We have a balmy 47° at 5am this morning which will more than likely be our high for today. Yesterday we reached a pleasant 61° which we may be hard pressed to reach again this year. Today I continue with another lesson in synoptic meteorology:
Origin of Wind
Wind is simply air in motion. Usually in meteorology, when we are talking about the wind it is the horizontal speed and direction we are concerned about. For example, if you hear a report of a west wind at 15 mph (24 km/h) that means the horizontal winds will be coming FROM the west at that speed.
Although we cannot actually see the air moving we can measure its motion by the force that it applies on objects. We use a wind vane to indicate the wind’s direction and an anemometer to measure the wind’s speed. But even without those instruments we can determine the direction.
For example, a flag points in the opposite direction of the wind. The wind blows leaves opposite the direction from which the wind is blowing. Airplanes taking off and landing at airports will be into the direction of the wind.
The vertical direction of wind motion is typically very small (except in thunderstorm updrafts) compared to the horizontal component, but is very important for determining the day to day weather. Rising air will cool, often to saturation, and can lead to clouds and precipitation. Sinking air warms causing evaporation of clouds and thus fair weather.
You have probably seen weather maps marked with H’s and L’s which indicate high- and low-pressure centers. Usually surrounding these “highs” and “lows” are lines called isobars. “Iso” means “equal” and a “bar” is a unit of pressure so an isobar means “equal pressure”. So everywhere along each line is the pressure has the same value.
With high-pressure systems, the value of air pressure along each isobar increases toward the center with each concentric line. The opposite is true for low-pressure systems in that with each concentric line toward the center represents lower pressure. Isobars may be close together or far apart.
The closer the isobars are drawn together the quicker the air pressure changes. This change in air pressure is called the “pressure gradient”. Pressure gradient is just the difference in pressure between high- and low-pressure areas.
The speed of the wind is directly proportional to the pressure gradient meaning that as the change in pressure increases (i.e. pressure gradient increases) the speed of the wind also increases at that location.
Also, notice that the wind direction (yellow arrows) is clockwise around the high-pressure system and counter-clockwise around the low-pressure system. In addition, the direction of the wind is across the isobars slightly, away from the center of the high-pressure system and toward the center of the low-pressure system.
Why does this happen? To understand we need to examine the forces that govern the wind. There are three forces that cause the wind to move as it does. All three forces work together at the same time.
The pressure gradient force (Pgf) is a force that tries to equalize pressure differences. This is the force that causes high pressure to push air toward low pressure. Thus, air would flow from high to low pressure if the pressure gradient force was the only force acting on it.
However, because of the earth’s rotation, there is second force, the Coriolis force that affects the direction of wind flow. Named after Gustav-Gaspard Coriolis, the French scientist who described it mathematically in 1835, this force is what causes objects in the northern hemisphere to turn to the right and objects in the southern hemisphere to turn to the left.
One way to see this force in action is to see what happens when a straight line becomes a curve. Picture the Earth as a turntable (see number 1) spinning counter-clockwise. A ruler is placed over the turntable (see number 2) and a pencil will move in a straight line from the center to the edge while the turntable spins underneath. The result is a curved line on the turntable (see number 3).
When viewed from space, wind travels in a straight line. However, when viewed from the Earth, air (as well as other things in flight such as planes and birds) is deflected to the right in the northern hemisphere (red arrow on image at right). The combination of the two forces would cause the wind to blow parallel to straight isobars with high pressure on the right.
So why does air spiral out from highs and into lows? There is one other force, called friction, which is the final component to determining the flow of wind. The surface of the earth is rough and it not only slows the wind down but it also causes the diverging winds from highs and converging winds near lows.
What happens to the converging winds near a low? A property called mass continuity states that mass cannot be created or destroyed in a given area. So air cannot “pile up” at a given spot.
It has to go somewhere so it is forced to rise. As it rises it cools. When air cools, condensation begins to exceed evaporation so the invisible vapor condenses, forming clouds and then precipitation. That is why there is often inclement weather near low-pressure areas.
What about the diverging air near a high? As the air spreads away from the high, air from above must sink to replace it. Sinking air warms. As air warms, evaporation begins to exceed condensation which means that clouds will tend to evaporate. That is why fair weather is often associated with high pressure.
Bring it!
https://forecast.weather.gov/glossary.php?word=trough
8 of the last 10 months in GR we have seen below normal temps! We are entrenched in a below normal temp pattern and heading into winter there is no change in sight! We could be looking at a brutally cold and snowy Winter! Get prepared now! Mark it down!
