Jock River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jock River Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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% 10% 4 8% 5% 5% 5% 4 5% 7% 32%	131959
	Night	17% 12% 4 9% 5% 5% 4 3 5% 6% 30%	130511
Transparency	Day	51% 5% 12% 21% 10% 1	135424
	Night	54% 5% 11% 19% 10% 1	135133
Seeing	Day	23% 15% 30% 21% 9% 3	16282
	Night	22% 12% 30% 26% 9% 1	25503

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	14% 16% 6% 13% 6% 5% 4 3 5% 6% 20%	4661
	11th to 20th	Day	13% 17% 7% 13% 7% 5% 5% 3 4 5% 20%	4650
	21st to end	Day	9% 14% 7% 14% 8% 8% 6% 4 5% 5% 19%	5346
February	1st to 10th	Day	14% 16% 4 12% 6% 5% 5% 4 5% 5% 25%	1890
	11th to 20th	Day	13% 16% 5% 10% 7% 4 4 3 5% 6% 28%	1855
	21st to end	Day	19% 15% 4 9% 6% 5% 4 4 5% 5% 25%	1730
March	1st to 10th	Day	18% 12% 4 11% 6% 5% 4 4 5% 5% 26%	4576
	11th to 20th	Day	12% 12% 4 9% 6% 5% 6% 4 5% 7% 30%	5082
	21st to end	Day	18% 11% 3 8% 4 3 3 3 4 5% 38%	5907
April	1st to 10th	Day	22% 11% 3 7% 5% 4 3 3 4 6% 32%	2520
	11th to 20th	Day	22% 10% 3 6% 4 4 4 3 4 5% 35%	2494
	21st to end	Day	22% 10% 3 7% 5% 4 4 3 4 5% 33%	2658
May	1st to 10th	Day	24% 10% 3 8% 5% 5% 4 4 6% 6% 26%	6360
	11th to 20th	Day	17% 9% 4 9% 6% 5% 5% 4 5% 7% 30%	6318
	21st to end	Day	20% 8% 3 7% 4 5% 5% 3 5% 7% 33%	6949
June	1st to 10th	Day	21% 8% 2 7% 5% 5% 5% 4 5% 6% 30%	2800
	11th to 20th	Day	14% 6% 2 7% 5% 4 5% 5% 6% 7% 39%	2800
	21st to end	Day	18% 7% 3 7% 6% 5% 5% 4 6% 7% 33%	2800
July	1st to 10th	Day	13% 6% 3 8% 5% 5% 6% 4 7% 9% 34%	6360
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 4 6% 9% 42%	6360
	21st to end	Day	9% 5% 2 5% 4 4 4 4 7% 10% 45%	6926
August	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 4 5% 8% 37%	4499
	11th to 20th	Day	16% 7% 2 6% 4 4 4 4 6% 8% 39%	4113
	21st to end	Day	15% 6% 2 6% 4 4 5% 4 7% 9% 39%	4312
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 5% 8% 43%	2400
	11th to 20th	Day	12% 5% 2 5% 5% 3 4 4 5% 7% 48%	2397
	21st to end	Day	18% 6% 2 6% 5% 4 4 4 5% 7% 40%	2140
October	1st to 10th	Day	20% 7% 2 6% 5% 4 4 3 5% 7% 37%	2000
	11th to 20th	Day	20% 8% 3 8% 7% 5% 5% 4 6% 6% 30%	2000
	21st to end	Day	24% 11% 3 7% 4 4 5% 3 4 5% 28%	2035
November	1st to 10th	Day	16% 10% 3 7% 5% 5% 5% 4 6% 7% 32%	1851
	11th to 20th	Day	18% 12% 4 9% 5% 5% 4 3 4 6% 29%	1696
	21st to end	Day	22% 14% 5% 8% 6% 6% 5% 3 5% 5% 21%	1680
December	1st to 10th	Day	20% 19% 6% 10% 5% 6% 4 4 5% 5% 15%	2680
	11th to 20th	Day	18% 15% 5% 12% 6% 5% 5% 3 4 4 23%	3066
	21st to end	Day	23% 15% 5% 12% 6% 5% 5% 3 3 4 21%	4048
January	1st to 10th	Night	14% 17% 8% 15% 6% 5% 4 3 4 5% 20%	8234
	11th to 20th	Night	12% 16% 6% 15% 8% 6% 5% 4 4 5% 18%	8235
	21st to end	Night	12% 16% 6% 11% 6% 6% 5% 4 5% 6% 23%	8818
February	1st to 10th	Night	13% 15% 5% 12% 7% 6% 5% 4 6% 5% 24%	2730
