[Chris Alder]

I'm sure I've read the somewhere record 34/24C on the 10/08/03. I'll do some digging!

[Dave W]

In my opinion high dewpoints are increasing across the Uk- we frequently reach the kind of values (like 19-20C) that we didnt generally see about three decades ago ..

[Nigel Bolton]

Quote

Chris Alder - 25/7/2007 07:06 I'm sure I've read the somewhere record 34/24C on the 10/08/03. I'll do some digging!

The really hot air on this day across the southeast was very dry, with dewpoints in single figures, and winds from the southeast.

To the northwest from this hot, dry airmass, there was a band of much higher humidities accompanied by northwesterly winds. It will be through this zone here that you may find an answer. The northwestern boundary of this humid air was accomapnied by severe thunderstorms, one of these allegedly giving nearly 50mm of rain in 10 minutes at Carlton in Cleveland.

N.

[Nigel Bolton]

Quote

Dave W - 25/7/2007 10:01 In my opinion high dewpoints are increasing across the Uk- we frequently reach the kind of values (like 19-20C) that we didnt generally see about three decades ago ..

During the mega-downpour days of the mid to late 60's dewpoints of 20 degrees or more were occasionally recorded. 1st July 1968 saw 20+ dewpoints across much of England and Wales before the severe thunderstorms kicked in, and I believe dew-points were almost as high in the warm sector that brought in excess of 100mm of rain from northeast Devon to Lincolnshire during the 10th-11th July of the same year.

N.

[Matt D]

Very high dewpoints were widely recorded across parts of Cent S England, E Wales, N England and the Midlands on the 19th June 2005 prior to the onset of the widespread storm outbreak over the N Midlands and N England during the afternoon. I recall mid-late morning obs with dewpoints of 21 or even 22C from Bham airport, as temps climbed into the mid-high 20s. The moist, low level airmass which may have had its origins from the S and W of Biscay and the W of Portugal was capped off by a dry layer at 850 hPa from the Spanish Plateau. In fact the cap held all day in the S and E Midlands and the S making it feel very opressive (even though dewpoints did fall back to 17-19C).

http://meteocentre.com/archive/analyse/2005/06/19/2005061912_eur.gif

[PaulKn]

Back in April just gone, I recall we saw dewpoints climbing towards 20C, which is pretty unusual at that time of year. I think as we go into August, with the chance of more plume activity, we should see some pretty good values, especially given the fairly high SSTs in parts of the Med.

[BUTTERFLY]

I imagine 3 decades ago dewpoints even if known were not widely publicised as there were not the number of amateur weather enthusiasts (especially on-line) that there are now. Gordon Manleys New Naturalist Book "Climate and the British Scene" makes reference to high "wet bulb" temperatures (not the same as dewpoint of course).

[Lian]

I know this might sound silly as im not that much switched on, but on friday, the day we had the torrential rain here, the humidity was 100%. i recorded it in the current and recent weather thread. do you think it might have been at 100% because of all that heavy rain? can we use the percentage to know then when flooding could be imminent? sorry id just thought id ask : )

[Nigel Bolton]

Lian,

Humidity can be 100% at any temperature, this when the dew-point of the air is the same as the actual air temp. Normally in this situation you would get fog, water fog if air temp is above freezing and ice or freezing fog if below.

One cannot predict rainfall on humidity alone, though high temperatures and high humidity combined do give conditions for torrential rain, hense why tropical thunderstorms produce so much rain. One also has to consider the interaction of different air-masses, the effect of high pressure and low pressure, of convergence in the lower atmosphere, divergence above, and the effect of jet-streams.

Your 100% humidity was caused by persitent torrential rain lowering the air temp to its dew-point! Hope this all makes sense.

N.

[Lian]

thanx nigel : )

[PaulKn]

Lian - what Nigel is referring to is "relative humidity", a measure of how saturated the air is. 100% means fuly saturated, and the air can absorb no more water vapour.

[Dave K]

Quote

PaulKn - 26/7/2007 19:07

Lian - what Nigel is referring to is "relative humidity", a measure of how saturated the air is. 100% means fuly saturated, and the air can absorb no more water vapour.

And indeed rainfall doesn't necessarily mean the air at ground level is fully saturated, nor does reaching 100% relative humidity necessarily mean it's going to start raining (but water vapour might condense out in the form of fog or frost) [he says hoping he's right...]

