Firefly Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Firefly Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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	11% 7% 3 7% 5% 5% 6% 5% 6% 8% 37%	101156
	Night	11% 8% 3 8% 5% 5% 5% 4 6% 8% 38%	97884
Transparency	Day	40% 9% 13% 19% 15% 4	104911
	Night	38% 9% 14% 20% 15% 5%	102268
Seeing	Day	19% 14% 24% 21% 15% 7%	15068
	Night	17% 12% 21% 28% 19% 3	25114

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	12% 6% 2 6% 4 4 4 4 7% 9% 41%	2836
	11th to 20th	Day	11% 7% 2 6% 5% 5% 6% 5% 6% 6% 42%	2840
	21st to end	Day	16% 13% 5% 7% 3 3 3 3 5% 6% 36%	3124
February	1st to 10th	Day	13% 8% 3 7% 5% 4 5% 3 6% 7% 39%	1786
	11th to 20th	Day	14% 11% 4 8% 4 4 4 4 4 6% 37%	1848
	21st to end	Day	13% 7% 4 8% 5% 4 5% 4 5% 6% 38%	1570
March	1st to 10th	Day	18% 9% 3 7% 4 4 3 4 5% 6% 37%	3365
	11th to 20th	Day	11% 7% 3 6% 4 4 4 3 4 5% 49%	3480
	21st to end	Day	15% 9% 3 7% 5% 4 4 4 6% 6% 39%	3815
April	1st to 10th	Day	10% 6% 2 6% 5% 5% 6% 4 6% 9% 42%	2090
	11th to 20th	Day	13% 8% 3 6% 5% 3 4 3 6% 8% 41%	2271
	21st to end	Day	11% 7% 2 7% 4 4 4 4 6% 6% 44%	2470
May	1st to 10th	Day	10% 8% 3 10% 6% 5% 6% 5% 7% 8% 33%	4082
	11th to 20th	Day	14% 8% 3 9% 6% 5% 6% 5% 7% 8% 29%	4081
	21st to end	Day	7% 5% 3 7% 5% 6% 6% 5% 8% 11% 38%	4476
June	1st to 10th	Day	9% 7% 2 7% 7% 7% 7% 5% 8% 9% 31%	2470
	11th to 20th	Day	6% 6% 3 8% 7% 6% 6% 6% 8% 10% 33%	2470
	21st to end	Day	7% 7% 3 7% 6% 6% 7% 6% 8% 9% 34%	2470
July	1st to 10th	Day	5% 6% 3 8% 7% 7% 8% 6% 8% 10% 32%	4120
	11th to 20th	Day	8% 6% 3 8% 7% 6% 8% 6% 8% 10% 30%	4120
	21st to end	Day	11% 9% 4 11% 9% 9% 9% 6% 8% 7% 17%	4466
August	1st to 10th	Day	10% 8% 3 9% 7% 7% 7% 6% 9% 11% 23%	4104
	11th to 20th	Day	7% 5% 3 7% 6% 6% 8% 6% 9% 11% 32%	4044
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 5% 6% 9% 46%	4198
September	1st to 10th	Day	9% 6% 3 8% 6% 6% 7% 5% 6% 8% 36%	2090
	11th to 20th	Day	14% 7% 2 7% 6% 6% 6% 5% 6% 9% 32%	2090
	21st to end	Day	12% 7% 2 7% 5% 6% 5% 6% 6% 7% 37%	2090
October	1st to 10th	Day	10% 7% 3 6% 4 4 4 4 5% 6% 48%	2053
	11th to 20th	Day	8% 6% 2 7% 3 3 4 3 4 6% 53%	1900
	21st to end	Day	11% 6% 3 5% 4 3 3 3 5% 5% 53%	2090
November	1st to 10th	Day	8% 8% 2 5% 4 3 3 3 3 6% 54%	1840
	11th to 20th	Day	10% 6% 3 6% 4 3 4 3 6% 6% 50%	1710
	21st to end	Day	12% 8% 2 6% 3 3 4 3 5% 7% 46%	1710
December	1st to 10th	Day	14% 10% 3 8% 5% 6% 5% 4 6% 6% 35%	1710
	11th to 20th	Day	12% 7% 4 6% 4 4 4 5% 6% 8% 41%	2153
	21st to end	Day	13% 9% 3 7% 5% 6% 5% 4 5% 7% 36%	3124
January	1st to 10th	Night	13% 8% 3 8% 6% 6% 6% 4 7% 8% 32%	4109
	11th to 20th	Night	12% 8% 3 9% 6% 3 3 3 6% 8% 39%	4120
	21st to end	Night	15% 14% 4 8% 4 4 4 3 5% 6% 34%	4532
February	1st to 10th	Night	11% 8% 3 7% 4 4 5% 4 6% 7% 40%	2390
	11th to 20th	Night	16% 9% 3 6% 5% 5% 5% 4 5% 6% 37%	2218
	21st to end	Night	13% 8% 3 9% 5% 6% 5% 4 6% 6% 35%	1884
