Rattle Snake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rattle Snake Observatory clear sky chart from 2005-11-06 to 2024-12-02.

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	12% 8% 3 6% 4 4 4 3 5% 7% 44%	101422
	Night	12% 8% 3 6% 4 4 4 3 5% 6% 46%	98297
Transparency	Day	38% 6% 12% 25% 16% 3	105068
	Night	37% 6% 11% 25% 18% 3	102791
Seeing	Day	17% 12% 28% 26% 14% 3	15729
	Night	15% 11% 32% 28% 12% 1	25581

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	13% 12% 4 8% 5% 4 4 3 5% 5% 37%	2760
	11th to 20th	Day	11% 12% 5% 10% 4 6% 6% 3 4 5% 36%	2850
	21st to end	Day	15% 16% 5% 10% 4 3 3 3 3 4 35%	3135
February	1st to 10th	Day	16% 12% 4 8% 5% 4 4 3 4 5% 35%	1710
	11th to 20th	Day	13% 10% 3 7% 5% 4 3 3 4 6% 40%	1670
	21st to end	Day	16% 10% 4 5% 4 4 3 4 5% 6% 39%	1603
March	1st to 10th	Day	16% 11% 3 5% 3 2 3 3 4 5% 46%	3436
	11th to 20th	Day	13% 8% 2 4 3 3 3 3 5% 6% 50%	3480
	21st to end	Day	17% 14% 3 7% 5% 4 4 3 4 6% 33%	3814
April	1st to 10th	Day	13% 7% 3 7% 5% 3 4 4 5% 7% 43%	2270
	11th to 20th	Day	18% 9% 2 5% 4 3 4 4 5% 6% 41%	2254
	21st to end	Day	19% 8% 3 7% 5% 4 4 3 5% 6% 35%	2280
May	1st to 10th	Day	16% 8% 3 7% 5% 4 4 4 6% 8% 35%	4078
	11th to 20th	Day	16% 8% 3 7% 4 5% 4 3 5% 6% 39%	4109
	21st to end	Day	11% 6% 2 6% 5% 4 5% 4 6% 8% 44%	4824
June	1st to 10th	Day	7% 4 2 5% 4 5% 5% 5% 7% 10% 46%	2660
	11th to 20th	Day	8% 4 2 5% 5% 4 4 5% 7% 9% 47%	2660
	21st to end	Day	6% 4 1 4 4 5% 4 5% 7% 10% 50%	2660
July	1st to 10th	Day	13% 7% 2 6% 4 4 4 4 5% 8% 42%	4411
	11th to 20th	Day	5% 4 2 6% 4 5% 5% 3 6% 10% 50%	4120
	21st to end	Day	7% 5% 2 5% 5% 5% 5% 5% 8% 11% 42%	4465
August	1st to 10th	Day	5% 4 1 5% 3 4 5% 5% 7% 10% 51%	4104
	11th to 20th	Day	11% 5% 2 5% 4 3 5% 3 6% 7% 46%	3977
	21st to end	Day	6% 3 2 5% 3 3 4 4 6% 9% 55%	4180
September	1st to 10th	Day	11% 5% 2 4 4 4 4 4 5% 6% 51%	2280
	11th to 20th	Day	10% 6% 2 5% 3 3 4 4 5% 7% 52%	2240
	21st to end	Day	8% 5% 2 6% 3 3 3 4 5% 6% 54%	2003
October	1st to 10th	Day	11% 5% 2 4 4 3 4 2 4 6% 56%	1900
	11th to 20th	Day	14% 6% 3 4 2 2 3 2 3 6% 54%	1900
	21st to end	Day	17% 8% 2 6% 3 3 3 3 3 6% 46%	2090
November	1st to 10th	Day	12% 6% 2 4 3 3 3 3 4 6% 53%	1943
	11th to 20th	Day	14% 7% 2 5% 3 3 3 3 4 7% 49%	1727
	21st to end	Day	15% 10% 3 6% 2 3 4 2 3 6% 45%	1600
December	1st to 10th	Day	12% 10% 4 6% 4 3 3 3 5% 7% 43%	1528
	11th to 20th	Day	12% 11% 5% 8% 5% 3 3 3 4 5% 42%	1918
	21st to end	Day	16% 17% 6% 10% 5% 4 4 3 4 5% 25%	2783
January	1st to 10th	Night	10% 11% 5% 14% 5% 4 5% 3 3 4 37%	4190
	11th to 20th	Night	12% 9% 4 11% 6% 7% 5% 4 4 4 33%	4120
	21st to end	Night	18% 16% 5% 9% 4 3 3 2 3 4 33%	4532
February	1st to 10th	Night	14% 11% 5% 7% 5% 4 5% 3 5% 6% 36%	2470
	11th to 20th	Night	13% 9% 3 7% 4 4 4 3 4 6% 42%	2395
	21st to end	Night	14% 10% 3 8% 3 3 4 4 4 5% 43%	1866
