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fxus63 kdtx 190434 
afddtx

Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1134 PM EST sun Nov 18 2018



Aviation...

VFR conditions expected tonight into much of Monday with thickening
mid/upper level cloudiness. Just stray patches of stratus aob 3500ft
kptk south overnight. Light snow and lower VFR to MVFR cigs settle
south into area late Monday with shortwave and associated frontal
boundary. South-southwest winds will veer to northwest with the passage of this front
late in the forecast period. Timing of light snow 01z-03z kmbs to
06z-08z kdtw.

For dtw...south-southwest flow under 10 knots into Monday evening before front
brings a shift to the west and then northwest late. Cigs aob 5kft will return
with this front with light snow showers after 06z Monday night.

Dtw threshold probabilities...

* medium for cigs aob 5kft by Monday evening.

* High precipitation type will be snow Monday night.

&&

Previous discussion...
issued at 326 PM EST sun Nov 18 2018

Discussion...

Upper level jet entrance region dynamics responsible in generating
narrow swath of light snow today for locations south of I 96 has
exited to the east. Thus, synoptic scale forcing for ascent has
ended for today.

For tonight, weather across Southeast Michigan will be driven by a
weak ridge of surface high pressure that will build directly over
the cwa. The surface ridge appears to be delicate and wedged between
a developing pseudo split flow aloft. Models do show some positive
Ava, although rather inconsequential. The main forecast question for
tonight is how progressive cloud clearing will be. Survey of
vertical moisture plan view progs support a deep layer of dry air
for the overnight. Model soundings do show sharp subsidence
inversion base down to around 2.5 kft agl. No shot at any tangible
advection overnight with neutral type flow with respect to
isentropic surfaces. Given the look of satellite imagery with
boundary layer cumulus/stratocumulus this afternoon and very shallow
depth to any saturation at the top of the boundary layer,
preferences is to maintain the inherited forecast of aggressive
clearing trend late this afternoon and tonight. As a result, did
blend some cold regional Canadian into the low temperature forecast
for tonight, ranging lower to mid 20s.

The first of a couple of Arctic boundaries will be pushing southward
through the northern Great Lakes as the developing northern stream
sets an edge. Combination of some entrance region dynamics to subtle
jetlet and some diffuse cyclonic vorticity advection will lead to
light preciptitation to the north of Saginaw Bay through Monday
afternoon. Center of 700 mb anticyclone will pass overhead during the
morning hours but as this becomes increasingly squeezed eastward,
mid to high clouds on the warm side of approaching frontal boundary
will lead to an increase in mid-high cloud Monday. Cannot rule out
some boundary layer cloud growth that may happen late. Message of
sunshine early with increasing cloud appears apt, highs in the
middle 30s.

Monday night. The midlevel anticyclone center will be well east of
Southeast Michigan. This will allow broad, disorganzied cyclonic
vorticity energy to wash across the state as a very deep midlevel
trough/associated cyclonic flow at the longwave arrives. Most likely
of responses will be some Lake Huron aggregate troughing as cold air
will be settling southward within the composite trough. Modest warm
advection centered around 600mb and magnitude of differential cva
will be enough to generate likely light snow pops. Main timing
appears set between midnight-7am Tuesday morning. Model soundings
show a favorable thermodynamic sounding for snow microphysics with
supersaturation with respect to ice throughout a deep layer. Current
indications are snow ratios will range between 12:1 to 16:1. Snow
accumulations of 1 to 2 inches appears possible north of M 59
conditional to how the atmosphere evolves, snow accumulation of less
than an inch for Metro Detroit. Higher amounts will be possible in
the eastern thumb, in closer proximity to Lake Huron shoreline.
Onshore flow may lead to some lake effect snow showers throughout a
portion of the day Tuesday.

A reinforced thermal trough will hold temperatures below normal
Wednesday into Thursday with h850 temperatures averaging -12c by 00z
Thursday. Overcast conditions and caa will cap temperatures in the
low to upper-30s on Wednesday, with the coldest temperatures seen
across the Tri-Cities region into The Thumb. An advancing surface
high pressure system will travel from western Ontario and will
center east of Lake Huron by Thursday afternoon, providing dry
weather both Wednesday and Thursday. Increasing subsidence will also
begin to produce breaks in cloud cover and will bring a mix of
clouds and sunshine by Thursday, however, the strong caa ahead of
the high will bring even cooler air into southeast mi, lowering daytime
highs down to the low-30s on Thanksgiving.

Upper-level troughing is expected to strengthen across the plains
late this week and will reinforce a ridge across the Great Lakes and
northeast U.S. Which will act elevate temperatures into the 40s for
a high Friday into the weekend. Anticylonic flow around high
pressure will increase h850 temperatures above the freezing mark,
averaging 4c by 18z Friday. Increasing surface temperatures in the
mid-40s are forecasted for the weekend, with a slight chance to peak
up into the upper-40s across the Metro region.

Advancing warm front will provide the chance to see precipitation
starting late Friday and into the weekend. At this time, confidence
is too low to discern type of precipitation if precip materializes
during the night and early morning hours, as temperatures fall into
the mid-30s for overnight lows. As a result, a blend of rain/snow
mix has been added to forecast until better convergence is noted
with new model suites.

Marine...

Moderate southwesterly flow of 20-30 knots will develop today as the
pressure gradient tightens between the center of high pressure
located over the Central Plains and low pressure tracking across
southern Hudson Bay. The strongest winds will occur over the
northern and Central Lake Huron basin. Moderate southwesterly flow
will continue into Monday before a cold front drops south across the
Great Lakes switching winds Post-front to the north with
accompanying chances for snow showers. A clipper will then track
southeast across the northern Great Lakes during the midweek period,
with the potential for northwest winds to gust to marginal gales on
Wednesday.

&&

DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Aviation.....Dg
discussion...cb/am
marine.......jvc

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