Sunday, April 6, 2014

Four Isobars off the Gulf

If you can count to four, you too can be a weather forecaster. Sorry for the humour! Meteorology and weather is never this simple except in this particular exception.
A time tested "rule of thumb" is to count the isobars originating from the warmth and moisture of the Gulf of Mexico. If you should count four isobars directed from this huge energy source then you predict precipitation in Toronto in 24 hours.
There was a tendency during my meteorological career to shun these techniques as cook book meteorology in favour of numerical modelling of the atmosphere. My response was that even the best chefs refer to a reference guide especially if these are based on solid science and knowledge. My illustrations for this are computer generated atmospheres produced by my friends in Boulder, Colorado. A hand drawn analysis from this morning would have sufficed but alas, I am retired and the rain has yet to fall anyway. I count a solid five isobars coming off the Gulf on the forecast chart for 2 pm this afternoon. This is going to be a wet event for Southern Ontario! The first observation of rain at Pearson International Airport should be at 2 pm EST on Monday afternoon - 24 hours later - plus or minus.
The ruler of thumb is based on the Conveyor Belt Conceptual Model. One of my modules on this topic was recently published by COMET and can be accessed at the following link.
COMET only requires a valid email address and then you have access to the most current environmental training and research found anywhere in the world - completely free. The conveyor belt conceptual model is summarized in three dimensions below with the isobars coming off the Gulf represented by the red conveyor belt of heat and moisture. This red arrow has the label "WCB" which fittingly stands for "Warm Conveyor Belt". Something that those in southern Ontario will appreciate after a long and cold winter.

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