Musings and forecasts of Andalusian weather and climate, from a veteran meteorologist.
By: esteban9, 6:30 AM GMT on April 28, 2010
I'm traveling on business in northern Spain this week, so taking a break from posting. But it looks like the weather has calmed down considerably and should continue to do so for the forthcoming week...so enjoy!
By: esteban9, 6:50 AM GMT on April 24, 2010
High pressure will build over the western continent, making for benign and dry weather through at least the end of the work week. Temperatures will be slightly above normal. Morning fog will be common, especially in valleys. Some middle and high clouds move in this afternoon, but these shouldn't affect the sensible conditions much. It looks like the weather magnet that draws tourists and expats to Andalucia is gaining strength...
By: esteban9, 6:47 AM GMT on April 22, 2010
So far, the weather has been strikingly well behaved and followed the forecast for Feria week. Pretty surprising for spring, since the weather models start degrading in their accuracy, compared to winter.
Anyway, a small but vigorous line of thundershowers is already striking Huelva province and, as advertised, these weather features will become widespread by this afternoon. The models are showing a rain focus on the coasts, but I don't think it will be any more intense there than inland.
Well, again, if the Feria-goers can endure today's rain, the remainder should be warmer, sunnier, and dry. All in all, this year's edition will be remembered not for its (foul) weather.
By: esteban9, 6:03 AM GMT on April 21, 2010
The forecast for the rest of the week looks unchanged. There are already showers in the west, mainly in Cordoba province. These showers will spread to the rest of Andalucia and maximize their coverage this afternoon. Nevertheless, the weakness of the low pressure over Iberia and lack of instability indicates that showers will be spotty and not drop a lot of precipitation. Tomorrow the showers will be more vigorous and widespread. Then, dry and sunnier conditions return for an extended stay beginning Friday.
By: esteban9, 6:26 AM GMT on April 20, 2010
The band of clouds that entered the area overnight will begin its exodus during the day. There are a few very light showers associated with this band, over northern Malaga province and adjoining areas...these may not even be reaching the ground. The back edge of the band is along the Costa de la Luz, so the southwest should clear out first, giving a fine start to the Feria. A few puffy (convective) clouds will linger, but these should not be much of a factor. The ongoing forecast for showers late tomorrow and Thursday looks on target.
For those attending the Feria this week, que lo disfrutéis!
By: esteban9, 8:07 AM GMT on April 19, 2010
There was a lot of widespread rain yesterday, as expected. But the intensity of the thunderstorms was a bit of a surprise. I think the additional forcing of the cyclone directly overhead outweighed the lesser instability. Precipitation totals in mm from yesterday:
Some clouds lie over far northern Andalucia today, but otherwise it's sunny. Middle and high clouds ahead of the next cyclone to the west will stream into the area tonight. But again, today and tomorrow will be dry and warmer.
Previous forecasts look good for the remainder of the week - showers will move in on Wednesday and Thursday they reach peak coverage and intensity. Clearing Friday through the weekend.
By: esteban9, 8:29 AM GMT on April 18, 2010
Yesterday was calmer than Friday, as precipitation was largely confined to the mountains. A well-defined north-south band of moderate rain translated across the west this morning, however, and is now draped across central Andalucia, from Cordoba to Malaga provinces. More rainbands are behind this large feature, hinting at a verification of the ongoing forecast of a wet day area-wide. All this is attributable to this week's offshore cyclone finally moving out - directly over Iberia (the "good news - bad news" for sun lovers). The atmosphere remains unstable and AEMET has yellow alerts for all but the southeast...given that the cyclone will provide plenty of "trigger" for convective clouds, this is eminently reasonable. Nevertheless, as broached previously, the cyclone will be weakening during the day, so I don't think the tormentas will be as strong as Friday's. So again, tomorrow and Tuesday should be dry, albeit with some mid and high clouds lingering, especially tomorrow.
The outlook for the Feria remains on track. There may be some better news for those who don't like to get wet walking around the casetas. There are suggestions that most (but not all) of Wednesday's and Thursday's precipitation may fall mainly to the north; plus, it may dry out completely for the last half of the festivities, Friday through Sunday. But just in case it doesn't, here's a humorous video about past Feria weather (in Spanish), to cheer you.
Looking back, here's another representation of the amazingly wet winter of 2009-2010. This map from AEMET shows the percentage of normal precipitation from December 1 through 28 February. What surprises me about this map is that, while the coastal southeast (Almeria and Granada provinces) may not have seen as much absolute precipitation amounts as the west, it was one of the two maxima in terms of percent of normal - over 300%! These rains have fed the drought-stricken reservoirs and furnished enough water storage for 2-5 years use! But, as surely as night follows day, drought will eventually return to the south...in fact, most of the climate models show the Mediterranean to dry out the most in the long run compared to the rest of Europe. It's important to bear in mind that there can be anomalous wet years within a long skein of dry ones.
