Darkfire Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Darkfire Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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	12% 6% 2 6% 4 4 4 4 6% 7% 43%	126464
	Night	13% 6% 2 6% 4 4 4 3 5% 7% 48%	124432
Transparency	Day	39% 4 10% 24% 19% 4	130113
	Night	37% 3 9% 24% 21% 6%	128860
Seeing	Day	14% 8% 22% 25% 21% 10%	16773
	Night	16% 7% 24% 32% 19% 3	26521

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	16% 11% 4 9% 3 3 2 2 3 5% 43%	3769
	11th to 20th	Day	16% 7% 2 8% 3 3 3 2 4 5% 49%	4080
	21st to end	Day	18% 9% 2 6% 4 3 3 2 3 5% 45%	4488
February	1st to 10th	Day	21% 9% 4 7% 5% 3 3 2 4 5% 38%	1948
	11th to 20th	Day	20% 9% 3 6% 4 3 4 3 4 6% 38%	1948
	21st to end	Day	22% 9% 3 6% 5% 3 3 2 5% 5% 37%	1650
March	1st to 10th	Day	17% 13% 4 9% 4 4 4 3 4 4 35%	4498
	11th to 20th	Day	13% 6% 3 6% 4 4 4 3 4 5% 48%	4980
	21st to end	Day	12% 7% 4 8% 5% 5% 4 3 4 6% 42%	5819
April	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 5% 7% 45%	2400
	11th to 20th	Day	15% 6% 2 6% 4 3 4 3 5% 6% 46%	2374
	21st to end	Day	14% 6% 2 6% 5% 5% 4 3 6% 7% 42%	2400
May	1st to 10th	Day	16% 7% 3 8% 5% 5% 5% 5% 6% 8% 33%	5405
	11th to 20th	Day	14% 7% 3 8% 5% 5% 5% 4 7% 10% 33%	5762
	21st to end	Day	17% 7% 2 7% 5% 5% 5% 4 7% 8% 34%	6745
June	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 8% 44%	2800
	11th to 20th	Day	5% 5% 2 5% 5% 5% 5% 5% 7% 11% 47%	2800
	21st to end	Day	4 3 2 5% 5% 5% 6% 5% 8% 10% 48%	2800
July	1st to 10th	Day	6% 5% 2 7% 6% 6% 6% 5% 8% 10% 40%	6360
	11th to 20th	Day	7% 4 2 5% 5% 6% 6% 6% 9% 12% 39%	6138
	21st to end	Day	11% 6% 3 7% 5% 5% 6% 5% 8% 10% 36%	6422
August	1st to 10th	Day	4 3 1 4 3 4 5% 3 6% 9% 58%	3920
	11th to 20th	Day	6% 3 2 5% 4 5% 5% 5% 8% 10% 47%	3849
	21st to end	Day	6% 4 2 5% 4 5% 5% 4 6% 8% 53%	4312
September	1st to 10th	Day	9% 4 2 6% 5% 5% 5% 4 7% 8% 45%	2400
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 3 7% 8% 46%	2335
	21st to end	Day	11% 5% 2 5% 4 3 3 3 4 7% 53%	2200
October	1st to 10th	Day	7% 3 1 5% 3 3 4 3 5% 5% 61%	2084
	11th to 20th	Day	11% 5% 2 4 2 2 4 3 5% 6% 58%	2000
	21st to end	Day	19% 6% 1 4 3 2 4 3 3 4 53%	2200
November	1st to 10th	Day	12% 6% 2 4 3 3 2 2 4 5% 57%	1892
	11th to 20th	Day	13% 5% 1 5% 3 3 3 3 5% 5% 53%	1890
	21st to end	Day	17% 7% 3 6% 4 3 3 2 4 5% 44%	1890
December	1st to 10th	Day	16% 10% 3 6% 3 3 3 2 3 4 47%	2916
	11th to 20th	Day	20% 8% 3 6% 5% 4 3 2 3 5% 42%	3008
	21st to end	Day	15% 10% 3 8% 5% 5% 5% 4 5% 6% 35%	3982
January	1st to 10th	Night	17% 8% 4 8% 4 3 3 2 4 4 43%	6192
	11th to 20th	Night	16% 7% 2 5% 3 3 3 2 4 4 50%	5900
	21st to end	Night	21% 8% 3 6% 3 2 3 2 3 5% 45%	6490
February	1st to 10th	Night	21% 9% 3 6% 4 3 3 3 3 5% 41%	2450
	11th to 20th	Night	20% 8% 3 7% 4 3 3 2 3 5% 41%	2338
	21st to end	Night	19% 7% 3 6% 4 4 4 2 4 5% 41%	1980
