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fxus63 kdtx 120010 
afddtx

Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
710 PM EST Mon Dec 11 2017

Update...

The relationship between predictability and scale rarely more evident
than this evening as a painfully small frontal band has developed
across lower Michigan. The northern tier of wwas has been cancelled
as the final position of the band is now evident. Elsehwere in the
advisory, the event is currently at its peak. Areas of heavy snow
reducing vsbys to 1/4 mile are evident along the i96/696 corridor.
These episodes of moderate to heavy snow will continue to track
across the same area for the next hour or two while the lead batch
that impacted Detroit area rush hour will lift into southern Saint
Clair County shortly. Event totals around 2 to 3 inches still look
reasonable between M59 and northern Washtenaw/Wayne counties where
the advisory remains in effect. Band will then diminish in intensity
as it sinks through the area 02-06z bringing an inch or less to the
southern portion of the advisory as it does so. Worth noting that
given the narrow zonal orientation of the band, traveling on east-
west roads will likely be slow in the Metro area, but those
traveling north- south will be most prone to encountering sudden
changes in conditions.

Temperatures will plummet from the upper 20s around 06z tonight to
around 10 by mid-morning Tuesday as cold air surges into the region.
Wind chills between 0 and -10 are possible north of 8 mile through
the daylight hours tues.

Finally, a Wind Advisory has been issued for Huron County as strong
gales force their way inland beginning late tonight. Depending on
inland penetration of marine winds, a Wind Advisory may also be
needed for Tuscola and Sanilac counties.

&&

Previous discussion...
issued at 641 PM EST Mon Dec 11 2017

Aviation...

Narrow but intense band of snowfall currently lifting across Metro
Detroit. Recent radar trends suggest ptk will serve as the northern
Pivot Point for this band of snow, leaving fnt/mbs largely removed
from any meaningful accumulation and visibility restrictions going
forward. Several hour window yet for IFR conditions in light to
moderate snow at ptk/dtw/yip. Improving conditions beyond midnight
as band exits to the southeast. Potential remains for a secondary
brief period of snow showers to accompany an Arctic front across the
region during the early morning period. Otherwise, attention turns
to increasing Post-frontal northwest winds expected to emerge by mid-
late morning. Gusts into the 30 knot range expected throughout
Tuesday. Low level drying as Arctic air plunges in will lift ceiling
heights during the morning, leaving predominately lower VFR stratus
for the daylight period.

For dtw...heaviest burst of snowfall now exiting to the northeast,
but potential remains for additional pockets of moderate intensity
snow to lift through over the next several hours /04z/. Improving
conditions after midnight as main snow band exits to the southeast.
Arctic front surges through during the mid morning period, strong
northwest winds developing in it's wake. Wind gusts to 30 knots
will bring crosswind threshold considerations on Tuesday.

//Dtw threshold probabilities...

* high confidence for ceilings at or below 5000 feet through
Tuesday.

* High confidence in precip type being snow this forecast.

* Moderate confidence in northwest crosswind thresholds being
exceeded Tuesday.

Previous discussion...
issued at 337 PM EST Mon Dec 11 2017

Discussion...

Winter Weather Advisory has been issued for a portion of Southeast
Michigan for 2-4 inches of snow this evening. More information below.

Active pattern remains in place across the eastern conus as very
energetic long wave trough sends a series of shortwaves down through
the region this week. There will be a couple opportunities for snow
Wednesday and Saturday as clippers slide through the region. In
addition to snow chances, the coldest airmass of the season will
arrive mid week dropping low temperatures to single digits with wind
chills at or below zero Tuesday and Tuesday night.

Current surface analysis is matching up well with guidance over the
last 24 hours with the tightly wound, but open shortwave diving
southeast through the Midwest states toward the Ohio Valley. One
detail we've been trying to peg was how the surface low would shape
out as the initial phasing processes begin with a strong vorticity
lobe that is fast on its heals rotating around the parent low.
Combination of shearing height falls along the trough axis with lake
aggregate troughing over the lakes, is leading to a pseudo split
low. The surface reflection that will track through the Ohio Valley
is the dominate feature, with the height fall center over The
Straits the secondary center. This southern low has already
generated a thin fgen band extending well east of the low which will
strengthen as it lifts up into Southeast Michigan. This will be the item of
interest for snowfall accumulations this evening. Models trends
through this afternoon have increased confidence in the placement of
this band. Latest runs of the rap, hrrr, and European model (ecmwf) all suggest a
slight shift back southward, although most models key in on the area
between i69 and i94 generally between 22-02z.

