Blazing Star Observatory
Clear Sky Chart
History

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

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	6% 7% 2 6% 4 4 4 4 6% 7% 49%	105395
	Night	8% 9% 3 7% 4 4 4 4 6% 7% 44%	102383
Transparency	Day	35% 5% 10% 24% 19% 8%	105164
	Night	40% 5% 11% 23% 15% 6%	102260
Seeing	Day	10% 13% 25% 29% 18% 5%	14321
	Night	11% 7% 21% 37% 21% 3	23287

By Month

Percentage Cloud Cover NW (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% 20% 5% 10% 5% 4 4 4 6% 6% 22%	2539
	11th to 20th	Day	12% 18% 5% 9% 5% 5% 5% 4 5% 6% 26%	2516
	21st to end	Day	21% 21% 9% 11% 5% 4 3 3 4 4 15%	2794
February	1st to 10th	Day	9% 14% 3 10% 6% 6% 6% 5% 7% 7% 28%	1638
	11th to 20th	Day	9% 11% 4 8% 4 5% 5% 4 5% 8% 37%	1665
	21st to end	Day	6% 10% 4 9% 6% 5% 5% 5% 7% 9% 33%	1569
March	1st to 10th	Day	6% 9% 3 8% 5% 5% 5% 4 7% 9% 39%	3138
	11th to 20th	Day	4 6% 2 4 4 5% 4 4 5% 7% 54%	3364
	21st to end	Day	9% 8% 3 8% 5% 5% 6% 5% 7% 9% 34%	4094
April	1st to 10th	Day	8% 7% 3 7% 6% 5% 7% 5% 7% 9% 37%	2280
	11th to 20th	Day	5% 7% 3 7% 6% 5% 5% 5% 8% 8% 42%	2252
	21st to end	Day	5% 7% 3 7% 5% 5% 5% 5% 6% 9% 43%	2527
May	1st to 10th	Day	5% 5% 2 5% 3 4 4 4 6% 8% 53%	4420
	11th to 20th	Day	4 3 1 5% 4 4 5% 4 6% 10% 53%	4377
	21st to end	Day	8% 8% 3 7% 6% 6% 6% 5% 7% 8% 37%	4813
June	1st to 10th	Day	8% 6% 2 5% 5% 4 5% 5% 7% 8% 45%	2660
	11th to 20th	Day	5% 5% 2 6% 4 5% 4 5% 7% 8% 50%	2660
	21st to end	Day	3 4 1 5% 4 3 4 4 5% 7% 59%	2660
July	1st to 10th	Day	1 1 1 3 2 2 3 2 4 4 78%	4420
	11th to 20th	Day	1 2 1 2 2 2 3 2 3 4 78%	4420
	21st to end	Day	2 1 1 1 1 2 2 2 3 4 80%	4790
August	1st to 10th	Day	2 2 1 3 2 2 3 3 5% 6% 72%	4401
	11th to 20th	Day	2 2 1 2 3 4 4 3 6% 8% 67%	4179
	21st to end	Day	4 4 1 4 3 4 4 3 5% 5% 63%	4187
September	1st to 10th	Day	3 2 1 2 2 3 3 3 5% 7% 68%	2280
	11th to 20th	Day	4 4 1 5% 4 4 5% 4 6% 8% 55%	2271
	21st to end	Day	6% 4 1 5% 4 3 4 3 5% 7% 58%	2062
October	1st to 10th	Day	3 4 2 5% 3 3 4 4 5% 8% 60%	3180
	11th to 20th	Day	5% 6% 2 6% 5% 5% 5% 4 7% 8% 47%	3140
	21st to end	Day	9% 5% 2 8% 4 5% 5% 4 6% 6% 45%	3101
November	1st to 10th	Day	11% 11% 3 8% 6% 5% 5% 4 7% 7% 34%	1719
	11th to 20th	Day	8% 13% 4 10% 5% 4 5% 4 6% 6% 34%	1520
	21st to end	Day	9% 14% 6% 10% 6% 5% 4 4 6% 8% 29%	1520
