Black Diamond
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Diamond clear sky chart from 2005-11-06 to 2024-11-04.

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	8% 8% 3 8% 5% 5% 5% 4 6% 8% 40%	105595
	Night	6% 9% 3 8% 5% 5% 5% 4 6% 8% 41%	102010
Transparency	Day	39% 8% 15% 24% 12% 2	105342
	Night	39% 8% 15% 23% 13% 3	101909
Seeing	Day	13% 11% 28% 30% 14% 4	15338
	Night	10% 9% 31% 34% 13% 2	24375

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	2 8% 5% 12% 6% 6% 4 4 8% 10% 35%	2219
	11th to 20th	Day	2 8% 3 11% 5% 7% 6% 5% 7% 8% 38%	2295
	21st to end	Day	2 9% 3 8% 6% 5% 5% 4 6% 9% 42%	2794
February	1st to 10th	Day	3 9% 4 12% 7% 4 6% 5% 8% 10% 33%	1520
	11th to 20th	Day	2 11% 4 10% 7% 6% 6% 6% 7% 9% 31%	1654
	21st to end	Day	1 11% 5% 12% 6% 7% 5% 5% 6% 7% 34%	1546
March	1st to 10th	Day	2 8% 4 12% 7% 8% 6% 4 6% 8% 35%	3138
	11th to 20th	Day	5% 10% 3 6% 4 4 4 4 6% 8% 47%	3444
	21st to end	Day	6% 19% 7% 14% 5% 4 4 4 5% 5% 25%	3903
April	1st to 10th	Day	8% 13% 5% 10% 6% 5% 5% 4 6% 9% 30%	2318
	11th to 20th	Day	9% 14% 4 8% 5% 4 5% 4 6% 8% 31%	2440
	21st to end	Day	11% 12% 3 7% 4 5% 5% 5% 7% 9% 33%	2470
May	1st to 10th	Day	16% 17% 4 7% 5% 5% 4 4 5% 6% 28%	4281
	11th to 20th	Day	9% 7% 4 9% 6% 5% 6% 5% 7% 9% 32%	4694
	21st to end	Day	17% 8% 3 9% 7% 7% 6% 5% 5% 8% 25%	5161
June	1st to 10th	Day	16% 8% 3 7% 6% 5% 6% 5% 7% 7% 29%	2850
	11th to 20th	Day	20% 8% 4 8% 5% 5% 6% 5% 6% 7% 26%	2850
	21st to end	Day	9% 4 2 6% 4 5% 5% 5% 7% 10% 41%	2850
July	1st to 10th	Day	8% 5% 2 5% 4 4 4 4 7% 8% 49%	4740
	11th to 20th	Day	6% 3 1 4 3 3 5% 5% 7% 10% 53%	4740
	21st to end	Day	3 3 1 3 3 3 4 4 6% 9% 59%	4960
August	1st to 10th	Day	9% 6% 2 6% 3 4 5% 5% 8% 9% 43%	4401
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 5% 8% 10% 45%	4066
	21st to end	Day	9% 4 1 4 4 3 4 3 6% 8% 53%	4521
September	1st to 10th	Day	11% 6% 2 6% 4 3 4 3 5% 7% 51%	2342
	11th to 20th	Day	12% 8% 2 5% 4 4 4 4 6% 7% 45%	2090
	21st to end	Day	8% 7% 2 7% 4 4 5% 3 7% 7% 46%	2090
October	1st to 10th	Day	6% 7% 3 7% 4 5% 4 3 6% 9% 46%	3369
	11th to 20th	Day	4 6% 3 7% 5% 4 4 4 8% 11% 44%	2906
	21st to end	Day	6% 8% 3 6% 4 4 5% 4 7% 7% 47%	3101
November	1st to 10th	Day	6% 14% 4 9% 5% 5% 4 4 6% 7% 35%	1605
	11th to 20th	Day	4 10% 5% 6% 5% 4 4 5% 6% 8% 43%	1453
	21st to end	Day	3 11% 4 9% 5% 5% 4 4 5% 11% 39%	1330
December	1st to 10th	Day	3 9% 5% 11% 6% 6% 5% 5% 6% 7% 37%	1330
	11th to 20th	Day	2 10% 5% 12% 6% 6% 6% 5% 8% 7% 33%	1682
	21st to end	Day	3 8% 3 7% 5% 4 4 4 6% 9% 46%	2442
January	1st to 10th	Night	2 11% 4 11% 8% 7% 6% 5% 7% 9% 30%	4726
	11th to 20th	Night	2 7% 4 13% 6% 6% 7% 6% 6% 8% 35%	4631
	21st to end	Night	3 10% 4 11% 7% 5% 5% 4 6% 7% 39%	4862
February	1st to 10th	Night	3 10% 4 11% 6% 6% 7% 3 8% 9% 34%	2660
	11th to 20th	Night	2 13% 6% 9% 5% 6% 5% 4 6% 8% 34%	2412
	21st to end	Night	3 8% 4 13% 8% 7% 6% 4 5% 6% 37%	1905
