Starlight Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starlight Ridge Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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	9% 6% 3 5% 4 3 4 4 5% 7% 49%	74899
	Night	9% 6% 3 5% 5% 3 4 4 5% 7% 49%	74927
Transparency	Day	35% 6% 13% 27% 16% 3	74607
	Night	34% 6% 13% 26% 17% 3	74743
Seeing	Day	12% 9% 32% 31% 13% 2	14704
	Night	12% 10% 38% 33% 8%	24777

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	6% 10% 4 5% 5% 3 5% 4 4 7% 46%	1518
	11th to 20th	Day	5% 8% 3 8% 6% 3 5% 5% 5% 7% 45%	1480
	21st to end	Day	9% 10% 4 8% 6% 3 5% 4 5% 6% 40%	1620
February	1st to 10th	Day	8% 9% 4 7% 7% 3 5% 5% 5% 7% 40%	1642
	11th to 20th	Day	7% 8% 4 8% 5% 3 4 4 4 6% 46%	1749
	21st to end	Day	9% 8% 3 6% 5% 3 5% 3 5% 5% 48%	1480
March	1st to 10th	Day	9% 7% 3 7% 5% 2 4 4 4 6% 50%	1800
	11th to 20th	Day	9% 8% 4 5% 4 3 4 4 6% 7% 46%	1957
	21st to end	Day	14% 10% 4 6% 5% 3 4 4 6% 8% 35%	2186
April	1st to 10th	Day	14% 6% 3 5% 5% 3 4 4 6% 7% 44%	2160
	11th to 20th	Day	17% 9% 3 6% 5% 2 4 4 4 6% 40%	2216
	21st to end	Day	16% 6% 2 5% 4 3 4 4 6% 7% 43%	2340
May	1st to 10th	Day	14% 6% 2 6% 5% 3 4 4 5% 8% 43%	2340
	11th to 20th	Day	16% 7% 2 5% 5% 3 4 5% 5% 7% 41%	2302
	21st to end	Day	15% 7% 3 6% 5% 3 4 5% 5% 8% 41%	2654
June	1st to 10th	Day	10% 4 2 4 4 3 4 5% 5% 8% 51%	2520
	11th to 20th	Day	11% 3 2 4 4 3 4 5% 5% 9% 51%	2520
	21st to end	Day	4 3 1 4 4 4 4 5% 7% 8% 56%	2520
July	1st to 10th	Day	5% 3 2 5% 4 3 5% 6% 7% 9% 51%	2520
	11th to 20th	Day	5% 3 1 3 3 2 4 5% 5% 8% 61%	2520
	21st to end	Day	5% 4 1 3 4 3 4 5% 7% 9% 54%	2706
August	1st to 10th	Day	8% 5% 2 6% 5% 4 6% 6% 7% 8% 43%	2328
	11th to 20th	Day	6% 4 3 4 3 3 4 6% 5% 7% 54%	2301
	21st to end	Day	6% 3 2 4 4 2 4 4 5% 7% 59%	2458
September	1st to 10th	Day	9% 4 2 4 3 2 2 4 4 6% 59%	2116
	11th to 20th	Day	7% 3 2 4 3 2 3 4 4 7% 60%	1980
	21st to end	Day	11% 4 1 4 3 2 3 3 5% 6% 58%	1980
October	1st to 10th	Day	14% 6% 2 3 3 1 3 3 4 5% 56%	1980
	11th to 20th	Day	10% 6% 1 4 3 2 2 3 3 7% 58%	1770
	21st to end	Day	11% 6% 3 5% 4 3 3 3 5% 5% 52%	1782
November	1st to 10th	Day	7% 6% 2 4 4 3 4 5% 5% 8% 53%	1673
	11th to 20th	Day	6% 7% 3 6% 5% 2 3 3 4 5% 54%	1710
	21st to end	Day	7% 9% 3 4 4 2 5% 4 5% 8% 50%	1710
December	1st to 10th	Day	6% 8% 4 6% 6% 3 4 3 6% 6% 47%	1641
	11th to 20th	Day	6% 6% 4 6% 4 3 4 4 6% 9% 49%	1926
	21st to end	Day	14% 13% 4 8% 6% 2 3 4 4 4 37%	2794
January	1st to 10th	Night	5% 9% 4 6% 7% 4 4 4 5% 7% 45%	2647
	11th to 20th	Night	5% 8% 3 7% 6% 3 4 5% 6% 7% 45%	2603
	21st to end	Night	6% 9% 4 9% 5% 3 4 4 6% 7% 42%	2734
February	1st to 10th	Night	10% 9% 4 6% 6% 3 4 5% 5% 7% 41%	2335
	11th to 20th	Night	6% 8% 4 6% 6% 3 5% 5% 6% 7% 44%	2098
	21st to end	Night	8% 7% 2 5% 5% 4 4 5% 5% 6% 47%	1776
March	1st to 10th	Night	8% 8% 3 5% 5% 3 5% 4 5% 6% 47%	2160
