Rockridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rockridge Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	12% 9% 3 8% 5% 4 4 4 6% 7% 38%	101589
	Night	12% 9% 3 8% 5% 4 4 3 5% 6% 40%	97556
Transparency	Day	44% 5% 13% 25% 12% 1	105209
	Night	44% 5% 12% 25% 13% 2	102076
Seeing	Day	17% 8% 30% 27% 14% 4	16009
	Night	16% 7% 32% 33% 11% 1	25866

By Month

Percentage Cloud Cover SE (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	10% 17% 7% 18% 5% 5% 4 4 4 5% 21%	2527
	11th to 20th	Day	5% 13% 5% 13% 9% 7% 8% 6% 8% 5% 20%	2595
	21st to end	Day	8% 20% 6% 13% 6% 5% 5% 3 5% 6% 22%	3135
February	1st to 10th	Day	8% 12% 5% 9% 7% 6% 5% 5% 5% 6% 30%	1710
	11th to 20th	Day	9% 11% 4 10% 6% 6% 4 5% 5% 6% 33%	1664
	21st to end	Day	12% 12% 4 9% 6% 5% 5% 4 5% 7% 31%	1467
March	1st to 10th	Day	13% 10% 4 7% 5% 4 4 3 5% 6% 40%	3392
	11th to 20th	Day	10% 10% 3 8% 4 5% 4 3 5% 8% 39%	3480
	21st to end	Day	25% 12% 5% 11% 6% 4 4 2 4 5% 22%	3840
April	1st to 10th	Day	16% 10% 4 8% 4 4 4 4 5% 7% 34%	2280
	11th to 20th	Day	20% 12% 4 6% 4 4 4 3 5% 5% 32%	2265
	21st to end	Day	21% 12% 4 6% 5% 4 4 4 4 6% 30%	2470
May	1st to 10th	Day	17% 7% 2 5% 4 4 5% 4 6% 8% 39%	4228
	11th to 20th	Day	12% 7% 3 6% 4 4 4 4 5% 7% 44%	4399
	21st to end	Day	16% 8% 3 7% 5% 5% 4 4 5% 7% 37%	4824
June	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 6% 8% 46%	2660
	11th to 20th	Day	13% 6% 3 7% 4 5% 5% 4 6% 9% 38%	2660
	21st to end	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 9% 40%	2660
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 8% 10% 37%	4440
	11th to 20th	Day	6% 3 1 4 3 3 4 4 7% 9% 57%	4440
	21st to end	Day	6% 4 2 6% 4 5% 5% 5% 7% 8% 49%	4703
August	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 5% 7% 7% 41%	4104
	11th to 20th	Day	12% 5% 2 6% 5% 4 5% 3 7% 8% 42%	4041
	21st to end	Day	9% 6% 3 7% 4 4 4 3 6% 7% 48%	4340
September	1st to 10th	Day	12% 5% 2 6% 4 4 4 4 5% 7% 49%	2280
	11th to 20th	Day	12% 6% 2 5% 3 4 4 4 6% 7% 48%	2239
	21st to end	Day	14% 7% 2 6% 4 4 4 3 6% 6% 45%	2005
October	1st to 10th	Day	15% 8% 2 7% 4 4 3 3 5% 5% 44%	1900
	11th to 20th	Day	14% 9% 2 6% 5% 4 4 3 4 7% 42%	1900
	21st to end	Day	18% 11% 4 6% 4 3 4 3 5% 6% 37%	2085
November	1st to 10th	Day	11% 10% 4 8% 5% 4 4 3 5% 6% 39%	1595
	11th to 20th	Day	11% 13% 6% 11% 6% 4 4 4 5% 6% 30%	1520
	21st to end	Day	13% 11% 3 8% 5% 4 4 3 5% 7% 37%	1520
December	1st to 10th	Day	11% 13% 4 11% 9% 5% 5% 5% 5% 5% 28%	1520
	11th to 20th	Day	11% 13% 5% 11% 6% 5% 5% 3 5% 6% 29%	1918
	21st to end	Day	19% 14% 6% 19% 5% 4 3 2 4 5% 19%	2783
January	1st to 10th	Night	9% 15% 7% 17% 7% 4 4 3 4 5% 26%	4428
	11th to 20th	Night	7% 11% 6% 15% 7% 7% 7% 7% 8% 5% 21%	4372
	21st to end	Night	10% 18% 8% 13% 6% 4 4 3 4 5% 26%	4532
February	1st to 10th	Night	7% 12% 6% 11% 6% 5% 4 4 4 7% 34%	2470
