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 2024-01-13.

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	12% 6% 3 5% 5% 3 5% 5% 5% 7% 44%	74735
	Night	12% 5% 2 5% 4 3 4 4 5% 7% 48%	75004
Transparency	Day	39% 4 10% 24% 18% 4	74449
	Night	36% 4 10% 24% 21% 5%	74811
Seeing	Day	14% 7% 21% 25% 22% 11%	14176
	Night	15% 7% 24% 32% 19% 3	24067

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	18% 9% 3 5% 4 2 3 3 3 5% 44%	1574
	11th to 20th	Day	21% 8% 3 5% 5% 3 4 4 5% 4 38%	1638
	21st to end	Day	15% 7% 2 5% 5% 2 3 3 4 5% 48%	1782
February	1st to 10th	Day	19% 8% 4 6% 5% 2 3 3 4 5% 40%	1753
	11th to 20th	Day	20% 8% 3 5% 4 3 4 4 4 6% 38%	1748
	21st to end	Day	24% 9% 3 5% 5% 3 3 3 4 5% 35%	1480
March	1st to 10th	Day	16% 7% 3 7% 5% 3 4 4 4 5% 42%	1804
	11th to 20th	Day	19% 8% 4 7% 6% 3 4 4 4 4 35%	1980
	21st to end	Day	17% 7% 4 6% 6% 3 4 4 4 8% 37%	2312
April	1st to 10th	Day	12% 5% 3 5% 4 3 5% 5% 4 7% 46%	2160
	11th to 20th	Day	16% 6% 2 5% 4 2 4 3 5% 7% 46%	2134
	21st to end	Day	14% 6% 3 5% 6% 4 4 4 6% 6% 43%	2160
May	1st to 10th	Day	14% 6% 3 6% 5% 3 5% 5% 4 7% 42%	2160
	11th to 20th	Day	11% 5% 2 5% 5% 2 4 5% 6% 9% 44%	2258
	21st to end	Day	8% 5% 3 5% 6% 4 6% 6% 8% 11% 38%	2647
June	1st to 10th	Day	9% 5% 2 5% 6% 3 5% 5% 6% 9% 45%	2520
	11th to 20th	Day	4 4 2 4 5% 3 6% 5% 7% 10% 50%	2520
	21st to end	Day	4 3 2 4 5% 4 6% 6% 7% 10% 49%	2520
July	1st to 10th	Day	6% 5% 3 6% 7% 4 7% 8% 8% 11% 36%	2520
	11th to 20th	Day	8% 4 2 5% 6% 4 6% 7% 8% 11% 40%	2438
	21st to end	Day	7% 4 2 5% 6% 4 6% 6% 8% 10% 42%	2546
August	1st to 10th	Day	6% 4 2 5% 6% 4 6% 6% 8% 11% 41%	2162
	11th to 20th	Day	8% 5% 2 5% 6% 4 6% 5% 7% 10% 42%	2125
	21st to end	Day	9% 5% 2 5% 5% 4 5% 6% 6% 10% 43%	2376
September	1st to 10th	Day	9% 3 2 5% 6% 4 5% 6% 6% 9% 44%	2160
	11th to 20th	Day	10% 5% 2 5% 5% 3 5% 4 6% 8% 46%	2102
	21st to end	Day	10% 5% 2 4 4 1 3 3 4 7% 56%	1980
October	1st to 10th	Day	7% 3 2 4 4 3 3 5% 5% 5% 59%	1876
	11th to 20th	Day	12% 5% 2 3 3 2 4 4 5% 6% 55%	1800
	21st to end	Day	19% 6% 1 3 3 2 3 4 3 4 52%	1980
November	1st to 10th	Day	12% 6% 2 3 3 2 2 3 3 5% 60%	1708
	11th to 20th	Day	13% 4 2 4 5% 2 3 4 5% 5% 53%	1710
	21st to end	Day	18% 6% 3 5% 5% 3 4 4 4 6% 44%	1710
December	1st to 10th	Day	20% 10% 3 5% 4 3 4 4 4 5% 40%	1691
	11th to 20th	Day	15% 7% 3 5% 6% 3 4 4 3 6% 44%	1918
	21st to end	Day	14% 11% 3 7% 6% 3 5% 5% 5% 6% 35%	2783
January	1st to 10th	Night	19% 7% 3 5% 4 2 3 3 4 5% 46%	2587
	11th to 20th	Night	19% 8% 3 6% 5% 3 3 3 4 5% 40%	2367
	21st to end	Night	17% 7% 2 5% 4 2 3 4 4 6% 48%	2574
February	1st to 10th	Night	19% 9% 3 6% 4 2 4 3 3 5% 41%	2205
	11th to 20th	Night	19% 7% 4 6% 5% 3 3 3 3 5% 42%	2098
	21st to end	Night	21% 7% 3 5% 4 3 5% 3 4 5% 40%	1776
March	1st to 10th	Night	16% 6% 2 4 5% 3 3 3 5% 5% 47%	2160
