Tom's Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tom's Ranch clear sky chart from 2005-11-06 to 2024-11-06.

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	8% 5% 2 5% 4 4 4 3 5% 7% 53%	100971
	Night	7% 5% 2 4 3 3 3 3 5% 7% 57%	98224
Transparency	Day	30% 6% 10% 21% 21% 12%	104867
	Night	26% 6% 11% 21% 21% 14%	102455
Seeing	Day	9% 7% 25% 33% 20% 5%	14826
	Night	9% 8% 33% 37% 12% 1	24755

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% 5% 2 5% 3 2 3 2 3 6% 60%	2847
	11th to 20th	Day	8% 7% 2 4 2 2 3 3 5% 5% 60%	2946
	21st to end	Day	11% 5% 2 5% 3 4 4 3 4 7% 51%	3487
February	1st to 10th	Day	10% 6% 3 5% 3 4 4 3 5% 5% 54%	1900
	11th to 20th	Day	11% 6% 2 5% 3 3 3 3 5% 6% 51%	1849
	21st to end	Day	11% 4 1 4 3 3 3 3 5% 6% 55%	1570
March	1st to 10th	Day	11% 7% 3 6% 4 4 3 3 4 5% 49%	3218
	11th to 20th	Day	15% 9% 3 7% 5% 4 5% 3 5% 5% 40%	3480
	21st to end	Day	7% 6% 2 5% 4 4 4 4 5% 7% 52%	3814
April	1st to 10th	Day	8% 6% 2 5% 4 4 4 4 5% 8% 51%	2099
	11th to 20th	Day	11% 6% 3 5% 4 4 4 3 5% 6% 50%	2254
	21st to end	Day	9% 6% 2 5% 4 4 4 3 4 6% 54%	2303
May	1st to 10th	Day	12% 7% 3 7% 5% 4 4 4 5% 7% 43%	4082
	11th to 20th	Day	11% 6% 2 6% 4 4 4 3 5% 6% 49%	4082
	21st to end	Day	7% 5% 2 6% 5% 4 5% 4 6% 9% 47%	4477
June	1st to 10th	Day	3 3 2 5% 4 4 4 4 6% 9% 56%	2470
	11th to 20th	Day	4 3 2 4 4 5% 5% 4 7% 10% 53%	2470
	21st to end	Day	5% 4 1 5% 5% 5% 6% 5% 7% 9% 47%	2470
July	1st to 10th	Day	5% 4 1 6% 4 5% 5% 4 6% 8% 51%	4120
	11th to 20th	Day	2 2 1 4 4 4 4 4 6% 10% 57%	4120
	21st to end	Day	7% 4 1 6% 4 4 5% 5% 8% 10% 46%	4444
August	1st to 10th	Day	1 2 1 3 3 3 3 3 5% 8% 70%	3785
	11th to 20th	Day	4 2 1 4 3 3 4 2 5% 7% 65%	3726
	21st to end	Day	4 4 2 6% 5% 5% 6% 4 6% 10% 49%	4180
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 4 4 6% 8% 45%	2097
	11th to 20th	Day	9% 6% 2 7% 4 5% 5% 4 6% 7% 44%	2090
	21st to end	Day	9% 5% 2 4 4 3 5% 3 7% 7% 51%	2090
October	1st to 10th	Day	5% 4 1 5% 3 4 4 3 5% 8% 59%	2090
	11th to 20th	Day	10% 4 2 5% 3 3 3 3 4 6% 56%	2075
	21st to end	Day	10% 4 2 4 2 2 3 3 3 6% 61%	2090
November	1st to 10th	Day	11% 6% 1 6% 3 3 3 3 5% 7% 53%	1820
	11th to 20th	Day	7% 5% 2 4 3 4 5% 3 5% 6% 56%	1710
	21st to end	Day	10% 7% 2 6% 3 3 2 3 4 6% 53%	1710
December	1st to 10th	Day	11% 7% 2 5% 2 3 3 3 5% 7% 52%	1710
	11th to 20th	Day	10% 7% 2 6% 4 4 4 3 5% 6% 50%	2161
	21st to end	Day	10% 5% 2 4 3 3 2 3 4 4 60%	3135
January	1st to 10th	Night	8% 5% 3 5% 3 3 3 2 4 7% 58%	4108
	11th to 20th	Night	8% 5% 1 3 2 2 2 2 3 5% 68%	4052
	21st to end	Night	13% 7% 2 4 3 3 3 2 4 7% 50%	4180
February	1st to 10th	Night	10% 6% 2 4 4 3 3 3 5% 6% 55%	2280
	11th to 20th	Night	11% 6% 2 5% 3 3 3 2 5% 5% 55%	2218
	21st to end	Night	10% 6% 2 4 4 3 3 3 5% 7% 53%	1884
March	1st to 10th	Night	7% 5% 2 5% 4 3 4 4 6% 8% 51%	3641
