11

The old adage "The calm before the storm" certainly has an observational scientific meaning to it -- something that many (including myself) have experienced -- that on a hot summer's day, when a change in the weather starts rolling in, humidity rises, but it becomes very calm with little to no wind, before the storm begins.

(This of course is not the only phenomenon associated with a change in weather).

What confluence of meteorological factors results in the 'calm before the storm'?

aparente001
  • 103
  • 3
  • 4
    I like simple questions like this, they have the potential to attract a larger membership, including kids & getting kids involved in Earth Science, or science in general is a good thing. Also, there is the potential for such questions to generate canonical answers (SE style) – Fred Mar 27 '15 at 09:08
  • 1
    But this is not always true. There are situations where we get a lot of blustery wind before a storm. –  Mar 27 '15 at 10:03
  • @gansub, yes, that is true, however, I am asking about the meteorological factors that cause this particular phenomena. –  Mar 27 '15 at 12:37
  • Isn't it obvious that there's going to be a calm before the storm? If it wasn't calm, then it would be a storm already. Calm is the opposite of storm. It's like asking why is dark before the light. Because otherwise it wouldn't be dark. You see my point? :) – Gimelist Mar 28 '15 at 04:55
  • @Michael yes, but as gansub points out, it is not always this way - also, I am asking about the meteorological mechanisms behind this calm –  Mar 28 '15 at 05:03
  • I believe the 'calm before the storm' is a period when winds actually die down from previous levels before the storm hits. I certainly have observed this happening. – haresfur Jul 16 '18 at 05:19

1 Answers1

8

Quoting from Is there really a "calm before the storm"? at howstuffworks.com this sometimes happens ("Other storms skip the calm and proudly announce their presence by instantly unleashing bad weather").

As warm, moist air is pulled into a storm system, it leaves a low-pressure vacuum in its wake. The air travels up through the storm cloud and helps to fuel it. The updrafts in the storm, however, quickly carry the air upward, and when it reaches the top of the cloud mass, this warm moist air gets spit out at the top. This air is sent rolling out over the big, anvil-shaped head of the thunderclouds or the roiling arms of hurricanes. From there, the air descends -- drawn back toward lower altitudes by the very vacuum its departure created in the first place.

That descending air becomes warmer and drier which is relatively stable, and once it blankets a region, it stabilizes that air in turn. This causes the calm before a storm.

Follow the link so see a more extended explanation with graphics.

hichris123
  • 1,920
  • 2
  • 23
  • 38
Jan Doggen
  • 2,679
  • 1
  • 25
  • 39
  • Honestly... this article seems pretty poor, at least to me. And it's result additionally isn't really very applicable to the question. – JeopardyTempest Jul 15 '18 at 20:34
  • Yes it's true that air that's been through storms is made more stable. Warm air at high levels would be a contributor, but believe that's primarily due to the release of heat from water condensation (and as important overall is the transport to low-levels of cold by water). I'd say the sinking itself (caused by high pressure from the extra rising air) rather than the stability is more of what mostly limits nearby clouds and storms. – JeopardyTempest Jul 15 '18 at 20:34
  • The process they (poorly) describe seems to be the inverse of cap erosion, and while I'd think it may have some small factor, wouldn't think it's much... – JeopardyTempest Jul 15 '18 at 20:34
  • But more importantly, if truly "stable air blankets the region ahead of a storm" in lower levels... the storm wouldn't continue in any strong fashion. And more important, the prevention of clouds/the stability of air near a storm doesn't really have anything do with wind speed, which is what I'd consider to be the primary constituent of calm. – JeopardyTempest Jul 15 '18 at 20:34
  • And one of the specifically poor statements among others: "The air descends -- drawn back toward lower altitudes by the very vacuum its departure created in the first place"??? No... it descends because the extra air creates high pressure at that those levels aloft and because it has become more dense than the air around it. If the low pressure at the low levels just sucked all air only its direction, and there were no other factors, we'd be out of air soon enough :-p – JeopardyTempest Jul 15 '18 at 20:35