Trowal or Occlusion?

[y2kunals]

What's the difference between a Trowal and an Occlusion? They both happen when the cold air catches up to the warm air don't they? I'm confused!

[YYZatcboy]

Just looked it up for you in the Air Command Weather Manual. From what I can tell, The difference is the strength of the low. When the low is at its maximum intensity it is an Occluded Front, and as the fronts collide more it becomes a TROWAL, as the cold air under cuts the warm front and forces it aloft.

[y2kunals]

Thanks, I just looked it up in there too, and it's so unclear really. Doesn't that still end up being the same thing, with just different names for when it happens? Seems a little gray!

Thanks for your help, Sir!

[YYZatcboy]

Yeah it is a bit gray.

I think it's mostly just the way people mark them. In Canada we use the TROWAL, and in other countries they mark the Occluded Front.

[y2kunals]

Thanks for your help again!

[Dagwood]

TROWAL = TRough Of Warm Air aLoft

As YYZatcboy said, Trowal is a Canadian term. It is shown on weather maps by red and blue hockey sticks

[y2kunals]

[loopa]

I was always under the assumption that the TROWAL was formed as a result of the OCCLUSION that occurs with the cold and warm fronts. Occlusion meaning that the cold front is running faster and catching up to the warm front, hence producing the TROWAL. If you look at it that way OCCLUSION is the process of one front catching up to another, while the TROWAL is the resultant of the OCCLUDING process.


Hope that helps!

[trampbike]

Loopa is right.

A trowal can also happen without an occlusion, like in the case of cold air trapped down in a valley and warm air overrunning it. The frontal surface in that case is horizontal.

[loopa]

And don't quote me on this, but I think the reason it's called a TROUGH of warm air aloft also has to do with the fact that the warm air that rises is foced up, exposed to a lower pressure than the low, and with it being warm air, sitting in the air, it's called trough of warm air aloft, or TROWAL.

Unless there's another explanation that I should know?

[dab81]

v. oc·clud·ed, oc·clud·ing, oc·cludes
v.tr.
1. To cause to become closed; obstruct: occlude an artery.
2. To prevent the passage of: occlude light; occlude the flow of blood.
3. Chemistry To absorb or adsorb and retain (a substance).
4. Meteorology To force (air) upward from the earth's surface, as when a cold front overtakes and undercuts a warm front.
5. Dentistry To bring together (the upper and lower teeth) in proper alignment for chewing.
v.intr. Dentistry
To close so that the cusps fit together. Used of the teeth of the upper and lower jaws.

[Lost Lake]

Hey dab81, it now makes perfect sense. Every time my teeth hurt, it's an occluded trowal.

[Ollie]

A TROWAL and an Occulded front are essentially the same thing. The major difference is where they are drawn on a weather map. An occulded front is drawn where the cold and cool air masses meet at the surface, whereas the TROWAL is drawn where the cold, cool and warm air meet somewhere aloft. This is where the precipitation occurs, and is also where the TROWAL is drawn. The occulded front is either drawn in front or behind the precipitation, depending on whether the system is a warm or cold occulsion.
Yes the rain is green

[Mclovin]

Ollie whats the black U weather forecast?

[Ollie]

It's Gonna Rain!!!

http://www.youtube.com/watch?v=pUuZHZPG ... re=related
Someone took the second half of this video a little too far.

[YYZatcboy]

That remix was fantastic

[Ref Plus 10]

It's essentially it's a Canadian American thing. Everyone is right, a TROWAL results from fronts occluding, it's just that in Canada, it becomes a trowal, in the States, it becomes an occluded front...either way,

IT'S GONNA RAIN!

edited:
trampbike: the situation you describe would then become an Upper Front, as the front is now entirely lifted off the ground over the valley, but no "trough" is created.

[trampbike]

You are right, my bad. In french the distinctions are not the exactly the same, so it looks like I got confused.

[Alam412]

HI FOLKS,
FRANKLY TELLING YOU ALL THE BOOKS DO NO COVER MUCH DETAILS TO SATISFY THE REQUIREMENT OF ATPL AND YOU NEED TO DO YOUR OWN RESEARCH WORK.
SO FAR SO GOOD THERE IS NO NEED TO WASTE LOTS OF YOUR PRECIOUS TIME IN SEARCHING OUT OF THESE BOOKS WHICH WE BUY FOR HIGH COST AND CAN EASILY GET THE DETAILED NOTES FROM A LITTLE GOOGLE WORK AND WE CAN FIND THE GOOD STUFF ON LINE.
TODAY WAS THE BAD DAY AS I, DESPITE BEING MY OWN WORK UNDER ESTIMATED THE . QUESTION PAPER BUT ALL WAS WASTE IN THE COURSE.
IF YOU ARE GOING FOR ATPL MUST STUDY IN DETAIL.
TROWAL AND FRONTS IN DETAIL.
LAST MINOR DETAILS FROM LIKE REMARKS OF METAR AND PIREP DECODING.
MUST PRACTICE DECODING IN OTW FOR UPPER CHARTS AND CNC
READ IN DETAIL ABOUT THE RMI AND NDB RELATION
SO FAR SO FOR THE NORTH AMERICA AND CANADA MAP MAKE SURE YOU KNOW GENERAL AREA OF THE IMPORTANT CITIES SURELY YOU WILL REPENT LATER IF YOU MISS IT.

BEST OF LUCK TO ALL