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fxus63 kdtx 142029 

Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
329 PM EST Sat Dec 14 2019


A stratus deck is rapidly advancing across the area within
strengthening west-northwest low level flow. Upstream radar with
some visibility restrictions do suggest some drizzle may be falling
out of this low cloud deck. Given that temps are near 40 over most
of the area and the boundary layer should remain relatively well
mixed this evening, suspect any light drizzle will occur with temps
just above freezing. A northern stream trough advancing across the
nrn Great Lakes tonight will drive colder air into se mi with 850mb
temps expected to drop into the negative teens by Sun afternoon. A
growing depth of the mixed layer tonight and cooling near the top of
the cloud layer should initiate ice nucleation, allowing snow
showers to become the dominate precip type. Convergence along a
passing sfc trough axis and an increase in the lake mi response will
be the main factors driving the snow shower activity overnight into
Sun morning. The brevity of snow shower activity and less than ideal
snow microphysics should keep any snow accums under an inch.
Significant drying during the day Sunday should temper any activity
that releases off lake mi to just flurries Sun afternoon.

The last couple model runs have shown a trend toward less amplified
waves (and suppressed to the south) in the southern stream Sun night
into Tuesday, likely due to more progressiveness in the northern
stream waves across central Canada and the Dakotas. This results in
the bulk of model solutions keeping precip assoicated with the
tightening low-mid level baroclinic zone across the Ohio Valley
south of the state. This has warranted a reduction in pops Sun night
and Monday. There remains some degree of uncertainty with respect to
the timing and amplitude of a strong wave forecast to eject out of
the southern rockies on Monday. The NAM and Canadian maintain enough
amplitude with this wave to clip portions of se mi with the
deformation axis, enough to maintain the chance of snow in the south
Mon night. The Euro and even the GFS (which was the more bullish
with this feature) are more sheared and essentially keep most of se
mi dry.

A polar low is forecast to drop out of central Canada and race
toward New England Wed to thurs. Relatively strong model agreement
and consistency with this feature leads to a relatively high
confidence that Arctic air will be driven into se mi tues night and
Wed morning. The progressive nature of this system will make this
Arctic air intrusion brief as rebounding mid level heights and a
rapid warming trend will already take hold by thurs and Fri.



Troughing over the lakes today with the center of a low pressure
system lifting across the northeastern US is leading to northwest
flow across the central Great Lake today into tonight. Tightening
pressure gradient into tonight along with the arrival of colder air
over the lakes will bring a set up capable of marginal gale force
winds across the northern half of Lake Huron. A Gale Warning is in
effect for these winds starting tonight and lasting into tomorrow
morning. Small Craft Advisory conditions will also be met for
northern portions of The Thumb as wave action increases tonight and
last into tomorrow afternoon. Winds begin easing up tomorrow
afternoon as the low lifts well to the northeast. Winds remain light
across the lakes on Monday into while a low pressure system moves
across the Ohio River valley bringing snow showers to the southern
lakes. More impactful surge of Arctic air with a low pressure system
comes late Tuesday into Wednesday.


Previous discussion...
issued at 1214 PM EST Sat Dec 14 2019


Some patchy haze leftover from this morning should linger through
the afternoon and evening although it should barely be MVFR. Once
the wind picks up out of the west northwest overnight expect vsbys
to improve to VFR. Cigs on the other hand should gradually drop to
near or slightly below IFR thresholds starting at mbs toward sunset
and spreading the rest of the way across Southeast Michigan through
the evening hours. Models continue to forecast convection in the
form of snow after midnight and lasting until right around sunrise.
Model soundings are pretty shallow on the moisture and not really
conducive to much more than lighter showers or even flurries this
far east. There is an outside shot at some evening drizzle forming
at the top of the cloud layer as winds pick up but suspect the
chances of that happening are pretty small.

For dtw...vsby near 5-6sm in haze likely to persist through this
evening before MVFR cigs move in from the northwest around 00-01z.
Expect cigs to then drop to less than 1kft around midnight with
scattered light snow showers possible roughly 06-10z. After that
conditions should improve back to MVFR tomorrow morning.

Dtw threshold probabilities...

* low for cigs aob 5000 feet afternoon. High for cigs aob 2000 feet
this evening and aob 1000 feet from midnight to sunrise Sunday.

* Ptype expected as snow late tonight with patchy coverage.


DTX watches/warnings/advisories...
Lake Huron...Small Craft Advisory from midnight tonight to 5 PM EST Sunday for

Gale Warning from midnight tonight to noon EST Sunday for

Lake St Clair...none.
Michigan waters of Lake Erie...none.



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