Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 170503
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1203 AM EST Tue Jan 17 2017

.AVIATION...

Decreased coverage of heavier precipitation will allow surface
temperature to creep a little more above freezing in those trouble
spots north of DTW but it will take a couple more hours from
issuance time for that to occur. A transition to all rain will then
spread from the DTW area northward along with the next round of
heavier showers. Upstream thunderstorm coverage has been too low to
mention at any one of the terminal sites but expect at least a round
of heavy rainfall to move in from Illinois/Indiana during
the night through about mid morning.

In addition to precipitation type challenges, ceiling and visibility
will continue the downward trend into LIFR as the surface low and
warm front approach and move through SE Michigan. The latest
projections take the low center toward FNT by late morning with low
ceiling and fog breaking out along and ahead of the track over all
of SE Michigan. This will also be accompanied by fog reducing
visibility down to 1/2-1/4SM in classic warm frontal fashion. Any
breaks of improvement in the warm sector will be short-lived as the
trailing cold front moves through the region with IFR ceiling later
in the afternoon through Tuesday evening.

For DTW... Surface temperature is expected to continue gaining
ground above freezing during the night and as the next round of
heavier rain showers moves into the region. Ceiling and visibility
will also continue to fall into LIFR through most of the morning.
Prospect for thunder looks slim based on upstream observations.

//DTW Threshold Probabilities...

* High for ceiling 5000 ft or less tonight through Tuesday evening.

* Moderate ceiling and/or visibility below 200 ft/one half mile
  through the morning.

* Low for thunderstorms through the morning.

&&

.PREV DISCUSSION...
Issued at 1015 PM EST Mon Jan 16 2017

UPDATE...

The headlines are holding up as the anticipated below freezing
dip in temperatures produced some extra icing through the advisory
areas during the early evening. Since then, temperatures remain
remarkably consistent within a degree plus or minus 32F while
dewpoint rises with boundary layer moistening. The dewpoint
recovery and temperature resilience up against widespread
precipitation lends some confidence to the gradual warming trend
shown in guidance for the overnight hours. Most locations will be
in the south will be in the upper 30s by 4 AM and mid 30s Tri
Cities and northern Thumb by 6 AM or so. The expiration times for
the advisories look good at this point. Plan to monitor the Tri
Cities and northern Thumb were media and spotter reports have
indicated trace to about 0.1 inch of icing mainly in Bay and
Midland counties. This would be the only problem are possibly
needing an upgrade as temperatures will be closer to freezing for
longer duration there. Otherwise pockets of slower travel are
shown around the entire area. There was a power outage in
southern Lapeer county earlier in the evening which has since be
removed from the map.

Rising temperatures overnight will be aided by low pressure
approaching through Illinois and into Michigan by late Tuesday
morning. Strong low to mid level moisture transport is generating
another round of showers with a few thunderstorms that will move
through ahead of the actual surface warm front, the bulk of which
will be east of SE Michigan before the morning peak travel period.
The main concern by then will be the potential for dense fog as
the warm front moves north of the border up to about the M-59
corridor by late morning.

PREV DISCUSSION...
Issued at 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 Michigan 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.

&&

.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.
&&

$$

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


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