This is a topic I thought I would revisit as it has been so prevalent this winter.
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.
High and low pressure indicated by lines of equal pressure called isobars.
Although we cannot actually see the air moving we can measure its motion by the force that it applies to 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.
Pressure gradient force extends from high pressure to low pressure.
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 maybe 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.
How the Coriolis force works on a rotating disk.
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.
How the Corilois force works on the earth.
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.
Airflow around highs and 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.
Check this out from the NWS!
This more amplified pattern looks to be an active one by midweek as
new southern Plains short wave trough/ closed low gets kicked
northeast during midweek…with the potential for a significant
system impacting the Great Lakes. This expected to be followed by a
dump of colder air during the latter half of the week. Will
consider starting to message the midweek system for the potential
for accumulating synoptic snow followed by lake effect snow
showers…through 20/12z
Lol!! Grasping at straws….
Don’t buy the cold weather fake news and collusion, anyone can see that there is only a very short few day cool down next week before we go right back above normal! The real facts will show that February will be just another in a long line of above normal temp months! And the snow deficit will just keep going and going!! BRING ON SPRING!!
https://weather.com/weather/tenday/l/7f39432f98eef2d300f773cf914253d5f248e7131cb69cb63b087ebda662f574
Does anyone know what March will bring?? Asking for a friend 😂😂😂😂😂 sorry I had to, this is funny!!!
March will end up slightly below normal for temps and we will see at least 2 snow storms! To soon for accumulation estimates!
The March and 3 month outlooks look fantastic too!! With normal temps in the 40’s looking at a lot of great spring weather coming soon!!! It’s like winter was never here this year!
The snow maps are trending the right direction! Who would have thought?
https://www.instantweathermaps.com/GFS-php/conussfc.php?run=2020022018&time=PER&var=ASNOWI&hour=324
The snow depth change looks amazing over that same period!! Bring It!!
https://www.instantweathermaps.com/GFS-php/conussfc.php?run=2020022018&time=PER&var=SNODICHANGE&hour=324
Currently 21* degrees out at thee YARDOFBRICKS Plainfield township it’s been a cold one that’s for sure looking more stormy again next week acoss the great lks get ready more snow and cold coming …INDY
It has been a very cold week and next week surely looks cold and snowy, just as we have been predicting for the last week or so! Stay tuned for the latest snow map!
I still have a solid 3 to 4 inches of snow on the ground! Great winter day!
I love this time of year. Even if the temperature is below freezing, the sun is warm enough to melt snow.
Yup, the bare spots on the ground grow bigger every day from the sun warming the ground and melting of the tiny snow pack. Put the snow blower back in the barn today, used it 2 whole times, and 1 was just to get it running for a while.
I am heading up to snow country for another weekend of perfect Winter sports conditions! I have been skiing since the beginning of November! I love these long winters!
It is great to see the CPC is now on board with my prediction of below normal temps for the end of this month right into March! Who would have thought? The warm weather fanatics were wrong again! Some things never change!
LOL you’ve been saying February would be cold for weeks and have been dead wrong.
That’s great news Rocky becouse mokkee says the CPC is spot on wow! ….Lots of cold air to the north ….Im seeing accumulating snow now on February 27th Who Knew …..INDY
There are indications that March could start colder then average but that is now unheard of and can almost be expected. As for snow fall that is something that may or may not happen. We can and have had snow fall into April. As for February while it could end up above average temperature wise and at this time it is too close to call for the snow fall. One thing that can be said is that February should be the coldest month of the winter of 2019/20 unless March is much below average. And this winter season should end… Read more »
I guarantee you that in GR February will end up with above normal snowfall! Take it to the bank and it is not a close call at all!
Great points and I am to the point I am not even reading mookies and Barry’s comments anymore! The warm weather hype and not facing reality is off he charts! Bring on the snow!
Once the wind starting to blow the snows Inland from Zland is about the time I gave up on berry’s post that about said it all for me!! Mookie’s post don’t bother me I get a good laugh sometimes almost like the fire that keeps on burning …..I’m sure they both love our post also no hard feelings lol….INDY
Rock on Indy!
Currently 18* degrees out at thee YARDOFBRICKS NE of GR lol we still have to put our location on here because of some still don’t understand love it …..BIG question today will we break 25* degrees?? stay warm INDY
Maybe because it’s a weather blog and people like to know what’s going on in certain areas around them? NE of GR could be anywhere from Plainfield to Bay City.
I agree that ever one should have their location known. Most of the ones that post on here live west of East Lansing. Of course with today’s fast internet one can live anywhere and make believe they live somewhere else.
Slim
Quite a cold stretch and more to come next week!
Wow close to 50 Sunday now and sunny! I love it!
Good read MV. Never hurts to have a refresher course!
https://www.mlive.com/weather/2020/02/see-michigan-snow-totals-so-far-grand-rapids-kalamazoo-getting-far-behind.html
Nice maps. You can really see the impact from no lake snow.
IMO the snow fall totals this winter are even worse then that map. Muskegon is now -27.2″ below average for the season. Grand Rapids is now -14.0″ I Lansing is almost average at -0.6″ On the east side of the state Detroit is now -7.4″ for the met winter. Up north the only locations with above average snow fall are the Sault and West Branch and Marquette in the UP.
Slim
It amazing that we are so close to average here. We’ve never had more than just a couple of inches on the ground at any given time and I’ve only shoveled three times.
Great news – all signs point towards a major cold front next week with plenty of snow chances! Rock n roll will never die!
It’s been a great winter. 60s in December, 40s in January, and 50s in February.
Yup, first Winter ever we’ve been out disc golfing in all three months. And so few times clearing the driveway you can count them on one hand. Perfect!
10 degrees this morning out at thee YARDOFBRICKS NE of GR we are talking January cold now in mid February I hope Slim coverd then flowers that where poking through or he maybe flowerlrss this spring…..Have a warm Thursday ….INDY
You know it, we are in quite a cold snap as we speak! Incredible!
Interesting… So what causes these Highs and Lows to form in the first place? Also, most surface analysis maps have several of each (forcasters talk about “double barrel Lows, for example, that are quite close together). This is confusing to me, and when these maps are put into motion, it gets even more confusing.