	11th to 20th	Night	7% 10% 3 8% 6% 6% 5% 3 5% 7% 39%	2403
	21st to end	Night	12% 10% 4 8% 5% 5% 5% 4 4 6% 37%	1986
March	1st to 10th	Night	9% 7% 2 7% 5% 3 4 3 5% 7% 47%	3491
	11th to 20th	Night	9% 7% 3 7% 5% 5% 6% 4 6% 7% 42%	3480
	21st to end	Night	26% 12% 4 9% 4 2 3 3 3 5% 29%	3791
April	1st to 10th	Night	14% 12% 3 7% 4 4 5% 3 5% 7% 37%	1900
	11th to 20th	Night	19% 9% 4 9% 4 4 4 3 4 6% 34%	1861
	21st to end	Night	18% 9% 4 6% 6% 4 4 3 4 6% 36%	1710
May	1st to 10th	Night	14% 7% 2 7% 4 4 4 4 5% 6% 42%	2677
	11th to 20th	Night	14% 5% 1 4 3 3 4 3 6% 7% 50%	2506
	21st to end	Night	14% 7% 3 6% 4 4 4 3 5% 7% 44%	2743
June	1st to 10th	Night	10% 5% 2 3 4 3 4 4 6% 9% 49%	1520
	11th to 20th	Night	9% 5% 2 6% 4 5% 5% 4 7% 7% 46%	1520
	21st to end	Night	8% 4 2 5% 3 4 3 4 6% 8% 53%	1520
July	1st to 10th	Night	10% 5% 1 5% 4 4 5% 4 8% 11% 44%	2530
	11th to 20th	Night	3 2 1 4 3 4 5% 4 5% 9% 61%	2530
	21st to end	Night	6% 3 2 5% 3 4 4 3 5% 8% 58%	2843
August	1st to 10th	Night	12% 7% 2 5% 4 4 4 3 5% 6% 47%	2836
	11th to 20th	Night	12% 5% 2 5% 2 3 3 3 4 8% 52%	2798
	21st to end	Night	9% 7% 2 6% 4 4 4 3 5% 7% 49%	3321
September	1st to 10th	Night	10% 4 1 4 3 3 4 2 5% 8% 55%	1900
	11th to 20th	Night	9% 5% 2 4 3 3 3 4 5% 8% 54%	1938
	21st to end	Night	11% 6% 2 5% 3 3 4 3 4 5% 52%	2155
October	1st to 10th	Night	13% 6% 2 6% 3 3 3 3 4 6% 51%	2280
	11th to 20th	Night	14% 9% 2 6% 4 4 4 3 5% 6% 43%	2280
	21st to end	Night	18% 11% 3 6% 4 3 3 3 4 6% 37%	2513
November	1st to 10th	Night	13% 9% 3 6% 4 4 4 4 4 6% 42%	2579
	11th to 20th	Night	12% 12% 5% 10% 5% 4 4 3 4 5% 35%	2660
	21st to end	Night	13% 9% 3 8% 6% 4 4 3 4 6% 38%	2660
December	1st to 10th	Night	9% 12% 5% 12% 6% 5% 4 4 5% 6% 32%	2660
	11th to 20th	Night	11% 12% 5% 11% 7% 6% 5% 4 5% 6% 28%	3279
	21st to end	Night	22% 13% 5% 13% 6% 4 4 3 4 5% 20%	4884

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	66% 5% 11% 15% 4	2528
	11th to 20th	Day	61% 6% 10% 17% 6%	2595
	21st to end	Day	63% 5% 14% 14% 4	3135
February	1st to 10th	Day	54% 4 14% 19% 9% 1	1710
	11th to 20th	Day	51% 6% 11% 24% 8% 1	1673
	21st to end	Day	52% 5% 12% 19% 12%	1467
March	1st to 10th	Day	45% 4 13% 26% 11% 1	3392
	11th to 20th	Day	43% 5% 9% 31% 10% 2	3480
	21st to end	Day	66% 5% 8% 16% 5%	3840
April	1st to 10th	Day	50% 5% 11% 22% 11% 1	2280
	11th to 20th	Day	54% 4 10% 19% 12% 2	2265
	21st to end	Day	55% 4 12% 19% 9% 1	2470
May	1st to 10th	Day	42% 6% 11% 26% 14% 1	4266
	11th to 20th	Day	38% 6% 10% 29% 15% 2	4403
	21st to end	Day	46% 6% 11% 26% 11% 1	4837
June	1st to 10th	Day	34% 6% 14% 30% 15% 2	2660
	11th to 20th	Day	42% 6% 13% 23% 15% 1	2660
	21st to end	Day	37% 7% 17% 26% 11% 2	2660
July	1st to 10th	Day	39% 7% 20% 23% 10% 1	4371
	11th to 20th	Day	23% 5% 16% 35% 19% 2	4365
	21st to end	Day	29% 8% 14% 30% 18% 1	4555
August	1st to 10th	Day	39% 6% 11% 29% 13% 1	4090
