Black River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black River Observatory clear sky chart from 2005-11-06 to 2024-11-25.

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% 10% 3 8% 5% 5% 5% 4 6% 7% 34%	101318
	Night	14% 10% 4 8% 5% 4 4 4 5% 7% 35%	98122
Transparency	Day	46% 7% 13% 21% 11% 1	104934
	Night	47% 7% 13% 21% 11% 1	102646
Seeing	Day	16% 11% 29% 25% 14% 5%	15360
	Night	18% 9% 30% 29% 12% 1	24861

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	15% 18% 7% 11% 5% 5% 5% 4 5% 4 22%	2527
	11th to 20th	Day	15% 20% 7% 12% 8% 6% 4 3 5% 6% 14%	2539
	21st to end	Day	24% 19% 7% 10% 5% 5% 4 3 4 4 16%	3124
February	1st to 10th	Day	14% 15% 5% 13% 8% 6% 6% 4 5% 5% 20%	1710
	11th to 20th	Day	14% 14% 5% 11% 7% 5% 4 4 6% 5% 26%	1739
	21st to end	Day	14% 16% 5% 13% 6% 5% 4 4 4 4 27%	1570
March	1st to 10th	Day	17% 15% 5% 9% 6% 4 3 2 4 5% 29%	3244
	11th to 20th	Day	11% 14% 5% 9% 6% 5% 5% 4 5% 6% 30%	3480
	21st to end	Day	18% 12% 3 10% 5% 5% 5% 3 5% 6% 27%	3815
April	1st to 10th	Day	15% 13% 4 8% 5% 4 4 4 5% 7% 30%	2175
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 4 6% 7% 36%	2442
	21st to end	Day	17% 9% 3 8% 5% 5% 4 4 5% 6% 34%	2470
May	1st to 10th	Day	15% 8% 3 8% 5% 4 4 4 5% 8% 36%	4082
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 34%	4081
	21st to end	Day	9% 7% 2 7% 5% 4 4 4 5% 8% 46%	4603
June	1st to 10th	Day	10% 7% 3 6% 5% 4 5% 5% 7% 9% 40%	2808
	11th to 20th	Day	10% 6% 2 6% 5% 5% 6% 5% 5% 9% 43%	2850
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 9% 40%	2850
July	1st to 10th	Day	10% 5% 3 7% 5% 5% 6% 5% 8% 9% 38%	4520
	11th to 20th	Day	8% 5% 2 6% 5% 4 5% 4 7% 10% 46%	4440
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 8% 10% 42%	4480
August	1st to 10th	Day	13% 5% 3 6% 5% 5% 6% 5% 7% 9% 38%	4104
	11th to 20th	Day	8% 6% 3 7% 5% 6% 6% 5% 7% 10% 38%	4044
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 5% 7% 9% 39%	4532
September	1st to 10th	Day	10% 6% 3 6% 5% 5% 5% 5% 7% 7% 41%	2162
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 3 6% 8% 47%	2090
	21st to end	Day	16% 7% 2 7% 4 5% 4 4 7% 9% 35%	2090
October	1st to 10th	Day	12% 7% 2 7% 5% 4 5% 4 5% 7% 40%	1999
	11th to 20th	Day	18% 9% 3 8% 5% 5% 5% 3 4 7% 33%	1900
	21st to end	Day	19% 11% 3 7% 5% 5% 5% 3 5% 7% 29%	1970
November	1st to 10th	Day	13% 8% 2 9% 6% 6% 4 4 6% 8% 34%	1762
	11th to 20th	Day	13% 11% 4 9% 7% 5% 4 4 6% 7% 29%	1755
	21st to end	Day	17% 13% 6% 9% 5% 4 4 4 5% 6% 27%	1552
December	1st to 10th	Day	14% 14% 5% 12% 6% 6% 6% 4 5% 5% 23%	1520
	11th to 20th	Day	16% 15% 5% 9% 6% 5% 4 3 5% 6% 25%	1792
	21st to end	Day	26% 21% 7% 9% 6% 4 3 3 5% 5% 12%	2497
January	1st to 10th	Night	16% 14% 6% 11% 6% 4 4 3 4 6% 26%	4428
	11th to 20th	Night	13% 17% 7% 14% 8% 7% 5% 4 5% 4 17%	4427
	21st to end	Night	22% 17% 8% 12% 5% 4 3 3 3 5% 19%	4532
February	1st to 10th	Night	14% 17% 5% 11% 7% 6% 4 4 4 5% 22%	2470
