Coast

Wind farms affect local weather

Wind farms can affect weather in their immediate locality, raising night-time temperatures on the ground, researchers working in Texas have shown. They used satellite data to show that land around newly constructed wind farms warmed more than next-door areas.

The result - published in the journal Nature Climate Change - confirms an earlier, smaller study from 2010. The scientists believe the effect is caused by turbines bringing relatively warm air down to ground level. They suggest that turbines in other places might not produce the same value of ground temperature change.

The study area, in west-central Texas, saw a major turbine building programme in the middle of the last decade, with the number soaring from 111 in 2003 to 2325 just six years later. Researchers used data from the Modis instruments on Nasa's Aqua and Terra satellites to measure ground temperatures across the study region and between the beginning and end of the construction boom, defined as as the difference between the average for 2003-5 and that for 2009-11.

The entire region saw a rise, but it was more pronounced around wind farms. The researchers looked for other factors that could have affected the results, such as changes in vegetation, but found these were too small to produce the observed change.

Limited reach

The change was not identical across all of the wind farms. Having averaged the data, the researchers say the scale of the effect they saw is equivalent to a warming of about 0.72C per decade. Recognising that this could wrongly be interpreted as suggesting the local temperature will continue to rise, lead researcher Liming Zhou cautioned: "The estimated warming trend only applies to the study region and to the study period, and thus should not be extrapolated linearly into other regions or over longer periods.

Could the local weather changes affect farming?

"For a given wind farm, the warming effect would likely reach a limit rather than continue to increase if no new wind turbines are added." At night, air above ground level tends to be warmer than the ground. Dr Zhou and his colleagues believe the turbine blades are simply stirring up the air, mixing warm and cold, and bringing some of the warmth down to ground level. "The result in the paper looks pretty solid to me," commented Prof Steven Sherwood from the Climate Change Research Centre at the University of New South Wales in Australia.

"Daytime temperatures do not appear to be affected. This makes sense, (and) this same strategy is commonly used by fruit growers who fly helicopters over their orchards to combat early morning frosts."

The 2010 study, also from the US, used data from a single location and computer modelling to show that wind turbines could produce local warming. Dr Zhou, from the State University of New York in Albany, US, now plans to look across bigger scales and to decipher the mechanisms better.

"This article is a first step in exploring the potential of using satellite data to quantify the possible impacts of big wind farms on weather and climate," he told BBC News. "We are now expanding this approach to other wind farms, and building models to understand the physical processes and mechanisms driving the interactions of wind turbines and the atmospheric boundary layer near the surface."

Storm Forecast
Valid: Mon 30 Apr 2012 06:00 to Tue 01 May 2012 06:00 UTC
Issued: Sun 29 Apr 2012 23:03
Forecaster: TUSCHY

A level 1 was issued for far SW/W-Germany, far NE France, Belgium, Luxembourg and parts of the Netherlands mainly for large hail and strong to severe wind gusts. An isolated tornado event is possible mainly during the evening hours.

A level 1 was issued for parts of CNTRL France mainly for large hail and strong to severe wind gusts. An isolated tornado event is possible.

SYNOPSIS

Large-scale cut-off low is situated over W-Europe with high pressure to the east. Lowering 500 hPa height levels occur over most of CNTRL Europe with increasing probabilities for isolated DMC even beneath the western fringe of the ridge. Progressive wave train of upper troughs still affects far N-/NE Europe with unsettled and cool conditions.

DISCUSSION

... Germany, Benelux, NE France and S-UK ...

20 Z synop data places a tongue of augmented LL moisture just south of the stalling warm front over N-Germany with readings in the lower to mid tens. This air mass advects to the SE in response to a weak thermal low, which drifts to NW Poland during the forecast. Best moisture will reside over Poland, the W-Czech Republic and probably also sneaks into far S-Germany. For the rest, marginal BL moisture with readings of 6-9 °C are expected during the forecast. However, outflow boundaries from convection of last night and other convergence zones on the mesoscale may serve as foci for better dewpoints. Impressive EML plume, which affected CNTRL Europe during the past 2 days, starts to fan out to the N/NW with diminishing intensity. Hence, final CAPE dispersal will be messy with most robust build-up along the moisture axis from Poland to S-Germany. 500 to 800 J/kg MLCAPE are possible with significantly lower values to the west. Again, better LL moisture/CAPE exists over Belgium.

Forecaster: Dan
Last Updated: 2012-04-29 21:52:00
Valid: 2012-04-30 00:00:00 - 2012-04-30 23:59:00



Areas Affected:

SLGT: N, C + E Wales, Midlands, Home Counties, SE + CS England
Synopsis:

A vertically-stacked area of low pressure will become centred to the southwest of the British Isles, developing an easterly flow from the continent.
Discussion:

Rising LSTs as a result of diurnal heating, with -24/-25C at 500mb, will result in a few hundred J/kg CAPE. Consequently, a scattering of showers is expected across parts of the Midlands down to the SE, drifting slowly westwards into Wales/West Country towards the evening. It is possible given ELTs down to -40C for sferics, especially given some 25kts LLS and 30-40kts DLS which should allow cells to become organised for a time later in the day, with a heightened chance of perhaps a funnel or tornado developing.

