Starmere Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starmere Observatory clear sky chart from 2005-11-06 to 2025-11-18.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	16% 8% 3 7% 5% 4 5% 4 6% 7% 35%	126908
	Night	17% 9% 3 8% 5% 4 4 3 5% 6% 35%	123426
Transparency	Day	44% 9% 14% 21% 12% 2	130397
	Night	46% 8% 13% 20% 12% 1	128024
Seeing	Day	21% 17% 30% 21% 9% 2	16196
	Night	21% 14% 31% 26% 7% 1	25242

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	11% 11% 5% 16% 5% 3 4 3 5% 6% 30%	3597
	11th to 20th	Day	13% 11% 4 10% 5% 5% 5% 4 5% 6% 31%	3570
	21st to end	Day	14% 10% 3 7% 7% 5% 4 4 6% 6% 35%	4126
February	1st to 10th	Day	15% 11% 4 8% 6% 6% 5% 5% 7% 6% 28%	1800
	11th to 20th	Day	12% 11% 4 9% 6% 6% 5% 4 6% 7% 32%	1935
	21st to end	Day	18% 9% 4 8% 6% 4 4 3 5% 6% 33%	1650
March	1st to 10th	Day	22% 13% 4 8% 4 3 3 2 4 5% 31%	4476
	11th to 20th	Day	13% 10% 3 7% 5% 4 5% 3 5% 6% 38%	4704
	21st to end	Day	20% 10% 3 8% 5% 4 4 3 4 6% 34%	5965
April	1st to 10th	Day	19% 10% 3 8% 5% 4 4 4 4 6% 34%	2400
	11th to 20th	Day	16% 8% 2 6% 5% 4 5% 3 5% 6% 38%	2374
	21st to end	Day	20% 6% 3 6% 5% 4 5% 3 5% 7% 35%	2480
May	1st to 10th	Day	28% 9% 2 7% 4 4 4 4 5% 7% 26%	5948
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 3 5% 7% 33%	6318
	21st to end	Day	20% 7% 3 6% 4 4 5% 4 7% 8% 32%	6949
June	1st to 10th	Day	15% 6% 3 6% 5% 5% 6% 5% 6% 9% 34%	2800
	11th to 20th	Day	15% 6% 2 6% 5% 5% 5% 5% 7% 10% 35%	2800
	21st to end	Day	14% 6% 3 7% 5% 5% 6% 5% 7% 8% 35%	2800
July	1st to 10th	Day	9% 7% 3 8% 6% 5% 5% 5% 8% 10% 35%	6360
	11th to 20th	Day	8% 5% 2 7% 5% 5% 6% 5% 9% 11% 36%	6360
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	6926
August	1st to 10th	Day	15% 7% 3 8% 5% 5% 6% 4 6% 8% 32%	4485
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 4 7% 10% 36%	3850
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 6% 9% 42%	4312
September	1st to 10th	Day	13% 5% 2 7% 4 4 5% 3 5% 7% 45%	2400
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 5% 8% 49%	2305
	21st to end	Day	15% 5% 2 6% 4 4 5% 4 6% 8% 40%	2200
October	1st to 10th	Day	19% 6% 3 7% 5% 4 5% 2 4 6% 40%	2095
	11th to 20th	Day	14% 8% 3 7% 4 3 4 3 5% 7% 41%	2000
	21st to end	Day	20% 9% 3 7% 5% 4 4 4 5% 6% 33%	1995
November	1st to 10th	Day	14% 8% 3 6% 4 4 3 3 6% 6% 44%	1851
	11th to 20th	Day	15% 8% 2 8% 5% 5% 4 3 6% 6% 37%	1863
	21st to end	Day	19% 9% 2 5% 5% 4 5% 4 5% 7% 34%	1668
December	1st to 10th	Day	15% 13% 3 7% 5% 4 6% 5% 5% 7% 30%	2600
	11th to 20th	Day	20% 10% 3 7% 5% 4 3 3 5% 6% 36%	2986
	21st to end	Day	20% 13% 4 9% 5% 4 4 3 5% 6% 28%	3960
January	1st to 10th	Night	14% 12% 6% 14% 5% 3 3 3 4 5% 31%	6349
	11th to 20th	Night	11% 11% 5% 15% 6% 5% 4 3 5% 7% 28%	6315
	21st to end	Night	16% 10% 4 8% 5% 5% 5% 4 5% 6% 32%	6812
February	1st to 10th	Night	16% 10% 4 9% 6% 5% 5% 4 5% 7% 31%	2600