March	1st to 10th	Night	17% 9% 3 6% 4 4 4 3 4 5% 41%	5373
	11th to 20th	Night	12% 6% 2 5% 4 4 3 3 5% 6% 51%	4990
	21st to end	Night	13% 6% 2 7% 4 4 4 3 5% 7% 45%	5110
April	1st to 10th	Night	11% 7% 2 5% 4 4 4 4 5% 6% 49%	2000
	11th to 20th	Night	14% 5% 2 4 3 3 4 3 4 6% 51%	1975
	21st to end	Night	11% 7% 2 6% 4 4 3 3 5% 7% 49%	2000
May	1st to 10th	Night	19% 9% 3 7% 4 4 3 3 5% 8% 37%	4490
	11th to 20th	Night	16% 9% 3 8% 4 4 4 3 5% 5% 37%	4129
	21st to end	Night	14% 7% 3 7% 6% 4 5% 4 7% 7% 37%	4119
June	1st to 10th	Night	7% 5% 2 6% 5% 5% 4 5% 7% 9% 46%	1600
	11th to 20th	Night	4 3 1 3 3 3 4 4 7% 9% 59%	1600
	21st to end	Night	2 3 1 3 4 4 5% 6% 6% 12% 54%	1600
July	1st to 10th	Night	6% 4 2 6% 4 4 5% 4 7% 11% 48%	3618
	11th to 20th	Night	5% 4 1 4 4 4 5% 4 7% 12% 51%	3835
	21st to end	Night	9% 6% 2 6% 4 4 5% 4 7% 12% 42%	4449
August	1st to 10th	Night	2 2 1 3 2 3 3 3 5% 8% 69%	3229
	11th to 20th	Night	4 3 2 4 4 4 4 4 6% 12% 55%	3200
	21st to end	Night	4 3 1 4 4 3 4 4 6% 8% 58%	3586
September	1st to 10th	Night	7% 4 2 6% 4 3 4 4 6% 8% 52%	2000
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 5% 7% 52%	2045
	21st to end	Night	10% 4 2 5% 3 4 3 3 4 5% 57%	2200
October	1st to 10th	Night	7% 4 1 4 2 3 3 2 4 6% 63%	2311
	11th to 20th	Night	10% 4 2 4 2 2 3 3 3 6% 60%	2400
	21st to end	Night	17% 6% 2 4 3 3 3 2 4 4 53%	2640
November	1st to 10th	Night	12% 4 2 4 3 4 3 3 4 6% 56%	2623
	11th to 20th	Night	10% 5% 2 4 3 3 3 3 5% 7% 54%	2730
	21st to end	Night	15% 6% 2 5% 4 3 3 3 4 6% 49%	2730
December	1st to 10th	Night	17% 7% 2 5% 3 3 3 2 3 6% 50%	4305
	11th to 20th	Night	19% 7% 3 5% 4 3 3 3 4 5% 44%	5199
	21st to end	Night	18% 7% 3 7% 4 5% 5% 4 5% 6% 37%	6996

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	47% 1 8% 24% 17% 2	3770
	11th to 20th	Day	41% 2 5% 29% 23% 1	4080
	21st to end	Day	44% 2 5% 19% 25% 6%	4488
February	1st to 10th	Day	51% 2 7% 23% 15% 2	1948
	11th to 20th	Day	50% 2 8% 19% 17% 5%	1958
	21st to end	Day	50% 2 8% 16% 18% 6%	1650
March	1st to 10th	Day	54% 2 5% 17% 13% 9%	4498
	11th to 20th	Day	40% 2 6% 21% 22% 8%	4980
	21st to end	Day	44% 2 8% 24% 20% 1	5821
April	1st to 10th	Day	39% 4 9% 25% 20% 3	2400
	11th to 20th	Day	40% 3 7% 24% 20% 6%	2374
	21st to end	Day	43% 3 9% 26% 18% 1	2400
May	1st to 10th	Day	49% 5% 11% 23% 11% 1	5440
	11th to 20th	Day	47% 5% 17% 20% 10% 1	5766
	21st to end	Day	47% 4 11% 25% 12% 2	6759
June	1st to 10th	Day	36% 6% 13% 25% 19% 2	2800
	11th to 20th	Day	30% 6% 13% 29% 19% 3	2800
	21st to end	Day	29% 7% 14% 28% 19% 4	2800
July	1st to 10th	Day	37% 7% 13% 26% 16% 1	6291
	11th to 20th	Day	33% 8% 18% 32% 7% 2	6063
	21st to end	Day	41% 8% 16% 29% 6%	6240
August	1st to 10th	Day	22% 5% 17% 31% 23% 3	3907
	11th to 20th	Day	30% 6% 17% 27% 17% 2	3885
	21st to end	Day	29% 6% 9% 28% 25% 3	4311