By: esteban9, 8:17 AM GMT on April 17, 2010
Since the models over-forecast precipitation on Wednesday and Thursday, I believed that they would again overdo it yesterday. Well, this time when they "cried wolf," there was indeed a wolf. Although the precipitation band(s) that came through the western provinces late yesterday evening had unimpressive radar intensities, they packed a wallop in terms of rainfall rates. Sevilla recorded 23.4 mm before midnight, and somewhere in the sierra of northwest Andalucia, almost 77 mm fell - see yesterday's precipitation map for the Guadalquivir Basin. Well, at least the forecasts of rain confined mainly to the western half of Andalucia has been accurate. Nevertheless, Malaga province is being belted by strong thunderstorms at present (Malaga, of course, straddles the fence between western and eastern Andalucia).
Indeed, if I had been around the computer to check on yesteday's noon balloon sounding from Gibraltar, I would have shed my aforementioned disbelief in short order. This sounding showed easily the most unstable atmosphere so far this year. I did allude to this instability yesterday morning, but its magnitude increased dramatically by midday, to levels that any "storm chaser" in the middle USA would be excited about. And, there was little change in these conditions shown by the midnight sounding last night. Therefore, it is clear that we will again see localized heavy thunderstorms throughout the western half of the region, and even some in the east. Mountainous areas, since they generate lift, will again be foci for these tormentas.
Beyond today, previous outlooks seem on track, with the low pressure center moving across the peninsula tomorrow and trggering more widespread showers and thunderstorms, including the eastern provinces. Then, a nice sunny break for Monday and the "alumbrao" (Tuesday in Sevilla). Alas, the "inching" of the models toward more rain for the remainder of the Feria has become more of a "walk." So, as was quoted here before, keep those umbrellas handy if you're planning to attend the festivities!
By: esteban9, 9:23 AM GMT on April 16, 2010
The rainband last night came through as expected last evening, but again it was not that strong, with only a few lightning flashes and light precipitation, mostly in the Sierra of northern Huelva and Sevilla provinces. This storm seems to be much more benign than I anticipated prior to its onset.
Another band is entering southwest Portugal and, although there is again considerable instability in the atmosphere, I now doubt that it will produce much precipitation. However, there are already smaller bands of thunderstorms ahead of it in Huelva province, so maybe the convective clouds will be deeper and more vigorous today. If there are heavy precipitation areas, they will be isolated in geographic coverage.
Yesterday's outlook for the Feria looks on track, but edging a bit toward more showery on Wednesday the 21st.
By: esteban9, 2:42 PM GMT on April 15, 2010
Pretty quiet on the radar screen so far today, but that's about to change. A "spoke" of thunderstorms is rapidly approaching the Portuguese coast, with about the same timing as last evening's spoke. A peek at the Gibraltar sounding reveals even more unstable conditions ahead of this feature, so I anticipate a more vigorous band of thunderstorms this time (maybe even a squall line). This is going to be interesting. I'd bring an umbrella if you're going out tonight in western Andalucia!
By: esteban9, 7:52 AM GMT on April 15, 2010
Yesterday a band of precipitation came through late afternoon/early evening in the western provinces, as expected. Nevertheless, despite its organized appearance on radar, it produced only light precipitation. Maximum amounts were in the Sierra de Aracena (northern Huelva province) and Sierra del Norte (Sevilla province), and this rain was associated with a different rainband that occurred yesterday morning (at press time for this blog).
All this leads me to question the heavy accumulations predicted by the models, as mentioned a couple days ago. And even the models are backing off those forecast totals of greater than 100 mm. That said, yesterday there weren't many thunderstorms. Early this morning, there were a lot of thunderstorms about. Furthermore, the Gibraltar sounding confirms greater instability than yesterday.
What does this mean? The precipitation today will primarily come from thunderstorms, which will be more scattered in coverage. Therefore, some local areas will receive a lot of precipitation in short bursts, while other areas will see little rain. AEMET has recognized this too, as it has raised yellow alerts for thunderstorms with greater than 15 mm/hour rain rates, across the western provinces. The mountainous areas will be a focus for thunderstorms. This unstable showery pattern will continue through the weekend, as mentioned previously. The models forecast the cyclone to move ashore into Iberia on Sunday; if it hasn't weakened too much, we could see more widespread precipitation area-wide on that day.