March	1st to 10th	Night	17% 14% 4 10% 5% 4 5% 4 5% 5% 27%	3486
	11th to 20th	Night	9% 6% 3 7% 5% 4 5% 4 6% 8% 45%	3480
	21st to end	Night	14% 7% 2 5% 5% 5% 4 4 5% 8% 40%	3817
April	1st to 10th	Night	11% 8% 3 5% 5% 4 4 4 6% 8% 43%	2090
	11th to 20th	Night	9% 8% 2 7% 4 4 4 4 6% 7% 45%	1869
	21st to end	Night	9% 7% 3 6% 4 3 4 3 5% 7% 47%	1710
May	1st to 10th	Night	10% 9% 3 9% 4 4 5% 4 7% 9% 35%	2813
	11th to 20th	Night	12% 9% 3 9% 5% 5% 5% 4 6% 8% 32%	2812
	21st to end	Night	6% 5% 2 7% 5% 5% 5% 5% 8% 12% 38%	3079
June	1st to 10th	Night	7% 7% 2 7% 5% 6% 7% 5% 8% 13% 34%	1710
	11th to 20th	Night	5% 7% 2 5% 6% 5% 4 4 9% 12% 40%	1710
	21st to end	Night	6% 6% 2 6% 5% 6% 5% 5% 8% 10% 42%	1710
July	1st to 10th	Night	5% 6% 3 9% 7% 7% 6% 6% 8% 11% 31%	2840
	11th to 20th	Night	6% 5% 2 7% 6% 6% 6% 6% 10% 11% 35%	2840
	21st to end	Night	10% 10% 4 13% 8% 8% 7% 6% 7% 8% 21%	3087
August	1st to 10th	Night	6% 7% 2 8% 6% 6% 7% 5% 9% 11% 31%	2825
	11th to 20th	Night	6% 7% 3 10% 7% 6% 6% 6% 7% 10% 30%	2785
	21st to end	Night	5% 5% 2 6% 4 4 5% 4 7% 10% 47%	3407
September	1st to 10th	Night	10% 5% 2 7% 6% 6% 5% 4 7% 9% 39%	2090
	11th to 20th	Night	12% 8% 3 9% 6% 4 5% 5% 6% 7% 35%	2090
	21st to end	Night	9% 7% 3 8% 5% 4 5% 3 6% 7% 44%	2090
October	1st to 10th	Night	13% 6% 2 6% 3 5% 3 4 5% 7% 47%	2125
	11th to 20th	Night	9% 7% 2 6% 4 4 3 4 6% 6% 48%	2280
	21st to end	Night	9% 7% 3 5% 3 2 4 3 5% 5% 52%	2508
November	1st to 10th	Night	11% 6% 2 6% 3 5% 4 4 6% 6% 48%	2394
	11th to 20th	Night	11% 7% 3 6% 4 5% 3 3 6% 7% 47%	2470
	21st to end	Night	12% 6% 2 6% 4 5% 4 4 5% 6% 44%	2470
December	1st to 10th	Night	15% 8% 4 8% 5% 5% 5% 4 5% 7% 33%	2470
	11th to 20th	Night	13% 10% 3 9% 4 4 4 3 5% 6% 38%	3042
	21st to end	Night	13% 11% 3 8% 5% 5% 5% 4 7% 8% 30%	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	33% 4 11% 25% 22% 5%	2837
	11th to 20th	Day	35% 7% 12% 15% 25% 6%	2840
	21st to end	Day	42% 7% 9% 18% 21% 3	3124
February	1st to 10th	Day	42% 5% 12% 20% 17% 4	1786
	11th to 20th	Day	45% 6% 11% 17% 17% 5%	1858
	21st to end	Day	45% 7% 10% 16% 17% 6%	1570
March	1st to 10th	Day	43% 7% 10% 18% 15% 7%	3365
	11th to 20th	Day	34% 6% 10% 20% 20% 10%	3480
	21st to end	Day	42% 7% 11% 22% 14% 4	3815
April	1st to 10th	Day	35% 9% 13% 21% 19% 4	2090
	11th to 20th	Day	40% 6% 9% 19% 20% 6%	2271
	21st to end	Day	38% 7% 13% 24% 15% 2	2470
May	1st to 10th	Day	45% 11% 14% 19% 11% 1	4120
	11th to 20th	Day	47% 13% 12% 18% 9% 1	4085
	21st to end	Day	35% 13% 16% 19% 16% 1	4489
June	1st to 10th	Day	45% 13% 17% 17% 7% 1	2470
	11th to 20th	Day	41% 12% 17% 18% 11% 2	2470
	21st to end	Day	42% 13% 15% 17% 11% 2	2470
July	1st to 10th	Day	43% 13% 18% 19% 7%	4055
	11th to 20th	Day	44% 12% 21% 17% 5% 1	4051
	21st to end	Day	61% 11% 14% 10% 4	4324
August	1st to 10th	Day	49% 10% 18% 19% 3	4091
	11th to 20th	Day	40% 9% 23% 16% 9% 3	4083