March	1st to 10th	Night	17% 11% 2 5% 3 3 3 2 4 5% 45%	3419
	11th to 20th	Night	13% 7% 2 4 3 2 3 3 5% 7% 51%	3480
	21st to end	Night	16% 11% 5% 8% 6% 5% 4 3 4 5% 33%	3817
April	1st to 10th	Night	11% 7% 3 6% 4 3 4 3 4 7% 49%	1910
	11th to 20th	Night	14% 9% 2 5% 4 3 3 3 5% 7% 45%	1875
	21st to end	Night	17% 6% 3 6% 5% 4 4 3 5% 6% 41%	1900
May	1st to 10th	Night	15% 8% 3 6% 4 4 4 3 6% 9% 39%	2823
	11th to 20th	Night	13% 8% 3 7% 4 4 4 3 5% 9% 41%	2792
	21st to end	Night	10% 5% 2 5% 3 3 4 4 6% 8% 50%	2743
June	1st to 10th	Night	6% 3 1 4 4 4 4 4 6% 10% 54%	1520
	11th to 20th	Night	6% 4 1 4 4 3 4 3 7% 12% 52%	1520
	21st to end	Night	4 2 1 3 4 4 5% 3 7% 9% 59%	1520
July	1st to 10th	Night	13% 6% 2 6% 3 3 3 3 5% 9% 47%	2553
	11th to 20th	Night	4 3 1 4 3 3 3 3 6% 10% 58%	2850
	21st to end	Night	6% 4 2 4 3 3 4 4 7% 10% 52%	3098
August	1st to 10th	Night	4 2 1 3 3 3 3 3 6% 10% 62%	2836
	11th to 20th	Night	10% 6% 2 5% 4 3 4 3 5% 6% 52%	2860
	21st to end	Night	5% 3 1 4 3 4 4 3 6% 8% 60%	3476
September	1st to 10th	Night	10% 4 1 4 2 2 3 3 4 7% 58%	1900
	11th to 20th	Night	9% 4 2 4 3 4 4 4 6% 7% 53%	1936
	21st to end	Night	8% 3 2 5% 4 3 3 3 5% 7% 58%	2157
October	1st to 10th	Night	8% 4 1 4 3 3 4 3 5% 6% 60%	2280
	11th to 20th	Night	14% 4 1 5% 4 4 3 3 4 5% 54%	2280
	21st to end	Night	16% 7% 2 5% 4 2 4 2 4 5% 50%	2508
November	1st to 10th	Night	11% 5% 2 3 2 3 3 3 4 5% 58%	2351
	11th to 20th	Night	11% 8% 2 6% 4 3 3 3 4 6% 50%	2670
	21st to end	Night	15% 10% 2 6% 3 3 3 2 4 5% 48%	2800
December	1st to 10th	Night	13% 10% 4 5% 5% 4 4 3 5% 6% 41%	2687
	11th to 20th	Night	13% 10% 3 8% 3 3 3 3 4 6% 42%	3279
	21st to end	Night	16% 17% 6% 10% 5% 4 3 3 3 5% 27%	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	48% 6% 9% 25% 12%	2761
	11th to 20th	Day	52% 5% 11% 21% 11%	2850
	21st to end	Day	53% 4 9% 17% 14% 2	3135
February	1st to 10th	Day	51% 5% 11% 20% 12% 1	1710
	11th to 20th	Day	45% 5% 12% 21% 14% 3	1679
	21st to end	Day	45% 4 9% 22% 15% 4	1603
March	1st to 10th	Day	42% 5% 8% 23% 19% 3	3436
	11th to 20th	Day	34% 6% 11% 28% 16% 4	3480
	21st to end	Day	51% 8% 17% 19% 6%	3814
April	1st to 10th	Day	40% 6% 12% 24% 16% 2	2270
	11th to 20th	Day	43% 5% 12% 23% 14% 2	2254
	21st to end	Day	49% 6% 11% 21% 12% 1	2280
May	1st to 10th	Day	44% 10% 13% 21% 12% 1	4116
	11th to 20th	Day	43% 9% 11% 23% 13%	4113
	21st to end	Day	36% 9% 11% 28% 16% 1	4837
June	1st to 10th	Day	30% 9% 16% 28% 15% 1	2660
	11th to 20th	Day	31% 9% 14% 27% 16% 3	2660
	21st to end	Day	27% 8% 16% 30% 14% 5%	2660
July	1st to 10th	Day	40% 6% 11% 25% 15% 3	4342
	11th to 20th	Day	29% 7% 13% 33% 17% 2	4051
	21st to end	Day	31% 9% 19% 29% 10% 1	4325
August	1st to 10th	Day	25% 8% 17% 31% 18% 1	4090
	11th to 20th	Day	36% 6% 14% 28% 15% 2	4016
	21st to end	Day	25% 7% 15% 36% 14% 4	4179