December	1st to 10th	Day	12% 13% 4 10% 6% 4 4 5% 5% 7% 29%	1520
	11th to 20th	Day	13% 16% 8% 14% 6% 4 4 4 5% 6% 19%	1925
	21st to end	Day	12% 20% 5% 15% 6% 6% 5% 3 4 5% 19%	2794
January	1st to 10th	Night	13% 19% 6% 12% 5% 5% 4 4 5% 7% 19%	4406
	11th to 20th	Night	14% 15% 3 9% 5% 4 5% 4 6% 9% 25%	4382
	21st to end	Night	19% 22% 11% 14% 5% 4 4 2 4 4 12%	4862
February	1st to 10th	Night	11% 12% 4 10% 6% 5% 6% 5% 6% 7% 29%	2540
	11th to 20th	Night	10% 9% 3 7% 5% 4 5% 4 8% 9% 36%	2402
	21st to end	Night	7% 11% 4 9% 5% 5% 5% 5% 8% 8% 34%	1884
March	1st to 10th	Night	7% 8% 2 7% 5% 5% 6% 5% 9% 12% 36%	3736
	11th to 20th	Night	5% 5% 2 4 3 3 4 3 5% 7% 59%	3613
	21st to end	Night	8% 10% 3 9% 7% 6% 6% 5% 7% 9% 31%	3558
April	1st to 10th	Night	6% 7% 3 6% 6% 6% 5% 6% 6% 8% 41%	1900
	11th to 20th	Night	4 9% 3 6% 5% 4 5% 4 6% 6% 48%	1879
	21st to end	Night	7% 6% 2 5% 4 4 5% 4 5% 8% 49%	1649
May	1st to 10th	Night	5% 4 2 5% 4 3 4 4 6% 7% 57%	2540
	11th to 20th	Night	5% 3 1 4 3 4 4 4 6% 8% 58%	2516
	21st to end	Night	4 3 2 4 4 4 5% 4 8% 11% 50%	2762
June	1st to 10th	Night	6% 5% 2 6% 5% 5% 4 4 7% 8% 49%	1520
	11th to 20th	Night	5% 5% 1 5% 4 5% 5% 4 7% 7% 53%	1520
	21st to end	Night	3 3 1 3 3 3 4 3 5% 7% 65%	1520
July	1st to 10th	Night	1 1 2 2 2 2 2 3 4 81%	2540
	11th to 20th	Night	1 1 1 1 1 2 1 2 4 84%	2540
	21st to end	Night	1 1 1 1 1 2 2 4 4 81%	2762
August	1st to 10th	Night	2 2 1 3 4 3 3 3 5% 5% 69%	2529
	11th to 20th	Night	2 2 1 3 2 3 3 3 5% 7% 68%	2650
	21st to end	Night	4 2 1 4 3 3 3 3 4 6% 66%	3490
September	1st to 10th	Night	2 2 1 3 3 3 3 3 5% 7% 68%	1900
	11th to 20th	Night	4 3 1 5% 3 3 4 2 6% 7% 61%	1909
	21st to end	Night	5% 4 1 4 3 4 4 4 6% 8% 59%	2116
October	1st to 10th	Night	4 4 1 4 3 4 5% 5% 6% 8% 57%	3800
	11th to 20th	Night	5% 5% 2 6% 4 5% 5% 4 7% 8% 50%	3797
	21st to end	Night	9% 7% 3 9% 4 4 4 4 6% 7% 44%	4457
November	1st to 10th	Night	14% 9% 3 7% 5% 4 5% 4 7% 8% 34%	2576
	11th to 20th	Night	10% 12% 3 6% 6% 5% 5% 5% 7% 7% 34%	2666
	21st to end	Night	11% 14% 5% 10% 5% 6% 5% 3 6% 7% 28%	2660
December	1st to 10th	Night	11% 15% 5% 10% 6% 5% 5% 4 6% 7% 28%	2660
	11th to 20th	Night	13% 15% 6% 16% 8% 6% 6% 4 5% 7% 13%	3280
	21st to end	Night	15% 22% 5% 11% 6% 5% 4 3 4 5% 19%	4862