	11th to 20th	Night	13% 11% 4 9% 6% 5% 5% 4 6% 6% 31%	2349
	21st to end	Night	17% 10% 3 8% 7% 4 5% 3 5% 6% 32%	1980
March	1st to 10th	Night	21% 10% 4 9% 5% 4 4 3 5% 5% 31%	5364
	11th to 20th	Night	17% 11% 4 7% 4 4 4 3 5% 6% 35%	5237
	21st to end	Night	20% 12% 3 8% 4 4 4 3 4 5% 32%	4967
April	1st to 10th	Night	18% 10% 4 8% 6% 4 5% 4 6% 7% 29%	2000
	11th to 20th	Night	21% 9% 3 6% 5% 4 3 3 4 6% 36%	1975
	21st to end	Night	20% 7% 2 7% 4 3 4 3 6% 5% 38%	1919
May	1st to 10th	Night	30% 10% 3 7% 4 4 4 3 4 6% 26%	4021
	11th to 20th	Night	19% 10% 3 8% 5% 5% 5% 4 5% 7% 30%	3575
	21st to end	Night	20% 8% 3 8% 4 5% 5% 4 6% 6% 31%	3926
June	1st to 10th	Night	17% 6% 3 7% 4 3 4 4 6% 8% 39%	1600
	11th to 20th	Night	14% 7% 2 5% 5% 5% 4 4 7% 9% 38%	1600
	21st to end	Night	12% 5% 2 6% 4 5% 5% 4 6% 8% 42%	1600
July	1st to 10th	Night	12% 6% 2 6% 5% 4 5% 4 6% 9% 41%	3600
	11th to 20th	Night	11% 7% 3 8% 5% 5% 6% 4 7% 10% 34%	3600
	21st to end	Night	10% 6% 2 6% 4 5% 4 3 6% 7% 46%	3926
August	1st to 10th	Night	19% 7% 3 8% 5% 5% 4 4 6% 6% 35%	2616
	11th to 20th	Night	13% 7% 3 7% 5% 5% 5% 4 6% 8% 39%	3196
	21st to end	Night	12% 5% 2 6% 4 5% 4 3 5% 7% 46%	3586
September	1st to 10th	Night	14% 6% 2 6% 4 5% 4 3 6% 6% 42%	2000
	11th to 20th	Night	12% 5% 1 4 3 3 4 2 4 7% 54%	2095
	21st to end	Night	15% 6% 3 7% 5% 4 4 3 5% 6% 43%	2200
October	1st to 10th	Night	18% 7% 2 7% 4 4 4 4 5% 6% 39%	2301
	11th to 20th	Night	16% 7% 2 6% 4 4 5% 4 5% 6% 41%	2400
	21st to end	Night	23% 9% 2 6% 4 4 4 3 5% 6% 34%	2844
November	1st to 10th	Night	15% 7% 2 6% 4 4 3 3 6% 7% 43%	2667
	11th to 20th	Night	18% 9% 3 7% 5% 4 4 3 4 6% 37%	2692
	21st to end	Night	16% 9% 3 7% 5% 5% 5% 3 6% 6% 36%	2730
December	1st to 10th	Night	18% 12% 5% 7% 6% 4 5% 3 5% 7% 29%	4580
	11th to 20th	Night	24% 10% 3 7% 4 3 3 3 4 5% 34%	5208
	21st to end	Night	21% 14% 4 9% 5% 5% 4 3 4 4 27%	6996

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	50% 6% 14% 22% 7%	3598
	11th to 20th	Day	48% 8% 13% 18% 10% 3	3600
	21st to end	Day	46% 9% 11% 21% 12% 1	4126
February	1st to 10th	Day	52% 9% 13% 17% 9% 1	1800
	11th to 20th	Day	48% 8% 12% 20% 10% 2	1944
	21st to end	Day	49% 7% 12% 19% 12% 1	1650
March	1st to 10th	Day	53% 6% 12% 15% 9% 6%	4479
	11th to 20th	Day	39% 10% 19% 22% 7% 3	4704
	21st to end	Day	48% 6% 9% 15% 18% 4	5965
April	1st to 10th	Day	50% 7% 10% 20% 12% 3	2400
	11th to 20th	Day	44% 7% 12% 20% 14% 2	2374
	21st to end	Day	46% 7% 11% 19% 14% 3	2480
May	1st to 10th	Day	55% 10% 11% 14% 8% 1	5959
	11th to 20th	Day	47% 9% 14% 19% 10% 1	6322
	21st to end	Day	45% 10% 13% 22% 10% 1	6949
June	1st to 10th	Day	44% 9% 15% 20% 11% 1	2800
	11th to 20th	Day	42% 10% 15% 21% 11% 1	2800
	21st to end	Day	44% 9% 14% 21% 11% 1	2800
July	1st to 10th	Day	43% 10% 13% 20% 13% 1	6290
	11th to 20th	Day	36% 12% 18% 23% 11%	6285
	21st to end	Day	38% 8% 15% 23% 15% 1	6728
August	1st to 10th	Day	46% 11% 16% 18% 9% 1	4471
