Bobcat Trail Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bobcat Trail Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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	5% 6% 2 5% 5% 3 5% 5% 6% 8% 50%	74810
	Night	4 5% 2 4 4 3 4 4 5% 8% 56%	75041
Transparency	Day	30% 6% 13% 25% 19% 7%	74513
	Night	25% 6% 14% 28% 20% 7%	74860
Seeing	Day	11% 16% 32% 24% 13% 4	14537
	Night	9% 20% 34% 26% 10% 1	24701

By Month

Percentage Cloud Cover SW (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	1 5% 3 6% 6% 3 3 3 6% 8% 56%	1518
	11th to 20th	Day	1 4 3 4 5% 3 4 5% 7% 8% 57%	1488
	21st to end	Day	2 4 3 6% 4 3 3 4 6% 9% 54%	1777
February	1st to 10th	Day	1 5% 3 6% 7% 4 4 4 5% 9% 52%	1620
	11th to 20th	Day	1 5% 3 6% 6% 3 4 4 6% 8% 55%	1687
	21st to end	Day	1 7% 3 7% 5% 2 3 4 6% 9% 54%	1480
March	1st to 10th	Day	3 6% 3 6% 4 2 3 4 5% 9% 54%	1800
	11th to 20th	Day	5% 7% 3 6% 5% 3 5% 4 6% 9% 48%	1952
	21st to end	Day	5% 8% 3 6% 6% 4 5% 5% 6% 9% 43%	2308
April	1st to 10th	Day	5% 7% 2 5% 5% 2 5% 5% 6% 8% 50%	2160
	11th to 20th	Day	8% 10% 4 6% 6% 3 4 5% 6% 7% 42%	2131
	21st to end	Day	10% 9% 3 5% 5% 3 5% 6% 6% 7% 39%	2160
May	1st to 10th	Day	12% 9% 4 6% 6% 4 5% 5% 7% 7% 36%	2368
	11th to 20th	Day	13% 10% 3 6% 5% 3 5% 6% 7% 8% 35%	2478
	21st to end	Day	8% 6% 3 6% 6% 4 7% 6% 8% 9% 36%	2724
June	1st to 10th	Day	5% 4 2 4 5% 4 7% 7% 8% 9% 45%	2520
	11th to 20th	Day	7% 5% 2 4 4 3 6% 6% 7% 8% 48%	2520
	21st to end	Day	4 3 1 3 5% 3 5% 7% 7% 9% 52%	2520
July	1st to 10th	Day	7% 5% 3 4 6% 4 5% 6% 8% 9% 44%	2520
	11th to 20th	Day	4 3 2 5% 5% 3 7% 6% 8% 9% 50%	2520
	21st to end	Day	6% 4 2 5% 6% 4 5% 7% 8% 9% 42%	2742
August	1st to 10th	Day	5% 5% 2 6% 6% 3 7% 7% 8% 10% 41%	2340
	11th to 20th	Day	5% 5% 1 4 6% 3 5% 5% 6% 8% 50%	2168
	21st to end	Day	5% 4 2 6% 6% 3 5% 6% 6% 7% 50%	2376
September	1st to 10th	Day	5% 5% 2 3 4 3 4 5% 5% 6% 58%	2160
	11th to 20th	Day	7% 3 1 4 3 2 4 4 5% 7% 59%	2148
	21st to end	Day	6% 5% 2 4 3 2 3 3 5% 7% 62%	1976
October	1st to 10th	Day	7% 7% 2 4 4 2 3 5% 4 6% 56%	1800
	11th to 20th	Day	4 4 2 4 4 2 3 4 5% 7% 62%	1800
	21st to end	Day	5% 6% 2 4 3 2 3 4 5% 7% 60%	1888
November	1st to 10th	Day	2 4 1 4 4 2 3 4 5% 8% 63%	1673
	11th to 20th	Day	2 5% 3 3 3 3 4 4 5% 9% 61%	1710
	21st to end	Day	2 5% 2 4 5% 2 5% 5% 6% 8% 55%	1538
December	1st to 10th	Day	2 4 2 4 4 3 4 4 6% 10% 57%	1520
	11th to 20th	Day	2 6% 2 5% 4 3 3 4 5% 8% 59%	1926
	21st to end	Day	1 5% 3 7% 6% 4 4 5% 5% 6% 54%	2794
January	1st to 10th	Night	1 5% 2 5% 5% 3 4 4 5% 7% 61%	2647
	11th to 20th	Night	1 3 2 4 4 2 4 4 5% 9% 61%	2617
	21st to end	Night	2 5% 2 6% 5% 3 4 4 5% 8% 57%	2596
February	1st to 10th	Night	1 5% 2 6% 5% 3 4 4 5% 8% 58%	2340
	11th to 20th	Night	2 5% 3 5% 5% 4 5% 4 5% 6% 57%	2159
	21st to end	Night	1 8% 3 5% 5% 3 3 4 4 6% 57%	1776
