Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 060846
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
346 AM EST Tue Dec 6 2016

.DISCUSSION...

Polar jet has taken a position across the northern tier of the US as
a strong upper low over the northern Plains drifts northeast through
the northern Great Lakes. A strong vort lobe wrapping tightly around
the low will surge through the straits this evening and overnight.
Accompanying cold front will work through southern MI later tonight.
Meanwhile, an open wave in the subtropical jet will be lifting from
the Gulf Coast to the mid Atlantic states. Deformation on the
northern flank of this subtropical low has been flirting with SE MI
for days now in the models. Not much has changed with the current
model cycle. We remain sandwiched in between the two stronger areas
of mid level lift, with only weak troughing connecting the two
lifting across lower MI today. Thinking is that the weak deformation
will lift into extreme southeastern MI this afternoon (15-18Z) and
slowly expand northeast through the early evening. Any precipitation
will come as light rain as the saturation layer fails to get colder
than -5C and forcing is quite weak. As the deformation region tried
to exit east, looks like there is some potential for the left exit
region of the approaching jet to regenerate some light rain or
drizzle over the thumb after 00Z. Drier air behind the cold front
will quickly end the rain/drizzle by 06Z.

This cold front will mark the beginning of a stretch of colder air
that will affect the region through the weekend. 850mb temps will
fall to around -5C on Wednesday and -10C by Thursday as the main
trough axis passes to the east allowing the northwesterly flow aloft
to advect much cooler air into the region. This airmass will knock
high temperatures down into the 20s through Saturday before ridging
over the central Plains starts building into the Midwest warming us
back into the 30s. Main concern with the cold airmass will be the
lake effect snow generated off Lake MI which will try to work into
SE MI. Westerly flow at the surface with initial cold airmass will
keep convective depths on the east side of Lake MI only around 6-
7kft so chances of the better snow bands reaching the east side of
the state aren`t great. Flurries and light snow showers will be
possible though Wednesday night into Thursday. Little better fetch
Thursday may enhance the convergence band south of I-94 but not
going to get too excited about that yet this far out.

The next low pressure system won`t arrive til Sunday/Monday but
model continuity has not been good with this one thus far stemming
from potential amplification of the jet stream. Euro is keeping flow
flatter resulting in cyclogenesis much further north while GFS
deepens the wave and resultant surface low at lower latitudes. They
have been consistent with timing so will keep pops enhanced for this
period.

&&

.MARINE...

Surface Winds will transition this morning to the southeast and
increase into the 20 to 30 knot range over the Lake Huron basin.
Small craft advisories are in effect this afternoon for the
nearshore waters of Lake Huron from Port Austin to Port Huron. Two
separate low pressure systems are expected to slide eastward
remaining to the north and south of southeastern Michigan. An
organized cold front will push through the area this evening opening
the door to an unmodified arctic push and stronger westerlies.
Latest forecast information continues to suggest that west wind
speeds will remain in the 30 to 34 knot range tonight and Wednesday.
Unstable conditions over area waters and fresh westerly surface flow
is likely to hang around through the end of the week.

&&

.PREV DISCUSSION...
Issued at 1156 PM EST Mon Dec 5 2016

AVIATION...

East winds off the Great Lakes will allow light fog (BR) and lower
stratus to fill in overnight across Southeast Michigan terminals.
Restrictions will most likely fall into the MVFR category, although
some lower ceilings are possible from PTK north. All hi-res model
data now supports improvement to vis/cigs near the Detroit terminals
around 12Z as easterly flow strengthens, and as warmer air arrives
in the low-levels to extreme Southeast Michigan and weakens the
inversion. Northern terminals should take longer to see some
improvement as the warmer wedge of air remains further south, with
only some improvement into higher MVFR at 14-15Z. Conditions will
then deteriorate again in the afternoon and evening as low pressure
lifting into the Ohio Valley spreads rain into the area. A cold
front pushing through during the evening will usher out
precipitation, but allow gusty west winds to develop.

For DTW...Flow off Lake Erie and earlier clearing to skies will
allow visibility to continue falling to MVFR early in the TAF period,
with eventual development of stratus around 1500ft expected to
follow. Warmer air in the low-level and increased easterly flow
should then allow for an improvement in ceilings/vis around 12Z
before conditions deteriorate again in the afternoon as rain spreads
into the area. Winds are expected to increase from the east-
northeast during the afternoon, between 10-15 knots. Stronger west
winds will then arrive with a cold front this evening.

//DTW Threshold Probabilities...

* Medium for cigs below 5000 feet after 08Z. High after 18Z Tuesday.

* High confidence precipitation Tuesday will be rain.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 10 AM this morning to 10 PM EST Wednesday
     FOR LHZ441>443.

     Small Craft Advisory from 10 PM this evening to 10 PM EST Wednesday
     FOR LHZ421-422.

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

$$

DISCUSSION...DRK
MARINE.......CB
AVIATION.....99


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at www.weather.gov/detroit.



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