Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 200736
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
236 AM EST Mon Nov 20 2017

.DISCUSSION...

As Alaska/NW Canada serve as the primary conduit of energy into the
consolidating Hudson Bay vortex, baroclinic westerlies will
strengthen and contract north over the next several days. During
this time, multiple mid-level impulses will track over or north of
the area with high confidence in a mean storm track north of Lake
Superior for the remainder of the week. Effects in Southeast
Michigan will be high variability in temperatures centered about
seasonal average values as a series of low impact cold front sweep
across the area Tuesday into next week. The first shortwave in this
prolonged sequence is evident over northwest Canada digging into
Alberta early this morning. Downstream ridging will translate across
Southeast Michigan forcing return flow to get underway in earnest as
high pressure slips east. 850mb temperatures are modeled to rebound
toward 5C by this evening after being below -10C 24 hours prior.
Gusty southwest gradient wind and mostly sunny skies will only help
matters as temperatures moderate by about 10 degrees compared to
yesterday, or low to mid 40s. The gradient will be sufficiently
strong to maintain a mechanically mixed boundary layer through
tonight, suggesting siding with the warmer guidance in the mid to
upper 30s. Airmass exchange will already be complete by Tuesday
raising potential high temps a few degrees further, toward 50
degrees, increasing high clouds limiting the potential to go any
higher. Once again leaned toward the warmer guidance; in this case
MOS and raw ECMWF output - some members of the NWP suite actually
have snowpack and thus keep temps far too low. Cold fropa Tues aftn
will be rather uneventful as the time window for good dynamic
forcing will be just be a couple of hours as the developing surface
front sweeps through coincident with strongly convergent mid-level
forcing aloft. Chc pops remain appropriate with just a
narrow/transient band of light rain transitioning to light non-
accumulating snow expected. Cold advection will dump 850mb temps
back toward -10C for Wednesday before the pattern approximately
repeats itself and a moderating trend back into the 40s to possibly
50 degrees gets underway for the second half of the week. Long range
modeling continues to suggest a couple more cold shots before
downstream effects of a Pac jet extension forces the polar low to
retreat suggesting a period of milder wx to close out the final days
of the month.

&&

.MARINE...

Winds will remain fresh today, as the region is sandwiched between
high pressure slipping through to the south and an approaching low
pressure system from the west. The current westerly flow will back
to southwesterly early in the day. Expectations are for a corridor
of higher speeds emerging from Saginaw Bay into the central body of
Lake Huron, with sustained winds increasing to near 30 knots. Near
surface stability will be increasing as warmer air washes across the
region. Therefore, wind gust potential will be limited to lower-end
gale gusts - mainly constrained to the central half of Lake Huron
(including Outer Saginaw Bay). Elsewhere, the fresh flow will
support small craft headlines. In the wake of the surface cold front
on Tuesday, the flow will veer to northwesterly with the strongest
flow confined to the northern half of Lake Huron - again gusts in
the 35-40 knot range. Significant waves on Lake Huron will peak
around 10 feet during the gale event with occasional waves exceeding
15 feet in the central basin. Otherwise, the near surface will
destabilize behind the cold front, reintroducing lake-effect showers
across the entire basin.

&&

.PREV DISCUSSION...
Issued at 1142 PM EST Sun Nov 19 2017

AVIATION...

Low level warm and dry air advection should lift the strato cu field
northeast of the terminals by 06z, leaving just higher based clouds
through the morning. Wind speeds have dropped with some boundary
layer decoupling. An increasing southwest gradient during the course
of the morning will lead to a slow increase in the wind speeds
toward daybreak, with peak daytime heating supporting some gusts
over 20 knots Mon afternoon.

//DTW THRESHOLD PROBABILITIES...

* None.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning from 7 PM this evening to 4 AM EST Tuesday for LHZ421-
     462.

     Small Craft Advisory from 7 PM this evening to 1 PM EST Wednesday
     for LHZ441.

     Small Craft Advisory from 7 PM this evening to 4 PM EST Tuesday for
     LHZ442-443.

     Gale Warning from 10 AM to 10 PM EST Tuesday for LHZ361.

     Gale Warning from 7 PM this evening to 10 AM EST Tuesday for LHZ363.

     Gale Warning from 7 PM this evening to 4 AM EST Wednesday for
     LHZ362.

     Small Craft Advisory from 7 PM this evening to 10 AM EST Tuesday
     for LHZ422.

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

$$

DISCUSSION...JVC
MARINE.......Mann
AVIATION.....SC


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at www.weather.gov/detroit.



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