Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 171107
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
707 AM EDT Tue Apr 17 2018


.AVIATION...

Moderate west to northwest wind will continue to carry colder air
into the region and produce borderline VFR/MVFR ceiling. The stage
is then set for another round of snow later tonight through about
mid morning capable of reducing visibility into IFR at times. Snow
showers enhanced by Lake Michigan are also expected to be near the
DTW corridor and will also be capable of IFR visibility. The system
supporting the overnight snow will then exit eastward by afternoon
however clouds will hold firm. Expect at least a broken MVFR ceiling
that will struggle to reach VFR toward Tuesday evening.

For DTW... Colder air moving into the region is expected to produce
snow showers enhanced by Lake Michigan later in the night through
mid morning. These are currently projected to occur mainly south of
I-94 but with increasing probability of a coating to half inch of
accumulation at DTW.

/DTW THRESHOLD PROBABILITIES...

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

* High for snow as precipitation type.

* Moderate for west to northwest wind approaching cross wind
  threshold late morning through afternoon.

&&

.PREV DISCUSSION...
Issued at 642 AM EDT Tue Apr 17 2018

UPDATE...

Reports have been rapidly coming in of very icy roads, expecially
between the I-94 and I-69 corridors. Wet roads last evening have
froze as temps droped below freezing. Morning snow showers only
worsened conditions. Given the road conditions, a winter wx advisory
will remain in effect through the morning rush.

PREV DISCUSSION...
Issued at 344 AM EDT Tue Apr 17 2018

DISCUSSION...

We`ll be dealing with some light snow heading into the morning hours
as we continue to reside in cyclonic flow around the expansive low
pressure system that`s been plaguing the region since the weekend.
The stacked low will finally move east today allowing improving
conditions across the state but not before one last push of wintry
precipitation. An upper level PV max has strengthened on the backside
of the broader upper low currently over Lake Superior which will
rotate down along Lake Huron through the afternoon hours today.
Regional radar shows this area of snow ongoing with the main
question being how much of SE MI will get clipped as it tracks
across Lake Huron? Looks like the best forcing will stay out over
the lake though affects will still be felt over the Thumb. POPs will
continue to be highest across the northern Thumb which will be
closest to the center of the PV max, tapering off southward where
the area will be more under weak cyclonic flow forcing. With a short
duration of snowfall and rates not too impressive with lack of
forcing in the DGZ, looking for up to an inch of snowfall in Thumb.
Areas southward could see a quick dusting to a half in or so. The
other area of interest this morning is lake effect showers releasing
from Lake Michigan as flow becomes more westerly, now tracking east
generally south of I94. Likely POPs for snow showers continue for
this region. Both areas of showers should be exiting the area this
morning with a possible transition to a mix of rain and snow before
ending.

Midlevel shortwave ridge and narrow surface ridge will then slide
over lower MI late in the day. Strong mid level confluent flow
combined with the stable airmass building into the region will act
to dry out the column for a short period. Temperatures will not show
much improvement as a thermal trough still resides over the region
with plenty of cloud cover to prevent much heating.

Not quite done with winter weather yet as the next system targets
southern MI Wednesday through Thursday morning with the bulk of the
precip occuring Wednesday night. The base of the trough over the
western conus will cutoff over the central Plains and quickly
occlude as it tracks through the southern Great Lakes. It will be
cutting through the broader upper level ridging in place which is
cutting it off from bringing in colder air, though it does feature a
cold pool cool enough to support a changeover to snow Wednesday
night. The compact mid level feature looks to stay pretty compact
while the occluding surface low shears itself out across southern
MI. Looks like the lead edge of the precip will move into SE MI
around 21Z Wednesday with the best forcing lining up overnight.
Thermal profile will be border line for snow vs rain with a gradient
likely across lower MI. Will continue to advertise light
accumulations as we continue to try to resolve the low level thermal
profile and ptype. With around 0.2 inch of QPF overnight, a quick
changeover to snow will likely result in a couple inches of
accumulation. In any event, model consistency with storm track thus
far has lead the coordination of categorical pops across lower MI.

This looks to be the last bit of wet weather for a while as ridging
builds across the plains into the Great Lakes heading into the
weekend with expansive surface high settling overhead. As the ridge
begins to build into the region, a tight northerly gradient will set
up leading to a breezy day. Lack of notable warm air advection
through the end of the period, will lead to a slow warming trend as
the airmass slowly modifies each day under the influence of the
build ridge. Temps will return to the 50s this weekend with 60s
possible next week.

MARINE...

The gradient on the back edge of departing low pressure and ample
mixing depths due to the degree of cold air over the lakes will
support gusty winds through the day. Peak gusts across the open
waters of Lake Huron will flirt with 30 knots at times. High
pressure will expand across the southern Great Lakes tonight. While
winds across Lake Huron will weaken as a result, there will remain
enough of a gradient to hold northwest winds in the 10 to 20 knot
range through the night. Winds will then weaken by Wednesday as the
high drifts overhead. A fast moving low pressure system will
traverse the northern Ohio Valley Wed night. A surge of cold air
will arrive in the wake of this system under strengthening northerly
winds Thursday. Gusts across the southern half of the lake are
likely to reach 30 knots, leading to hazardous small craft
conditions.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 10 AM EDT this morning for MIZ060>063-
     068>070-075-076-082-083.

Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-441.

Lake St Clair...NONE.
Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EDT this afternoon for LEZ444.

&&

$$

AVIATION.....SC
UPDATE.......SC
DISCUSSION...DRK
MARINE.......SC


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