	21st to end	Day	34% 10% 13% 32% 10% 1	4198
September	1st to 10th	Day	42% 11% 12% 17% 15% 3	2090
	11th to 20th	Day	46% 10% 11% 17% 14% 2	2090
	21st to end	Day	43% 9% 13% 16% 14% 4	2090
October	1st to 10th	Day	28% 6% 7% 20% 26% 12%	3417
	11th to 20th	Day	22% 4 7% 21% 24% 22%	3140
	21st to end	Day	27% 3 9% 25% 21% 15%	3428
November	1st to 10th	Day	32% 4 10% 20% 26% 8%	1840
	11th to 20th	Day	34% 5% 8% 21% 25% 7%	1710
	21st to end	Day	36% 6% 8% 23% 22% 5%	1710
December	1st to 10th	Day	48% 7% 8% 18% 15% 5%	1710
	11th to 20th	Day	35% 6% 11% 20% 22% 6%	2150
	21st to end	Day	41% 7% 10% 24% 17% 2	3124
January	1st to 10th	Night	36% 6% 15% 20% 17% 6%	4109
	11th to 20th	Night	36% 7% 11% 17% 22% 7%	4120
	21st to end	Night	47% 5% 9% 15% 19% 5%	4532
February	1st to 10th	Night	40% 6% 13% 19% 18% 4	2390
	11th to 20th	Night	43% 6% 12% 18% 16% 5%	2219
	21st to end	Night	45% 7% 11% 15% 16% 5%	1884
March	1st to 10th	Night	51% 10% 12% 12% 13% 4	3486
	11th to 20th	Night	30% 9% 10% 23% 18% 10%	3480
	21st to end	Night	41% 8% 10% 22% 12% 6%	3817
April	1st to 10th	Night	34% 7% 15% 22% 19% 3	2090
	11th to 20th	Night	34% 8% 11% 22% 20% 4	1869
	21st to end	Night	34% 9% 14% 25% 16% 2	1710
May	1st to 10th	Night	41% 12% 15% 23% 9% 1	2840
	11th to 20th	Night	42% 14% 15% 20% 8%	2813
	21st to end	Night	29% 14% 21% 26% 10% 1	3087
June	1st to 10th	Night	38% 15% 19% 20% 7% 1	1710
	11th to 20th	Night	32% 13% 23% 22% 9% 1	1710
	21st to end	Night	33% 14% 19% 19% 13% 2	1710
July	1st to 10th	Night	43% 12% 20% 19% 6%	2795
	11th to 20th	Night	36% 16% 26% 17% 4 1	2786
	21st to end	Night	54% 14% 16% 11% 4	2988
August	1st to 10th	Night	43% 13% 26% 15% 4	2814
	11th to 20th	Night	44% 10% 23% 15% 8%	2812
	21st to end	Night	30% 9% 17% 34% 8% 1	3407
September	1st to 10th	Night	39% 11% 14% 20% 13% 3	2090
	11th to 20th	Night	45% 10% 13% 16% 15% 1	2090
	21st to end	Night	38% 10% 11% 21% 17% 3	2090
October	1st to 10th	Night	29% 5% 10% 20% 24% 11%	3541
	11th to 20th	Night	24% 5% 7% 20% 24% 20%	3779
	21st to end	Night	30% 4 6% 23% 22% 15%	4120
November	1st to 10th	Night	35% 8% 10% 19% 21% 8%	2394
	11th to 20th	Night	34% 5% 10% 19% 24% 9%	2470
	21st to end	Night	37% 6% 8% 23% 21% 6%	2470
December	1st to 10th	Night	46% 7% 13% 16% 14% 4	2470
	11th to 20th	Night	38% 8% 10% 17% 22% 4	3044
	21st to end	Night	44% 7% 12% 19% 16% 2	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	31% 29% 30% 7% 2	270
	11th to 20th	Day	36% 24% 24% 14% 2	270
	21st to end	Day	28% 33% 28% 8% 2	297
February	1st to 10th	Day	29% 26% 31% 13% 1	270
	11th to 20th	Day	43% 30% 20% 7%	270
	21st to end	Day	41% 29% 22% 7% 1	225
March	1st to 10th	Day	27% 21% 29% 17% 6%	412
	11th to 20th	Day	28% 25% 26% 16% 4 1	460
	21st to end	Day	27% 24% 26% 17% 5%	506
April	1st to 10th	Day	25% 21% 25% 20% 8% 1	460
	11th to 20th	Day	22% 21% 24% 20% 10% 3	452
	21st to end	Day	20% 17% 28% 20% 11% 4	460
