Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 110503
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1203 AM EST Wed Jan 11 2017

.AVIATION...

Strong westerly wind will ramp down quickly as low pressure
continues to move into Quebec during the night. That will leave
coverage and duration of MVFR ceiling as the main concern through
the morning. The latest observations support a short window of lake
effect activation augmenting MVFR clouds that will impact FNT to MBS
for a longer time period while the wind direction backs toward the
south. Much lighter south wind will then help maintain VFR through
mid afternoon.

A new low pressure system developing in the Plains states during the
day will move toward Lake Michigan by Wednesday evening. This system
will pull a warm front into SE Michigan which will bring a steep
decline in conditions through MVFR into IFR. Rain is expected to
break out with the front and move all the way north through MBS
before the front moves back south later Wednesday night.

For DTW... Wind gusts running around 40 knots will diminish quickly
during the early morning while remaining from about 250 degree
direction. Colder and drier air moving in is expected to break up
the low clouds and allow VFR through mid afternoon. Confidence is on
the high side for a new round of IFR by late in the day.

//DTW Threshold Probabilities...

* High for ceiling below 5k ft during the night then low through the
  day. High late afternoon into Wednesday night.

* Moderate for exceeding cross wind threshold from 250/G40
  at the start of the forecast.

&&

.PREV DISCUSSION...
Issued at 935 PM EST Tue Jan 10 2017

UPDATE...

The high wind warning will remain in effect through the evening with
no changes as solid mid 40 knot wind gusts, with a few peak 50s,
continue to be reported from SE Wisconsin (01Z at SBM and 02Z at
FWA) through northern Indiana. There remains a few more hours of
damaging wind gusts for SE Michigan in this scenario then
diminishing to advisory levels shortly after midnight.

The damaging wind field is being supported by strong low pressure
that continues to deepen during the mid evening while exiting
eastern Lake Superior. There were a few surges of mid 50 mph gusts
and isolated power outages in the warm sector with showers and as
temperatures rose into the mid and upper 40s throughout the
region. Now, the associated cold front is on the way through SE
Michigan as of this writing. Dynamic forcing with the front and strong
cold advection immediately behind will steepen lapse rates below
800-850 mb where a mid 50 knot wind field continues to reside
based on the latest RAP model soundings and radar VWP. Wind gusts
in the 40 to 50 knot range will then remain possible at all
locations through about 1 AM as the low level thermal trough
surges into the region. The wind field will then quickly diminish
as the low continues to move rapidly toward James Bay. The low
level thermal trough will also lift north of the region and leave
more neutral thermal and shallow boundary layer conditions over
SE Michigan. This may allow a downgrade to advisory by then,
especially in the Detroit area.

PREV DISCUSSION...
Issued at 300 PM EST Tue Jan 10 2017

DISCUSSION...

Strong cyclone, impressive in appearance on water vapor imagery, is
rapidly deepening over the western Great Lakes at press time. At
approximately 986mb, RAP13 progs suggest another 10mb to go in the
next 9 hours or so. Accompanying wind field has ramped up
considerably over the last couple of hours and will continue to
rapidly strengthen over the next several hours.

Radar mosaic indicates to well-defined lines of showers. The first
is along the convergent right side of the 80kt low-level jet. The
second is positioned immediately along a strong cold front that is
anchored firmly to the left side of the LLJ. The corridor in between
will contain the greatest threat for wind gusts to approach 60 mph
through approximately 02z. 0-1km Richardson numbers of 0.2 to 0.35
indicating a stability balance capable of supporting eddies that
will mix down bursts of higher momentum. Mean wind within this layer
will increase to 50 to 55kts between now and fropa. Widespread
upstream peak wind gusts of 40 to 45 kts offer certainty in meeting
wind advisory criteria this evening. However, increasing
availability of higher winds within the column along with some
potential for deeper mixing associated with cold fropa and/or
attendant convection warrant issuance of the High Wind Warning.
Confidence is highest along and east of the glacial ridge where most
favorable Ri values and strongest mean winds will be juxtaposed.

Post-fropa environment will be characterized by a slightly weaker
wind field, but far more favorable dynamic forcing. Once again,
confidence is high in meeting high-end advisory level winds through
at least 06z. Given existing HWW headline, simply extended it
through this period. Isolated wind gust reaching warning criteria
post-fropa not out of the question. Best chance north of M59.