March	1st to 10th	Night	1 8% 4 13% 9% 7% 7% 5% 6% 7% 33%	3736
	11th to 20th	Night	3 9% 2 6% 4 5% 4 4 7% 8% 48%	3535
	21st to end	Night	9% 21% 6% 11% 6% 4 4 4 7% 6% 23%	3750
April	1st to 10th	Night	7% 15% 4 9% 5% 4 5% 5% 6% 7% 33%	1861
	11th to 20th	Night	10% 12% 5% 10% 6% 4 4 4 5% 5% 34%	1691
	21st to end	Night	9% 12% 4 7% 5% 5% 4 3 6% 8% 36%	1710
May	1st to 10th	Night	16% 15% 3 8% 4 5% 4 3 5% 6% 31%	2679
	11th to 20th	Night	10% 7% 3 8% 5% 5% 6% 5% 6% 10% 35%	2199
	21st to end	Night	14% 8% 3 8% 5% 6% 6% 5% 6% 8% 31%	2414
June	1st to 10th	Night	13% 9% 3 6% 5% 4 4 3 7% 8% 36%	1330
	11th to 20th	Night	19% 9% 2 7% 4 4 4 5% 5% 9% 32%	1330
	21st to end	Night	8% 4 2 5% 4 4 5% 4 7% 10% 48%	1330
July	1st to 10th	Night	7% 5% 2 6% 5% 4 3 4 6% 8% 50%	2220
	11th to 20th	Night	5% 2 2 4 4 4 5% 4 7% 8% 56%	2220
	21st to end	Night	5% 4 1 4 3 3 3 3 4 7% 62%	2589
August	1st to 10th	Night	11% 5% 2 5% 4 4 5% 4 7% 9% 44%	2529
	11th to 20th	Night	6% 5% 2 5% 5% 4 5% 4 7% 9% 47%	2772
	21st to end	Night	8% 3 2 3 3 3 4 3 6% 9% 55%	3146
September	1st to 10th	Night	10% 5% 2 5% 3 3 4 3 5% 7% 53%	1834
	11th to 20th	Night	13% 8% 2 4 2 3 3 2 5% 7% 51%	2090
	21st to end	Night	10% 7% 2 5% 4 3 4 3 6% 8% 49%	2090
October	1st to 10th	Night	7% 6% 2 5% 3 3 4 4 6% 8% 53%	3606
	11th to 20th	Night	5% 7% 2 5% 3 3 4 4 6% 8% 52%	4019
	21st to end	Night	4 9% 3 6% 4 4 5% 4 6% 7% 48%	4457
November	1st to 10th	Night	6% 13% 4 8% 4 4 6% 5% 6% 7% 37%	2527
	11th to 20th	Night	4 9% 3 7% 6% 4 5% 4 6% 8% 44%	2726
	21st to end	Night	3 10% 4 9% 5% 5% 4 4 7% 9% 41%	2850
December	1st to 10th	Night	3 10% 4 9% 6% 5% 6% 4 7% 9% 37%	2850
	11th to 20th	Night	1 8% 4 12% 7% 6% 6% 5% 7% 9% 35%	3510
	21st to end	Night	2 9% 3 9% 5% 5% 5% 4 6% 7% 44%	5214

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	40% 9% 16% 23% 10% 3	2219
	11th to 20th	Day	41% 7% 11% 18% 18% 4	2316
	21st to end	Day	34% 11% 16% 29% 9% 1	2794
February	1st to 10th	Day	46% 10% 14% 18% 9% 3	1520
	11th to 20th	Day	47% 8% 14% 19% 10% 2	1663
	21st to end	Day	47% 8% 14% 17% 13% 1	1546
March	1st to 10th	Day	45% 7% 16% 17% 14% 1	3138
	11th to 20th	Day	33% 7% 18% 27% 15% 1	3445
	21st to end	Day	58% 8% 13% 16% 5%	3903
April	1st to 10th	Day	50% 7% 17% 17% 8% 1	2318
	11th to 20th	Day	49% 7% 14% 19% 10% 1	2440
	21st to end	Day	47% 8% 15% 20% 9% 1	2470
May	1st to 10th	Day	55% 8% 10% 22% 5%	4281
	11th to 20th	Day	43% 10% 14% 23% 9%	4698
	21st to end	Day	52% 9% 16% 13% 8% 1	5162
June	1st to 10th	Day	49% 10% 13% 17% 9% 1	2850
	11th to 20th	Day	53% 10% 13% 15% 8% 2	2850
	21st to end	Day	34% 11% 17% 23% 12% 2	2850
July	1st to 10th	Day	30% 8% 13% 26% 18% 5%	4666
	11th to 20th	Day	25% 7% 18% 32% 16% 2	4659
	21st to end	Day	19% 6% 11% 28% 24% 12%	4803
August	1st to 10th	Day	33% 9% 14% 36% 8% 1	4384
	11th to 20th	Day	30% 9% 24% 28% 8% 2	4105
	21st to end	Day	27% 6% 16% 35% 14% 2	4520
