Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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616
FXUS63 KDTX 232001
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
301 PM EST Thu Nov 23 2017

.DISCUSSION...

Skies are clearing this afternoon across southeast Michigan,
allowing temps to climb into the upper 30s to around 40 degrees.
Aggressive warm advection pattern ramping up through tomorrow with
increasing/deepening southwest flow, as strong shortwave trough moves
into Western Great Lakes tomorrow afternoon. Opportunity for winds
to decouple this evening, and with the dry airmass (dew pts in low to
mid 20s), a dip into upper 20s to around 30 degrees appears likely
before midnight, with temps steady or rising slightly overnight.

850 mb temps progged to reach 10+ C by 00z Saturday over southeast
Michigan, with 6 C noted at 925 MB, per 12z NAM, which is supportive
of highs in the mid 50s for Friday, but mixing depths probably
coming up just short of that level and went with temps predominantly
in the lower 50s. 850 MB Theta-E ridge well out ahead of the upper
level support early Friday evening, likely resulting in a mainly dry
cold front passage Friday Evening/Night. Post frontal surge of low
level cold advection and west/northwest flow off Lake Michigan may
provide better chance for sprinkles/light showers, with perhaps
enough cold air (-7 C at 850 MB) to support a few flurries on
Saturday. Regardless, expecting mostly cloudy skies, but mild start
should allow for maxes in the low/mid 40s before the deeper cold air
takes hold late in the day. Clouds slow to clear Saturday evening
and winds staying up much of the night expected to hold mins in the
upper 20s to around 30 degrees Saturday Night.

High pressure will build into the region on Sunday while a shortwave
pivoting southeastward tracks north of Lake Huron. This shortwave
will delay the onset of warm advection with highs in the low 40s on
Sunday. As the expansive region of high pressure becomes established
along the East Coast, southwest gradient flow will increase across
the region ahead of the next low pressure system tracking eastward
across Southern Canada.  This will help boost highs to near 50 on
Monday and well into the 50s on Tuesday.

Upper level ridging will also build across the region early next
week as a strong wave splits into a faster northern and slower
southern wave across the Western US. The northern wave will drive
the Canadian low eastward pulling a cold front through the Great
Lakes late Tuesday. The next chance for rain will accompany this
frontal passage before highs return closer to normal in the low to
mid 40s on Wednesday. Will then need to monitor the evolution of the
southern wave as it could bring another chance of rain/snow to the
region during the middle part of next week.

&&

.MARINE...

Area lakes will remain under gusty southwest conditions through
tonight, as return flow strengthens behind surface high pressure
over the eastern U.S. While the gustiest of the southwest winds will
occur out over the open waters of the Lake Huron basin during this
time, wave heights and wind gusts will respond enough in the long
southwest fetch to necessitate a small craft advisory over outer
Saginaw Bay.  The gradient will strengthen Friday in advance of an
approaching cold front. This will bring southwest winds of 25 to 30
knots across lake Huron.  While increasing stability may tend to
limit the overall gust potential, this will allow gusts to reach
gales for a period over the open waters. Winds turn west-northwest
and remain strong as colder air arrives Saturday.

&&

.PREV DISCUSSION...
Issued at 630 AM EST Thu Nov 23 2017

AVIATION...

Midlevel thetae advection ahead of approaching shortwave energy has
resulted in a solid opaque altostratus deck across all of
southeastern Michigan. Trajectory of cyclonic circulation through
far northern IN today should keep cloud in place for a good portion
of today. Uncertainty remains high with exactly how cloud trends
will play out later this afternoon. Model data suggests active
midlevel subsidence developing during the afternoon hours, but
forecast soundings are not overly convincing that it will be deep
enough to totally erode out the mid cloud. Active pattern will then
allow moisture from the next system to begin spilling down into the
Great Lakes late tonight.

//DTW THRESHOLD PROBABILITIES...

* None.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning from noon Friday to midnight EST Friday night for
     LHZ462>464.

     Small Craft Advisory from 7 AM Friday to midnight EST Friday night
     for LHZ422-441>443.

     Gale Warning from 7 AM Friday to midnight EST Friday night for
     LHZ362-363.

     Small Craft Advisory until midnight EST Friday night for LHZ421.

Lake St Clair...Small Craft Advisory from noon Friday to 4 AM EST Saturday for
     LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from noon Friday to 4 AM EST Saturday for
     LEZ444.

&&

$$

DISCUSSION...SF/JD
MARINE.......MR
AVIATION.....CB


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