Given PWAT of 16-18mm, there is likely to be some slow-moving heavy downpours. Hail up to 1.0cm in diameter is possible in stronger cells, with convective gusts potentially >35kts. These showers/storms will gradually decay during the evening hours as they continue to drift ever further west/southwest-wards.

Attention thereafter turns to northern France/Belgium as an approaching developing front advects some much higher WBPT westwards across southern Britain on Monday night, increasing moisture convergence. Scattered thunderstorms are expected to develop over these areas late in the afternoon and evening hours, forming multicell clusters and drifting gradually W/NW'wards towards southern Britain throughout the evening. While sferic activity may be high over France/Belgium, as they begin to cross the English Channel/southern North Sea with SSTs ~10C, it is quite likely that the resultant surface inversion will result in such storms becoming rapidly elevated, still with several J/kg MLCAPE initially, but eventually losing the majority of sferic activity as vertical profiles become increasingly saturated.

As a result, most storms will begin to merge into a large area of heavy rain, and given advection of high PWAT this will result in heavy downpours increasing the risk of local flooding given the already saturated ground. There is some considerable model disagreement on areas most prone, but the general consensus appears to be Kent/Sussex and Hampshire northwards into Essex and Suffolk through the late evening and overnight period. Given the elevated nature, this limits the potential for severe weather somewhat, despite significantly high values of shear and helicity over East Anglia in particular.

With an ever-changing forecast with regards to Monday night's event, we may issue an update if necessary.

SKYWARN UK SEVERE WEATHER WARNING #015
ISSUED: 1730UTC SATURDAY 28TH APRIL 2012 (GJ/SM)

SKYWARN UK HAS ISSUED A SEVERE WEATHER WARNING FOR THE FOLLOWING REGIONS:
ENGLAND
WALES
CHANNEL ISLANDS & IOM

IN EFFECT UNTIL 1200UTC MONDAY 30TH APRIL

DEEPENING BISCAY LOW OVER W FRANCE BRINGING A WARM OCCLUSION WITH HEAVY PRECIP AND GALES NORTHWARD

SEVERE WEATHER IS EXPECTED IMMINENTLY, OR OCCURRING, SOMEWHERE WITHIN THE REGIONS INDICATED. THREATS WITHIN THIS WARNING INCLUDE, BUT ARE NOT LIMITED TO:
HEAVY RAIN...FLOODING...STRONG WINDS...DAMAGING GUSTS

DISCUSSION:

THERE IS STRONG MODEL CONFIDENCE OF A SEVERE WEATHER RISK THROUGH SUNDAY INTO MONDAY. A LOW PRESSURE DEEPENING TO ~990MB FROM W FRANCE INTO THE SW APPROACHES WILL ENTRAIN VERY WARM AND SATURATED AIR FROM THE CONTINENT, WITH PRECIPITABLE WATER VALUES OVER 2.5CM. AS A RESULT RAINFALL ACCUMULATIONS OF UP TO 40MM MAY BE POSSIBLE, PERHAPS GREATER OVER HIGHER GROUND WHERE ENHANCED BY GALE FORCE WINDS. INTENSE RAINFALL IS EXPECTED ACROSS SOUTHERN, CENTRAL AND EASTERN ENGLAND DURING THE MORNING AND OVER HIGHER GROUND OF NORTHERN ENGLAND THROUGH THE AFTERNOON, WITH GENERAL ACCUMULATIONS OF BETWEEN 20MM TO 40MM. SOUTHWEST ENGLAND AND WALES MAY SEE SOME VERY INTENSE RAIN DURING THE EARLY HOURS, WITH PERSISTENT BOUTS OF CONVECTIVELY ENHANCED RAINFALL THROUGH SUNDAY PROVIDING 30MM GENERALLY. AVERAGE WIND SPEEDS THROUGH THE MORNING WILL BE AROUND 40MPH ACROSS WALES AND THE SOUTHERN HALF OF ENGLAND, WITH 50MPH POSSIBLE OVER HIGH GROUND AND EXPOSED COASTS, CONTINUING BUT WEAKENING FURTHER NORTH IN ASSOCIATION WITH THE FRONT INTO MONDAY MORNING. FURTHER GALES ARE POSSIBLE FOR THE CHANNEL ISLANDS LATER SUNDAY INTO MONDAY. CONVECTIVE ELEMENTS WITHIN THE FRONTAL ZONE ACROSS WALES AND SOUTHWEST ENGLAND MAY ENCOURAGE POTENTIALLY DAMAGING GUSTS UP TO 70MPH LOCALLY. OWING TO THE INTENSITY OF THE OCCLUDING FRONTAL SYSTEM OVER THE EASTERN SIDE OF THE WARNING AREA, SURFACE AND CATCHMENT FLOODING IS POSSIBLE. PERSISTENT SHOWERS OF HEAVY RAIN OVER WESTERN AREAS MAY LEAD TO MORE PROLONGED RIVER FLOODING AND FLASH FLOODING DISRUPTING INFRASTRUCTURE. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY. THIS WARNING MAY BE UPDATED.