Blazny Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blazny Observatory clear sky chart from 2005-11-06 to 2025-01-22.

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	14% 10% 4 8% 5% 5% 5% 4 5% 7% 33%	104751
	Night	15% 12% 4 9% 5% 5% 4 4 5% 6% 30%	104731
Transparency	Day	27% 47% 7% 12% 6%	108230
	Night	30% 46% 8% 11% 5%	109327
Seeing	Day	19% 17% 33% 21% 8% 2	15772
	Night	20% 13% 31% 26% 9% 1	25374

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	12% 16% 7% 15% 7% 7% 5% 5% 5% 6% 13%	2541
	11th to 20th	Day	11% 17% 5% 15% 12% 7% 6% 4 6% 6% 10%	2610
	21st to end	Day	12% 21% 10% 14% 7% 6% 5% 3 4 5% 11%	2791
February	1st to 10th	Day	10% 14% 6% 12% 8% 6% 6% 5% 6% 7% 21%	1643
	11th to 20th	Day	12% 13% 5% 12% 7% 6% 5% 4 4 6% 26%	1765
	21st to end	Day	10% 13% 6% 14% 7% 6% 5% 3 4 7% 25%	1570
March	1st to 10th	Day	11% 13% 4 8% 5% 4 4 2 5% 8% 36%	3118
	11th to 20th	Day	9% 14% 4 9% 7% 5% 5% 3 5% 6% 32%	3447
	21st to end	Day	15% 11% 7% 13% 7% 5% 5% 4 5% 5% 25%	3868
April	1st to 10th	Day	17% 13% 4 8% 6% 5% 5% 3 4 6% 29%	2280
	11th to 20th	Day	19% 10% 3 7% 4 4 4 3 4 6% 34%	2413
	21st to end	Day	16% 10% 3 9% 5% 4 4 3 5% 7% 34%	2470
May	1st to 10th	Day	17% 8% 3 5% 4 4 5% 4 6% 8% 37%	4108
	11th to 20th	Day	11% 7% 3 8% 4 4 4 3 5% 9% 41%	4207
	21st to end	Day	14% 6% 2 5% 4 4 4 3 6% 8% 45%	5083
June	1st to 10th	Day	13% 6% 2 5% 5% 4 4 4 7% 8% 40%	2850
	11th to 20th	Day	12% 7% 2 7% 5% 4 5% 4 6% 9% 40%	2850
	21st to end	Day	15% 7% 3 6% 4 4 3 4 5% 8% 41%	2850
July	1st to 10th	Day	15% 8% 3 6% 4 4 4 4 5% 7% 39%	4700
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 6% 10% 46%	4440
	21st to end	Day	9% 6% 2 5% 4 3 4 4 6% 9% 48%	4814
August	1st to 10th	Day	8% 6% 3 7% 5% 5% 5% 5% 7% 9% 41%	4217
	11th to 20th	Day	13% 5% 2 5% 4 5% 4 4 6% 8% 45%	4044
	21st to end	Day	13% 7% 3 6% 3 4 3 3 5% 7% 46%	4500
September	1st to 10th	Day	16% 6% 2 5% 3 4 4 4 4 7% 44%	2223
	11th to 20th	Day	13% 6% 2 5% 5% 4 5% 4 6% 8% 42%	2090
	21st to end	Day	14% 8% 3 7% 4 5% 5% 4 6% 8% 38%	2090
October	1st to 10th	Day	18% 9% 3 7% 5% 4 4 3 5% 7% 35%	2048
	11th to 20th	Day	20% 12% 3 11% 7% 5% 4 4 6% 7% 21%	1822
	21st to end	Day	22% 12% 3 9% 7% 5% 6% 4 5% 7% 20%	1881
November	1st to 10th	Day	19% 12% 4 9% 5% 4 4 3 6% 7% 26%	1762
	11th to 20th	Day	15% 16% 7% 11% 6% 5% 6% 4 5% 5% 19%	1724
	21st to end	Day	21% 19% 5% 11% 7% 6% 5% 3 4 4 14%	1555
December	1st to 10th	Day	14% 19% 5% 12% 7% 6% 6% 5% 6% 5% 15%	2280
	11th to 20th	Day	17% 16% 6% 12% 7% 5% 5% 4 6% 5% 16%	2621
	21st to end	Day	26% 23% 7% 11% 5% 4 3 2 4 4 13%	3476
January	1st to 10th	Night	15% 16% 5% 13% 6% 5% 5% 4 6% 8% 18%	4629
	11th to 20th	Night	12% 15% 7% 15% 9% 7% 6% 5% 5% 5% 14%	4580
	21st to end	Night	16% 19% 7% 15% 7% 5% 5% 3 4 4 14%	4899
February	1st to 10th	Night	9% 16% 6% 12% 8% 6% 5% 5% 5% 5% 23%	2537
