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Barcelona, 7-9 May 2010 (Round 5)

(This forecast will be regularly updated. This entry: SundayÌý09 May, 09:50hrs BST)

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Nowcast/Forecast Update, SUN - RACE; 09:50hrs:

Sunday: The last twoÌýforecast updates I addedÌý(below) re today noted how our higher-resolution Met Office modelling wanted to take the heaviest of the rain north-northwest of the circuit by a fair margin, up into the Pyrenees. Comparison of versus the latest (00z) model prediction strongly supports this outcome. The spells of rain have duly arrived and indeed passed well to the N-NW of the circuit,Ìýwith the rainfall pattern across much of SpainÌýshowing the clear effects of being influenced by orography (high ground).Ìý Latest radar shows a couple of small-scale convectiveÌýdevelopments south of Barcelona, being fed northwards off the sea; a chance of some isolated light showers around MontmeloÌýthis afternoon cannot be dismissed, but is a low likelihood.

So, the forecast emphasis I penned yesterdayÌý- i.e., "...leaning towards a drier rather than wetter outcome" -Ìýstill looks very likely, with the broad thrust remaining one of dry conditions, with aÌýlatent (low) chance of scattered light showers. The Spanish modelling still calls for a rain chance of 65% today,Ìýbut on balance,ÌýI'd call it closer to 30% or less.

The , meanwhile,Ìýshows an extensive veil of high cirrus and cirrostratusÌýabove Barcelona as it sits in theÌý, with muchÌýof the earlier lower-level cloud coverÌýnow readily fragmenting to offer brighter / hazy sunnier spells around the circuit. A milder southerly flow off the Catalan Sea will help today's temperatures reach around the expected 19-20C (perhaps a little more, givenÌýsufficient sunshine).

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Saturday:ÌýHow hard can this forecast get? Well, very (oh, and incidentally: early prognosis suggests a wet Monaco GP).

Firstly: Worth noting that the spectre of volcanic ash has returned and especially soÌýinto northern Spain and across above southern France. The Met Office has reliable aviation reports of fairly significant ash above the Pyrenees during SaturdayÌýand we might well see some further issues tomorrow. I do hope those of you travelling home from the race tomorrow aren't affected in the manner we witnessed after the Shanghai weekend.

So, onto the action at ground level. Sunday's latest prognosis continues to offer a chance of rain, but by no means a certainty. The heaviestÌýof this wet weatherÌýtomorrow will afffect districtsÌýto theÌýnorth / northwest of the circuit. The latest higher-resolution modelling leans (marginally)Ìýtowards a drier rather than wetter outcome, but with a threat of some (mostly light) showers or rain never too far away, possibly from the race outset.

Saturday:ÌýNo change to the qualifying forecast - looks dry, with sunny spells and ambient temperature around 19-20C; a very outside chanceÌýof isolated showers later,Ìýbut mostly well west of the circuit.ÌýIncidentally, tomorrow's developments are very evident across Portugal in the .

Saturday: Continued forecast confidence in a dry, sunny theme for FP3. Early this morning, a thundery trough departed northeastwards, having brought a band of showers through Barcelona and environs. There's a small chance of showers later today, but highly likely we'll continue with dry, partly sunny weather into qualifying. Ambient temp. around 19C.

Sunday: No significant change to previous forecast. UK Met Office predicts the cold front will sit not far westÌýof Catalonia by race start, but most of the forcing (and attendant shower risk)Ìýis likely to affect areas west and northwest of Barcelona. Still a likelihood of light to moderate showers later inÌýthe race however, so a dry event is by no means guaranteed.

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Forecast Headlines:

Friday, FP1 & 2: Likely to be dry. Small chance of showers.

Saturday, FP3 & Qualifying: Likely to be dry. AÌýsmall chance of showers.

Sunday, Race: Some mostly light showers / rainÌýpossible, especially later.

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So, here'sÌýa teaserÌýfor all you pub quiz types and fact-collecting geeks: When was the last time an F1 season sawÌýfour out of the first five race weekends affected, at some stage,Ìýby rain?

I haven't even started to research the answer, but I'mÌýsure someone with an encyclopaedicÌýknowledge ofÌýthe sportÌýwill promptly tellÌýus the answer!?ÌýPlease do share it, in the comments section below this blog... thanks!

Why am I asking? BecauseÌýfor the fourth time this season, ÌýtheÌýforecast prospects for the next round -Ìýat Spain's Circuit de Catalunya - alsoÌýinclude a periodic chance of wet weather,ÌýincludingÌýon race day itself.

