White Rock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Rock clear sky chart from 2005-11-06 to 2024-09-14.

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	20% 8% 3 6% 4 4 4 3 5% 6% 37%	101188
	Night	25% 9% 3 7% 4 4 4 3 4 6% 31%	96789
Transparency	Day	25% 49% 9% 11% 5% 1	100938
	Night	28% 50% 7% 10% 5% 1	96685
Seeing	Day	25% 6% 18% 25% 20% 6%	15146
	Night	32% 5% 14% 24% 21% 5%	23314

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	40% 13% 3 9% 5% 4 4 3 4 5% 11%	2219
	11th to 20th	Day	28% 13% 4 8% 4 4 3 3 3 6% 23%	2209
	21st to end	Day	51% 12% 3 7% 4 3 3 2 3 3 10%	2827
February	1st to 10th	Day	33% 12% 3 8% 5% 4 4 3 5% 5% 18%	1710
	11th to 20th	Day	30% 10% 3 8% 5% 5% 4 3 4 5% 22%	1665
	21st to end	Day	26% 13% 4 7% 5% 4 5% 4 4 5% 23%	1437
March	1st to 10th	Day	22% 15% 3 9% 5% 6% 4 3 5% 6% 21%	3230
	11th to 20th	Day	20% 9% 3 7% 5% 4 4 4 6% 7% 32%	3490
	21st to end	Day	25% 12% 3 8% 5% 3 4 3 5% 6% 25%	3936
April	1st to 10th	Day	24% 11% 3 7% 6% 4 5% 4 5% 7% 23%	2280
	11th to 20th	Day	20% 10% 3 7% 6% 5% 5% 3 6% 6% 29%	2331
	21st to end	Day	22% 10% 3 7% 5% 4 4 4 6% 6% 30%	2528
May	1st to 10th	Day	15% 7% 2 6% 4 3 4 3 4 6% 45%	4420
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 7% 10% 41%	4377
	21st to end	Day	24% 9% 3 7% 4 4 4 4 5% 6% 29%	4864
June	1st to 10th	Day	20% 7% 3 5% 5% 4 5% 4 6% 7% 34%	2850
	11th to 20th	Day	20% 7% 2 8% 5% 4 4 4 5% 7% 33%	2850
	21st to end	Day	12% 7% 2 6% 5% 4 6% 3 6% 7% 42%	2850
July	1st to 10th	Day	7% 3 1 4 2 2 3 2 4 5% 67%	4740
	11th to 20th	Day	5% 3 1 3 2 2 2 2 3 5% 72%	4740
	21st to end	Day	11% 4 1 4 3 2 3 2 4 6% 60%	4832
August	1st to 10th	Day	5% 3 1 3 2 3 2 2 3 7% 69%	4372
	11th to 20th	Day	10% 6% 2 5% 4 4 4 3 5% 7% 49%	4026
	21st to end	Day	15% 7% 3 6% 4 4 5% 3 5% 6% 43%	4403
September	1st to 10th	Day	11% 6% 3 6% 4 4 4 3 5% 7% 49%	2280
	11th to 20th	Day	16% 8% 2 7% 4 4 4 3 4 7% 40%	2198
	21st to end	Day	22% 8% 2 6% 4 3 4 3 5% 7% 36%	1896
October	1st to 10th	Day	22% 8% 2 7% 4 3 4 4 5% 8% 32%	1800
	11th to 20th	Day	28% 9% 3 8% 5% 3 4 4 6% 8% 23%	1800
	21st to end	Day	32% 9% 3 8% 5% 4 4 3 4 6% 24%	1842
November	1st to 10th	Day	37% 9% 2 7% 4 5% 3 4 5% 5% 19%	1488
	11th to 20th	Day	34% 11% 2 8% 4 3 3 3 4 5% 23%	1520
	21st to end	Day	35% 12% 3 7% 5% 4 4 3 4 4 18%	1520
December	1st to 10th	Day	32% 14% 3 5% 5% 3 4 3 4 3 24%	1520