	11th to 20th	Night	13% 14% 5% 10% 6% 4 4 4 5% 6% 28%	2325
	21st to end	Night	18% 11% 4 11% 7% 5% 4 3 5% 5% 27%	1884
March	1st to 10th	Night	14% 15% 4 8% 5% 4 4 3 4 6% 35%	3608
	11th to 20th	Night	10% 8% 3 6% 5% 5% 5% 5% 6% 8% 39%	3480
	21st to end	Night	16% 9% 3 8% 5% 4 4 3 4 5% 38%	3817
April	1st to 10th	Night	19% 11% 3 7% 5% 3 3 3 5% 8% 34%	2021
	11th to 20th	Night	19% 6% 3 6% 4 5% 4 3 6% 7% 37%	1687
	21st to end	Night	17% 8% 3 6% 5% 4 4 4 7% 7% 36%	1710
May	1st to 10th	Night	16% 8% 3 7% 4 4 4 4 6% 8% 36%	2813
	11th to 20th	Night	13% 8% 2 7% 5% 5% 5% 4 5% 6% 40%	2812
	21st to end	Night	11% 5% 1 5% 3 4 4 3 6% 8% 50%	2934
June	1st to 10th	Night	12% 5% 2 6% 4 4 4 5% 6% 8% 45%	1367
	11th to 20th	Night	9% 5% 2 6% 4 5% 4 4 6% 9% 45%	1330
	21st to end	Night	8% 5% 2 5% 5% 5% 4 4 5% 8% 48%	1330
July	1st to 10th	Night	7% 5% 2 6% 4 4 4 4 6% 11% 48%	2431
	11th to 20th	Night	9% 4 1 5% 3 4 4 4 5% 8% 52%	2530
	21st to end	Night	4 4 1 6% 5% 6% 6% 5% 8% 10% 47%	3069
August	1st to 10th	Night	10% 6% 2 7% 3 4 4 4 6% 8% 46%	2825
	11th to 20th	Night	9% 7% 3 7% 4 4 4 4 5% 7% 45%	2785
	21st to end	Night	7% 6% 2 6% 5% 5% 5% 4 6% 8% 46%	3124
September	1st to 10th	Night	10% 6% 2 7% 4 5% 5% 4 5% 7% 46%	1995
	11th to 20th	Night	9% 5% 2 5% 3 3 4 4 4 6% 54%	2090
	21st to end	Night	16% 6% 2 6% 4 4 5% 3 5% 7% 42%	2090
October	1st to 10th	Night	13% 7% 3 7% 4 3 4 3 5% 8% 44%	2180
	11th to 20th	Night	19% 8% 2 8% 4 4 4 3 5% 6% 36%	2280
	21st to end	Night	21% 9% 3 7% 4 4 5% 3 5% 7% 30%	2627
November	1st to 10th	Night	13% 9% 3 7% 4 4 4 3 5% 7% 41%	2536
	11th to 20th	Night	15% 11% 3 9% 5% 5% 5% 4 6% 7% 30%	2642
	21st to end	Night	19% 13% 3 8% 5% 4 4 4 5% 5% 29%	2723
December	1st to 10th	Night	16% 14% 5% 11% 6% 5% 4 4 5% 7% 23%	2660
	11th to 20th	Night	14% 14% 5% 11% 6% 5% 4 3 6% 7% 25%	3393
	21st to end	Night	26% 21% 5% 9% 5% 4 3 3 4 5% 14%	5167

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	64% 8% 10% 13% 4 1	2528
	11th to 20th	Day	71% 7% 11% 8% 3	2539
	21st to end	Day	71% 5% 12% 7% 3	3124
February	1st to 10th	Day	65% 6% 10% 13% 6%	1710
	11th to 20th	Day	57% 7% 10% 17% 8% 1	1748
	21st to end	Day	60% 5% 12% 14% 7% 2	1570
March	1st to 10th	Day	58% 5% 12% 18% 5% 1	3244
	11th to 20th	Day	51% 7% 14% 19% 8% 1	3480
	21st to end	Day	55% 8% 12% 14% 10% 2	3815
April	1st to 10th	Day	52% 6% 13% 19% 10% 1	2175
	11th to 20th	Day	47% 6% 12% 19% 14% 2	2442
	21st to end	Day	49% 7% 13% 16% 12% 2	2470
May	1st to 10th	Day	44% 8% 12% 20% 13% 3	4120
	11th to 20th	Day	45% 9% 15% 21% 9% 1	4085
	21st to end	Day	35% 7% 11% 18% 23% 5%	4617
June	1st to 10th	Day	38% 8% 14% 25% 14% 1	2808
	11th to 20th	Day	37% 7% 14% 24% 16% 2	2850
	21st to end	Day	38% 8% 14% 24% 15% 1	2850
July	1st to 10th	Day	39% 8% 15% 21% 15% 2	4451
	11th to 20th	Day	30% 8% 13% 34% 13% 1	4365
	21st to end	Day	34% 9% 16% 20% 19% 1	4338
