Penellype's Weather Channel

[Scoot]

About time we had a bit of nice weather. Hello spring.

[muck lover]

Penellype looking at your ensemble chart nothing at all is clear to me. However I am happy to bow to your expertise if it’s going to warm up a bit.
This afternoon it got apocalyptically dark. There was lightening and it started chucking down hailstones followed by driving icy rain. Not gentle rain from heaven dropping on the earth beneath as one would expect in April. I’m really looking forward to some warmth even if there isn’t much sunshine.

[Penellype]

Penellype looking at your ensemble chart nothing at all is clear to me. However I am happy to bow to your expertise if it’s going to warm up a bit.
This afternoon it got apocalyptically dark. There was lightening and it started chucking down hailstones followed by driving icy rain. Not gentle rain from heaven dropping on the earth beneath as one would expect in April. I’m really looking forward to some warmth even if there isn’t much sunshine.

Perhaps I should explain what the ensemble chart means. There are 22 different members of the same model, all run at the same time from very slightly different starting conditions (within experimental error). These are represented on the chart by 22 different coloured lines - the 20 colours on the left plus the thick green line (operational run, highest resolution) and the thick blue line (control run, 2nd highest resolution). In general you would expect the operational and control runs to be the most accurate. The average of all 22 members is shown in white.

The upper lines are the temperature at 850hpa, that's approx 5000 ft up in the atmosphere. The red line is the 30 year average temperature for this time of year. These temperature charts show the upper air temperature, which helps to determine the temperature at ground level, but more clearly show changes due to different air masses as day and night variation is much smaller up there. Basically a sharp change in the 850hpa temperature means a change of air mass, usually involving a front (= rain). Air masses are very important in determining the weather and temperature at the surface - those originating from the pole are cold, those coming from the tropics are warm, others are in between. Basically if the white line is above the red line there is a good chance of warmer than average temperatures, if it is below the red line it is likely to be colder than average for the time of year.

The lower lines at the bottom are the precipitation forecasts (rainfall or snowfall). The higher the spikes the more intense the rain. You can see towards the left of the chart in the above post that there was a sharp rise in 850hpa temperature forecast for yesterday, coinciding with a big rainfall spike. This corresponded to the warm front which moved up from the south yesterday bringing large amounts of rain (snow in places at first) and replacing a cold air mass with a much warmer one.

With regard to today's showers, these are typical convective April showers, which can be very heavy with hail and thunder. These are caused by unstable air (typically associated with low pressure systems) with fairly cold upper air temperatures and surface heating from increasingly strong spring sunshine. The wet ground also helps as the sun evaporates the water, which then condenses into clouds higher up. These clouds can form really quite quickly, seemingly out of nowhere, and can be very tall, resulting in big updraughts and conditions suitable for forming hail stones and lightning. The bigger the temperature gradient the taller the clouds and the heavier the rain. Expect showers like these to form from late morning onwards, and die away as the sun goes down, unless they are associated with a front or convergence zone.

[Potstubsdustbins]

Thanks for that explanation Pen.

Would you be disappointed if I said after the first five lines I gave up and am happy to bow to your expertise......

[muck lover]

I think I need to lie down.

[Penellype]

Sorry, its really difficult to explain it in words that are easy to understand, but once you understand it its much easier to see what the charts mean. I find it all fascinating...

[Greenleaves]

I don't need to understand, I take you at your word Penellype

[Bacchus]

Is there a really good site that has a 5 day, minimum temperature, locally based, forecast available. That would be quite useful I think. Something that will let me guage when it's safe to leave the tomato plants overnight in the polytunnel.

[KevinM67]

Is there a really good site that has a 5 day, minimum temperature, locally based, forecast available. That would be quite useful I think. Something that will let me guage when it's safe to leave the tomato plants overnight in the polytunnel.

I just use the BBC one. Just put in your location and it gives you 14 day forecast with expected min/max temps.

We've got quite a sharp frost tonight - however, after that it's looking good (I might put the onions in the ground at the weekend.
https://www.bbc.com/weather/0/6296697

[Penellype]

I use https://www.windfinder.com - you can find your nearest forecast station and see the forecast for 10 days or a more detailed 3 day one, for example https://www.windfinder.com/forecast/york_river-ouse. I also like to check the Arpege model https://www.theweatheroutlook.com/twodata/arpege.aspx? as this has a higher resolution than the GFS which most weather apps and sites use.

[Penellype]

Sharp frost expected tonight especially in the west - bring in or cover up anything that isn't hardy.

[1Bee]

Rushed happily to windfinder.... and our plot is in the middle of a big gap on the map. *eyeroll* Actually I have no idea what I'm looking at on that site... :-/ Which is definitely a problem with me, not the site!

[Penellype]

Rushed happily to windfinder.... and our plot is in the middle of a big gap on the map. *eyeroll* Actually I have no idea what I'm looking at on that site... :-/ Which is definitely a problem with me, not the site!

If you type in a large town near you you should find that places with weather stations appear on the map as spots that you can click on - click the nearest one to you and click through to forecast. for example this is the forecast for Carlisle https://www.windfinder.com/forecast/carlisle. Then for the more detailed forecast click on Superforecast at the top.

You are unlikely to get a forecast for exactly where you are - I am mid way between York River Ouse and Linton On Ouse, but I choose York because Linton is rather more rural than I am.

[1Bee]

It's snowing... ��

Yeah, we're in the edge of the coastal plain and pretty much everywhere round here has its own localised weather from coastal influence, fell influence, altitude, shelter... It's common to drive ten miles and get snow, rain and sunshine without really trying.

[Penellype]

To be fair the Carlisle forecast on Windfinder does say snow for this evening as the cold air moves back in briefly on the back edge of the low. After a chilly but much brighter day tomorrow things should warm up a bit for the weekend.