Who would have thought?
http://wxcaster.com/gis-gfs-snow-overlays2.php?STATIONID=GRR
Winter Weather Advisory’s close to us as central Illinois and further west with Winter storm watches now here it comes ….The Euro MODEL gives GR 5 inch’s iof snow on Halloween Thursday and 7 to 10 inches of snow just to our north great Scotty like I said last week records maybe broke on Halloween stay tuned …INDY…
Bring it!
It will be interesting if we have a Winter weather advisory on Halloween probably the first time ever good chance of it especially Friday we have a big storm coming starting out as yes more rain tomorrow changing to snow Thursday and snow Friday the GFS and Euro MODELS are both in agreement more and more blue on the map everyday this week following by some good lk effect snows Sunday Rocky Slim MV thoughts ? INDY ..
I think you have been on the money by giving us a heads up on snow and cold for Halloween and beyond. It looks like by Thursday evening the roads may get slippery so a wwa is certainly possible! Keep up the good work! Rock n roll will never die!
Thanks.. Yes rock n roll will never die..INDY
Last week it was mentioned that every day for the rest of October would be below normal temp wise. Yet the past couple days have either been above normal or exactly even.
Facts! October will be the 8th below normal month this year! What an incredible cool stretch we are in!
Wasn’t talking about that. As for incredible stretch, why don’t you give us the monthly stats on the past 5 years?
The trees here on Michigan State’s campus are still all full of leaves, with a few trees still mostly green. I would have to imagine that this is not only due to warm temperatures, but also due to the rainy year we have been experiencing. There has also not yet been a hard freeze. The week ahead looks chilly, but none of the low-temperatures look awfully cold.
Most years our Halloween pumpkins that we set out will turn to mush after a hard freeze, but not this year. Looks like we’ will be well past Halloween before our first hard freeze.
Currently 40* degrees out at thee YARDofBRICKS NE of GR im thinking that’s about 15 degrees below normal right now cold I have the hoodie and winter hat on love it. INDY
Near peak color now in our area, less as you head towards Holland. Still some green trees around, but the oaks have just started to yellow a bit in the last day or two. Still waiting for our first hard freeze, lowest temp so far is 31. Could be well into November before it happens.
So yesterday in Montana the coldest temperature ever recorded for October in the United States -37* degrees that’s cold that’s a shivering snowman ….That air is moving east ….INDY
A lot of good reading the past two days MV! I expect a trivia quiz Friday on everything you post this week?
At this time, it looks like October will end up being colder than average this year. Now as for any snow we will see in the next 3 days (October) or for that matter the whole month of November that will not tell us if the winter as a whole will be cold and snow or not. There have been years with a lot of cold and snow in November and very little after that. And the same can be said for October. Any way that said here are some of the snowiest Octobers of recorded history at Grand Rapids
1. 1967 8.4”
2. 1925 7.5”
3. 1989 5.8”
4. 1917 3.0”
5. 1962 2.6”
6. 1997 2.6”
7. 1992 2.4”
8. 2006 2.1”
I would go back and see how each winter’s total snow fall was but as I have said my go to site is still down’
Slim
That was true just last year. We had a little October snow last year, but November was cool with above average snow (which it looks like this November is shaping up to be the same way), and then what happened once we hit December? Almost nothing for snow for over a month and a half, the time when we average the most snow.
What 8 out of the last 10 months now below normal amazing numbers let’s keep it going into November December January February March April and May ….Thanks Slim your a great stats MODEL lol…INDY
Good morning. Here at my house I recorded 0.05” of rain and the temperature here in now at 40°. Yesterday the official H/L at Grand Rapids was 59/38 here at my house it was a little cooler with a high of 56. For today the average H/L is 55/38. The record high is 77 way back in 1901 and the record low is 20 set in 1969. Last year the H/L was 54/36.
Slim
Thanks for all the good information MV
Slim
6 to 10 day out look Blue 11 to 15 day Outlook Blue for a big area all of Michigan “GFS MODLE” a below average November?? stay tuned….INDY
The latest gfs model.
https://www.instantweathermaps.com/GFS-php/conussfc.php?run=2019102906&time=PER&var=ASNOWI&hour=336
What is so Interesting about that MODEL look at all the snow just to our north building.. Which could give us a cold snowy Winter around here early.. Sorry for the caps on the MODEL word but some get confused on our post lol …..INDY
Yes the snowpack to our north is building fast! This could be a wild winter this year and yes if you post a model the warm weather fanatics assume that this is your forecast! Incredible and ridiculous!
+1000….INDY