August	1st to 10th	Day	39% 9% 14% 22% 14% 1	4091
	11th to 20th	Day	37% 9% 15% 28% 9% 1	4083
	21st to end	Day	37% 8% 14% 29% 11% 1	4531
September	1st to 10th	Day	38% 9% 15% 24% 13% 1	2162
	11th to 20th	Day	33% 7% 14% 32% 13% 1	2090
	21st to end	Day	44% 8% 14% 23% 10% 1	2090
October	1st to 10th	Day	32% 6% 11% 32% 16% 2	3324
	11th to 20th	Day	42% 5% 12% 23% 17% 1	3140
	21st to end	Day	46% 6% 14% 22% 11%	3220
November	1st to 10th	Day	47% 8% 12% 22% 9% 1	1762
	11th to 20th	Day	53% 6% 14% 16% 9%	1755
	21st to end	Day	57% 6% 13% 18% 5% 1	1552
December	1st to 10th	Day	61% 8% 14% 13% 4	1520
	11th to 20th	Day	58% 7% 14% 16% 5%	1788
	21st to end	Day	74% 7% 10% 7% 2	2497
January	1st to 10th	Night	58% 7% 14% 15% 6%	4428
	11th to 20th	Night	68% 8% 10% 11% 3	4427
	21st to end	Night	68% 5% 10% 15% 3	4532
February	1st to 10th	Night	62% 7% 10% 14% 7% 1	2470
	11th to 20th	Night	56% 6% 11% 17% 9% 1	2327
	21st to end	Night	58% 7% 10% 17% 8% 1	1884
March	1st to 10th	Night	51% 5% 14% 24% 6%	3608
	11th to 20th	Night	39% 7% 17% 21% 14% 1	3480
	21st to end	Night	47% 6% 11% 23% 12% 1	3817
April	1st to 10th	Night	49% 5% 11% 21% 12% 2	2021
	11th to 20th	Night	45% 6% 10% 19% 17% 2	1687
	21st to end	Night	45% 7% 11% 18% 15% 4	1710
May	1st to 10th	Night	44% 8% 11% 20% 13% 5%	2840
	11th to 20th	Night	42% 8% 12% 25% 12% 2	2813
	21st to end	Night	30% 9% 12% 22% 19% 8%	2941
June	1st to 10th	Night	35% 8% 11% 27% 17% 2	1367
	11th to 20th	Night	34% 8% 14% 24% 19% 2	1330
	21st to end	Night	33% 8% 14% 25% 20% 1	1330
July	1st to 10th	Night	30% 5% 14% 29% 16% 6%	2391
	11th to 20th	Night	28% 7% 13% 34% 18% 1	2482
	21st to end	Night	29% 10% 18% 21% 20% 3	2971
August	1st to 10th	Night	34% 7% 15% 26% 16% 2	2814
	11th to 20th	Night	35% 8% 15% 29% 11% 2	2812
	21st to end	Night	34% 8% 13% 30% 14% 1	3124
September	1st to 10th	Night	36% 7% 14% 27% 15% 2	1995
	11th to 20th	Night	29% 7% 12% 31% 19% 1	2090
	21st to end	Night	41% 7% 11% 29% 11% 1	2090
October	1st to 10th	Night	26% 5% 11% 31% 26% 1	3635
	11th to 20th	Night	44% 5% 11% 24% 16%	3779
	21st to end	Night	43% 5% 12% 27% 12% 1	4327
November	1st to 10th	Night	41% 6% 14% 25% 12% 1	2536
	11th to 20th	Night	52% 7% 14% 18% 8% 1	2642
	21st to end	Night	56% 6% 15% 17% 5% 1	2723
December	1st to 10th	Night	60% 7% 15% 14% 4	2660
	11th to 20th	Night	57% 7% 15% 15% 6%	3396
	21st to end	Night	72% 7% 11% 7% 3	5167

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	20% 18% 37% 17% 7% 1	270
	11th to 20th	Day	20% 15% 44% 17% 3 1	270
	21st to end	Day	25% 14% 36% 19% 5% 1	297
February	1st to 10th	Day	21% 20% 42% 12% 4 1	270
	11th to 20th	Day	24% 17% 37% 20% 2	270
	21st to end	Day	19% 24% 41% 14% 2	225
March	1st to 10th	Day	24% 17% 38% 16% 4 1	342
	11th to 20th	Day	21% 15% 33% 24% 7% 1	460
	21st to end	Day	24% 13% 33% 24% 5% 1	506
April	1st to 10th	Day	17% 17% 37% 20% 8% 1	460
	11th to 20th	Day	25% 14% 28% 19% 9% 5%	452
