Speleotrove weather analyses

Pembrey Sands, 18:00 to 20:00, 1997–2020

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Met Office station 1226: Pembrey Sands, Dyfed (SA17 4); OS grid reference: SN 365043.
Coordinates: N51°42'47" W4°22'05" (51.713 -4.368), elevation 3 m.
Note: gusts not recorded in 8 out of the 24 years, 2.8% of daylight visibility records missing, 2.3% of daylight precipitation records missing, 2.3% of daylight wind records missing.

This is the analysis for the average of 24 years (1997–2020).
Time slot: 18:00 to 20:00 (two hours); click below for any-hour analysis, or a different start time, or for whole day analysis (all times are GMT):

any-hour 06:00 08:00 10:00 12:00 14:00 16:00 18:00 all-day

‘Flyable days’ analysis

This is the number of days in each month, on average, for which (in this timeslot) the visibility was adequate, and there was no bad weather, and the wind speed was less than or equal to that shown on the left.

	Apr	May	Jun	Jul	Aug	Total
≤ 5 mph	1	2	2	1	1	6	2%
≤ 10 mph	2	7	6	6	4	25	7%
≤ 15 mph	4	15	15	14	9	57	16%
≤ 20 mph	5	20	20	21	14	79	22%
≤ 30 mph	6	25	24	26	17	98	27%
≤ 40 mph	6	26	25	26	18	101	28%
any wind	6	26	25	26	18	101	28%

‘Total’ shows the total flyable days, on average, in a year, and the same as a percentage.

Trend analysis

This is the average change (per year, over the 24 years) in the average number of days in each month for which (in this timeslot) the visibility was adequate, and there was no bad weather, and the wind speed was less than or equal to that shown on the left.

For example, if a value of +0.5 is shown for a given month then that implies that since 1997 the number of flyable days in that month has increased by (on average) half a day per year.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total
≤ 5 mph +0.1 −0.1 −0.1
≤ 10 mph −0.1 +0.1 −0.1 −0.2 −0.3
≤ 15 mph −0.2 −0.2
≤ 20 mph +0.1 −0.2
≤ 30 mph +0.1 +0.1 +0.1
≤ 40 mph +0.1 +0.1 +0.1 +0.2
any wind +0.1 +0.1 +0.1 +0.3
Empty cells indicate negligible change; ‘Total’ shows the sum of the trends over the whole year.

Visibility analysis

This is the number of days in each month, on average, for which (in this timeslot) the visibility was adequate. That is, for the entire timeslot:

both hours were daylight (no more than 30 minutes before sunrise or after sunset)
horizontal visibility was at least 5000m (UK VFR rules » for class F or G »)
cloudbase was above 1000′ or less than 6/8 coverage.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Total
Good days	0	0	0	7	27	26	28	19	0	0	0	0	107	29%

Bad weather analysis

This is the number of days in each month, on average, for which (in this timeslot) no bad weather occurred. That is, for the entire timeslot, there was no rain, hail, snow, snow on the ground, icing conditions, thunderstorms, etc.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Total
Good days	26	25	28	27	28	28	28	28	27	26	25	25	322	88%

Wind speed analysis

This is the number of days in each month, on average, for which (in this timeslot) the maximum (gust) wind speed was less than or equal to the value shown on the left.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Total
≤ 5 mph	3	3	3	3	3	2	2	2	3	2	3	3	32	9%
≤ 10 mph	10	9	10	9	9	8	7	7	9	10	10	11	108	30%
≤ 15 mph	17	16	19	19	18	17	16	17	18	18	17	17	208	57%
≤ 20 mph	21	20	24	24	23	23	23	24	22	21	20	21	266	73%
≤ 30 mph	27	25	29	29	30	29	30	30	28	28	26	27	337	92%
≤ 40 mph	30	27	31	30	31	30	31	31	30	30	29	29	357	98%

Please send any comments, questions, or corrections to me, Mike Cowlishaw, at mfc@speleotrove.com.

	May	Jun	Jul	Aug	Total
≤ 5 mph		+0.1	−0.1		−0.1
≤ 10 mph	−0.1	+0.1	−0.1	−0.2	−0.3
≤ 15 mph				−0.2	−0.2
≤ 20 mph	+0.1			−0.2
≤ 30 mph		+0.1	+0.1		+0.1
≤ 40 mph	+0.1	+0.1	+0.1		+0.2
any wind	+0.1	+0.1	+0.1		+0.3