Do temperature swings on cold fronts affect the severity of the storms ahead of it?

[Ivan Reid]

Like when you have a strong cold front come through. Does the big temperature swing on the front affect the severity of the storms ahead of the front?

 

[rdale]

No, the dynamics of a system strong enough to bring dramatic temps can be an increase but it's more than just "warm temp minus cold temp = storm strength."

 

[Dan Robinson]

A colder air mass behind a front will more quickly undercut storms that fire on it, so at least in that sense, the tornado risk is usually less with "colder" cold front. As far as storm/updraft strength, there is no real correlation between low-level temperature contrasts and updraft strength. The temperature contrast that matters is what is above the warm side of the front (lapse rates).

 

[Ethan Lang]

One thing to remember also is that as you go up in the vertical your fronts are not completely vertical. For example the cold front will not be in the same place at 850mb than it is at the surface etc. So you will want to look at the way the front is oriented in the vertical.

 

[Jeff House]

I actually prefer less temp contrast for tornado chasing. In the Plains, that's why we prefer the dry line over a cold front. Keep in mind intersecting boundaries is best. Ex. Dry line with outflow OFB or warm front WF.

Down in Dixie dry lines are less common, but a pre-frontal trough is sometimes present. Again, look for intersection with OFB/WF. Sunday was an example. Tennessee was very cold. However the core of cold had not plunged into southeastern Alabama at the time of the tornadoes. Prefrontal trough intersection with Georgia warm front was a focus of tornado activity.

As we discuss the science of it, of course our thoughts are with the victims of those tornadoes.

 

[Marshall Stoner]

The whole "warm air clashing with cold air causes severe weather" is a popular misnomer spread by non-meteorologists. It's not completely false so much as a half-truth. What you really need for severe thunderstorms a combination of strong wind shear (winds increasing with height) and moist instability (temperatures decreasing quickly with height + surface humidity). The former is roughly correlated with the "temperature clash" claim, but in the case of tornado outbreaks it's only a weak correlation. The strong jet responsible for wind shear can be displaced from any surface front, and it usually becomes especially decoupled from surface temperature features as it crosses the high terrain of the western US and emerges over the plains. The latter has very little correlation to surface front strength, as the vertical gradient is much more important than the horizontal gradient.

 

[Lawrence Burkett]

Like when you have a strong cold front come through. Does the big temperature swing on the front affect the severity of the storms ahead of the front?

Sharp temperature difference at the surface across a front generate high wind at altitude in the vicinity of the front. Hence, a front that separate two airmasses with markedly different temperatures will force a more favorably sheared environment for severe thunderstorm activity than a front that separate two airmasses with nearly the same temperature.

 

[Marshall Stoner]

Sharp temperature difference at the surface across a front generate high wind at altitude in the vicinity of the front. Hence, a front that separate two airmasses with markedly different temperatures will force a more favorably sheared environment for severe thunderstorm activity than a front that separate two airmasses with nearly the same temperature.

Yea. The thermal wind balance equation will support a vertical wind shear vector that points in a direction such that the cold air is on the left (warm air on the right). The thing with thermal wind though is you have to integrate through the entire depth of the troposphere. A frontal zone aloft can just as easily generate wind shear as a surface front.

Also, while the atmosphere tends to move towards geostrophic balance (wind is sheared with warm air to the right of the shear vector), it is usually somewhat out of balance (i.e. winds have an ageostrophic component). While the a strong upper-jet will usually develop over a zone of strong horizontal temperature gradient (baroclinic zone), the jet can move under it's own momentum such that at a later time it is no longer correlated with a surface front. This happens often over the Rocky Mountains. The surface cold front will not pass over the high terrain, but the associated strong mid-upper level winds will. This is helpful for severe weather because the jet will often emerge off the mountains directly over the warm sector.

When winds are in geostrophic balance, the core of the wind shear is over the baroclinic zone which is almost always north of the warm sector. This is unfavorable for severe weather because the zone of favorable shear is north of the front in an area with little or no surface instability. To have a setup favorable for severe weather, you need an upper level patter that is not in geostrophic balance. The Rocky Mountains in the western US are very good at disrupting geostrophic balance by disrupting low level winds as described before. This is especially true when a strong upper trough crosses from the Pacific Ocean.