NWS Forecast Discussion

000
FXUS63 KDTX 140504
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1204 AM EST Thu Nov 14 2019


.AVIATION...

The combination of broad warm air advection, upper level jet
forcing, and diffuse differential cyclonic vorticity advection will
lead to favorable synoptic scale conditions for ascent tonight
across the Central Great Lakes. The forecast soundings continue to
look very good for light snow tonight with a very clean frontal
signature at 800mb and saturation through a shallow DGZ. Given the
cold thermal profile, still expecting light accumulations of an inch
or less primarily north of KFNT. Most recent observational trend is
the potential for some moisture to lift northeastward into the
souther sections of the forecast area. Introduced a light snow
mention for DTW. Very little snow accumulation expected at the
Detroit terminals. Cold front settling through the area will then
lead to lower tropospheric saturation and cloud lingering in the
boundary layer later Thursday. Not anticipating any drizzle or
freezing drizzle Thursday evening. Winds will veer to the west
Thursday afternoon and remain modest at approximately 10 knots.

For DTW...Based on trends upstream, did introduce a prevailing group
for light snow 7-10Z at DTW.

DTW THRESHOLD PROBABILITIES...

*  High confidence for ceilings at or below 5000 ft the latter half
   of tonight and daybreak Thursday and again by Thursday evening.

*  Low to moderate confidence for light snow 07-10Z late tonight.

&&

.PREV DISCUSSION...
Issued at 1056 PM EST Wed Nov 13 2019

UPDATE...

No changes planned for the forecast this evening. Latest model data
supports bringing lead edge of 825-550mb equivalent potential
temperature advection into Southeast Michigan between 03-06Z. Ceiling
trends over the northern cwa have been sluggish, with BKN
stratocumulus at 7.0 to 8.0 kft agl only being reported now. Deep
column supersaturation with respect to ice and weak ascent through
the DGZ will support some light snow the latter half of the night.
Recent guidance has supported snowfall accumulations of under an inch
north of M46 with spotty coverage of snow to the south. Given some
reports of light snow over northern Indiana, cannot rule out some
light snowflakes to reach the ground in Metro Detroit. No significant
accumulation anticipated across the south.

PREV DISCUSSION...
Issued at 303 PM EST Wed Nov 13 2019

DISCUSSION...

A broad region of mid level warm air advection/moist isentropic
ascent now overspreading the Saginaw Valley/thumb region will expand
across the remainder of the remainder of the forecast area during
the course of the night. Overall, mid level moisture quality is
fairly respectable and there will be some degree of reduction in
mid/upper level stability. There will however be a substantial layer
of dry air below 800 MB, particularly south of the I-69 corridor
which will limit coverage of snow and keep any accumulations to a
minimum in these locations. Better ascent and veering of the flow
toward the west-southwest over Lake Mi later tonight will produce
better moisture quality generally along/north of the I-69 corridor
tonight. This will warrant not only higher pops but some light snow
accumulations (.5 to 1.5 inches).

The departure of high pressure to the east and approach of a sfc
trough associated with a broad upper short wave traversing Lower Mi
late tonight/Thurs morning will establish increasing south-southwest
low level flow tonight into Thursday. This will result in a slow
warming trend, with temps rising into the mid/upper 20s tonight and
low-mid 30s on Thursday. The mid level trough is forecast to weaken
as it tracks across Se Mi Thurs morning. West-southwest flow off
Lake Mi should however sustain ample strato cu with some scattered
light snow showers/flurries.

Another polar low is forecast to drop from central Canada into the
Hudson Bay region Thurs and then across eastern Canada Friday. This
system and the associated core of coldest air will remain much
farther north and east than the arctic intrusion of the past couple
days. This system will drive a cold front across the eastern lakes
late Friday, with the better push of colder air holding off until
Friday night. This front will be significantly lacking moisture so
will pass largely dry. Arctic high pressure expanding into the
eastern Great Lakes by the start of the weekend will ensure dry
conditions with temps remaining on the cold side of seasonal
averages.

The extended period starting Saturday through Wednesday still looks
to be well below normal but gradually moderating towards it.  High
pressure over the region Saturday will slowly move to the east
providing dry conditions and plenty of clear sky. Daytime highs
Saturday will barley make it to around 30 Saturday but slowly
moderate to around 40 by Wednesday on return flow around departing
high.  Lows will start out in the 20s but moderate to the 30s by
Wednesday night. A mid level trough will expand over the Great Lakes
first half of next week producing plenty of clouds and a slight
chance for some precip but with deeper moisture lacking will keep
the extended dry for now. One nice thing about the extended is the
surface pressure pattern will become quite relax resulting in a
lengthy period of relatively light winds.

MARINE...

High pressure centered over the mid-Atlantic is breaking down this
evening as a weak surface trough slides through northern Lower
Michigan. Winds will remain a bit elevated out of the S/SSW through
most of the overnight period gusting 20-30 knots. Nearshore winds
today have over-performed across Saginaw Bay thus the Small Craft
headline in effect through late tonight. Winds will weaken and back
to the WSW on Thursday allowing for more tranquil boating conditions
for the daylight hours. The surface pressure gradient then contracts
heading into Thursday night as a cold front slowly moves Lower
Michigan amplifying gusts to near 30 knots, especially over central
Lake Huron. Small Craft Advisories may be needed again for Lake
Huron Thursday night through Friday morning.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 4 AM EST Thursday for LHZ421-422.

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

$$

AVIATION.....CB
UPDATE.......CB
DISCUSSION...SC/DRC
MARINE.......KK


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NWS DTX Office Area Forecast Discussion