Penellype's Weather Channel

[Thelma Sanders]

1.4C inside mine - thought that was cold enough

[Lumpy]

Woolly knicker time here this morning............................role on May.

[Penellype]

This weekend's chilly snap seems to have moderated somewhat, with the worst of the cold air just to the east of us. It will still be chilly at night, but not as cold as looked likely a couple of days ago.

That's the good news. Monday is now coming into the more reliable 5-day forecast period, and it looks uncomfortably like option 2 in post #199.



High pressure is ridging towards Greenland and a cold front is moving south over the UK with the isobars stretching directly north towards the arctic. This is colder than what we have just had.

By midnight on Wednesday the -5 isotherm at 850mb (as on the ensemble charts) is covering the whole of the UK as well as parts of France and Germany and the -10 isotherm is well into Scotland.



This is cold enough for snow if other conditions are right. This is the corresponding minimum temperature chart for 6am Wednesday:



The other models also see this northerly plunge, although they are not quite as extreme as the GFS. Unlike recent frosty nights when it has been dead calm, there will be a significant breeze at times, leading to considerable wind chill - this really is wintery.

Beyond the middle of next week uncertainty takes over, with large differences in outcomes from one run to the next. This is the current ensemble chart for York:



The unanimous plunge to much colder than average on Monday is clear to see.

So, keep anything that isn't frost hardy indoors until at least next weekend. Make sure you have plenty of fleece - if the current forecasts are correct my potatoes and strawberries will either be moved into the garage over night or covered with both fleece and bubble wrap. Keep an eye on the local forecasts, as the temperatures on these maps tend to be for towns, and it can be rather colder in the countryside. Beware also that there is a significant risk of snow especially in the north and over hills (note the precipitation spikes along the bottom during the cold spell). If you have nets covering plants and snow is forecast it may be wise to take them off or drop them onto the plants so that the supports don't break under the weight.

Let's hope this forecast is OTT, because currently it looks very nasty indeed.

[1Bee]

Thanks, Pene, you're a star.

[Nicos]

Thanks for the warning....much appreciated!

[Bigmallly]

Good work Pene, cheques in't post.....................

[Penellype]

By now everyone is probably aware that temperatures are going to take a plunge tomorrow night. What some people may not realize is that this time things are very different from the frosty nights that we have had so far this spring.

Up to now frosty nights have occurred under high pressure when skies are clear and winds are light. This situation allows for cold air to sink to the ground as the heat radiates into space. The lack of wind means that the air can form layers, with the coldest at the bottom, because there is no air movement to mix things up. The upper air can be quite warm and yet it is still freezing on the surface. This situation is relatively easy to deal with - you cover up plants with fleece etc. and the fleece stays put because there is little or no wind.

Tomorrow night's frost is going to be due to cold upper air temperatures from an air mass originating from the north pole. There is no requirement for clear skies or for light winds in order for temperatures to be freezing, and there is an added hazard - wind chill. Wind chill makes the air feel colder than it actually is due to the moving air causing a reduction in pressure and evaporation of moisture. Evaporation causes cooling so if you stand in the wind it feels colder than if you are sheltered a few feet away.

The problem we have tomorrow night is that a cold front is moving down from the north bringing with it a cold arctic air mass, fairly strong winds and rain or snow. The forecast temperature may be -1, but the temperature your plants will feel if unprotected may be more like -5 or -6. Any coverings of fleece or plastic will need to be weighted down well or they will blow away or partly expose plants. Anything that attempts to make a barrier out of fleece (for example to protect fruit blossom) may act like a sail (especially if it is wet) and damage the plant. I once had a tower pot made up of layers of pots full of soil (not compost) knocked over by a fleece barrier that I put up to protect the strawberries from a cold wind. The planter was far too heavy for me to lift other than in slices, but the whole thing was knocked over by a simple piece of fleece.

My advice as far as I can give it is to put anything vulnerable and moveable either under glass or in a shed or building for tomorrow night. If you cant move it, make sure that any fleece or plastic is well fastened down and can't flap about. Think twice about draping fleece around fruit trees as anything loose may well knock the blossom off.

I haven't decided what to do about my apple tree (in full flower) yet. Its a really tricky one, with the weather playing just about the worst card it can at this time of year as far as gardeners are concerned.

Here is the current ensemble chart for York:



The coming cold spell is very clear, but thankfully once we get towards next weekend the trend is definitely warmer. It may also be wetter, but I'd rather have that than frost, and some of us could do with some rain.

[1Bee]

Thanks Pene.

It was 0.1C on our plot on Sat night, but no colder last night. The forecast was dry for early this morning, but we had heavy rain instead... interesting to see how the next few days play out.

[Penellype]

The current air stream is very unstable and showery. Not everyone will get showers, and my forecast for today was also dry but we have had several light showers so far.

Over the next few days expect anything - sun, wind, thunder, lightning, rain, hail, sleet, snow and frost are all on the menu - just about everything you can think of except fog!

Oh, and the models are starting to forecast something a bit like a mini heatwave next week...

We will see.

[Bigmallly]

It's bladdy April, where's the flippin' rain?........................My butts are empty...........

[1Bee]

I'm uncomfortable with talk of your butt, Bigmal...

It's currently hailing!

[Pants]

What do I need to fleece?

I am very much a novice gardener, but loving it. With the cold evening weather coming, I have put fleece over my strawberrys and potatoes.

What else needs covering, I currently have:
Peas
Garlic
Onions
Leeks
Raspberrys
Blueberry

Will they survive a frost?

[Penellype]

Leeks wouldn't mind a fleece - getting too cold can cause them to bolt early. The rest should be ok - I haven't covered my blueberries and I'm hoping they will eb ok as they are flowering. They survived the frost this time last year.

[Penellype]

It's bladdy April, where's the flippin' rain?........................My butts are empty...........

Bit of rain possible BM - note the rainfall spikes along the bottom of the chart:



Much of it could be showers though, so a bit hit and miss.

Notice also that it is looking warmer, possibly much warmer after the next few days.

[Potstubsdustbins]

Thanks Pen, the dustbin lids are on and the fleeces weighed down with lumps of timber thanks to your advice.