Penellype's Weather Channel

[sandspider]

Had our first butterfly in the house for a couple of weeks now, but I fear he's dead - woke up too early.

Did see a first big bumble bee pottering on the lawn yesterday though.

[Penellype]

It's s very unusual for us to get strong winds from southeast here in west Cornwall.

Yes, its a somewhat unusual pattern with a high forming over Scandinavia dragging the wind into the easterly quarter, but also a ridge from the Azores high to the south west. In between (which is where Cornwall is). low pressure is being squeezed southwards towards Spain and the isobars are therefore pushed closer together.

[sandspider]

There are a couple of free courses at futurelearn on understanding the weather if anyone's interested. E.g. https://www.futurelearn.com/courses/learn-about-weather

[Penellype]

Please be aware that it is looking increasingly likely that there will be a cold snap at the end of March into the beginning of April - possibly colder than we have seen over the winter.



There is pretty good agreement for quite cold upper air temperatures as the wind turns into the north. This is easily cold enough for snow if there is any precipitation and nights could be really very cold if skies are clear.

The coldest spell looks to last about 2-3 days at the moment, but we remain below average for some time afterwards. It is too soon to say when it will warm up, but towards the end of the ensembles low pressure could move in again, shown by the up and down temperatures and increasing precipitation spikes.

[quanglewangle]

^^Useful heads up

[Mr H]

Just been out to the plot. Took my chitted spuds up to the shed until I can get them in the ground.

Temperature at 6am was -2c. Lovely and white on the ground.

Just hope peas are hardy

[Penellype]

Peas are pretty hardy - they will grow more slowly in cold weather but should be fine.

[Chippy Minton]

Please be aware that it is looking increasingly likely that there will be a cold snap at the end of March into the beginning of April - possibly colder than we have seen over the winter.

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There is pretty good agreement for quite cold upper air temperatures as the wind turns into the north. This is easily cold enough for snow if there is any precipitation and nights could be really very cold if skies are clear.

The coldest spell looks to last about 2-3 days at the moment, but we remain below average for some time afterwards. It is too soon to say when it will warm up, but towards the end of the ensembles low pressure could move in again, shown by the up and down temperatures and increasing precipitation spikes.

Hi Penellype, how are the models looking now? Just watching the local weather and they're talking of a dip in temperature over the weekend but then a slight rise. Still doing the hardening off hokey cokey.

[Chippy Minton]

There are a couple of free courses at futurelearn on understanding the weather if anyone's interested. E.g. https://www.futurelearn.com/courses/learn-about-weather

Saw this yesterday for anyone with spare time at the minute

https://www.zooniverse.org/projects/...escue/classify

[Penellype]

Hi Penellype, how are the models looking now? Just watching the local weather and they're talking of a dip in temperature over the weekend but then a slight rise. Still doing the hardening off hokey cokey.

Still on course for a cold snap over the weekend, with the -10 isotherm making inroads into parts of the country. Pressure is high so there is unlikely to be any snow except possibly a few showers blowing in from the east. The coldest weather will last a couple of days before it gets somewhat less cold, but it will still be well below normal. Things become very uncertain after about 2nd April, with huge differences between ensemble members and model runs:

[Penellype]

Just to reinforce the uncertainty about what happens in the medium term, compare the position of the thick green line (highest resolution of these members) on the graph from the midday run (below) with that in the 6am run (previous post) for 6th April! The 6am run is very cold, the midday run is rather warm.

[Chippy Minton]

Just to reinforce the uncertainty about what happens in the medium term, compare the position of the thick green line (highest resolution of these members) on the graph from the midday run (below) with that in the 6am run (previous post) for 6th April! The 6am run is very cold, the midday run is rather warm.

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I'd like to order the midday run please, home delivery of course!

It is interesting though how divergent that is from the others (and the ensemble average)

[Penellype]

I'd like to order the midday run please, home delivery of course!

It is interesting though how divergent that is from the others (and the ensemble average)

This is one of those occasions where the average tells you absolutely nothing. If you look carefully at the lines you will see that although many of them cross the average from time to time, there are none that even vaguely follow it. There are at least 3 potential scenarios here - high pressure and warm (like the thick green line on the midday run), high pressure and cold (like the thick blue line) and low pressure, which would result in the up and down lines of many of the ensemble members.

As for which is right, we will have to wait and see, but a 2nd cold spell, potentially with snow and lasting longer than the current one cannot be ruled out. This morning's runs show more members going down the low pressure route with only about 5 or 6 going cold, but very few staying warm.

[quanglewangle]

No contrails - more sun

Down here near Land's End we are under one of main transatlantic air corridors. Usually the sky is crisscrossed with contrails (or vapor trails, depending on your upbringing) from high flying aircraft. Inbound in the morning and outbound after lunch.

Now there are none.

They are like bands of cirrus clouds and they have gone. NOAA in the US have done measurements over the years and found that these artificial clouds do block sunlight to some extent.

So, more sun - maybe?

[Penellype]

Down here near Land's End we are under one of main transatlantic air corridors. Usually the sky is crisscrossed with contrails (or vapor trails, depending on your upbringing) from high flying aircraft. Inbound in the morning and outbound after lunch.

Now there are none.

They are like bands of cirrus clouds and they have gone. NOAA in the US have done measurements over the years and found that these artificial clouds do block sunlight to some extent.

So, more sun - maybe?

Contrails form as a result of tiny particles in the exhaust from the aircraft. Water vapour in the air, which is supercooled at that altitude, requires a nucleus to condense around to form water or ice, and these tiny particles provide that nucleus. How long the contrails remain visible depends on how dry the air is - in a high pressure system like we have had this week the air is very dry. Therefore the lack of aircraft may not have made much difference to cloud cover. In damper air the contrails can thicken as more and more supercooled water condenses on them. This is often the first sign of an approaching front and can happen a day or so before the frontal rain arrives.