Archives For July 2013

Reigate should see 30ºC Tmax for the first day of August and high 20’s on Friday. The cause is a warm tropical plume of air flooding over the south of the UK from Iberia (Spain) and Africa brought in as the jetstream moves north and a LOW to our west and HIGH to the east builds a brisk Southerly airstream. Thursday will be dry and bright and the night will feel very muggy with high dew points and lows of over 20ºC at midnight: warm and damp, the air will feel close! Friday will be warm too but slightly less so for Reigate, dawning bright but with cloud spilling in associated with a weakening cold front pushing east across the country. Little frontal rain is expected but the cooler upper temps could release the huge heat energy built up in the lower atmosphere and kick off heavy / thundery showers for a while, especially Friday morning. Confidence is low currently but this might occur, the potential is there with all that heat.  

Every thunderstorm indicator is giving green lights to thunderstorms in the SE sometime in the next few days BUT the airstream is capped with warm uppers: this appears to be the only factor stopping convective action. This means heat building in the lower atmosphere will stay put until forced to rise into the unstable layers above (see sounding graph above). The approaching cold front might be sufficient to produce something of convective interest on Friday, morning especially… before the warm Euro air retreats back to east. So far Reigate has seen little of the impressive thundery activity elsewhere in the UK this summer. You might be forgiven for thinking it must be our turn soon! It’s unlikely to be in the next few days as the risk is small for any major thundery outbreak.
The synoptic situation remains similar over the next few days with HIGH pressure over the continent and LOWS edging close to the NW of the UK bringing rain and wind to the NW. The SE should escape with any trailing fronts weakening and Reigate should remain largely dry but for any threat of isolated thunderstorms in building heat.

Spectacular thunderstorms, lightning and flash flooding drifted west to east across the UK today on a blustery unstable SW airstream but the SE and Reigate missed out on any cumulonimbus and we experienced no thunderstorms at all which would please most people but rather upsets weather enthusiasts looking for interesting weather!

Lumpy cumulus congestus and some perky showers with bright blustery conditions in beautiful bubbly convective skies which cleared at night were all the SE could manage. North and West of the region saw amazing convective cumulonimbus with towering cells producing hail thunder and lightning with flash floods here and there.  Spotting the clues as to why the SE missed out is tricky… a combination of factors reduced the Tstorm risk.
The general synoptic situation was higher pressure in SE, soundings with lower CAPE values (600 v >1000) and higher lifted index were also evident.  Lower 700hPa humidity in the SE was noticeable but possibly irrelevant.  The ThetaE map showed considerably higher values away from the SE too.

Soundings for the SE compared with a thundery location (Fairford) to the west show Reigate with less instability through the lower and higher elevations, less depth of saturated air, a stronger cap and less steep lapse rates.  Significantly lower dew points in the SE would also reduce humidity and water available for cloud development.  Winds were also SSW and thunderstorms developing in the SW early on (Bath and Bristol first) simply drifted to the NW of the area and clipped the North of London missing the SE altogether.  More broadly the overall synoptic situation had higher pressure for the SE as well which would inhibit convection.  I’ll add to this as more thoughts and ideas arise… why did the SE miss out?  Thanks to @MillinMan and @marknealweather with their expert ideas for this quick review! More ideas most welcome @RGSweather. Thunderstorms: edgy stuff but our weather today nothing like as extreme as that in Italy… watch this

sounding reigate

sounding tstorms fairford

RGSweather is closing for a few weeks until August. Off to a log cabin in the Tatra Mts of S Poland. I think the weather there is edgy at the moment… perhaps some nice thunderstorms! Back posting and tweeting very soon.  Meanwhile, enjoy the beautiful July weather and remember…the best view is always up (but wear sunglasses this time of year!) Happy Hols, enjoy 🙂

poland hol

The HIGH pressure now building over the UK looks like persisting for at least a week and possibly for longer with a breakdown only hinted at from 15 July or later on current model runs. High pressure brings warm, dry weather with mostly clear skies as air sinks from aloft and warms and dries out as it does so. High pressure has pushed the jetstream (which guides LOW pressure storms at the surface) well north towards Iceland. So GREAT summer weather for Reigate and the UK over the next week and beyond!