	11th to 20th	Night	13% 8% 2 6% 4 4 4 3 5% 6% 43%	3480
	21st to end	Night	6% 7% 2 5% 4 4 4 3 4 7% 53%	3817
April	1st to 10th	Night	5% 4 2 4 4 4 4 4 6% 7% 55%	2076
	11th to 20th	Night	8% 6% 3 5% 4 3 4 3 5% 6% 53%	1877
	21st to end	Night	9% 4 2 3 3 3 3 3 5% 7% 57%	1876
May	1st to 10th	Night	11% 6% 2 5% 4 4 4 4 5% 8% 47%	2823
	11th to 20th	Night	7% 5% 2 5% 3 4 4 3 5% 7% 55%	2823
	21st to end	Night	7% 4 2 5% 3 4 4 3 6% 9% 53%	3090
June	1st to 10th	Night	2 2 1 3 3 2 2 3 6% 13% 62%	1710
	11th to 20th	Night	2 1 1 2 3 3 4 3 7% 9% 64%	1710
	21st to end	Night	4 3 1 3 3 3 4 4 6% 9% 59%	1710
July	1st to 10th	Night	3 2 2 3 3 4 4 4 7% 10% 59%	2850
	11th to 20th	Night	2 1 1 2 2 3 3 3 7% 9% 66%	2850
	21st to end	Night	4 4 1 5% 4 3 4 4 6% 10% 53%	3114
August	1st to 10th	Night	1 1 1 2 2 3 3 3 4 6% 75%	3155
	11th to 20th	Night	2 2 1 3 2 3 3 4 7% 9% 64%	3113
	21st to end	Night	4 3 1 5% 3 3 4 4 7% 11% 54%	3487
September	1st to 10th	Night	7% 5% 2 4 3 3 4 4 6% 8% 54%	2081
	11th to 20th	Night	8% 4 2 6% 4 4 4 3 7% 8% 51%	2090
	21st to end	Night	8% 3 1 4 3 4 4 3 6% 8% 55%	2090
October	1st to 10th	Night	4 2 1 3 2 3 3 3 5% 8% 66%	2090
	11th to 20th	Night	8% 4 2 4 3 3 3 3 5% 5% 60%	2090
	21st to end	Night	10% 4 1 4 3 2 3 2 3 4 63%	2503
November	1st to 10th	Night	8% 5% 2 4 3 3 3 2 4 6% 60%	2378
	11th to 20th	Night	7% 4 1 4 3 3 3 3 5% 7% 60%	2470
	21st to end	Night	12% 5% 2 5% 4 3 3 3 5% 7% 52%	2470
December	1st to 10th	Night	10% 5% 2 3 3 3 3 3 5% 6% 56%	2470
	11th to 20th	Night	9% 7% 2 6% 4 4 4 3 4 6% 51%	3036
	21st to end	Night	10% 6% 2 5% 3 2 3 2 3 6% 59%	4532

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	26% 4 7% 15% 23% 25%	2848
	11th to 20th	Day	27% 4 6% 14% 31% 18%	2946
	21st to end	Day	33% 6% 6% 14% 29% 11%	3487
February	1st to 10th	Day	34% 4 7% 13% 21% 20%	1900
	11th to 20th	Day	35% 4 7% 18% 20% 17%	1859
	21st to end	Day	30% 4 8% 15% 24% 20%	1570
March	1st to 10th	Day	37% 5% 6% 14% 19% 19%	3218
	11th to 20th	Day	45% 7% 8% 12% 17% 11%	3480
	21st to end	Day	29% 7% 10% 15% 20% 19%	3814
April	1st to 10th	Day	32% 6% 9% 17% 19% 16%	2099
	11th to 20th	Day	35% 6% 8% 16% 21% 15%	2254
	21st to end	Day	33% 5% 9% 20% 20% 13%	2303
May	1st to 10th	Day	39% 8% 11% 13% 18% 10%	4120
	11th to 20th	Day	35% 7% 10% 16% 22% 10%	4086
	21st to end	Day	32% 9% 13% 25% 15% 6%	4489
June	1st to 10th	Day	24% 9% 13% 29% 21% 4	2470
	11th to 20th	Day	25% 8% 14% 25% 22% 6%	2470
	21st to end	Day	32% 8% 13% 23% 19% 5%	2470
July	1st to 10th	Day	29% 9% 16% 37% 8% 1	4056
	11th to 20th	Day	22% 6% 14% 35% 19% 3	4051
	21st to end	Day	30% 8% 18% 29% 15% 1	4304
August	1st to 10th	Day	15% 4 10% 39% 31% 1	3772
	11th to 20th	Day	20% 6% 18% 41% 13% 2	3762
	21st to end	Day	29% 10% 16% 24% 20% 2	4179
September	1st to 10th	Day	37% 8% 11% 18% 17% 8%	2097
