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 2025-11-03.

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% 52%	126668
	Night	8% 5% 2 4 3 3 3 3 5% 7% 56%	123674
Transparency	Day	30% 6% 10% 21% 21% 13%	130525
	Night	27% 6% 11% 21% 21% 15%	127880
Seeing	Day	9% 7% 26% 32% 20% 5%	16148
	Night	10% 8% 33% 37% 12% 1	26045

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	11% 4 4 5% 3 2 3 2 3 6% 59%	4077
	11th to 20th	Day	9% 6% 2 4 2 2 3 3 4 6% 59%	4218
	21st to end	Day	17% 5% 2 5% 3 3 3 3 4 5% 49%	4994
February	1st to 10th	Day	10% 6% 3 5% 3 4 3 3 4 5% 54%	2000
	11th to 20th	Day	11% 6% 2 5% 4 4 3 3 5% 6% 51%	1949
	21st to end	Day	12% 5% 2 4 3 3 3 3 5% 6% 55%	1650
March	1st to 10th	Day	8% 5% 2 5% 3 3 3 3 4 5% 58%	4627
	11th to 20th	Day	10% 6% 2 5% 3 3 3 2 3 5% 56%	4980
	21st to end	Day	7% 6% 2 6% 4 4 4 3 5% 6% 54%	5462
April	1st to 10th	Day	8% 7% 2 5% 4 4 4 4 5% 8% 51%	2210
	11th to 20th	Day	10% 6% 3 5% 4 4 4 3 5% 5% 51%	2374
	21st to end	Day	9% 6% 2 5% 5% 4 4 3 4 6% 53%	2424
May	1st to 10th	Day	11% 7% 3 6% 5% 4 4 4 6% 7% 44%	5862
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 6% 7% 50%	5862
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	6434
June	1st to 10th	Day	3 3 1 5% 4 4 4 4 6% 10% 56%	2600
	11th to 20th	Day	4 3 2 4 4 5% 5% 4 7% 10% 53%	2600
	21st to end	Day	5% 4 1 5% 5% 5% 6% 5% 7% 9% 47%	2600
July	1st to 10th	Day	11% 7% 2 7% 4 5% 5% 4 6% 8% 40%	5900
	11th to 20th	Day	3 4 2 6% 5% 5% 5% 4 7% 9% 50%	5900
	21st to end	Day	5% 4 1 6% 4 4 4 4 7% 10% 50%	6387
August	1st to 10th	Day	1 2 1 3 3 3 3 2 5% 8% 70%	3905
	11th to 20th	Day	4 2 1 4 3 3 4 3 5% 7% 64%	3846
	21st to end	Day	4 4 2 6% 5% 5% 6% 4 6% 10% 49%	4312
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 4 3 6% 8% 45%	2207
	11th to 20th	Day	9% 6% 2 7% 4 5% 6% 4 6% 7% 45%	2200
	21st to end	Day	8% 5% 2 4 4 3 5% 3 7% 7% 51%	2200
October	1st to 10th	Day	4 4 1 4 3 4 4 3 5% 8% 60%	2200
	11th to 20th	Day	9% 4 2 5% 3 3 3 3 4 5% 58%	2184
	21st to end	Day	9% 4 2 4 3 2 3 2 3 5% 62%	2200
November	1st to 10th	Day	12% 5% 1 6% 3 3 3 3 5% 7% 53%	1885
	11th to 20th	Day	7% 5% 2 4 2 4 5% 3 5% 6% 58%	1800
	21st to end	Day	10% 7% 2 6% 3 3 2 3 4 6% 53%	1800
December	1st to 10th	Day	19% 9% 3 6% 3 2 3 2 4 5% 44%	2940
	11th to 20th	Day	9% 7% 3 7% 5% 5% 4 3 5% 6% 47%	3391
	21st to end	Day	8% 5% 2 4 2 3 2 2 3 4 64%	4488
January	1st to 10th	Night	10% 5% 2 5% 3 2 2 2 4 6% 58%	5888
	11th to 20th	Night	8% 4 1 2 2 2 2 2 4 6% 67%	5790
	21st to end	Night	23% 6% 1 4 3 3 2 2 4 6% 46%	5984
February	1st to 10th	Night	10% 6% 1 4 4 3 3 3 4 6% 57%	2400
	11th to 20th	Night	11% 6% 2 5% 3 3 3 2 5% 5% 54%	2338
	21st to end	Night	10% 6% 2 4 4 3 3 3 5% 7% 53%	1980
March	1st to 10th	Night	6% 4 1 5% 3 3 4 3 7% 9% 55%	5239
	11th to 20th	Night	9% 6% 2 4 3 3 3 2 4 6% 57%	4980