I'm sure many of you are looking forward to a forecast for the Feria de Sevilla, which begins next Tuesday. Jose Maldonado's blog from yesterday has an interesting "alternate" telling of the origins of the fair. Jose is annually bombarded with questions about rain for the event, and he concluded yesterday by saying that "...the heat will be conspicuous by its absence" and that one would be well advised to keep the umbrellas handy. Sound advice! But I'll get a jump on Jose by predicting a mostly sunny "alumbrao" (start) to the Feria. After the initial day, things become more muddled as low pressure builds in from the west. Right now, the models show the bulk of precipitation staying to our north for the remainder of the fair. I'm sure most of the nearly 1 million visitors would like such an outcome, but it's too early to take the bait and say so with certainty. Stay tuned, citizens!
By: esteban9, 7:19 AM GMT on April 14, 2010
A well organized band of moderate rain has been affecting western Huelva province, with more rain offshore to the south. And this rain is emanating from clouds that aren't that deep. The much deeper clouds are still well southwest of Portugal; these look to arrive this afternoon and produce the heavier rains that the models have been advertising. Given the warm air being pumped in ahead of the cyclone, the atmosphere is destabilizing and there will be widespread thunderstorms too. These thunderstorms will bring bouts of torrential rain.
As mentioned before, there will be patches of clear or partly cloudy skies between the rain bands, perhaps a big one tomorrow. These patches of clear skies are caused by descending motions that compensate for the ascending motions in the bands. This is characteristic of convective cloud organization that is more common in spring, as distinct from the more overcast cloudiness of winter storms. But don't be fooled by the clear patches and think that the rain is over. We used to call these "sucker holes," because they can sucker a forecaster into calling for an end to precipitation. But enough folklore. The storm buffs and I will watch the evolution of this first spring event with interest.
Again, because of the location and stationarity of the cyclone, western Andalucia will bear the brunt of the rainfall for the next few days, although the east will also see significant amounts.
Updated: 7:28 AM GMT on April 14, 2010
By: esteban9, 2:39 PM GMT on April 13, 2010
Well, there's a lot more sun out there than I thought in the West...so I guess that's a pleasant surprise to those who enjoy that kind of thing.
While I'm here, I present a little amusement. Remember how I was saying that the low pressure system to our west was "sitting and spinning" in the same spot? Here's a little illustration, which shows the surface pressure pattern (isobars) and precipitation forecast (blue shades)every six hours, from today through Monday. Why, the low even wobbles westward ("retrogrades") later in the week. This is why we expect several days of rain showers.
By: esteban9, 7:36 AM GMT on April 13, 2010
The low, shallow clouds in the west hung on longer than I expected yesterday; low clouds (like stratus) and fog are common in low-lying areas such as the coasts and up the Guadalquivir river valley, even in summer. Yesterday's clouds were caused by moisture and nocturnal cooling of the lowest atmospheric layers (in meteorological-speak, the boundary layer). It is difficult to predict when these clouds/fog will break up with heating during the day; apparently there was some lifting in the atmosphere yesterday that kept them bubbling up well into the afternoon. I know this from years of experience trying to forecast them on the central California coast. But, since they are around again this morning, I am obliged to take a stab at forecasting them again.
As I said yesterday, clouds from the developing closed low to our southwest will begin to invade Andalucia today. So, given the current cloudiness and those clouds, the western provinces will see little sunshine today. The eastern half should see a bit more sun. Nevertheless, the Gibraltar sounding showed a deeper moist layer than yesterday, so this sun will be short-lived.
There is a front draped west-to-east across central Spain, which triggered some thunderstorms just north of Andalucia yesterday. This front should again be the focus of precipitation today, but except for a few stray showers in the north, Andalucia will be precipitation-free. Our precipitation will begin in earnest after midday tomorrow, when the first "spoke" of rain rotates into the area from the cyclone. And, as discussed yesterday, this will be the pattern for several days. There may be a few breaks in the clouds in between these "spokes," but overall it will be mostly cloudy for the remainder of the week.
Well, it looks like the actual weather is going to follow the climatology of early spring, so this precipitation is not unexpected.
Updated: 7:41 AM GMT on April 13, 2010
By: esteban9, 7:39 AM GMT on April 12, 2010
Today should be the last day with predominantly sunny skies for some time, as cloudiness increases tomorrow ahead of the cyclone to the west of Iberia. The western provinces have low stratus clouds this morning, but these should burn off around midday.