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	65% 5% 8% 13% 9% 1	2539
	11th to 20th	Day	59% 5% 12% 18% 3 1	2540
	21st to end	Day	78% 3 7% 9% 3	2794
February	1st to 10th	Day	57% 7% 14% 16% 5% 1	1638
	11th to 20th	Day	49% 6% 16% 19% 9% 1	1674
	21st to end	Day	47% 8% 15% 19% 9% 1	1569
March	1st to 10th	Day	40% 6% 10% 25% 18% 1	3138
	11th to 20th	Day	29% 4 13% 43% 10% 1	3364
	21st to end	Day	45% 7% 16% 20% 11% 1	4094
April	1st to 10th	Day	42% 6% 14% 23% 12% 2	2280
	11th to 20th	Day	38% 5% 14% 22% 16% 5%	2252
	21st to end	Day	38% 6% 11% 26% 16% 4	2527
May	1st to 10th	Day	27% 5% 7% 25% 30% 6%	4420
	11th to 20th	Day	23% 7% 9% 36% 20% 5%	4380
	21st to end	Day	43% 6% 12% 26% 12% 2	4814
June	1st to 10th	Day	36% 5% 9% 26% 17% 6%	2660
	11th to 20th	Day	32% 5% 9% 29% 19% 6%	2660
	21st to end	Day	25% 4 9% 30% 25% 8%	2660
July	1st to 10th	Day	11% 3 4 16% 29% 36%	4351
	11th to 20th	Day	13% 2 3 12% 24% 46%	4345
	21st to end	Day	11% 2 3 22% 35% 27%	4639
August	1st to 10th	Day	13% 3 5% 22% 39% 19%	4384
	11th to 20th	Day	16% 4 11% 36% 27% 7%	4221
	21st to end	Day	24% 3 8% 29% 29% 7%	4186
September	1st to 10th	Day	16% 3 8% 31% 32% 10%	2280
	11th to 20th	Day	27% 5% 11% 26% 24% 7%	2271
	21st to end	Day	28% 3 16% 29% 18% 5%	2062
October	1st to 10th	Day	24% 4 13% 37% 21% 2	3180
	11th to 20th	Day	34% 6% 18% 23% 19% 1	3140
	21st to end	Day	39% 5% 12% 25% 15% 4	3101
November	1st to 10th	Day	49% 7% 14% 18% 11% 1	1719
	11th to 20th	Day	53% 6% 14% 18% 7% 2	1520
	21st to end	Day	57% 7% 14% 13% 8% 1	1520
December	1st to 10th	Day	57% 6% 13% 16% 8%	1520
	11th to 20th	Day	70% 6% 10% 8% 5%	1928
	21st to end	Day	72% 5% 7% 11% 6%	2794
January	1st to 10th	Night	67% 5% 10% 12% 5% 1	4406
	11th to 20th	Night	56% 5% 14% 19% 6%	4420
	21st to end	Night	78% 4 7% 8% 2 1	4862
February	1st to 10th	Night	53% 8% 16% 16% 6% 1	2540
	11th to 20th	Night	44% 9% 17% 19% 9% 1	2404
	21st to end	Night	47% 9% 12% 21% 10% 1	1884
March	1st to 10th	Night	39% 6% 12% 25% 15% 2	3736
	11th to 20th	Night	27% 4 15% 39% 13% 1	3614
	21st to end	Night	48% 7% 16% 24% 4 1	3558
April	1st to 10th	Night	40% 6% 15% 26% 11% 2	1900
	11th to 20th	Night	35% 6% 12% 27% 17% 3	1879
	21st to end	Night	34% 5% 11% 29% 18% 2	1649
May	1st to 10th	Night	26% 4 8% 23% 35% 4	2540
	11th to 20th	Night	22% 5% 9% 35% 27% 3	2516
	21st to end	Night	27% 6% 16% 38% 12% 1	2762
June	1st to 10th	Night	33% 6% 9% 28% 19% 5%	1520
	11th to 20th	Night	29% 5% 12% 31% 20% 3	1520
	21st to end	Night	21% 4 10% 32% 27% 6%	1520
July	1st to 10th	Night	9% 2 5% 17% 30% 37%	2500
	11th to 20th	Night	7% 2 4 15% 26% 46%	2492
	21st to end	Night	8% 2 4 24% 32% 30%	2674
August	1st to 10th	Night	16% 4 6% 23% 29% 22%	2521
	11th to 20th	Night	16% 5% 11% 37% 25% 6%	2674
	21st to end	Night	21% 3 8% 29% 29% 9%	3490
September	1st to 10th	Night	17% 3 8% 28% 32% 11%	1900
	11th to 20th	Night	23% 4 10% 28% 27% 8%	1909
	21st to end	Night	25% 4 13% 34% 17% 7%	2116
October	1st to 10th	Night	25% 5% 10% 40% 19% 1	3800
	11th to 20th	Night	33% 6% 14% 28% 18% 1	3797
	21st to end	Night	40% 5% 12% 27% 13% 3	4457
November	1st to 10th	Night	47% 6% 17% 18% 9% 2	2576
	11th to 20th	Night	48% 8% 15% 19% 8% 2	2666
	21st to end	Night	57% 6% 13% 16% 8% 1	2660
December	1st to 10th	Night	56% 6% 14% 19% 4	2660
	11th to 20th	Night	73% 7% 9% 8% 3	3276
	21st to end	Night	69% 5% 7% 10% 8% 1	4862