	11th to 20th	Night	19% 8% 2 6% 5% 3 3 4 4 6% 41%	1990
	21st to end	Night	16% 5% 2 5% 5% 3 5% 5% 6% 7% 41%	2044
April	1st to 10th	Night	10% 5% 3 4 4 3 5% 5% 5% 7% 49%	1800
	11th to 20th	Night	14% 5% 2 4 4 2 3 4 4 7% 50%	1775
	21st to end	Night	11% 6% 2 5% 5% 2 4 4 5% 7% 50%	1800
May	1st to 10th	Night	13% 5% 3 4 5% 2 3 3 5% 8% 50%	1800
	11th to 20th	Night	11% 4 2 5% 5% 4 5% 5% 6% 6% 46%	1633
	21st to end	Night	5% 5% 3 4 7% 3 5% 5% 8% 11% 42%	1624
June	1st to 10th	Night	7% 5% 2 5% 6% 3 5% 5% 6% 9% 47%	1440
	11th to 20th	Night	3 2 1 3 3 2 4 5% 6% 10% 61%	1440
	21st to end	Night	2 3 1 3 3 2 5% 7% 6% 12% 55%	1440
July	1st to 10th	Night	3 3 2 4 5% 4 6% 6% 7% 12% 48%	1440
	11th to 20th	Night	6% 4 1 3 4 3 5% 5% 7% 10% 51%	1518
	21st to end	Night	4 3 1 3 4 2 4 5% 7% 11% 55%	1772
August	1st to 10th	Night	3 3 1 3 4 3 5% 6% 7% 11% 54%	1776
	11th to 20th	Night	5% 3 2 4 5% 3 5% 6% 6% 12% 48%	1776
	21st to end	Night	6% 4 2 4 5% 3 4 6% 7% 10% 49%	1980
September	1st to 10th	Night	7% 4 3 5% 4 3 3 5% 6% 8% 53%	1800
	11th to 20th	Night	9% 5% 2 4 4 2 4 4 5% 7% 52%	1840
	21st to end	Night	9% 4 2 4 4 3 4 3 4 5% 59%	1980
October	1st to 10th	Night	7% 4 1 4 3 2 3 3 4 7% 61%	2079
	11th to 20th	Night	11% 4 2 4 3 2 3 4 3 6% 57%	2160
	21st to end	Night	17% 6% 2 4 3 2 3 3 4 4 52%	2376
November	1st to 10th	Night	11% 3 2 3 3 3 4 3 4 6% 58%	2367
	11th to 20th	Night	11% 5% 2 4 4 3 3 4 5% 7% 53%	2470
	21st to end	Night	15% 5% 2 4 5% 3 4 4 4 7% 49%	2470
December	1st to 10th	Night	17% 8% 3 5% 4 3 3 3 3 6% 45%	2484
	11th to 20th	Night	16% 6% 2 4 4 3 3 4 4 6% 47%	3279
	21st to end	Night	15% 8% 3 6% 6% 4 5% 5% 5% 7% 36%	4884

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	45% 2 7% 24% 17% 5%	1575
	11th to 20th	Day	51% 3 8% 21% 16% 2	1638
	21st to end	Day	41% 2 9% 25% 21% 3	1782
February	1st to 10th	Day	49% 2 7% 24% 16% 2	1753
	11th to 20th	Day	50% 2 7% 19% 17% 4	1758
	21st to end	Day	52% 2 7% 16% 17% 6%	1480
March	1st to 10th	Day	46% 2 8% 18% 18% 8%	1804
	11th to 20th	Day	54% 3 6% 18% 16% 2	1980
	21st to end	Day	48% 3 10% 24% 14% 1	2312
April	1st to 10th	Day	39% 4 9% 26% 20% 3	2160
	11th to 20th	Day	40% 3 7% 24% 20% 5%	2134
	21st to end	Day	43% 3 9% 25% 19% 1	2160
May	1st to 10th	Day	42% 4 11% 22% 18% 2	2160
	11th to 20th	Day	38% 5% 16% 23% 16% 2	2262
	21st to end	Day	39% 7% 16% 28% 10% 2	2647
June	1st to 10th	Day	36% 5% 12% 25% 19% 1	2520
	11th to 20th	Day	28% 6% 13% 31% 19% 4	2520
	21st to end	Day	29% 7% 13% 28% 19% 5%	2520
July	1st to 10th	Day	38% 7% 17% 22% 14% 3	2451
	11th to 20th	Day	35% 7% 18% 24% 11% 5%	2363
	21st to end	Day	36% 7% 16% 29% 11% 1	2405
August	1st to 10th	Day	34% 6% 19% 27% 13% 1	2149
	11th to 20th	Day	35% 6% 14% 26% 16% 3	2125
	21st to end	Day	36% 6% 12% 25% 16% 4	2376
September	1st to 10th	Day	36% 6% 10% 25% 18% 5%	2160
