Climate Zones & Our Finicky Weather HereJanuary 3rd, 2013 at 9:41 pm by Chad Evans under Chad's WLFI Weather Blog
I have received several questions recently regarding the tendency for the heart of winter storms to go north of south of us this winter. I also had several ask the question, “why does our viewing area miss everything, specifically Lafayette?”
Here are my thoughts on the whole thing………
One, I think it is circumstance that this year we have missed out on the worst of it. However, once you do lay a deep snow pack down, new storm systems often tend to follow a baroclinic zone or area of surface temperature change. This usually is on the edge of a deep snow pack, so the next system after the first will tend to ride that gradient (this happened recently in southern Indiana). So the saying that snow breeds more snow is partially true.
We have been nailed many times by major snow & ice & severe weather, but we will not get that every time of course. It would seem sometimes we totally miss everything every time, but I know since I have been here there have been many times chunks of our area have taken the worst of severe snows, winter storms & severe weather to flooding & history shows us this, too.
In summer dry soil makes more dry weather, while wet soil makes more wet weather, as soil moisture & temps act as feedback mechanisms for storms. So, a same pattern of rainfall or dry weather in the same place will often occur.
Also, the jet stream that guides storms may set up in a similar position due to some sort of blocking downstream or push upstream, leading to the same places getting rough weather & other places missing out.
Now, there is a good reason why sometimes we do miss big storms in summer. The difference in cooling (often between the Rockies & Plains due to changes in humidity & height of the terrain) creates a gradient at 5,000′ of higher wind. Earth’s spin creates Coriolis Force which curves the winds to the right. This is the low-level jet. This wind often picks up moisture & instability & blows up storm clusters at night to our northwest as nocturnal MCSs (Mesoscale Convective Systems or clusters of organized storms with heavy rainfall that are often at peak in the night). These often account for +70% of the summer rainfall in the Plains. These MCSs move east & southeast (often on periphery of heatwaves) & approach us normally at what is called diurnal minimum. This is typically when heating & instability is the least in the given day & as the temp gradient decreases, the low-level jet weakens. So, they often gust out & weaken with approach, then the MCSs outflow boundaries & MCVs (Mesoscale Vortices) blow up new storms in the heating of the afternoon to our south & east. The MCV occurs when there is so much rising are motion with an MCS that the surface pressure drops quite a bit & Earth’s Coriolis creates a spinning meso-low.
Two, tornado alleys & sharp shifts in weather & climate are usually climate zone shifts.
In Indiana, we have several climate zone changes: