Bluebird Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bluebird Observatory clear sky chart from 2005-11-06 to 2024-04-10.

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	15% 6% 2 5% 5% 3 5% 5% 6% 7% 42%	83209
	Night	15% 6% 2 5% 5% 3 4 5% 5% 7% 44%	85552
Transparency	Day	40% 7% 12% 23% 16% 3	82919
	Night	39% 6% 11% 23% 16% 3	85361
Seeing	Day	19% 12% 28% 23% 14% 5%	14145
	Night	18% 10% 30% 29% 12% 1	23767

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	17% 5% 2 4 4 3 4 5% 4 6% 46%	2530
	11th to 20th	Day	14% 10% 3 8% 5% 3 4 4 4 5% 39%	2840
	21st to end	Day	19% 8% 3 6% 5% 3 5% 5% 4 5% 36%	3124
February	1st to 10th	Day	14% 6% 2 6% 6% 3 4 6% 7% 6% 39%	1710
	11th to 20th	Day	18% 6% 3 5% 5% 3 5% 5% 5% 6% 40%	1723
	21st to end	Day	18% 8% 3 6% 5% 3 4 3 4 5% 40%	1570
March	1st to 10th	Day	22% 6% 2 4 5% 3 4 4 5% 7% 36%	3342
	11th to 20th	Day	10% 5% 3 4 5% 3 5% 5% 6% 7% 48%	3480
	21st to end	Day	20% 6% 2 5% 5% 3 4 4 5% 6% 41%	3900
April	1st to 10th	Day	14% 6% 2 5% 5% 3 4 5% 6% 8% 41%	2270
	11th to 20th	Day	14% 4 2 6% 5% 2 4 3 5% 6% 47%	2134
	21st to end	Day	19% 6% 2 4 4 3 4 4 5% 7% 41%	2160
May	1st to 10th	Day	15% 7% 2 6% 5% 3 5% 4 7% 9% 38%	2290
	11th to 20th	Day	20% 6% 3 6% 5% 3 5% 4 5% 7% 36%	2442
	21st to end	Day	13% 5% 2 6% 5% 4 4 5% 6% 9% 41%	2725
June	1st to 10th	Day	11% 5% 2 5% 6% 3 5% 5% 7% 10% 41%	2520
	11th to 20th	Day	12% 5% 3 6% 6% 4 5% 5% 7% 8% 40%	2520
	21st to end	Day	11% 3 2 4 4 3 5% 6% 6% 10% 45%	2520
July	1st to 10th	Day	10% 4 2 5% 7% 4 5% 6% 6% 8% 44%	2520
	11th to 20th	Day	6% 3 2 4 6% 4 7% 7% 8% 11% 44%	2484
	21st to end	Day	10% 5% 3 5% 6% 3 6% 7% 7% 9% 37%	2547
August	1st to 10th	Day	11% 5% 2 6% 6% 4 6% 6% 8% 9% 36%	2327
	11th to 20th	Day	11% 6% 3 6% 6% 4 5% 5% 6% 9% 40%	2205
	21st to end	Day	12% 5% 2 4 5% 3 6% 6% 6% 9% 41%	2376
September	1st to 10th	Day	14% 5% 3 4 5% 3 4 4 5% 7% 45%	2160
	11th to 20th	Day	12% 5% 2 4 5% 3 4 4 5% 8% 48%	2160
	21st to end	Day	18% 7% 3 6% 5% 2 4 5% 5% 6% 39%	1900
October	1st to 10th	Day	16% 6% 3 5% 4 3 3 4 4 7% 45%	1800
	11th to 20th	Day	18% 4 2 3 4 3 4 4 6% 5% 47%	1800
	21st to end	Day	14% 6% 2 5% 5% 3 3 4 5% 6% 47%	1980
November	1st to 10th	Day	12% 5% 2 4 4 2 4 4 5% 7% 52%	1735
	11th to 20th	Day	15% 4 2 4 4 2 4 5% 5% 6% 50%	1693
	21st to end	Day	16% 4 2 4 4 3 5% 4 4 5% 47%	1520
December	1st to 10th	Day	17% 6% 2 5% 3 4 5% 4 7% 7% 40%	1520
	11th to 20th	Day	16% 6% 2 5% 5% 3 4 3 5% 8% 42%	1910
	21st to end	Day	18% 7% 3 6% 5% 4 5% 4 5% 7% 37%	2772
January	1st to 10th	Night	15% 7% 3 5% 5% 3 4 4 5% 7% 43%	4401
	11th to 20th	Night	18% 8% 2 4 4 2 3 5% 4 6% 45%	4120
	21st to end	Night	21% 9% 3 4 4 2 3 4 4 6% 40%	4532
February	1st to 10th	Night	15% 8% 2 5% 4 4 4 4 5% 7% 41%	2470
	11th to 20th	Night	18% 7% 3 5% 4 3 3 3 4 6% 43%	2342
	21st to end	Night	17% 7% 2 6% 5% 3 4 3 5% 5% 42%	1884
