Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 160154
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
854 PM EST Mon Jan 15 2018

.UPDATE...

Southeast Michigan to hold position overnight within the broad
eastern cyclonic extension of an elongated trough/closed low
currently residing over northern IL/southern WI.  Earlier spike in
associated cva prompting an uptick in dentrite production and
subsequent flake size now exiting to the east. The underlying moist
cyclonic flow aided by favorable thermal placement of a moist layer
supersaturated with respect to ice with sustain lower intensity
light snow showers or flurries through the night. A more localized
focus for higher intensity snow showers may emerge within the
convergence axis governed by placement of the inbound cold frontal
occlusion set to stall over lower Michigan overnight and early
Tuesday. Not a convincing signal per recent model guidance to suggest
a strong response, as would be more typical if this were a lake
convergence band. Nonetheless, potential does exist for some heavier
snow showers to eventually develop during the morning period
somewhere within the I-94 to I-69 corridor. Those locations will be
susceptible to a quick accumulation /inch range/. Otherwise, a
general accumulation at half inch or less expected moving forward
overnight.

&&

.PREV DISCUSSION...
Issued at 620 PM EST Mon Jan 15 2018

AVIATION...

Extensive area of light snow will persist through the late evening
hours, as the region remains within the influence of cold, cyclonic
mid level flow associated with an upper low. A more localized focus
for some heavier bursts remains tied to convergence that develops
tonight along an attendant frontal boundary. Confidence in the
occurrence, location and intensity of any heavier snow showers will
remain low until placement of this convergence becomes clear.
Greater potential likely resides from the Detroit corridor up
through PTK throughout Tuesday morning, where periodic IFR
conditions will be more probable. Otherwise, trending toward a broad
coverage of MVFR/VFR light snow showers across the SE Michigan
airspace as the degree of forcing eases with time tonight. Passage of
a surface trough will provide a secondary focus for snow shower
development on Tuesday. A possible diurnal contribution to the
coverage will make all terminals suscipitible to scattered to
numerous snow showers lasting through late Tuesday.

For DTW...Broad region of light snow will persist over the airspace
late this evening. Frontal boundary will lift into the region
overnight, potentially providing a greater focus for some heavier
snow showers through Tuesday morning. Some uncertainty yet on the
possible occurrence, timing and duration

/DTW THRESHOLD PROBABILITIES...

* High for cig aob 5kft

PREV DISCUSSION...
Issued at 307 PM EST Mon Jan 15 2018

DISCUSSION...

A lead mid level short impulse associated with an upper low now over
the Upper Mississippi Valley has been pivoting from south to north
across the forecast area this afternoon. Decent mid level height
falls and strongly difluent upper level flow have sustained light
snow throughout the day. While strong moist isentropic ascent has
shifted across Ohio within the warm conveyor, a narrow ribbon of
better ascent developed along the lead edge of the mid level PV max,
resulting in a brief period of higher intensity snowfall rates now
lifting northward across Se Mi as of 19Z. The water vapor loop shows
a region of mid level dry air now approaching the MI/IN/OH border,
set to lift across Se Mi during the evening behind the mid level
short wave feature. The result will be a gradual decrease in the
areal coverage of the light snow. By this time, total accumulations
since this morning of around 2 inches still seems reasonable.

The upper low is forecast to elongate as it rotates into Lower Mi by
Tues morning, while the associated surface low extends across
roughly the I-94 corridor as it stretches into srn Ontario overnight.
Although the mid level moisture will strip away this evening, ample
low level moisture will reside across Se Mi through the night. The
low level airmass will be cold enough for ice nucleation within
these lower clouds. So while the more widespread light snow
diminishes this evening with waning synoptic scale ascent,
increasing forcing in the boundary layer will result in nmrs to sct
snow showers. The greater focus will be across metro Detroit/Ann
Arbor and points south with the approach of the sfc low and
associated sfc trough axis. The region of ascent in these showers
will be focused more within the thermal regime for good dendrites,
so snowfall rates are likely to be greater than what occurred earlier
today. This suggests at least some additional minor accums tonight.

The elongated upper low will gradually push off to the east late
Tues/Tues night. The associated surface low will in turn exit to the
east of the region. There will however be a couple lingering surface
troughs holding back across Se Mi, providing a focus for sct to nmrs
snow showers to persist through Tues afternoon. Steepening low level
lapse rates due to diurnal contributions may support some brief
intense snowfall, warranting at least minor (less than one inch)
accums. Lake enhancement under northerly flow may however support
locally high totals across NE Huron County. Overall expect little
variation in temps this evening through Tuesday with persistent cloud
cover and limited thermal advections.

Weak ridging ahead of a quick-moving shortwave trough will bring dry
conditions midweek. Recent model guidance then indicates the
shortwave will quickly move across Lower Michigan Thursday night.
With limited moisture available, impacts will be limited to an
increase in cloud cover with a few light showers at most before dry
conditions return to end the workweek. High pressure centered over
the Southeast US will allow return southwesterly flow to begin
advecting milder air into the region during the late week period with
highs reaching the upper 30s by Friday.

An upper level trough digging into the Southwestern US on
Saturday will induce lee cyclogenesis over the Southern Plains. This
low pressure system will further strengthen southwesterly flow over
the region advecting warmer, moister air northward through the
weekend. This will allow temperatures to warm further into the 40s
both Saturday and Sunday. However, the increased moisture will lead
to cloudy, damp conditions with increasing shower chances late
Saturday into Sunday.

MARINE...

Southeast winds will gradually decrease during the night as low
pressure tracks into far southern Lower Michigan. The low will track
into southern Ontario late tonight into Tuesday morning. This will
result in a veering of the winds to the north-northeast. While
colder air will spill across the lake in the wake of this low, a
decreasing gradient will keep peak wind gusts under 25 knots. A
strengthening southwesterly gradient will develop mid week as strong
high pressure slides across the southern US and a slow moving cold
front pushes across northern Ontario. Warmer air advancing across
the lakes will inhibit mixing depths, thus the chances for gale
force wind gusts Wed and Thurs appear too low to carry a gale watch.

&&

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

$$

UPDATE.......MR
AVIATION.....MR
DISCUSSION...SC/JD
MARINE.......SC

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