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Weather Talk
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WARMER AIR TRYING TO GET INTO SCOTTISH AIR SPACE, COLD AIR ABOVE, MAKING FOR NICE CLOUD FORMATIONS AND TORRENTIAL DOWNPOURS!
Despite a continued unsettled pattern with heavy showers one minute and sunshine and warmth the next, I am seeing what's going on up there by simply looking at the sky and what it's telling me, how so? Notice those clouds, their appearance, without feeling the air, their a good indicator that warmth is at the low levels... just feel it in the air. No it's not all that warm but it's certainly not cold, there's also a stickiness to the air also, even when it's cloudy, that's telling me it's coming up from the sub-tropics... that means warmer Atlantic air is coming from the southwest, not west, then look at the sky and see those towering clouds and their "dark underbelly". The good large-scale clear, sunny skies have embedded within them, large clouds and these clouds are coming from the northwest. What does that mean? Whilst surface air is coming up from a southwest direction bringing warmth and moisture (adding humidity and the sticky feeling), colder air is riding over top of the warm low-level air from a northwest direction. By Bringing these two air masses together, sliding one under or over the other you've got the ingredients in which to produce cloud formation, warmth and heavy downpours. In order for these clouds to build or rise vertically from the warm low to mid-levels into the much colder upper levels, they must rise, what will force it to rise? Surface warmth! As the sun heats the ground, this ignites the "thermals" or rising columns of air, the colder to upper levels and the warmer the low levels, the faster the air will excellerate vertically. The clouds are already there and fully formed as stratus, but these clouds then transition into what is close to becoming the classic thunderstorm cloud, the "Cumulonimbus". As the warm air is heated by the sun, bouyancy is created and with the clouds already in place, they simply build vertically, rise into the colder upper levels, as they climb, they grow, cool further and condense, producing more water droplets, eventually they rise to a point, building their droplets ever bigger until their too heavy to be supported or suspended in the air, once at that level and height of saturation, they, they then fall to the earth bringing pockets of torrential rains which create big hazrads to road users, lowering visability extremely fast.. What's stopping these towering clouds from becoming thunder and lightening producers is that they don't have enough surface heat to generate the sufficient motion in the atmosphere.
If we were seeing temps push into the mid to upper 70s or warmer, then these clouds would rise even higher bringing the right ingredients for positive and negative charging of the cloud from bottom to top, the updrafts would be stronger allowing a charging up of the cloud with downward and upward air flow, ultimately electrically charging the cloud this would happen more in Scotland if we had more heat. Stronger thermals and updrafts move the molecules faster and as they collide and rube together, tiny little ice crystals grow as they rise by collecting moisture, once heavy enough they begin falling downwards back through the cloud they climbed into at the start of their life cycle, as you descend down through the cloud, thy collide with rising water droplets and ice crystals, thus creating an electrical charge, eventually, a build-up of negative charge is accumulated at the bottom of the cloud and positive at the top, like a giant battery in the sky is created, eventually a spark is created and lightening is formed... the lightening bolt rips through the sky to neautralise the opposing charge, with this lightening bolt, comes a rumble of thunder, the shockwave the the lightening creates....
Thunderstorms are relatively rare in Scotland thanks to several factors.
Our northerly latitude means cold air masses are easier to tap than hot ones. We also are on a small island, surrounded by cool waters. Those cool waters moderate warm air masses as they travel over the UK land mass, meaning there is a limited amount of heat that can be accumulated at the surface, therefore meaning a limited intensity of upwards motion can be created... The past few days and even weeks are a great example of this, though we've been under a trough much of the summer, we have seen sunny periods and warmth (mid 60s to low 70s) thanks to two things... (1) sunshine in August is strong and heats the ground easily, (2) the air is cold aloft.. if there was stronger surface warmth, these half hearted stratus clouds would become fully fledged thunderstorm clouds but the limuted warming of the surface means they stop half way through the process, meaning all we see from these towers of the sky are eye-catching clouds and these passing overgead bringing downpours... nothing more. England being that little bit further south sees more thunderstorms thanks to warmer temperatures. We would be much hotetr in summer, even at this high latitude, if we didn't sit underneath the prevailing westerly flow and sitting right on the doorstep of the Atlantic, means milder, oceanic air masses visit more than hot, high pressure cells that migrate north during the Northern Hemisphere summer. Remember we do live close to due north of the Sahara, however these air masses need to travel over both the Med Sea as well as over the England Channel, two bodies of water that can take the heat out of the air mass itself. This is wahy central Europe, though can get hot, doesn't match those numbers seen on the Sahara.. The Med modifies and humidifies the air whilst travelling from Africa to Europe. Also it's departing it's point of origin, therefore loosing some intensity.