	11th to 20th	Day	36% 5% 10% 20% 24% 6%	2102
	21st to end	Day	30% 3 8% 24% 28% 8%	1980
October	1st to 10th	Day	28% 4 9% 25% 24% 9%	1876
	11th to 20th	Day	31% 3 7% 22% 29% 8%	1800
	21st to end	Day	38% 3 4 23% 24% 8%	1980
November	1st to 10th	Day	30% 2 6% 27% 26% 9%	1708
	11th to 20th	Day	34% 3 7% 23% 26% 7%	1710
	21st to end	Day	43% 3 7% 20% 23% 5%	1710
December	1st to 10th	Day	49% 2 7% 20% 18% 4	1691
	11th to 20th	Day	45% 2 6% 21% 23% 4	1915
	21st to end	Day	50% 3 8% 23% 14% 2	2783
January	1st to 10th	Night	43% 1 7% 22% 22% 4	2587
	11th to 20th	Night	49% 3 8% 21% 17% 3	2367
	21st to end	Night	39% 2 7% 25% 23% 4	2574
February	1st to 10th	Night	48% 2 9% 18% 20% 3	2205
	11th to 20th	Night	47% 2 6% 22% 17% 5%	2099
	21st to end	Night	48% 2 7% 17% 19% 7%	1776
March	1st to 10th	Night	41% 3 8% 17% 22% 10%	2160
	11th to 20th	Night	46% 4 9% 20% 17% 4	1990
	21st to end	Night	42% 4 10% 24% 17% 3	2044
April	1st to 10th	Night	35% 4 11% 25% 21% 5%	1800
	11th to 20th	Night	35% 3 7% 24% 24% 7%	1775
	21st to end	Night	36% 3 9% 27% 22% 3	1800
May	1st to 10th	Night	35% 3 13% 26% 20% 5%	1800
	11th to 20th	Night	37% 5% 13% 24% 18% 2	1634
	21st to end	Night	33% 8% 13% 28% 15% 2	1625
June	1st to 10th	Night	33% 6% 11% 23% 24% 2	1440
	11th to 20th	Night	18% 4 16% 32% 24% 5%	1440
	21st to end	Night	20% 6% 17% 29% 22% 5%	1440
July	1st to 10th	Night	27% 5% 20% 29% 15% 3	1400
	11th to 20th	Night	27% 6% 20% 28% 13% 6%	1470
	21st to end	Night	23% 6% 20% 34% 17% 1	1673
August	1st to 10th	Night	24% 6% 17% 36% 17% 1	1765
	11th to 20th	Night	30% 6% 17% 27% 17% 3	1776
	21st to end	Night	29% 6% 16% 26% 18% 6%	1980
September	1st to 10th	Night	30% 4 10% 25% 23% 7%	1800
	11th to 20th	Night	31% 5% 9% 22% 27% 6%	1840
	21st to end	Night	30% 2 8% 25% 26% 9%	1980
October	1st to 10th	Night	25% 3 8% 28% 25% 12%	2079
	11th to 20th	Night	30% 3 6% 21% 30% 10%	2160
	21st to end	Night	38% 3 5% 20% 26% 9%	2376
November	1st to 10th	Night	29% 2 6% 24% 29% 8%	2367
	11th to 20th	Night	32% 3 6% 22% 26% 10%	2470
	21st to end	Night	37% 3 7% 21% 26% 6%	2470
December	1st to 10th	Night	44% 3 8% 23% 18% 5%	2484
	11th to 20th	Night	40% 3 6% 23% 24% 5%	3281
	21st to end	Night	48% 3 7% 21% 16% 4	4884

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% 14% 38% 16% 8% 1	270
	11th to 20th	Day	26% 14% 34% 21% 4 1	246
	21st to end	Day	20% 16% 42% 17% 4 1	264
February	1st to 10th	Day	25% 13% 40% 15% 7% 1	240
	11th to 20th	Day	34% 17% 36% 10% 4	240
	21st to end	Day	38% 16% 30% 11% 6%	198
March	1st to 10th	Day	24% 14% 34% 20% 6% 2	240
	11th to 20th	Day	23% 19% 33% 23% 1	240
	21st to end	Day	22% 16% 32% 21% 9% 1	398
April	1st to 10th	Day	15% 16% 32% 25% 10% 1	420
	11th to 20th	Day	20% 11% 32% 24% 9% 4	412
	21st to end	Day	19% 11% 30% 24% 13% 4	420
May	1st to 10th	Day	17% 10% 26% 29% 16% 2	423