The cyclone does not appear to be strong in the sense of high rainfall rates; nevertheless, the remarkable aspect of the storm is its longevity. Since it is isolated from the principal polar jet stream and is embedded in a "stagnant" flow regime, it is forecast to just spin in an almost stationary position to our west until it finally weakens next Monday. This means that it have ample time to draw warm moist air ahead of it, dropping on-and-off precipitation to mainly the western half of Andalucia for for five days! As testament to the prolonged nature of the precipitation, a couple models show maximum precipitation accumulations well over 100 mm by this weekend, around the Sierra de Aracena. If so, this storm would be worthy of being classed with some of the stronger storms of the past winter...veremos a ver.
By: esteban9, 7:48 AM GMT on April 11, 2010
Well, those clouds I predicted on Friday for this weekend have finally arrived, leisurely wending their way from the south as part of the weak cyclonic gyre over the Moroccan coast. There are even a few showers over Malaga and Cadiz provinces, although most of this rain is not reaching the ground. The cyclonic circulation will weaken further as it moves over Andalucia, so I will stick to my guns and say there will be little precipitation over the area (maybe some light showers over mountains). There will be much more cloudiness today than yesterday, however, particularly over the eastern half of the region. As posited yesterday, the Levante is already beginning to weaken (Gibraltar winds down to 24 knots).
There will be substantial clearing overnight. Nevertheless, today's cloudiness heralds the end of our predominantly sunny pattern, at least for the coming week. A major closed low is forming to the southwest of Iberia and wobble slowly across the peninsula during the last half of the week. The first band of significant precipitation associated with this low should arrive early Wednesday, and showers will linger until at least Saturday. So, we'll have something more to discuss than the Levante this week, as spring finally demonstrates that it's not going to remain tame during its entire tenure in the south of Spain!
Updated: 7:55 AM GMT on April 11, 2010
By: esteban9, 12:00 PM GMT on April 10, 2010
As discussed yesterday, the Levante winds are stronger today, but not by much compared to yesterday (what's a few knots amongst friends?). Speeds at Gibraltar have been running between 30 and 34 knots, with one gust to 40 knots. The overall surface pressure gradient has caused stronger winds inland today, however, especially in western Andalucia.
Some models have a few spots of rain moving across the sea from North Africa tomorrow; however, since this doesn't seem to be a consensus and because the forecasted mid/high clouds have not even made this excursion today, I'll go with no precipitation tomorrow. The major storm to our west is progged to develop a trough over Spain with associated precipitation on Tuesday. Because the main cyclone remains to our west in a weak state, however, I'm pessimistic about rain chances on Tuesday as well. The good news (apparently very good for those wishing to cross the Strait by ferry) about this change in the pressure pattern is that the Levante should weaken beginning tomorrow afternoon.
In my last blog I mentioned a scientific article about the various causes of a Levante, which I failed to bookmark. Nevertheless, I located some online training about the Levante from AEMET (Spanish meteorological service). So yours truly is going back to school for a bit!
By: esteban9, 8:09 AM GMT on April 09, 2010
The Levante developed on cue yesterday, but was not as strong as I might have guessed. But then again, I'm new to this phenomenon, one of the world's most important winds from a historical perspective.
Sustained winds at Gibraltar yesterday did not exceed 30 knots, with one gust to 36. I examined yesterday's model forecasts, and they did a good job at estimating the magnitudes observed at this station. This is surprising, since I came across a research paper on the web (which unfortunately I didn't bookmark) that stated that the Levante is not simply caused by the Bernoulli effect (constriction of flow by the adjoining land masses, as when one squeezes a water hose); there were also thermodynamic, mesoscale effects at work. The mesoscale is smaller than the larger, synoptic-scale that numerical weather models traditionally operate on.
But models are increasingly run at meso-scales, so apparently capture the Levante (at least in this instance). For a good illustration of the importance of model scale (or, more precisely, resolution), examine the following forecasts of wind speed (in km/hour, slightly greater than half a knot) at 10 meter height, from the GFS and NAE models. Both forecasts are for the maximum predicted speeds of this Levante event, at 10 PM tonight. If the Bernoulli effect was the major factor in controlling wind speed, one would expect the maximum speed-up in the Strait and just downwind. Such a situation is more apparent with the NAE; the GFS has a more symmetric isotach pattern to the east and west of the Strait. The NAE has considerably higher resolution (spacing between grid points) than the GFS, resulting particularly in improved modeling of the terrain. This should improve the wind forecast. There are other factors besides resolution (e.g., physics, parameterization for you weather geeks) in model accuracy, and these will be related to the thermodynamics effects mentioned earlier. But resolution definitely is important.