	11th to 20th	Night	10% 13% 5% 12% 8% 6% 5% 3 6% 6% 26%	2300
	21st to end	Night	12% 14% 5% 12% 8% 5% 5% 4 5% 5% 25%	1884
March	1st to 10th	Night	15% 10% 3 7% 4 4 3 3 4 7% 39%	3722
	11th to 20th	Night	10% 12% 5% 8% 5% 5% 3 3 4 7% 38%	3511
	21st to end	Night	15% 9% 6% 8% 6% 4 5% 4 6% 6% 32%	3791
April	1st to 10th	Night	18% 11% 4 8% 5% 5% 5% 4 5% 6% 29%	1900
	11th to 20th	Night	19% 9% 4 6% 4 4 4 3 5% 6% 35%	1716
	21st to end	Night	18% 9% 4 7% 6% 4 3 3 5% 6% 36%	1710
May	1st to 10th	Night	18% 8% 3 6% 5% 4 5% 4 4 6% 36%	2833
	11th to 20th	Night	13% 7% 3 8% 6% 5% 4 4 7% 6% 38%	2674
	21st to end	Night	16% 7% 2 7% 4 3 4 4 6% 7% 41%	2501
June	1st to 10th	Night	13% 6% 2 6% 5% 4 4 4 7% 10% 39%	1330
	11th to 20th	Night	12% 7% 2 6% 4 5% 5% 4 7% 8% 41%	1330
	21st to end	Night	13% 8% 3 6% 4 3 4 3 6% 6% 43%	1330
July	1st to 10th	Night	14% 6% 2 7% 3 4 5% 4 6% 8% 42%	2265
	11th to 20th	Night	8% 5% 1 6% 4 3 5% 4 5% 7% 52%	2530
	21st to end	Night	10% 6% 2 5% 3 4 4 3 5% 8% 50%	2750
August	1st to 10th	Night	9% 7% 3 6% 5% 5% 5% 4 6% 9% 44%	2702
	11th to 20th	Night	12% 5% 2 5% 4 3 3 3 5% 9% 49%	2785
	21st to end	Night	10% 5% 2 6% 4 3 4 2 4 6% 52%	3151
September	1st to 10th	Night	12% 6% 2 6% 4 4 5% 4 5% 7% 46%	1938
	11th to 20th	Night	15% 5% 2 5% 4 3 3 4 5% 8% 46%	2090
	21st to end	Night	18% 7% 2 6% 3 5% 4 4 6% 7% 39%	2090
October	1st to 10th	Night	18% 8% 2 6% 3 4 3 3 5% 7% 40%	2130
	11th to 20th	Night	20% 11% 2 8% 6% 5% 4 4 4 6% 30%	2356
	21st to end	Night	25% 12% 3 9% 6% 4 4 3 4 5% 24%	2717
November	1st to 10th	Night	18% 11% 3 8% 5% 4 4 4 5% 7% 31%	2536
	11th to 20th	Night	18% 15% 5% 10% 6% 5% 5% 4 5% 6% 21%	2675
	21st to end	Night	19% 19% 5% 10% 6% 4 4 3 5% 5% 18%	2841
December	1st to 10th	Night	13% 17% 6% 12% 7% 6% 6% 5% 6% 6% 16%	4910
	11th to 20th	Night	15% 18% 5% 13% 6% 5% 5% 3 5% 6% 18%	5586
	21st to end	Night	24% 23% 8% 12% 4 3 3 2 3 4 13%	7502

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	44% 42% 11% 3 1	2542
	11th to 20th	Day	44% 44% 7% 4 1	2610
	21st to end	Day	51% 42% 4 2 1	2791
February	1st to 10th	Day	21% 67% 5% 5% 2	1643
	11th to 20th	Day	22% 65% 4 5% 4	1774
	21st to end	Day	21% 65% 4 6% 4	1570
March	1st to 10th	Day	27% 43% 12% 11% 7% 1	3120
	11th to 20th	Day	34% 41% 9% 12% 3 1	3447
	21st to end	Day	40% 43% 6% 5% 6% 1	3868
April	1st to 10th	Day	20% 65% 5% 6% 3	2280
	11th to 20th	Day	18% 66% 3 7% 5% 1	2413
	21st to end	Day	17% 66% 3 8% 6% 1	2470
May	1st to 10th	Day	25% 42% 8% 15% 8% 1	4120
	11th to 20th	Day	22% 42% 9% 18% 9%	4211
	21st to end	Day	23% 41% 9% 12% 12% 2	5083
June	1st to 10th	Day	15% 66% 4 9% 5% 2	2850
	11th to 20th	Day	17% 65% 5% 8% 5% 1	2850
	21st to end	Day	15% 64% 6% 10% 5% 1	2850
July	1st to 10th	Day	31% 39% 9% 13% 7% 1	4627
	11th to 20th	Day	19% 39% 12% 25% 5% 1	4365
	21st to end	Day	18% 38% 6% 22% 15% 1	4662
