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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
720 PM EDT Friday Jul 3 2015


Surface high pressure centered over lower Michigan will maintain VFR
conditions tonight and will be strong enough to absorb a weak cold
front moving through northern lower Michigan Saturday. The front is
expected to settle into the mbs area during the Saturday afternoon
where VFR ceiling around 5000 feet is expected...and an isolated
shower is possible...before the front dissipates by Saturday
evening. Just scattered cumulus and light southwest wind is
expected farther south through the dtw area.

//Dtw threshold probabilities...

* none.


Previous discussion...issued 342 PM EDT Friday Jul 3 2015

Short term...tonight

Split northwest flow persists across the Great Lakes through
tonight. Yesterday's upstream shear maximum is undergoing amplification
as it pivots through the Ohio Valley this afternoon and tonight,
shedding stray cirrus into Southeast Michigan as it does so. Weak shortwave
over central Ontario will drive increasingly cyclonic flow aloft
through tonight, but with little consequence as the atmosphere over
Southeast Michigan remains very dry and advections weak. At the
surface, upstream high pressure centered over the middle MS valley will
still manage to nose into the lower peninsula tonight with some help
from the lake aggregate, but lack of support aloft will still lead
to a fairly non-descript pressure pattern locally. Mostly clear
skies and a light gradient, especially south of I-69, will favor
another good radiating night, though the developing weak gradient
may lead to light mixing toward morning north of I-69. Will favor
12z met/mav blend once again with lows in the 50s...upper 40s in the
coldest spots.

Long term...Saturday through Thursday

High pressure will continue to dominate the area through the Holiday
weekend leading to dry and warm conditions. The Fly in the ointment
will be a shortwave tracking from Ontario to Quebec on Saturday
which will drop a weakening midlevel trough axis through the area in
the afternoon hours. The surface front will be nearly non-existent by
the time it reaches middle Michigan but the suite of hires models continue to
advertise a thermal trough developing over northern lower in the
afternoon which will then feed off the strong ll lapse rates and
diurnal instability to develop some isolated showers and possibly
thunderstorm. Models are all over the place in terms of instability
ranging from less than 100 j/kg MLCAPE to over 1500...but the high
end values are the result of the typical model biases of the GFS/NAM
to exaggerate ll moisture fields so will disregard them. Also
working against precipitation over the area will be the rapidly building
heights over southern Michigan with the longwave ridge moving into the
region. All in all think the current isolated probability of precipitation across the
Saginaw Valley will be warranted to cover the potential developing
between about 20-00z Saturday afternoon/evening.

Temperatures will become pretty mild Saturday compared to what we
have been experiencing of late. Ridging aloft with decent mixing
depths to around 5kft and clear skies should allow most places to
hit the 80 degree mark once again. Additional heating will come on
Sunday as the surface ridge sets up further east allowing for some
southeasterly return flow adding more of an advective component to
the temperatures. This could result in temperatures reaching into the middle 80s for
many locations.

Monday night/early Tuesday morning...a cold front begins its descent
into Southeast Michigan with chances of showers and thunderstorms
developing. By Tuesday afternoon chances are pushed into the likely
category with all of Southeast Michigan under the influence to
front. At this time the severe weather potential does not look
overly impressive...though it cannot be completely dismissed. There
is enough increase in cape over the southern most counties of the
County Warning Area combined with some forcing to perhaps generate a threat. Bares
watching. Temperature drop behind the front is marginal and brief. High
temperatures Wednesday predominately in the middle 70s and overnight lows
around 60. Remainder of the period carries weak chances of showers
and thunder storms.



High pressure will lead to favorable marine conditions across the
Great Lakes this weekend although a weakening cold front is forecast
to slide south through the region on Saturday. This system should
have minimal impacts on the marine areas. High pressure will then
build back into the region for the rest of the weekend and into next
week. The next significant weather system forecast to impact the
region will be a cold front Monday night into Tuesday. This will
provide the next good chance for shower/thunderstorm development.


DTX watches/warnings/advisories...

Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.



short term...jvc
long term....drk

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