	21st to end	Night	7% 7% 2 5% 3 3 3 3 5% 6% 54%	5467
April	1st to 10th	Night	6% 4 2 4 4 4 4 4 6% 7% 55%	2185
	11th to 20th	Night	8% 6% 3 5% 3 3 4 3 5% 6% 54%	1977
	21st to end	Night	9% 5% 2 4 3 3 3 3 5% 7% 56%	1975
May	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 7% 47%	4053
	11th to 20th	Night	5% 4 2 5% 4 4 4 4 6% 8% 54%	4053
	21st to end	Night	8% 5% 2 6% 4 4 4 4 7% 11% 45%	4443
June	1st to 10th	Night	2 2 1 3 3 2 3 3 7% 13% 62%	1800
	11th to 20th	Night	2 2 1 3 3 3 4 3 8% 9% 63%	1800
	21st to end	Night	4 3 1 3 3 4 4 4 6% 9% 59%	1800
July	1st to 10th	Night	6% 5% 2 5% 4 5% 5% 4 7% 11% 46%	4078
	11th to 20th	Night	2 1 1 3 3 4 4 4 7% 10% 62%	4077
	21st to end	Night	3 4 2 4 3 3 4 4 6% 10% 56%	4465
August	1st to 10th	Night	1 1 1 2 2 3 2 3 4 6% 76%	3255
	11th to 20th	Night	2 2 1 3 3 3 4 4 7% 9% 64%	3213
	21st to end	Night	4 3 1 5% 3 3 4 4 7% 11% 54%	3597
September	1st to 10th	Night	7% 5% 2 5% 3 4 4 4 6% 8% 54%	2191
	11th to 20th	Night	8% 4 2 5% 4 4 4 3 7% 9% 51%	2200
	21st to end	Night	8% 3 1 4 3 4 4 3 6% 8% 56%	2200
October	1st to 10th	Night	3 2 1 3 2 3 3 3 5% 8% 66%	2200
	11th to 20th	Night	8% 4 2 4 3 3 3 3 5% 5% 62%	2200
	21st to end	Night	9% 4 1 4 3 2 3 2 3 4 64%	2635
November	1st to 10th	Night	9% 5% 2 4 3 3 3 3 4 6% 60%	2455
	11th to 20th	Night	7% 4 1 4 3 3 3 3 5% 7% 61%	2600
	21st to end	Night	11% 5% 2 5% 4 3 3 3 5% 7% 53%	2600
December	1st to 10th	Night	20% 6% 2 5% 3 4 4 3 4 5% 44%	4250
	11th to 20th	Night	11% 8% 2 5% 4 3 3 3 4 6% 51%	4816
	21st to end	Night	8% 6% 2 4 2 2 2 2 3 6% 63%	6490

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	28% 4 5% 22% 22% 19%	4078
	11th to 20th	Day	27% 3 5% 17% 27% 21%	4218
	21st to end	Day	37% 4 6% 11% 28% 14%	4994
February	1st to 10th	Day	33% 4 7% 13% 21% 22%	2000
	11th to 20th	Day	34% 4 7% 19% 19% 16%	1959
	21st to end	Day	31% 3 7% 14% 24% 21%	1650
March	1st to 10th	Day	29% 4 5% 16% 16% 30%	4627
	11th to 20th	Day	32% 5% 6% 9% 16% 33%	4980
	21st to end	Day	30% 6% 8% 16% 22% 19%	5464
April	1st to 10th	Day	32% 6% 9% 17% 19% 17%	2210
	11th to 20th	Day	34% 6% 8% 16% 21% 15%	2374
	21st to end	Day	33% 5% 9% 20% 20% 13%	2424
May	1st to 10th	Day	38% 7% 10% 15% 20% 10%	5900
	11th to 20th	Day	31% 6% 11% 15% 23% 14%	5866
	21st to end	Day	36% 8% 11% 25% 16% 4	6447
June	1st to 10th	Day	24% 9% 13% 30% 21% 3	2600
	11th to 20th	Day	25% 8% 14% 25% 23% 6%	2600
	21st to end	Day	32% 8% 14% 23% 18% 5%	2600
July	1st to 10th	Day	41% 8% 15% 29% 7%	5836
	11th to 20th	Day	29% 7% 14% 33% 15% 2	5831
	21st to end	Day	28% 7% 18% 27% 19% 1	6205
August	1st to 10th	Day	14% 4 10% 39% 31% 1	3892
	11th to 20th	Day	20% 6% 19% 41% 13% 2	3882
	21st to end	Day	28% 10% 16% 24% 20% 2	4311
September	1st to 10th	Day	37% 8% 11% 18% 18% 8%	2207
