April 2016: rather cold and thundery

April 2016 has seen more occurrences of thunder than we can expect during a typical July.

radar hail
About an inch of hail collected on borders in gardens in Plaistow during a thunderstorm on 29th. This stuck around for over an hour thanks to the low humidity

A persistent flow of unstable Polar maritime air, coupled together with strong sunshine, provided the perfect ingredients for some really beefy showers.

The mean temperature of 9C was 0.8C cooler than average, the coldest April for three years and in stark contrast to the previous two Aprils that were mild and very dry. Air frost, notable for its absence in the previous two Aprils, returned with four incidences where the temperature dipped below freezing

Apart from a dry slot in the third week rainfall was fairly steady: 52.5mm is 124% of average for this area. It was the wettest April for four years.

A depression on 15th led to the wettest 24hrs of April

Sunshine was just below average. Over 153 hours were recorded, 96% of what we can expect to see during an average April.

The wettest day occurred on the 15th with 15.9mm, rain associated with a depression that ran along the Channel coast out into the North Sea, a system that heralded the colder pattern that defined the rest of the month.

Air frosts: 4, Ground frosts: 12

So what has May got in store weatherwise? The models on the 1st suggest that rather warmer weather will develop as we finally lose the northerly-sourced airflow and low pressure across the UK.

hail radar
The radar on 29th shows a thunderstorm right over Plaistow to the south of Wanstead

Low pressure to the NW will become influential with strong and milder WSW winds driving wind and rain bearing fronts east and SE across the UK late on Sunday and Monday. A bright and brisk NWly flow with sunshine and showers then looks likely to be replaced by a ridge of high pressure and drier weather. It will begin to feel quite warm in any sunshine across the south from midweek.

Beyond that the outlook is uncertain though it appears warmer, if changeable, conditions will prevail.

Beyond the grasp of the models my long range outlook method has conflicting signals. The highest probability is 32% for something rather cool. Average is 28% while rather mild comes in at 20% probability. Something cool comes in at 12%, while mild is 8% probability. Both cool and very mild have a probability of just 4%.

A wetter than average month looks most likely at 48% probability. Sunshine probably about average.

So to sum up: Mean: 12.8C (0.2C below average), rainfall 58mm, sunshine 179 hours.

My April outlook for temperature was good. I predicted a mean of 9.2C (outcome: 9C). Rainfall was also good: 57mm (outcome: 52.5mm). Sunshine also good: 149 hours (outcome: 153.9 hours).

Here follows the full weather diary for April. To view full stats follow this link:http://1drv.ms/1kiTuzv

1st: Sunny start though lots of haze around from late morning.
2nd: Sunny until 2pm before cloud then light rain spread in – this lasting into the evening.
3rd: Sunny start with hazy cumulus building through the day.
4th: Bright start though lots of cloud around. Some gin clear spells of sunshine.
5th: Sunny start though with variable cloud through the morning.
6th: Drizzly start, giving way to sunny spells and showers.
7th: Cloudy after recent light rain. Windy and cold. Some heavy showers mid to late afternooon with flash of lightning and thunder at 4pm and hail >5mm.
8th: Bright start though with much cloud around. Some brief sunny spells and v light showers.
9th: Cloudy, damp start after morning rain. This broke to sunny spells at 1pm ish. Cloudy again later but clearing at dusk to allow a frosty night.
10th: Sunny start but soon turned hazy with keen, cold SE wind building through the day.
11th: Cloudy start but brief brightness early afternoon. Rain at 2.15pm – this lasted until 5pm. More rain in the early hours, heaviest just before 5am.
12th: Bright start though hazy with lots of cirruo stratus. Clear and cold overnight.
13th Glorious sunny start and warm in the sunshine. Some patchy cloud at times. More cloud bubbled up late afternoon with a shower at 8pm and midnight. Clear and cold overnight.
14th: Sunny start though with much more cloud at times to 2pm. Showery rain in the evening lasted through the night.
15th: Cloudy with rain at 9.45am until 10.15 then turned a bit brighter before cloudy again at 11.45am. Rain set in at 12.30pm with thunder at 1.07pm then rain on and off into the evening. Clearing overnight and cold.
16th: Cloudy and cold start. Stayed cloudy all day with brief light rain shower. Cold and frosty overnight.
17th: Sunny, gin clear start with cloud gradually bubbling up. Sunny periods throughout the day.
18th: Sunny start with cumulus bubbling up.
19th: Mostly sunny start but then turned very cloudy. This cloud cleared just before noon.
20th: Sunny, clear start with just a few cirrocumulus drifting around during the day. Cold wind.
21st: Bright start but much cloud around. Some spells of hazy sun through the afternoon.
22nd: Cloudy, cold feeling start. Rain by 5pm, this heavier than expected. Next day dawned clear but cloud soon bubbled up.
23rd: Sunny start, cloud bubbled up with a shower at 12.25pm, clearing by 1pm. Early rain on 24th before obs time.
24th: Bright start, cloud bubbled up with light shower at midnight.
25th: Cloudy, cold start with lots of Arctic cumulus. Showers soon arrived that were mostly sharp but brief and heavier in the east. These cleared to leave a cold, breezy night.
26th: Sunny start but cloud quickly bubbled up. Some heavy showers of soft hail with odd snow flake. Thunder at 2.45pm.
27th: Sunny start though cloud quickly started building with snow and soft hail at 12.30pm. Further showers at 1712 and 2330. Clear, cold and frosty overnight.
28th: Sunny and mostly clear up until  12 noon.
29th: Sunny start though cloud quickly bubbled up. Some very heavy hail in Plaistow with an accumulation of one inch – this hung around for a while due to the low dew point and low humidity – less in Wanstead. Thunder and lightning too.
30th: Sunny, clear start though cloud began to bubble up. Felt cold in the wind as it became overcast last afternoon. Cleared overnight to give frost.

Another superb display of bluebells burst into life in Chalet Wood, Wanstead Park, this month