Musings and forecasts of Andalusian weather and climate, from a veteran meteorologist.
By: esteban9, 8:28 AM GMT on November 30, 2010
Well, cyclone "Crassus" turned out to be more like "Wimpus", not much more powerful than its predecessor and sidekick "Charley". The most rain was in the usual spot, the mountains north of Algeciras - Torre Toma De Charco Redondo with 83.5 mm. Also, as expected, the heavier amounts shifted between the storms from Seville to the Costa del Sol.
The computer models predictions, as tracked herein, weakened Crassus with time. This turned out correct, and the runs of the past two days were the most accurate. The lesson for me is not to get too excited when the models are "bullish" on a storm from 3-5 days in advance of the event. The development stage of storms is the hardest for models to simulate, and in this case they were much too strong in the early days. This is why we cannot rely on model predictions alone (there's still a role for meteorologists, especially ones that learn from their mistakes!). On the other hand, it's important to follow the predictions, since there will be storms that live up to their bullish advance billing (witness several from last winter and spring).
As the last "spoke" of low pressure rotates into the region, today and tomorrow will be chilly, mostly cloudy and showery. But the precipitation will not be nearly as widespread as with the last two storms.
The next big, mean-looking storm is foreshadowed for Sunday, but this forecaster is chastened and will wait to see the whites of its eyes before going out on the next limb. I think I will also put on hold the practice of naming storms, by the same rationale. Bueno, fue un poco de diversión.
By: esteban9, 7:11 AM GMT on November 29, 2010
The rains have commenced in the western half of Andalucia, being widespread but light. Rainfall rates should increase through the remainder of the morning and spread to the eastern half.
High winds are not as big a concern now, as first broached yesterday. However, the steady rains of today will fall on already wet soil and full rivers, so flooding is definitely a concern, even more than with yesterday's rains. This is especially true in Cadiz and Malaga provinces, where today's rains will be heaviest. The "bullseye" could again be the areas between Malaga and Estepona, particularly in the mountains just inland of the coast.
Beware of crossing flooded streets and streams - less than a third of a meter depth of running water can carry away a car!
By: esteban9, 2:57 PM GMT on November 28, 2010
Here's a story about some (mainly) street flooding along the Costa del Sol yesterday. So "Charley" was a nasty little brat. "Crassus" coming tomorrow to exacerbate things.
By: esteban9, 11:29 AM GMT on November 28, 2010
To all you folks who enjoy sunshine, and I know that there are many of you...
I hope you're out enjoying the (cool) sunshine today...for it is very ephemeral (see all my recent posts).
I'm afraid I'm going to soon be called "Mr. Doom and Gloom," for mine is not a fine bedside manner. ;^)
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!
By: esteban9, 6:47 PM GMT on November 27, 2010
Just an update on rain amounts thus far today. The maxima were around 60 mm at two sites, both about 50 km east of Seville. This is more than I expected. This is something to bear in mind when considering Monday's storm and the potential for flooding.
Updated: 6:48 PM GMT on November 27, 2010
By: esteban9, 10:14 AM GMT on November 27, 2010
The maximum precipitation amounts so far are around Seville, with one gauge just north of the city reporting 25 mm on the day. Perhaps Cyclone One will be a more muscular sidekick after all. Maybe we should name him - I lean toward "Charley." You are welcome to submit an alternative via the comments.
Sound silly? Well, I heard some forecaster in the UK gave the name "Becky" after an acquaintance or some such. I can proudly state that our rationale here at AW is no less silly. On the other hand, it all seems like "Hurricane Envy."
By: esteban9, 9:33 AM GMT on November 27, 2010
As predicted, the bully's sidekick, AKA cyclone one, has started producing measurable rains, heaviest in the west but also some in the southeast. Several precipitation bands have been moving north and intensifying slightly over the mouth of the Guadalquivir. We should tally the accumulations by the end of the day to gauge possible flooding threats with "bully Crassus" (AKA cyclone two) on Monday. Again as predicted, the center of cyclone one will move across Andalucia today, spreading rains to the eastern half of the area as it does so. A major question will be how cold the air will be as it is dragged in behind this low. The current temperature in Madrid is -1C, so there is ample supply of such chilly air.
The reason why this cold air mass matters is not only for the development of snow on Monday, but where the front (boundary between warm and cold air) sets up. This frontal area will likely provide a focus for the development of cyclone two. The trend of the models is to place this boundary slightly further south with each run. Now it is forecast to be near the Straits. This seems reasonable. Therefore cyclone two will not zip up the Atlantic coast as earlier foreseen, but take a more inland path, making landfall in southern Iberia early Monday. There is still a strong pressure gradient ahead of this landfall point, but given the shift in the models' positioning of the low center, I am thinking that the Straits may be the area of greatest concern for high wind. The channeling effect of westerly winds would give cause for this concern. Even as we approach zero hour (Monday morning), the models still have some uncertainty. The models tend to forecast upper level patterns better than lower-level ones, however, and they are placing the jet stream in a favorable area for intensification of cyclone two; therefore I am not yet buying the downgrade of the wind threat.