September	1st to 10th	Day	36% 6% 9% 26% 18% 6%	2400
	11th to 20th	Day	36% 5% 10% 21% 23% 5%	2335
	21st to end	Day	32% 3 8% 22% 27% 8%	2200
October	1st to 10th	Day	18% 3 5% 15% 34% 25%	3396
	11th to 20th	Day	19% 2 4 22% 38% 16%	3240
	21st to end	Day	28% 2 3 27% 31% 9%	3538
November	1st to 10th	Day	32% 2 6% 26% 26% 8%	1892
	11th to 20th	Day	33% 3 8% 24% 26% 7%	1890
	21st to end	Day	43% 3 6% 20% 24% 4	1890
December	1st to 10th	Day	43% 2 5% 25% 22% 2	2916
	11th to 20th	Day	48% 2 5% 23% 18% 4	3005
	21st to end	Day	50% 3 7% 26% 13% 1	3982
January	1st to 10th	Night	47% 2 8% 21% 18% 3	6192
	11th to 20th	Night	40% 1 6% 22% 26% 5%	5900
	21st to end	Night	45% 1 5% 22% 22% 4	6490
February	1st to 10th	Night	49% 2 8% 18% 20% 3	2450
	11th to 20th	Night	48% 2 6% 21% 17% 5%	2339
	21st to end	Night	46% 2 6% 17% 21% 7%	1980
March	1st to 10th	Night	48% 2 6% 16% 20% 9%	5373
	11th to 20th	Night	36% 2 6% 22% 18% 15%	4990
	21st to end	Night	40% 3 8% 24% 22% 3	5110
April	1st to 10th	Night	36% 4 10% 24% 21% 5%	2000
	11th to 20th	Night	35% 3 7% 24% 24% 7%	1975
	21st to end	Night	37% 3 10% 26% 21% 3	2000
May	1st to 10th	Night	48% 3 13% 22% 12% 2	4520
	11th to 20th	Night	50% 3 12% 24% 10% 1	4130
	21st to end	Night	45% 5% 10% 24% 14% 3	4127
June	1st to 10th	Night	33% 6% 12% 24% 24% 2	1600
	11th to 20th	Night	21% 5% 15% 30% 24% 5%	1600
	21st to end	Night	21% 6% 18% 29% 22% 5%	1600
July	1st to 10th	Night	30% 6% 18% 27% 18% 2	3580
	11th to 20th	Night	25% 6% 21% 35% 10% 2	3790
	21st to end	Night	35% 6% 19% 30% 9% 1	4320
August	1st to 10th	Night	15% 4 11% 42% 26% 2	3218
	11th to 20th	Night	24% 5% 20% 31% 19% 2	3230
	21st to end	Night	23% 5% 13% 27% 28% 4	3586
September	1st to 10th	Night	31% 4 10% 24% 23% 8%	2000
	11th to 20th	Night	32% 4 9% 23% 26% 6%	2045
	21st to end	Night	32% 2 8% 23% 26% 9%	2200
October	1st to 10th	Night	16% 2 5% 18% 32% 27%	3779
	11th to 20th	Night	18% 2 3 17% 36% 24%	3899
	21st to end	Night	27% 2 4 27% 25% 15%	4252
November	1st to 10th	Night	31% 2 6% 24% 28% 8%	2623
	11th to 20th	Night	31% 3 6% 24% 26% 10%	2730
	21st to end	Night	38% 3 7% 22% 25% 6%	2730
December	1st to 10th	Night	40% 2 6% 28% 20% 3	4305
	11th to 20th	Night	44% 2 5% 23% 21% 4	5201
	21st to end	Night	49% 3 7% 24% 14% 3	6996

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	23% 15% 39% 15% 7% 1	300
	11th to 20th	Day	25% 16% 36% 18% 4 1	300
	21st to end	Day	22% 16% 41% 17% 3 1	330
February	1st to 10th	Day	26% 13% 39% 14% 7% 1	300
	11th to 20th	Day	33% 19% 34% 11% 3 1	300
	21st to end	Day	32% 18% 34% 10% 5%	249
March	1st to 10th	Day	25% 16% 34% 18% 6% 1	300
	11th to 20th	Day	22% 19% 35% 22% 1	300
	21st to end	Day	21% 17% 34% 20% 8% 1	480
April	1st to 10th	Day	19% 17% 31% 23% 9% 1	500
	11th to 20th	Day	20% 14% 33% 23% 8% 3	492
	21st to end	Day	18% 11% 32% 23% 12% 4	500