	11th to 20th	Day	38% 6% 13% 33% 10%	4080
	21st to end	Day	35% 5% 16% 29% 14% 1	4339
September	1st to 10th	Day	35% 5% 13% 31% 15%	2280
	11th to 20th	Day	34% 5% 17% 33% 11%	2239
	21st to end	Day	39% 4 12% 32% 12% 1	2005
October	1st to 10th	Day	31% 3 7% 36% 23% 1	3160
	11th to 20th	Day	39% 4 11% 25% 20% 1	3140
	21st to end	Day	43% 3 14% 29% 10%	3411
November	1st to 10th	Day	46% 4 13% 20% 14% 3	1595
	11th to 20th	Day	54% 4 12% 18% 10% 1	1520
	21st to end	Day	47% 5% 17% 23% 7% 1	1520
December	1st to 10th	Day	58% 6% 15% 14% 7%	1520
	11th to 20th	Day	55% 5% 19% 16% 5%	1915
	21st to end	Day	69% 5% 9% 12% 5%	2783
January	1st to 10th	Night	61% 4 10% 19% 6%	4428
	11th to 20th	Night	60% 6% 11% 18% 5%	4372
	21st to end	Night	63% 3 10% 18% 6% 1	4532
February	1st to 10th	Night	51% 3 12% 22% 10% 1	2470
	11th to 20th	Night	45% 5% 14% 25% 9% 2	2404
	21st to end	Night	49% 4 11% 23% 12% 2	1986
March	1st to 10th	Night	37% 4 12% 28% 18% 1	3491
	11th to 20th	Night	39% 5% 8% 29% 17% 1	3480
	21st to end	Night	60% 3 7% 21% 8% 1	3791
April	1st to 10th	Night	47% 4 9% 25% 14% 1	1900
	11th to 20th	Night	52% 3 8% 19% 16% 3	1861
	21st to end	Night	49% 4 9% 22% 14% 2	1710
May	1st to 10th	Night	41% 7% 10% 20% 21% 2	2704
	11th to 20th	Night	32% 5% 11% 27% 20% 5%	2507
	21st to end	Night	40% 6% 11% 26% 16% 1	2751
June	1st to 10th	Night	31% 6% 13% 31% 18% 2	1520
	11th to 20th	Night	36% 4 15% 23% 19% 3	1520
	21st to end	Night	28% 5% 15% 32% 16% 3	1520
July	1st to 10th	Night	32% 7% 20% 26% 13% 2	2490
	11th to 20th	Night	20% 5% 15% 40% 18% 2	2482
	21st to end	Night	25% 5% 16% 32% 19% 3	2752
August	1st to 10th	Night	37% 5% 11% 29% 14% 4	2826
	11th to 20th	Night	33% 4 14% 33% 16% 1	2825
	21st to end	Night	34% 6% 17% 28% 14% 2	3321
September	1st to 10th	Night	27% 5% 13% 35% 20% 1	1900
	11th to 20th	Night	29% 5% 15% 33% 18% 1	1938
	21st to end	Night	33% 4 11% 31% 18% 1	2155
October	1st to 10th	Night	24% 2 5% 36% 28% 4	3800
	11th to 20th	Night	32% 5% 12% 25% 22% 4	3779
	21st to end	Night	43% 4 11% 29% 12% 1	4137
November	1st to 10th	Night	42% 5% 12% 24% 15% 2	2579
	11th to 20th	Night	52% 4 11% 20% 12% 1	2660
	21st to end	Night	48% 4 16% 24% 8% 1	2660
December	1st to 10th	Night	52% 4 15% 21% 7% 1	2660
	11th to 20th	Night	55% 6% 13% 19% 6% 1	3281
	21st to end	Night	66% 5% 9% 15% 4	4884

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	13% 10% 38% 29% 9% 2	270
	11th to 20th	Day	16% 12% 42% 24% 6%	270
	21st to end	Day	19% 9% 35% 25% 9% 3	297
February	1st to 10th	Day	14% 16% 45% 21% 4 1	270
	11th to 20th	Day	17% 15% 38% 22% 7% 1	270
	21st to end	Day	20% 12% 38% 27% 3	225
March	1st to 10th	Day	21% 11% 41% 19% 7%	270
	11th to 20th	Day	22% 11% 37% 21% 9% 1	270
	21st to end	Day	31% 11% 27% 22% 8% 2	311
April	1st to 10th	Day	24% 11% 37% 20% 7%	460
	11th to 20th	Day	29% 13% 24% 23% 10% 1	463
	21st to end	Day	28% 9% 29% 22% 10% 2	650