	11th to 20th	Day	35% 14% 4 8% 4 5% 5% 3 4 5% 14%	1696
	21st to end	Day	33% 14% 5% 10% 6% 5% 4 3 4 4 11%	2442
January	1st to 10th	Night	37% 14% 4 9% 5% 4 4 3 4 4 12%	4726
	11th to 20th	Night	32% 9% 2 6% 4 3 4 3 5% 7% 25%	4686
	21st to end	Night	49% 12% 3 7% 3 3 2 2 3 4 11%	4827
February	1st to 10th	Night	34% 12% 3 8% 4 4 3 3 5% 5% 20%	2470
	11th to 20th	Night	29% 12% 3 8% 5% 4 4 3 4 5% 24%	2402
	21st to end	Night	30% 11% 3 7% 4 4 4 4 4 6% 25%	2016
March	1st to 10th	Night	25% 16% 4 8% 5% 4 4 3 5% 6% 20%	3643
	11th to 20th	Night	22% 7% 2 6% 4 4 4 4 6% 9% 31%	3489
	21st to end	Night	30% 15% 4 9% 5% 3 4 3 4 5% 18%	3716
April	1st to 10th	Night	27% 11% 4 8% 4 5% 4 4 5% 6% 23%	1900
	11th to 20th	Night	22% 10% 3 8% 4 4 5% 3 5% 6% 30%	1796
	21st to end	Night	25% 9% 4 8% 6% 5% 4 4 5% 6% 25%	1651
May	1st to 10th	Night	16% 9% 3 6% 3 4 3 2 3 4 46%	2540
	11th to 20th	Night	10% 6% 2 6% 4 3 4 3 6% 7% 47%	2516
	21st to end	Night	20% 10% 3 9% 6% 5% 5% 4 4 6% 28%	2708
June	1st to 10th	Night	21% 7% 3 8% 4 5% 4 4 6% 6% 33%	1330
	11th to 20th	Night	17% 10% 4 8% 5% 4 5% 5% 6% 5% 30%	1330
	21st to end	Night	13% 6% 2 5% 5% 5% 3 4 6% 8% 44%	1330
July	1st to 10th	Night	5% 3 1 4 3 3 3 2 4 6% 66%	2220
	11th to 20th	Night	4 3 1 3 2 2 2 2 2 4 76%	2220
	21st to end	Night	8% 5% 2 4 4 3 3 2 4 6% 59%	2718
August	1st to 10th	Night	4 2 1 2 2 2 3 3 4 6% 72%	2556
	11th to 20th	Night	10% 5% 2 5% 4 3 3 3 4 8% 52%	2812
	21st to end	Night	12% 4 2 6% 5% 4 4 3 7% 8% 43%	3267
September	1st to 10th	Night	9% 3 2 4 3 3 3 3 5% 8% 56%	1900
	11th to 20th	Night	19% 6% 2 6% 5% 3 3 2 6% 5% 43%	1840
	21st to end	Night	19% 5% 3 7% 4 3 3 3 5% 7% 40%	2061
October	1st to 10th	Night	20% 6% 2 6% 5% 4 5% 3 5% 5% 39%	2160
	11th to 20th	Night	29% 6% 3 6% 3 4 4 3 5% 6% 30%	2160
	21st to end	Night	31% 7% 2 7% 4 3 3 3 4 7% 29%	2510
November	1st to 10th	Night	38% 9% 3 7% 5% 5% 4 3 4 5% 18%	2590
	11th to 20th	Night	36% 9% 2 6% 4 4 4 2 4 6% 22%	2660
	21st to end	Night	34% 12% 3 8% 5% 4 4 3 4 4 19%	2660
December	1st to 10th	Night	31% 9% 4 5% 4 3 5% 4 5% 6% 24%	2660
	11th to 20th	Night	41% 13% 4 8% 4 3 4 3 3 4 12%	3505
	21st to end	Night	35% 14% 4 8% 5% 4 3 2 3 4 16%	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	47% 41% 5% 4 2 1	2219
	11th to 20th	Day	39% 37% 8% 10% 5% 3	2230
	21st to end	Day	55% 40% 2 3	2827
February	1st to 10th	Day	26% 65% 3 2 2 2	1710