Even if we dodge the bullet of high winds, the question of heavy rains is still very much with us. On Monday, the cyclone will have an elongated shape, extending well out to our west. This will foster a long "tube" of precipitation being fed from moisture-rich ocean areas to our southwest. This could generate a "train" of rain bands repeatedly striking our region. Since it is still early in the season and today's storm will be the first to significantly moisten the soil, flooding may not ensue on Monday. Unfortunately, the longer-term outlook may not be rosy. The upper-air pattern is characterized by a major "blocking" ridge of high pressure over the North Atlantic, allowing the persistence of a large trough of low pressure over northern and western Europe (I mentioned this recently). This pattern looks to persist through at least a week and a half. More rain, albeit more showery, will occur Thursday and Friday. The accumulated affect will warrant vigilance toward flooding. Will this Fall take up where last spring left off?
Updated: 10:07 AM GMT on November 27, 2010
By: esteban9, 9:31 AM GMT on November 26, 2010
If I use a mixed metaphor, then something is seriously weighing on my mind. In this case, the weather on Monday.
To continue my strange state of mind, I'm starting to anthropomorphize the upcoming storms. Tomorrow, we're going to experience the irritating little sidekick of the bully, i.e., a weak cyclone with light-moderate rains area-wide. After a dry respite on Sunday, the big bully comes in on Monday. And he is the one we should be concerned about.
Unlike "temporal Becky" on the 9th, which raised huge waves and damaged Spain's north coast, Monday's storm will first take aim on Andalucia's Atlantic coast. Here is the latest forecast of the surface pressure pattern for 1900 hours Monday. Note the tight packing of the lines (isobars) on the southwest Spanish coast, near Huelva. Here is a forecast from the same model, but from yesterday's run, showing the maximum wind gusts for six hours later (0100 hours Tuesday). Gusts from 59-65 knots (110-120 km per hour) are painted over Western Andalucia. Although the more recent run has decreased the wind forecast a bit, the model has been "waffling" between runs. Therefore, we should take this wind threat seriously.
Also, heavy rains still appear as likely accompaniment to the winds on Monday. However, the models seem to be accelerating the speed of the cyclone with each run, and based on past experience, I agree. This cyclone center will scoot along the Portuguese coast rapidly, deepening as it does so. This means that northwest Iberia will likely get second taste of damaging winds this month. The good news for Andalucia is that, owing to the rapid acceleration of the storm to the north, the heavy rains will not be long-lived, reducing the threat of flooding.
Stay tuned to this blog for updates on this rapidly developing temporal. I'm waiting with bated breath to see if this storm is given a name. Since I've anthropomorphized it already, then that would be apropos. I'm leaning toward "Crassus".
Updated: 9:37 AM GMT on November 26, 2010
By: esteban9, 8:24 AM GMT on November 25, 2010
The computer models are "wobbling" in their predictions for the weekend and early next week. This uncertainty is typical for such a strong, developing storm event, 2-5 days away from its occurrence. Now, the models are showing the coldest air being pinched off over the North Atlantic, away from Europe. This would mean a less pronounced cold wave for us. However, this also means that the region will instead be dominated by strong low pressure and southerly or southwesterly flow. This spells heavier precipitation.
It still appears that the first batch of precipitation will come late tomorrow night into Saturday morning, followed by a second, heavier batch during Monday. The latter will be triggered by an elongated band of low pressure extending from Andalucía well out into the ocean to the west. The British Met Office's latest surface pressure forecast for Monday midday shows the cyclone center at less than 984 millibars, which is very deep, and a warm front draped across Andalucía. This "snapshot" would in itself be a major precipitation producer. Further, this low isn't going anywhere fast, persisting until at least mid-week.
Since the forecasts are evolving, it's prudent to wait before giving more details. I would say, however, a prolonged "wet" is a high probability. For those looking to go outside to play in the coming few days, a different period might be preferable. Stay tuned, weather aficionados.
By: esteban9, 10:19 AM GMT on November 24, 2010
Yesterday, I first alluded to this weekend's developing situation. The forecast remains the same, but it can be fleshed out a bit more. Again, a powerful blast of cold air will drive south this weekend from the British Isles toward Spain. Andalucia will initially be ahead of this cold air mass, in the area of a front that will generate significant precipitation.
The first dose of this precipitation should occur Friday through Saturday. As it departs, it will usher in cold air on Sunday. Then another, possibly heavier and longer-lived, precipitation episode will ensue Monday through Wednesday. Given that the first system over the weekend will ensconce the cold air mass, the second system during the early part of next week will likely dump snow in many higher elevation locations of Andalucía. It is too early to tell the elevation at which rains will become snow, but in this article AEMET is estimating it will be 500 meters in the north of the peninsula.
So, for those averse to cold, wet and dreary weather, the upcoming prolonged event will make the recent weak rain systems look like brief walks in the park. Don't shoot the messenger...
