Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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537
FXUS63 KDTX 160834
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
334 AM EST Tue Jan 16 2018

.DISCUSSION...

NEAR TERM / TODAY THROUGH TONIGHT

As of 330 AM EST...Clipper low that brought light snowfall to the
region yesterday continues to linger across southern Lake Huron early
this morning, with a bent-back occluded front draped near the M-59
corridor. Convergence along this front, coupled with lingering large-
scale ascent from a closed upper low in place over southern
Wisconsin/northern Illinois has resulted in periods of light snow
continuing through much of the night across portions of southeast
Michigan. Local topographic effects have resulted in localized areas
of more enhanced radar reflectivities, particularly along the glacial
ridge, but overall flake size is small with weak omega in near the
DGZ. Thus, accumulations overnight will likely be on the order of a
few tenths to around a half of an inch for most areas. Light snow is
expected to expand gradually northward into the morning hours,
although most areas of southeast Michigan will still be capable of
seeing flurries and occasionally more steady light snow showers.

The exception will be across far northeastern Huron county, where a
convergent near surface wind field will allow for lake enhanced
activity through the morning and into the afternoon. Tough call on
whether the meat of the band actually makes it onshore, as hi-res
guidance indicates a largely offshore component to the low-level
flow, but this could be modulated by more persistent onshore
north/northeasterly flow developing later this morning as the
decaying clipper tracks slightly further east. Will continue to
monitor closely, but given the light rates expected, will hold off
on an advisory for now.

Later this morning, northern stream PV streamer moves across the
region as the upper low becomes elongated and eventually opens up as
core of 140+ kt jet streak moves off to the northeast of the trough
axis. This lingering synoptic scale lift coupled with increasing
boundary layer forcing due to diurnal effects will promote a
potential round of more persistent light snow this afternoon and
evening with slightly higher rates (0.2 to 0.4 inch per hour) and
better dendrite production, especially east of the I-75 corridor.
These trends are supported by multiple hi-res model sources, as the
trough axis swings through.

Given all these factors in play, another inch or so of fluffy
accumulation will be possible through this evening for most areas,
with locations closer to Lake Huron possibly seeing as high as 2
inches in spots. Highest totals are expected over northeastern Huron
county, where 2-4 inches are possible, especially if the core of the
aforementioned band can move onshore. After low temperatures in the
upper single digits to mid teens (warmest between M-59 and I-94),
highs will reach into the lower 20s for most areas.

Snow chances end by late this evening as flow trajectories become
increasingly anticyclonic. With light winds, favorable radiational
cooling will allow low temperatures tonight to fall into the single
digits for most areas.

SHORT TERM / WEDNESDAY THROUGH FRIDAY NIGHT

A period of more tranquil weather will occur during the short term
period, as the upper-level trough axis exits east of the region and
is replaced by rising heights and increasingly anticyclonic
northwest flow aloft. At the surface, strong high pressure will
crest across the Tennessee River Valley. This pattern will usher in
drier air through the column resulting in a period of dry weather
and partly cloudy skies, although pesky residual boundary layer
moisture trapped beneath the subsidence inversion could lead to
periods of more cloudy skies. Highs on Wednesday will continue to be
below normal and in the 20s, but the onset of weak return flow
around the surface high will allow temperatures to moderate
beginning Thursday and continuing into Friday. Highs Thursday will
make a run at the freezing mark and warm into the mid and upper 30s
for Friday. A passing northern stream shortwave trough Thursday
night into Friday will do nothing more than increase cloud cover as
limited moisture will accompany it.

LONG TERM / SATURDAY THROUGH MONDAY

Unsettled weather returns for the weekend and into early next week
as vigorous Pacific energy moving ashore the west coast carves out a
deep upper-level trough and eventual lee cyclogenesis in the south-
central Plains. Both the GFS and ECMWF are in fairly good agreement
with the PV energy moving onshore late Friday into Saturday, and the
downstream synoptic pattern favoring the aforementioned lee
cyclogenesis. The low pressure will deepen as it tracks northeast
towards the Great Lakes region Sunday into Monday, with a slowing
trend noted in the last few runs of model guidance. Broad
southwesterly flow ahead of the low, aided by strengthening return
flow around high pressure situated across the southeast states will
overspread the region ahead of this system allowing for a warmup in
temperatures with daytime highs reaching into the 40s. Despite the
milder temperatures advecting in, so will the moisture along with
increasing rain chances for the latter half of the weekend into
Monday.

&&

.MARINE...

Low pressure will track into southern Ontario this morning wind
winds veering to the north-northeast in its wake. While colder air
will spill across the lake in the wake of this low, a decreasing
gradient will limit peak wind gusts at 20 knots or less on Lake
Huron.

A strengthening southwesterly gradient will develop by mid week as
strong high pressure slides across the southern United States 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 on Wednesday and Thursday still
appear too low to carry a Gale Watch. The most likely period for
marginal gale force gusts seems to be limited to the late afternoon
and early evening period on Wednesday before stable conditions fully
develop. Central Lake Huron, downwind of the funneling effect of
Saginaw Bay, will be most vulnerable to a period of gusts pushing 35
knots.

&&

.PREV DISCUSSION...
Issued at 1155 PM EST Mon Jan 15 2018

AVIATION...

Areas of light snow showers and flurries will continue to develop
across the region overnight. Conditions generally at MVFR/VFR
restrictions given the light intensity, with minimal accumulation.
Potential for a more localized focus for some heavier snow showers
will be tied to convergence that develops during the early and mid
morning hours along a stalled frontal boundary. IFR conditions
plausible should these snow showers materialize, greatest potential
Detroit corridor up through PTK.  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 susceptible to scattered to numerous snow showers lasting
through late Tuesday.

For DTW...Light snow showers and flurries will persist overnight.
There remains the potential for a brief increase in intensity near a
frontal boundary during the early-mid morning period, but confidence
in occurrence remains low.

/DTW THRESHOLD PROBABILITIES...

* Medium for cig aob 5kft


&&

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

$$

DISCUSSION...IRL
MARINE.......DG
AVIATION.....MR


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