May	1st to 10th	Day	18% 12% 26% 28% 14% 2	503
	11th to 20th	Day	15% 6% 25% 23% 22% 9%	527
	21st to end	Day	12% 3 21% 30% 23% 11%	703
June	1st to 10th	Day	10% 5% 14% 27% 26% 18%	730
	11th to 20th	Day	6% 2 14% 31% 33% 14%	730
	21st to end	Day	5% 1 14% 31% 32% 16%	730
July	1st to 10th	Day	7% 2 9% 27% 31% 24%	721
	11th to 20th	Day	7% 2 8% 24% 38% 20%	718
	21st to end	Day	8% 2 8% 26% 36% 20%	794
August	1st to 10th	Day	7% 3 7% 29% 36% 19%	541
	11th to 20th	Day	9% 2 8% 28% 37% 15%	519
	21st to end	Day	10% 2 7% 21% 34% 25%	583
September	1st to 10th	Day	9% 3 9% 28% 34% 18%	530
	11th to 20th	Day	10% 2 11% 23% 33% 20%	530
	21st to end	Day	15% 5% 15% 29% 25% 12%	530
October	1st to 10th	Day	7% 3 17% 35% 29% 9%	414
	11th to 20th	Day	10% 7% 34% 28% 16% 5%	330
	21st to end	Day	23% 8% 30% 26% 10% 2	363
November	1st to 10th	Day	18% 7% 26% 32% 14% 3	330
	11th to 20th	Day	10% 13% 38% 27% 12% 1	330
	21st to end	Day	22% 13% 30% 19% 12% 3	330
December	1st to 10th	Day	23% 15% 33% 20% 8% 2	306
	11th to 20th	Day	25% 13% 34% 18% 8% 1	300
	21st to end	Day	22% 16% 37% 18% 5% 1	330
January	1st to 10th	Night	24% 12% 34% 26% 5%	1000
	11th to 20th	Night	24% 13% 34% 25% 3	1000
	21st to end	Night	22% 10% 40% 27% 2	1100
February	1st to 10th	Night	25% 10% 34% 26% 4	850
	11th to 20th	Night	25% 14% 36% 23% 3	783
	21st to end	Night	23% 15% 36% 24% 2	660
March	1st to 10th	Night	21% 13% 32% 29% 5%	800
	11th to 20th	Night	24% 9% 35% 27% 5% 1	610
	21st to end	Night	18% 10% 34% 28% 10%	660
April	1st to 10th	Night	16% 11% 35% 30% 9% 1	600
	11th to 20th	Night	16% 9% 31% 31% 11% 1	593
	21st to end	Night	15% 6% 33% 32% 12% 2	600
May	1st to 10th	Night	16% 7% 23% 40% 14% 2	600
	11th to 20th	Night	14% 6% 21% 38% 18% 4	591
	21st to end	Night	8% 3 17% 41% 25% 5%	650
June	1st to 10th	Night	9% 2 13% 38% 32% 6%	600
	11th to 20th	Night	4 1 10% 39% 44% 3	600
	21st to end	Night	3 1 10% 40% 40% 6%	600
July	1st to 10th	Night	3 2 9% 32% 44% 10%	585
	11th to 20th	Night	6% 2 7% 29% 43% 12%	582
	21st to end	Night	6% 1 6% 31% 45% 11%	657
August	1st to 10th	Night	5% 1 5% 31% 50% 8%	597
	11th to 20th	Night	5% 2 6% 35% 45% 8%	594
	21st to end	Night	7% 2 6% 29% 46% 10%	660
September	1st to 10th	Night	7% 3 8% 35% 42% 5%	600
	11th to 20th	Night	12% 3 8% 32% 37% 8%	645
	21st to end	Night	11% 4 13% 35% 34% 4	800
October	1st to 10th	Night	8% 4 17% 36% 32% 4	800
	11th to 20th	Night	12% 5% 23% 39% 19% 2	800
	21st to end	Night	21% 4 25% 34% 15% 1	880
November	1st to 10th	Night	13% 6% 25% 38% 17% 2	820
	11th to 20th	Night	13% 7% 34% 35% 11% 1	840
	21st to end	Night	19% 9% 31% 30% 11% 1	840
December	1st to 10th	Night	22% 11% 30% 31% 6%	824
	11th to 20th	Night	24% 9% 28% 32% 7%	1000
	21st to end	Night	25% 12% 30% 28% 5%	1100

Page generated at 2025-11-30 00:00:52. Version ac07

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