Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
332 PM EDT Friday Aug 22 2014
Short term...through tonight
Southeast Michigan holding firmly on the immediate downstream portion of
high amplitude ridging that will take a progressive hold locally by
this weekend. This pattern retaining a somewhat diffuse low level
frontal boundary in the vicinity of the in/Michigan border...the elevated
portion of the frontal slope and an associated Theta-E gradient
nosing northeast into southeast lower Michigan. Recent satellite presentation
suggests a gradually destabilizing boundary layer aided by the high
ambient low level moisture will maintain a window for possible lower
end coverage of showers/thunderstorms through the evening hours.
Any storm that develops would be capable of generating intense
rainfall rates given the moisture quality.
Frontal boundary will sink south tonight as high pressure over
Quebec takes a stronger hold. The light east to northeast flow off
the lakes may help augment an already moist near surface
environment...pointing toward a higher likelihood of some degree of
fog and low cloud development through the early morning period.
This will cap lows predominately in the lower and middle
60s...slightly cooler across The Thumb.
An upper level ridge axis centered over the Mississippi River valley
today will continue to amplify/build...with the top of the ridge
spilling over into the Great Lakes region over the weekend...as the
deep upper level low moving through the Pacific northwest slowly
works through The Rockies. With the building heights over lower
Michigan (588+ dam at 500 mb) coupled with the low level
easterly/stable flow emitting from the surface high over southern
Ontario/Quebec...the weekend is shaping up to be warm but dry. It
would take a well organized mesoscale convective system to develop and survive the trip into
the hostile environment this far east...as overall mean moisture/precipitable water
values will actually be declining slightly Saturday/Sunday.
Monday has the potential for being one the warmest days of the
extended period as the ridge axis slides east and deepening
southwest flow develops ahead of approaching cold front...as 850 mb
temperatures warm into the upper teens to around 20 c...supportive of 90
degrees. However...there is subtle upper level wave/pv filament over
the western Gulf coasts which may become captured/absorb within the
burgeoning southwest flow. Also...the low level moisture (surface
dew points middle/upper 60s) will also help temper the rise in
temperatures...along with the possible morning fog/low cloud burnoff
process. Overall...inherited temperatures look reasonable...and made few if
The cold front/frontal boundary looks to be getting caught
up/parallel to mean flow over the southern Great Lakes
Tuesday-Thursday time frame...per 12z Euro. The forecasted probability of precipitation are
highest for Wednesday...but may need to be adjusted higher for both
Tuesday and Thursday...depending on timing/magnitude adjustments.
850 mb dew points in excess of 15 c and possible training of storms
will support a heavy rain threat.
A large high pressure center extending from southern Ontario/Quebec
will expand across the eastern Great Lakes over the weekend. This
will lead to light east-southeast winds across the lakes. Some
slightly gustier (15 knots) northeast winds may occur
within the warmer waters of Saginaw Bay from time to time as the
wind gets funneled into the Bay. Otherwise...winds and waves will
provide favorable boating conditions...right into early next
week...although an increasing chance of showers and thunderstorms
will exist as a cold front makes it way through the area.
Aviation...issued 112 PM EDT Friday Aug 22 2014
Moist low level environment sustained within light east/southeast
flow north of a frontal boundary will remain in place through
tonight. Blossoming region of higher based VFR diurnal cumulus will
remain prevalent through evening hours...diminishing in coverage
with the loss of heating. There remains a very low probability for
thunderstorms in the Detroit corridor...chances still limited enough
to preclude a specific mention. The existing environment will
remain conducive for some degree of low cloud and/or fog development
during the early morning hours. At this time...will continue to
favor a stronger fog/visibility component.
//Dtw threshold threats...
* moderate confidence on ceiling at intermittently below 5000 feet
this afternoon...low confidence tonight.
* Very low confidence in coverage and timing of any thunderstorms
20z-24z late today.
* Low confidence on visibility dropping below a 1/2sm tonight.
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).