Albert L. Ruppel Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Albert L. Ruppel Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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% 7% 3 6% 4 4 4 4 6% 8% 43%	101192
	Night	13% 8% 3 7% 4 4 4 3 5% 6% 43%	97864
Transparency	Day	38% 5% 12% 25% 17% 2	104812
	Night	39% 5% 11% 24% 18% 3	102385
Seeing	Day	17% 12% 28% 26% 14% 4	15625
	Night	17% 11% 30% 28% 13% 1	25425

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	9% 12% 7% 10% 6% 5% 5% 4 6% 7% 30%	2527
	11th to 20th	Day	12% 10% 4 8% 5% 6% 5% 3 5% 6% 36%	2758
	21st to end	Day	21% 17% 6% 7% 4 3 3 3 4 4 30%	3135
February	1st to 10th	Day	15% 11% 4 9% 5% 3 4 4 6% 5% 34%	1710
	11th to 20th	Day	15% 9% 3 7% 5% 5% 5% 4 5% 6% 38%	1820
	21st to end	Day	15% 11% 3 8% 4 4 3 3 4 7% 39%	1570
March	1st to 10th	Day	18% 12% 3 6% 3 3 3 3 4 5% 41%	3184
	11th to 20th	Day	12% 8% 2 5% 4 3 4 3 4 6% 49%	3480
	21st to end	Day	15% 9% 3 7% 5% 4 5% 4 6% 7% 35%	4003
April	1st to 10th	Day	11% 7% 2 7% 5% 4 5% 3 6% 7% 43%	2280
	11th to 20th	Day	16% 8% 2 6% 4 4 4 3 5% 6% 41%	2254
	21st to end	Day	17% 7% 2 8% 5% 5% 5% 4 5% 6% 37%	2280
May	1st to 10th	Day	14% 8% 3 7% 5% 5% 6% 5% 7% 9% 32%	3829
	11th to 20th	Day	18% 8% 2 6% 4 4 4 3 6% 7% 38%	4366
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 3 6% 7% 44%	4824
June	1st to 10th	Day	8% 5% 2 5% 5% 5% 5% 4 6% 8% 47%	2660
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 6% 10% 51%	2660
	21st to end	Day	5% 4 2 5% 4 5% 5% 4 8% 11% 47%	2660
July	1st to 10th	Day	13% 5% 2 6% 5% 5% 5% 4 6% 9% 40%	4440
	11th to 20th	Day	4 4 2 5% 4 4 5% 4 7% 11% 50%	4440
	21st to end	Day	7% 5% 2 7% 4 5% 6% 5% 7% 10% 41%	4540
August	1st to 10th	Day	5% 4 1 4 4 5% 5% 4 7% 10% 51%	4104
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 4 6% 9% 42%	3729
	21st to end	Day	7% 4 2 4 4 4 4 4 6% 9% 53%	4180
September	1st to 10th	Day	13% 4 2 5% 3 3 3 3 5% 8% 50%	2280
	11th to 20th	Day	10% 5% 2 6% 3 3 4 3 5% 9% 49%	2262
	21st to end	Day	8% 5% 2 5% 4 3 4 3 5% 8% 53%	2072
October	1st to 10th	Day	9% 5% 2 4 4 3 3 2 5% 6% 55%	1900
	11th to 20th	Day	13% 6% 2 6% 3 3 3 2 4 5% 53%	1900
	21st to end	Day	17% 8% 2 5% 3 4 3 2 4 5% 47%	2083
November	1st to 10th	Day	11% 5% 1 4 4 3 4 3 4 6% 55%	1699
	11th to 20th	Day	13% 7% 3 6% 3 3 3 3 5% 6% 47%	1710
	21st to end	Day	16% 10% 3 6% 4 4 4 3 4 5% 42%	1632
December	1st to 10th	Day	13% 11% 3 6% 4 4 4 3 5% 6% 40%	1520
	11th to 20th	Day	13% 11% 4 7% 4 4 4 4 5% 5% 39%	1918
	21st to end	Day	19% 14% 5% 9% 5% 5% 4 3 5% 5% 26%	2783
January	1st to 10th	Night	15% 10% 6% 10% 5% 4 4 3 4 5% 35%	4428
	11th to 20th	Night	13% 10% 4 11% 6% 7% 6% 3 4 4 31%	4211
	21st to end	Night	23% 17% 5% 8% 4 3 3 3 3 5% 28%	4532
February	1st to 10th	Night	16% 12% 4 8% 5% 4 4 3 5% 5% 34%	2470
	11th to 20th	Night	14% 8% 3 8% 5% 4 3 3 4 6% 42%	2244