March	1st to 10th	Night	1 5% 3 6% 4 3 5% 4 5% 9% 55%	2160
	11th to 20th	Night	3 7% 2 5% 5% 2 4 4 4 8% 55%	2003
	21st to end	Night	5% 9% 3 4 5% 3 5% 5% 5% 7% 49%	2047
April	1st to 10th	Night	4 7% 3 4 4 3 5% 5% 5% 7% 55%	1800
	11th to 20th	Night	7% 9% 2 4 5% 2 4 5% 5% 7% 51%	1777
	21st to end	Night	10% 9% 3 5% 3 2 4 4 4 8% 49%	1800
May	1st to 10th	Night	11% 7% 3 6% 4 3 4 6% 7% 8% 41%	1589
	11th to 20th	Night	13% 10% 2 4 4 2 4 5% 5% 8% 43%	1417
	21st to end	Night	7% 6% 2 5% 4 3 5% 5% 6% 10% 47%	1552
June	1st to 10th	Night	6% 3 1 3 4 3 4 6% 7% 12% 53%	1440
	11th to 20th	Night	5% 3 1 4 4 2 4 4 6% 8% 58%	1440
	21st to end	Night	4 3 1 3 3 3 3 3 5% 8% 61%	1440
July	1st to 10th	Night	6% 4 1 3 4 3 4 5% 5% 10% 53%	1440
	11th to 20th	Night	3 2 2 4 4 3 4 5% 7% 9% 58%	1440
	21st to end	Night	4 3 1 4 5% 3 5% 6% 8% 9% 52%	1576
August	1st to 10th	Night	5% 4 2 5% 5% 3 5% 5% 7% 9% 50%	1596
	11th to 20th	Night	4 3 2 3 4 2 4 3 5% 9% 62%	1731
	21st to end	Night	3 4 2 4 4 3 4 5% 6% 8% 56%	1980
September	1st to 10th	Night	6% 4 2 3 4 2 4 4 5% 7% 59%	1800
	11th to 20th	Night	6% 3 2 3 4 3 4 4 5% 6% 63%	1810
	21st to end	Night	6% 4 1 3 3 2 3 4 4 6% 62%	1980
October	1st to 10th	Night	8% 6% 2 3 4 2 3 3 6% 7% 56%	2160
	11th to 20th	Night	4 4 2 3 3 2 3 3 4 7% 66%	2160
	21st to end	Night	4 7% 3 4 4 2 3 4 4 6% 59%	2448
November	1st to 10th	Night	3 3 1 3 3 2 4 3 6% 9% 62%	2405
	11th to 20th	Night	2 5% 2 3 3 2 3 3 5% 9% 61%	2470
	21st to end	Night	2 5% 3 4 3 3 4 5% 6% 7% 58%	2641
December	1st to 10th	Night	1 4 2 5% 4 3 4 4 5% 9% 60%	2660
	11th to 20th	Night	2 6% 3 4 4 2 4 5% 5% 10% 56%	3271
	21st to end	Night	2 5% 3 5% 5% 3 5% 5% 6% 8% 53%	4873

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% 5% 15% 33% 16% 4	1519
	11th to 20th	Day	23% 6% 21% 26% 20% 4	1488
	21st to end	Day	25% 6% 19% 32% 14% 4	1777
February	1st to 10th	Day	29% 8% 20% 26% 14% 4	1620
	11th to 20th	Day	26% 6% 14% 29% 19% 5%	1696
	21st to end	Day	27% 5% 15% 30% 17% 6%	1480
March	1st to 10th	Day	26% 5% 15% 29% 21% 3	1800
	11th to 20th	Day	32% 7% 14% 27% 16% 5%	1952
	21st to end	Day	35% 6% 15% 27% 13% 3	2308
April	1st to 10th	Day	30% 6% 15% 26% 15% 7%	2160
	11th to 20th	Day	40% 6% 14% 22% 14% 4	2134
	21st to end	Day	40% 8% 10% 26% 14% 1	2160
May	1st to 10th	Day	45% 7% 14% 20% 13% 2	2368
	11th to 20th	Day	45% 7% 14% 22% 11% 1	2482
	21st to end	Day	40% 8% 15% 21% 13% 3	2724
June	1st to 10th	Day	31% 8% 18% 20% 16% 6%	2520
	11th to 20th	Day	30% 7% 10% 19% 21% 12%	2520
	21st to end	Day	25% 7% 10% 25% 18% 14%	2520
July	1st to 10th	Day	32% 7% 12% 18% 21% 10%	2451
	11th to 20th	Day	26% 7% 12% 20% 20% 15%	2445
	21st to end	Day	33% 8% 12% 23% 18% 8%	2590
August	1st to 10th	Day	33% 8% 14% 21% 15% 9%	2324
	11th to 20th	Day	30% 5% 10% 19% 23% 13%	2168
	21st to end	Day	29% 6% 9% 20% 25% 10%	2376