Temperatures will mostly be in the high 20’s and could climb to 30ºC locally. Night time temperatures are also going to remain well in double figures for most of this period.
One potential spoiler for east and SE England could be the build up of brisk NE and E winds swinging round the edge of the HIGH as it continues to build in pressure during next week and slips north. The forecast Northerly / NE winds running south down the North Sea and swinging east into the Channel could reach 20mph and inland could be 10-15mph (supergeostrophic = surprisingly breezy in high pressure as winds swing out round the pressure gradient). The North Sea is still only around 13C sea surface temp and this will have a cooling effect on the breeze and east coast areas especially.  This wind might even pick up some low cloud and mist for the east coast. How far inland this effect reaches remains uncertain but most likely the cooling will be restricted to the immediate coast. So, warm everywhere but west is certainly best!

SE heat 7 JulyUpdate: scorchio for Sunday but thereafter in SE and Reigate it will be pleasant and “normally” summery and warm.  The NE breeze will take edge of scorching temps in SE and especially near coasts.  The NE may also bring cloud which will further peg back temps to a more normal feel at mid-20’s rather than high 20’s. 

monday 8 july

June in Reigate was dry and mostly rather cool apart from a notable warm plume event after the middle of the month.  Post Tropical storm Andrea pepped up the weather from early June and an interesting JET STREAK on the June 11 were expected to deliver a lot of rain but, in the event, it was merely blustery and quite wet for Reigate.  Thereafter, a meridional jetstream developed and looped right down across Europe and eventually formed a large cut-off low over Spain and a persistent trough over Europe made the continent extremely wet with flooding in Germany, Austria and Czech Rep.  Whilst the UK sat on the cooler side of the trough, the warm low over Spain / France edged closer to the UK through mid-June and dominated our weather with the threat of downpours from a warm upper plume.  Large hail and near super-cell storms developed over France and Netherlands.  However, the expected thunderstorms for the UK slipping over the Channel associated with the warm LOW approaching from the South never arrived but delivered big Tstorms to Europe and some ran up the Channel and S North Sea.  Nevertheless, interesting clouds like Kelvin-Helmholtz waves in warm plume alto-cumulus created a rare treat for cloud collectors!

In general, models struggled to predict convective storms / any rain during this unusual Southerly and Easterly flow with Europe stuck in a trough delivering warm uppers to the UK and the jet stream proper cut off to the North of the UK.  NMM, NAE and GFS kept predicting significant downpours for the SE with high CAPE and lifted index values when no rain arrived at all as CAPES and LIs repeatedly melted away on 00Z runs!  High res UKMO and Hirlam delivered more accurate predictions but only nearer the time.  Rainfall was low. Overall, June did not “bust out all over” rather she teased with plenty of near-miss extreme weather events here in the SE. More on the continuing COOL 2013 here

Meanwhile, the Mid-West USA experienced some of the largest tornado events in history: El Reno tornado was the widest ever recorded and wind speeds exceeded 200mph.

Reigate June statistics:

June Average temp 14.4C
June Tmax 26.8C
June Tmin 5.2C

Total rainfall 18mm

JUNE data available to download on DATA page now!

The predicted heat wave (or should that be “warm wave”?!) is showing up nicely on latest runs with 30C quite possible in some parts of the South. The lack of rainfall over the next 10 days is also significant. High pressure stays in charge for at least a week with the jetstream being shifted north to Iceland where it belongs in summer!  

pressure builds july

Pressure will build right over the UK from the weekend bringing warm, sunny and dry conditions possibly for another 10 days!

july high blocksAn anticyclone building over the UK will dominate our weather for at least next week and possibly beyond.  Upper air flow over the weekend will direct warm tropical air from the south and sw over the UK. Thereafter upper air flow will shift to a more northerly flow, slightly cooler.  So hottest temps are likely this weekend.  Surface winds will be more NE and easterly as the HIGH slips to the North. Whilst winds inland will be light, E and NE winds in the Channel could build through to Monday as easterly winds drain away from the HIGH located over the North Sea. 

Sea surface temperatures are reaching the low teens around the UK.

Very strong sunshine and high temperatures: enjoy and don’t forget to slip, slap and slop! (slip on a Tshirt, slap on a hat and slop on the sun cream!).

To become a “Heat wave” the weather must reach a technical threshold and, whilst Sunday will be v warm for the UK, the rest of the week will be just a bit above average: a heat wave is where daily max temperatures for more than 5 consecutive days exceed the average max temperature by 5°C.

For the SE England Max temps must exceed 31°C and min temps exceed 16ºC at night.  So technically this is unlikely to be labelled a heat wave, more like a warm wave 🙂