	21st to end	Night	16% 9% 4 9% 4 3 3 2 5% 4 40%	1884
March	1st to 10th	Night	22% 11% 2 4 4 3 2 2 3 4 43%	3683
	11th to 20th	Night	14% 7% 2 5% 3 3 3 2 4 6% 51%	3480
	21st to end	Night	17% 9% 3 9% 5% 5% 4 4 4 6% 33%	3626
April	1st to 10th	Night	12% 6% 2 7% 4 3 4 3 5% 6% 47%	1900
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 6% 7% 44%	1875
	21st to end	Night	18% 8% 3 6% 4 3 3 3 5% 7% 41%	1900
May	1st to 10th	Night	17% 8% 2 5% 4 3 4 3 5% 8% 39%	3050
	11th to 20th	Night	16% 7% 2 5% 3 4 4 4 4 8% 43%	2522
	21st to end	Night	8% 6% 2 7% 5% 4 5% 4 7% 10% 42%	2743
June	1st to 10th	Night	8% 5% 1 6% 4 4 3 5% 7% 10% 48%	1520
	11th to 20th	Night	6% 4 1 4 3 4 5% 3 5% 9% 56%	1520
	21st to end	Night	4 4 1 4 4 4 5% 4 6% 9% 55%	1520
July	1st to 10th	Night	13% 5% 2 5% 3 4 4 3 5% 10% 45%	2530
	11th to 20th	Night	5% 4 2 5% 3 3 3 3 5% 9% 56%	2530
	21st to end	Night	7% 6% 2 7% 5% 4 5% 5% 7% 10% 42%	3019
August	1st to 10th	Night	5% 3 1 5% 3 3 4 3 6% 8% 58%	2836
	11th to 20th	Night	10% 5% 2 6% 4 4 4 3 6% 8% 47%	3099
	21st to end	Night	5% 3 1 4 3 4 4 4 5% 9% 58%	3476
September	1st to 10th	Night	12% 5% 2 5% 3 3 4 3 5% 6% 53%	1900
	11th to 20th	Night	9% 5% 2 5% 4 4 4 3 5% 7% 52%	1900
	21st to end	Night	10% 4 2 5% 3 4 4 3 4 7% 53%	2102
October	1st to 10th	Night	8% 4 1 5% 3 3 3 3 4 6% 60%	2280
	11th to 20th	Night	13% 6% 2 4 2 3 3 3 4 6% 54%	2280
	21st to end	Night	17% 8% 2 5% 3 3 4 2 4 5% 48%	2513
November	1st to 10th	Night	10% 5% 2 4 4 3 3 3 4 5% 57%	2452
	11th to 20th	Night	14% 6% 3 5% 4 3 3 3 4 6% 49%	2470
	21st to end	Night	18% 8% 3 5% 3 3 2 3 5% 6% 44%	2546
December	1st to 10th	Night	15% 12% 3 6% 6% 4 4 3 5% 6% 37%	2660
	11th to 20th	Night	16% 9% 3 7% 5% 4 3 3 4 5% 41%	3279
	21st to end	Night	17% 18% 5% 10% 5% 4 4 3 5% 4 23%	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	50% 7% 12% 22% 9% 1	2528
	11th to 20th	Day	47% 5% 12% 22% 13%	2758
	21st to end	Day	58% 4 9% 16% 12% 1	3135
February	1st to 10th	Day	51% 4 11% 23% 10% 1	1710
	11th to 20th	Day	47% 5% 10% 20% 15% 3	1830
	21st to end	Day	46% 4 9% 23% 14% 4	1570
March	1st to 10th	Day	47% 3 8% 20% 18% 5%	3184
	11th to 20th	Day	36% 4 11% 26% 17% 5%	3480
	21st to end	Day	45% 7% 17% 22% 8% 1	4003
April	1st to 10th	Day	39% 5% 11% 26% 18% 1	2280
	11th to 20th	Day	44% 4 10% 23% 15% 3	2254
	21st to end	Day	47% 5% 11% 23% 13% 1	2280
May	1st to 10th	Day	45% 7% 14% 23% 10% 1	3864
	11th to 20th	Day	45% 6% 11% 25% 12% 1	4370
	21st to end	Day	37% 6% 11% 23% 21% 1	4837
June	1st to 10th	Day	34% 6% 14% 27% 17% 2	2660
	11th to 20th	Day	28% 6% 13% 27% 23% 3	2660
	21st to end	Day	28% 7% 18% 26% 16% 5%	2660
July	1st to 10th	Day	39% 6% 12% 29% 12% 2	4371
	11th to 20th	Day	27% 7% 15% 32% 17% 2	4365
	21st to end	Day	36% 7% 18% 27% 11% 1	4397
August	1st to 10th	Day	27% 6% 15% 37% 14%	4090
	11th to 20th	Day	37% 6% 14% 25% 17% 1	3765
