Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 151724

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1224 PM EST Mon Jan 15 2018


IFR -sn will continue for the next several hours, winding down by
00z with improving vsbys as precipitation stops saturating the
boundary layer. Flow will remain on the light side, backing around
the compass from ESE at forecast issuance time to WSW Tuesday
morning - interrupted by several hours of VRB in the Detroit area as
the surface low passes overhead. Convergent flow lifting from the
south will bring potential for banded -shsn 03-12z for the Detroit
area while moist cyclonic flow supports 6sm -sn elsewhere. Second
trough will begin to pivot into the area from the north Tuesday,
reaching MBS/FNT by the end of the pd and likely producing another
transient window of banded showers. Cig forecast is uncertain, but
expect no better than MVFR at any time.

For DTW...If there is any potential for a modest increase in snow
rates it will likely fall 20-23z as the NW periphery of the warm
conveyor currently responsible for more organized echoes over NE
Indiana lifts NE and possibly clips the Detroit area. Included 3/4SM
tempo to acct for this potential. The banded showers that are
expected to pivot into the area from the south are already noted on
radar in the Chicago area.


* High for cig aob 5kft


Issued at 930 AM EST Mon Jan 15 2018


The forecast remains on target as light snow is now occurring across
the entire forecast area and will persist through the afternoon.
There has been some enhancement in the radar returns across northern
Indiana this morning. This is occurring within a ribbon of stronger
moist isentropic ascent along the lead edge of a mid level short
wave trough. As this trough slowly rotates into Se Mi over the next 6
to 10 hours, this enhanced region of ascent will rotate from south to
north across the forecast area. The flow will become less
perpendicular to the theta surfaces as it lifts into Se Mi, resulting
in a more gradual region of ascent across the forecast area in
comparison to what is now occurring in Indiana. This combined with
the lack of dendrites (smaller snowflake size) will support minimal
total accumulations today (1 to 2 inches).

A plume of drier mid level air will slowly translate from south to
north in the wake of the aforementioned push of ascent. This will
occur between 21Z and 03Z. While this will end the more widespread
light snow, enhanced boundary layer to 925mb forcing associated with
the sfc low and trough axis (forecast to lift into the I-94 corridor
this evening) will support some residual snow showers into the

Issued at 341 AM EST Mon Jan 15 2018



As of 340 AM EST...Forecast continues to remain on track for a long
duration, light snowfall event today as a clipper low approaches the
region. High confidence forecast as the model suite has been in good
agreement handling the evolution of this system over the past several
model runs. The clipper will track across southern Lake Michigan and
into southwestern Michigan today, gradually weakening with time as
it occludes and becomes vertically-stacked with its parent 500 hPa

Latest regional radar continues to depict returns increasing in
coverage from west to east across lower Michigan, although it will
still take another few hours for the column to saturate with
abundant antecedent dry air in the 850-500 hPa layer. Onset of light
snow still looks to be in the 4am-7am timeframe for most areas,
although lingering dry air across the Thumb may postpone onset there
by another hour or two. Hi-res guidance is in good agreement that
there will be two surges in activity, again with the overall nature
light in intensity. The first will occur early this morning as broad
isentropic lift in the 1000-700 hPa layer overspreads the region.
After column saturation, snowfall rates will range from a tenth to
two tenths of an inch, with most areas seeing a half of an inch to
slightly over 1 inch by noontime. Snow may briefly taper off to a
very light intensity late morning into the early afternoon across
central lower Michigan as the occlusion process begins, but again,
splitting hairs as light snow will continue to be ongoing throughout
the entire day.