	11th to 20th	Day	37% 9% 11% 20% 17% 6%	2090
	21st to end	Day	31% 6% 12% 20% 19% 12%	2090
October	1st to 10th	Day	16% 4 7% 13% 26% 33%	3480
	11th to 20th	Day	27% 4 6% 17% 21% 24%	3431
	21st to end	Day	22% 3 6% 17% 40% 13%	3428
November	1st to 10th	Day	32% 6% 10% 20% 20% 12%	1820
	11th to 20th	Day	29% 5% 8% 18% 22% 17%	1710
	21st to end	Day	34% 4 6% 17% 23% 15%	1710
December	1st to 10th	Day	33% 5% 8% 17% 26% 11%	1710
	11th to 20th	Day	35% 5% 8% 11% 23% 18%	2159
	21st to end	Day	29% 4 5% 16% 27% 20%	3135
January	1st to 10th	Night	28% 5% 5% 11% 27% 24%	4108
	11th to 20th	Night	22% 3 5% 18% 26% 27%	4052
	21st to end	Night	35% 6% 5% 12% 28% 14%	4180
February	1st to 10th	Night	30% 5% 9% 12% 23% 21%	2280
	11th to 20th	Night	32% 5% 7% 16% 22% 19%	2218
	21st to end	Night	31% 5% 7% 13% 23% 20%	1884
March	1st to 10th	Night	28% 9% 11% 15% 22% 15%	3641
	11th to 20th	Night	42% 8% 8% 13% 15% 14%	3480
	21st to end	Night	31% 7% 9% 16% 17% 19%	3817
April	1st to 10th	Night	29% 6% 11% 19% 17% 19%	2076
	11th to 20th	Night	32% 7% 12% 14% 18% 18%	1877
	21st to end	Night	29% 6% 11% 21% 20% 12%	1876
May	1st to 10th	Night	35% 10% 11% 18% 14% 12%	2850
	11th to 20th	Night	27% 10% 12% 22% 19% 10%	2824
	21st to end	Night	27% 9% 16% 27% 12% 8%	3099
June	1st to 10th	Night	14% 9% 18% 34% 22% 2	1710
	11th to 20th	Night	16% 9% 17% 28% 24% 6%	1710
	21st to end	Night	23% 7% 17% 29% 19% 5%	1710
July	1st to 10th	Night	19% 10% 23% 40% 8% 1	2805
	11th to 20th	Night	15% 7% 17% 38% 20% 2	2796
	21st to end	Night	25% 7% 21% 33% 13% 1	3015
August	1st to 10th	Night	11% 5% 14% 41% 28% 1	3144
	11th to 20th	Night	15% 7% 25% 39% 12% 2	3143
	21st to end	Night	23% 11% 21% 25% 18% 2	3487
September	1st to 10th	Night	28% 8% 14% 22% 19% 9%	2081
	11th to 20th	Night	31% 8% 15% 23% 16% 6%	2090
	21st to end	Night	26% 7% 13% 23% 18% 13%	2090
October	1st to 10th	Night	13% 4 9% 15% 22% 37%	3480
	11th to 20th	Night	21% 4 10% 16% 29% 21%	3460
	21st to end	Night	21% 3 6% 21% 34% 16%	4115
November	1st to 10th	Night	27% 5% 9% 19% 25% 15%	2378
	11th to 20th	Night	25% 6% 9% 21% 21% 18%	2470
	21st to end	Night	34% 5% 9% 15% 22% 16%	2470
December	1st to 10th	Night	30% 5% 10% 17% 24% 14%	2470
	11th to 20th	Night	35% 5% 6% 14% 18% 22%	3037
	21st to end	Night	29% 4 5% 15% 29% 18%	4532

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	12% 14% 46% 21% 7% 1	270
	11th to 20th	Day	17% 13% 34% 28% 7% 2	270
	21st to end	Day	9% 12% 46% 24% 9%	297
February	1st to 10th	Day	19% 15% 38% 19% 10%	270
	11th to 20th	Day	22% 13% 40% 22% 3	270
	21st to end	Day	16% 13% 49% 21% 1	225
March	1st to 10th	Day	14% 16% 44% 23% 3	270
	11th to 20th	Day	14% 14% 42% 20% 9%	270
	21st to end	Day	12% 16% 47% 18% 6%	297
April	1st to 10th	Day	12% 19% 44% 23% 2	279
	11th to 20th	Day	11% 17% 42% 24% 4	452
