Scientific Forecaster Discussion
fxus63 kdtx 221533
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1133 am EDT Tue may 22 2018
Minor adjustments to pops through the afternoon to time the possible
showers and thunderstorms. Things are lining up pretty much as
expected so far. The circulation in the base of the upper level
trough can be seen now on satellite spinning over Southern Lake Michigan
with the mid level jet Max surging eastward just to the south.
Surface cold front now taking shape as the surface low drifts into
southern Ontario. Rap continues to advertise 500-1000 j/kg of MLCAPE
lifting north into extreme southern Michigan supported by most recent Storm Prediction Center
mesoanalysis. Visible satellite shows clouds thinning in the
developing dry slot/warm sector just ahead of the mid level trough.
This will add some destabilization to the low levels adding to low
level wind shear and moisture pooling. Most model soundings show a
cap around 700mb which will try to suppress convection so will have
to see how fast we can warm up with thinning clouds and southerly
warm air advection. Best chance of storms remains south of M59, with
a slight chance farther north. Do not expect storms to be severe but
could see heavy rain as precipitable waters are around 1.25".
issued at 637 am EDT Tue may 22 2018
An elongated region of low pressure will extend across southern mi
this morning through much of this afternoon. The development of a
shallow inversion overnight with ample low level moisture advecting
into se mi from the southwest has produced a considerable amount of
low stratus (ifr and lower). Abundant boundary layer moisture has
also supported some vsby restrictions, especially in and around
Metro Detroit. Persistent low level moisture advection into the
afternoon will cause stratus to remain rather persistent through the
day, with mid may sunshine allowing a slow but steady lifting of
cloud bases. High pressure will expand into the area this evening.
The associated push of drier air will result in some degree of
clearing trend during the course of the evening.
For dtw...despite the sfc low overhead, the main instability axis is
expected to remain southeast of Metro Airport this afternoon and
evening. Given the ongoing low level moisture advection the current
LIFR conditions are likely to hold through much of the morning.
Dtw threshold probabilities...
* high for ceiling 5000 ft or less today.
* Low in thunderstorms today and this evening.
issued at 315 am EDT Tue may 22 2018
Latest water vapor imagery shows upper level wave/circulation
tracking over Northern Lake Michigan, with corresponding mid level
jet (500 mb) of 45 knots tracking through Southeast Michigan around
noon. A pool of low level moisture seen coming out of northern
Indiana (see NAM 850-700 mb Theta-E/surface dew pts) looks like it
will be sufficient to generate at least scattered showers and
isolated thunderstorms as MLCAPES reach and exceed 500 j/kg toward
the Ohio border (per local probabilistic guidance), as surface winds
flip around to light southwest and surface dew pts climb above 60
degrees south of M-59. The low levels (925 mb) look to remain fairly
saturated/low clouds, but with the surface boundary straddling The
Heart of the cwa, and differences in wind direction, probably looking
at highs ranging from 65 (north) to 75 (south). If instability does
ramp up a little more than expected, there is concern for locally
heavy rain as inland inverted surface trough arches back and
hovers/persists this afternoon over central sections of the state, as
good push of dry air does not look to occur until/toward 00z.
However, preference is toward a more muted response such as 00z hires
Surface ridging building in tonight could set the stage for fog
development, but there is some uncertainty whether low clouds
are going to fully dissipate in a timely fashion.
A significant warmup will occur over the end of the work week, as
pronounced 500 mb upper level ridge over the Mississippi River
valley slowly advances east, with the ridge axis arriving Friday
morning in a slightly flattened/weakened Mode. None-the-less,
strengthening low level southwest winds will advect a lot of warmth
into lower Michigan, and 850 mb temps of 16+ c will supports temps
well into the 80s on Friday, as frontal boundary looks to be
sufficiently north over the northern Great Lakes.
Height falls over the weekend as upper level low coming out of the
northern rockies gradually slides into the western Great Lakes. Bulk
of 12z Euro ensembles keep County Warning Area within the warm sector on Saturday,
supporting temps still in the 80s with good chance of showers and
thunderstorms. Obviously, timing of any thunderstorm complex during
the mid day hours could easily short circuit temps.
Weak low pressure will track across Southern Lower Michigan and Lake
Erie today, leading to generally light and variable winds across
lakes St Clair and Erie. On Lake Huron, light east-northeast winds
will back to the north-northwest during the afternoon and evening as
the low advances into the eastern Great Lakes. High pressure will
expand into the region from the west tonight into Wednesday. This
high will reside over the region through Thursday, providing
generally light and variable winds.
Lake St Clair...none.
Michigan waters of Lake Erie...none.