Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1152 PM EDT Monday Jun 29 2015
The low level S-southeast winds have been advecting a stratus deck
northward this evening. Satellite trends suggest these clouds will
eventually lift north into fnt and mbs by or shortly after 06z.
Cloud bases are expected to trend toward MVFR over the next few
hours as additional low level moisture arrives from the southeast.
These low clouds will likely persist through daybreak under a
shallow inversion before daytime heating lifts the clouds to a VFR
strato cumulus field by afternoon.
For dtw...there have been a few observations across Northern Ohio with
IFR ceilings in the vicinity of a weak surface low. This feature will
lift east of metropolitan Detroit 08-12z and will supply some additional
low level moisture advection. This will remain supportive of a
period of IFR ceilings at metropolitan early Tuesday morning.
//Dtw threshold probabilities...
* high in ceilings below 5000 feet tonight and Tuesday morning.
* Medium in thunderstorms Tuesday afternoon and evening.
Previous discussion...issued 654 PM EDT Monday Jun 29 2015
Earlier showers and isolated thunderstorms have lifted north of
the region...with little instability remaining over Southeast Michigan. A middle
level short wave now rotating along the Michigan/in border will provide
a chance for some light showers/sprinkles across metropolitan Detroit
and points south tonight...but that is about it. In light of
current observations...the forecast will be updated to reduce
cloud cover this evening and lower probability of precipitation substantially tonight.
Previous discussion...issued 322 PM EDT Monday Jun 29 2015
Sunny start to the day allowed temperatures to push to around 80
degrees over Tri-Cities region...Flint vicinity...and northern thumb
region this afternoon...coupled with modest moisture advection
allowing some (sct) showers and isolated thunderstorms to go up with
MUCAPES around 500 j/kg.
Positively tilted upper level longwave trough in place over the
western/Great Lakes...with seasonably cold middle levels...as 12z DTX
sounding indicated a 500 mb temperature of -15 c. One shortwave which
produced heavier shortwave activity over Northwest Ohio early today
has passed just to our southeast...taking with it the majority of
the deeper moisture. However...a second pv maximum/shortwave near
Chicago will skim across the southern Michigan border...and 850-700
mb circulation is forecasted to slowly lift through Southeast
Michigan this evening. This feature will have little instability to
work with...but should allow low clouds and moisture to spread up
from the south with a chance of some drizzle or light rain showers
with the weak circulation. Surface dew points holding in the upper 50s
to around 60 degrees will provide the bottom for mins.
Long term...Tuesday through Sunday
Longwave trough will hold over the region through the week but with
many small scale features to try to account for. Models have been
struggling with this pattern and these smaller waves throughout the
past weekend and expect this to continue moving forward through middle
week. For this reason it will be hard to go with probability of precipitation higher than
chance for any period until the shortwaves and surface features start to
show themselves and their locations.
The upper level trough axis will reach central Michigan Tuesday morning.
The track of an exiting surface low over Lake Erie may keep the
weakening deformation band and precipitation shield over the eastern
counties. A shortwave ridge will be sliding across northern lower
which may put an earlier end to the lingering showers though. Chance
of showers/thunderstorms will return early Tuesday afternoon as the next
wave tracks through lower Michigan along a frontal boundary on the
backside of the longwave trough. The wave and associate surface
reflection are forecast to track right through lower Michigan during peak
heating between 18-00z which should aide in convection. Models show
cape peaking under 500 j/kg with less than 20 knots throughout the
column. So could see some scattered showers/thunderstorms pop
up...especially close to the front in the late afternoon. Though
overall forcing is not overwhelming...precipitable waters on will remain near 1.5
inches and when combined with slow storm motion could lead to some
heavy rainfall. With the longwave trough axis pivoting through the
area overnight...expect some showers to linger overnight as the low
slowly lifts NE out of the area.
Additionally...a secondary trailing cold front/trough will drift
southward into middle Michigan which may need to be watched for potential
shower activity. More likely the trough will not ignite showers
until next round of diurnal instability building on Wednesday. High
pressure will be building in from the northwest behind the exiting trough
so precipitation should wane Wednesday into the overnight accordingly.
Baggy longwave upper trough in place Thursday into the weekend.
Aside from Thursday which has had the best signal for
subsidence...cannot rule out precipitation through the weekend...but until
a more coherent forcing signal is depicted with any sort of
continuity will keep the forecast dry. Warming trend for the weekend
into early next week as models hinting at upper flow reorganizing
into more of a zonal configuration.
Fairly light winds will persist across the central Great Lakes for
the better part of the upcoming weak. A low pressure system tracking
through up through Lake Erie this evening will produce locally
higher winds over Western Lake Erie into the overnight. A Small
Craft Advisory continues for the Michigan waters of Lake Erie for
increased wind gusts. Winds will weaken late tonight as the low
lifts into Ontario. An upper level disturbance will then drop into
region on Tuesday which will result in low pressure returning over
the central Great Lakes.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).