	21st to end	Day	21% 10% 31% 25% 10% 3	460
May	1st to 10th	Day	19% 13% 29% 23% 13% 3	463
	11th to 20th	Day	18% 7% 28% 25% 15% 6%	487
	21st to end	Day	14% 7% 20% 33% 19% 8%	529
June	1st to 10th	Day	11% 6% 32% 31% 16% 4	638
	11th to 20th	Day	10% 8% 31% 32% 15% 5%	680
	21st to end	Day	12% 8% 27% 32% 17% 4	680
July	1st to 10th	Day	8% 5% 23% 31% 22% 11%	671
	11th to 20th	Day	10% 4 26% 34% 18% 8%	668
	21st to end	Day	7% 3 22% 35% 24% 10%	546
August	1st to 10th	Day	9% 5% 18% 31% 24% 14%	486
	11th to 20th	Day	9% 5% 19% 31% 23% 13%	479
	21st to end	Day	13% 5% 19% 26% 25% 11%	539
September	1st to 10th	Day	12% 6% 24% 25% 22% 11%	490
	11th to 20th	Day	9% 5% 17% 24% 28% 16%	490
	21st to end	Day	16% 9% 25% 24% 17% 9%	490
October	1st to 10th	Day	15% 11% 26% 24% 18% 7%	490
	11th to 20th	Day	18% 16% 34% 24% 7% 1	490
	21st to end	Day	22% 15% 38% 18% 5% 1	419
November	1st to 10th	Day	18% 18% 35% 21% 7% 1	300
	11th to 20th	Day	22% 22% 31% 17% 6% 1	277
	21st to end	Day	24% 20% 38% 14% 3	188
December	1st to 10th	Day	21% 19% 36% 17% 5% 1	180
	11th to 20th	Day	24% 21% 37% 15% 3 1	180
	21st to end	Day	27% 18% 35% 17% 3	218
January	1st to 10th	Night	23% 14% 37% 20% 5% 1	950
	11th to 20th	Night	24% 15% 34% 22% 4 1	937
	21st to end	Night	19% 12% 36% 27% 6%	836
February	1st to 10th	Night	22% 12% 41% 22% 2	760
	11th to 20th	Night	21% 14% 35% 26% 4	743
	21st to end	Night	22% 13% 40% 21% 3	628
March	1st to 10th	Night	19% 13% 35% 27% 5%	760
	11th to 20th	Night	17% 11% 37% 28% 6% 1	760
	21st to end	Night	22% 10% 31% 29% 7% 1	836
April	1st to 10th	Night	21% 13% 35% 25% 5%	700
	11th to 20th	Night	20% 10% 33% 25% 9% 2	563
	21st to end	Night	19% 8% 31% 32% 9% 1	570
May	1st to 10th	Night	18% 5% 29% 33% 13% 1	570
	11th to 20th	Night	18% 4 27% 36% 13% 1	561
	21st to end	Night	12% 4 23% 36% 23% 2	536
June	1st to 10th	Night	13% 4 24% 39% 19%	380
	11th to 20th	Night	13% 4 26% 40% 17% 1	380
	21st to end	Night	10% 3 21% 46% 18% 1	380
July	1st to 10th	Night	7% 1 16% 43% 28% 4	495
	11th to 20th	Night	11% 2 17% 41% 26% 4	552
	21st to end	Night	7% 2 19% 45% 25% 3	624
August	1st to 10th	Night	7% 3 15% 40% 31% 3	567
	11th to 20th	Night	7% 2 17% 34% 36% 4	564
	21st to end	Night	11% 3 19% 36% 28% 4	627
September	1st to 10th	Night	10% 5% 23% 34% 23% 5%	711
	11th to 20th	Night	10% 3 18% 35% 27% 6%	760
	21st to end	Night	17% 6% 21% 32% 19% 4	760
October	1st to 10th	Night	15% 9% 27% 29% 18% 2	760
	11th to 20th	Night	22% 12% 29% 27% 8% 1	760
	21st to end	Night	25% 10% 35% 25% 5%	836
November	1st to 10th	Night	18% 12% 32% 26% 12% 1	780
	11th to 20th	Night	20% 15% 37% 21% 7% 1	800
	21st to end	Night	24% 13% 35% 22% 6%	779
December	1st to 10th	Night	21% 14% 41% 18% 5%	760
	11th to 20th	Night	22% 15% 39% 20% 3	831
	21st to end	Night	30% 12% 34% 21% 3	1045

Page generated at 2024-11-22 08:02:25. Version ac07

Copyright © 2024 Attilla Danko.