confused about weather conditions

[russell]

So I look at the weather forecast for Tuesday on Monday. It doesn't look good lows of -2C. So I fleece everything up last night.

I look again this morning and it's now showing lows of +5C for tonight. I know the answer but just need it confirming - how likely is the weather to change in the next 20 hours or so?

We live in S Yorks.

Thanks

[snuffer]

Frost

Understanding frost and its formation isn't as easy as you'd think. I always thought temperatures needed to drop to freezing or below but this isn't the case. Ice crystals can start forming at temperatures well above freezing point. Somewhere nearer 4 degrees I think. It's all do do with the differance in temperature between what the frost forms on (our veg) and the surrounding air.

Lowest temperature here during the night was 3 degrees, (not 'The Three Degrees'), but we awoke to a good covering of frost. Fortunately plenty of fleece on standby but not enough to protect everything. Seem to have gotten away with it though.

[zazen999]

Ice crystals can form at 4 degrees ambient temperature or falling [i used to call a halt to laying the cement base for blacktop for roads when it hit 3 degrees - when I was in that game].

Oh the joy of telling 5 burly beefy blacktoppers to stop work for the day [stop work = earn less that week] - how popular was I???

[P.s. when I was on holiday they didn't stop laying the base under 3 degrees, and had to dig it all back up again when I got back as it all broke up underneath - har de har]

I'm over it all now - but back to the veg issue.

There's no way of knowing what the weather will actually do - I had to get a cardi on during the night - but my toms/courgettes seem fine this morning.

If in doubt, I'd check early evening and fly out there with protection if it looks and feels cold and if the weatherbob agrees.

[bazzaboy]

Fascinating.... I'm a few miles north of you, Snuffer (and a few miles south of Russell) - it was 2C here at 1 a.m. but no white frost this morning. Sounds as if you might be the person to explain (as also asked on another thread) the difference between "air frost", "ground frost" and a new one "grass frost" (which I assume technically means a bit more than frost on the grass ). RustyLady explained how misting can save apple blossom, is that technique used/available for veg? - probably not economic but (heresy) GYO isn't necessarily economic.... To address Russell's initial question, yes, the general trend on the BBC forecasts is for night temperatures to get a bit milder this week, last night was the coldest they're predicting for this week. Longer term records do show that frosts have been experienced in these parts as late as mid June but of course exceptions rather than the rule. Impossible to predict, yous pays your money and takes your choice... bb.

[blue411]

I had the same problem, weather said could be as low as -1, so i fleeced everything in sight! get up next morning and not a speck of frost to be seen! but i have kept all my fleece on everything just in case, as this week doesnt seem to have made its mind up on whether it wants to be freezing or mild!!!

[T-lady]

And is it the frost on the vegetables that damages them? As in, I'm hoping it has worked but does just covering them with fleece let them cope with a sudden temperature drop to 2 degrees.

I've got climbing beans, potatoes and tomatoes in the garden that got voered last night but it was darned cold. Will they be ok?

[SlugLobber]

It's the expansion of water as ice crystals which damages them, so if there is no visible frost I would think you're ok, but I am not an expert by any means (just a Biochemist!). The expansion disrupts the cell walls and tears membranes. No frost round here, but I'm glad my new boiler was installed ready for the sudden temperature drop!!