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Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
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FXUS63 KDTX 010457
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1157 PM EST Tue Jan 31 2017


.AVIATION...

CIGS have been slowly improving to low end VFR as deep midlevel
deformation forcing peels away and deeper dry air advects into the
region. Still will be watching an area of confined FGEN forcing
track out of WI into far southern sections of Lower Michigan
overnight. The lead edge of this FGEN forcing is interacting with
favorable midlevels in generating some midlevel snow convection. The
potential exists for this to streak across the Detroit terminals
between 06-08Z. Uncertainty is very high with coverage, but the
potential does exist for short duration burst of vsby restrictions
of 1sm. Otherwise, another midlevel trough axis will swing through
the state later today, maintaining cold cylonic flow. Another period
of persitent MVFR cigs.

For DTW...Potential exists for IFR vsby restrictions with short
duration SHSN burst. Have included a tempo mention between 06-09Z.
Otherwise, another period of borderline MVFR/VFR cigs with continued
cold cyclonic flow.

//DTW Threshold Probabilities...

* High for cig aob 5kft.

* High for ptype of snow. Low confidence in coverage of snow showers
  early this morning.

&&

.PREV DISCUSSION...
Issued at 1057 PM EST Tue Jan 31 2017

UPDATE...

Overall the forecast remains in good shape with likely PoPs
between 06-12Z for the far southern CWA. The curious item for the
overnight is what will happen to the elevated convection (snow)
that has been very long lived today across portions of MN and WI.
Recently, the radar network has picked up on some expansion of the
convection to far western sections of Lower Michigan west of KAZO.
Ingredients for this convection are a combination of 700-500mb
Frontogenesis due to left exit region dynamics from an embedded
upper level Jet streak and very favorable midlevel thermodynamics.
The steep 700-500mb lapse rates (reference the KMPX raob and SPC
mesoanalysis), are upper echelon and with the saturation are quite
uncommon for this time of the year. Some in-house theta t progs
show the overlap of forcing/moisture well, and string out the
trajectory through the far southern cwa between 06-08Z tonight.
Earlier model data suggested that best likelihood for activity
was farther south down into Ohio, but latest 00Z nam is bringing
it across the detroit Metro area. Still have some reservations
that current activity will be able to hold its current strength as
character of the forcing will really change here moving forward
with jet streak flipping curvature. Activity has been dodging
observing sites, however, earlier obs upstream were showing legit
moderate snow with vsbys at 1/2sm mile or less. This does seem
reasonable if activity holds together.

PREV DISCUSSION...
Issued at 311 PM EST Tue Jan 31 2017

DISCUSSION...
Pseudo warm front extends from departing clipper system back across
south central lower Michigan. Large area of light to briefly
moderate snow is occurring along and north of this aided by
isentropic lift along the front and a mid level wave crossing the
state.  The snow is currently affecting the areas from northern metro
Detroit on north.  This snow will gradually lift northeast with the
front as the wave passes through.  Can still receive around a half
inch of snow south of I69 corridor to around an inch in the northern
Thumb through early tonight. South of all of this may see some
lighter snow shower activity through evening as lake enhance
activity pushes eastward aided by daytime heating.  Some rain could
also be mixed in with this activity  as temperatures have warmed into
the the 30s.

Later tonight as snow activity weakens and lifts out of the area a
secondary batch of snow may effect the far southern counties after
midnight.  Models show very stretched out vorticity along the
southern base of the upper trough over moist low levels.  A strong
jet core 150kts plus is moving southeast across MN and will round
the base of the trough across northern Ohio and Indiana.  Models
indicate a compact area of moderate lift in the left exit region
passing across the border.  This may produce a couple hours of light
to possibly moderate snow over Lenawee and Monroe counties and
possibly southern Wayne and Washtenaw. Duration would be short so
only expecting up to inch possible.

Wednesday may see a few break in the clouds the first half of the
day but a cold front will work its way through in the afternoon.
This will lead to snow shower activity across the north half
closer to the weak wave center and slight chance for snow showers
or flurries possibly mixed with rain across the south as temps
there will warm to the mid 30s.

Much colder air will filter in Wednesday night and Thursday along
with drier air which may lead to a fair amount of sunshine or at
least a lot more then we have had in the past few weeks.  Highs
though will basically in the low 20s though.

Surface high pressure from the northern Central Plains will start to
push east into the Great Lakes region Friday into Saturday, keeping
conditions dry, as we have the chance to see a healthy mix of clouds
and sunshine. The break from the clouds will be short-lived, as low
pressure from the Plains pushes east over Michigan early Sunday,
increasing cloud cover and bringing the chance for light snowfall
throughout the morning. A couple of changes to note for early next
week... New model runs are now honing in on an aggressive low
pressure system, expected to develop over the Central Plains late
Monday into Tuesday morning. In addition to this low pressure system
being stronger compared to yesterday`s 12Z runs (in particular the
GEM runs), the low takes on a more northeasterly path, pushing over
central Michigan by Tuesday/Wednesday. As a result, strong WAA is
being seen across GFS/ECMWF/GEM models, ushering in 850 mb degree
temperatures between 5-9 degrees C by 18Z Monday. As a result,
temperatures have been increased to the upper 30s by Monday, and mid
to upper 40s by Tuesday. Additionally, this low brings a large
precipitation shield to Michigan throughout Tuesday, with
precipitation cutting off Wednesday as the dry slot moves in. While
too far out to say with certainty, this system has the potential to
bring a fair amount of rain if the WAA holds up. In any case, this
low will be a feature of interest throughout the week and
adjustments will be made as new solutions come in.

MARINE...

South to southeast flow gusting possibly into the 20 to 25 knot
range over southern Lake Huron will ease this morning as low
pressure crosses Lake Erie. A weaker secondary low will then
track across Lake Huron late tonight into Wednesday. This will
make for a complex wind pattern Tuesday into Wednesday as several
cold fronts push across the area.

The initial cold front will first bring a westerly wind shift to
Lake Erie, Lake St Clair and Southern Lake Huron late today with
a second frontal passage behind the second low veering winds to the
west northwest area-wide by Wednesday. West to northwest gusts
will increase to 25 to 30 knots Wednesday into Wednesday night as
colder air spills into the region. These moderately gusty conditions
will then be maintained through early Saturday between several weak
areas of low pressure dropping through Ontario and high pressure
over the Northern Plains and Central Canada.

&&

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

$$

AVIATION.....99
UPDATE.......CB
DISCUSSION...DRC/AM
MARINE.......DRC


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