Blazer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blazer Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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	13% 6% 2 6% 4 4 4 4 6% 8% 42%	101371
	Night	13% 7% 2 6% 4 4 4 3 5% 7% 45%	98078
Transparency	Day	37% 7% 11% 21% 18% 6%	105161
	Night	36% 6% 10% 20% 20% 7%	102427
Seeing	Day	16% 10% 23% 25% 18% 9%	15028
	Night	16% 8% 23% 28% 20% 4	24631

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	16% 13% 3 6% 3 3 4 2 4 6% 39%	2547
	11th to 20th	Day	21% 8% 3 6% 3 2 2 2 3 5% 45%	2984
	21st to end	Day	23% 10% 2 4 2 2 2 2 4 6% 43%	3476
February	1st to 10th	Day	19% 11% 3 6% 4 3 3 3 4 6% 40%	1900
	11th to 20th	Day	22% 7% 2 6% 4 4 3 2 4 5% 40%	1848
	21st to end	Day	22% 8% 3 6% 4 4 3 2 5% 5% 39%	1570
March	1st to 10th	Day	25% 8% 2 7% 4 4 4 4 4 5% 33%	3120
	11th to 20th	Day	14% 7% 3 6% 4 3 5% 4 6% 7% 42%	3255
	21st to end	Day	15% 7% 3 7% 5% 5% 4 4 6% 7% 38%	4165
April	1st to 10th	Day	13% 6% 2 5% 5% 4 3 4 5% 7% 47%	2280
	11th to 20th	Day	15% 6% 2 5% 4 4 4 3 5% 6% 46%	2254
	21st to end	Day	10% 5% 2 6% 4 5% 4 3 6% 10% 47%	2280
May	1st to 10th	Day	12% 5% 2 6% 5% 5% 4 4 6% 8% 43%	3889
	11th to 20th	Day	15% 6% 3 6% 4 4 5% 4 6% 8% 39%	4081
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 4 6% 10% 40%	4476
June	1st to 10th	Day	9% 6% 2 7% 5% 6% 6% 4 8% 10% 37%	2470
	11th to 20th	Day	5% 4 2 6% 5% 6% 5% 4 8% 11% 43%	2601
	21st to end	Day	7% 5% 2 5% 5% 5% 6% 5% 7% 9% 45%	2660
July	1st to 10th	Day	6% 6% 2 9% 6% 7% 7% 6% 9% 12% 30%	4440
	11th to 20th	Day	9% 5% 2 6% 5% 7% 7% 6% 9% 13% 32%	4285
	21st to end	Day	13% 9% 3 9% 7% 7% 7% 5% 7% 9% 25%	4191
August	1st to 10th	Day	3 3 1 5% 3 4 5% 5% 6% 9% 55%	3785
	11th to 20th	Day	6% 4 2 6% 5% 5% 5% 4 7% 11% 46%	3729
	21st to end	Day	7% 4 2 5% 4 5% 5% 3 7% 8% 50%	4180
September	1st to 10th	Day	9% 5% 3 7% 5% 6% 4 4 7% 8% 44%	2280
	11th to 20th	Day	12% 6% 2 7% 5% 5% 4 4 5% 6% 44%	2108
	21st to end	Day	11% 6% 2 5% 4 3 5% 4 4 6% 51%	2090
October	1st to 10th	Day	9% 5% 2 5% 3 4 3 3 4 6% 55%	2090
	11th to 20th	Day	9% 5% 1 5% 4 3 3 3 4 6% 57%	1997
	21st to end	Day	14% 5% 1 4 3 3 4 3 4 5% 54%	2018
November	1st to 10th	Day	11% 5% 2 4 4 4 3 3 4 6% 53%	1762
	11th to 20th	Day	13% 6% 2 5% 3 3 3 3 4 5% 53%	1800
	21st to end	Day	16% 7% 2 5% 3 3 4 4 5% 6% 45%	1773
December	1st to 10th	Day	21% 9% 2 6% 4 4 4 3 4 5% 37%	1710
	11th to 20th	Day	18% 8% 3 6% 4 4 4 2 4 4 43%	2153
	21st to end	Day	17% 9% 3 6% 4 4 5% 3 5% 6% 38%	3124
January	1st to 10th	Night	19% 12% 2 5% 4 3 3 3 4 5% 40%	4378
	11th to 20th	Night	18% 8% 3 7% 3 2 3 2 4 4 45%	3950
	21st to end	Night	22% 12% 2 6% 3 3 3 2 3 3 41%	4180
February	1st to 10th	Night	19% 8% 3 6% 3 3 3 3 4 5% 42%	2280
	11th to 20th	Night	22% 8% 2 5% 5% 3 3 3 3 4 43%	2218
	21st to end	Night	21% 7% 3 6% 5% 3 4 3 5% 6% 37%	1884