Now that the lesson is over, look for a day similar to yesterday with somewhat stronger winds. The low pressure center along the Moroccan coast is deepening, which is the main culprit for augmented winds. Furthermore, this low will send considerable cloudiness (mostly at middle and high levels) our way for the weekend. Temperatures will remain at or slightly above seasonal norms.
By: esteban9, 8:45 AM GMT on April 07, 2010
The upper level disturbance and its overcast high cloudiness has passed to the east, leaving brilliant clear skies across Andalucia. These conditions will persist through the day, with relatively light winds...temperatures will be similar to yesterday. Tomorrow, as mentioned previously, easterly winds will pick up considerably and produce a vigorous Levante in the Straits. AEMET has already hoisted a yellow risk for the Straits tomorrow. Perhaps our friends at Gibraltar weather station can chime in with a forecast of how strong they anticipate the Levante winds will be there?
The recent dominance of high pressure appears to be coming to an end, at least temporarily, next Tuesday and Wednesday (13th-14th). The long-range models all show a closed low pressure area developing to our southwest during those days. The amount of forecast precipitation associated with this feature when it moves northeast over Andalucia varies considerably. In any case, for you "non-fair weather" aficionados, this will likely be the next big thing. Keep in mind that climatologically normal precipitation doesn't start dropping off for the warm season until May, particularly for the western provinces. So it's not time to rely on the lazy hazy days of (late spring and) summer just yet!
Updated: 8:49 AM GMT on April 07, 2010
By: esteban9, 7:26 AM GMT on April 06, 2010
The last of the mid/high cloud mass is leaving eastern Andalucia, giving way to mostly sunny skies area-wide today. This will finally open the door to the long-awaited warming trend. Nevertheless, a fly is appearing on the horizon, ready to pounce in the ointment (sorry for the mixed metaphor).
Low pressure over the Sahara will combine with high pressure to the north of Spain, generating a strong pressure gradient over the area the last half of the week. This will result in strong easterly winds, and will set up a vigorous Levante wind over the Strait of Gibraltar. This simple explanation of the Levante has a figure (the second on the page) that strongly resembles the forecast surface pressure pattern (pattern "a" in the adjoining text). Not being terribly familiar with the Levante, I will watch with interest the maximum winds in the Straits area. The east side of the Sierra de Alcornocales and Sierra de Grazalema will be cloud-covered, owing to strong upslope flow there.
An upper level disturbance will bring some (mainly middle and high) clouds overnight, but except for the aforementioned mountainous regions, skies will be mainly clear for remainder of the week.
By: esteban9, 10:05 AM GMT on April 05, 2010
The low pressure trough in Morocco is deeper than expected, causing strong easterly winds in southern Andalucia. These winds, combined with thick mid clouds (also produced by the trough), have made for a chillier start this morning. There are even a few showers evident on the radar over Malaga province, but this rain will not likely reach the ground. The main forecast changes are the cloudier and windier conditions, meaning that the several degrees of warming today will likely not occur, and it will feel chillier than yesterday.
Nevertheless, the influence of the Moroccan low will weaken and move south over the next 24 hours, promising a sunnier and warmer day tomorrow (the cloud shield is already clearing in the western provinces). Given the source of the disturbance, "Inshallah" seems appropriate to use in this instance.
Updated: 10:09 AM GMT on April 05, 2010
By: esteban9, 8:52 AM GMT on April 04, 2010
The front didn't bring too many clouds to the area last night, and now it's crystal clear across the region today. A few clouds from the south will approach late this afternoon; otherwise sunny and breezy conditions will prevail today. The warming trend mentioned yesterday commences tomorrow. All you fair weather fans out there - enjoy!
By: esteban9, 8:57 AM GMT on April 03, 2010
A few middle and high clouds are streaming from the southwest across the Costa del Sol this morning. However, the principal intruder into our otherwise clear skies will come this afternoon, as a dying cold front enters from the northwest. This front is already weak, but is generating some showers across northern Portugal and Galicia. Its main effects will be to increase total cloud coverage (including some low clouds) across the eastern provinces from mid-afternoon through evening; I don't anticipate any rain with these clouds.
Northerly flow behind the front should keep temperatures slightly below normal tomorrow, despite more sunshine. More clouds arrive from the south tomorrow afternoon, associated with very weak low pressure in northwest Africa. But again, there will be no rain, and temperatures will increase during the early part of the week, with the southerly flow generated by this weak disturbance.
The dry spell will persist for at least another week. This will help me recover from my recent late nights attending Semana Santa processions!
By: esteban9, 8:07 AM GMT on April 01, 2010
Indeed, Semana Santa appears to be favored by the weather gods this year. Today will be sunny again with light winds. There will be a slight warming through the weekend.
For those attending the holiday events...enjoy!