Forecast thoughts - through Tonight

Se 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/mi border, the elevated portion of the frontal slope and
an associated theta-e gradient nosing northeast into se 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.

.

Remaining Forecast discussion -

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 mcs to develop and survive the trip
into the hostile environment this far east, as overall mean moisture/pw 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 temps
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 pts mid/upper 60s ) will also
help temper the rise in temperatures, along with the possible morning fog/low cloud burnoff process.
Overall, inherited temps look reasonable, and made few if any changes.

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 pops are highest for
Wednesday, but may need to be adjusted higher for both Tuesday and Thursday, depending on
timing/magnitude adjustments. 850 mb dew pts in excess of 15 C and possible training of storms will
support a heavy rain threat.

. . posted at 332 PM EDT Friday August 22 2014


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