March	1st to 10th	Night	20% 7% 3 5% 5% 3 4 4 4 6% 39%	3496
	11th to 20th	Night	11% 5% 2 5% 4 3 4 5% 5% 6% 50%	3480
	21st to end	Night	14% 9% 3 5% 4 2 3 3 4 5% 47%	3732
April	1st to 10th	Night	16% 6% 3 5% 5% 3 5% 5% 5% 7% 41%	1900
	11th to 20th	Night	14% 5% 2 5% 5% 2 4 5% 4 7% 46%	1775
	21st to end	Night	18% 6% 2 4 4 3 4 5% 6% 7% 43%	1800
May	1st to 10th	Night	16% 7% 3 5% 4 4 3 5% 6% 7% 40%	1684
	11th to 20th	Night	20% 7% 3 5% 4 2 4 4 6% 8% 38%	1451
	21st to end	Night	13% 5% 2 4 5% 2 6% 6% 7% 10% 41%	1550
June	1st to 10th	Night	11% 4 2 4 5% 3 4 5% 8% 10% 44%	1440
	11th to 20th	Night	12% 5% 3 5% 6% 3 6% 5% 6% 8% 41%	1440
	21st to end	Night	10% 4 2 4 6% 4 5% 5% 7% 10% 43%	1440
July	1st to 10th	Night	9% 4 3 6% 6% 4 7% 7% 7% 8% 38%	1440
	11th to 20th	Night	6% 3 3 5% 5% 3 6% 7% 7% 9% 46%	1471
	21st to end	Night	7% 4 2 5% 5% 4 5% 6% 7% 12% 43%	1771
August	1st to 10th	Night	10% 5% 2 6% 5% 3 6% 8% 7% 9% 39%	1611
	11th to 20th	Night	11% 6% 2 7% 6% 2 5% 6% 6% 6% 42%	1677
	21st to end	Night	11% 4 3 5% 5% 3 5% 5% 5% 9% 43%	1980
September	1st to 10th	Night	15% 6% 2 5% 4 2 3 5% 4 7% 46%	1800
	11th to 20th	Night	10% 6% 2 6% 4 2 3 4 4 6% 52%	1800
	21st to end	Night	17% 6% 2 5% 6% 3 4 4 5% 7% 41%	2053
October	1st to 10th	Night	19% 6% 2 4 3 3 3 4 4 5% 45%	2160
	11th to 20th	Night	16% 5% 2 4 4 2 3 3 4 6% 51%	2160
	21st to end	Night	16% 6% 2 4 4 3 3 4 4 7% 48%	2376
November	1st to 10th	Night	12% 5% 2 4 4 2 3 3 4 6% 53%	2343
	11th to 20th	Night	14% 6% 2 5% 4 2 4 4 4 5% 50%	2484
	21st to end	Night	14% 4 2 4 5% 3 5% 4 5% 7% 47%	2660
December	1st to 10th	Night	16% 7% 3 5% 5% 3 5% 5% 5% 7% 40%	2660
	11th to 20th	Night	17% 5% 3 5% 5% 2 4 4 5% 6% 43%	3285
	21st to end	Night	16% 7% 2 5% 6% 3 5% 5% 6% 8% 37%	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	38% 4 9% 31% 14% 4	2531
	11th to 20th	Day	46% 5% 11% 21% 13% 4	2840
	21st to end	Day	48% 7% 11% 22% 11% 2	3124
February	1st to 10th	Day	43% 7% 12% 25% 12% 2	1710
	11th to 20th	Day	43% 5% 10% 25% 14% 3	1732
	21st to end	Day	47% 4 11% 19% 15% 4	1570
March	1st to 10th	Day	44% 7% 11% 23% 12% 2	3342
	11th to 20th	Day	32% 7% 10% 28% 20% 4	3480
	21st to end	Day	45% 5% 10% 20% 17% 3	3900
April	1st to 10th	Day	39% 8% 12% 20% 17% 4	2270
	11th to 20th	Day	38% 5% 10% 22% 19% 6%	2134
	21st to end	Day	42% 6% 11% 20% 18% 4	2160
May	1st to 10th	Day	42% 8% 12% 19% 16% 2	2290
	11th to 20th	Day	45% 8% 12% 19% 13% 2	2446
	21st to end	Day	40% 9% 14% 23% 12% 2	2725
June	1st to 10th	Day	37% 8% 14% 24% 16% 1	2520
	11th to 20th	Day	39% 10% 12% 22% 14% 2	2520
	21st to end	Day	32% 9% 15% 25% 17% 2	2520
July	1st to 10th	Day	38% 10% 13% 21% 16% 3	2450
	11th to 20th	Day	30% 10% 15% 27% 15% 3	2409
	21st to end	Day	39% 11% 14% 18% 15% 2	2405
August	1st to 10th	Day	39% 10% 14% 23% 12% 1	2314
	11th to 20th	Day	40% 9% 14% 20% 16% 2	2205
	21st to end	Day	38% 9% 14% 22% 15% 3	2376