May	1st to 10th	Day	17% 21% 26% 21% 11% 5%	463
	11th to 20th	Day	18% 12% 24% 24% 14% 8%	487
	21st to end	Day	13% 9% 26% 22% 18% 12%	529
June	1st to 10th	Day	13% 6% 25% 28% 19% 10%	490
	11th to 20th	Day	9% 6% 25% 23% 24% 13%	490
	21st to end	Day	11% 8% 26% 27% 17% 12%	490
July	1st to 10th	Day	8% 3 16% 27% 28% 17%	485
	11th to 20th	Day	8% 4 15% 27% 24% 22%	484
	21st to end	Day	9% 4 13% 28% 29% 18%	532
August	1st to 10th	Day	17% 6% 20% 21% 18% 17%	486
	11th to 20th	Day	10% 4 22% 25% 23% 17%	479
	21st to end	Day	11% 3 17% 25% 29% 16%	539
September	1st to 10th	Day	9% 5% 18% 29% 26% 14%	490
	11th to 20th	Day	16% 6% 18% 22% 27% 11%	490
	21st to end	Day	16% 8% 21% 28% 22% 5%	490
October	1st to 10th	Day	16% 11% 21% 28% 18% 6%	490
	11th to 20th	Day	15% 16% 24% 26% 15% 4	490
	21st to end	Day	19% 14% 25% 27% 13% 2	539
November	1st to 10th	Day	21% 13% 27% 27% 10% 3	396
	11th to 20th	Day	24% 20% 31% 19% 5% 1	270
	21st to end	Day	20% 20% 34% 18% 7% 1	270
December	1st to 10th	Day	29% 26% 30% 13% 2	270
	11th to 20th	Day	24% 21% 31% 17% 6% 1	270
	21st to end	Day	27% 23% 31% 14% 4 1	297
January	1st to 10th	Night	26% 20% 25% 23% 6%	760
	11th to 20th	Night	22% 20% 27% 25% 5%	760
	21st to end	Night	21% 21% 30% 25% 3	836
February	1st to 10th	Night	20% 18% 28% 29% 4	760
	11th to 20th	Night	27% 25% 25% 22% 1	743
	21st to end	Night	24% 24% 29% 21% 3	628
March	1st to 10th	Night	20% 20% 28% 28% 4	760
	11th to 20th	Night	23% 16% 31% 23% 7% 1	760
	21st to end	Night	20% 19% 30% 24% 8%	836
April	1st to 10th	Night	19% 20% 25% 28% 8% 1	760
	11th to 20th	Night	19% 17% 25% 27% 11% 1	659
	21st to end	Night	14% 13% 21% 35% 16% 1	570
May	1st to 10th	Night	16% 10% 24% 31% 18% 1	570
	11th to 20th	Night	15% 7% 21% 31% 23% 2	561
	21st to end	Night	10% 4 18% 27% 33% 7%	617
June	1st to 10th	Night	10% 4 14% 34% 31% 6%	570
	11th to 20th	Night	8% 3 15% 31% 33% 11%	570
	21st to end	Night	6% 3 12% 33% 39% 6%	570
July	1st to 10th	Night	9% 2 10% 26% 46% 7%	555
	11th to 20th	Night	9% 2 9% 22% 45% 12%	552
	21st to end	Night	8% 1 7% 27% 45% 12%	624
August	1st to 10th	Night	10% 1 12% 25% 41% 10%	567
	11th to 20th	Night	10% 3 13% 26% 38% 9%	564
	21st to end	Night	10% 1 9% 27% 43% 10%	679
September	1st to 10th	Night	9% 3 15% 29% 38% 6%	760
	11th to 20th	Night	15% 4 17% 25% 33% 6%	760
	21st to end	Night	16% 6% 16% 32% 26% 4	760
October	1st to 10th	Night	15% 10% 19% 25% 24% 7%	760
	11th to 20th	Night	15% 12% 22% 31% 18% 2	760
	21st to end	Night	16% 13% 18% 35% 16% 2	836
November	1st to 10th	Night	17% 8% 23% 32% 16% 3	771
	11th to 20th	Night	19% 13% 22% 34% 12% 1	760
	21st to end	Night	19% 16% 21% 31% 13% 1	760
December	1st to 10th	Night	25% 18% 21% 29% 7%	760
	11th to 20th	Night	19% 16% 25% 31% 8% 1	760
	21st to end	Night	25% 16% 23% 29% 5%	836

Page generated at 2024-11-05 08:15:52. Version ac07

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