	11th to 20th	Night	13% 14% 5% 12% 6% 5% 4 4 5% 4 28%	2650
	21st to end	Night	16% 14% 4 10% 6% 5% 4 4 4 5% 28%	2076
March	1st to 10th	Night	22% 14% 4 9% 5% 4 3 3 4 4 29%	5484
	11th to 20th	Night	14% 12% 4 8% 5% 5% 4 4 6% 8% 31%	5094
	21st to end	Night	19% 11% 4 8% 4 4 4 3 5% 5% 34%	5266
April	1st to 10th	Night	21% 11% 3 7% 5% 4 4 4 4 6% 32%	2100
	11th to 20th	Night	20% 10% 3 8% 5% 4 4 3 4 5% 36%	2075
	21st to end	Night	22% 8% 3 7% 4 4 3 2 5% 7% 35%	1979
May	1st to 10th	Night	23% 9% 3 8% 5% 5% 6% 5% 7% 7% 24%	3602
	11th to 20th	Night	15% 8% 3 7% 5% 4 4 4 5% 7% 37%	3575
	21st to end	Night	17% 10% 3 7% 5% 5% 5% 4 6% 7% 32%	3926
June	1st to 10th	Night	16% 7% 3 7% 6% 5% 6% 4 6% 8% 33%	1600
	11th to 20th	Night	16% 5% 3 7% 3 4 4 4 5% 8% 42%	1600
	21st to end	Night	20% 6% 2 7% 5% 4 4 4 6% 7% 35%	1600
July	1st to 10th	Night	13% 6% 3 9% 5% 5% 5% 4 6% 9% 34%	3600
	11th to 20th	Night	12% 5% 2 7% 5% 5% 5% 4 6% 8% 43%	3600
	21st to end	Night	9% 6% 2 7% 5% 4 4 4 6% 8% 46%	3926
August	1st to 10th	Night	12% 7% 2 7% 4 4 4 5% 6% 8% 40%	2646
	11th to 20th	Night	13% 7% 3 6% 5% 4 5% 4 6% 7% 41%	2903
	21st to end	Night	12% 6% 2 7% 4 4 5% 4 6% 8% 41%	3586
September	1st to 10th	Night	11% 5% 2 7% 5% 4 4 3 5% 7% 47%	2000
	11th to 20th	Night	14% 4 1 6% 3 3 3 3 5% 7% 50%	2002
	21st to end	Night	16% 6% 3 6% 5% 4 4 3 4 6% 44%	2257
October	1st to 10th	Night	17% 7% 3 6% 3 4 4 3 6% 6% 40%	2400
	11th to 20th	Night	20% 10% 3 8% 5% 4 4 4 5% 6% 33%	2400
	21st to end	Night	23% 10% 4 7% 5% 5% 4 3 5% 6% 29%	2803
November	1st to 10th	Night	20% 11% 3 8% 5% 4 3 2 4 6% 34%	2667
	11th to 20th	Night	17% 11% 3 9% 6% 5% 4 3 5% 6% 31%	2919
	21st to end	Night	21% 14% 4 9% 5% 5% 4 3 5% 6% 24%	2940
December	1st to 10th	Night	19% 17% 5% 11% 6% 6% 5% 4 5% 6% 17%	4720
	11th to 20th	Night	23% 15% 4 10% 6% 4 4 3 3 4 25%	5348
	21st to end	Night	26% 17% 3 10% 4 4 4 3 4 4 20%	7150

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	65% 4 13% 14% 4	4662
	11th to 20th	Day	68% 3 9% 11% 9%	4680
	21st to end	Day	65% 5% 11% 10% 8%	5346
February	1st to 10th	Day	60% 4 9% 20% 5% 1	1890
	11th to 20th	Day	57% 4 11% 18% 8% 1	1864
	21st to end	Day	62% 4 10% 14% 9% 1	1730
March	1st to 10th	Day	59% 4 10% 14% 11% 3	4579
	11th to 20th	Day	52% 5% 17% 16% 9% 1	5082
	21st to end	Day	51% 3 6% 20% 17% 3	5907
April	1st to 10th	Day	54% 4 7% 20% 12% 3	2520
	11th to 20th	Day	52% 3 6% 22% 15% 2	2494
	21st to end	Day	55% 3 8% 17% 14% 4	2658
May	1st to 10th	Day	57% 5% 9% 19% 8% 2	6371
	11th to 20th	Day	53% 5% 12% 19% 10% 1	6322
	21st to end	Day	51% 4 11% 21% 11% 1	6949
June	1st to 10th	Day	54% 5% 9% 19% 12% 1	2800
	11th to 20th	Day	42% 6% 12% 25% 13% 2	2800
	21st to end	Day	49% 6% 13% 21% 10% 1	2800
July	1st to 10th	Day	43% 7% 15% 25% 10%	6290
	11th to 20th	Day	37% 7% 14% 30% 13%	6285
	21st to end	Day	33% 7% 14% 36% 10%	6728
