Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 182038
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
338 PM EST Wed Jan 18 2017

.DISCUSSION...

They story for the week will be the warming trend. It appears the
warm air is here to stay for the next week with temperatures only
falling below freezing Thursday night. Otherwise highs will run
around 10-15 degrees above normal for the week, whereas lows run 15-
20 degrees above normal. This all as 850mb temps hover around +5C
for the better part of the week.

For tonight the main issue will be cloud and fog trends. We
currently reside on the north side of a surface high tracking
through the Ohio Valley. A well saturated boundary layer has lead to
2 days of fog and low stratus sub 1000 ft. With the ridge axis now
passing over the area, some mid level drying is occuring with
satellite imagery showing clouds scattering out upstream. Question
remains as to how much this will affect cloud trends tonight? Belief
is that with the wealth of moisture in the boundary layer and at the
surface, even with a weak inversion we should remain socked in with
low stratus with some fog present but likely remaining more in the 2-
4 mile range. Southwest winds should stay up around 5 knots helping
to mitigate some of the fog in favor of stratus but abundant
moisture (and persistence forecasting) should still see some degree
of fog out there.

Longwave pattern will be undergoing a transition from broad and
amplified ridge across the central conus up into Canada, to a trough
expanding across the western conus and into the plains. This will
keep SE MI in a southwest flow pattern just down stream of the
trough keeping ample warm air advection and moisture return into the
region. Nice pipeline of moisture seen on water vapor this afternoon
originating from the equatorial Pacific, extending northeast into the
southern plains. An upper low over cutoff over Texas will draw
additional moisture from the Gulf of Mexico. A strong wave will
force the developing trough eastward, and with the assistance of
southern stream 100+ knot jet streak, will eject the cutoff low
northeastward Thursday. This low will shear out as it lifts into the
Great Lakes. An east/west oriented fgen band into southern MI late
Thursday night. Weakening isentropic ascent up the frontal slope
with strong moisture advection into the forcing, should result in a
band of showers lifting north through Lower MI through Friday. Ptype
may be an issue at onset as temperatures will start off around 30F.
May see some mixed precip (sleet or freezing rain) before warmer air
advects in and changed it over to all rain. Rain will taper off
through the late afternoon but a second system following closely
behind will pull another front through the area keeping chances of
pops in the forecast Friday night.

A trough extending southeastward over the Great Lakes from a weak
low pressure pushing slowly northward through Minnesota will keep
the chance for showers in the forecast through the weekend.
Southerly flow on Saturday will pump warm, moist air into the Great
Lakes with high temperatures in the low 50s possible both Saturday
and Sunday across Southeast Michigan. Low pressure developing over
the Southern Plains on Saturday will move into the Tennessee Valley
on Sunday. While earlier model guidance suggested this low would
track northward over the Eastern Great Lakes, more recent guidance
now suggests the low will track northward along the East Coast. Even
with the eastward trend, the chance for precipitation remains for
Southeast Michigan early next week with a trough remaining over the
Great Lakes. With marginal cold air on the backside of the low, a
rain/snow mix will be possible early next week.

&&

.MARINE...
Moderate southwest flow will weaken tonight and then gradually back
to the south-southeast late Thursday and remain that way into the
weekend.  There will be a slight chance for rain over the weekend.
Wind flow will increase from the east Sunday as a low pressure
system lifts northward towards the Great Lakes for the beginning of
next week.  Temperatures will remain mild for the next week so any
precipitation will remain rain.

&&

.PREV DISCUSSION...
Issued at 1246 PM EST Wed Jan 18 2017

AVIATION...

Low level moisture/stratus continues to be locked in under inversion
across the area. A weak surface trough has been in place along
the glacial ridge from ARB-PTK-BAX. Along this line and to the
north ceilings have remain below 1kft along with visbys 4 to 6
miles. This mainly effecting PTK and FNT. Other taf sites have
improved slightly in visibility and ceilings from diurnal heating.
Mid level ridging will slowly work overhead by Thursday afternoon.
This warming will strengthen low level inversion but also bring
increasing subsidence and drier air aloft. Could see some breaking
up of stratus overnight, however, any clearing will likely lead to
increased radiational fog. So any taf site tonight that receives
fair amount of clearing will end up with denser fog. IFR
conditions will likely start improving towards end of taf period
as drier air and stronger subsidence will bring more clearing
Thursday afternoon. Wind flow will start off from the west around
10kts but back slightly and decrease this afternoon through
period.

For DTW...downsloping off of glacial ridge has helped ceiling rise
to or slightly above 1k ft and will likely remain like this into the
night.  Some partial clearing possible overnight which will lead to
some fog development.  The more clearing, the denser the fog
formation.  So may end up being bkn-ovc ceilings around 1k ft with
mvfr fog or sct-bkn ifr ceilings and fog.   Conditions will
gradually go vfr Thursday afternoon. Winds will begin westerly
around 10kts but back slightly while decreasing later this
afternoon.

//DTW Threshold Probabilities...

* High for ceilings below 5000 ft through the TAF period.

* Low for ceilings and/or visibility below 200 ft/one half mile this
  tonight and Thursday morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

DISCUSSION...DRK/JD
MARINE.......DRC
AVIATION.....DRC


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