March	1st to 10th	Night	24% 11% 2 6% 3 3 3 2 4 5% 35%	3733
	11th to 20th	Night	14% 7% 1 5% 4 3 4 3 6% 8% 46%	3705
	21st to end	Night	18% 8% 3 7% 5% 4 4 3 4 5% 40%	3466
April	1st to 10th	Night	12% 6% 2 5% 4 4 5% 4 5% 7% 47%	1900
	11th to 20th	Night	13% 4 2 5% 4 3 4 3 6% 7% 48%	1875
	21st to end	Night	11% 5% 1 5% 4 4 4 3 4 8% 50%	1900
May	1st to 10th	Night	11% 7% 3 7% 4 3 3 3 5% 8% 45%	3002
	11th to 20th	Night	16% 7% 2 6% 4 3 4 3 6% 7% 42%	2812
	21st to end	Night	8% 4 2 5% 4 4 5% 5% 8% 11% 44%	3079
June	1st to 10th	Night	7% 5% 2 6% 5% 5% 5% 5% 8% 10% 42%	1710
	11th to 20th	Night	4 4 1 4 4 4 5% 4 6% 11% 53%	1572
	21st to end	Night	5% 4 2 5% 4 5% 5% 4 7% 10% 49%	1520
July	1st to 10th	Night	6% 6% 2 7% 6% 6% 6% 5% 7% 12% 37%	2530
	11th to 20th	Night	7% 5% 2 6% 4 5% 5% 5% 8% 13% 40%	2675
	21st to end	Night	9% 9% 4 10% 7% 5% 6% 5% 8% 9% 27%	3358
August	1st to 10th	Night	2 2 1 4 3 3 4 4 7% 10% 61%	3144
	11th to 20th	Night	4 3 1 5% 4 4 5% 4 7% 11% 53%	3100
	21st to end	Night	6% 3 2 5% 3 4 4 4 7% 9% 54%	3476
September	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 5% 8% 48%	1900
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 7% 8% 45%	2052
	21st to end	Night	8% 4 2 5% 3 4 4 4 7% 7% 53%	2090
October	1st to 10th	Night	8% 4 2 4 2 3 3 2 4 6% 62%	2090
	11th to 20th	Night	11% 6% 2 5% 3 2 4 2 4 6% 55%	2178
	21st to end	Night	15% 6% 2 4 2 3 2 2 4 5% 55%	2579
November	1st to 10th	Night	11% 5% 2 4 5% 3 3 3 4 5% 54%	2536
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 7% 53%	2600
	21st to end	Night	16% 6% 2 4 4 3 3 3 4 5% 48%	2562
December	1st to 10th	Night	19% 7% 2 6% 4 4 4 4 4 6% 41%	2470
	11th to 20th	Night	16% 7% 2 6% 3 4 3 3 4 5% 47%	3042
	21st to end	Night	18% 8% 3 6% 4 5% 5% 4 7% 7% 33%	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	47% 4 5% 18% 21% 4	2548
	11th to 20th	Day	44% 4 6% 23% 21% 3	2984
	21st to end	Day	45% 3 7% 19% 20% 5%	3476
February	1st to 10th	Day	47% 3 7% 19% 19% 5%	1900
	11th to 20th	Day	48% 3 5% 18% 19% 7%	1858
	21st to end	Day	48% 4 6% 13% 22% 7%	1570
March	1st to 10th	Day	52% 6% 8% 10% 15% 9%	3120
	11th to 20th	Day	40% 6% 8% 21% 18% 7%	3255
	21st to end	Day	43% 7% 10% 18% 17% 5%	4165
April	1st to 10th	Day	36% 6% 10% 21% 19% 8%	2280
	11th to 20th	Day	37% 5% 7% 22% 21% 7%	2254
	21st to end	Day	33% 6% 10% 25% 23% 3	2280
May	1st to 10th	Day	36% 10% 11% 27% 13% 2	3924
	11th to 20th	Day	40% 8% 14% 25% 12% 1	4085
	21st to end	Day	37% 10% 13% 25% 14% 1	4489
June	1st to 10th	Day	39% 10% 13% 20% 16% 2	2470
	11th to 20th	Day	31% 9% 15% 24% 19% 2	2601
	21st to end	Day	33% 9% 16% 21% 16% 4	2660
July	1st to 10th	Day	40% 13% 20% 20% 6% 1	4371
	11th to 20th	Day	38% 12% 22% 22% 5% 1	4210
	21st to end	Day	53% 11% 13% 17% 6%	4057
August	1st to 10th	Day	22% 9% 13% 34% 21% 1	3773
	11th to 20th	Day	31% 9% 16% 27% 15% 3	3765
	21st to end	Day	29% 9% 13% 22% 23% 4	4179