Cold advection will drive temps into the 20s tonight. Persistent jet
over the great lakes will strengthen existing baroclinic zone as
another shortwave ejects out of the west. Gradient will respond by
turning southerly as the boundary wavers to the north. High temps
easily approach 40 on Wednesday. Isentropic ascent on the warm side
of the frontal zone will increase Wednesday afternoon into Wednesday
night. Surface-850mb layer fgen will favor a corridor of enhanced
precip rates, but attm vast majority appears to fall as rain.
Departure of the wave will force the front south...any lingering
precip falling as sleet/fzra across the far NW CWA late Wednesday
night. Similar scenario unfolds on Thursday, but nudged further
south. Higher chance for fzn precip, but QPF likely to remain on
the lower side.

A high pressure system pushing in from the Northern Central Plains
into the Great Lakes region Thursday into Friday will keep
conditions dry throughout the day on Friday, as winds remain light.
For the weekend, a stationary front will set up across the Ohio
Valley, which will keep the bulk of the precipitation south of
Michigan, however, overrunning along the front will bring the chance
light snow across the southern half of Michigan throughout Saturday
morning and afternoon. The better chance for precipitation will come
during the early part of next week as low pressure pushing from
Texas moves northeast into the Great Lakes region. Much like
yesterday, there are still large variations across the long range
models regarding the timing of the low. The GFS model pushes the low
over Michigan throughout Tuesday, while ECMWF model runs now push
the low over us by Wednesday. Both models still exhibit decent WAA
as above freezing 850 mb temperatures are ushered into the region.
As this potential event is still a week out, convergence between new
model runs will be needed to solidify timing and precipitation type.

MARINE...

The existing gusty conditions expected to steadily increase through
the evening, enhanced by developing cold air advection accompanying
a strong frontal passage. This will lead to an extended period of
high end gales across a large portion of Lake Huron.  Potential for
gusts to approach storm force tonight, particularly from Saginaw Bay
into central Lake Huron.   Rapid reduction in wind gust magnitude
then expected by the mid morning hours on Wednesday.  Moderate
southerly flow throughout Wednesday, but with gust potential limited
by an increasingly warm and stable overlake environment.  Winds turn
northwesterly by Thursday as a frontal boundary sags across the
region.  This may provide a period of stronger winds by the end of
the week as colder works back in.

PREV DISCUSSION...
Issued at 946 AM EST Tue Jan 10 2017

Winter Weather Advisory will be expiring on schedule this morning as
ptype transition through sleet/fzra to rain is occuring on schedule.
Focus for this afternoon will be on wind potential. High Wind Watch
still looks good based on latest data. Surface low over Iowa is
progged to deepen at a rate of about 1mb/hr for the next 12 hours,
reaching 980mb just north of the straits. Wind field will be very
strong, with the NAM/RAP modeling nearly 90kts at 850mb. Common
ingredient often missing in potential high wind scenarios is dynamic
forcing. However, ARW/RAP/EC all indicating very strong isentropic
descent associated with incoming cold advection. Continue to shy
away from NAM/NMM due to terrible handling of the surface layer due
to snowpack and resultant erroneously high boundary layer stability.
High wind warning criteria of 50kts reasonably attainable within the
frontal zone itself followed by either warning or high-end advisory
thereafter. In addition, convective showers leading the front will
provide another mechanism by which warning criteria may be reached.
Plan to hang on to the high wind watch until aftn package.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...High Wind Warning until 4 AM EST Wednesday FOR MIZ047>049-053>055-
     060>063-068>070-075-076-082-083.

Lake Huron...Storm Warning until 7 AM EST Wednesday FOR LHZ363-421-422-441-462.

     Gale Warning until 7 AM EST Wednesday FOR LHZ361-362-463-464.

     Gale Warning until 4 AM EST Wednesday FOR LHZ442-443.

Lake St Clair...Gale Warning until 4 AM EST Wednesday FOR LCZ460.

Michigan waters of Lake Erie...Gale Warning until 4 AM EST Wednesday FOR LEZ444.

&&

$$

AVIATION.....BT
UPDATE.......BT
DISCUSSION...JVC/AM
MARINE.......MR


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