Blue Braille Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Braille Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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	16% 10% 4 7% 6% 3 5% 5% 5% 7% 32%	74777
	Night	18% 11% 4 7% 6% 3 5% 5% 5% 6% 31%	75260
Transparency	Day	52% 7% 12% 18% 9% 1	74493
	Night	57% 7% 10% 16% 9% 1	75078
Seeing	Day	20% 13% 27% 23% 13% 4	13429
	Night	21% 12% 28% 26% 11% 1	23002

By Month

Percentage Cloud Cover NE (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% 17% 8% 11% 9% 4 6% 4 5% 5% 14%	1517
	11th to 20th	Day	19% 18% 7% 13% 8% 3 5% 4 4 5% 14%	1685
	21st to end	Day	16% 17% 8% 12% 11% 5% 6% 5% 5% 4 11%	1836
February	1st to 10th	Day	19% 17% 6% 13% 8% 5% 5% 5% 4 5% 14%	1620
	11th to 20th	Day	15% 17% 7% 14% 8% 4 4 5% 4 4 18%	1573
	21st to end	Day	22% 12% 5% 13% 8% 4 5% 4 5% 5% 19%	1400
March	1st to 10th	Day	17% 12% 7% 10% 6% 5% 4 4 5% 5% 24%	1977
	11th to 20th	Day	14% 16% 6% 7% 6% 3 4 4 4 6% 31%	1980
	21st to end	Day	20% 12% 5% 7% 5% 3 4 4 5% 6% 28%	2178
April	1st to 10th	Day	18% 13% 4 7% 5% 3 3 5% 4 6% 31%	2132
	11th to 20th	Day	19% 9% 3 5% 5% 3 4 4 5% 6% 37%	2161
	21st to end	Day	20% 10% 4 6% 6% 3 5% 4 4 5% 34%	2340
May	1st to 10th	Day	17% 9% 2 6% 5% 4 5% 5% 5% 8% 34%	2340
	11th to 20th	Day	15% 7% 3 6% 5% 4 5% 4 6% 6% 38%	2446
	21st to end	Day	11% 6% 2 5% 4 3 4 5% 6% 9% 44%	2725
June	1st to 10th	Day	15% 6% 3 5% 5% 3 4 5% 6% 7% 40%	2520
	11th to 20th	Day	12% 4 2 5% 6% 4 4 5% 6% 9% 41%	2520
	21st to end	Day	14% 6% 2 4 4 2 4 4 6% 8% 45%	2520
July	1st to 10th	Day	8% 4 2 4 4 3 5% 6% 6% 10% 49%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 6% 7% 10% 39%	2520
	21st to end	Day	10% 4 2 6% 6% 4 7% 6% 7% 9% 39%	2548
August	1st to 10th	Day	9% 5% 2 5% 5% 3 5% 6% 7% 10% 43%	2327
	11th to 20th	Day	10% 4 2 6% 6% 4 5% 6% 7% 11% 38%	2303
	21st to end	Day	11% 5% 3 4 4 3 4 5% 7% 9% 44%	2449
September	1st to 10th	Day	15% 5% 2 5% 4 3 4 5% 6% 7% 42%	2160
	11th to 20th	Day	12% 4 2 4 5% 4 4 4 6% 7% 46%	2070
	21st to end	Day	15% 6% 3 6% 6% 4 5% 6% 5% 8% 35%	1932
October	1st to 10th	Day	20% 8% 2 6% 5% 3 4 6% 4 6% 35%	1800
	11th to 20th	Day	20% 10% 4 8% 6% 4 5% 5% 5% 6% 28%	1800
	21st to end	Day	25% 12% 5% 8% 6% 4 5% 3 4 5% 22%	1980
November	1st to 10th	Day	15% 10% 3 7% 6% 4 5% 5% 5% 6% 33%	1660
	11th to 20th	Day	16% 12% 5% 6% 7% 3 4 4 5% 7% 30%	1520
	21st to end	Day	22% 14% 4 7% 7% 3 4 5% 5% 7% 23%	1520
December	1st to 10th	Day	20% 17% 6% 9% 7% 4 4 4 5% 6% 16%	1520
	11th to 20th	Day	20% 19% 7% 9% 5% 3 5% 5% 5% 6% 16%	1906
	21st to end	Day	28% 22% 6% 10% 6% 3 3 3 3 4 12%	2772
January	1st to 10th	Night	20% 18% 6% 10% 7% 4 4 4 4 4 18%	2649
	11th to 20th	Night	19% 20% 6% 10% 8% 4 5% 5% 4 6% 14%	2493
	21st to end	Night	17% 17% 6% 11% 9% 4 5% 5% 3 5% 18%	2664
February	1st to 10th	Night	20% 16% 6% 12% 8% 3 4 4 4 4 18%	2340
	11th to 20th	Night	19% 14% 5% 9% 7% 4 6% 4 6% 5% 21%	2273
	21st to end	Night	20% 15% 5% 10% 7% 4 5% 4 5% 6% 19%	1850
March	1st to 10th	Night	16% 11% 5% 8% 7% 3 5% 5% 4 5% 30%	1970
	11th to 20th	Night	18% 12% 4 7% 5% 3 4 4 4 6% 33%	1979
	21st to end	Night	18% 11% 4 8% 5% 3 4 4 4 5% 34%	2178
April	1st to 10th	Night	22% 9% 4 7% 6% 3 4 4 5% 5% 32%	1828
	11th to 20th	Night	18% 8% 3 6% 6% 3 4 5% 5% 6% 36%	1763
	21st to end	Night	17% 9% 3 5% 5% 3 6% 5% 5% 5% 35%	1620
May	1st to 10th	Night	17% 8% 3 7% 5% 3 5% 5% 5% 7% 35%	1620
	11th to 20th	Night	14% 4 3 5% 6% 4 6% 6% 6% 8% 39%	1446
	21st to end	Night	12% 5% 1 5% 6% 3 5% 5% 6% 7% 44%	1550
June	1st to 10th	Night	13% 5% 3 6% 6% 4 6% 6% 7% 7% 37%	1440
	11th to 20th	Night	11% 5% 2 5% 6% 5% 5% 5% 5% 8% 43%	1440
	21st to end	Night	14% 6% 2 4 5% 4 6% 4 6% 7% 42%	1440
July	1st to 10th	Night	7% 3 2 5% 5% 4 4 4 6% 7% 53%	1440
	11th to 20th	Night	11% 5% 2 4 5% 4 5% 5% 6% 8% 45%	1440
	21st to end	Night	11% 4 2 5% 6% 3 4 6% 6% 8% 45%	1766
August	1st to 10th	Night	8% 6% 2 4 5% 3 5% 6% 6% 9% 46%	1611
	11th to 20th	Night	10% 5% 3 6% 4 3 5% 5% 6% 8% 45%	1598
	21st to end	Night	9% 6% 2 5% 5% 3 5% 4 5% 9% 46%	1887
September	1st to 10th	Night	15% 6% 2 5% 5% 3 4 4 5% 6% 45%	1800
	11th to 20th	Night	13% 3 2 5% 3 2 3 3 5% 7% 53%	1885
	21st to end	Night	16% 6% 3 6% 5% 4 5% 5% 7% 6% 39%	2027
October	1st to 10th	Night	18% 6% 3 6% 5% 3 4 4 5% 7% 39%	2160
	11th to 20th	Night	22% 9% 3 6% 5% 4 6% 5% 4 6% 30%	2160
	21st to end	Night	25% 8% 4 7% 5% 4 5% 5% 6% 6% 26%	2376
November	1st to 10th	Night	18% 9% 3 5% 4 3 4 4 4 6% 40%	2415
	11th to 20th	Night	15% 12% 4 7% 6% 4 5% 5% 5% 8% 30%	2660
	21st to end	Night	20% 12% 5% 8% 6% 3 5% 5% 5% 7% 24%	2660
December	1st to 10th	Night	22% 18% 6% 7% 6% 3 5% 5% 4 6% 18%	2660
	11th to 20th	Night	18% 19% 7% 9% 6% 3 5% 4 4 5% 20%	3288
	21st to end	Night	31% 16% 6% 7% 6% 3 5% 4 5% 5% 13%	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	77% 6% 7% 7% 2	1518
	11th to 20th	Day	79% 5% 7% 6% 2	1685
	21st to end	Day	77% 6% 9% 6% 2	1836
February	1st to 10th	Day	74% 9% 9% 7% 1	1620
	11th to 20th	Day	70% 6% 8% 12% 3	1582
	21st to end	Day	64% 7% 10% 12% 6% 1	1400
March	1st to 10th	Day	59% 7% 13% 15% 6% 1	1980
	11th to 20th	Day	54% 7% 12% 17% 9% 1	1980
	21st to end	Day	57% 6% 6% 19% 10% 2	2178
April	1st to 10th	Day	53% 5% 12% 19% 10% 1	2132
	11th to 20th	Day	47% 5% 11% 21% 13% 2	2161
	21st to end	Day	52% 5% 11% 17% 13% 2	2340
May	1st to 10th	Day	49% 7% 11% 22% 10% 2	2340
	11th to 20th	Day	45% 8% 11% 21% 13% 2	2450
	21st to end	Day	37% 8% 16% 24% 13% 2	2725
June	1st to 10th	Day	42% 7% 13% 22% 15% 1	2520
	11th to 20th	Day	38% 8% 14% 26% 13% 1	2520
	21st to end	Day	36% 8% 14% 26% 14% 1	2520
July	1st to 10th	Day	30% 8% 15% 28% 17% 2	2450
	11th to 20th	Day	36% 9% 16% 25% 14%	2445
	21st to end	Day	38% 8% 16% 23% 13% 1	2405
