Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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981
FXUS63 KDTX 251008
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
608 AM EDT Sat Mar 25 2017


.AVIATION...

A stalled surface front lingering just south of the Michigan border
will bring a lengthy period of IFR (possibly LIFR) conditions across
the region today and tonight. Increasing moisture field over a
cooling surface layer will result in low stratus and/or fog concerns
through most of the taf forecast. In addition there will likely be
several waves of rainfall that sweep across the area that will need
timing refinement as the individual waves become more evident.
Models continue to advertise an afternoon lull in precipitation but
overall, low stratus and fog should prevail through the day.

For DTW...The terminal remains just south of the main band of
rainfall and IFR stratus this morning but models show rain filling
in early this morning. An afternoon lull looks to develop but ample
moisture should keep a fog and/or drizzle presence. Expect MVFR or
lower conditions through the period as the front responsible moves
very little through the forecast.

//DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5000 FT through the forecast.

* Low for cigs/vsby aob 200 FT or 1/4SM today or tonight.

&&

.PREV DISCUSSION...
Issued at 306 AM EDT Sat Mar 25 2017

DISCUSSION...

There is a tight low to mid level baroclinic zone draped across the
Great Lakes early this morning. Meanwhile, the circulation
associated with the upper low now churning over Oklahoma is feeding
a plume of deep layer moisture into Illinois. During the night, the
frontal boundary across Lower Michigan has remained active in two
locations; across northern Lower Mi within the 700-600mb layer and
across the central portions of the forecast area (M59 to I-69
corridors) closer to the 925mb portion of the frontal zone.

The hi res model suite all suggest the 925-850mb layer will become
more active during the early morning, aided by the ongoing deep
layer moisture feed across Illinois. This will support increasing
coverage of showers across the forecast area (aside from perhaps
locals south of the I-94 corridor). Weak elevated instability
along/south of the I-96 corridor has supported some thunderstorms
overnight. The overall persistence of this weak instability will
continue to support some additional thunderstorms. Enhancing the
forcing along the front is the ageostrophic response within a 140+
knot upper jet streak centered over srn Quebec. This forcing will
persist through the first half of the day today. The upper jet
streak will then become focused much farther east this afternoon. In
fact, some mid level ridging will develop across the ern Great Lakes
today as the upper low rotates into Missouri. These factors will
fracture/weaken the frontal forcing, leading to a diminishing trend
to the coverage of showers during the course of the afternoon and
evening.

Despite the approach of the associated sfc low pressure into
Missouri today, strengthening sfc high pressure across northern
Ontario drove the sfc cold front across the forecast area last
night. Marine modification under the post frontal northeast winds
have resulted in a rather shallow but cold near sfc layer across Se
Mi. Temps actually dropped a good 20 to 30 degrees following fropa
last night. The easterly component of the sfc winds will persist
through the day, while post frontal stratus continues to expand
across Se Mi. This will keep the front south of the area today and
will only support temps in the 30s and 40s, with the coolest
readings downwind of Saginaw Bay and Lake Huron with the NE winds.

The upper low will lift into the nrn Ohio Valley and srn Great Lakes
on Sunday but will dampen considerably as it does so. There are
differences among the 00Z model suite with respect to timing and
location of this system as it approaches the region. Some upper
level diffluence and mid level deformation forcing will support some
regions of more persistent rainfall, the locations of which carries
a high degree of uncertainty at this time. Indications among the 00Z
model suite are that the better rain chance overnight into Sun
morning will be to the west of north of Se Mi, with rainfall
probabilities over the forecast area increasing Sun afternoon. The
low level wind fields will turn more southern Sunday as the
associated sfc low lifts across Lower Mi. This will allow temps to
make a run into the 50s.

Mid level subsidence will overspread the region by Monday as the
remnant upper wave lifts off the northeast. There will not be any
cold air intrusions in the wake of this system, so Monday highs will
possibly rise into the 60s, dependent upon the degree of lingering
low clouds. There has been a noted trend toward a weaker and farther
south mid level short wave feature Mon night into Tuesday. Precip
chances have therefore been lower accordingly. Mid level ridging and
sfc high pressure will dominate during the mid week period. Easterly
sfc flow will however keep temps somewhat on the cool side. The
approach of yet another upper low by the medium range suite will
warrant the next chance of rain the end of the work week.

MARINE...

The slow moving frontal boundary has dropped south of Lake Erie
overnight bringing a wind shift to the northeast across all of the
eastern lakes. Winds will increase this morning reach 25 to 30 knots
across central Lake Huron which will lead to waves in excess of 4
feet impacting the nearshore waters over the northern Thumb region
during the day. Small craft advisories are in effect for Saginaw Bay
and a portion of the nearshore waters through most of the tonight
period. High pressure building across Ontario and Quebec with a low
tracking into the western Ohio Valley will then cause the winds to
veer more easterly which will take the higher winds into Northern
Lake Huron for the rest of tonight and Sunday. The weak low then
looks to slowly pass through Lake Huron on Monday, with generally
light winds right into Tuesday, but from the north behind the low.

HYDROLOGY...

Periodic showers will affect the region through the weekend as a
frontal boundary stalls just south of the state line. Though a
lengthy period with on and off showers, rainfall totals are only
expected reach 0.5 to 0.75 inches through the duration of the event.
The resultant runoff will likely increase flow rates and water
levels in local streams and rivers but flooding risks are mitigated
by the long duration of this rainfall.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 1 AM EDT Sunday for LHZ421-422-441.

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

$$

AVIATION.....DRK
DISCUSSION...SC
MARINE.......DRK
HYDROLOGY....DRK


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