Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 261935
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
335 PM EDT Sun Mar 26 2017
Stacked/occluded low pressure system now lifting across northern IL
will continue northeast and across lower MI while gradually
weakening tonight. Steady moisture transport within the immediate
downstream warm conveyor will maintain a presence through this
evening, before the inbound height falls squeeze this moisture plume
eastward. This will continue to support convective shower develop
as periodic episodes of greater ascent/convergence emerge within the
existing perturbed cyclonic flow and across the warm frontal zone.
Weak instability off the surface to maintain a shot at embedded
thunder, small hail a possibility given suppressed freezing levels.
Slow northward advancement of the surface warm front thus far, but a
late push may still provide a quick climb in temperatures /50s/ this
evening. Diminishing mid level ascent as the weakening circulation
passes overhead will sustain a disorganized and diminishing coverage
of showers through the overnight hours.
Trailing weak frontal passage Monday morning will provide a
minor/brief period of cold air advection across the 850-925 mb
layer, but will have little impact at the surface aside from a wind
shift to west-southwest. This advection combined with an already
moist low level profile will favor greater retention and/or renewed
development of clouds during the daylight period. In addition,
thickening mid level cloud associated with the next inbound
shortwave becomes a factor by afternoon. Despite this, resident
airmass remains relatively mild, arguing for modest recovery that
results in temperatures peaking above normal.
Attention for the Monday night period focused on the shortwave now
lifting out of the southern Rockies. This system will make a
progressive move east-northeast over the next 36 hours, still
projected to translate across the Ohio valley by Monday night. Lower
Michigan will remain along the northern extent of any corresponding
increase in system relative isentropic ascent during this time. In
addition, model variance remains high in projecting a possible
trailing deformation axis, owing to continued differences in both
the strength and exact trajectory of the key features. 12z NAM
unsurprisingly the most robust in development of this wave and a
corresponding maturation of the mid level dynamics to the north.
This solution would favor a more expansive and potentially heavier
rainfall scenario. 12z GFS arriving more in tune with the
ECMWF/Canadian, providing simply a period of isentropic ascent.
Outgoing forecast will continue to hold the line with the less
dynamic model solution space, maintaining a measured stance on
precipitation chances and QPF totals with northward extent.
Increasing influence of 1035 mb high pressure centered over eastern
Manitoba will then define conditions heading into the midweek
period. This in conjunction with confluent mid level flow will
establish a drying and more stable environment beginning Tuesday.
Cooler northerly flow with residual cloudiness will bring
temperatures back down toward seasonal averages for late March
/around 50 degrees/.
Surface high pressure will continue to keep conditions dry
throughout Wednesday as temperatures push into a seasonal lower 50s
for a daytime high. The GFS has finally come into better agreement
with both the ECMWF and GEM model runs regarding a developing low
pressure system that is expected to move from TX into MI/Ohio Valley
Wednesday through Friday. Confidence is much higher regarding the
chance for precipitation starting Thursday morning/afternoon, with
PoP values increasing late Thursday into Friday. Both the ECMWF and
GEM models continue to exhibit a more northerly track with the low
compared to the GFS, pushing the low across southern Michigan
through Friday afternoon. The GFS run tracks just south of Michigan,
moving across the Ohio Valley throughout Friday.
In any case, while confidence in precipitation has risen, still some
minor questions remain regarding precipitation type. A warm column
of air overhead will bring rain throughout Thursday. Internal model
blends opted for a rain/snow mix and snow through Friday morning,
however, going to keep mostly rain for the CWA, except portions of
the thumb, as ECMWF and GEM models keep us mild through the morning.
While the GFS is cooler at this time for the forecasted period,
forecasted soundings did not give any solid indication for a wintry
mix or snow through Friday morning. Additional tweaks in timing and
possibly precipitation type will be needed as the end of the week
Winds will become fairly light this evening, gradually shifting from
southerly to westerly overnight as low pressure tracks through the
Central Great Lakes. Rain showers will continue to affect the area,
with a few thunderstorms also possible over southern Lake Huron,
Lake St Clair and western Lake Erie through late tonight. A ridge of
high pressure will briefly build into the region Monday, keeping
winds light and bringing drier weather. The next low pressure system
will track close to the Michigan/Ohio border Monday night into
Tuesday, bringing another round of rain showers and a modest
increase in north winds.
Rain showers will become less widespread by late evening before
tapering off overnight. Additional rain amounts for the late
afternoon and evening will generally range around 0.25 inches or
less, but will be locally higher in any thunderstorms or stronger
showers that develop. Rain should be mainly out of the area by 2AM.
Issued at 227 PM EDT Sun Mar 26 2017
IFR to MVFR conditions and rain will prevail through 20-22Z as
deformation axis lifts through the area. Brief drops to VLIFR can
also be expected. Conditions will then transition to more MVFR, with
possible interludes of VFR, as the upper low passes over the area
and numerous showers develop for the late afternoon and evening.
This is supported by upstream observations over Indiana. A few
thunderstorms will also be possible until about 06Z as the cold pool
associated with the upper low passes overhead. Attention will then
turn to lowering visibilities and ceilings overnight as the low
passes east. Slight southerly gradient will favor low stratus over
BR/FG. Introduced IFR ceilings overnight, but cannot rule out VLIFR.
For DTW...Pockets of VLIFR may impact the terminal through 19-20Z
before upper low begins to work into the area and conditions improve
to predominantly MVFR. Ceilings may show wide variation however as
numerous showers also work up into Southeast Michigan. Deterioration
of ceilings/vis then expected overnight, particularly with ceilings.
IFR conditions look most probable at this time.
//DTW THRESHOLD PROBABILITIES...
* High for cigs below 5000 feet through the TAF period.
* Low for thunderstorms in the DTW airspace through 06Z.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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