	11th to 20th	Day	37% 8% 12% 21% 17% 5%	2200
	21st to end	Day	31% 6% 12% 20% 19% 12%	2200
October	1st to 10th	Day	16% 4 7% 13% 27% 33%	3590
	11th to 20th	Day	26% 4 6% 18% 22% 24%	3540
	21st to end	Day	22% 3 5% 17% 40% 13%	3538
November	1st to 10th	Day	32% 5% 10% 19% 21% 13%	1885
	11th to 20th	Day	28% 5% 8% 18% 22% 19%	1800
	21st to end	Day	34% 4 6% 19% 23% 15%	1800
December	1st to 10th	Day	45% 3 6% 16% 20% 11%	2940
	11th to 20th	Day	37% 5% 8% 13% 23% 15%	3389
	21st to end	Day	26% 3 4 18% 28% 22%	4488
January	1st to 10th	Night	29% 4 6% 16% 29% 17%	5888
	11th to 20th	Night	20% 2 4 19% 28% 27%	5790
	21st to end	Night	42% 4 4 10% 22% 18%	5984
February	1st to 10th	Night	29% 5% 9% 12% 23% 22%	2400
	11th to 20th	Night	32% 5% 7% 17% 21% 18%	2338
	21st to end	Night	32% 5% 7% 13% 23% 21%	1980
March	1st to 10th	Night	25% 7% 9% 18% 21% 20%	5239
	11th to 20th	Night	31% 6% 6% 10% 16% 32%	4980
	21st to end	Night	31% 6% 7% 17% 21% 19%	5467
April	1st to 10th	Night	29% 6% 11% 18% 16% 20%	2185
	11th to 20th	Night	31% 7% 12% 15% 18% 17%	1977
	21st to end	Night	30% 6% 12% 21% 19% 12%	1975
May	1st to 10th	Night	37% 8% 9% 19% 15% 13%	4080
	11th to 20th	Night	26% 8% 12% 19% 21% 15%	4054
	21st to end	Night	32% 9% 16% 25% 13% 6%	4452
June	1st to 10th	Night	14% 9% 19% 35% 21% 2	1800
	11th to 20th	Night	17% 9% 17% 28% 23% 6%	1800
	21st to end	Night	22% 7% 18% 29% 18% 5%	1800
July	1st to 10th	Night	32% 10% 22% 30% 6% 1	4035
	11th to 20th	Night	18% 8% 20% 37% 16% 1	4026
	21st to end	Night	23% 7% 21% 30% 17% 2	4336
August	1st to 10th	Night	11% 5% 14% 41% 29% 1	3244
	11th to 20th	Night	16% 7% 25% 39% 11% 1	3243
	21st to end	Night	23% 10% 21% 25% 18% 2	3597
September	1st to 10th	Night	29% 8% 14% 22% 19% 8%	2191
	11th to 20th	Night	30% 8% 16% 24% 16% 6%	2200
	21st to end	Night	26% 7% 12% 24% 18% 13%	2200
October	1st to 10th	Night	13% 4 9% 15% 22% 36%	3590
	11th to 20th	Night	20% 3 10% 17% 28% 21%	3570
	21st to end	Night	21% 3 6% 20% 34% 17%	4247
November	1st to 10th	Night	27% 5% 9% 19% 25% 15%	2455
	11th to 20th	Night	24% 6% 9% 21% 21% 19%	2600
	21st to end	Night	32% 5% 9% 16% 22% 16%	2600
December	1st to 10th	Night	44% 4 8% 16% 16% 13%	4250
	11th to 20th	Night	35% 4 6% 14% 21% 19%	4817
	21st to end	Night	25% 4 4 18% 30% 19%	6490

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% 45% 21% 7% 1	300
	11th to 20th	Day	16% 13% 36% 27% 6% 2	300
	21st to end	Day	12% 12% 47% 22% 8%	330
February	1st to 10th	Day	18% 13% 37% 20% 11%	300
	11th to 20th	Day	20% 14% 40% 22% 3	300
	21st to end	Day	16% 13% 49% 21% 2	249
March	1st to 10th	Day	14% 18% 42% 22% 3	300
	11th to 20th	Day	15% 15% 43% 19% 8%	300
	21st to end	Day	12% 15% 48% 18% 7%	330
April	1st to 10th	Day	12% 19% 43% 23% 3	310
	11th to 20th	Day	10% 18% 43% 24% 4	492
