Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 150447
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1147 PM EST Tue Nov 14 2017


.AVIATION...

A fairly extensive cloud deck above 6k ft will remain across the
region this morning as a result of continued mid level moisture
transport into Lower Mi. Brief high based showers/sprinkles are
possible during the morning within this moisture plume. A rapid
influx of moisture preceding the cold front will result in a quick
decrease in cigs in the 15 to 19Z time frame as rain overspreads the
region. The bulk of the rain will exit east around 00Z following the
passage of the sfc cold front.

For DTW...The increasing mid cloud deck will lift vsby`s back above
5SM around TAF issuance. Otherwise, widespread rain is not expected
to push into metro until the 17-19Z time frame.

//DTW THRESHOLD PROBABILITIES...

* High for ceilings below 5kft Wednesday afternoon and evening.

* High precipitation will fall as all rain Wednesday afternoon and
  evening.

&&

.PREV DISCUSSION...
Issued at 903 PM EST Tue Nov 14 2017

UPDATE...

A plume of mid level moisture will continue to be driven into Lower
Mi tonight in advance of a mid level trough. While the better
isentropic ascent will remain focused to the north and west, a
region of steeper mid level lapse rates nudging into the area from
the west will support some high based light showers overnight. This
will be more probable across the tri cities region, closer to the
stronger isentropic ascent. Farther south and east, weaker forcing
and a more pronounced dry layer from 900-800MB should keep showers
very light. Have therefore nudged overnight pops down a little across
the eastern half of the forecast area. The influx of deep moisture
and stronger large scale ascent and thus widespread rain will hold
off until late Wed morning/afternoon.

PREV DISCUSSION...
Issued at 353 PM EST Tue Nov 14 2017

DISCUSSION...

RAINY DAY EXPECTED WEDNESDAY...

NEAR TERM / TODAY THROUGH TONIGHT

As of 350 PM EST...Earlier stratus which plagued the region with
dreary cloud cover has finally dissipated across the region as high
pressure continues to shift off to the east. Low-level warm air
advection continues in the south/southwest return flow on the west
side of the high, with temperatures warming into the mid and upper
40s. Filtered sunshine and dry weather will continue through the
remainder of the afternoon hours, with high clouds gradually on the
increase especially across central Michigan ahead of the next
approaching storm system discussed in further detail in the short
term section below.

For tonight, most areas will continue to be dry with low
temperatures settling in the mid and upper 30s, roughly 5-10 degrees
warmer than last night with the continued warm air advection and
increasing high/mid cloud cover. Towards daybreak, warm advection
precip will be possible across far northwestern areas in the form of
drizzle, but 850 hPa temps warming to around 5C will keep this
activity in the form of liquid precipitation.

SHORT TERM / WEDNESDAY THROUGH THURSDAY NIGHT

A wet day is expected Wednesday across the region as the
aforementioned storm system approaches and tracks across the region.
Consolidating northern stream PV energy and a strengthening upper-
level jet streak ejecting out of the northern Rockies will spur
fairly substantial midlevel height falls across the upper Great
Lakes during the day Wednesday. Multiple pieces of shortwave energy
within the consolidating dynamical flow will also aide in a
widespread area of enhanced isentropic and QG lift, leading to a
developing low pressure system that will track across the UP into
Lake Superior. Strengthening frontal system aided by a tightening
confluent flow and convergent midlevel Q-vectors will lead to a
strengthening cold front as it approaches the region during the late
morning/afternoon hours. Strengthening jet streak aloft (approaching
120+kt) and isallobaric response will allow the system`s warm front
to push northward through at least the I-69 corridor, with southern
areas firmly in the warm sector of the system.

All of these factors in play will lead to a quick shot of rain ahead
of the passing cold front, mainly during the afternoon hours.
Rainfall amounts will generally range from a quarter to half of an
inch. There are hints of some weak elevated instability immediately
preceding the cold frontal passage, although not enough it appears
for any thunderstorms. Still, an enhanced line of showers may be
possible as the front moves through, with some gusty winds of around
35 mph possible as the showers tap into 50+kt winds just above the
boundary layer. Outside of these winds, it will be a gusty day, with
south/southwest winds gusting to 20-30 mph at times. High
temperatures will reach into the mid and upper 40s, limited by
abundant cloud cover and limited solar insolation.

