Major Atantic Low due to hit British Isles on Monday 8th Nov

Graham64 · **Posted:** Mon Nov 08, 2010 12:21 am

Here in north Cornwall the pressure change is currently -4.39 mb/hr.

The wind is rising, temperature dropping and rain falling - I am going to bed!

Graham

sjukmidlands · **Posted:** Mon Nov 08, 2010 2:57 am

Ok... my weather station is recording the pressure dropping at a fairly steady 3.00Mb / hour, it's just broken its previous record low back in March

geoffw · **Posted:** Mon Nov 08, 2010 7:47 am

Looks like pressure is levelling off at 969.4mb here (a record since May 2009), though the wind was not as fierce as one might have expected with the highest gust only touch F7

steve · **Posted:** Mon Nov 08, 2010 8:50 am

RayProudfoot wrote:

Do we have a webtag for maximum pressure change/hr?

Not currently, because all Cumulus does with the pressure change value is display the current value, it doesn't record or track it anywhere.

steve · **Posted:** Mon Nov 08, 2010 8:56 am

Ned wrote:

What are the transition values some people are using to describe pressure change rates in their banners, from slow to moderate to rapid to very rapid? Are they the same as Cumulus uses, whatever they are?

Cumulus uses the UK Met Office terminology:

Rising (or falling) slowly
Pressure change of 0.1 to 1.5 hPa in the preceding three hours
Rising (or falling)
Pressure change of 1.6 to 3.5 hPa in the preceding three hours
Rising (or falling) quickly
Pressure change of 3.6 to 6.0 hPa in the preceding three hours
Rising (or falling) v. rapidly
Pressure change of more than 6.0 hPa in the preceding three hours

Davis users have the option of using the terms provided by the station instead.

M1DUL · **Posted:** Mon Nov 08, 2010 9:06 am

Hi all,
mine has beaten the last record of Lowest Pressure (sl) of 967.9 hPa at 03:06 on 23rd January 2009, to now of 967.3 at 8:48 8th of November 2010.

The pressure has gone up a bit since then to 967.5.

nking · **Posted:** Mon Nov 08, 2010 9:08 am

geoffw wrote:

Looks like pressure is levelling off at 969.4mb here (a record since May 2009), though the wind was not as fierce as one might have expected with the highest gust only touch F7

I think you will see the pressure fall as low as 963 later today (PM) as the eye passes over you. We have another low brewing over the Atlantic for the later part of the week - overall a very unsettled week ahead.

RayProudfoot · **Posted:** Mon Nov 08, 2010 9:14 am

My All-Time low pressure record has been well and truly smashed. Previous low was 978.9. It now stands at 969.6 and is still dropping.

Highest gust overnight was 33mph at 03:40. I suspect that will go higher.

RayProudfoot · **Posted:** Mon Nov 08, 2010 9:15 am

steve wrote:

RayProudfoot wrote:

Do we have a webtag for maximum pressure change/hr?

Not currently, because all Cumulus does with the pressure change value is display the current value, it doesn't record or track it anywhere.

Thanks Steve.

Gina · **Posted:** Mon Nov 08, 2010 9:42 am

Well, the BIG STORM went through in the early hours though not as bad as predicted here. Heaviest winds were Force 6 gusting 7 occasionally. Much worse out to sea apparently though. We did have torrential rain for a couple of hours. Started around 11pm last night, building up to a peak between 5 and 6 this morning, then stopped. Barometric pressure went down to just under 970mb - just above the predicted low of 964mb.

This morning is fine with sunny spells and some cloud. A lot milder than yesterday at 8C and rising. Just a light NW breeze now.

Regarding converting pressure trend to string, here's the code I'm using :-

Code:

def pressure_trend_text(trend):
    """Convert pressure trend to a string, see
    http://www.reedsonline.com/weather/weather-terms.htm."""
    if trend > 6.0:
        return _('rising very rapidly')
    elif trend > 3.5:
        return _('rising quickly')
    elif trend > 1.5:
        return _('rising')
    elif trend >= 0.1:
        return _('rising slowly')
    elif [b]trend < -6.0[/b]:
        return _([b]'falling very rapidly'[/b])
    elif trend < -3.5:
        return _('falling quickly')
    elif trend < -1.5:
        return _('falling')
    elif trend <= -0.1:
        return _('falling slowly')
    return _('steady')

This uses the same break points as Cumulus and the British MET office.

So, with a reading of 'falling very rapidly' the pressure was falling at more than 6mb/hr!

Ned · **Posted:** Mon Nov 08, 2010 10:34 am

Thanks Steve and Gina for the data.
I've divided the values quoted by 3 to get hourly change rates, which I presume is how it's being sent in realtime.txt, and assume is the same as that showing on the main Cumulus page - tell me if I'm wrong

Then the bit of code I've added to banner.php is looking like this (strings abbreviated for want of room):

// Pressure trend string generation
$barotrend = "steady";
if (ret_value("presstrend") > 0.1 ) {
$barotrend = "slow rise";}
if (ret_value("presstrend") > 0.5 ) {
$barotrend = "rising";}
if (ret_value("presstrend") > 1.2 ) {
$barotrend = "rapid rise";}
if (ret_value("presstrend") > 2 ) {
$barotrend = "v.rapid rise";}

if (ret_value("presstrend") < -.1 ) {
$barotrend = "slow fall";}
if (ret_value("presstrend") < -0.5 ) {
$barotrend = "falling";}
if (ret_value("presstrend") < -1.2 ) {
$barotrend = "rapid fall";}
if (ret_value("presstrend") < -2 ) {
$barotrend = "v.rapid fall";}

($barotrend gets called a bit further down in the code to display)

It's working OK, but I've only experienced 3 different states here so far.
Now wondering if there should be an 'extreme' string for the changes you guys have just experienced, say for 3 or 4mb/hr and over :shock:

cheers!

steve · **Posted:** Mon Nov 08, 2010 10:54 am

Ned wrote:

I've divided the values quoted by 3 to get hourly change rates, which I presume is how it's being sent in realtime.txt, and assume is the same as that showing on the main Cumulus page

That's right. Cumulus basically takes the change over the preceding three hours and divides that by 3 to give a 'per hour' figure. In Cumulus I use the original 'three hour' figure to compare against the figures I've quoted. You're just doing it the other way round, with the same result.

Quote:

Now wondering if there should be an 'extreme' string for the changes you guys have just experienced, say for 3 or 4mb/hr and over :shock:

cheers!

Perhaps in places where rapid pressure changes occur more often, e.g. in Tropical Storm and Hurricane areas, they have alternative descriptions with greater scope.

RayProudfoot · **Posted:** Mon Nov 08, 2010 2:29 pm

Pressure has started to rise after bottoming out at 967.0Hpa. Now heading over to post my new all-time low pressure in this thread.

Looks like my high wind gust record is safer for a little longer.

geoffw · **Posted:** Mon Nov 08, 2010 3:25 pm

I'm down to 964.1 and STILL falling!

M1DUL · **Posted:** Mon Nov 08, 2010 3:26 pm

Pressure is still falling slowly Now at -0.3 hPa/hr
heading over to post my new all time low pressure in this thread.

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Major Atantic Low due to hit British Isles on Monday 8th Nov

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