By: esteban9, 8:11 AM GMT on November 23, 2010
The progression of weak rain-producing systems every 3 days or so continues today. This system is a bit different in that the low pressure center will move directly over Andalucía from the west, unlike the last two systems that were accompanied by cold fronts from the northwest. Today's system will, however, be even weaker than the prior fronts, and rain accumulations will accordingly be lighter and more isolated. In fact, the only significant accumulations may occur in the western provinces, especially Huelva province.
More interesting is the longer-term outlook. A major change in our weather pattern is foreseen, beginning this weekend. A major anticyclone will build southward over the North Atlantic, combining with deepening low pressure over northwest Europe to generate a strong jet stream that plunges southward between the two. This means that colder air will plunge with it toward Spain. Iberia will be on the periphery of the polar air mass, in a "favored" area for storm development. This means that strong, persistent fronts will form over our region, fostering steadier and heavier rains. I will follow this development over the coming week, so look for updates. But, I'd prepare for more inclement weather, for sure.
Updated: 8:12 AM GMT on November 23, 2010
By: esteban9, 7:03 AM GMT on November 19, 2010
A weak upper level disturbance has brought cloudiness to Andalucía this morning. This feature will not generate any rain and skies will clear this afternoon. Nevertheless, another weak cold front from the northwest will bring light rain tomorrow. Just like the last front, it will weaken during the day. So, the next 48 hours will be predominately cool and damp. Not a good period to hang laundry to dry.
Updated: 7:03 AM GMT on November 19, 2010
By: esteban9, 7:40 AM GMT on November 17, 2010
Widespread but light showers are indicated by radar this morning in western Andalucía. This precipitation will move east, but weaken as it does so. So, despite the grey skies, not much in the way of accumulations will result, particularly outside the western provinces. Clearing should ensue this afternoon and evening.
By: esteban9, 8:12 AM GMT on November 14, 2010
A single wide rain band accompanying the cold front (see yesterday's post) is entering Huelva province. This band should steadily make its way across the region during the day today, dropping light to moderate rain. The front will weaken with time, so rain may not appear in the eastern parts of Andalucía. Clearing should occur rapidly behind the front tonight, ushering in cooler air.
By: esteban9, 8:09 AM GMT on November 13, 2010
A cold front will barge in from the northwest tomorrow afternoon, bringing with it bands of showers. This "party crasher" will only bring light precipitation, however, and be gone by Monday. There will not be the strong winds of the last storm. Perhaps the main change brought on by the front's passage will be 3-4 degrees of cooling for the first half of the week, despite sunny skies.
Another, probably more potent storm will come Thursday through Friday. This cyclone will hang around a bit longer and consequently drop more rain over Iberia. One thing looks certain - the North Atlantic jet stream is fully "open for business" and it will be producing disturbances that will affect Spain every 3-4 days for foreseeable (November) future.
By: esteban9, 8:57 AM GMT on November 09, 2010
The current storm is behaving according to forecast. Showers are building in the sierra north of Seville, and these should increase in intensity and coverage toward afternoon, when heating of the ground caused convective instability. Thunderstorms and heavy rain appear unlikely though. It should be another windy day, and AEMET has maintained high wind watches for the Sierra Nevada, citing wind gusts to 100 km/hour at high elevations.
High pressure, sunny skies and calmer winds will return tomorrow, to stay for the remainder of the work week. Temperatures will remain on the cool side, however.
By: esteban9, 7:55 AM GMT on November 07, 2010
The forecast of yesterday remains on track, with clouds moving in midday tomorrow followed by showers in the evening. The big story with this deep cyclone, which will be centered well north of us near the English channel, will be powerful winds. Strong pressure gradients over Iberia will foster winds in some locations over 100 km per hour. The "favored" places for these winds will of course be the mountains and offshore. AEMET has already posted an orange (important risk) advisory for high seas and winds off the coast of Granada province. I'm sure more advisories elsewhere will follow. Wind directions will be predominantly westerly.
As broached yesterday, the main threat for damaging winds will be the north coast of Spain, Galicia, Asturias, Cantabria. Nevertheless, in the higher mountains of eastern Andalucia, winds will also be extreme. Beware when driving through mountain passes, as winds accelerate through them.
Again, precipitation will be light and showery. It appears that the best chance of rain will be Tuesday afternoon, as the day's heating triggers convective clouds in the cooler, unstable air mass behind a cold front. After this front has passed in earnest on Wednesday, snow showers will develop over the high elevations of the Sierra Nevada.
So change is in the air!
By: esteban9, 7:56 AM GMT on November 05, 2010
Apologies for not covering last week's rains, but I was in Madrid attending the 10th meeting of meteorological aficionados. This is a fine group of folks with a passion for all things weather (including storm chasing). I learned a lot about weather in Spain and made some good friends in the process. Here is a group photo (I'm the bald guy in the back row).
I'll be ready for the next storm, which is bearing down on Spain Monday and Tuesday. This "borrasca" (low pressure system) is dropping straight from the north into Iberia. It appears that this system will not be a major precipitation producer for Andalucía, but it will have to be watched, especially for high winds. It is likely that the strongest winds will be confined to the north coast of Spain, but the situation could change. Stay tuned.
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.