August	1st to 10th	Day	45% 6% 15% 25% 9%	4485
	11th to 20th	Day	42% 5% 15% 28% 8% 1	4152
	21st to end	Day	40% 6% 15% 26% 12%	4312
September	1st to 10th	Day	39% 6% 14% 31% 11%	2400
	11th to 20th	Day	35% 5% 12% 33% 14% 1	2397
	21st to end	Day	44% 5% 15% 25% 11%	2140
October	1st to 10th	Day	46% 5% 12% 30% 8%	3260
	11th to 20th	Day	46% 5% 15% 24% 8% 1	3240
	21st to end	Day	49% 5% 17% 21% 7%	3260
November	1st to 10th	Day	50% 6% 14% 22% 7% 1	1851
	11th to 20th	Day	57% 4 13% 16% 9% 1	1696
	21st to end	Day	65% 5% 13% 10% 6%	1680
December	1st to 10th	Day	70% 6% 11% 10% 2	2680
	11th to 20th	Day	63% 6% 10% 15% 6%	3066
	21st to end	Day	68% 4 8% 15% 4	4048
January	1st to 10th	Night	68% 3 11% 13% 4 1	8234
	11th to 20th	Night	68% 4 10% 12% 6%	8280
	21st to end	Night	61% 4 9% 14% 11% 1	8818
February	1st to 10th	Night	61% 4 9% 17% 7% 1	2730
	11th to 20th	Night	59% 3 10% 19% 8%	2652
	21st to end	Night	57% 4 9% 18% 10% 1	2076
March	1st to 10th	Night	60% 3 8% 15% 11% 3	5494
	11th to 20th	Night	52% 4 17% 16% 8% 3	5095
	21st to end	Night	52% 3 6% 22% 14% 2	5266
April	1st to 10th	Night	54% 4 8% 18% 13% 2	2100
	11th to 20th	Night	51% 4 7% 21% 15% 1	2075
	21st to end	Night	51% 3 7% 18% 17% 3	1979
May	1st to 10th	Night	58% 5% 10% 18% 8% 3	3608
	11th to 20th	Night	46% 5% 14% 20% 14% 1	3576
	21st to end	Night	50% 5% 12% 18% 14% 1	3927
June	1st to 10th	Night	48% 6% 12% 21% 12% 1	1600
	11th to 20th	Night	40% 5% 12% 24% 17% 2	1600
	21st to end	Night	48% 5% 12% 20% 14% 1	1600
July	1st to 10th	Night	45% 8% 16% 19% 12% 1	3560
	11th to 20th	Night	37% 8% 13% 31% 12%	3552
	21st to end	Night	36% 6% 12% 30% 15%	3809
August	1st to 10th	Night	40% 7% 15% 26% 11%	2636
	11th to 20th	Night	40% 7% 16% 29% 8%	2930
	21st to end	Night	39% 6% 15% 26% 12% 2	3586
September	1st to 10th	Night	37% 5% 11% 31% 15% 1	2000
	11th to 20th	Night	34% 4 13% 36% 11% 1	2002
	21st to end	Night	42% 4 12% 29% 13%	2257
October	1st to 10th	Night	40% 5% 13% 29% 12% 1	3920
	11th to 20th	Night	45% 5% 15% 25% 10%	3899
	21st to end	Night	48% 6% 16% 21% 8%	4528
November	1st to 10th	Night	52% 4 14% 21% 9% 1	2667
	11th to 20th	Night	55% 4 12% 18% 9% 1	2919
	21st to end	Night	62% 4 13% 16% 5%	2940
December	1st to 10th	Night	68% 6% 12% 12% 3	4720
	11th to 20th	Night	64% 4 7% 14% 10% 1	5348
	21st to end	Night	68% 3 7% 13% 9%	7150

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	22% 20% 31% 22% 5%	220
	11th to 20th	Day	30% 17% 35% 13% 4 1	220
	21st to end	Day	19% 23% 35% 17% 6%	283
February	1st to 10th	Day	30% 20% 33% 15% 2	330
	11th to 20th	Day	25% 26% 37% 11%	342
	21st to end	Day	28% 19% 35% 16% 2	446
March	1st to 10th	Day	26% 19% 34% 16% 5%	540
	11th to 20th	Day	29% 18% 32% 17% 4	540
	21st to end	Day	30% 21% 27% 14% 7% 1	594
April	1st to 10th	Day	31% 21% 29% 14% 4 1	540
	11th to 20th	Day	33% 21% 21% 14% 9% 2	532
	21st to end	Day	33% 18% 29% 13% 6% 1	540
