Stark weather contrasts across the USA

18 02 2015

While the UK continues to see fairly typical winter weather, over the other side of the Atlantic the US is experiencing some stark contrasts.

While some parts in the west are seeing warm and dry conditions, eastern areas are seeing very cold weather.

This week will see a continuation of warmer-than-average conditions in western parts of the USA, with little or no rainfall in the forecast.

Map showing air temperatures across the US, with white (-24C) and blue (below 0C) showing cold air and yellows and oranges showing warm air. From the Met Office's Global Model for 1200HRS GMT on 20 February 2015

Map showing air temperatures across the US, with white (-24C) and blue (below 0C) showing cold air and yellows and oranges showing warm air. From the Met Office’s Global Model for 1200HRS GMT on 20 February 2015

Despite some welcome rainfall at the start of February, California remains in drought, with a large swathe in exceptional drought – which is the highest category that the US Drought Monitor report.

In San Francisco, no rain fell at the downtown observation station or the airport during the whole of January 2015. This is the first January without rainfall since records began in 1850. Normally January is the wettest month of the year, with an average 119mm.

The dry conditions have also resulted in the Sierra Nevada snow pack being at less than 50% of where it should be as we head towards the end of winter.

Meanwhile, the very cold spell of weather is expected to continue across a large part of eastern and northeastern USA, with air originating from the Arctic keeping things icy.

There will be some snow at times, although not as significant as some recent events, though localised heavy ‘lake effect’ snow is likely this week off the Great Lakes.

However, the most noteworthy element will be the extreme cold. Another arctic front will arrive across the East Coast, bringing exceptionally cold conditions.

Places from the Carolinas to the Mid-Atlantic may see some of the coldest weather since the mid-1990s, with numerous record low temperatures expected.

In fact this cold air is expected to reach as far south as Florida, with even the Caribbean expecting well below average temperatures throughout the rest of this week.





Arthur becomes first Atlantic hurricane of the season

3 07 2014

Hurricane Arthur has become the first hurricane of this year’s Atlantic season, which started at the beginning of June.

Arthur is currently located close to the coast of south-eastern USA and is expected to move north-east, parallel to the coast, in the next few days.

Although the centre of the hurricane may only graze the coast it is likely to produce a storm surge several feet above normal tide levels and cause strong surf and rip currents along stretches of the US east coast.

Hurricane warnings have been issued by the National Hurricane Center for the North Carolina coast.

Hurricane Arthur - Image from NASA’s Aqua satellite courtesy of Colorado State University

Hurricane Arthur – Image from NASA’s Aqua satellite courtesy of Colorado State University

Seasonal forecasts for the Atlantic mostly indicate that there is likely to be a slightly below normal level of activity this season.

The Met Office forecast is for the most likely number of tropical storms in the season to be 10 with six of these likely to become hurricanes.

Further details can be found in our North Atlantic tropical storm seasonal forecast web page.

Meanwhile in the west Pacific a tropical depression has formed just south of the island of Guam.

This is expected to strengthen into a powerful typhoon over the weekend and could potentially threaten parts of Japan or Korea by the middle of next week.

Official forecasts of Atlantic and east Pacific tropical storms are provided by the National Hurricane Center.

Official warnings of west Pacific tropical storms are produced by the Japanese Meteological Agency (JMA).

The Met Office routinely supplies predictions of cyclone tracks from its global forecast model to regional meteorological centres worldwide, which are used along with guidance from other models in the production of forecasts and guidance.

Met Office StormTracker provides a mapped picture of tropical cyclones around the globe with access to track history and six-day forecast tracks for current tropical cyclones from the Met Office global forecast model and latest observed cloud cover and sea surface temperature. We also provide updates on current tropical storms via @metofficestorms on Twitter.





What is a heat wave?

4 07 2013

This weekend and into next week temperatures are expected to reach the high twenties Celsius in southern England. This is certainly warmer than we would expect at this time of year – the average maximum temperature for July in England is 20.9 °C – but does it constitute a heat wave?

How hot is a heat wave?

There’s actually no official definition of a heat wave in the UK. In America, where high temperatures are more likely, the official classification is based on the Heat Index. The Heat Index temperature is a ‘feels-like’ temperature calculated by combining the temperature and relative humidity.

Depending on the local climate, an excessive heat warning is issued when the Heat Index is expected to exceed 105 °- 110 °F (40 °C – 43 °C) for at least two consecutive days.

Australia also has variable definitions depending on the state. In Adelaide, a heat wave is defined as five consecutive days at or above 35 °C, or three consecutive days at or over 40 °C.

Heat health watch

Working in association with the Department of Health, the Met Office provides a heat health warning system for England.

The Heat-health watch system comprises four levels of response based upon threshold maximum daytime and minimum night-time temperatures. These thresholds vary by region, but an average threshold temperature is 30 °C by day and 15 °C overnight for at least two consecutive days.

When was the last time we had a prolonged spell of hot weather in the UK?

The last time we saw a long spell of warm weather was in July 2006, where temperatures were above 28 °C in many areas for a fortnight. We have had shorter spells of warm weather since, however, such as the 23 – 26 July last year, when temperatures peaked at 30.7 °C.

How hot will it get this weekend?

You can see the expected maximum temperature range for your area on our website. Temperatures are not currently expected to exceed the heat health watch threshold, but keep up to date with warnings on our website.

temprangelondon

Visit our summer pages for activity ideas for hot and sunny weather.

http://www.youtube.com/watch?v=GrBuD9eAmsk








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