Welcome to the first day of meteorological fall. The fall equinox begins September 22nd. We have an equinox twice a year – spring and fall – when the tilt of the Earth’s axis and Earth’s orbit around the sun combine in such a way that the axis is inclined neither away from nor toward the sun. A solstice is either of the two times in the year, the summer solstice and the winter solstice, when the sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days.
Meteorologists and climatologists break the seasons down into groupings of three months based on the annual temperature cycle as well as our calendar. We generally think of winter as the coldest time of the year and summer as the warmest time of the year, with spring and fall being the transition seasons, and that is what the meteorological seasons are based on. Meteorological spring includes March, April, and May; meteorological summer includes June, July, and August; meteorological fall includes September, October, and November; and meteorological winter includes December, January, and February.
As far as the Labor day forecast goes here are the NAM forecast graphics through Monday afternoon.
A large Canadian Polar high pressure system is moving over Michigan today and will be east of this area by Saturday. That surface high will effectively block the remnants of Harvey from reaching this area. Being on the west side of the departing high and north of the remnants of Harvey on Saturday will mean more clouds but no rain.
Patchy frost is expected north and east of Big Rapids Saturday morning. Another Canadian Cold Front will bring the risk of showers and thunderstorms on Labor Day. The southerly flow ahead of the cold front will bring a surge of warm air allowing highs to reach the lower to mid 80s. Behind the front expect much cooler weather for mid week.
HRRR and Futurecast models runs are for 12 hours beginning at 7am – a second model run begins at 3pm
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We have little in the way of impact weather to concern ourselves with through Sunday. I do however expect patchy frost north and east of Big Rapids Saturday morning as the coldest air will be in our area then. The large Canadian high in combination with the polar jet being north and east of this area will help to keep the remnants of Harvey south of the GRR CWA tonight into Saturday.
All we will get will be the high and mid clouds from the system. On Sunday a weak frontal system comes through the area but there is not enough moisture to get much precipitation from it so I keep the forecast dry for the most part. I do have some low chance POP for early Sunday morning but do not expect much in the way of significant rainfall from this. Sunday during the day time should be partly cloudy with highs in the mid to upper 70s. .
A fairly strong cold front will move south across Lower Michigan Monday afternoon. There are a few ingredients that may come together to produce strong to severe storms. It`s a narrow window time-wise, but the potential is there.
The cold front is progd to be near central Lower Michigan by 2pm Monday, which is around peak heating. Li`s near -5c, coupled with shear values near 35 knots and a LLJ around 45 knots could result in some organization Monday afternoon over the southern cwa. The best chance for severe storms seems to be south of a Lansing to South Haven line between 2pm-6pm. It`s in that area that MUCAPE spikes to around 2k j/kg around 5pm. We`ll certainly keep an eye on the situation as it unfolds.
Monday will be the warmest day with highs in the lower to mid 80s. After the cold front moves through, temperatures will fall into the mid 60s by Wednesday. Lows in the 40s are expected Tuesday night and Wednesday night and there appears to be a frost potential over the northern cwa Wednesday night.