"This post was published by Intern Sid Abramson"
We talk a lot about the weather pattern, what causes the pattern changes in addition to what brings us the storms we see in the Ohio Valley. This post is going to briefly highlight some of the weather terms meteorologists often refer to.
This isn't a common front we talk about in our area but for the upcoming week, we will because this is the front that will be moving in beginning Tuesday. An easy way of explaining what an occluded front is would be to say when a cold front overtakes a warm front.
When a low pressure intensifies, the cold front rotates around the storm and will eventually catch up with the warm front. This is when an occluded front forms, separating the newer cold air mass (located to the west) and the older cold air that is already in place.
This graphic below shows the process of an occluded front fairly clear--
The different between an occluded front and any other front is the process of cold air moving in. In most cases when we are dealing with warm and cold air, it is typical to see the classic rain to snow set up. With rain at the onset of the warm front, once cold air moves through-- the transition to a wet snow occurs and at times significant accumulations can occur
With an occluded front-- it is still possible to see a transition to snow but the process takes longer due to the "top/down idea". This idea is because of the slower than usual cooling process which takes place in the upper levels of the atmosphere and eventually working its way down to the surface.
So-- what does an occluded front look like on surface maps?
It is most common to see both warm and cold fronts depticted on a weather map using red lines (warm front) and blue line (cold front) with alternating triangles and cirlces. With an occluded front, the same type of line is used but shown in purple--
Upper Level Low--
An upper level low is a very important term for our area as we focus on these types of system a lot-- especially during the winter months.
Upper level lows rotate counterclockwise, which in most cases causing storms to intensify. The rotation that is present in upper level lows can eventually reach the surface over time.
The huge forecasting problem when dealing with upper level lows is determining whether the low will strengthen or weaken over time. Upper level lows are best viewed on satellite imagery. When the cloud cover brightens (turns white) in association with the upper level low, this indicates that the low is strengthening.
During the winter months, upper level lows have been responsible for heavy snow events. So for the BOTS fans, you like these types of lows!
The rotation in an upper level low causes air to rise and cool. In most cases, these upper levels lows are tilted over cold air, which causes colder surface temperatrues. With the upper level lift combined with this cold air, wintry precipitation forms-- at times creating a fairly strong winter storm.
We often refer to "convective snow showers" in our area and this is common to see during upper level lows, especially if any clearing takes place. These can drop quick accumulations of 1-2 inches--which we have seen numerous times in the Ohio Valley.
S0-- I do appologize if this post is somewhat technical but it is the easiest way of explaining what this all means. It is important for you all to understand what we talk about and forecast on TV.
Brian and I will be doing a video blog update later this morning, covering the upcoming weather for this week in addition to the long term pattern--which according to the latest data rolling in looks quite interesting and possibly "wintry" for this time of year! Don't give up yet BOTS fans....