May	1st to 10th	Day	25% 16% 31% 21% 6% 2	507
	11th to 20th	Day	19% 17% 32% 20% 9% 2	527
	21st to end	Day	19% 16% 29% 24% 11% 1	573
June	1st to 10th	Day	25% 11% 29% 23% 9% 2	530
	11th to 20th	Day	16% 15% 32% 25% 10% 2	530
	21st to end	Day	21% 14% 30% 22% 10% 3	530
July	1st to 10th	Day	13% 8% 31% 29% 16% 3	525
	11th to 20th	Day	12% 8% 32% 30% 14% 3	524
	21st to end	Day	12% 8% 32% 30% 14% 4	576
August	1st to 10th	Day	13% 8% 26% 32% 17% 4	526
	11th to 20th	Day	14% 8% 24% 29% 17% 8%	519
	21st to end	Day	14% 10% 30% 26% 13% 7%	583
September	1st to 10th	Day	17% 11% 29% 20% 15% 9%	530
	11th to 20th	Day	12% 7% 24% 25% 20% 12%	530
	21st to end	Day	18% 10% 32% 21% 14% 5%	530
October	1st to 10th	Day	23% 13% 24% 22% 12% 5%	530
	11th to 20th	Day	25% 17% 31% 20% 6% 1	530
	21st to end	Day	30% 15% 28% 22% 5%	492
November	1st to 10th	Day	27% 17% 29% 18% 7% 1	425
	11th to 20th	Day	25% 19% 36% 14% 4 3	236
	21st to end	Day	32% 18% 32% 13% 4 1	220
December	1st to 10th	Day	29% 18% 33% 16% 4	220
	11th to 20th	Day	31% 24% 30% 11% 3	220
	21st to end	Day	32% 19% 32% 13% 3 1	242
January	1st to 10th	Night	25% 16% 35% 20% 4	840
	11th to 20th	Night	28% 17% 29% 21% 5%	840
	21st to end	Night	20% 14% 36% 25% 5% 1	924
February	1st to 10th	Night	22% 15% 36% 23% 4	840
	11th to 20th	Night	21% 17% 38% 20% 4	823
	21st to end	Night	24% 19% 30% 24% 3	692
March	1st to 10th	Night	25% 15% 35% 21% 4	840
	11th to 20th	Night	24% 20% 32% 20% 5%	840
	21st to end	Night	26% 16% 27% 23% 7%	924
April	1st to 10th	Night	28% 14% 30% 23% 5%	840
	11th to 20th	Night	25% 16% 29% 23% 7%	831
	21st to end	Night	26% 14% 28% 24% 7% 1	719
May	1st to 10th	Night	24% 11% 29% 26% 8% 1	402
	11th to 20th	Night	22% 10% 27% 31% 9%	394
	21st to end	Night	14% 6% 40% 28% 12%	433
June	1st to 10th	Night	18% 6% 32% 36% 8% 1	400
	11th to 20th	Night	18% 8% 29% 34% 11% 1	400
	21st to end	Night	21% 7% 32% 27% 13% 1	400
July	1st to 10th	Night	9% 6% 29% 42% 13%	390
	11th to 20th	Night	12% 5% 24% 44% 14% 1	388
	21st to end	Night	10% 4 29% 40% 15% 2	438
August	1st to 10th	Night	12% 3 24% 41% 20%	432
	11th to 20th	Night	13% 4 21% 38% 23% 2	609
	21st to end	Night	13% 6% 27% 32% 19% 2	880
September	1st to 10th	Night	14% 7% 28% 33% 17% 1	800
	11th to 20th	Night	16% 6% 21% 31% 23% 4	800
	21st to end	Night	18% 8% 26% 26% 20% 2	800
October	1st to 10th	Night	19% 9% 29% 27% 15% 2	800
	11th to 20th	Night	25% 12% 30% 25% 8% 1	800
	21st to end	Night	26% 14% 27% 27% 6%	880
November	1st to 10th	Night	28% 14% 27% 23% 8% 1	820
	11th to 20th	Night	24% 17% 33% 17% 9% 1	840
	21st to end	Night	29% 17% 27% 21% 6%	840
December	1st to 10th	Night	30% 15% 28% 22% 4	840
	11th to 20th	Night	28% 17% 30% 19% 5% 1	840
	21st to end	Night	35% 13% 30% 19% 4	924

Page generated at 2026-04-29 02:21:41. Version ac07

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