Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 161750
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
150 PM EDT Mon Oct 16 2017


.AVIATION...

Mostly VFR conditions for all sites through this TAF period with
light westerly to southwesterly winds this afternoon. There are
pockets of MVFR CIGS moving across far southern Michigan, but expect
those to lift throughout the afternoon. Winds will become light
after 0Z and clouds will also begin to clear out. A tightening
surface pressure gradient will allow winds to pick up overnight into
tomorrow morning and could bring gusts up to 20 knots out of the
southwest.

For DTW...CIGS will hover right around 5000 feet this afternoon as
clouds move in from the west. The cloud deck could dip below 5000
feet from time to time throughout the afternoon.

//DTW THRESHOLD PROBABILITIES...

* Low in ceilings at or below 5000 ft today.

&&

.PREV DISCUSSION...
Issued at 341 AM EDT Mon Oct 16 2017

DISCUSSION...

Near Term / Through 6 PM Monday evening

As of 340 AM EDT...A much quieter night has been ongoing across
southeast Michigan compared to the active weather last night. The low
pressure and cold front which brought widespread rain and gusty
winds over the past 24 hours continues to quickly move northeast,
with the parent low moving into Newfoundland with the trailing cold
front progressing across the east coast. Across southeast Michigan,
high pressure at the surface continues to build into the region under
a predominately northwest flow. Aloft, a trailing shortwave trough
continues to progress eastward just north of the Straits in the
larger longwave trough regime currently in place across the eastern
third of the CONUS. Mainly dry weather will prevail through the rest
of the night, but a few sprinkles cannot be ruled out across the Tri-
Cities region, but of little consequence to mention in the grids.

Despite a still fairly tight, but gradually weakening pressure
gradient, the shortwave trough has helped to disrupt the low-level
flow allowing winds to continue to subside across the region early
this morning. Still, enough of a gradient flow, around 5 mph, will
lead to a modestly well-mixed nocturnal boundary layer helping to
limit the fall of low temperatures despite a strong cold advection
regime (850 hPa temp drop in the past 24 hours from 13 C to -1 C)
and clearing skies. Because of these factors, low temperatures will
bottom out in the upper 30s across the Thumb and Tri-Cities to lower
and mid 40s in the metro and towards the Ohio border, vs. a scenario
of more mid 30s and a more substantial threat of frost. With the
continued surface winds just above 5 mph through the night, however,
not anticipating any frost issues.

The shortwave trough will also aid in enhancing lake instability
over Lake Huron through the remainder of tonight and into the day
today, with sfc-850 hPa delta-T values approaching 18-21 C (latest
Lake Huron water temp readings generally around 60  to low 60s F).
Cloud cover aided by the cyclonic flow associated with the shortwave
trough and general lake instability combined with the thermodynamic
instability will lead to a chance of waterspouts through the morning
hours over the Lake Huron waters. One potential limiting factor
though will be the effective depth of the convective cloud layer,
which does not look to be as deep and favorable as a classic event,
but nevertheless the potential is there and will raise the awareness
as we get into more of these types of flow regimes this fall and
early winter.

For today, the aforementioned surface high pressure will continue to
build across the region, along with increasing heights aloft as the
shortwave trough exits north and east of the immediate region. With
the core of the surface high across the central Plains, surface
winds will gradually become more west/southwesterly through the day,
but on the lighter side under 10 mph. Dry weather will prevail with
diurnally-driven, lake-enhanced stratocu leading to partly cloudy
skies by this afternoon. High temperatures will only rise into the
mid and upper 50s under a lingering weak cold advection regime.

Short Term / 6 PM Monday evening through Wednesday

The short term period will be dominated by tranquil and gorgeous
fall weather for mid October as high pressure settles across the
southeast CONUS with gradually rising midlevel heights with time.
Low wave number Northern Hemispheric flow will help contribute to
the stagnant synoptic flow pattern, which will remain locked in
place well into the extended portion of the forecast as well. Dry
weather will continue to prevail under mostly sunny skies.
Occasional thin cirrus may impact mainly areas north and west of
Detroit as pieces of potent shortwave energy rotate through an
active polar jet well north into Canada. The pressure gradient will
gradually tighten in time during the short term as well between the
high pressure across the Southeast and deep surface low in the
northern stream flow west of Hudson Bay, allowing for some breezy
southwest winds Tuesday and Wednesday.

Temperatures will begin to moderate to above normal through midweek
as low-level southwesterly return flow becomes firmly entrenched
across the region. High temperatures will warm well into the mid and
upper 60s for Tuesday and Wednesday, with a few readings near 70 not
out of the question with deep boundary layer mixing realized under
the tight pressure gradient regime. Low temperatures will be in the
40s.

Long Term / Thursday through Sunday

More of the same for the extended portion of the forecast as high
pressure remains locked in place across the eastern third of the
CONUS will expanding ridging aloft. A weak and dry cold frontal
passage will occur on Thursday with no noticeable sensible weather
difference other than a brief shot of low-level drier air.

High amplitude upper-level ridging will keep the synoptic pattern
quiet into the first half of the weekend. Long range guidance then
shows signals of potent Pacific energy moving into the west coast,
which looks to gradually breaking down the upper-level ridging as
low pressure develops along a tightening baroclinic zone across the
central CONUS. Still a lot of time to watch this potential system
which looks to be the next chance for widespread rainfall across the
region.

Temperatures will continue to run above normal through the long term
period, with lower 70s high temperatures looking likely heading into
the weekend.

MARINE...

A modest north to west wind will persist over the central Great
Lakes region today and tonight as surface high pressure builds
across the mid Mississippi and Ohio River Valleys. Potential for
waterspouts will also continue through the first half of today as
lake effect continues out over Lake Huron. The pressure gradient
will strengthen substantially late tonight and into Tuesday as the
region is sandwiched between the southeastern U.S. high pressure
and low pressure near James Bay. Unstable conditions will still be
in place off of the below normal airmass setting up what should be
gusty weather. Southwest winds of around 30 knots are anticipated
for much of the Lake Huron basin and Saginaw Bay with a favorably
long southwest fetch. Persistent gradient winds over the region
should then result in surface winds remaining between 20-30 knots
for Wednesday and a good chunk of Thursday.

&&

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

$$

AVIATION.....AA
DISCUSSION...IRL
MARINE.......CB


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