September	1st to 10th	Day	38% 8% 12% 21% 17% 4	2160
	11th to 20th	Day	35% 5% 10% 24% 21% 4	2160
	21st to end	Day	44% 6% 8% 20% 19% 2	1900
October	1st to 10th	Day	40% 6% 10% 23% 19% 3	1800
	11th to 20th	Day	37% 6% 11% 23% 21% 3	1800
	21st to end	Day	38% 5% 9% 26% 20% 2	1980
November	1st to 10th	Day	33% 5% 13% 26% 20% 4	1735
	11th to 20th	Day	35% 5% 10% 23% 23% 4	1693
	21st to end	Day	39% 5% 11% 27% 16% 2	1520
December	1st to 10th	Day	41% 7% 13% 24% 12% 2	1520
	11th to 20th	Day	39% 6% 11% 30% 11% 2	1906
	21st to end	Day	45% 6% 15% 22% 12% 1	2772
January	1st to 10th	Night	41% 5% 11% 25% 15% 3	4401
	11th to 20th	Night	41% 5% 12% 25% 16% 3	4120
	21st to end	Night	46% 5% 8% 26% 14% 1	4532
February	1st to 10th	Night	42% 6% 12% 25% 13% 2	2470
	11th to 20th	Night	43% 4 9% 22% 18% 4	2344
	21st to end	Night	44% 4 10% 22% 15% 5%	1884
March	1st to 10th	Night	45% 6% 9% 26% 12% 2	3496
	11th to 20th	Night	32% 7% 10% 31% 17% 3	3480
	21st to end	Night	41% 5% 9% 20% 20% 5%	3732
April	1st to 10th	Night	41% 7% 11% 19% 19% 4	1900
	11th to 20th	Night	37% 6% 11% 20% 19% 6%	1775
	21st to end	Night	39% 7% 11% 22% 16% 5%	1800
May	1st to 10th	Night	43% 6% 11% 22% 13% 4	1684
	11th to 20th	Night	43% 8% 11% 18% 18% 2	1452
	21st to end	Night	36% 10% 19% 20% 13% 2	1551
June	1st to 10th	Night	33% 9% 11% 27% 17% 2	1440
	11th to 20th	Night	38% 10% 13% 23% 14% 2	1440
	21st to end	Night	35% 8% 13% 24% 18% 2	1440
July	1st to 10th	Night	42% 10% 16% 17% 12% 4	1400
	11th to 20th	Night	31% 10% 16% 25% 15% 3	1423
	21st to end	Night	30% 9% 19% 24% 16% 2	1672
August	1st to 10th	Night	36% 12% 15% 21% 15% 1	1600
	11th to 20th	Night	40% 10% 13% 20% 15% 2	1677
	21st to end	Night	36% 9% 13% 23% 15% 4	1980
September	1st to 10th	Night	38% 7% 11% 20% 18% 5%	1800
	11th to 20th	Night	34% 5% 10% 25% 23% 3	1800
	21st to end	Night	43% 7% 9% 19% 19% 3	2053
October	1st to 10th	Night	41% 5% 11% 22% 18% 3	2160
	11th to 20th	Night	35% 5% 9% 28% 20% 2	2160
	21st to end	Night	36% 5% 10% 25% 21% 3	2376
November	1st to 10th	Night	33% 5% 9% 26% 21% 5%	2343
	11th to 20th	Night	37% 5% 9% 23% 21% 5%	2484
	21st to end	Night	36% 6% 11% 25% 19% 3	2660
December	1st to 10th	Night	43% 6% 12% 24% 13% 2	2660
	11th to 20th	Night	41% 5% 11% 22% 18% 3	3288
	21st to end	Night	42% 7% 16% 23% 11% 1	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	29% 20% 32% 14% 4 1	186
	11th to 20th	Day	29% 24% 31% 13% 3	270
	21st to end	Day	23% 24% 34% 15% 3 1	297
February	1st to 10th	Day	24% 21% 39% 11% 4	270
	11th to 20th	Day	32% 21% 39% 7% 1	330
	21st to end	Day	30% 20% 29% 19% 2	382
March	1st to 10th	Day	24% 22% 30% 19% 4	460
	11th to 20th	Day	28% 19% 32% 16% 4 1	460
	21st to end	Day	24% 20% 32% 18% 5% 1	506
April	1st to 10th	Day	21% 22% 34% 18% 5% 2	457
	11th to 20th	Day	18% 16% 32% 18% 13% 3	412
	21st to end	Day	26% 13% 34% 17% 8% 2	420