August	1st to 10th	Day	21% 40% 9% 22% 8%	4202
	11th to 20th	Day	26% 39% 9% 20% 6%	4083
	21st to end	Day	25% 39% 12% 19% 5%	4499
September	1st to 10th	Day	17% 61% 7% 10% 4	2223
	11th to 20th	Day	14% 61% 6% 14% 5%	2090
	21st to end	Day	17% 62% 8% 10% 4	2090
October	1st to 10th	Day	20% 39% 10% 20% 11%	3399
	11th to 20th	Day	28% 39% 9% 22% 2	2999
	21st to end	Day	41% 39% 7% 11% 2	3081
November	1st to 10th	Day	26% 57% 7% 8% 2	1762
	11th to 20th	Day	29% 59% 5% 5% 2	1724
	21st to end	Day	32% 59% 4 4 1	1555
December	1st to 10th	Day	45% 40% 8% 6% 1	2280
	11th to 20th	Day	46% 35% 8% 8% 3	2621
	21st to end	Day	56% 28% 4 6% 5%	3476
January	1st to 10th	Night	38% 40% 11% 7% 3	4629
	11th to 20th	Night	43% 42% 9% 5% 1	4580
	21st to end	Night	48% 43% 6% 3 1	4899
February	1st to 10th	Night	21% 66% 4 6% 3	2537
	11th to 20th	Night	20% 65% 5% 8% 2	2302
	21st to end	Night	19% 66% 5% 5% 5%	1884
March	1st to 10th	Night	26% 42% 12% 14% 6%	3733
	11th to 20th	Night	26% 42% 10% 16% 6% 1	3512
	21st to end	Night	32% 43% 8% 12% 4 1	3791
April	1st to 10th	Night	21% 65% 3 6% 4	1900
	11th to 20th	Night	18% 66% 3 8% 4 2	1716
	21st to end	Night	19% 65% 4 7% 5% 1	1710
May	1st to 10th	Night	28% 43% 6% 14% 7% 1	2840
	11th to 20th	Night	25% 43% 5% 19% 8%	2675
	21st to end	Night	27% 42% 8% 10% 8% 4	2502
June	1st to 10th	Night	14% 66% 4 8% 7% 1	1330
	11th to 20th	Night	17% 66% 3 7% 4 2	1330
	21st to end	Night	15% 64% 4 12% 4 2	1330
July	1st to 10th	Night	31% 37% 9% 14% 9% 1	2229
	11th to 20th	Night	19% 37% 12% 22% 10%	2482
	21st to end	Night	19% 38% 9% 19% 15% 2	2662
August	1st to 10th	Night	24% 38% 7% 20% 10%	2693
	11th to 20th	Night	24% 40% 8% 20% 6% 1	2812
	21st to end	Night	21% 39% 8% 24% 8%	3151
September	1st to 10th	Night	15% 62% 6% 11% 6%	1938
	11th to 20th	Night	14% 61% 6% 13% 5% 1	2090
	21st to end	Night	17% 62% 7% 11% 4	2090
October	1st to 10th	Night	25% 40% 9% 20% 7%	3559
	11th to 20th	Night	23% 39% 13% 20% 6%	3905
	21st to end	Night	34% 40% 12% 13% 2	4467
November	1st to 10th	Night	26% 57% 7% 7% 3	2536
	11th to 20th	Night	26% 59% 8% 5% 2	2675
	21st to end	Night	31% 59% 5% 5% 1	2841
December	1st to 10th	Night	41% 41% 10% 6% 1	4910
	11th to 20th	Night	44% 35% 10% 6% 4	5585
	21st to end	Night	59% 28% 4 7% 3	7502

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	21% 16% 41% 16% 6%	280
	11th to 20th	Day	23% 17% 43% 12% 6%	300
	21st to end	Day	25% 15% 35% 21% 3 1	300
February	1st to 10th	Day	21% 28% 33% 13% 4 1	270
	11th to 20th	Day	22% 33% 30% 13% 2	270
	21st to end	Day	22% 32% 33% 12%	225
March	1st to 10th	Day	19% 30% 33% 16% 2	270
	11th to 20th	Day	21% 19% 36% 17% 5% 1	440
	21st to end	Day	27% 19% 27% 19% 7% 1	506
April	1st to 10th	Day	25% 18% 35% 16% 5% 1	460
	11th to 20th	Day	30% 22% 23% 15% 8% 2	452
	21st to end	Day	24% 20% 30% 17% 7% 2	460
May	1st to 10th	Day	24% 18% 32% 15% 9% 2	463
