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 2024-05-13.

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%	84053
	Night	8% 5% 2 4 3 3 3 3 5% 7% 56%	85532
Transparency	Day	32% 6% 10% 19% 21% 12%	83779
	Night	28% 7% 11% 20% 21% 14%	85326
Seeing	Day	9% 8% 26% 32% 20% 5%	14107
	Night	10% 8% 33% 36% 12% 1	24206

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	10% 7% 3 6% 5% 4 4 4 6% 8% 45%	2470
	11th to 20th	Day	11% 7% 2 7% 4 4 5% 3 5% 7% 44%	2330
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 4 6% 8% 43%	2531
June	1st to 10th	Day	3 3 1 5% 4 4 4 4 6% 9% 56%	2340
	11th to 20th	Day	3 3 2 4 4 5% 5% 4 7% 10% 53%	2340
	21st to end	Day	5% 4 1 5% 5% 5% 6% 5% 7% 9% 46%	2340
July	1st to 10th	Day	8% 6% 2 7% 5% 6% 6% 5% 7% 9% 40%	2340
	11th to 20th	Day	4 3 1 4 4 5% 4 3 6% 9% 58%	2340
	21st to end	Day	4 3 1 4 4 3 4 4 7% 11% 54%	2538
August	1st to 10th	Day	1 2 1 3 4 4 3 3 5% 9% 65%	2149
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 3 6% 7% 50%	2123
	21st to end	Day	5% 5% 2 6% 5% 5% 5% 4 6% 10% 48%	2376
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 4 6% 9% 45%	1987
	11th to 20th	Day	9% 6% 2 7% 5% 6% 6% 4 6% 7% 42%	1980
	21st to end	Day	9% 5% 2 5% 4 4 5% 3 6% 7% 50%	1980
October	1st to 10th	Day	5% 4 1 5% 3 4 4 3 5% 8% 57%	1980
	11th to 20th	Day	10% 5% 2 5% 3 3 3 3 4 6% 55%	1966
	21st to end	Day	10% 4 2 4 2 2 3 3 3 5% 61%	1980
November	1st to 10th	Day	11% 5% 1 6% 3 3 3 3 5% 7% 53%	1770
	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	8% 5% 2 4 4 4 5% 4 5% 8% 51%	1710
	11th to 20th	Night	8% 6% 2 5% 4 4 4 4 6% 8% 50%	1620
	21st to end	Night	7% 5% 2 5% 3 5% 4 3 6% 10% 50%	1745
June	1st to 10th	Night	2 2 1 3 3 2 2 3 7% 14% 62%	1620
	11th to 20th	Night	2 1 2 3 4 4 3 8% 9% 64%	1620
	21st to end	Night	4 3 1 3 3 4 4 4 7% 9% 58%	1620
July	1st to 10th	Night	5% 3 2 4 4 5% 5% 5% 8% 11% 49%	1620
	11th to 20th	Night	2 1 1 2 3 3 2 3 7% 8% 67%	1620
	21st to end	Night	2 2 1 2 3 2 3 4 6% 11% 65%	1775
August	1st to 10th	Night	2 1 1 1 1 2 2 3 5% 8% 74%	1790
	11th to 20th	Night	4 3 1 4 4 4 4 4 7% 9% 54%	1778
	21st to end	Night	5% 3 2 5% 3 3 4 5% 7% 9% 54%	1980
September	1st to 10th	Night	7% 4 2 4 3 4 4 4 6% 8% 54%	1971
	11th to 20th	Night	8% 4 2 6% 4 4 4 3 7% 8% 50%	1980
	21st to end	Night	8% 3 1 4 3 4 4 3 7% 8% 55%	1980
October	1st to 10th	Night	4 3 1 3 2 3 3 3 5% 8% 64%	1980
	11th to 20th	Night	9% 4 2 4 3 3 3 3 5% 5% 59%	1980
	21st to end	Night	10% 4 1 4 3 2 3 2 3 4 63%	2371
November	1st to 10th	Night	9% 5% 1 4 3 3 3 2 4 6% 61%	2305
	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	38% 7% 11% 14% 21% 9%	2470
	11th to 20th	Day	38% 8% 11% 19% 20% 4	2334
	21st to end	Day	40% 8% 11% 21% 18% 3	2531
June	1st to 10th	Day	24% 9% 13% 29% 21% 4	2340
	11th to 20th	Day	25% 8% 15% 26% 20% 6%	2340
	21st to end	Day	33% 9% 13% 22% 18% 5%	2340
July	1st to 10th	Day	37% 12% 15% 25% 10% 1	2276
	11th to 20th	Day	22% 8% 16% 28% 22% 3	2271
	21st to end	Day	20% 9% 24% 33% 13% 1	2397
August	1st to 10th	Day	17% 6% 15% 40% 21% 1	2136
	11th to 20th	Day	31% 9% 14% 29% 13% 3	2123
	21st to end	Day	32% 10% 16% 26% 14% 3	2376