September	1st to 10th	Day	25% 4 8% 19% 28% 16%	2160
	11th to 20th	Day	23% 5% 8% 24% 26% 13%	2148
	21st to end	Day	23% 3 8% 23% 34% 8%	1976
October	1st to 10th	Day	28% 6% 9% 24% 25% 9%	1800
	11th to 20th	Day	22% 6% 8% 32% 25% 8%	1800
	21st to end	Day	24% 4 13% 30% 22% 7%	1888
November	1st to 10th	Day	19% 7% 12% 29% 26% 7%	1673
	11th to 20th	Day	21% 5% 12% 33% 23% 6%	1710
	21st to end	Day	24% 6% 12% 29% 21% 7%	1538
December	1st to 10th	Day	23% 6% 19% 30% 16% 6%	1520
	11th to 20th	Day	24% 5% 13% 35% 19% 4	1924
	21st to end	Day	29% 6% 13% 25% 18% 8%	2794
January	1st to 10th	Night	23% 5% 16% 31% 18% 6%	2647
	11th to 20th	Night	19% 5% 20% 30% 19% 6%	2617
	21st to end	Night	25% 5% 16% 32% 18% 4	2596
February	1st to 10th	Night	25% 6% 18% 30% 17% 4	2340
	11th to 20th	Night	27% 6% 14% 30% 20% 3	2160
	21st to end	Night	27% 4 13% 27% 22% 7%	1776
March	1st to 10th	Night	26% 6% 12% 30% 22% 4	2160
	11th to 20th	Night	28% 5% 10% 29% 23% 5%	2003
	21st to end	Night	32% 7% 15% 28% 15% 3	2047
April	1st to 10th	Night	28% 7% 14% 27% 18% 6%	1800
	11th to 20th	Night	32% 6% 14% 29% 14% 5%	1777
	21st to end	Night	36% 4 11% 29% 19% 1	1800
May	1st to 10th	Night	36% 8% 15% 26% 14% 1	1589
	11th to 20th	Night	39% 5% 17% 26% 12%	1418
	21st to end	Night	31% 9% 18% 24% 14% 3	1552
June	1st to 10th	Night	23% 8% 24% 27% 13% 5%	1440
	11th to 20th	Night	23% 5% 13% 23% 21% 14%	1440
	21st to end	Night	20% 6% 9% 30% 23% 12%	1440
July	1st to 10th	Night	26% 7% 13% 26% 21% 8%	1400
	11th to 20th	Night	22% 5% 13% 25% 21% 15%	1392
	21st to end	Night	24% 7% 15% 30% 17% 7%	1488
August	1st to 10th	Night	28% 6% 18% 24% 16% 7%	1588
	11th to 20th	Night	21% 4 11% 28% 22% 13%	1731
	21st to end	Night	24% 6% 11% 24% 25% 11%	1980
September	1st to 10th	Night	25% 5% 9% 20% 24% 17%	1800
	11th to 20th	Night	21% 5% 10% 25% 25% 14%	1810
	21st to end	Night	23% 4 7% 26% 32% 8%	1980
October	1st to 10th	Night	27% 5% 12% 25% 24% 8%	2160
	11th to 20th	Night	20% 4 10% 31% 23% 12%	2160
	21st to end	Night	27% 5% 11% 27% 23% 7%	2448
November	1st to 10th	Night	19% 5% 14% 27% 28% 7%	2405
	11th to 20th	Night	20% 4 13% 34% 22% 7%	2470
	21st to end	Night	24% 5% 10% 30% 24% 7%	2641
December	1st to 10th	Night	23% 5% 17% 29% 19% 6%	2660
	11th to 20th	Night	22% 8% 14% 35% 19% 2	3272
	21st to end	Night	26% 7% 13% 27% 19% 7%	4873

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	14% 24% 38% 15% 6% 3	270
	11th to 20th	Day	10% 38% 34% 15% 4	258
	21st to end	Day	10% 35% 47% 6% 2 1	264
February	1st to 10th	Day	11% 43% 40% 5% 1	240
	11th to 20th	Day	11% 37% 39% 10% 3	240
	21st to end	Day	11% 33% 43% 12% 1	198
March	1st to 10th	Day	12% 26% 37% 20% 4 1	240
	11th to 20th	Day	16% 22% 40% 15% 7%	392
	21st to end	Day	14% 24% 40% 16% 5% 1	462
April	1st to 10th	Day	15% 26% 36% 17% 5%	420
	11th to 20th	Day	22% 23% 38% 14% 3	412
