Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KDTX 191719
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1219 PM EST Mon Nov 19 2018


.AVIATION...

Dense fog finally burned off late this morning, giving way to
expanding MVFR stratocu beneath a transparent canopy of higher
clouds. Snow showers will expand in coverage overnight as the cold
front currently entering northwest Lower Michigan moves through the
area from northwest to southeast 00-12z. With lake effect relegated
to north and east of the forecast points, confidence is high in an
MVFR type of snow with occl IFR in heavier, transient showers. Wind
will increase out of the northwest in the wake of the front,
gustiness likely limited by the abundance of boundary layer
moisture. Cigs then gradually improve late in the period as depth of
cold air deepens.


.DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5kft

* High for ptype of snow

&&

.PREV DISCUSSION...
Issued at 349 AM EST Mon Nov 19 2018

DISCUSSION...

NEAR TERM / TODAY THROUGH TONIGHT

As of 345 AM EST...Another chilly November night continues across
the region with surface high pressure ridging into the central Great
Lakes. Increased subsidence earlier during the night allowed for most
areas to briefly see eroded cloud cover, but mid and high clouds are
quickly filling back in ahead of an approaching arctic boundary
currently draped over the northern Great Lakes. Closer to the Ohio
border, weak low-level southwesterly flow has allowed for some
moisture to spill north of the Ohio border resulting in low stratus
and patchy, locally dense fog south of the I-94 corridor. The degree
of moisture has also been noticeable with favorable frost conditions
further north. Dry weather will continue the remainder of tonight
with temperatures hovering in the mid/upper 20s. The exception will
be the Detroit metro where temperatures will be closer to freezing.

The arctic boundary will begin sagging southward as the day
progresses, but will remain far enough north of immediate southeast
Michigan to result in a dry day through the early evening hours with
a thick canopy of mid/high clouds. High temperatures will be similar
to yesterday reaching into the mid 30s for most areas with a light
southwest wind.

Attention then shifts to the late evening into the overnight hours
as the arctic boundary drops further south across the region. This
boundary will be accompanied by an enhanced piece of northern stream
PV energy diving southeast within a deepening trough regime. This PV
energy looks to sync with the front roughly during the timing of the
trough axis swinging through to enhance dynamic support. Winds
flipping to the north along and behind the front will also allow for
a favorable lake-enhanced moisture fetch off Lake Huron into the
northern Thumb. The result will be a period of light to moderate
snow, mainly confined to the east of a Saginaw/Flint line with
southward extent brushing the northern Detroit metro. In Huron
county, fairly steep low-level lapse rates and deepening inversion
depths will pose an increased potential for snow squalls and
embedded heavier cellular segments that will need to be closely
monitored. Favorable snow microphysics with a deep layer of
saturation with respect to ice in the DGZ will likely raise snow
ratios more into the 15:1 to 20:1 allowing for a roughly 6-9 hr
window overnight of efficient snow processes and the potential for 2-
4 inches of accumulation in portions of Huron county stretching into
northern Sanilac county. Will hold off on a Winter Weather Advisory
for now to let the day crew see more hi-res guidance, but the signal
is certainly there for an overperforming lake-enhanced event in the
northern Thumb. Across the rest of southeast Michigan, more drier
air intruding with the front and lack of lake enhancement will limit
snow totals to generally under an inch south of I-69, with 1-2
inches possible across the remainder of the Thumb.

Timing now appears to be a little earlier with snow onset more in
the 6pm-8pm timeframe continuing through much of the nighttime hours
with the peak centered around midnight. The boundary will continue
to move south of the region by daybreak Tuesday morning ending the
threat for more widespread snow with the exception being along the
eastern Thumb shoreline. Low temperatures will be limited to the
mid/upper 20s with low clouds associated with the front.

SHORT TERM / TUESDAY THROUGH THURSDAY NIGHT

Broad surface high pressure settling over the lower Mississippi
Valley will ridge northward into the region post-frontal passage
Tuesday. Cold air advection behind the front coupled with lake
aggregate moisture will likely keep some degree of cloud cover
around, but enough surface ridging may allow for intervals of
sunshine. Thermal trough swinging through characterized by 850 hPa
temps dropping to -14C will keep high temperatures below freezing
for most areas, with fairly widespread upper 20s north of the
Detroit metro.

A second arctic front will sweep across the region Tuesday night
associated with a weak clipper-type low diving southeast across
Georgian Bay. Moisture along this front looks to be lacking but
enough for scattered snow shower activity with minimal
accumulations. Low temperatures Tuesday night will be limited by
front-associated cloud cover and generally be in the 20s.

Continued cold, but dry weather will prevail Wednesday and on into
Thanksgiving as strong high pressure settles over the lower Great
Lakes. High temperatures Wednesday and Thanksgiving will struggle to
reach freezing, with Wednesday night being the coldest night of the
stretch with lows dipping into the teens.

LONG TERM / FRIDAY THROUGH SUNDAY

A pattern shift will be ensuing across the eastern CONUS at the
start of the long term period as shortwave upper-level ridging
briefly takes hold. Increasing low-level temps will allow for highs
Friday to reach into the lower 40s. Forecast confidence decreases
into the weekend as North American flow becomes highly amplified and
energized by the subtropical jet. Long range guidance currently
brings potential surface low development through the Ohio Valley
this weekend, with the ECMWF continuing to be the most aggressive
solution with a Miller B setup and southeast Michigan being on the
northwest flank of the precip shield. The GFS is starting to catch
onto this trend as well, although with a different synoptic
evolution. The end result is for a murky weekend forecast that will
continue to be advertised as wet, although exact details will be
crucial to the temperature profile and liquid vs. frozen
precipitation. Highly energetic flow looks to continue into next
week as well with the potential for a second system to impact the
region.

MARINE...

Light to moderate southwest wind precedes a strong cold front that
is projected to drop south across northern Lake Huron during the
afternoon, southern Lake Huron this evening, and then passing south
of Lake Erie late tonight. A surge of northerly wind is expected to
gust near 30 knots while the cold air produces lake enhanced snow
showers that will be heavy at times over southern Lake Huron. The
wind diminishes with high pressure Tuesday but is quickly followed
by another low pressure system and cold front. This system will be
strong enough for northwest wind trailing the system to approach
gales late Tuesday night into Wednesday. A Gale Watch may be needed
in upcoming forecast updates.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from midnight tonight to 4 PM EST Tuesday for
     LHZ421-441>443.

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

$$

AVIATION.....JVC
DISCUSSION...IRL
MARINE.......BT


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.