August	1st to 10th	Day	32% 10% 17% 28% 12% 1	2314
	11th to 20th	Day	36% 11% 17% 26% 10% 1	2303
	21st to end	Day	35% 8% 15% 27% 13% 1	2449
September	1st to 10th	Day	41% 8% 14% 25% 11% 1	2160
	11th to 20th	Day	35% 8% 12% 29% 15% 1	2070
	21st to end	Day	46% 9% 13% 21% 10% 1	1932
October	1st to 10th	Day	50% 8% 14% 15% 12% 1	1800
	11th to 20th	Day	57% 9% 12% 14% 7% 1	1800
	21st to end	Day	67% 5% 10% 11% 6% 1	1980
November	1st to 10th	Day	55% 8% 11% 16% 8% 2	1660
	11th to 20th	Day	59% 9% 13% 12% 5% 2	1520
	21st to end	Day	68% 7% 11% 10% 4	1520
December	1st to 10th	Day	77% 7% 9% 7% 1	1520
	11th to 20th	Day	74% 8% 10% 6% 2	1906
	21st to end	Day	79% 7% 7% 6%	2772
January	1st to 10th	Night	78% 6% 6% 7% 3	2649
	11th to 20th	Night	77% 7% 8% 6% 2	2493
	21st to end	Night	75% 6% 6% 8% 3	2664
February	1st to 10th	Night	74% 8% 8% 8% 2	2340
	11th to 20th	Night	68% 6% 9% 11% 5%	2275
	21st to end	Night	67% 7% 7% 12% 6%	1850
March	1st to 10th	Night	59% 8% 10% 16% 7% 1	1980
	11th to 20th	Night	55% 6% 10% 17% 10% 2	1980
	21st to end	Night	55% 5% 7% 17% 13% 3	2178
April	1st to 10th	Night	55% 5% 10% 18% 10% 1	1828
	11th to 20th	Night	49% 7% 10% 19% 14% 2	1763
	21st to end	Night	50% 5% 11% 19% 14% 2	1620
May	1st to 10th	Night	50% 7% 7% 20% 13% 3	1620
	11th to 20th	Night	44% 7% 11% 22% 13% 3	1447
	21st to end	Night	39% 7% 13% 22% 17% 3	1551
June	1st to 10th	Night	43% 9% 9% 22% 16% 1	1440
	11th to 20th	Night	41% 8% 11% 21% 18% 2	1440
	21st to end	Night	42% 8% 11% 23% 14% 2	1440
July	1st to 10th	Night	32% 8% 10% 26% 18% 5%	1400
	11th to 20th	Night	37% 7% 13% 26% 15% 2	1392
	21st to end	Night	36% 8% 15% 23% 15% 2	1668
August	1st to 10th	Night	33% 9% 15% 30% 12% 1	1600
	11th to 20th	Night	36% 9% 14% 28% 12%	1598
	21st to end	Night	36% 9% 13% 26% 13% 2	1887
September	1st to 10th	Night	42% 8% 12% 22% 14% 2	1800
	11th to 20th	Night	35% 6% 12% 29% 17% 1	1885
	21st to end	Night	46% 9% 11% 21% 13% 1	2027
October	1st to 10th	Night	48% 7% 11% 20% 14% 1	2160
	11th to 20th	Night	58% 7% 12% 14% 8% 1	2160
	21st to end	Night	63% 7% 9% 13% 7% 1	2376
November	1st to 10th	Night	53% 7% 10% 18% 11% 2	2415
	11th to 20th	Night	60% 8% 10% 14% 6% 2	2660
	21st to end	Night	66% 10% 10% 12% 3	2660
December	1st to 10th	Night	77% 8% 8% 6% 2	2660
	11th to 20th	Night	74% 9% 9% 7% 2	3288
	21st to end	Night	78% 7% 8% 6%	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% 23% 31% 14% 7% 2	180
	11th to 20th	Day	28% 22% 32% 11% 5% 1	258
	21st to end	Day	26% 21% 28% 20% 5%	282
February	1st to 10th	Day	28% 24% 36% 11% 2	240
	11th to 20th	Day	25% 25% 37% 12%	240
	21st to end	Day	30% 21% 34% 14% 1	239
March	1st to 10th	Day	22% 18% 35% 19% 5%	420
	11th to 20th	Day	23% 16% 33% 22% 5% 1	420
	21st to end	Day	29% 11% 31% 22% 6% 1	462
April	1st to 10th	Day	22% 16% 32% 21% 7% 2	420
	11th to 20th	Day	25% 17% 25% 18% 11% 4	412