	11th to 20th	Night	12% 7% 3 4 5% 2 4 5% 5% 7% 46%	2003
	21st to end	Night	13% 8% 4 7% 5% 3 5% 5% 5% 8% 37%	2165
April	1st to 10th	Night	12% 6% 3 6% 5% 3 4 4 5% 9% 43%	1800
	11th to 20th	Night	14% 7% 3 6% 4 2 4 4 5% 7% 44%	1690
	21st to end	Night	14% 6% 3 5% 6% 2 4 5% 5% 7% 43%	1620
May	1st to 10th	Night	11% 7% 2 4 5% 3 4 5% 6% 8% 44%	1620
	11th to 20th	Night	16% 7% 2 4 5% 3 4 5% 5% 7% 43%	1593
	21st to end	Night	14% 6% 2 6% 4 2 5% 5% 6% 9% 40%	1618
June	1st to 10th	Night	9% 4 1 3 3 2 4 4 5% 10% 54%	1440
	11th to 20th	Night	11% 4 2 4 4 3 5% 4 6% 7% 50%	1440
	21st to end	Night	4 3 1 3 4 3 6% 5% 7% 9% 55%	1440
July	1st to 10th	Night	6% 3 2 4 3 3 4 5% 8% 9% 54%	1440
	11th to 20th	Night	4 3 1 4 4 3 3 4 6% 6% 62%	1440
	21st to end	Night	4 4 2 5% 5% 3 4 5% 6% 9% 53%	1608
August	1st to 10th	Night	4 3 1 5% 6% 3 4 7% 7% 10% 50%	1611
	11th to 20th	Night	6% 3 1 4 4 2 4 4 6% 9% 57%	1600
	21st to end	Night	5% 3 2 3 3 2 3 3 5% 8% 61%	1895
September	1st to 10th	Night	9% 3 2 3 4 2 3 4 5% 6% 59%	1844
	11th to 20th	Night	7% 3 2 3 3 1 3 3 5% 7% 63%	1980
	21st to end	Night	10% 4 2 3 3 2 3 3 4 6% 61%	1980
October	1st to 10th	Night	15% 6% 2 4 4 2 3 3 4 6% 51%	1980
	11th to 20th	Night	11% 4 2 3 3 2 2 3 4 6% 60%	2168
	21st to end	Night	12% 6% 2 5% 4 2 3 4 4 6% 53%	2574
November	1st to 10th	Night	7% 5% 2 5% 4 3 3 3 6% 6% 55%	2405
	11th to 20th	Night	6% 6% 2 5% 5% 2 4 4 5% 8% 52%	2470
	21st to end	Night	6% 7% 3 5% 4 2 4 4 5% 8% 52%	2470
December	1st to 10th	Night	6% 7% 3 6% 5% 3 4 5% 4 6% 51%	2536
	11th to 20th	Night	5% 8% 3 6% 4 2 3 4 5% 8% 51%	3271
	21st to end	Night	17% 12% 3 8% 4 2 3 3 4 6% 38%	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	40% 5% 13% 25% 17% 1	1519
	11th to 20th	Day	39% 7% 18% 24% 11% 2	1480
	21st to end	Day	45% 6% 16% 20% 11% 3	1620
February	1st to 10th	Day	44% 5% 15% 21% 13% 2	1642
	11th to 20th	Day	40% 5% 14% 24% 13% 5%	1759
	21st to end	Day	40% 4 14% 23% 14% 5%	1480
March	1st to 10th	Day	35% 4 12% 26% 19% 3	1800
	11th to 20th	Day	38% 6% 12% 26% 17% 2	1957
	21st to end	Day	48% 7% 15% 21% 7% 2	2186
April	1st to 10th	Day	39% 5% 15% 25% 14% 2	2160
	11th to 20th	Day	45% 5% 12% 22% 14% 2	2219
	21st to end	Day	40% 5% 14% 27% 13%	2340
May	1st to 10th	Day	41% 6% 14% 25% 14%	2340
	11th to 20th	Day	43% 6% 15% 26% 9% 1	2306
	21st to end	Day	42% 6% 15% 21% 13% 1	2654
June	1st to 10th	Day	29% 8% 18% 31% 12% 2	2520
	11th to 20th	Day	31% 6% 16% 27% 17% 4	2520
	21st to end	Day	24% 7% 15% 32% 19% 3	2520
July	1st to 10th	Day	28% 8% 14% 30% 18% 2	2451
	11th to 20th	Day	22% 6% 12% 28% 23% 8%	2445
	21st to end	Day	23% 9% 13% 29% 19% 6%	2556
August	1st to 10th	Day	35% 9% 16% 23% 13% 4	2314
	11th to 20th	Day	28% 7% 11% 32% 19% 2	2301
	21st to end	Day	24% 7% 12% 29% 22% 7%	2458
September	1st to 10th	Day	26% 5% 12% 26% 22% 9%	2116