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	25% 11% 18% 25% 16% 5%	180
	11th to 20th	Day	22% 8% 19% 28% 17% 6%	180
	21st to end	Day	22% 8% 17% 31% 18% 4	198
February	1st to 10th	Day	12% 11% 32% 31% 12% 2	298
	11th to 20th	Day	12% 13% 33% 29% 10% 4	365
	21st to end	Day	9% 17% 32% 25% 14% 2	382
March	1st to 10th	Day	10% 15% 32% 27% 14% 2	460
	11th to 20th	Day	10% 17% 21% 28% 21% 3	460
	21st to end	Day	10% 22% 27% 27% 13% 1	506
April	1st to 10th	Day	14% 21% 27% 25% 10% 3	460
	11th to 20th	Day	9% 27% 28% 22% 10% 5%	452
	21st to end	Day	10% 19% 29% 23% 15% 4	460
May	1st to 10th	Day	8% 14% 29% 31% 15% 3	463
	11th to 20th	Day	13% 14% 22% 27% 19% 5%	488
	21st to end	Day	9% 14% 22% 29% 19% 7%	529
June	1st to 10th	Day	11% 17% 29% 24% 17% 3	490
	11th to 20th	Day	9% 18% 33% 27% 11% 3	490
	21st to end	Day	6% 12% 24% 30% 22% 7%	490
July	1st to 10th	Day	5% 9% 24% 37% 22% 3	486
	11th to 20th	Day	3 10% 27% 30% 24% 6%	484
	21st to end	Day	3 10% 19% 37% 23% 8%	531
August	1st to 10th	Day	5% 5% 22% 34% 24% 9%	487
	11th to 20th	Day	3 6% 22% 33% 26% 11%	477
	21st to end	Day	4 12% 23% 31% 20% 10%	539
September	1st to 10th	Day	4 9% 23% 29% 23% 10%	490
	11th to 20th	Day	7% 11% 22% 30% 22% 7%	490
	21st to end	Day	9% 13% 24% 30% 19% 4	490
October	1st to 10th	Day	8% 16% 22% 27% 18% 8%	490
	11th to 20th	Day	10% 12% 21% 27% 21% 8%	481
	21st to end	Day	15% 12% 26% 29% 14% 3	330
November	1st to 10th	Day	16% 12% 22% 31% 18% 1	277
	11th to 20th	Day	14% 19% 22% 19% 16% 9%	180
	21st to end	Day	12% 8% 23% 31% 21% 6%	180
December	1st to 10th	Day	21% 9% 18% 22% 19% 11%	180
	11th to 20th	Day	16% 9% 22% 36% 13% 5%	180
	21st to end	Day	18% 6% 19% 35% 18% 5%	198
January	1st to 10th	Night	21% 9% 23% 28% 15% 3	760
	11th to 20th	Night	21% 8% 16% 36% 17% 3	760
	21st to end	Night	19% 5% 18% 36% 20% 3	836
February	1st to 10th	Night	16% 6% 22% 39% 14% 2	760
	11th to 20th	Night	14% 6% 24% 36% 19% 2	744
	21st to end	Night	11% 10% 27% 31% 16% 4	628
March	1st to 10th	Night	14% 6% 22% 40% 17% 2	760
	11th to 20th	Night	9% 9% 24% 34% 21% 2	760
	21st to end	Night	12% 9% 28% 38% 13% 1	836
April	1st to 10th	Night	9% 10% 22% 36% 21% 2	760
	11th to 20th	Night	8% 9% 29% 33% 18% 2	751
	21st to end	Night	9% 9% 30% 33% 17% 2	509
May	1st to 10th	Night	5% 6% 26% 41% 19% 2	380
	11th to 20th	Night	10% 5% 17% 39% 26% 2	374
	21st to end	Night	8% 5% 14% 42% 28% 2	411
June	1st to 10th	Night	8% 7% 21% 43% 21% 1	380
	11th to 20th	Night	5% 8% 25% 42% 19% 1	380
	21st to end	Night	2 6% 20% 43% 27% 2	380
July	1st to 10th	Night	2 3 15% 49% 30% 1	370
	11th to 20th	Night	2 4 20% 47% 27% 1	368
	21st to end	Night	1 4 15% 46% 34% 1	416
August	1st to 10th	Night	2 3 12% 39% 42% 3	378
	11th to 20th	Night	2 2 12% 38% 41% 6%	464
	21st to end	Night	3 4 17% 41% 30% 4	828
September	1st to 10th	Night	3 4 18% 38% 32% 5%	760
	11th to 20th	Night	6% 5% 16% 30% 34% 9%	760
	21st to end	Night	6% 6% 18% 39% 26% 6%	760
October	1st to 10th	Night	11% 6% 16% 38% 26% 3	760
	11th to 20th	Night	7% 8% 21% 37% 23% 4	760
	21st to end	Night	14% 8% 22% 36% 16% 3	836
November	1st to 10th	Night	19% 6% 22% 39% 13%	780
	11th to 20th	Night	16% 8% 24% 33% 16% 4	762
	21st to end	Night	16% 8% 19% 35% 19% 4	760
December	1st to 10th	Night	18% 7% 18% 37% 18% 2	760
	11th to 20th	Night	18% 6% 19% 41% 14% 1	760
	21st to end	Night	21% 8% 19% 40% 10% 1	836

Page generated at 2024-11-08 03:44:44. Version ac07

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