Though there's pleasant conditions at the surface it's be no means warm or hot, merely comportably pleasant, in fact, the clouds seen across Scotland and the rest of the UK's airspace of late is indicative to a very cold upper atmosphere associated with the trough, not so much the warmth at the surface.
During my drive in my truck between Bathgate, West Lothian and Aberdeen, I've enjoyed seeing the towering clouds and have ran into some torrential rains at times, whilst the sun is out, it feels wonderful and pretty warm. The past couple of days, it's been very nice with the best of the sunshine and pleasant weather more so between Dundee and Aberdeen with today (Friday) being a particularly nice and sunny day with truck temperatures registering between 22-24C or 72-75 degrees under mostly sunny skies, this was at the same time my wife was texting me to say it was raining, cloudy and sticky back here at my house in Lennoxtown, East Dumbartonshire.
Vagaries of the Weather
India & Sub-Continental Asia Weather
By Rajesh Kapadia
Friday, August 20, 2010
Its been a day of mixed re-actions. weather-in-Mumbai wise.
Started of with the potential of good, heavy rains, with a big cloud mass forming overnite, and threatening the city with torrential rains. The satellite images put up, in the morning were indicative enough.
Then, during the day, it was yes and no.
Yes in South and Central Mumbai. Heavy, very heavy, rains lashed Central Mumbai right thru noon to evening hours. Flooding was the scene !
Colaba saw 55 mms till evening, while it was more in Central areas.
On the other hand, for some unanswerable reason, suburbs in the North had hardly any rains ! S'cruz recorded just 9 mms in the same period ! 9 mms, when conditions were very favourable for it to pour, and with dark overcast skies all day.( Maybe wanted to hold on to "vagaries" original forecast of yesterday -:)
No. I do not understand the differentiating. In fact, Colaba has been favoured throughout this season :)
I see the rains easing out in South Mumbai,(will have to bifurcate North n South now), and surely lessening, and back to heavy shorter duration showers, with around 15 mms of rain on Saturday, and sunny intervals with 15-20 mms on Sunday.Monday forecast will be put up tomorrow night.
As long as the trough along the west coast holds on, the possibility of vortice formations are always there. The trough has now shrunk, and runs from Karnataka to South Gujarat coast.
Now, there is a distinct possibility of a low forming in the bay, by the 23rd.
Forming at 100 mb,may go deep to 998 mb, before crossing the A.P. coast around the 26th. This is as per the NGP forecast model. (Which I feel may hold good).
ECMWRF estimates no system at all for around this date!
There is a dim possibility, maybe 20% chance, for this new low to move Northwards instead, and cross straight into North Orissa coast.I say this,as the time of approaching the East coast, there is a strongish W.D. approaching, which may alter the track of the system.
Rain and track, will discuss as the low forms.
Rains have also eased off along the T.N. coast, with chances of a push again from the 24th.
By the way, Delhi recieved its heavy rains (forecasted in "vagaries"), with almost 200 mms in 2 days. Thats quite a lot, what with Parliament House roof leaking !
The axis has moved North, and estimates of very heavy rains in U.P. and Nepal holds good for the next 2/3 days.
What's Reaching Today's Blogs?
Weekend Update
Valley Weather Blog (Montreal, Quebec)
An unusually cool summer continues over California; long-term prospects interesting
California Weather Blog
Today's US Extremes
Courtesy of AccuWeather
High: 115 degrees at Death Valley, CA
Low: 27 degrees at Bodie State Park, CA
Today's UK Extremes
Courtesy of the Met Office
High: 72 degrees at Coningsby
Low: 35 degrees at Braemar
Today's Extremes here at my house
High: 67 degrees
Low: 55 degrees
Thanks for reading.
-Mark
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