Boundary Waters Quetico Forum :: Group Forum: WEATHER STUFF :: Back country weather (off the grid) forecasting
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LindenTree |
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Jaywalker |
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WhiteWolf |
First up is types of clouds and today's cloud is ACC- or altocumulus castellanus. Probably one of the most tried and true methods of predicting afternoon strong/severe thunderstorms is the presence of altocumulus castellanus clouds in the morning, say between 8am-10am. Translated from latin, meaning castle,the castellanus species of cloud is uncommon, but can be expected to be seen on days when the atmosphere is unstable. Altocumulus castellanus clouds are a particular favorite kind of cloud amongst storm chasers because they usually point to unstable air, which can mean for thunderstorm development sometime during the day. Castellanus clouds in the morning indicate stormy weather in the afternoon. Basically they are showing that mid to upper levels of the atmosphere (at least for thunderstorm development) from about 7000' to around 20,000' are all ready unstable and all it takes is basically heating of the day and connecting to surface instability and BOOM- Thunderstorms. Altocumulus castellanus 1 ACC 2 probably the best pic I've seen on the net is that with ACC 2 link on wiki- blow that pic up as it's an excellent pic of ACC clouds. Here are several other good examples- this link (don't be concerned about the top- just the pics) shows a progression of ACC from what many would consider not much. However- you can add in this pic at tail end of those 4 and this is what happens most times when you have ACC in the mid morning hours around 2-3pm a full blown TS is not far off. Winds from a southerly direction - especially SE, with a falling barometer along with ACC would be as much a slam dunk for PM thunder as you can get. |