September	1st to 10th	Day	32% 7% 14% 24% 17% 5%	2342
	11th to 20th	Day	37% 8% 14% 26% 13% 2	2090
	21st to end	Day	35% 7% 14% 28% 13% 3	2090
October	1st to 10th	Day	34% 7% 15% 35% 9% 1	3369
	11th to 20th	Day	31% 6% 21% 26% 13% 3	2906
	21st to end	Day	35% 6% 12% 31% 13% 2	3101
November	1st to 10th	Day	48% 8% 13% 19% 12% 1	1605
	11th to 20th	Day	38% 7% 18% 23% 11% 2	1453
	21st to end	Day	39% 9% 19% 21% 10% 3	1330
December	1st to 10th	Day	43% 8% 13% 18% 13% 4	1330
	11th to 20th	Day	45% 10% 16% 19% 9% 1	1684
	21st to end	Day	33% 7% 11% 24% 18% 6%	2442
January	1st to 10th	Night	46% 11% 13% 21% 8% 2	4726
	11th to 20th	Night	44% 7% 13% 16% 14% 6%	4672
	21st to end	Night	39% 10% 14% 23% 12% 1	4862
February	1st to 10th	Night	45% 8% 13% 20% 11% 3	2660
	11th to 20th	Night	46% 8% 15% 18% 12% 2	2413
	21st to end	Night	47% 6% 11% 21% 12% 3	1905
March	1st to 10th	Night	46% 9% 13% 20% 11% 1	3736
	11th to 20th	Night	31% 10% 21% 22% 16% 1	3535
	21st to end	Night	59% 8% 12% 15% 5% 1	3750
April	1st to 10th	Night	48% 7% 13% 20% 11% 1	1861
	11th to 20th	Night	50% 8% 13% 20% 9% 1	1691
	21st to end	Night	44% 10% 13% 23% 8% 2	1710
May	1st to 10th	Night	53% 7% 9% 24% 6%	2679
	11th to 20th	Night	40% 9% 13% 28% 9% 1	2199
	21st to end	Night	46% 11% 16% 18% 8% 1	2414
June	1st to 10th	Night	43% 7% 15% 23% 11% 1	1330
	11th to 20th	Night	47% 8% 14% 19% 10% 2	1330
	21st to end	Night	30% 9% 20% 26% 14% 2	1330
July	1st to 10th	Night	32% 7% 15% 23% 18% 4	2185
	11th to 20th	Night	24% 7% 21% 34% 11% 4	2178
	21st to end	Night	21% 5% 10% 31% 23% 10%	2507
August	1st to 10th	Night	35% 6% 15% 28% 14% 2	2521
	11th to 20th	Night	31% 8% 22% 27% 10% 1	2799
	21st to end	Night	25% 5% 19% 34% 15% 2	3146
September	1st to 10th	Night	30% 6% 16% 26% 17% 5%	1834
	11th to 20th	Night	33% 6% 14% 28% 14% 4	2090
	21st to end	Night	32% 6% 17% 26% 14% 4	2090
October	1st to 10th	Night	28% 7% 13% 29% 21% 2	3606
	11th to 20th	Night	30% 6% 20% 24% 19% 2	4019
	21st to end	Night	35% 6% 12% 31% 16% 1	4457
November	1st to 10th	Night	44% 9% 13% 20% 13% 2	2527
	11th to 20th	Night	37% 9% 15% 21% 17% 2	2726
	21st to end	Night	38% 8% 16% 21% 12% 4	2850
December	1st to 10th	Night	42% 8% 15% 20% 11% 4	2850
	11th to 20th	Night	41% 12% 19% 21% 8% 1	3507
	21st to end	Night	36% 7% 12% 25% 14% 6%	5214

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	2 7% 29% 36% 16% 10%	180
	11th to 20th	Day	7% 7% 29% 37% 15% 5%	180
	21st to end	Day	8% 5% 28% 45% 11% 4	198
February	1st to 10th	Day	8% 13% 37% 28% 11% 3	180
	11th to 20th	Day	5% 10% 39% 32% 11% 2	265
	21st to end	Day	5% 12% 35% 32% 15% 1	358
March	1st to 10th	Day	6% 14% 39% 28% 10% 3	460
	11th to 20th	Day	9% 13% 31% 29% 15% 3	460
	21st to end	Day	11% 13% 36% 25% 11% 4	506
April	1st to 10th	Day	14% 13% 31% 31% 10% 1	460
	11th to 20th	Day	16% 10% 29% 27% 14% 3	452
	21st to end	Day	17% 16% 29% 24% 10% 4	460
