Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 162013
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
313 PM EST Mon Jan 16 2017

.DISCUSSION...

Closed mid level circulation now over Kansas on track to lift across
lower Michigan by Tuesday morning.  Short term attention through the
early evening period still focused on the solid mid level fgen
response ongoing well downstream of the main system dynamics and
moisture advection. The maintenance of this ascent across the 700-
850 mb layer sustained thanks to favorable repositioning within the
right entrance region of an exiting northern stream upper jet axis.
Magnitude of this forcing enough to overcome the residual dry low
level environment, and will sustain pockets of light precipitation
this evening as this band of forcing drifts northeast with time.
Lack of saturation down low will continue to yield a myriad of
precipitation types through the evening commute. Window for
meaningful precipitation appears to briefly close for points
along/south of the I-94 corridor here shortly, as fgen pulls north
while the main band of moist isentropic ascent now holds off until
after 02z.  With temperatures now creeping above freezing and
dewpoints closing in on 30 degrees, this corridor will simply
maintain a very small window this evening to see freezing rain.
Conditions currently do not warrant an upgrade to an advisory and
will continue to highlight any localized episodes with
SPS/graphicast products.

Ensuing increase in isentropic ascent in advance of the main pv
anomaly, with an accompanying plume of deeper moisture overtaking
the region 02z-04z tonight.  This will result in a period of
widespread precipitation that continues through early Tuesday.
Existing near or sub-freezing surface temperature from the M-59
corridor northward solidified by a solid component of evaporative
cooling, effectively sustains a longer window for freezing rain.
Temperatures then slowly lift above freezing southwest to northeast
across the advisory area through the early morning period. Ice
accretion amounts in excess of a tenth of an inch certainly possible
/particularly north/ given the residence time.

Secondary pop of strong forcing tied to the shortwave passage mid-
late morning Tuesday to provide a renewed period of rainfall.
Diminishing mid level stability under a high degree of dynamic
forcing may also yield some embedded thunderstorms over southern
sections during this time.  Position/track of the surface low may
pinch the warm sector off to the east before it intrudes, but still
looking at highs pushing into the 40s most locations during the day.
Residual pockets of light rain/drizzle possible into the afternoon
under moist low level conditions.

Northern stream wave tracks through early Tuesday night.  Enough
lingering moisture depth to yield a low coverage of showers with the
associated increase in PVA, but the better ascent may pass by just
to the south.  Cooler air drains in overnight, but timing lags the
exit of the better moisture so the window for a changeover to snow
will be limited.  Low and mid level ridging to then support dry
conditions with above normal temperatures heading into Wednesday.

Southwesterly flow will allow milder air to flow into Southeast
Michigan on Thursday while ridging builds over the Great Lakes. An
upper level low moving northward out of the Southern Plains on
Friday will bring the next chance of precipitation to Southeast
Michigan Friday into Saturday as a band of vorticity pushes
northward. While some differences regarding the track of the low and
thus precip chances for Michgian exist between model solutions at
this time, enough warm air will be in place to keep precip type as
rain. A low pressure system developing over the Southern Plains this
weekend then strengthens as it moves into the Ohio Valley early next
week bringing the next chance of precipitation to Michigan early
next week.

&&

.MARINE...

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 continue
tonight and into Tuesday morning, supporting widespread
precipitation. Most of this will fall as rain. There is a high
probability that 24-hour QPF 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.

&&

.PREV DISCUSSION...
Issued at 1239 PM EST Mon Jan 16 2017

AVIATION...

Waves of precipitation are expected to continue this afternoon into
Tuesday morning as they slowly lift northward ahead the approaching
upper wave. The initial influx of moisture has already produced
sleet and freezing rain for the Detroit area TAFs. The degree of wet
bulb cooling continues to suggest freezing rain and sleet for the
afternoon and early evening for the Detroit area. Expect a slightly
deeper cooler air mass and wet bulb potential to bring some snow
chances for FNT and MBS before changing over to all freezing rain
this evening. Freezing rain changes over to all rain by 01z for
Detroit TAFs but lingers to around 06z for PTK, FNT, and MBS. Should
produce a light glaze of ice...especially for the northern TAF
sites. Rain will then continue through daybreak Tuesday

Ceilings and visibilities will continue to lower through the
afternoon and evening. After 06z tonight and into Tuesday morning
all TAF sites will have LIFR Ceilings with visibilities between 1/2
mile and one mile.

For DTW...The potential for freezing rain through about 00z to 02z.
Still some concern for a little ice 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 through evening. Around midnight and later, ceilings
lower below 1000 feet and will remain there through Tuesday morning.
Ceilings could get close to the 200 ft thresholds toward daybreak
Tuesday morning.

//DTW Threshold Probabilities...

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

* Moderate for 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.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 5 AM EST Tuesday FOR MIZ047>049-
     053>055.

     Freezing Rain Advisory until 2 AM EST Tuesday FOR MIZ060>063-
     068>070.

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

$$

DISCUSSION...MR/JD
MARINE.......RBP
HYDROLOGY....RBP
AVIATION.....RBP


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