Dry weather prevailed as Lewis Hamilton took 2nd place at the Circuit de CatalunyaÌýon 13ÌýMay 2007 (above); it was a similarly dry story for theÌýrace weekendsÌýin 2008 and 2009.ÌýBut will wet weather add any extra spice inÌý2010? (Photo: Bryn Lennon / Getty Images)

Forecast summary:
It's an unsettled weekend brewing across Iberia and at no stage of the race event is there a compelling signal for any prolongedÌýdry conditions. The broad earlyÌýexpectationsÌýare for:

• Friday:ÌýMostly cloudy at first butÌýsome brighterÌýspells developing;Ìýcomparatively cool nonetheless, with anÌýambient temperature around 15-17C.ÌýOn balance, dry conditions are expected for both practice sessions with only aÌýlow chance of showers.
• Saturday:ÌýBrighter conditions expected, with temperatures around 18-19C accompanied by sunny spells. AÌýsmall risk of scattered showers later,Ìýhowever.
• Sunday:ÌýReasonableÌýinter-model continuity as of the 12zÌýoutput today (Sat) continues to offerÌýthe likelihood of light to moderateÌýrain / showers starting to affectÌýNE SpainÌýduring the late morning and afternoon, as per previous forecast updates. The latest prognosis from the various models we useÌý(e.g., UK Met Office NAE and Global Model; ECMWF ensemble products; US-GFS; French Arpege; Canadian and German models) lean more towards a largely dry but increasingly cloudy morning; then a prospect of light to moderateÌýshowers / rainÌýeasing towardsÌýBarcelona and environs as the race is underway. Worth noting, however,Ìýhow some recent model runs (including at 12z Saturday)Ìýhave been a tad more more bullish, offering anÌýearlier eastward spread of precipitation to influence the race from the outset.

Synoptic situation:
High pressure will remain ¾±²Ô-²õ¾±³Ù³ÜÌýwest of the British Isles over the Atlantic for much of this week, keeping our own weather lockedÌýinto an unseasonablyÌýcool northerly to northeasterlyÌýflow whilstÌýalso maintaining a blocked pattern of similarly cool weatherÌýfor much of northwestern Europe.

The will loop down southwards east of the Azores, whileÌýa largeÌý grows to dominate east of SpainÌýand yield a low pressure centre across the Western Mediterranean and southern France. This combination will help serve-up some distinctlyÌýinclementÌýweatherÌýacross parts of the NW Mediterranean - including Catalunya andÌýthe Balearics - especially between now and midweek.Ìý

By Friday, the core remnants of the vortex will feed a small-scale low pressure centre eastwards out of southern Biscay - with a lot of moisture entrained in it -Ìýand across northern Spain, offering some spells of rain and showers into the Pyrenees and Catalunya during the late afternoon and eveningÌýbut unlikely to arrive while the practice sessions are underway. It'll be rather cool. Indeed into theÌýweekend of track action, ambient temperatures are unlikely to top 17 to 21C.

The Met Office's Global Model, above, shows an Atlantic depression centred just west of PortugalÌýduring Sunday.ÌýThroughout the day, it will migrate eastwards across northern Spain, bringingÌýthe potential for outbreaks of rainÌýinto Barcelona and environsÌýduring the afternoon - but will its arrival coincide with the race itself?

Into the weekend, aÌýslack southerly feedÌýof warmer, moisterÌýairÌýwill tend to flow up across the Catalan Sea and Costa Brava, whilstÌýcooler airÌýremainsÌýaloft over northern Spain. By Saturday,Ìýthe previously all-dominantÌýsurface low (and upper vortex)Ìýover Western Europe will beÌýcirculating above southern Bay of Biscay and withdrawingÌýas a much weakerÌýbut still influential entity, with some troughs arcing away east from it to provide a chance of some showers into Catalunya. TheseÌýwill obviously prove a hit-and-miss affair and couldÌýhave a small probabilityÌýbearingÌýon the qualifying session. On statistical balance however, it's likely to remain dry.

But the key change then comesÌýinto Sunday. By then, theÌýjetstream - now positioned further north into the Bay of BiscayÌý-Ìýensures mobility in the Iberian weather is resumed from the West. It will steer anÌýarea of low pressureÌýin off the Atlantic, across Portugal and mainland Spain. It'll then track eastwards / east-northeastwards,ÌýbringingÌýwet weather to much of Iberia in the process. A ratherÌýcloudy warm sectorÌýwill sit above Barcelona by race start, which is likely to be dry. Later in the afternoon, troughs willÌýpep-up the shower threat ahead ofÌýan advancingÌýcoldÌýfront. However, most of theseÌýwill affect areas slightly further north and west. So a reasonable chance of a dry race start, with a threat of light to moderate showers and rainÌýappearing later, seems the most probable outcome.

It'll be another radar-watching story if you want to keep up with the minute-by-minute weather prospects... the , with an alternative . Take your pick!

More willÌýfollow in my further updates...