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fxus63 kdtx 161101 
afddtx

Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
601 am EST Mon Jan 16 2017



Aviation...

Multiple waves of precipitation are expected this afternoon into
Tuesday morning within moisture advection ahead the approaching
upper wave. The initial influx of moisture will occur in the mid
levels and is already tracking into Southern Lake Michigan. Given
the appearance on radar and upstream sfc reports, it stands to
reason that there will be an initial burst of precip early this
afternoon. The degree of wet bulb cooling suggests a mix of snow,
sleet and freezing rain. Amounts will be very light, with a steady
influx of moisture and thus better precip chances arriving after 22z
and persisting through the night. For ptk, fnt and mbs, the
predominate precip type this evening will be freezing rain with a
glazing of icing expected.

For dtw...the potential for a quick burst(s) of wintry precip this
afternoon does raise some concern for a little ice/sleet
accumulation. The degree of warm air aloft and rising temperatures
through the night will sustain mostly rain. There will however be a
period this evening, especially between 5 PM and 9 PM, where sfc
temps may drop to freezing or a touch below. This will warrant at
least a mention of freezing rain in the taf this evening.

//Dtw threshold probabilities...

* high in ceilings 5000 ft or less by mid afternoon through Tuesday
morning.

* Moderate for wintry mixed precipitation or freezing rain
this afternoon and evening.

* Low for ceilings and/or visibilities below 200 ft/one half mile
Tuesday morning.

* Low in thunderstorms Tuesday morning.

&&

Previous discussion...
issued at 331 am EST Mon Jan 16 2017

Discussion...

Upper wave as seen on dynamic tropopause coming out of
northern Texas, to be positioned over/near Kansas City Missouri
late today as the northern shortwave trough axis coming out of the
northern rockies helps draw the system northeast. Shearing out
upper level pv anomaly center looks to be over/near Southern Lake
Michigan early tomorrow morning.

Very dry airmass currently in place, per 00z DTX sounding, making for
difficult call when exactly overrunning precipitation will develop
over Southeast Michigan today as low level jet remains well to the
west through the day. Will be favoring a drier/virga/spotty
precipitation scenario during much of the daytime hours with lead
850-700 mb Theta-east moisture gradient lifting north. On flip side,
surface/low level anticyclonic flow and wet bulbing effects should
be able to hold surface temps around the freezing mark through
much of the evening hours as deeper moisture arrives (pw values
pushing up to 1 inch), and will be going ahead and issue a Winter
Weather Advisory for mainly freezing rain for northern two thirds
of County Warning Area (north of Eight Mile road). Deep enough cold air at the
start to even offer up a period of sleet/snow (mainly north)
before Max warm layer exceeds 3 c, and thus have issued Winter
Weather Advisory north of I-69, but snow/sleet accumulations
expected to be less than 1 inch, with freezing rain the bigger
concern.

Overall, surface temperatures look to be more in the marginal 30-32
degree range, which should help diminish/limit impacts (icing on
roads) somewhat. Although, have noted the colder raw regional Gem
and arw surface temps. Local probabilistic sref guidance indicating
low chance of a tenth of inch of ice accumulation across most
locations, but preference was to go a bit more aggressive with the
favorable sunset/Post sunset timing and just enough of dry/cold
southeast feed from southern Ontario to help offset the self
limiting freezing rain sensible heat release. Light glaze of ice
accumulation south of M-59, with a tenth to two tenths north before
the transition to all rain occurs overnight. Most of ice
accumulations occuring on the higher/elevated surfaces, such
as Tree Tops/wires. Will issue 2 segment advisory for differing
transition timing from south to north, 2 am, 6 am. Day shift
will have to watch southern four counties (especially
Washtenaw/lenawee) for short period of light icing, and can handle
it with Special Weather Statement or short fused advisory (4-10 pm).

Moist/warm conveyor belt clipping Southeast Michigan late tonight,
as 850 mb dew pts of 5 to 6 c move through. Steep mid level lapse
rates of 7 c/km from 700-500 mb with showalter index near zero
support slight chance of a thunderstorm.

Surface-700 mb lows/circulations tracking close to the Tri-Cities region
during the day on Tuesday, and should see good deformation rain
shield sweeping across Southeast Michigan during the day. Still
some mixed signals in how much warm air at the surface infiltrates
across the southern Michigan border as triple Point May not get past
Western Lake Erie, and will continue to highlight just 40s, but 50+
degrees possible in/around Monroe County.

Modest low level cold advection and cyclonic flow Tuesday night
supporting low clouds and possible drizzle/light rain showers, along
with light fog continuation. Not so sure there will be enough cold
air around to support much of a changeover to snow/sleet, as 00z Euro
maintaining 850 mb temps above 1 c, with any precipitation likely
shutting down before this marginally colder air arrives.

Polar jet displaced north of the Continental U.S. Will result in much above
normal temperatures for Southeast Michigan to end the work week
as southwest flow increases, with another moisture laden
low potentially approaching from the south by Friday morning (per
00z euro). The Canadian and GFS keep the system just to our south of
Friday, but it looks to be a real close call.

Marine...

A ridge of high pressure will hold across srn lower mi and Lake Erie
today, keeping winds light across the Southern Lake Huron basin and
points south. While southwest winds will hold through the day across
central and Northern Lake Huron, fairly stable conditions over the
lake will keep gusts under 20 knots. Low pressure will move into
Southern Lake Michigan from the southwest late tonight. While this
will lead to the development of east-southeasterly winds tonight
into Tuesday morning, strong over lake stability and a relatively
weak sfc low will keep peak wind gusts at or below 20 knots. The low
will track across Southern Lake Huron tues afternoon, supporting a
brief uptick in northeast winds across Northern Lake Huron. A
weakening gradient will ensue tues night as the sfc low departs the
region to the east, leading to weakening winds.

Hydrology...

An strong influx of moisture into Southeast Michigan will occur late
today into Tuesday morning, supporting widespread precipitation.
Most of this will fall as rain. There is a high probability that 24-
hour quantitative precipitation forecast totals will range between a half an inch and an inch. The
period of heaviest rain will occur between midnight and noon on
Tuesday. With no snow cover and frozen ground, there should be good
run off, so rises in area rivers are expected. Based on forecast
precip totals, river levels will remain below flood stage.

&&

DTX watches/warnings/advisories...
Michigan...Winter Weather Advisory from 7 PM this evening to 5 am EST Tuesday
for miz047>049-053>055.

Freezing Rain Advisory from 5 PM this afternoon to 2 am EST Tuesday
for miz060>063-068>070.

Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Aviation.....SC
discussion...sf
marine.......SC

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