Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 121744
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
144 PM EDT Thu Oct 12 2017


.AVIATION...

Moist east to southeast low-level flow will continue at the TAF
sites through at least tomorrow morning. Borderline IFR/MVFR
ceilings will continue through most of the period, with ceilings
slowly lifting to MVFR primarily after 15z Friday. Forecast
confidence increasing in fog potential overnight, with lighter
surface winds and more stable static stability profile in the
boundary layer from recent model guidance suggesting better
environment for fog development. Best chance for fog will be tonight
as surface layer decouples. Potential for LIFR visibilities
possible, but confidence not yet high enough to include in the TAFs
at this time. Northeasterly winds will continue to slowly slacken
through the day, becoming light and variable overnight, and
southerly Friday at 5-10 knots.

For DTW...Northeast winds will continue to decrease into the evening
hours before becoming light and variable overnight and
south/southwesterly Friday. Persistent IFR, with occasional brief
dips to MVFR ceilings possible through at least 12z tomorrow, before
ceilings lift to MVFR to end the period. Increasing chances for IFR
fog in visibility restrictions overnight.

//DTW THRESHOLD PROBABILITIES...

* High for ceilings below 5000 ft through most of the TAF period.

* Low for visibilities at or below 1/2 SM tonight.

&&

.PREV DISCUSSION...
Issued at 355 AM EDT Thu Oct 12 2017

DISCUSSION...

Extensive low clouds are blanking much of the lower Great Lakes
region to the Ohio River Valley early this morning. A quick passing
upper ridge that has trapped this low level moisture will drift east
into the eastern Great Lakes by the afternoon. Surface high pressure
to our northeast and a progressive trough digging through the
Intermountain West will allow return flow out of the south. This will
keep the low level moisture in place throughout the day and continue
the mostly cloudy conditions. A few transient showers could occur
with the available moisture across southeast Michigan throughout the
day. It will not take much ascent in the lower levels within the
theta-e gradient to squeeze out some light rain showers. A subtle
surface trough edging into far southeast Michigan could also aid in
development, so will keep low end PoPs in the forecast. Cloudy
conditions will make it difficult for much of a warm up and it will
struggle to get out of the 50s aside from locations in the far east
near the lakes that could see lower 60s.

The trough now entering the Intermountain West will dig across the
Rockies on Friday as southwest flow aloft brings warm air advection
to Michigan. Temperatures at 850 mb will rebound from around 7C
Friday morning into the lower teens by Saturday morning. Clouds will
begin to clear a little Friday as well and allow a slight warm up. A
warm front will begin to orient itself across central Michigan
overnight Friday into Saturday and will be the focal point to the
start of a rainy weekend. Greatest chances for rain overnight Friday
through Saturday will reside along and north of the I-69 corridor
with decreasing chances south to the OH/MI border. Precipitation
chances continue and spread further south late Saturday into Sunday
as surface low pressure deepens across the Mississippi River Valley
and crosses through the Great Lakes. Warm air advection continues
with 850 mb temps reaching up to around 16C by Saturday evening. The
stalled frontal boundary will begin to lift north in response to the
the approaching system, leaving the forecast area in the moist warm
sector ahead of cold front pushing east. This will keep rain and
thunderstorm chances through Sunday afternoon.

Tightening surface pressure gradient will bring breezy conditions on
Sunday ahead and behind the cold front. Colder air behind the front
will help bring more seasonal temperatures to start the week. Less
active weather is in store as well with a surface high pressure
residing behind the front. High pressure drifts across the Ohio
River Valley into the eastern US while mostly zonal flow persists
from mid to late next week.

MARINE...

Moderate east to southeast winds hold firm over lake Huron today and
tonight north of weak low pressure lingering over Ohio. Continued
onshore flow will maintain rough boating conditions, with waves of 5
to 8 feet over the openwaters and 3 to 5 feet along the nearshore
waters. Small craft advisories remain in effect for appropriate
nearshore zones through tonight. Winds will slacken considerably
across lakes St Clair and western lake Erie during this time.

Fresh southwesterlies develop Friday downstream of an approaching
frontal boundary. This boundary will slowly settle into northern
sections of lake Huron Friday night and Saturday, providing a period
of unsettled weather with periodic showers. A period of stronger
southerly winds may emerge as warmer air lifts into the region south
of this boundary late Saturday and Saturday night.  Increasing
stability under this pattern will limit the gust potential and wave
growth.

HYDROLOGY...

A frontal boundary will gradually ease southeast and into central
lower Michigan Friday night.  This boundary will serve as an initial
focus for shower development as it lingers across this area Saturday
Low pressure tracking along this boundary will maintain the
potential for periodic showers and possible thunderstorms through
the remainder of the weekend.  Closer proximity to the frontal
boundary and eventual track of the low pressure system suggests the
greater rainfall potential will exist with northward extent, with
the highest rainfall totals likely north of the I-69 corridor.
Rainfall amounts in excess of one inch will be possible across
at least a portion of southeast Michigan this weekend.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 8 AM EDT Friday for LHZ421-441>443.

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

$$

AVIATION.....IRL
DISCUSSION...AA
MARINE.......MR
HYDROLOGY....MR

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at www.weather.gov/detroit.



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