May	1st to 10th	Day	21% 10% 34% 25% 9% 1	653
	11th to 20th	Day	20% 9% 28% 26% 14% 3	675
	21st to end	Day	18% 7% 25% 32% 14% 3	734
June	1st to 10th	Day	11% 7% 27% 31% 19% 6%	680
	11th to 20th	Day	15% 5% 35% 30% 12% 3	680
	21st to end	Day	13% 6% 29% 30% 18% 5%	680
July	1st to 10th	Day	10% 4 20% 32% 25% 10%	671
	11th to 20th	Day	9% 5% 26% 31% 22% 7%	668
	21st to end	Day	7% 3 23% 40% 21% 7%	739
August	1st to 10th	Day	12% 3 22% 33% 25% 6%	676
	11th to 20th	Day	15% 3 19% 34% 24% 6%	665
	21st to end	Day	11% 3 26% 34% 19% 7%	634
September	1st to 10th	Day	16% 5% 27% 31% 17% 5%	490
	11th to 20th	Day	15% 4 27% 30% 20% 4	449
	21st to end	Day	17% 9% 31% 22% 14% 6%	300
October	1st to 10th	Day	17% 8% 29% 26% 15% 6%	300
	11th to 20th	Day	17% 16% 37% 22% 7% 1	300
	21st to end	Day	25% 13% 35% 19% 7% 1	330
November	1st to 10th	Day	19% 11% 38% 20% 10% 1	282
	11th to 20th	Day	16% 15% 44% 21% 4	270
	21st to end	Day	21% 11% 44% 19% 5%	270
December	1st to 10th	Day	16% 10% 41% 26% 6% 1	270
	11th to 20th	Day	19% 13% 38% 24% 6%	270
	21st to end	Day	27% 9% 43% 16% 4	297
January	1st to 10th	Night	13% 9% 39% 30% 7% 1	950
	11th to 20th	Night	17% 9% 37% 30% 7% 1	950
	21st to end	Night	19% 8% 35% 31% 6%	1045
February	1st to 10th	Night	13% 10% 40% 30% 7% 1	950
	11th to 20th	Night	13% 10% 41% 28% 7% 1	929
	21st to end	Night	17% 10% 36% 29% 8% 1	730
March	1st to 10th	Night	17% 9% 38% 27% 9% 1	620
	11th to 20th	Night	18% 8% 39% 28% 6% 1	570
	21st to end	Night	23% 9% 28% 27% 11% 2	627
April	1st to 10th	Night	20% 9% 36% 28% 7%	570
	11th to 20th	Night	23% 9% 30% 29% 8%	563
	21st to end	Night	22% 7% 33% 28% 9% 1	570
May	1st to 10th	Night	20% 6% 33% 32% 8% 1	570
	11th to 20th	Night	18% 7% 28% 35% 12% 1	561
	21st to end	Night	16% 5% 27% 38% 13% 1	617
June	1st to 10th	Night	13% 3 27% 40% 16%	570
	11th to 20th	Night	12% 3 31% 45% 9%	570
	21st to end	Night	9% 3 22% 48% 16% 1	570
July	1st to 10th	Night	7% 2 20% 43% 26% 3	555
	11th to 20th	Night	5% 3 22% 49% 19% 3	552
	21st to end	Night	5% 1 18% 54% 20% 2	624
August	1st to 10th	Night	9% 2 17% 47% 23% 2	567
	11th to 20th	Night	13% 2 15% 41% 26% 3	564
	21st to end	Night	10% 2 24% 38% 25% 2	627
September	1st to 10th	Night	12% 2 22% 42% 18% 4	570
	11th to 20th	Night	12% 4 30% 35% 16% 3	570
	21st to end	Night	14% 7% 30% 33% 15% 1	635
October	1st to 10th	Night	18% 7% 29% 31% 15% 1	760
	11th to 20th	Night	19% 9% 35% 30% 7% 1	760
	21st to end	Night	25% 9% 27% 31% 7%	836
November	1st to 10th	Night	18% 10% 34% 30% 8% 1	869
	11th to 20th	Night	18% 10% 38% 27% 6% 1	950
	21st to end	Night	17% 11% 39% 25% 8%	950
December	1st to 10th	Night	17% 8% 38% 30% 7% 1	950
	11th to 20th	Night	19% 7% 39% 27% 7% 1	950
	21st to end	Night	25% 10% 32% 27% 5%	1045

Page generated at 2024-11-03 01:11:10. Version ac07

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