Second uptick looks to occur this afternoon as the occluded front
focuses some weak unpacking of the theta-e field along with slightly
enhanced low-level omega as the region is placed in the left exit
region of an increasingly cyclonically-curved upper-level jet.
Snowfall rates may increase back to around 0.2 inch per hour this
afternoon with another inch or so of accumulation. By this evening,
most areas are expected to see roughly 2 inches of accumulation,
with a few isolated readings of 2-3 inches. Looks to be hard to
exceed these amounts due to small snowflake size, limited overlap of
best omega lift with DGZ, and overall lack of available moisture
(QPF amounts 0.1 to 0.15 inches and specific humidity under 1.5

The long duration nature of the event though will still lead to
hazardous travel conditions throughout the day, especially for
untreated roadways. Small snowflake size will lead to reductions in
visibility as well. Will hold off on issuing an advisory as snow
rates should be low enough to limit more significant travel
concerns, and will highlight the snow with periodic Special Weather
Statements throughout the day. Occluded front lingers across the
region into tonight as the clipper continues tracking eastward, with
continued light snow showers more scattered in nature as best
moisture axis is lost. Additional accumulations up to a half of an
inch will be possible especially east of the I-75 corridor. After
high temperatures in the 20s, low temperatures will settle in the
teens, with upper single digits possible near the Ohio border.


Upper-level trough axis will remain in place across southeast
Michigan during the day on Tuesday under north/northwest flow,
leading to a period of lingering flurries/scattered light snow
showers aided in part by the lake aggregate moisture plume and
cyclonic flow for much of the day. This activity will largely be
minor in nature with accumulations under an inch, although a more
persistent band may set up across the northern Thumb with a more
northerly flow trajectory given the relative proximity of the
decaying clipper in southern Ontario. Low confidence at this point
in terms of more significant accumulations as convective depths will
be on the shallow side along with a fair amount of directional shear
in the lowest 10 kft, but still something to watch closely as the
CAMs better resolve the mesoscale environment as the predictive
window narrows. High temperatures Tuesday will range from upper
teens near the Ohio border to lower 20s north.

The trough will remain positively-tilted and exit off to the east
Tuesday night as upper-level ridging builds in its wake while
surface high pressure crests across the Tennessee River Valley. The
combination of light winds and the renewed snowpack will allow low
temperatures to fall into the single digits for most areas Tuesday
night, with lower teens in the vicinity of the Detroit metro.

Dry and quiet weather will prevail Wednesday and despite rising
heights aloft, the region will continue to remain under the
influence of northern stream flow and below normal temperatures,
with highs Wednesday in the lower to mid 20s and lows Wednesday
night in the teens. Plenty of lake-induced stratus/stratocu will
likely linger around for most areas Wednesday with mostly cloudy


The long term period will feature a pattern change as a deepening
upper-level trough over the southwest CONUS associated with potent
Pacific energy allows the northern stream to retreat northward this
weekend. Before this occurs, however, one more bowling ball of
Canadian PV will make its way towards the Great Lakes region late
Thursday into Friday, although there remains considerable
uncertainty with the track of this feature. The GFS has the energy
diving just south of the region resulting in a quick shot of
potential light snow, while the ECMWF tracks it across the Straits.
This feature has yet to move onshore to be better sampled by the
model guidance, so will continue to go with a dry forecast to end
the work week.

The aforementioned upper-level trough over the southwestern CONUS
will spawn lee cyclogenesis over the central Plains during the first
half of the weekend, with southwesterly flow out ahead of it
allowing for an increase in temperatures and moisture. Depending on
the ultimate track of the developing surface low as it moves
northeast towards the region over the weekend, temperatures could
rise well into the 40s along with increasing rain chances.


Winds will gradually back from south to southeast overnight into
Monday morning as low pressure moves from the upper Midwest into
Illinois. Respectable over-lake mixing depths will support gusts in
the 25 to 30 knot range. Winds across southern Lake Huron will
gradually decrease during the day monday as the low tracks into
southern Lower Michigan. Meanwhile, winds will continue backing
toward the east across northern Lake Huron with gusts holding in the
25 to 30 knot range. The low pressure system will expand as it
meanders across the eastern Great Lakes Monday night into Tuesday.
Northerly winds will expand across Lake Huron Monday night as the
low drifts toward the east. The weakening gradient will then cause
wind speeds to decrease on Tuesday.


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



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