow moving front will bring a good chance for rain with a few
thunderstorms possible.

HYDROLOGY...

A slow moving cold front combined with a region of relatively high
moisture content that will lift into the region within the pre
frontal southwest flow will provide increasing chances for rain late
Saturday night through Sunday night. Total rainfall amounts between
a half inch and an inch are highly probable. The pattern is also one
that will be conducive to supportive locally heavy rainfall.

&&

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

$$

AVIATION.....SC
DISCUSSION...DRK
MARINE.......SC
HYDROLOGY....SC


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at www.weather.gov/detroit.



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