September	1st to 10th	Day	32% 6% 11% 26% 18% 6%	2280
	11th to 20th	Day	31% 6% 9% 26% 25% 3	2240
	21st to end	Day	30% 6% 11% 26% 24% 3	2003
October	1st to 10th	Day	18% 3 6% 20% 38% 15%	3160
	11th to 20th	Day	22% 3 5% 23% 39% 9%	3140
	21st to end	Day	36% 3 8% 24% 26% 3	3428
November	1st to 10th	Day	33% 5% 13% 24% 21% 5%	1943
	11th to 20th	Day	36% 4 10% 23% 22% 4	1727
	21st to end	Day	43% 3 8% 29% 16% 1	1600
December	1st to 10th	Day	42% 4 11% 29% 13% 1	1528
	11th to 20th	Day	45% 4 12% 25% 11% 2	1915
	21st to end	Day	61% 5% 10% 14% 9% 1	2783
January	1st to 10th	Night	51% 6% 10% 21% 11% 1	4190
	11th to 20th	Night	54% 5% 10% 20% 10% 1	4120
	21st to end	Night	56% 4 10% 19% 10% 1	4532
February	1st to 10th	Night	49% 6% 11% 20% 13% 2	2470
	11th to 20th	Night	43% 5% 11% 21% 17% 3	2396
	21st to end	Night	44% 4 10% 21% 17% 5%	1866
March	1st to 10th	Night	43% 5% 9% 22% 18% 4	3419
	11th to 20th	Night	33% 6% 9% 25% 24% 4	3480
	21st to end	Night	51% 8% 12% 22% 7% 1	3817
April	1st to 10th	Night	35% 6% 10% 25% 20% 4	1910
	11th to 20th	Night	38% 7% 8% 26% 17% 5%	1875
	21st to end	Night	44% 5% 10% 23% 16% 1	1900
May	1st to 10th	Night	41% 10% 14% 19% 15% 2	2850
	11th to 20th	Night	39% 9% 13% 28% 11% 1	2793
	21st to end	Night	31% 9% 13% 24% 22% 1	2751
June	1st to 10th	Night	24% 8% 16% 32% 16% 4	1520
	11th to 20th	Night	24% 9% 13% 28% 23% 4	1520
	21st to end	Night	19% 8% 15% 31% 20% 6%	1520
July	1st to 10th	Night	35% 5% 12% 27% 18% 3	2513
	11th to 20th	Night	20% 7% 12% 39% 20% 2	2796
	21st to end	Night	25% 7% 21% 34% 12% 1	2999
August	1st to 10th	Night	17% 7% 22% 29% 24% 2	2826
	11th to 20th	Night	33% 5% 12% 30% 19% 1	2887
	21st to end	Night	22% 5% 14% 37% 17% 4	3476
September	1st to 10th	Night	26% 6% 12% 25% 24% 8%	1900
	11th to 20th	Night	28% 7% 11% 24% 26% 4	1936
	21st to end	Night	27% 5% 8% 28% 28% 4	2157
October	1st to 10th	Night	16% 3 6% 22% 42% 11%	3800
	11th to 20th	Night	22% 3 7% 22% 29% 17%	3779
	21st to end	Night	35% 4 7% 28% 25% 3	4120
November	1st to 10th	Night	29% 5% 11% 28% 21% 6%	2351
	11th to 20th	Night	35% 4 7% 24% 24% 5%	2670
	21st to end	Night	41% 4 9% 27% 17% 3	2800
December	1st to 10th	Night	43% 5% 11% 25% 14% 1	2687
	11th to 20th	Night	43% 5% 10% 27% 13% 1	3281
	21st to end	Night	61% 6% 8% 15% 8% 2	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	23% 23% 34% 16% 3	270
	11th to 20th	Day	30% 20% 39% 9% 1	270
	21st to end	Day	19% 25% 41% 12% 3	297
February	1st to 10th	Day	26% 29% 32% 11% 2	270
	11th to 20th	Day	22% 27% 37% 11% 3	270
	21st to end	Day	33% 27% 30% 8% 2	225
March	1st to 10th	Day	20% 25% 44% 10% 1	270
	11th to 20th	Day	33% 17% 34% 15% 1	270
	21st to end	Day	37% 22% 28% 9% 3	297
April	1st to 10th	Day	21% 18% 39% 17% 5% 1	450
	11th to 20th	Day	23% 20% 32% 18% 6%	452
	21st to end	Day	28% 14% 33% 20% 6%	460
