Frost this weekend!!!

[Jennysheepdog]

Oh Lordy

I think I must be doing this wrong

I have had my spuds in for a month. Early ones and then main crop. All growing

Oooopps

[fishpond]

I have just transferred two Courgettes from the G/H to the garden as they were getting too big.
Double Oooopps
Still got 2 left in there though.

[Penellype]

The problem is that the models are not handling the current situation very well. A cold front (blue) is hovering just north of Scotland and is forecast to move south during the next few days - behind it is MUCH colder air:



(Map from metoffice.gov.uk)

The question is, how far south is this cold front actually going to go. Early forecasts were for it to completely clear the country, leaving us all in the cold air mass. However, things are rather less clear now. This is the forecast of upper air temperature (top) and rain (bottom) from 20 different runs of the GFS model for Manchester at midday today:



(Picture from http://www.wetterzentrale.de/pics/MT...hester_ens.png).

Basically the closer together the coloured lines are, the more certain the forecast. The temperatures are at 850mb, which is about 5,000 ft, so surface temperatures are rather warmer. The red line is the 30 year average and the white line is the average of all of the 20 runs. The steep temperature drop and high rainfall peak mark the time of the cold front. You can see that by 2nd May there is considerable disagreement, with a couple of the runs even staying above the red line implying that the cold front won't have reached as far south as Manchester, while some of the colder runs would imply well below average temperatures for much of the first half of May. Extremes like the pale blue line at the bottom are "outliers" which can probably safely be ignored, but plenty of runs make it quite cold enough for frost on friday night.

These charts change radically with every run, 4 times a day. Only a day or 2 ago the white line was below the red for the whole of the first week in May, and this latest chart is the warmest yet. The wide scatter of lines shows a high degree of uncertainty, much higher than is usually the case at the 4-5 day range.

Similar charts are available for London and Aberdeen by replacing "Manchester" in the url.

[AllInContainers]

Aside from the vagaries of the weather, I'm concerned about causing damage by putting on and removing the fleece.

Were my plants still dormant - not an issue, but with young leaves and shoots, and delicate blossom (whether or not it's pollinated), the thought of wrapping things up in fleece concerns me. Dragging the fleece on and off, and a breeze tugging at the fleece when it's on, increasing the force of the wind like a kite ... I think I'll take my chances with the cold. I reckon a few hours of cold might actually do less damage than I would trying to keep that cold out

[Bill HH]

And now they are forecasting a heat wave for the weekend!!!

[Martin H]

Nice graphs, great explanation, thanks Penellype. I can see why weather forecasts are rubbish outside of 3 days and why the extra computer power they've lavished on the problem haven't improved things much. If they did 2000 simulations instead of 20 we'd still be none the wiser!

I pulled out the London one, doesn't diverge quite as quickly as for Manchester but still pretty wild from 2nd May:

[AllInContainers]

And now they are forecasting a heat wave for the weekend!!!

Maybe I ought to fleece them up after all then, based on their recent accuracy ...

[MrsCordial]

AiC I think the same. I've asked on the Newbies board about bubble-wrapping the tiny carrot leaves that are just poking through, but I dread to think what a bubble wrap blanket could do to the delicate little things. Hard call, isn't it?

[RaptorUK]

BBC and MetCheck both say there will be no frost for me this weekend, MetCheck were saying it was going to be -2C on Sunday morning but now says it will be +3C.

Will keep an eye on it, and make a decision 12 - 24 hrs before.

[Kristen]

I wouldn't be too worried about this 'cold snap'. Some reassurance from the met office...

I don't know where you are in the country, but its a risky approaching assuming that the plants will be fine based on a forecast several days out ... although you may be down South somewhere warm? (Pls put your Location in your Profile)

BBC and MetCheck both say there will be no frost for me this weekend, MetCheck were saying it was going to be -2C on Sunday morning but now says it will be +3C.

My forecast has warmed by two degrees over the last couple of days - I was getting optimistic that it would keep doing that, but this morning it has gone down a degree with Saturday night now forecast as 2C (although the "range" of possible values is still wide at 0C - 9C, so clearly the models are still all over the place, so might change to anything as yet)

Will keep an eye on it, and make a decision 12 - 24 hrs before.

That's the only way . Bit tough for anyone planning to be "away" this weekend though ...

[snakeshack]

ice in the trays in my garden this morning as I was shuttling plants out to harden off !was thinking about planting out my toms & chillies this weekend into their final pots ,not so sure now

[gardening_gal]

I've just spent the last hour or so, in the pouring rain and windy weather, bringing in as much as I could from my tunnel.

I was originally going to chance it and leave them out covered with bubble wrap, but the weather suddenly turned very cold, wet and windy and this is only Wed afternoon. The forecast for 4am is 4 degrees.

4am the next day is supposed to be 2 degrees although this was stated as '0' earlier on.

Mostly every young plant is in a lidless polystyrene box with bubble wrap over the top and on shelves in the porch, which itself isn't exactly a warm place but is bound to be better than the tunnel. What I couldn't bring in, I covered as best as I could. It was mostly the remaining strawberry plants that were left in the tunnel along with 2 raspberries and a blackberry. They are all off the floor by at least 15 inches and are sat on upturned polystyrene boxes, and then covered.

They are on their own now, they either toughen up or perish.

I hope you all don't have any/many casualties.

I'm off to find my hot water bottle.

[treepixie]

will my onions need covering if there is a frost, they have been in for about 3 weeks

[Kristen]

will my onions need covering if there is a frost, they have been in for about 3 weeks

I ain't going to cover mine

[greenishfing]

It looks as if we're going to get a very cold night here in Yorkshire tomorrow, but that is normal. I'm expecting a few more before the end of May. The things I'll be protecting are my grape vines in the greenhouse which are flowering (I lost all my crop one year) I keep bubble wrap handy for this. My row of early "early" potatoes in the allotment will be covered with fleece as well. Everything else should be fine. Strawberries (perpetual) will get black flowers but they will reflower in time for a June crop and all the toms and peppers are safely at home on the windowsills.