	11th to 20th	Day	14% 5% 22% 23% 24% 11%	447
	21st to end	Day	10% 2 19% 30% 26% 13%	601
June	1st to 10th	Day	10% 4 12% 26% 28% 20%	630
	11th to 20th	Day	4 1 14% 32% 33% 15%	630
	21st to end	Day	5% 1 15% 32% 31% 16%	630
July	1st to 10th	Day	7% 2 8% 26% 31% 26%	621
	11th to 20th	Day	8% 2 8% 22% 38% 22%	618
	21st to end	Day	6% 2 8% 25% 37% 21%	684
August	1st to 10th	Day	8% 3 6% 27% 36% 20%	460
	11th to 20th	Day	10% 2 6% 29% 38% 14%	439
	21st to end	Day	11% 2 4 18% 38% 27%	495
September	1st to 10th	Day	8% 2 7% 26% 36% 20%	450
	11th to 20th	Day	9% 2 11% 22% 33% 22%	450
	21st to end	Day	14% 3 13% 30% 27% 13%	450
October	1st to 10th	Day	7% 4 17% 33% 30% 10%	346
	11th to 20th	Day	11% 7% 34% 29% 14% 4	270
	21st to end	Day	24% 8% 28% 28% 10% 3	297
November	1st to 10th	Day	15% 6% 25% 35% 15% 4	270
	11th to 20th	Day	8% 12% 38% 28% 13% 1	270
	21st to end	Day	23% 11% 29% 20% 14% 3	270
December	1st to 10th	Day	23% 15% 33% 20% 8% 2	270
	11th to 20th	Day	22% 12% 35% 20% 9% 1	270
	21st to end	Day	22% 16% 38% 18% 5% 1	297
January	1st to 10th	Night	24% 11% 34% 25% 5%	950
	11th to 20th	Night	25% 12% 33% 26% 4	911
	21st to end	Night	21% 10% 39% 28% 2	990
February	1st to 10th	Night	24% 11% 35% 26% 4	765
	11th to 20th	Night	23% 14% 37% 24% 3	703
	21st to end	Night	24% 15% 35% 24% 3	592
March	1st to 10th	Night	20% 12% 33% 30% 6%	720
	11th to 20th	Night	25% 8% 33% 28% 5% 1	550
	21st to end	Night	19% 9% 32% 29% 12%	594
April	1st to 10th	Night	14% 10% 34% 32% 9% 1	540
	11th to 20th	Night	16% 8% 30% 32% 12% 1	533
	21st to end	Night	15% 5% 34% 32% 12% 2	540
May	1st to 10th	Night	15% 6% 22% 41% 14% 2	540
	11th to 20th	Night	13% 5% 21% 39% 19% 4	531
	21st to end	Night	8% 2 14% 42% 28% 6%	584
June	1st to 10th	Night	9% 2 11% 38% 34% 7%	540
	11th to 20th	Night	2 1 10% 39% 46% 3	540
	21st to end	Night	4 11% 41% 39% 6%	540
July	1st to 10th	Night	2 2 9% 33% 44% 11%	525
	11th to 20th	Night	6% 2 7% 28% 43% 13%	522
	21st to end	Night	5% 1 6% 29% 46% 12%	591
August	1st to 10th	Night	5% 5% 30% 52% 8%	537
	11th to 20th	Night	6% 1 5% 35% 45% 7%	534
	21st to end	Night	8% 2 5% 27% 48% 10%	594
September	1st to 10th	Night	7% 2 6% 34% 45% 6%	540
	11th to 20th	Night	11% 3 9% 31% 37% 8%	580
	21st to end	Night	10% 3 13% 35% 35% 4	720
October	1st to 10th	Night	8% 3 17% 35% 32% 4	720
	11th to 20th	Night	13% 5% 24% 38% 17% 2	720
	21st to end	Night	21% 4 25% 34% 15% 1	792
November	1st to 10th	Night	12% 5% 24% 38% 18% 2	740
	11th to 20th	Night	13% 7% 33% 35% 11% 1	760
	21st to end	Night	18% 8% 32% 30% 11% 1	760
December	1st to 10th	Night	22% 11% 29% 32% 7%	774
	11th to 20th	Night	24% 9% 27% 32% 8%	950
	21st to end	Night	25% 12% 31% 28% 5%	1045

Page generated at 2024-01-10 00:25:04. Version ac07

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