May	1st to 10th	Day	21% 16% 35% 21% 6%	649
	11th to 20th	Day	20% 13% 26% 27% 12% 2	675
	21st to end	Day	15% 10% 33% 26% 12% 4	734
June	1st to 10th	Day	8% 6% 24% 35% 23% 5%	680
	11th to 20th	Day	9% 4 27% 39% 19% 3	680
	21st to end	Day	7% 7% 33% 35% 15% 3	680
July	1st to 10th	Day	12% 4 16% 30% 28% 9%	671
	11th to 20th	Day	5% 3 26% 34% 26% 6%	668
	21st to end	Day	9% 3 17% 34% 30% 6%	739
August	1st to 10th	Day	8% 3 20% 39% 25% 4	676
	11th to 20th	Day	10% 4 22% 34% 25% 5%	627
	21st to end	Day	9% 2 16% 33% 32% 8%	539
September	1st to 10th	Day	14% 3 17% 35% 27% 5%	490
	11th to 20th	Day	8% 4 21% 38% 24% 6%	450
	21st to end	Day	13% 11% 25% 32% 15% 4	300
October	1st to 10th	Day	15% 8% 32% 29% 13% 4	300
	11th to 20th	Day	17% 22% 34% 21% 6%	300
	21st to end	Day	29% 22% 31% 17% 1 1	330
November	1st to 10th	Day	18% 16% 38% 20% 7% 2	300
	11th to 20th	Day	21% 21% 32% 19% 5% 1	300
	21st to end	Day	29% 18% 29% 20% 3	300
December	1st to 10th	Day	18% 23% 34% 18% 7% 1	273
	11th to 20th	Day	23% 20% 36% 19% 2 1	270
	21st to end	Day	25% 30% 36% 9%	297
January	1st to 10th	Night	17% 17% 39% 21% 6%	950
	11th to 20th	Night	20% 21% 36% 18% 4 1	950
	21st to end	Night	18% 18% 39% 22% 2	1045
February	1st to 10th	Night	20% 17% 41% 19% 3	950
	11th to 20th	Night	20% 17% 38% 23% 2	921
	21st to end	Night	23% 18% 40% 15% 3	610
March	1st to 10th	Night	19% 15% 41% 21% 4	570
	11th to 20th	Night	21% 15% 32% 28% 4	570
	21st to end	Night	26% 16% 34% 20% 4	627
April	1st to 10th	Night	14% 19% 37% 25% 4 1	570
	11th to 20th	Night	20% 13% 32% 26% 8% 1	563
	21st to end	Night	19% 11% 38% 24% 8%	570
May	1st to 10th	Night	17% 7% 36% 32% 8%	570
	11th to 20th	Night	16% 7% 27% 34% 15% 1	561
	21st to end	Night	12% 8% 28% 32% 18% 2	617
June	1st to 10th	Night	7% 2 20% 44% 25% 1	570
	11th to 20th	Night	7% 2 25% 45% 20% 2	570
	21st to end	Night	3 3 31% 44% 18% 2	570
July	1st to 10th	Night	12% 2 12% 41% 28% 5%	555
	11th to 20th	Night	4 1 19% 42% 32% 2	552
	21st to end	Night	9% 1 17% 40% 30% 3	624
August	1st to 10th	Night	6% 3 15% 41% 34% 2	567
	11th to 20th	Night	7% 2 16% 45% 28% 3	564
	21st to end	Night	6% 1 15% 38% 37% 3	627
September	1st to 10th	Night	11% 2 18% 39% 26% 4	570
	11th to 20th	Night	11% 3 19% 36% 26% 5%	570
	21st to end	Night	9% 6% 24% 38% 20% 3	637
October	1st to 10th	Night	10% 6% 28% 31% 21% 3	760
	11th to 20th	Night	16% 9% 38% 27% 9%	760
	21st to end	Night	19% 14% 34% 25% 8%	836
November	1st to 10th	Night	13% 13% 36% 30% 8%	780
	11th to 20th	Night	15% 17% 37% 25% 6%	870
	21st to end	Night	21% 15% 36% 22% 5%	1000
December	1st to 10th	Night	19% 13% 39% 22% 6%	960
	11th to 20th	Night	22% 13% 38% 23% 4	950
	21st to end	Night	22% 19% 38% 19% 2	1045

Page generated at 2024-11-29 09:43:06. Version ac07

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