[BUTTERFLY]

Surprising also that the wind at Shannon on 12th July 1983 was from the NE, which would mean a long travel over land. The same day (12th July 1983) Northern Ireland recorded its joint highest official air temperature (30.8 deg. C. at Shaws Bridge, Belfast); a similar temperature was also recorded at Knockarevan, Co. Fermanagh, on 30th June 1976. I remember July 1983 as very dry, sunny and very warm, rather than sticky and humid.

I think July (not August) 1995 would have had some high dewpoints. I can remember a day when despite being cloudy overcast and with a strong wind, the shade temperature (admittedly as indicated by a non-standard thermometer and exposure) was above 80 deg. F. (c. 26.7 deg. C.) at my place of work near Portadown, Co. Armagh. The highest for July 1995 (a sunny scorching day) at this site was 29.7 deg. C. on 31st, although 29th June (32.0) and 20th August (31.5 deg. C.) were higher. The official highest temperature in Northern Ireland in 1995 was 30.6 deg. C. at Ballylisk, Co. Armagh, on 2nd August (also NI's highest official August temperature and within 0.2 deg. C. of the overall record for any month).

[Chris CW (aka Seedubs)]

Quote

Nigel Bolton - 25/7/2007 19:00

Lian,

Humidity can be 100% at any temperature, this when the dew-point of the air is the same as the actual air temp. Normally in this situation you would get fog, water fog if air temp is above freezing and ice or freezing fog if below.

One cannot predict rainfall on humidity alone, though high temperatures and high humidity combined do give conditions for torrential rain, hense why tropical thunderstorms produce so much rain. One also has to consider the interaction of different air-masses, the effect of high pressure and low pressure, of convergence in the lower atmosphere, divergence above, and the effect of jet-streams.

Your 100% humidity was caused by persitent torrential rain lowering the air temp to its dew-point! Hope this all makes sense.

N.

Many thanks for that Nigel, I was about to ask the same or similar question, ie my station has often told me that the humidity was around 98% but the air didnt feel sticky/humid. 

And then when watching the weather forecast I would often hear them telling us that it would be a sticky day with humidity up to around 80%, now obviously they are not talking about what I am recording as humidity but they are talking about dew point?  Am I right in that presumption?  Generally the higher the dew point the more humid it feels and also the more probabilty of some storm activity/lightening?  So why record humidity on my station if it isnt really what we all mean as humidity?  I think I am loosing myself here....

I know its a basic question, but I am a basic person....thanks!

[PaulKn]

Humidity can be defined in various ways - you station measures "relative humidity", that is how much moisture is in the air compared to how much the air can hold (colder air can hold less moisture before condensation than warm air). Absolute humidity is the other measure, which measures the absolute amount of moisture in the air, measured in grams of moisture per kg of air.

[MungoJP]

Can someone tell me where I can find an up to the minute dewpoint field for the UK? There's certainly no such thing on UK Met O website. In fact no metion of dewpoints at all there.

[Dave K]

http://www.weatheronline.co.uk/ will give either a table or map of latest recorded dewpoints, select Temperature, United Kingdom from WorldWide Weather Ranking and you get choices of plenty other parameters, one being dewpoint and time of reading

[MungoJP]

Thanks, but even this site won't reveal dewpoints when I tried it.

[Matt D]

It works fine for me Mungo, here's some of the table for 14:00 BST.

Rhyl (76 m) 19.2° Church Lawford (106 m) 19.0° Kenley (170 m) 18.3° Machrihanish (10 m) 17.0° Charterhall (111 m) 16.6° Ballypatrick Fst (156 m) 16.3° Castlederg (50 m) 16.3° Trawscoed (62 m) 16.0° Ballykelly (5 m) 16.0° Portglenone (65 m) 16.0° Belfast/Aldergrove Airport (68 m) 15.9° Glenanne (160 m) 15.8° Bingley (267 m) 15.8° St Angelo (47 m) 15.7° Holbeach (2 m) 15.6° Glasgow Bishopton (59 m) 15.6° Topcliffe (28 m) 15.5° Loftus Samos (159 m) 15.5° West Freugh (10 m) 15.5° Hereford/Credenhill (76 m) 15.4° Leeming (32 m) 15.4° Plymouth MtBatten (50 m) 15.4° Lough Fea (227 m) 15.4° Prestwick (27 m)

Go to Current Weather in the selection list down the LHS, then tick dewpoint and also tick table and then set your time.

[MungoJP]

Working now, thanks.