	11th to 20th	Day	39% 10% 19% 26% 6%	3886
	21st to end	Day	34% 10% 16% 28% 11% 1	4312
September	1st to 10th	Day	39% 8% 13% 24% 15% 1	2400
	11th to 20th	Day	33% 7% 13% 24% 21% 2	2305
	21st to end	Day	39% 8% 15% 22% 14% 2	2200
October	1st to 10th	Day	39% 8% 10% 21% 22% 1	3407
	11th to 20th	Day	34% 6% 11% 27% 21% 1	3240
	21st to end	Day	35% 8% 14% 26% 14% 2	3195
November	1st to 10th	Day	39% 6% 15% 25% 14% 2	1851
	11th to 20th	Day	44% 7% 13% 19% 15% 2	1863
	21st to end	Day	46% 8% 15% 22% 7% 1	1668
December	1st to 10th	Day	49% 9% 16% 21% 5%	2600
	11th to 20th	Day	46% 8% 15% 20% 10% 1	2986
	21st to end	Day	52% 7% 11% 17% 12% 1	3960
January	1st to 10th	Night	52% 8% 12% 18% 10% 1	6349
	11th to 20th	Night	50% 10% 14% 15% 9% 3	6360
	21st to end	Night	49% 7% 12% 15% 14% 3	6812
February	1st to 10th	Night	50% 8% 13% 19% 8% 1	2600
	11th to 20th	Night	49% 8% 13% 17% 11% 2	2351
	21st to end	Night	48% 8% 14% 19% 9% 3	1980
March	1st to 10th	Night	49% 8% 13% 17% 11% 2	5374
	11th to 20th	Night	45% 9% 18% 18% 8% 2	5238
	21st to end	Night	50% 6% 8% 15% 18% 3	4967
April	1st to 10th	Night	53% 6% 11% 18% 10% 2	2000
	11th to 20th	Night	47% 6% 11% 18% 16% 1	1975
	21st to end	Night	46% 6% 10% 19% 15% 3	1919
May	1st to 10th	Night	58% 8% 12% 12% 8% 2	4027
	11th to 20th	Night	50% 11% 12% 16% 10% 1	3576
	21st to end	Night	49% 10% 13% 17% 10% 1	3927
June	1st to 10th	Night	42% 7% 13% 23% 13% 2	1600
	11th to 20th	Night	40% 11% 15% 23% 10%	1600
	21st to end	Night	36% 11% 15% 23% 14% 1	1600
July	1st to 10th	Night	39% 9% 15% 20% 15% 1	3560
	11th to 20th	Night	42% 10% 16% 20% 11%	3552
	21st to end	Night	35% 7% 15% 28% 14% 1	3809
August	1st to 10th	Night	47% 9% 15% 19% 9% 1	2606
	11th to 20th	Night	40% 10% 17% 25% 8%	3226
	21st to end	Night	33% 8% 15% 32% 11% 1	3586
September	1st to 10th	Night	39% 7% 12% 25% 16% 1	2000
	11th to 20th	Night	31% 6% 12% 27% 23% 1	2095
	21st to end	Night	39% 7% 12% 24% 18% 1	2200
October	1st to 10th	Night	42% 8% 13% 22% 14% 1	3769
	11th to 20th	Night	31% 7% 12% 26% 23%	3899
	21st to end	Night	36% 6% 14% 29% 14% 1	4594
November	1st to 10th	Night	39% 8% 12% 23% 17% 2	2667
	11th to 20th	Night	46% 6% 13% 20% 13% 3	2692
	21st to end	Night	45% 8% 17% 22% 7% 1	2730
December	1st to 10th	Night	51% 8% 15% 21% 5%	4580
	11th to 20th	Night	51% 6% 14% 14% 14% 1	5208
	21st to end	Night	54% 8% 12% 14% 10% 2	6996

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	27% 26% 31% 12% 5%	200
	11th to 20th	Day	27% 26% 33% 12% 3	200
	21st to end	Day	23% 26% 34% 14% 3 1	257
February	1st to 10th	Day	34% 25% 32% 8% 1	300
	11th to 20th	Day	29% 29% 30% 11% 1	483
	21st to end	Day	27% 25% 34% 12% 2	414
March	1st to 10th	Day	26% 22% 35% 14% 2	500
	11th to 20th	Day	25% 25% 33% 14% 2 1	500
	21st to end	Day	33% 21% 27% 12% 5% 2	550
April	1st to 10th	Day	31% 23% 26% 14% 5%	500
	11th to 20th	Day	27% 26% 26% 15% 5% 1	492