	21st to end	Day	12% 17% 43% 23% 5%	483
May	1st to 10th	Day	11% 11% 45% 28% 5%	653
	11th to 20th	Day	14% 8% 33% 33% 10% 1	675
	21st to end	Day	10% 8% 33% 38% 10% 1	734
June	1st to 10th	Day	4 2 22% 48% 21% 3	680
	11th to 20th	Day	3 1 24% 48% 21% 3	680
	21st to end	Day	4 2 15% 45% 29% 6%	680
July	1st to 10th	Day	6% 2 11% 37% 34% 10%	671
	11th to 20th	Day	2 6% 46% 37% 8%	668
	21st to end	Day	3 1 7% 40% 37% 12%	730
August	1st to 10th	Day	2 4 37% 43% 14%	487
	11th to 20th	Day	7% 1 5% 35% 39% 14%	477
	21st to end	Day	6% 1 6% 29% 42% 17%	539
September	1st to 10th	Day	10% 2 7% 25% 38% 19%	307
	11th to 20th	Day	5% 1 4 27% 45% 18%	300
	21st to end	Day	12% 1 6% 29% 38% 14%	300
October	1st to 10th	Day	4 3 13% 36% 37% 7%	300
	11th to 20th	Day	9% 4 21% 42% 21% 3	300
	21st to end	Day	14% 12% 26% 31% 13% 4	330
November	1st to 10th	Day	17% 6% 28% 33% 13% 2	285
	11th to 20th	Day	16% 11% 29% 26% 13% 6%	270
	21st to end	Day	15% 20% 37% 19% 7% 2	270
December	1st to 10th	Day	14% 9% 31% 31% 11% 3	270
	11th to 20th	Day	11% 16% 40% 25% 8%	270
	21st to end	Day	12% 13% 38% 28% 9%	297
January	1st to 10th	Night	13% 10% 38% 31% 8% 1	950
	11th to 20th	Night	15% 9% 40% 30% 6%	908
	21st to end	Night	15% 10% 41% 28% 6%	836
February	1st to 10th	Night	13% 14% 39% 28% 5%	760
	11th to 20th	Night	14% 15% 41% 27% 2	744
	21st to end	Night	14% 16% 51% 19% 1	628
March	1st to 10th	Night	13% 14% 47% 22% 3	706
	11th to 20th	Night	14% 10% 44% 29% 4	570
	21st to end	Night	7% 15% 55% 20% 2	627
April	1st to 10th	Night	7% 12% 55% 23% 3	570
	11th to 20th	Night	9% 14% 56% 19% 1	563
	21st to end	Night	11% 12% 52% 21% 4	570
May	1st to 10th	Night	8% 11% 54% 24% 3	570
	11th to 20th	Night	9% 8% 44% 30% 9%	561
	21st to end	Night	7% 7% 44% 33% 8%	617
June	1st to 10th	Night	2 1 33% 50% 14%	570
	11th to 20th	Night	2 1 38% 52% 7%	570
	21st to end	Night	4 2 23% 51% 19% 1	570
July	1st to 10th	Night	5% 1 13% 55% 24% 2	555
	11th to 20th	Night	2 1 11% 62% 23% 1	552
	21st to end	Night	3 1 9% 61% 25% 2	624
August	1st to 10th	Night	2 1 7% 62% 27% 2	567
	11th to 20th	Night	4 1 7% 56% 30% 2	564
	21st to end	Night	4 1 8% 48% 36% 3	627
September	1st to 10th	Night	6% 2 10% 48% 31% 3	570
	11th to 20th	Night	9% 1 10% 46% 32% 2	570
	21st to end	Night	9% 2 12% 50% 25% 2	570
October	1st to 10th	Night	5% 1 18% 49% 26% 1	570
	11th to 20th	Night	9% 5% 26% 43% 16% 1	570
	21st to end	Night	11% 9% 32% 32% 16% 1	831
November	1st to 10th	Night	11% 5% 30% 40% 14% 1	850
	11th to 20th	Night	9% 6% 36% 34% 13% 2	950
	21st to end	Night	13% 10% 34% 32% 9% 1	950
December	1st to 10th	Night	13% 8% 32% 38% 8% 1	950
	11th to 20th	Night	15% 10% 38% 32% 5%	950
	21st to end	Night	12% 12% 37% 32% 7%	1045

Page generated at 2024-11-03 12:19:05. Version ac07

Copyright © 2024 Attilla Danko.