Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
337 PM EDT Tuesday Aug 4 2015
Short term...this evening and tonight
The strong upper level low over Hudson Bay has sent another surface
trough/cold front south through the Great Lakes today...very similar
to that which we experienced yesterday. The front is currently
draped across middle Michigan and will be dropping through Southeast Michigan early
tonight while further weakening. Just ahead of the front we were
able to generate a few hundred j/kg of cape as temperatures once again made
it into the upper 70s. Dewpoints only in the middle 50s...vs middle 60s
yesterday...are limiting the instability thus the coverage of
showers today. Additional middle level dry air across the southern half
of the area has kept all shower activity north of ptk. With the loss
of daytime heating...convection will end quickly this evening and
skies will clear out for the overnight. The clearing skies and dry
northerly flow will set US up for another night of effective
radiative cooling with temperatures falling to into the low 50s north of
M59 and middle 50s south of M59.
As strong upper low over eastern Canada pulls off to the east and
northeast...expect dry weather into during the Wednesday/Thursday
time frame. Surface high pressure will settle over the region by
Wednesday and hold into Thursday as low pressure emerging from the
Central Plains is shunted southeast around confluence northwest
upper level flow on the back side of mean upper trough axis over
eastern Canada/northeast Continental U.S..
With a dry and cool to mild airmass in place with this area of high
pressure...expect maximum temperatures to range...on average...in
the middle 70s both days and lows to fall into the 50s to around
60...some 3 to 5 degrees below average for early August.
Friday through Tuesday.
Model agreement continues to struggle for the long range in terms of
timing and low intensity. Suffice to say a series of upper level
disturbances will keep at least some chances for showers in the
forecast through early next week. Temperature trend still aiming
below average through the period.
Northwest flow will develop in the wake of a passing cold front.
Wind gusts may approach 25 knots over the open waters of Lake Huron
at times as this cooler air pushes southeast. While waves will
increase over the nearshore waters...the northwest trajectory should
limit waves enough to preclude small craft advisories. Winds will
slowly decrease on Wednesday as a high pressure system approaches
with a light and variable wind field expected Thursday into
Friday as this high settles over the region.
Aviation...issued 124 PM EDT Tuesday Aug 4 2015
An agitated cumulus field is developing ahead of the next weak frontal
boundary currently dropping through central Michigan. VFR conditions
should prevail through much of the forecast with high based ceilings
staying up around 5-6kft. Some isolated shower/thunderstorm activity
will pass through the area during peak heating this afternoon but
mainly only affect fnt and mbs...possibly brushing ptk. Westerly
flow will remain elevated this afternoon with gusts to 20 knots.
Winds will relax tonight while becoming northwest under clearing
For dtw...daytime heating...coupled with a weak frontal boundary
swinging south through lower Michigan...is expected to result an
enhanced cumulus field but ceilings should remain VFR...generally above
5000 feet. Shower/thunderstorms activity is expected to remain north
of the Airport.
//Dtw threshold probabilities...
* low for ceilings below 5000 feet above ground level this afternoon.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
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