May	1st to 10th	Day	21% 11% 22% 26% 15% 5%	476
	11th to 20th	Day	18% 11% 22% 26% 19% 5%	675
	21st to end	Day	20% 10% 19% 29% 18% 4	734
June	1st to 10th	Day	17% 12% 27% 29% 11% 4	680
	11th to 20th	Day	23% 13% 25% 25% 11% 3	680
	21st to end	Day	11% 10% 25% 31% 19% 4	680
July	1st to 10th	Day	11% 7% 22% 35% 21% 5%	671
	11th to 20th	Day	12% 7% 25% 32% 19% 4	668
	21st to end	Day	5% 8% 31% 33% 19% 5%	636
August	1st to 10th	Day	12% 9% 26% 35% 15% 4	487
	11th to 20th	Day	8% 9% 29% 31% 16% 6%	477
	21st to end	Day	11% 11% 30% 28% 16% 5%	539
September	1st to 10th	Day	14% 13% 29% 26% 14% 4	490
	11th to 20th	Day	19% 9% 25% 30% 13% 3	490
	21st to end	Day	13% 19% 30% 26% 9% 3	490
October	1st to 10th	Day	14% 12% 28% 28% 14% 4	421
	11th to 20th	Day	12% 12% 29% 30% 12% 5%	300
	21st to end	Day	15% 15% 32% 25% 10% 3	330
November	1st to 10th	Day	18% 11% 32% 24% 11% 3	279
	11th to 20th	Day	13% 12% 33% 31% 10% 2	238
	21st to end	Day	8% 13% 24% 34% 12% 9%	180
December	1st to 10th	Day	7% 8% 30% 39% 12% 3	180
	11th to 20th	Day	6% 15% 29% 37% 9% 4	180
	21st to end	Day	7% 8% 25% 39% 16% 6%	198
January	1st to 10th	Night	8% 14% 37% 31% 9% 1	950
	11th to 20th	Night	7% 9% 43% 30% 9% 1	908
	21st to end	Night	6% 16% 35% 33% 8% 2	836
February	1st to 10th	Night	6% 12% 36% 28% 12% 5%	760
	11th to 20th	Night	7% 8% 35% 37% 11% 1	744
	21st to end	Night	6% 6% 35% 32% 17% 4	628
March	1st to 10th	Night	6% 7% 39% 33% 11% 4	760
	11th to 20th	Night	8% 9% 37% 33% 11% 2	760
	21st to end	Night	11% 8% 27% 39% 11% 3	836
April	1st to 10th	Night	13% 7% 34% 30% 14% 2	721
	11th to 20th	Night	16% 7% 32% 34% 11%	563
	21st to end	Night	16% 8% 28% 35% 11% 2	570
May	1st to 10th	Night	18% 8% 22% 34% 16% 2	481
	11th to 20th	Night	14% 6% 23% 35% 21% 1	374
	21st to end	Night	22% 7% 18% 33% 18% 2	411
June	1st to 10th	Night	18% 7% 22% 36% 14% 2	380
	11th to 20th	Night	23% 5% 24% 33% 13% 1	380
	21st to end	Night	9% 4 22% 38% 26% 1	380
July	1st to 10th	Night	11% 4 14% 43% 27% 1	370
	11th to 20th	Night	9% 3 17% 49% 18% 4	368
	21st to end	Night	8% 4 16% 45% 24% 3	416
August	1st to 10th	Night	13% 1 11% 43% 29% 3	378
	11th to 20th	Night	10% 2 17% 43% 24% 3	537
	21st to end	Night	10% 6% 20% 42% 20% 2	627
September	1st to 10th	Night	13% 4 20% 38% 19% 5%	685
	11th to 20th	Night	18% 5% 18% 35% 21% 4	760
	21st to end	Night	13% 7% 29% 36% 11% 5%	760
October	1st to 10th	Night	14% 6% 27% 35% 15% 3	760
	11th to 20th	Night	11% 8% 31% 33% 14% 3	760
	21st to end	Night	10% 10% 33% 36% 10% 1	836
November	1st to 10th	Night	13% 13% 35% 29% 8% 1	831
	11th to 20th	Night	9% 18% 38% 28% 5% 1	950
	21st to end	Night	7% 12% 41% 29% 8% 2	950
December	1st to 10th	Night	7% 9% 39% 31% 11% 3	950
	11th to 20th	Night	5% 12% 40% 33% 8% 2	950
	21st to end	Night	8% 11% 37% 30% 11% 2	1045

Page generated at 2024-11-01 20:47:42. Version ac07

Copyright © 2024 Attilla Danko.