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area forecast discussion
national weather service detroit/pontiac mi
317 am edt tue jun 18 2019

.discussion...

moist low level airmass remains in place over southeast michigan
early this morning, as 00z dtx sounding indicated a saturated 850 mb
level, with a temp/dew pt of 11 c. the rest of the atmospheric
profile is relatively dry (outside of the current surface temp/dew pt
spreads), and with breaks in the clouds around today, max temps
should reach into the mid to upper 70s (still slightly below normal),
as yesterday we still did make it into the upper 60s to lower 70s,
even with the thicker cloud cover.

energetic westerly flow over the northern conus with additional
upper level energy ejecting out of the four corners region, making
for a difficult forecast over the next couple of days with pretty
good moisture content (pw values 1.25-1.75 inches)/(125-150 percent
of normal) stretched from the central plains to the mid atlantic
coast.

strong consensus with deepening surface wave slowly tracking through
the ohio valley in the wednesday-thursday time frame. but this wave
will probably end up being fairly compact with increasing fgen
forcing, and northern fringe of the instability gradient (negative
li`s) looks to barely reach/slip past the southern michigan border.

weak northern stream trough axis and associated cold front tracking
through the central great lakes on wednesday, and there is a narrow
850- 700 mb theta-e ridge and moisture pooling (pw values up to 1.5
inches) which will track across southeast michigan during the day.
this will probably be sufficient for at least scattered showers, but
instability is weak, with 1000-850 mb capes progged under 500 j/kg.
this is good news as 0-6 km bulk shear is progged to be a healthy 40
knots.

post trough/upper level ridging will then attempt to help push the
boundary a bit south wednesday evening. however, consolidating upper
level pv taking place across the midwest/western ohio valley, spins
up low pressure which slowly tracks east along the tightening
baroclinic zone wednesday night-thursday. if the wave ends up
weaker/flatter, there is a chance the rain shield or certainly the
bulk of the heavy rain will skirt to the south of the state (see 12z
euro), as we will need a stronger wave/low level jet to shift the
stout 850 mb fgen over southeast michigan (see 00z nam/regional gem).
with 850 mb dew pts of 12-14 c, even with the lack of
instability/thunderstorms, efficient/heavy rain producing showers
will be a concern with relatively slow movement of the focused
forcing which looks to quickly wane thursday afternoon. 00z gfs
ensemble members actually look a bit more variable than last night.
one cluster of surface lows of northern ohio on thursday, with bigger
cluster over southern ohio. this does not give one confidence to
increase pops much over southeast michigan, but the 00z euro has
trended back north again, and will be carrying high likely pops for
the south half of the cwa.

the forecast for the weekend looks even more complicated and wet as
the large upper level low slipping into the pacific northwest pivots
through the northern plains, allowing for a building/dirty upper
level ridge over the mississippi river into ontario. warm
front/baroclinic zone over the western great lakes into lower
michigan through much of the weekend, with high degree of instability
developing over the western ohio valley for complexes (mcs) to tap
into. large degree of timing uncertainty this far out however.

&&

.marine...

favorable marine conditions continue today and tonight with weak
high pressure positioned over lake huron and lower michigan. this
promotes light and variable wind and nearly calm waves through
tonight. dry weather is also expected with the exception of
scattered showers possibly brushing northern lake huron tonight. the
showers are connected to a weak front that brings just a light
northerly wind shift as it settles across the central great lakes to
south of lake erie by wednesday. the next low pressure system
develops over the central plains and moves along the front toward
the west end of lake erie thursday. this system produces a moderate
increase in ne wind and brings a new round of rain mainly from
saginaw bay southward from wednesday night through thursday. weak
high pressure follows by friday.

&&

.hydrology...

weak high pressure brings one more day of dry weather before rain
probability increases wednesday and thursday. midnight wednesday
night to noon thursday is the primary time window for rainfall as a
low pressure system tracks near the southern michigan border. totals
are projected to range from around a quarter inch across the saginaw
valley and northern thumb to around three quarters inch toward the
ohio border. locally higher totals of 1 to 2 inches remain possible
depending on thunderstorm coverage and duration. given this
scenario, the potential for shorter time period flooding is limited
to poor drainage areas while possibly contributing more runoff into
already swollen creeks and streams across the area in the longer
term.

&&

.prev discussion...
issued at 1047 pm edt mon jun 17 2019

aviation...

cigs in the vfr range with occasional mvfr can be expected into
tuesday morning kptk south with deformation gradually shifting to the
east late tonight into tuesday. vfr conditions by afternoon with a
better period of clearing after 00z. with a surface ridge over and
north of the area, wind will remain under 5 knots for the most part.

dtw threshold probabilities...

* medium for ceiling 5 kft or less tonight into tuesday morning.


&&

.dtx watches/warnings/advisories...
mi...none.
lake huron...none.
lake st clair...none.
michigan waters of lake erie...none.
&&

$$

discussion...sf
marine.......bt
hydrology....bt
aviation.....dg


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