September	1st to 10th	Day	37% 8% 12% 19% 17% 7%	1987
	11th to 20th	Day	39% 9% 11% 20% 16% 5%	1980
	21st to end	Day	32% 6% 12% 20% 19% 10%	1980
October	1st to 10th	Day	26% 7% 11% 23% 24% 9%	1980
	11th to 20th	Day	32% 5% 8% 15% 23% 17%	1966
	21st to end	Day	29% 4 5% 16% 27% 20%	1980
November	1st to 10th	Day	32% 5% 10% 20% 21% 12%	1770
	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	30% 7% 13% 20% 19% 11%	1710
	11th to 20th	Night	33% 9% 11% 25% 17% 5%	1621
	21st to end	Night	31% 8% 16% 27% 15% 3	1746
June	1st to 10th	Night	14% 9% 18% 34% 22% 3	1620
	11th to 20th	Night	16% 9% 17% 29% 22% 6%	1620
	21st to end	Night	23% 8% 18% 28% 18% 5%	1620
July	1st to 10th	Night	26% 14% 21% 27% 10% 2	1575
	11th to 20th	Night	14% 8% 18% 32% 25% 3	1566
	21st to end	Night	12% 7% 27% 38% 15% 1	1676
August	1st to 10th	Night	10% 7% 18% 41% 22% 1	1779
	11th to 20th	Night	23% 11% 19% 28% 17% 3	1778
	21st to end	Night	25% 10% 22% 25% 14% 3	1980
September	1st to 10th	Night	27% 9% 15% 23% 19% 7%	1971
	11th to 20th	Night	32% 9% 16% 23% 17% 5%	1980
	21st to end	Night	27% 8% 13% 23% 19% 11%	1980
October	1st to 10th	Night	19% 7% 15% 26% 21% 12%	1980
	11th to 20th	Night	28% 5% 11% 17% 23% 17%	1980
	21st to end	Night	28% 3 7% 16% 23% 23%	2371
November	1st to 10th	Night	27% 5% 9% 20% 25% 14%	2305
	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% 44% 28% 5%	653
	11th to 20th	Day	16% 8% 32% 33% 11% 2	637
	21st to end	Day	10% 8% 32% 38% 10% 1	679
June	1st to 10th	Day	4 2 22% 48% 22% 2	630
	11th to 20th	Day	3 1 24% 48% 22% 2	630
	21st to end	Day	4 2 15% 46% 29% 5%	630
July	1st to 10th	Day	6% 2 11% 37% 34% 9%	621
	11th to 20th	Day	2 4 47% 39% 8%	618
	21st to end	Day	2 5% 40% 39% 13%	676
August	1st to 10th	Day	2 4 38% 44% 13%	447
	11th to 20th	Day	7% 1 5% 33% 39% 15%	437
	21st to end	Day	6% 1 5% 29% 41% 17%	495
September	1st to 10th	Day	9% 1 6% 23% 41% 21%	277
	11th to 20th	Day	5% 1 3 26% 46% 19%	270
	21st to end	Day	13% 1 6% 28% 38% 14%	270
October	1st to 10th	Day	4 4 14% 37% 36% 6%	270
	11th to 20th	Day	10% 5% 22% 39% 21% 3	270
	21st to end	Day	16% 12% 26% 30% 13% 2	297
November	1st to 10th	Day	17% 6% 27% 34% 14% 2	270
	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	10% 7% 44% 29% 9%	540
	21st to end	Night	7% 7% 43% 34% 8%	584
June	1st to 10th	Night	2 1 31% 51% 14%	540
	11th to 20th	Night	1 1 38% 52% 8%	540
	21st to end	Night	4 1 23% 51% 20% 1	540
July	1st to 10th	Night	5% 1 13% 55% 24% 2	525
	11th to 20th	Night	2 1 10% 63% 23% 1	522
	21st to end	Night	2 1 9% 62% 25% 2	591
August	1st to 10th	Night	2 1 7% 62% 27% 2	537
	11th to 20th	Night	4 1 7% 55% 31% 2	534
	21st to end	Night	4 1 8% 48% 37% 3	594
September	1st to 10th	Night	5% 2 10% 48% 32% 3	540
	11th to 20th	Night	10% 1 10% 46% 32% 2	540
	21st to end	Night	9% 2 12% 50% 25% 2	540
October	1st to 10th	Night	5% 1 19% 49% 25% 1	540
	11th to 20th	Night	10% 6% 26% 42% 16% 1	540
	21st to end	Night	12% 9% 32% 31% 16% 1	787
November	1st to 10th	Night	11% 5% 29% 40% 14% 1	825
	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 2024-05-10 11:39:01. Version ac07

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