	11th to 20th	Day	19% 16% 36% 20% 7% 3	561
	21st to end	Day	14% 16% 36% 24% 8% 2	734
June	1st to 10th	Day	14% 17% 37% 24% 7% 1	680
	11th to 20th	Day	16% 16% 37% 22% 6% 2	680
	21st to end	Day	19% 14% 32% 25% 8% 2	680
July	1st to 10th	Day	10% 11% 39% 27% 9% 3	671
	11th to 20th	Day	12% 12% 35% 27% 10% 4	668
	21st to end	Day	11% 9% 34% 28% 13% 4	739
August	1st to 10th	Day	11% 8% 32% 31% 13% 5%	561
	11th to 20th	Day	13% 7% 23% 31% 17% 9%	479
	21st to end	Day	17% 10% 29% 26% 15% 4	539
September	1st to 10th	Day	16% 14% 26% 24% 15% 4	490
	11th to 20th	Day	14% 11% 27% 30% 14% 4	490
	21st to end	Day	18% 14% 23% 30% 12% 3	490
October	1st to 10th	Day	21% 20% 31% 16% 11% 2	490
	11th to 20th	Day	22% 22% 34% 18% 3 1	412
	21st to end	Day	32% 21% 33% 12% 2	330
November	1st to 10th	Day	24% 22% 36% 14% 3 1	300
	11th to 20th	Day	22% 28% 34% 10% 5% 1	262
	21st to end	Day	25% 27% 38% 10% 1	200
December	1st to 10th	Day	29% 16% 34% 15% 5% 2	200
	11th to 20th	Day	30% 26% 32% 10% 3 1	200
	21st to end	Day	32% 23% 30% 10% 5%	220
January	1st to 10th	Night	22% 18% 34% 22% 4	1000
	11th to 20th	Night	22% 17% 34% 21% 7%	1000
	21st to end	Night	21% 12% 36% 23% 7%	1051
February	1st to 10th	Night	17% 19% 36% 24% 5%	827
	11th to 20th	Night	18% 20% 32% 23% 6%	743
	21st to end	Night	19% 19% 36% 21% 4	628
March	1st to 10th	Night	18% 14% 40% 21% 6% 1	760
	11th to 20th	Night	18% 18% 35% 22% 6%	760
	21st to end	Night	19% 14% 34% 27% 6%	822
April	1st to 10th	Night	21% 13% 32% 28% 4 1	570
	11th to 20th	Night	23% 13% 29% 27% 8% 1	563
	21st to end	Night	22% 11% 34% 24% 8% 1	570
May	1st to 10th	Night	18% 11% 32% 29% 9% 1	570
	11th to 20th	Night	18% 8% 32% 31% 10% 1	561
	21st to end	Night	13% 10% 33% 31% 12%	472
June	1st to 10th	Night	14% 11% 33% 35% 8%	380
	11th to 20th	Night	13% 10% 30% 34% 13% 1	380
	21st to end	Night	17% 8% 28% 35% 11% 1	380
July	1st to 10th	Night	11% 5% 28% 41% 13% 1	398
	11th to 20th	Night	9% 6% 26% 34% 22% 3	552
	21st to end	Night	13% 4 23% 38% 20% 2	624
August	1st to 10th	Night	12% 4 27% 37% 18% 1	567
	11th to 20th	Night	10% 5% 21% 34% 27% 3	564
	21st to end	Night	14% 5% 24% 40% 17% 1	627
September	1st to 10th	Night	15% 7% 26% 30% 19% 3	608
	11th to 20th	Night	15% 8% 28% 29% 17% 3	760
	21st to end	Night	20% 8% 25% 29% 15% 3	760
October	1st to 10th	Night	21% 9% 28% 28% 12% 1	760
	11th to 20th	Night	25% 17% 28% 23% 6%	760
	21st to end	Night	32% 12% 29% 22% 4	836
November	1st to 10th	Night	24% 16% 33% 21% 6% 1	780
	11th to 20th	Night	24% 22% 29% 21% 5%	800
	21st to end	Night	29% 19% 30% 18% 4	841
December	1st to 10th	Night	23% 19% 32% 19% 6% 1	1000
	11th to 20th	Night	27% 18% 34% 15% 5% 1	1000
	21st to end	Night	32% 17% 27% 18% 5%	1100

Page generated at 2025-01-19 03:06:44. Version ac07

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