	21st to end	Day	27% 19% 32% 16% 5% 1	500
May	1st to 10th	Day	30% 20% 27% 16% 6% 1	503
	11th to 20th	Day	21% 17% 34% 19% 7% 1	527
	21st to end	Day	20% 12% 29% 26% 10% 2	573
June	1st to 10th	Day	19% 11% 32% 25% 11% 2	530
	11th to 20th	Day	17% 15% 30% 25% 11% 2	530
	21st to end	Day	15% 12% 32% 26% 12% 2	530
July	1st to 10th	Day	10% 8% 33% 30% 16% 3	525
	11th to 20th	Day	10% 7% 30% 33% 17% 3	524
	21st to end	Day	11% 9% 33% 31% 15% 2	576
August	1st to 10th	Day	10% 6% 28% 35% 16% 5%	526
	11th to 20th	Day	14% 6% 26% 30% 17% 7%	519
	21st to end	Day	10% 9% 30% 30% 15% 6%	583
September	1st to 10th	Day	18% 9% 23% 30% 14% 6%	530
	11th to 20th	Day	12% 10% 27% 24% 16% 12%	530
	21st to end	Day	19% 9% 28% 27% 13% 4	530
October	1st to 10th	Day	21% 13% 25% 21% 14% 6%	530
	11th to 20th	Day	20% 17% 32% 21% 8% 2	530
	21st to end	Day	25% 15% 33% 19% 7% 1	470
November	1st to 10th	Day	22% 21% 27% 20% 9% 1	425
	11th to 20th	Day	21% 25% 30% 18% 5% 1	421
	21st to end	Day	28% 19% 29% 21% 1	268
December	1st to 10th	Day	23% 26% 30% 16% 7%	200
	11th to 20th	Day	28% 31% 29% 10% 4	200
	21st to end	Day	21% 21% 40% 14% 4	220
January	1st to 10th	Night	21% 19% 38% 19% 2	800
	11th to 20th	Night	24% 20% 35% 20% 1	800
	21st to end	Night	19% 20% 38% 20% 2	880
February	1st to 10th	Night	23% 19% 36% 21% 2	800
	11th to 20th	Night	24% 21% 39% 16%	783
	21st to end	Night	26% 18% 36% 17% 2	660
March	1st to 10th	Night	24% 21% 35% 18% 2	800
	11th to 20th	Night	23% 21% 37% 17% 3	800
	21st to end	Night	25% 22% 31% 18% 5%	880
April	1st to 10th	Night	24% 22% 32% 20% 3	800
	11th to 20th	Night	26% 18% 32% 18% 6%	791
	21st to end	Night	25% 17% 31% 21% 5%	719
May	1st to 10th	Night	25% 16% 32% 21% 6%	593
	11th to 20th	Night	19% 13% 37% 27% 4	394
	21st to end	Night	15% 10% 30% 36% 8%	433
June	1st to 10th	Night	17% 9% 31% 35% 9% 1	400
	11th to 20th	Night	17% 7% 31% 33% 11% 1	400
	21st to end	Night	13% 6% 27% 42% 12% 1	400
July	1st to 10th	Night	15% 4 22% 42% 16% 1	390
	11th to 20th	Night	12% 4 23% 41% 18% 1	388
	21st to end	Night	12% 5% 24% 46% 13% 1	438
August	1st to 10th	Night	11% 3 20% 47% 17% 1	415
	11th to 20th	Night	13% 4 19% 40% 21% 2	789
	21st to end	Night	15% 5% 24% 37% 19% 2	880
September	1st to 10th	Night	16% 6% 28% 34% 15% 1	800
	11th to 20th	Night	14% 8% 24% 30% 20% 5%	800
	21st to end	Night	17% 8% 27% 34% 12% 2	800
October	1st to 10th	Night	23% 9% 24% 28% 14% 2	800
	11th to 20th	Night	18% 12% 33% 28% 7% 1	800
	21st to end	Night	27% 13% 31% 25% 4	880
November	1st to 10th	Night	21% 14% 33% 25% 7%	820
	11th to 20th	Night	24% 14% 34% 21% 7% 1	829
	21st to end	Night	19% 17% 35% 24% 5% 1	800
December	1st to 10th	Night	25% 18% 34% 19% 5%	800
	11th to 20th	Night	25% 17% 32% 25% 2	800
	21st to end	Night	26% 17% 36% 19% 2	880

Page generated at 2025-11-15 00:56:00. Version ac07

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