	21st to end	Day	27% 6% 15% 34% 15% 3	4179
September	1st to 10th	Day	34% 4 10% 27% 20% 5%	2280
	11th to 20th	Day	32% 4 9% 27% 24% 3	2262
	21st to end	Day	30% 5% 8% 30% 24% 3	2072
October	1st to 10th	Day	18% 3 5% 20% 47% 7%	3160
	11th to 20th	Day	24% 2 6% 22% 37% 9%	3140
	21st to end	Day	33% 3 7% 28% 26% 3	3409
November	1st to 10th	Day	32% 4 12% 26% 21% 5%	1699
	11th to 20th	Day	38% 3 10% 25% 21% 5%	1710
	21st to end	Day	45% 4 8% 27% 15%	1632
December	1st to 10th	Day	45% 5% 11% 26% 12% 1	1520
	11th to 20th	Day	47% 4 11% 23% 14% 2	1915
	21st to end	Day	59% 4 11% 15% 9% 1	2783
January	1st to 10th	Night	52% 4 10% 24% 10% 1	4428
	11th to 20th	Night	57% 5% 8% 20% 9% 1	4211
	21st to end	Night	60% 4 8% 20% 7% 1	4532
February	1st to 10th	Night	52% 4 10% 20% 13% 1	2470
	11th to 20th	Night	45% 4 9% 21% 18% 2	2245
	21st to end	Night	48% 3 11% 20% 14% 4	1884
March	1st to 10th	Night	47% 3 7% 24% 16% 2	3683
	11th to 20th	Night	36% 4 12% 24% 21% 4	3480
	21st to end	Night	51% 6% 11% 24% 7%	3626
April	1st to 10th	Night	37% 6% 10% 26% 18% 4	1900
	11th to 20th	Night	39% 4 11% 24% 19% 4	1875
	21st to end	Night	44% 4 8% 26% 17% 2	1900
May	1st to 10th	Night	42% 6% 16% 20% 13% 1	3080
	11th to 20th	Night	40% 6% 12% 28% 12% 1	2523
	21st to end	Night	36% 7% 15% 24% 17% 2	2751
June	1st to 10th	Night	30% 5% 16% 27% 17% 4	1520
	11th to 20th	Night	25% 5% 11% 29% 26% 4	1520
	21st to end	Night	24% 6% 16% 28% 19% 7%	1520
July	1st to 10th	Night	36% 5% 12% 29% 15% 3	2490
	11th to 20th	Night	24% 4 11% 38% 20% 3	2482
	21st to end	Night	35% 7% 18% 25% 13% 1	2923
August	1st to 10th	Night	23% 7% 17% 34% 18% 1	2826
	11th to 20th	Night	36% 5% 13% 26% 19% 2	3129
	21st to end	Night	23% 5% 15% 35% 18% 3	3476
September	1st to 10th	Night	33% 4 9% 25% 23% 6%	1900
	11th to 20th	Night	31% 5% 8% 26% 25% 4	1900
	21st to end	Night	31% 6% 8% 25% 27% 4	2102
October	1st to 10th	Night	16% 2 6% 18% 50% 8%	3800
	11th to 20th	Night	22% 3 7% 23% 36% 10%	3779
	21st to end	Night	31% 3 9% 26% 27% 5%	4137
November	1st to 10th	Night	30% 4 11% 25% 23% 6%	2452
	11th to 20th	Night	37% 3 8% 25% 23% 4	2470
	21st to end	Night	42% 3 11% 25% 17% 2	2546
December	1st to 10th	Night	48% 4 9% 24% 12% 1	2660
	11th to 20th	Night	46% 3 10% 24% 16% 1	3281
	21st to end	Night	62% 6% 9% 14% 7% 1	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	22% 22% 37% 15% 4	270
	11th to 20th	Day	32% 20% 35% 12%	270
	21st to end	Day	23% 24% 36% 15% 2	297
February	1st to 10th	Day	24% 23% 38% 12% 3	270
	11th to 20th	Day	26% 28% 30% 13% 3	270
	21st to end	Day	31% 23% 36% 9% 1	225
March	1st to 10th	Day	20% 23% 46% 9% 1	270
	11th to 20th	Day	31% 21% 33% 11% 3 1	270
	21st to end	Day	33% 19% 31% 13% 4	409
April	1st to 10th	Day	21% 18% 37% 16% 7% 1	460
	11th to 20th	Day	26% 17% 31% 18% 8%	452
	21st to end	Day	25% 15% 38% 16% 6%	460