September	1st to 10th	Day	36% 9% 13% 18% 19% 5%	2280
	11th to 20th	Day	40% 7% 11% 15% 21% 5%	2108
	21st to end	Day	33% 6% 10% 22% 21% 8%	2090
October	1st to 10th	Day	20% 4 5% 15% 28% 27%	3480
	11th to 20th	Day	19% 3 5% 17% 32% 25%	3302
	21st to end	Day	25% 4 4 21% 34% 12%	3308
November	1st to 10th	Day	33% 4 8% 19% 28% 9%	1762
	11th to 20th	Day	33% 4 6% 18% 28% 10%	1800
	21st to end	Day	39% 5% 7% 19% 23% 8%	1773
December	1st to 10th	Day	49% 6% 6% 15% 19% 6%	1710
	11th to 20th	Day	46% 3 7% 18% 22% 5%	2150
	21st to end	Day	46% 5% 9% 20% 18% 2	3124
January	1st to 10th	Night	47% 4 6% 15% 25% 3	4378
	11th to 20th	Night	43% 4 6% 21% 19% 7%	3950
	21st to end	Night	49% 4 3 20% 19% 5%	4180
February	1st to 10th	Night	46% 3 6% 19% 20% 6%	2280
	11th to 20th	Night	47% 4 5% 17% 19% 8%	2219
	21st to end	Night	47% 6% 5% 15% 18% 9%	1884
March	1st to 10th	Night	51% 4 9% 12% 15% 9%	3733
	11th to 20th	Night	35% 5% 9% 21% 20% 10%	3705
	21st to end	Night	47% 4 6% 18% 21% 3	3466
April	1st to 10th	Night	36% 5% 11% 22% 20% 6%	1900
	11th to 20th	Night	35% 4 9% 20% 22% 10%	1875
	21st to end	Night	32% 6% 10% 24% 23% 5%	1900
May	1st to 10th	Night	35% 9% 12% 22% 19% 3	3032
	11th to 20th	Night	39% 8% 13% 25% 13% 2	2813
	21st to end	Night	28% 11% 15% 26% 17% 2	3087
June	1st to 10th	Night	34% 10% 13% 23% 18% 3	1710
	11th to 20th	Night	25% 8% 15% 28% 20% 4	1572
	21st to end	Night	28% 11% 16% 22% 20% 4	1520
July	1st to 10th	Night	36% 12% 23% 19% 7% 2	2490
	11th to 20th	Night	31% 12% 24% 25% 7% 1	2627
	21st to end	Night	49% 12% 16% 16% 6% 1	3251
August	1st to 10th	Night	16% 8% 13% 37% 23% 2	3132
	11th to 20th	Night	24% 9% 20% 29% 16% 2	3130
	21st to end	Night	25% 8% 16% 21% 24% 6%	3476
September	1st to 10th	Night	34% 7% 16% 20% 17% 7%	1900
	11th to 20th	Night	35% 7% 13% 18% 20% 6%	2052
	21st to end	Night	28% 6% 10% 24% 23% 8%	2090
October	1st to 10th	Night	17% 3 6% 17% 31% 26%	3480
	11th to 20th	Night	20% 3 5% 15% 32% 27%	3612
	21st to end	Night	22% 3 4 24% 30% 17%	4239
November	1st to 10th	Night	32% 4 7% 18% 25% 13%	2536
	11th to 20th	Night	32% 4 6% 18% 29% 12%	2600
	21st to end	Night	38% 4 5% 21% 23% 9%	2562
December	1st to 10th	Night	43% 5% 8% 18% 21% 4	2470
	11th to 20th	Night	40% 4 6% 19% 25% 5%	3044
	21st to end	Night	45% 7% 10% 17% 18% 3	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% 24% 29% 14% 3	270
	11th to 20th	Day	33% 21% 28% 13% 4 1	270
	21st to end	Day	26% 23% 37% 11% 2 1	297
February	1st to 10th	Day	28% 22% 33% 13% 3	270
	11th to 20th	Day	36% 19% 32% 10% 1 1	270
	21st to end	Day	35% 24% 32% 8% 1	225
March	1st to 10th	Day	27% 20% 34% 14% 4 1	270
	11th to 20th	Day	22% 22% 37% 15% 3 1	308
	21st to end	Day	25% 15% 34% 19% 6%	506
April	1st to 10th	Day	20% 18% 32% 20% 9% 1	460
	11th to 20th	Day	22% 16% 28% 21% 11% 2	452
	21st to end	Day	16% 13% 31% 27% 13% 1	460