Surface low pressure exits off to the northeast as the cold front
also exits east by the evening hours, with precipitation ending from
west to east. The exception will be for portions of the Thumb and
Lake Huron where another piece of shortwave energy looks to swing
through Wednesday night providing another round of scattered
showers. Lows Wednesday night will fall into the 30s.

850 hPa temps dive back to between -5 and -7C by Thursday morning as
cold air advection ensues in earnest and the flow shifts to the
northwest, remaining breezy. Enhanced upper-level ridging builds in
for Thursday along with drying midlevels leading to a dry Thursday,
with the exception being some possible Lake Huron induced showers
early Thursday morning. Dry weather continues into Thursday night as
ridge axis peaks overhead. High temperatures Thursday will range
from the upper 30s to lower 40s with lows Thursday night in the mid
20s to lower 30s.

LONG TERM / FRIDAY THROUGH MONDAY

Warm, moist southerly flow ahead of the next system will begin to
move in on Friday. The chance for showers increases through the day
as the warm front passes through, with the best chance for
widespread rainfall beginning in the evening and persisting through
the overnight. Highs Friday will be limited by cloud cover, but will
still approach the mid 40s. A few rumbles of thunder possible for
the southern counties overnight Friday into Saturday, though the
best dynamics and instability look to remain farther to our south.

The deepening low is progged to pass over the CWA on Saturday which
will keep the chance for rain around through the day. Continued warm
air advection will help highs reach the upper 40s and even mid 50s
for some areas before cold air wraps around the system late
Saturday. The system has been trending weaker with each model
update, but some gusty winds still possible Saturday and Sunday.

Some snow is likely to mix in behind the system late on Saturday and
snow showers are possible through the day Sunday as strong cold air
advection takes over. Highs will hover in the mid 30s on Sunday.
Ridging at the surface and aloft will return to the area Sunday and
Monday as the low continues to deepen and head for the Canadian
martimes. This will lead to quiet conditions for the early part of
the work week. Slight chance for another round of snow showers
Tuesday as a low drops through the northern Great Lakes, but will
continue to monitor this trend in the long range models.

MARINE...

The Gale Watch has been upgraded to a Gale Warning over the Lake
Huron open waters for Wednesday and Thursday. Small Craft Advisories
will also be issued for the nearshore waters and Lake St Clair.

Southerly winds will increase late tonight into Wednesday morning
within tightening pressure gradient between high pressure over the
New England states and low pressure and the attending cold front
approaching through the upper midwest. While this relatively mild
southerly flow will lead to increasing stability, it still appears
that wind speeds will reach 20 to 30 knots with gusts to near 35
knot gales over parts of the open waters by early Wednesday morning.

Similar wind speeds continue into Wednesday evening, veering to the
southwest as the aforementioned low pressure tracks to near northern
Lake Huron and the cold front sweeps through the region. Greater
instability within colder northwest flow in the wake of this system
will lead to a second maximum in wind gust potential late Wednesday
night into Thursday morning. During this time frame, wind gusts over
parts of the open waters may reach 40 knots.

HYDROLOGY...

A shortwave trough will cross the northern tier of the CONUS and
induce cyclogenesis over the upper Mississippi Valley and northern
Great Lakes late tonight into Wednesday. Decent moisture transport
within south southwest flow in advance of the cold front extending
south from this low pressure will lead to widespread rain across the
area on Wednesday. Average rainfall amounts between 0.25" and 0.50"
can be expected with local amounts perhaps approaching 0.75". This
amount of rainfall will not lead to flooding. Showers may linger to
some extent into the evening, but drier conditions will then develop
Wednesday night.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning from 6 PM Wednesday to 5 PM EST Thursday for
     LHZ361>363-462>464.

     Small Craft Advisory from 6 PM Wednesday to 5 PM EST Thursday for
     LHZ421-422-441>443.

Lake St Clair...Small Craft Advisory from 6 PM Wednesday to 5 PM EST Thursday for
     LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 6 PM Wednesday to 5 PM EST Thursday for
     LEZ444.

&&

$$

AVIATION.....SC
UPDATE.......SC
LONG TERM....IRL/TF
MARINE.......DG
HYDROLOGY....DG


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