	21st to end	Day	11% 17% 43% 23% 6%	524
May	1st to 10th	Day	11% 11% 45% 28% 5%	703
	11th to 20th	Day	13% 9% 35% 32% 10% 1	725
	21st to end	Day	10% 8% 34% 37% 10% 1	789
June	1st to 10th	Day	4 2 23% 48% 20% 2	730
	11th to 20th	Day	4 1 24% 49% 20% 2	730
	21st to end	Day	4 2 15% 44% 30% 6%	730
July	1st to 10th	Day	8% 2 11% 37% 33% 9%	721
	11th to 20th	Day	3 1 6% 47% 36% 8%	718
	21st to end	Day	3 1 7% 40% 37% 12%	784
August	1st to 10th	Day	2 1 4 36% 43% 14%	527
	11th to 20th	Day	6% 1 5% 35% 38% 15%	517
	21st to end	Day	5% 1 5% 29% 42% 17%	583
September	1st to 10th	Day	10% 1 7% 24% 40% 18%	337
	11th to 20th	Day	4 1 4 29% 45% 17%	330
	21st to end	Day	12% 1 6% 28% 38% 14%	330
October	1st to 10th	Day	3 3 12% 35% 39% 8%	330
	11th to 20th	Day	8% 4 21% 41% 23% 3	330
	21st to end	Day	13% 11% 27% 31% 14% 3	363
November	1st to 10th	Day	17% 7% 28% 33% 14% 2	306
	11th to 20th	Day	15% 11% 30% 25% 13% 6%	300
	21st to end	Day	14% 18% 39% 20% 7% 2	300
December	1st to 10th	Day	16% 10% 30% 31% 11% 3	300
	11th to 20th	Day	11% 15% 39% 25% 9% 1	300
	21st to end	Day	12% 14% 38% 28% 9%	330
January	1st to 10th	Night	13% 10% 38% 31% 7% 1	1000
	11th to 20th	Night	14% 10% 41% 30% 5%	955
	21st to end	Night	16% 10% 41% 28% 5%	880
February	1st to 10th	Night	13% 14% 39% 29% 5%	800
	11th to 20th	Night	15% 16% 41% 26% 2	784
	21st to end	Night	14% 15% 50% 18% 2	660
March	1st to 10th	Night	13% 15% 47% 22% 3	743
	11th to 20th	Night	13% 11% 44% 28% 4	600
	21st to end	Night	7% 16% 53% 21% 2	660
April	1st to 10th	Night	8% 13% 54% 23% 3	600
	11th to 20th	Night	9% 15% 55% 19% 2	593
	21st to end	Night	11% 13% 51% 21% 4	600
May	1st to 10th	Night	9% 11% 53% 24% 3	600
	11th to 20th	Night	9% 8% 44% 30% 9%	591
	21st to end	Night	7% 8% 45% 32% 8%	650
June	1st to 10th	Night	2 1 34% 49% 13%	600
	11th to 20th	Night	2 1 38% 50% 8%	600
	21st to end	Night	4 2 23% 52% 19% 1	600
July	1st to 10th	Night	5% 2 13% 55% 23% 2	585
	11th to 20th	Night	3 1 11% 61% 23% 1	582
	21st to end	Night	3 1 9% 60% 25% 2	657
August	1st to 10th	Night	2 1 6% 62% 28% 2	597
	11th to 20th	Night	4 1 8% 56% 30% 2	594
	21st to end	Night	4 1 7% 48% 37% 3	660
September	1st to 10th	Night	6% 3 10% 47% 33% 3	600
	11th to 20th	Night	9% 1 10% 47% 32% 2	600
	21st to end	Night	8% 2 12% 51% 25% 2	600
October	1st to 10th	Night	5% 1 17% 49% 27% 1	600
	11th to 20th	Night	9% 5% 25% 44% 17% 1	600
	21st to end	Night	11% 9% 31% 33% 16% 1	875
November	1st to 10th	Night	11% 6% 29% 40% 14% 1	879
	11th to 20th	Night	10% 6% 37% 34% 13% 2	1000
	21st to end	Night	13% 10% 36% 32% 9% 1	1000
December	1st to 10th	Night	14% 7% 32% 38% 8% 1	1000
	11th to 20th	Night	15% 10% 37% 32% 6%	1000
	21st to end	Night	12% 11% 37% 33% 7%	1100

Page generated at 2025-10-31 01:02:37. Version ac07

Copyright © 2025 Attilla Danko.