May	1st to 10th	Day	17% 10% 26% 30% 13% 5%	463
	11th to 20th	Day	12% 5% 30% 28% 16% 9%	487
	21st to end	Day	11% 5% 25% 29% 19% 12%	529
June	1st to 10th	Day	12% 4 20% 29% 24% 12%	490
	11th to 20th	Day	7% 2 15% 33% 27% 15%	621
	21st to end	Day	10% 3 15% 30% 30% 13%	680
July	1st to 10th	Day	9% 2 10% 31% 33% 16%	671
	11th to 20th	Day	9% 3 10% 22% 31% 25%	578
	21st to end	Day	10% 2 9% 23% 31% 24%	532
August	1st to 10th	Day	8% 2 10% 27% 32% 21%	486
	11th to 20th	Day	9% 2 12% 29% 32% 17%	479
	21st to end	Day	13% 2 9% 26% 31% 20%	539
September	1st to 10th	Day	10% 3 10% 36% 30% 11%	490
	11th to 20th	Day	12% 3 13% 25% 32% 15%	490
	21st to end	Day	14% 4 15% 30% 29% 8%	490
October	1st to 10th	Day	11% 4 23% 31% 23% 7%	490
	11th to 20th	Day	11% 11% 28% 37% 12% 1	397
	21st to end	Day	20% 13% 25% 30% 11% 1	330
November	1st to 10th	Day	21% 9% 29% 28% 11% 2	300
	11th to 20th	Day	16% 18% 36% 23% 5% 1	300
	21st to end	Day	20% 18% 34% 18% 9% 1	291
December	1st to 10th	Day	31% 18% 30% 16% 3 1	270
	11th to 20th	Day	24% 19% 34% 14% 8%	270
	21st to end	Day	27% 18% 36% 15% 3	297
January	1st to 10th	Night	24% 18% 32% 21% 5%	926
	11th to 20th	Night	25% 16% 30% 23% 7%	811
	21st to end	Night	22% 15% 38% 23% 3	836
February	1st to 10th	Night	25% 12% 33% 25% 5%	760
	11th to 20th	Night	27% 15% 32% 24% 3	743
	21st to end	Night	24% 20% 33% 22% 1	628
March	1st to 10th	Night	21% 15% 30% 28% 5%	760
	11th to 20th	Night	19% 12% 34% 27% 8% 1	757
	21st to end	Night	20% 12% 34% 24% 10%	627
April	1st to 10th	Night	16% 15% 31% 26% 11% 1	570
	11th to 20th	Night	15% 10% 34% 28% 12% 2	563
	21st to end	Night	14% 9% 31% 29% 14% 1	570
May	1st to 10th	Night	12% 4 29% 32% 22% 2	570
	11th to 20th	Night	13% 3 23% 33% 22% 6%	561
	21st to end	Night	9% 1 16% 35% 33% 6%	617
June	1st to 10th	Night	8% 3 14% 34% 33% 8%	570
	11th to 20th	Night	5% 2 12% 29% 42% 10%	570
	21st to end	Night	6% 2 9% 32% 39% 11%	570
July	1st to 10th	Night	5% 1 7% 30% 44% 13%	555
	11th to 20th	Night	7% 2 8% 26% 39% 18%	552
	21st to end	Night	7% 1 8% 26% 43% 15%	624
August	1st to 10th	Night	5% 5% 29% 45% 15%	567
	11th to 20th	Night	7% 1 9% 31% 41% 11%	564
	21st to end	Night	11% 1 10% 28% 40% 11%	627
September	1st to 10th	Night	11% 2 13% 31% 37% 6%	570
	11th to 20th	Night	13% 4 12% 28% 37% 5%	722
	21st to end	Night	9% 3 16% 32% 36% 4	760
October	1st to 10th	Night	9% 4 19% 33% 29% 6%	760
	11th to 20th	Night	14% 7% 23% 36% 18% 2	760
	21st to end	Night	19% 7% 20% 33% 19% 2	836
November	1st to 10th	Night	13% 9% 22% 34% 19% 2	780
	11th to 20th	Night	14% 11% 32% 31% 12% 2	800
	21st to end	Night	20% 9% 30% 28% 12% 1	789
December	1st to 10th	Night	24% 11% 27% 29% 8%	760
	11th to 20th	Night	23% 12% 30% 27% 8%	760
	21st to end	Night	24% 14% 31% 25% 6%	836

Page generated at 2024-11-24 23:22:20. Version ac07

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