Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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075
FXUS63 KDTX 261447
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1047 AM EDT Sun Mar 26 2017

.UPDATE...

Late morning upper air analysis shows the upper circulation now
centered over west-central IL.  Prominent warm conveyer belt
anchored along the eastern flank evident on water vapor sustaining
steady 850-925 mb waa/moisture advection across the existing warm
frontal slope.  This process driving the initial expansion of
convective showers north of the surface warm front still draped
south of a Fort Wayne to Findley line.  Higher coverage through the
early afternoon period likely focused along/west of the I-75
corridor.  Even greater eastward expansion expected moving forward
from mid afternoon through the evening, as focused areas of
convergence/cva pivoting through the cyclonic eastern periphery
migrate through.  Recent hi-res model output holding with this
expectation, reaffirming high categorical pops remain warranted.

The temperature forecast is a different story, as the muted response
thus far both locally and just upstream casting greater doubt in
attaining greater recovery. With that said, noting virtually all
guidance sans the NAM still support readings lifting into the 50s
late today as the warm frontal boundary arcs into the region. Will
elect to slow the diurnal curve through early-mid afternoon, but
allowing for a late push early this evening to achieve these values
/particularly south of M-59/.

&&

.PREV DISCUSSION...
Issued at 607 AM EDT Sun Mar 26 2017

AVIATION...

With a front still lingering just south of the Michigan border, and
the associated low pressure center forecast to lift northeast
through central lower MI later this evening, TAFs will be quite
pessimistic. Increasing moisture field over cool easterly flow will
keep a low stratus deck with possible vsby restrictions most of the
forecast. Add to that a band of showers that will impact the region
generally between 16-22Z with some additional showers lingering
after. Question remains as to how much CIG/VSBY improvement will
occur within the area of showers, but looks like once we come out of
the more widespread showers, conditions will try to drop again
overnight. There is a chance of some isolated thunderstorms this
afternoon/evening but coverage and confidence is too low to include
in the taf.

For DTW...A brief break in the IFR/MVFR conditions with stratus
breaking up near the front.  This will be short lived as the low
will continue closer to the terminal through the day with enhanced
moisture plume and showers lifting through which will reduce
cigs/vsbys once again.

//DTW THRESHOLD PROBABILITIES...

* High for cigs below 5000 feet much of the forecast.

PREV DISCUSSION...
Issued at 311 AM EDT Sun Mar 26 2017

DISCUSSION...

With the exception of the tri cities region, Se Mi has remained
largely dry during the night. This is due to the fact that the mid
level deformation has held north and west of the forecast area,
while mid level ridging has held firm across the eastern Great
Lakes. An upper low is churning over the MO/IA/IL border region
early this morning. The water vapor imagery shows a steady stream of
deep layer moisture into the wrn/cntl Ohio Valley within the warm
conveyor belt of this system.

The mid level circulation is forecast to elongate as it rotates into
far srn Lake Mi this afternoon, with the mid level trough axis
taking on a negative tilt as it lifts into srn Lower Mi. This will
result in a fairly good region of mid level height falls
overspreading Se Mi this afternoon and evening. An axis mid level
deformation is forecast to pivot from SW to NE across the forecast
area this afternoon within a region of good upper level difluent
flow. These forcing mechanisms combined with the deep moist plume
being driven into the area will support widespread showers today
into this evening. The showers will increase in coverage across the
southern sections of the forecast area late this morning before
lifting northward during the afternoon. The upper low is forecast to
transition to an open wave as it lifts across Lower Mi this evening.
There will still be decent mid level cooling (especially south of
the I-69 corridor). This will warrant isolated to scattered
thunderstorms during the latter half of the day.

As is often the case this time year, the afternoon temperature
forecast carries a high degree of uncertainty. Temperatures are
likely to vary widely across the forecast area today. The cold front
which rolled across the area Fri night/Sat morning is still located
over central IN/OH early this morning. The associated sfc low will
lift into central Michigan this evening. The sfc low is weak and
there is some concern that the front will not make it this far north
given the dense near sfc cold layer to the north. The ARW and HRRR
do at least lift the front into srn Mi, suggesting some locations
may be able to see temps into the 50s and possibly low 60s.

This upper wave will rapidly dampen as it exits northeast of the
region late tonight allowing mid level short wave ridging to
overspread the area by Monday, supporting a dry forecast. There will
be little cold air intrusion into srn Mi in the wake of this system.
While there is likely to be some residual cloud cover, diurnal
mixing with light w-sw flow will support daytime highs into the 50s
to low 60s. THere are model differences with respect to a mid level
short wave firecast to lift out of the srn plains and across the
Ohio Valley Mon night along with the amplitude of a northern stream
wave fcst to drop into the nrn Great Lakes. The GFS is much more
amplified with this northern stream wave. This causes the model to
produce a region of stronger moist isentropic ascent across Lower Mi
and even suggests some interaction with the southern stream
triggering enhanced mid level deformation right over Se Mi. This GFS
solution is thus rather bullish on precip chances Mon night into
Tues morning. The ECMWF and Canadian on the other hand are weaker
and suggest much lower precip probabilities. Given the uncertainty,
a chance of rain will suffice attm.

Expanding high pressure into the northern Great Lakes by mid week
will support a northeast component to the sfc wind across srn Mi and
thus relatively cool temperatures. The potential for another wave to
lift into the region from the srn plains will support the next
chance of rain late in the work week.

MARINE...

A weakening low pressure system will track northeastward through the
Great Lakes today and tonight bringing lighter winds to the region.
Initially easterly winds funneling between the low and high pressure
to the north will stay slightly elevated but should remain below 25
knots for the entire Huron basin. Highest winds will be located
across the northern third of the lake. Light winds will persist into
early next week as high pressure tries to build into the region.

HYDROLOGY...

Periodic rain showers will continue for yet another day across
southeast Michigan. So far the two day totals across the area are
around 1 inch with an additional quarter inch expected today. A
thunderstorm or two may lead to locally higher amount. Regardless of
todays totals, no flooding is anticipated due to the long duration
of the event and relatively low totals over the course of 3 days.

&&

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

$$

UPDATE.......MR
AVIATION.....DRK
DISCUSSION...SC
MARINE.......DRK
HYDROLOGY....DRK


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