	21st to end	Day	20% 19% 34% 16% 9% 3	420
May	1st to 10th	Day	19% 16% 30% 23% 11% 2	571
	11th to 20th	Day	20% 9% 28% 28% 11% 3	625
	21st to end	Day	11% 14% 28% 27% 17% 4	679
June	1st to 10th	Day	7% 7% 27% 33% 19% 7%	630
	11th to 20th	Day	10% 9% 37% 28% 13% 3	630
	21st to end	Day	6% 5% 33% 33% 17% 6%	630
July	1st to 10th	Day	9% 3 19% 33% 29% 8%	621
	11th to 20th	Day	5% 4 23% 40% 22% 8%	618
	21st to end	Day	7% 4 18% 33% 30% 8%	684
August	1st to 10th	Day	9% 3 29% 33% 21% 5%	459
	11th to 20th	Day	6% 6% 21% 40% 19% 8%	437
	21st to end	Day	8% 7% 26% 33% 20% 6%	495
September	1st to 10th	Day	7% 8% 29% 34% 17% 4	450
	11th to 20th	Day	8% 9% 31% 29% 18% 5%	438
	21st to end	Day	10% 8% 31% 27% 14% 10%	270
October	1st to 10th	Day	12% 10% 29% 27% 15% 7%	270
	11th to 20th	Day	11% 19% 39% 20% 9% 3	270
	21st to end	Day	11% 25% 36% 23% 4 1	297
November	1st to 10th	Day	7% 21% 46% 15% 8% 3	270
	11th to 20th	Day	14% 27% 38% 17% 3	270
	21st to end	Day	14% 33% 35% 14% 4	270
December	1st to 10th	Day	14% 36% 32% 13% 5%	270
	11th to 20th	Day	16% 36% 39% 9%	270
	21st to end	Day	12% 39% 32% 11% 4 1	297
January	1st to 10th	Night	11% 34% 34% 15% 4 2	950
	11th to 20th	Night	11% 42% 30% 12% 4 1	935
	21st to end	Night	6% 39% 39% 11% 4	814
February	1st to 10th	Night	7% 40% 39% 10% 3	720
	11th to 20th	Night	9% 34% 39% 16% 2	704
	21st to end	Night	10% 30% 46% 13% 1	592
March	1st to 10th	Night	6% 27% 41% 21% 4	720
	11th to 20th	Night	8% 20% 40% 25% 7% 1	720
	21st to end	Night	9% 20% 42% 22% 6% 1	661
April	1st to 10th	Night	11% 19% 42% 25% 3	540
	11th to 20th	Night	13% 17% 43% 21% 6% 1	533
	21st to end	Night	15% 16% 30% 30% 9%	540
May	1st to 10th	Night	15% 11% 31% 31% 11% 1	540
	11th to 20th	Night	20% 4 28% 34% 12% 2	531
	21st to end	Night	9% 8% 33% 31% 17% 2	584
June	1st to 10th	Night	6% 6% 27% 40% 19% 2	540
	11th to 20th	Night	8% 7% 32% 43% 10%	540
	21st to end	Night	5% 6% 28% 41% 19% 2	540
July	1st to 10th	Night	7% 2 18% 45% 26% 3	525
	11th to 20th	Night	3 2 21% 47% 25% 3	522
	21st to end	Night	5% 2 14% 44% 33% 2	591
August	1st to 10th	Night	8% 3 15% 50% 21% 2	537
	11th to 20th	Night	4 1 22% 48% 21% 3	534
	21st to end	Night	5% 3 20% 42% 29% 2	594
September	1st to 10th	Night	9% 4 19% 43% 21% 3	540
	11th to 20th	Night	7% 4 24% 41% 19% 3	540
	21st to end	Night	9% 6% 32% 39% 14% 1	540
October	1st to 10th	Night	10% 12% 32% 30% 12% 4	720
	11th to 20th	Night	8% 15% 41% 25% 9% 1	720
	21st to end	Night	8% 21% 41% 23% 5% 1	864
November	1st to 10th	Night	7% 19% 43% 24% 6% 1	925
	11th to 20th	Night	9% 29% 42% 17% 2 1	950
	21st to end	Night	7% 26% 44% 19% 3	950
December	1st to 10th	Night	11% 34% 38% 13% 3	950
	11th to 20th	Night	9% 35% 38% 14% 3 1	950
	21st to end	Night	11% 39% 34% 12% 3 1	1045

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