WHAT IS A FRONT?
Written by: Brian Neudorff
Over the next 24 hours you are going to hear us mention a "Warm Front" a lot with this next system. We seem to have a very educated group who participate in discussion but I thought that there may be a silent group that may be afraid to pipe up and ask the "simple" questions. We want to hear from you too!
I'm sure you're all familiar with the "high and dry" weather we've been experiencing for almost a full week now. Aside from that being super-rare in these parts in March (or even any other time of year!), it has to come to an end sometime. That sometime is basically now.
A front is essentially a dividing line or boundary between to distinct air masses of different densities. Because the densities of these air masses are determine by their temperature characterize these air masses based on their temperatures. It's either a warm or cold front depending on which air masses is moving. If the cold air is advancing then the leading edge of cold air is the cold front in the case of our weather the end of the week, warmer air advancing the leading edge is the warm front.
Cold fronts and warm fronts behave independently of one another. Cold fronts arrive fast and hard, bringing us our ripping thunderstorms in the summer, and a blast of cold, you can see this in graphic below. The warm front is the gentle giant, taking its time moving in, slowly increasing clouds and the temperatures, as you can see above.
This morning started off almost clear for most of the area. As of this writing (11am) you could already see the clouds filling in from the upper levels. Often times preceding a warm front will be the high, thin cirrus clouds. Check. Then when looking at the image above, the layers fill in through the stratus deck eventually arriving in the cumulus form. The reason for the slower, less abrupt arrival is the slope of the warm front. Notice how there is a nice slow grade between the cirrus levels and cumulus? This causes slowly rising air, making for consistent cloud cover and a light, steady rain.
Cold fronts on the other hand have a very sharp gradient between the cold and warm air. As a cold front races in, warm air rises abruptly, meaning stronger rain over a shorter time period.
Hi Brian,
ReplyDeleteI got a question related to warm and cold fronts. It seems like in the summer around here the thunderstorms from cold fronts fizzle out before they reach us, or they flare up just to our east instead. But then we seem to get our best thunderstorms ahead of a warm front. Or at least warm front thunderstorms seem to hold together better crossing our region, and especially at night. Is there a reason for that, or am I just imagining it?
That would be the lakes kicking in their influence. Remember that during the summer, the lake water temperatures are relatively cold compared to low level atmospheric warm air. This actually makes the air more stable, thus limiting thunderstorm development on some occasions.
ReplyDeleteBut you may suffer from the same disease we do: "Why does everything good miss us?!"
Very observant and no your not imagining this, one big reason we see these storms fizzle in the summer can be attributed to the lake. During the summer, the lake and the air over the lake is usually much cooler than the air on land surrounding the lake. This causes the air to sink which stabilizes the air over the lake as this air sinks it spreads out and that's why we get cooler lake breezes in the summer.
ReplyDeleteThese now cooler drier lake breezes act as micro cold fronts. So as a larger cold font slides from the west to the east and depending on when it reaches western New York, lets use the afternoon/ evening for this example then storms will fire along this lake breeze boundary usually south and east of the Rochester area.
With warm front we can see clusters of thunderstorms ride along this boundary. This is what happened last August, I remember this cause I was at the NASCAR race in Watkins Glen and there were several convective thunderstorm clusters riding along a stalled warm front (or stationary front). This is also the same system that produced the devastating flash flooding in Gowanda, NY. A warm front will allow for moisture and warmth all the ingredients storms need. If the warm front is close enough then it provides the added lift needed to get these storms to fire.
We may need to revisit this again as a completely different post on summer storms
-Brian
Very educational. Thank you Brian for providing this.
ReplyDeleteI do have a question concerning this weekends forecast of rain.
Do you believe there will be concern with flooding considering the snowpack of late?
Also in relation to the above question, at what point does the ground thaw out below the frost line to absorb runoff. The reason I ask is beacause always in the Spring, during a thaw and heavy rain, I end up getting ponding in my yard. In the summer however, even after a heavy downpour, there is no ponding.
Thank you.