	11th to 20th	Day	24% 5% 12% 31% 23% 4	1980
	21st to end	Day	28% 4 9% 32% 26% 2	1980
October	1st to 10th	Day	33% 4 9% 26% 26% 3	1980
	11th to 20th	Day	28% 3 13% 30% 21% 6%	1770
	21st to end	Day	34% 4 11% 30% 15% 6%	1782
November	1st to 10th	Day	30% 6% 13% 27% 20% 4	1673
	11th to 20th	Day	34% 3 12% 28% 18% 5%	1710
	21st to end	Day	33% 4 14% 27% 18% 4	1710
December	1st to 10th	Day	38% 4 13% 28% 15% 2	1641
	11th to 20th	Day	33% 5% 17% 30% 15% 1	1924
	21st to end	Day	50% 5% 8% 27% 9% 1	2794
January	1st to 10th	Night	40% 5% 14% 25% 15% 2	2647
	11th to 20th	Night	37% 6% 16% 27% 13% 1	2603
	21st to end	Night	41% 6% 15% 25% 12% 1	2734
February	1st to 10th	Night	43% 5% 15% 22% 12% 2	2335
	11th to 20th	Night	38% 6% 13% 26% 13% 4	2098
	21st to end	Night	37% 4 14% 26% 14% 6%	1776
March	1st to 10th	Night	37% 5% 14% 25% 16% 3	2160
	11th to 20th	Night	37% 5% 11% 26% 20% 2	2003
	21st to end	Night	44% 7% 14% 23% 12% 1	2165
April	1st to 10th	Night	38% 6% 15% 22% 16% 3	1800
	11th to 20th	Night	40% 6% 11% 24% 16% 2	1690
	21st to end	Night	39% 7% 13% 26% 14% 1	1620
May	1st to 10th	Night	36% 8% 17% 23% 15% 1	1620
	11th to 20th	Night	41% 7% 13% 26% 12% 1	1594
	21st to end	Night	39% 9% 18% 20% 11% 2	1619
June	1st to 10th	Night	26% 7% 18% 31% 16% 3	1440
	11th to 20th	Night	33% 7% 14% 26% 16% 5%	1440
	21st to end	Night	23% 9% 17% 32% 17% 3	1440
July	1st to 10th	Night	24% 8% 17% 31% 18% 3	1400
	11th to 20th	Night	22% 6% 11% 30% 22% 9%	1392
	21st to end	Night	27% 9% 12% 25% 21% 5%	1519
August	1st to 10th	Night	27% 10% 22% 24% 14% 3	1601
	11th to 20th	Night	24% 7% 13% 32% 20% 4	1600
	21st to end	Night	21% 6% 12% 27% 26% 8%	1895
September	1st to 10th	Night	26% 5% 11% 25% 25% 7%	1844
	11th to 20th	Night	22% 4 14% 32% 25% 4	1980
	21st to end	Night	26% 5% 8% 31% 28% 3	1980
October	1st to 10th	Night	35% 5% 10% 25% 23% 2	1980
	11th to 20th	Night	27% 3 11% 28% 24% 6%	2168
	21st to end	Night	34% 4 12% 23% 22% 6%	2574
November	1st to 10th	Night	29% 5% 13% 25% 22% 6%	2405
	11th to 20th	Night	31% 4 11% 26% 21% 6%	2470
	21st to end	Night	32% 4 12% 28% 20% 3	2470
December	1st to 10th	Night	34% 5% 15% 27% 16% 3	2536
	11th to 20th	Night	32% 4 13% 36% 14% 1	3272
	21st to end	Night	50% 4 9% 25% 10% 1	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	10% 15% 33% 26% 14% 3	270
	11th to 20th	Day	11% 18% 36% 24% 11% 1	255
	21st to end	Day	18% 12% 42% 20% 6% 2	264
February	1st to 10th	Day	10% 14% 46% 26% 3	240
	11th to 20th	Day	14% 14% 43% 21% 8% 1	240
	21st to end	Day	16% 15% 45% 21% 3	198
March	1st to 10th	Day	14% 11% 35% 28% 9% 3	240
	11th to 20th	Day	14% 9% 36% 29% 10% 2	240
	21st to end	Day	21% 14% 33% 20% 11% 2	272
April	1st to 10th	Day	18% 17% 41% 21% 3	420
	11th to 20th	Day	25% 16% 33% 23% 4	497
	21st to end	Day	19% 14% 31% 27% 7% 2	600