It appears the fgen band will lift up across the Michigan border late this
afternoon through the Detroit Metro before stalling around the M59
corridor. This will last a few hours as the low slide south of the
Michigan border but snowfall will continue as the trailing deformation
band then pivots through the area tonight. In the end we are still
looking for a widespread 1-2 inches of snow across most of the area
with a band of 2-4 inches setting up where the advisory is. Note
that there could be a decent gradient of accumulations across Wayne
and Washtenaw with locations across southern portions of those
counties likely not seeing 3+ inches. Similarly for counties along
the i69 corridor, higher chances to see 3+ inches will occur across
southern portions of those counties.

By Tuesday morning the trough will have swung through the area
opening the door for strong northwest flow and good cold air
advection. Thermal trough drops over the Great Lakes with a broad
area of 850mb temps of -20c. With winds gusting to around 30 mph and
highs only around 20-25f, winds chill values will range from -5 to
5f. This will continue through the overnight before winds fall off
enough Wednesday to allow some recovery. Other potential concern for
late Tuesday is the threat of a lake effect snow band to brush the
eastern thumb. A difficult feature to ever forecast, but hires
models are starting capture the time period starting around 20z.
Confidence remains high that the band will develop but models have
been trending east with the meso low over Northern Lake Huron
dropping southward. A further west track would act to push the band
closer to shore. So potential is there a quick accumulation of
snowfall along the Eastern Shore of The Thumb.

Wednesday is looking quite similar to today with a clipper tracking
southeast through the Ohio Valley. NAM. GFS, and European model (ecmwf) are all
showing around 0.2 inches of qpf across the southern half of the
County Warning Area. With the thermal profile in place, another 2 inches of snowfall
wouldn't be out of the question.

The longwave trough over the eastern Continental U.S. Will remain in place and
allow for a series of shortwaves to pivot over the area Thursday
through Saturday. The active pattern will result in a small chance
for snow showers each day, with the better chance on Friday and
Saturday as the longwave trough takes on a negative tilt and a
surface low develops over the northern Great Lakes. Temperatures
will begin a slow upward trend as the coldest dome aloft moves off
to the east, though still remaining below average with highs
Thursday and Friday reaching the mid to upper 20s. Saturday will see
the return of above freezing temps with highs pushing the mid 30s.

Model guidance is suggesting a shortwave and low pressure system
will move across the central Continental U.S. And eventually to our area late
Saturday into Sunday, though the placement and timing have not been
well resolved this far out. A more southern track like the European model (ecmwf)
currently suggests could lead to another light snowfall for the
area, while a more northern track per the GFS would leave Southeast
Michigan mostly out of the best chance for precip. Will monitor
trends in this system over the next week.

Marine...

A strong cold front will transit the waters late tonight. Strong
northwest gales will develop with gusts approaching or briefly
reaching storm-force over the exposed nearshore waters of The Thumb
and the open waters of central and Southern Lake Huron. Gale
warnings are now in effect for all marine zones. Temperatures
falling through the 20s into the teens and significant wave heights
of 10 to 15 feet also warrant issuance of a heavy freezing spray
warning. Maximum wave heights will easily exceed 25 feet.

&&

DTX watches/warnings/advisories...
Michigan...Wind Advisory from 4 am to 4 PM EST Tuesday for miz049.

Winter Weather Advisory until 2 am EST Tuesday for miz068>070-075-
076.

Winter Weather Advisory until 2 am EST Tuesday for miz063.

Lake Huron...heavy freezing spray warning from 7 am Tuesday to 4 am EST
Wednesday for lhz361>363-421-441>443-462>464.

Gale Warning from 1 am Tuesday to 5 am EST Wednesday for lhz362-363-
462>464.

Gale Warning from 4 am to 4 PM EST Tuesday for lhz422.

Gale Warning from 4 am Tuesday to 4 am EST Wednesday for lhz421-
441>443.

Gale Warning from 1 am to 11 PM EST Tuesday for lhz361.

Lake St Clair...Gale Warning from 4 am to 4 PM EST Tuesday for lcz460.

Michigan waters of Lake Erie...Gale Warning from 4 am to 4 PM EST Tuesday for lez444.

&&

$$

Update.......mr
aviation.....Mr
discussion...drk/tf

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