	21st to end	Day	23% 13% 31% 22% 8% 2	420
May	1st to 10th	Day	25% 13% 26% 23% 9% 3	423
	11th to 20th	Day	17% 11% 27% 26% 16% 4	447
	21st to end	Day	14% 6% 26% 30% 17% 7%	485
June	1st to 10th	Day	17% 10% 29% 32% 11% 1	450
	11th to 20th	Day	13% 12% 23% 30% 18% 4	450
	21st to end	Day	15% 7% 31% 30% 13% 3	450
July	1st to 10th	Day	8% 6% 20% 31% 27% 7%	445
	11th to 20th	Day	13% 8% 23% 29% 20% 7%	444
	21st to end	Day	11% 5% 28% 31% 19% 5%	488
August	1st to 10th	Day	7% 7% 22% 32% 23% 10%	446
	11th to 20th	Day	12% 5% 21% 29% 23% 10%	439
	21st to end	Day	12% 5% 24% 29% 19% 10%	495
September	1st to 10th	Day	16% 7% 21% 28% 19% 9%	450
	11th to 20th	Day	10% 6% 18% 28% 25% 13%	450
	21st to end	Day	16% 13% 24% 22% 17% 8%	450
October	1st to 10th	Day	20% 14% 23% 18% 19% 7%	450
	11th to 20th	Day	23% 17% 29% 22% 7% 2	450
	21st to end	Day	33% 17% 25% 17% 7%	495
November	1st to 10th	Day	22% 18% 30% 19% 9% 3	311
	11th to 20th	Day	27% 23% 24% 19% 4 3	180
	21st to end	Day	33% 19% 33% 12% 3	180
December	1st to 10th	Day	27% 22% 33% 13% 5% 1	180
	11th to 20th	Day	27% 27% 28% 14% 4	180
	21st to end	Day	28% 28% 30% 12% 2 1	198
January	1st to 10th	Night	28% 21% 30% 15% 6%	760
	11th to 20th	Night	30% 20% 29% 17% 4	760
	21st to end	Night	25% 15% 33% 22% 5%	820
February	1st to 10th	Night	28% 21% 31% 18% 2	720
	11th to 20th	Night	25% 17% 35% 19% 4	703
	21st to end	Night	28% 14% 35% 21% 2	592
March	1st to 10th	Night	22% 13% 35% 25% 5%	720
	11th to 20th	Night	24% 15% 31% 23% 7%	720
	21st to end	Night	22% 9% 31% 26% 11% 1	792
April	1st to 10th	Night	23% 12% 31% 28% 4	720
	11th to 20th	Night	22% 11% 31% 25% 9% 1	699
	21st to end	Night	21% 8% 27% 34% 10% 1	540
May	1st to 10th	Night	20% 6% 24% 33% 14% 2	540
	11th to 20th	Night	14% 5% 28% 40% 12% 1	385
	21st to end	Night	14% 4 25% 34% 20% 2	389
June	1st to 10th	Night	13% 3 30% 37% 16% 1	360
	11th to 20th	Night	13% 6% 28% 38% 16%	360
	21st to end	Night	13% 6% 26% 41% 15%	360
July	1st to 10th	Night	7% 3 21% 43% 25% 2	350
	11th to 20th	Night	11% 3 22% 41% 21% 2	348
	21st to end	Night	11% 3 22% 41% 22% 2	586
August	1st to 10th	Night	9% 4 15% 41% 28% 3	537
	11th to 20th	Night	9% 5% 17% 34% 33% 3	534
	21st to end	Night	10% 2 22% 37% 25% 3	699
September	1st to 10th	Night	16% 6% 18% 36% 21% 4	720
	11th to 20th	Night	14% 5% 19% 29% 27% 6%	720
	21st to end	Night	17% 7% 22% 31% 19% 4	720
October	1st to 10th	Night	20% 7% 25% 26% 19% 3	720
	11th to 20th	Night	26% 15% 26% 24% 8% 1	720
	21st to end	Night	30% 13% 29% 23% 5%	792
November	1st to 10th	Night	23% 11% 29% 26% 10% 1	740
	11th to 20th	Night	22% 17% 35% 17% 8% 2	760
	21st to end	Night	25% 17% 33% 18% 6%	760
December	1st to 10th	Night	32% 19% 28% 16% 4	760
	11th to 20th	Night	26% 21% 32% 18% 4	760
	21st to end	Night	32% 16% 33% 17% 2	836

Page generated at 2024-01-24 09:37:26. Version ac07

Copyright 2024 Attilla Danko