Tuesday, September 25, 2018

Storm Bronagh

Storm Bronagh, the second named storm of the season, brought heavy rain and strong winds to the UK on 20th and 21st September 2018. See here for a full summary of Storm Ali and Storm Bronagh.

The footprint of Storm Bronagh was clearly visible in surface analyses based on WOW observations. The dense network of WOW observations over England and Wales, along with other sources of observations, meant that we could track this storm in great detail. See below for the evolution of the storm. At each time step an analysis chart showing the position of the low pressure centre and associated weather fronts has been provided, along with an analysis produced from WOW observations. The colours on which represent temperature, the arrows are wind vectors, and the dark blue lines show surface pressure.

                                                       20/09/2018 1800 GMT

Strong SSW winds can be seen in the warmer air (the warm sector, between the warm and cold fronts) across much of England and Wales.

21/09/2018 0000 GMT

The centre of the storm is now over NE England. Cooler air can be seen moving into the West behind the cold front. The wind is still very strong across Eastern England.

21/09/2018 0600 GMT

Bronagh has moved off into the North Sea. Cooler air and Westerly winds can now been seen across England and Wales.

Monday, September 17, 2018

Guest Blog from a WOW Observer

I have a huge passion for the weather and I have always had weather stations whilst growing up, starting with the basic rain gauge and outside thermometer to now owning a “Netatmo” Smart Weather station kit, which is an all singing and dancing wifi and smart phone enabled device.

The reason I got this weather station was the ease of being able to see my weather data straight from my phone, no matter where I am. I also really enjoy sharing my weather data with other people and have created a Twitter account @CranbrookWx where my data is fed into tweets for all to follow and view.

I then discovered that with a little programming my Netatmo Weather station could be linked to the Met Office WOW website and my data could help contribute to observations.
I found it very easy to create my WOW profile and account, even giving the details on how exposed or not my weather station kit is. However, I did struggle slightly setting up the correct coding for the program to run between my Netatmo weather station and the WOW website. I was then pointed in the direction of a website called “Plus.Meteoware.com” where all I had to do was link both my Netatmo weather station details and my WOW details together on the website and then it did all the hard work for me. Now my data automatically appears on the WOW website with ease. As my weather station is permanently connected via wifi there are no breaks in observations to WOW. I have also set up my account on WOW to public so anyone who is on there can see my observations, which are updated frequently, and compare them to nearby values too.

Note from the WOW team: We are always interested to add to the list of useful third party software on our support pages. Share your experiences in the comments below to help other users link up with WOW!

Tuesday, September 4, 2018

26th & 27th July 2018: Thunderstorms over Eastern England

After the highest temperature recorded in the UK since July 2015 was recorded, a News Release from the Met Office described how the hot conditions would end in a bang, with intense thunderstorms forecast.

Summer showers and thunderstorms are notoriously difficult to forecast, we know if the conditions are right for them to develop, but predicting the exact time and location can be likened to trying to predict bubbles in a pan of boiling water! That said, thanks to WOW observations, Meteorologists now have one more tool to help predict when and where damaging thunderstorms are likely to occur.

High resolution surface analyses, which include input from WOW observations, were being trialled by  Met Office Meteorologists to help inform where thunderstorms were most likely to break out on the 26th and 27th July. The thunderstorms on the 27th July produced damaging winds and hail across Eastern England.

26th July

These plots, based on data from WOW observations, are from the afternoon of 26th July. The shading shows surface temperatures, the lines are surface pressure, and the arrows are wind vectors. A growing area of cooler air and higher pressure can be seen over North East England. This was a ‘cold pool’ associated with an area of thunderstorms, which can be seen on this rainfall radar image from around the same time:

Cooler, denser, air from the downdraught of a thunderstorm meeting warmer air at the surface can lead to further developments. The thermal boundary between cooler and warmer air highlighted on the plots from the WOW observations pinpointed where further heavy showers and thunderstorms would develop over the coming hours. An hour later the thunderstorms had developed further and the radar image looked like this:

27th July

These plots from July 27th show convergence, where air travelling in different directions meets (converges) and is forced to rise. Rising air is one of the ingredients for heavy showers and thunderstorms. The pink areas over East Anglia and Lincolnshire on the plots, which are again based on WOW data, highlighted an area likely to see thunderstorms develop on the 27th. Thunderstorms were expected to develop here once the temperatures were high enough for them to do so. Reaching a certain ‘trigger’ temperature is often another ingredient for thunderstorm development.

Nothing can be seen on the radar image over East Anglia in the morning, but by late afternoon intense thunderstorms had developed in this area:                                                  

There were other factors that led to the development of these thunderstorms, in addition to those discussed above, and Met Office Meteorologists would have been using all the different sources of information available to them to monitor the situation. The analyses drawn up from the WOW observations are just one of many tools our Meteorologists use, but the observations provided by our voluntary observers are certainly being put to good use.