May	1st to 10th	Day	24% 15% 30% 17% 9% 4	423
	11th to 20th	Day	21% 12% 28% 26% 11% 2	447
	21st to end	Day	18% 5% 23% 26% 24% 5%	485
June	1st to 10th	Day	14% 9% 28% 22% 19% 7%	450
	11th to 20th	Day	15% 8% 25% 27% 19% 5%	450
	21st to end	Day	10% 4 27% 34% 19% 5%	450
July	1st to 10th	Day	12% 4 17% 31% 23% 13%	445
	11th to 20th	Day	4 3 18% 34% 30% 11%	444
	21st to end	Day	13% 2 22% 31% 25% 7%	488
August	1st to 10th	Day	12% 2 18% 30% 26% 11%	446
	11th to 20th	Day	13% 3 19% 30% 22% 12%	439
	21st to end	Day	10% 2 22% 29% 24% 13%	495
September	1st to 10th	Day	16% 6% 18% 24% 22% 14%	450
	11th to 20th	Day	13% 3 21% 31% 20% 12%	450
	21st to end	Day	22% 10% 21% 30% 13% 5%	450
October	1st to 10th	Day	22% 6% 23% 23% 20% 6%	450
	11th to 20th	Day	18% 13% 26% 27% 14% 2	450
	21st to end	Day	17% 12% 35% 25% 8% 2	495
November	1st to 10th	Day	16% 12% 32% 25% 13% 3	397
	11th to 20th	Day	18% 14% 34% 22% 11% 1	353
	21st to end	Day	23% 17% 34% 20% 7%	180
December	1st to 10th	Day	21% 21% 38% 14% 4 2	180
	11th to 20th	Day	27% 18% 28% 19% 7%	180
	21st to end	Day	25% 13% 36% 20% 6%	198
January	1st to 10th	Night	19% 18% 40% 20% 3	760
	11th to 20th	Night	22% 16% 35% 23% 4	760
	21st to end	Night	19% 18% 39% 22% 1	836
February	1st to 10th	Night	19% 16% 36% 27% 2	760
	11th to 20th	Night	27% 20% 35% 17% 1	743
	21st to end	Night	23% 18% 38% 18% 3	628
March	1st to 10th	Night	19% 16% 39% 23% 4	760
	11th to 20th	Night	22% 17% 35% 21% 5% 1	760
	21st to end	Night	19% 14% 42% 20% 4 1	836
April	1st to 10th	Night	21% 17% 38% 21% 4	760
	11th to 20th	Night	16% 14% 33% 30% 7% 1	711
	21st to end	Night	22% 9% 34% 27% 8%	720
May	1st to 10th	Night	20% 8% 31% 30% 10%	604
	11th to 20th	Night	24% 7% 28% 32% 9% 1	390
	21st to end	Night	17% 4 20% 35% 21% 3	389
June	1st to 10th	Night	14% 3 25% 37% 22%	360
	11th to 20th	Night	13% 4 23% 37% 22% 1	360
	21st to end	Night	11% 1 22% 48% 17%	360
July	1st to 10th	Night	9% 3 17% 41% 27% 3	350
	11th to 20th	Night	8% 1 13% 40% 36% 3	379
	21st to end	Night	9% 1 15% 43% 28% 4	591
August	1st to 10th	Night	11% 2 11% 43% 30% 3	537
	11th to 20th	Night	13% 3 15% 39% 27% 3	613
	21st to end	Night	12% 3 15% 38% 27% 5%	792
September	1st to 10th	Night	16% 3 18% 34% 25% 4	720
	11th to 20th	Night	12% 3 17% 36% 28% 4	720
	21st to end	Night	20% 4 22% 34% 18% 2	720
October	1st to 10th	Night	21% 5% 22% 29% 19% 4	720
	11th to 20th	Night	18% 7% 29% 32% 13% 1	720
	21st to end	Night	20% 10% 31% 27% 11%	792
November	1st to 10th	Night	16% 7% 32% 34% 9% 2	740
	11th to 20th	Night	17% 16% 30% 28% 8% 1	760
	21st to end	Night	17% 15% 32% 29% 7% 1	760
December	1st to 10th	Night	23% 13% 36% 20% 7% 1	760
	11th to 20th	Night	17% 11% 43% 23% 5%	760
	21st to end	Night	19% 13% 37% 29% 2	836

Page generated at 2024-04-07 09:28:12. Version ac07

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