May	1st to 10th	Day	22% 15% 34% 22% 6% 2	463
	11th to 20th	Day	18% 13% 30% 25% 12% 2	655
	21st to end	Day	13% 9% 34% 27% 12% 5%	734
June	1st to 10th	Day	11% 5% 25% 33% 20% 5%	680
	11th to 20th	Day	8% 5% 24% 40% 19% 5%	680
	21st to end	Day	6% 7% 33% 34% 15% 5%	680
July	1st to 10th	Day	12% 4 15% 29% 27% 12%	671
	11th to 20th	Day	6% 4 23% 38% 24% 6%	668
	21st to end	Day	9% 3 20% 34% 29% 5%	739
August	1st to 10th	Day	9% 3 17% 38% 26% 7%	676
	11th to 20th	Day	13% 5% 18% 33% 23% 8%	479
	21st to end	Day	10% 2 15% 32% 30% 11%	539
September	1st to 10th	Day	13% 4 18% 30% 27% 8%	490
	11th to 20th	Day	11% 2 16% 32% 26% 13%	490
	21st to end	Day	11% 9% 22% 31% 20% 7%	472
October	1st to 10th	Day	10% 11% 27% 34% 12% 6%	300
	11th to 20th	Day	21% 18% 30% 22% 8%	300
	21st to end	Day	31% 18% 29% 17% 5%	330
November	1st to 10th	Day	15% 11% 38% 23% 10% 4	279
	11th to 20th	Day	21% 19% 31% 20% 7% 2	270
	21st to end	Day	27% 16% 31% 19% 6% 1	270
December	1st to 10th	Day	17% 25% 36% 14% 6% 3	270
	11th to 20th	Day	21% 22% 33% 20% 3	270
	21st to end	Day	27% 23% 37% 10% 2	297
January	1st to 10th	Night	20% 17% 38% 20% 4	950
	11th to 20th	Night	23% 21% 33% 18% 4	950
	21st to end	Night	19% 19% 39% 21% 2	1045
February	1st to 10th	Night	23% 17% 37% 21% 2	950
	11th to 20th	Night	22% 18% 38% 20% 2	769
	21st to end	Night	24% 18% 37% 18% 2	628
March	1st to 10th	Night	23% 16% 38% 19% 4	736
	11th to 20th	Night	24% 12% 38% 21% 5%	570
	21st to end	Night	27% 14% 34% 21% 4	627
April	1st to 10th	Night	17% 17% 37% 23% 6%	570
	11th to 20th	Night	19% 13% 35% 25% 8%	563
	21st to end	Night	21% 12% 38% 23% 6%	570
May	1st to 10th	Night	18% 6% 36% 30% 8% 1	570
	11th to 20th	Night	19% 5% 29% 31% 14% 2	561
	21st to end	Night	12% 6% 26% 36% 19% 2	617
June	1st to 10th	Night	10% 3 21% 39% 25% 1	570
	11th to 20th	Night	7% 2 24% 46% 19% 1	570
	21st to end	Night	5% 3 26% 45% 19% 2	570
July	1st to 10th	Night	11% 2 12% 38% 31% 6%	555
	11th to 20th	Night	6% 2 16% 43% 29% 3	552
	21st to end	Night	7% 2 16% 42% 31% 3	624
August	1st to 10th	Night	7% 2 13% 41% 35% 3	567
	11th to 20th	Night	7% 2 14% 41% 31% 4	564
	21st to end	Night	6% 1 14% 39% 36% 3	627
September	1st to 10th	Night	13% 3 13% 37% 28% 5%	570
	11th to 20th	Night	10% 4 16% 33% 32% 5%	570
	21st to end	Night	11% 7% 23% 31% 24% 4	758
October	1st to 10th	Night	9% 5% 29% 31% 22% 4	760
	11th to 20th	Night	16% 13% 31% 28% 11% 1	760
	21st to end	Night	24% 11% 35% 24% 6%	836
November	1st to 10th	Night	13% 10% 39% 26% 11% 1	755
	11th to 20th	Night	18% 16% 34% 26% 6%	760
	21st to end	Night	23% 14% 34% 23% 6% 1	836
December	1st to 10th	Night	23% 14% 36% 23% 4 1	950
	11th to 20th	Night	24% 13% 31% 27% 5%	950
	21st to end	Night	27% 17% 34% 20% 3	1045

Page generated at 2024-11-01 21:47:48. Version ac07

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