May	1st to 10th	Day	16% 11% 32% 30% 9% 1	603
	11th to 20th	Day	21% 11% 28% 26% 12% 2	625
	21st to end	Day	17% 8% 31% 31% 11% 2	679
June	1st to 10th	Day	8% 7% 29% 32% 17% 7%	630
	11th to 20th	Day	10% 7% 35% 31% 15% 2	630
	21st to end	Day	6% 7% 30% 38% 18% 3	630
July	1st to 10th	Day	6% 3 27% 38% 21% 5%	621
	11th to 20th	Day	7% 4 29% 41% 18% 2	618
	21st to end	Day	6% 3 26% 46% 18% 2	684
August	1st to 10th	Day	7% 3 22% 43% 21% 4	626
	11th to 20th	Day	9% 4 26% 39% 20% 3	615
	21st to end	Day	5% 3 29% 38% 22% 3	577
September	1st to 10th	Day	7% 4 31% 38% 16% 4	406
	11th to 20th	Day	7% 4 30% 30% 25% 4	270
	21st to end	Day	17% 10% 30% 28% 14% 1	270
October	1st to 10th	Day	19% 7% 23% 30% 16% 4	270
	11th to 20th	Day	13% 16% 37% 24% 7% 3	270
	21st to end	Day	15% 16% 31% 27% 9% 2	297
November	1st to 10th	Day	15% 8% 37% 26% 9% 4	270
	11th to 20th	Day	13% 11% 44% 22% 9%	270
	21st to end	Day	14% 14% 37% 23% 11% 1	270
December	1st to 10th	Day	10% 15% 44% 20% 9% 2	270
	11th to 20th	Day	11% 13% 42% 23% 9% 1	270
	21st to end	Day	18% 17% 39% 19% 7% 1	297
January	1st to 10th	Night	10% 14% 43% 26% 6%	950
	11th to 20th	Night	9% 17% 41% 27% 5%	930
	21st to end	Night	11% 13% 44% 26% 6%	990
February	1st to 10th	Night	15% 12% 42% 26% 5%	895
	11th to 20th	Night	10% 13% 47% 25% 6%	704
	21st to end	Night	12% 10% 43% 29% 5% 1	592
March	1st to 10th	Night	11% 12% 39% 34% 4	720
	11th to 20th	Night	15% 9% 40% 28% 6% 1	563
	21st to end	Night	18% 10% 38% 26% 8%	594
April	1st to 10th	Night	16% 12% 44% 26% 2	540
	11th to 20th	Night	18% 12% 41% 26% 4	533
	21st to end	Night	18% 10% 34% 30% 8% 1	540
May	1st to 10th	Night	15% 9% 36% 32% 9%	540
	11th to 20th	Night	20% 9% 31% 30% 9% 1	531
	21st to end	Night	16% 9% 35% 34% 6%	584
June	1st to 10th	Night	10% 5% 29% 39% 14% 2	540
	11th to 20th	Night	11% 5% 37% 39% 8%	540
	21st to end	Night	5% 4 32% 48% 11%	540
July	1st to 10th	Night	6% 3 31% 44% 16%	525
	11th to 20th	Night	5% 3 31% 49% 12%	522
	21st to end	Night	5% 4 29% 51% 11%	591
August	1st to 10th	Night	6% 2 26% 50% 16% 1	537
	11th to 20th	Night	8% 3 29% 46% 15%	534
	21st to end	Night	7% 4 31% 42% 15% 1	594
September	1st to 10th	Night	10% 5% 31% 43% 11%	540
	11th to 20th	Night	8% 4 32% 43% 13% 1	540
	21st to end	Night	12% 9% 36% 33% 10% 1	540
October	1st to 10th	Night	19% 9% 31% 31% 10%	540
	11th to 20th	Night	14% 10% 36% 31% 8% 1	728
	21st to end	Night	14% 13% 35% 29% 9%	990
November	1st to 10th	Night	10% 9% 42% 31% 7% 1	925
	11th to 20th	Night	10% 13% 40% 29% 7%	950
	21st to end	Night	10% 10% 43% 30% 7%	950
December	1st to 10th	Night	10% 14% 45% 25% 6%	950
	11th to 20th	Night	11% 10% 42% 31% 6%	950
	21st to end	Night	17% 13% 36% 27% 6%	1045

Page generated at 2024-01-13 08:37:52. Version ac07

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