Will my (tree) limb break?

By: esteban9 , 9:07 AM GMT on November 28, 2010

"When all the (computer) models don't agree, it's time to check out the astrology." This old saw applies to tomorrow's forecast. Despite being only 24 hours away from the most intense part of the storm, there is still considerable disagreement as to the fine-scale, sensible weather forecast for Andalucia. I will try to wade through this uncertainty as best I can.

There is a model trend toward continuing to move the front and its associated heavy precipitation southward than earlier forecasts. This would mean that the heaviest precipitation would fall on the other side of the Straits, in North Africa. The satellite imagery indeed show the system dropping south quickly over the Atlantic. Nevertheless, I'm going to stick by my earlier prognostication of the front lodging itself over the Straits themselves. This is a climatologically favored area for strong temperature gradients (in meteorology-speak, a "baroclinic" zone). Andalucia is currently on the cold air side of the front (witness 4C temperatures this morning in Seville and Jerez de la Frontera).

As described yesterday, I'm relying on the the upper-level (polar jet stream) model forecasts, in the face of their "wobbly" surface pressure forecasts. Now, some models are even redeveloping the main center of Cyclone Two ("Crassus") well to the north, off the northwest Iberian coast. I don't buy this, since the jet stream's favored area is still to the southwest of Iberia. Moreover, there are hints that this favored area will be further favored by the merging with the subtropical jet stream. Therefore I still anticipate the main low center to make its entrance around the Gulf of Cadiz tomorrow morning. Which brings us to the question broached a few days ago - will it be accompanied by high winds?

One model, the Canadian or CMC, has been recently consistent, even in its surface pressure forecast. And this model maintains a strong pressure gradient ahead of the cyclone center. So, although not as strong as foreseen a couple days ago (and southerly flow is not accelerated by channeling through the Strait), I still expect vigorous onshore winds along the Costa de la Luz and Costa del Sol in the morning hours tomorrow. These coasts will also "enjoy" the heaviest rains, so expect some horizontal, sleeting drops.

So I'm staying out on my limb for now; we'll see if it holds my prodigious weight!

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Musings and forecasts of Andalusian weather and climate, from a veteran meteorologist.

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