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damianslaw

First air frost watch season 2015-2016

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I've started one of these threads past couple of years, they often get forgotton about come mid Oct as people's attentions turn to winter proper, but anyway its apt time I start this season's thread, especially given the immediate outlook promises some chilly nights for the time of year under high pressure.

 

I'm not sure of mins last night, did anywhere in Scotland go down to 0 degrees?

 

Anyhow please use this thread to post speculations, and reports of your first air frost of the season. Air frost isn't the same as a ground frost, it require an air temp of 0 degrees being recorded at some point.. not at the ground which can easily occur with air temps of around 2-4 degrees under the right set up, usually when there is dry air aloft and low dewpoints.

 

Here we tend to record our first air frost by around the 2nd week of October, and its rare to have to wait until November before such one occurs. Under cloudless skies, light winds and polar air we can see air frost by late Sept, 23rd Sept 2012 was a good example from memory or was it 2013.. have to check. Ground frosts can occur as early as now under synoptics like we have now, but more likely come late September.

 

I think we got down to about 3 degrees last night, notably chilly for early September.

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A couple of sites in northern England got down to 1c last night, can't find anything at or below zero.

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according to wx online the air mins were 1C, see below

Stations: 176 Temp. Shap (249 m) 1.0 °C Benson (57 m) 1.0 °C Aonach Mòr (1130 m) 1.0 °C Cairngorms (1245 m) 1.0 °

 with grass mins

 
 
Stations: 125 Temp. Benson (57 m) -2.0 °C Leeming (32 m) -1.0 °C High Wycombe (205 m) -1.0 °C Shap (249 m) -1.0 °C RAF Lyneham (156 m) -1.0 °C Pershore (31 m) -1.0 °C Strathallan (35 m) -1.0 °C Spadeadam II (286 m)

-1.0 °C

 

so several spots and some of them well south

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It got down to 3C in Gatwick that is very chilly for the Southeast region very unusual.

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You shoul discount mountain stations I think. Aonach Mor was under 0C a couple of days ago at 7AM and I am fairly sure Cairngorm has been under as well. For lower stations somewhere may well go under tonight as the Northerly wind has abated.

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according to wx online the air mins were 1C, see below

Stations: 176 Temp. Shap (249 m) 1.0 °C Benson (57 m) 1.0 °C Aonach Mòr (1130 m) 1.0 °C Cairngorms (1245 m) 1.0 °

 with grass mins

 
 

 

Stations: 125 Temp. Benson (57 m) -2.0 °C Leeming (32 m) -1.0 °C High Wycombe (205 m) -1.0 °C Shap (249 m) -1.0 °C RAF Lyneham (156 m) -1.0 °C Pershore (31 m) -1.0 °C Strathallan (35 m) -1.0 °C Spadeadam II (286 m)

-1.0 °C

 

so several spots and some of them well south

 

Sorry John, are the second lot ground temps?

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Nevis Range down to -0.3c last night.

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Sorry John, are the second lot ground temps?

 

yep, it quotes values at 5cm, which is about the height that a grass minimum thermometer would be placed. What is not clear is over what surface the temperatures are recorded. Is it grass, soil or man made(asphalt, concrete etc). The surface will make a difference.

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yep, it quotes values at 5cm, which is about the height that a grass minimum thermometer would be placed. What is not clear is over what surface the temperatures are recorded. Is it grass, soil or man made(asphalt, concrete etc). The surface will make a difference.

The vast majority of stations will be over grass as this is what the standard measurement requires. There is the odd exception like London WC, I think that is on a roof.

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Must have been close to it this morning here as at 0730 when I got into may car in the sunshine, outside temp was just 4.5 deg...

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Must have been close to it this morning here as at 0730 when I got into may car in the sunshine, outside temp was just 4.5 deg...

 

Shap was down to 2C so it looks like the Lake District was pretty cold this morning.

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Katesbridge, NI fell to -1C in July. Would that be the first or last of the season?

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Katesbridge, NI fell to -1C in July. Would that be the first or last of the season?

 

I would say last with the longest frost free period occurring afterwards, from 15th July to yesterday interestingly enough.

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Must have been close to it this morning here as at 0730 when I got into may car in the sunshine, outside temp was just 4.5 deg...

 

 

Yes preety cold here this morning, and pleased to see this thread back in action, given the outlook certainly more chances of air frost in the not too distant future.

 

I think Katesbridge NI got down to -1 degrees last night, it must be a notorious frost hollow, it often seems to be the coldest spot in the UK, colder than highland regions which is unsual. Anyone explain factors at play which allow such low temps in Katesbridge?

 

Also good to see a member from Coniston, not too far from me.. look forward to talking to you on the far northern England / NW England threads..

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I would say last with the longest frost free period occurring afterwards, from 15th July to yesterday interestingly enough.

 

I was thinking first, if you split year up, 30th June would be last, 1st July first

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I have just reset the min/max on my station.

 

I was amazed to see my dew point temp had dropped to -0.1C on the 9th, at 05:00. My station is 7foot in the air!

I had cleared the min for the air temp and so was not able to add any other information. Was it correct?

Does this constitute as an air frost or a ground frost (or neither!)

 

MIA 

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I have just reset the min/max on my station.

 

I was amazed to see my dew point temp had dropped to -0.1C on the 9th, at 05:00. My station is 7foot in the air!

I had cleared the min for the air temp and so was not able to add any other information. Was it correct?

Does this constitute as an air frost or a ground frost (or neither!)

 

MIA 

 

Neither. Dew point is just an indicator of moisture in the air. Even the hottest deserts get dew points well below zero.

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Got down to 6c last night. Last week we had a low of 4.1c. Getting ever closer.

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Neither. Dew point is just an indicator of moisture in the air. Even the hottest deserts get dew points well below zero.

 

Thanks Nick, I suspected as much!

 

MIA

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Looking at the outlook I suspect we won't see an air frost this month, nothing unusual, absolutely normal, though on occasion late Sept can deliver air frost. Plenty of fairly chilly nights ahead though - the most notable aspect of September 2015, min temps have consistently been significantly below average here.

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