	11th to 20th	Day	25% 64% 3 5% 2	1674
	21st to end	Day	22% 65% 5% 5% 2 1	1437
March	1st to 10th	Day	35% 43% 11% 8% 3	3230
	11th to 20th	Day	26% 42% 11% 18% 3	3490
	21st to end	Day	36% 43% 11% 7% 3	3936
April	1st to 10th	Day	21% 66% 6% 6% 1	2280
	11th to 20th	Day	21% 66% 5% 6% 2 1	2331
	21st to end	Day	20% 65% 5% 7% 3	2528
May	1st to 10th	Day	21% 42% 9% 17% 10%	4420
	11th to 20th	Day	19% 45% 19% 15% 2	4380
	21st to end	Day	33% 44% 14% 8% 1	4865
June	1st to 10th	Day	16% 65% 9% 7% 2	2850
	11th to 20th	Day	17% 65% 7% 8% 3	2850
	21st to end	Day	15% 64% 9% 9% 3	2850
July	1st to 10th	Day	12% 36% 5% 17% 21% 9%	4666
	11th to 20th	Day	7% 35% 8% 28% 20% 2	4659
	21st to end	Day	22% 36% 18% 17% 6% 1	4679
August	1st to 10th	Day	9% 37% 8% 32% 14% 1	4355
	11th to 20th	Day	26% 37% 22% 11% 3 1	4065
	21st to end	Day	30% 37% 12% 12% 8%	4402
September	1st to 10th	Day	19% 61% 6% 9% 4 1	2280
	11th to 20th	Day	20% 62% 5% 7% 5% 1	2198
	21st to end	Day	18% 63% 6% 8% 4	1896
October	1st to 10th	Day	21% 63% 5% 7% 3	1800
	11th to 20th	Day	25% 63% 4 6% 2	1800
	21st to end	Day	24% 62% 4 6% 4	1842
November	1st to 10th	Day	28% 60% 6% 6% 1	1488
	11th to 20th	Day	23% 61% 5% 7% 2 2	1520
	21st to end	Day	25% 60% 5% 5% 4 1	1520
December	1st to 10th	Day	26% 61% 2 7% 4	1520
	11th to 20th	Day	39% 50% 5% 4 2 1	1699
	21st to end	Day	48% 41% 6% 4 1	2442
January	1st to 10th	Night	47% 41% 4 6% 2 1	4726
	11th to 20th	Night	33% 39% 8% 12% 6% 1	4727
	21st to end	Night	53% 40% 3 3	4827
February	1st to 10th	Night	24% 65% 3 3 2 3	2470
	11th to 20th	Night	25% 64% 4 4 2	2404
	21st to end	Night	18% 65% 5% 6% 3 1	2016
March	1st to 10th	Night	36% 44% 8% 7% 5%	3643
	11th to 20th	Night	22% 43% 14% 19% 3	3490
	21st to end	Night	41% 44% 8% 6% 1	3716
April	1st to 10th	Night	22% 66% 4 8% 1	1900
	11th to 20th	Night	20% 66% 5% 6% 3 1	1796
	21st to end	Night	21% 65% 4 5% 4	1651
May	1st to 10th	Night	24% 41% 6% 20% 8% 1	2540
	11th to 20th	Night	18% 43% 20% 14% 5%	2516
	21st to end	Night	35% 44% 11% 8% 2	2708
June	1st to 10th	Night	15% 65% 7% 10% 2 1	1330
	11th to 20th	Night	17% 65% 6% 9% 2	1330
	21st to end	Night	15% 64% 9% 8% 4	1330
July	1st to 10th	Night	10% 35% 5% 22% 20% 9%	2185
	11th to 20th	Night	7% 35% 5% 30% 22% 2	2178
	21st to end	Night	23% 35% 10% 19% 12% 1	2632
August	1st to 10th	Night	6% 36% 9% 26% 22% 1	2548
	11th to 20th	Night	27% 36% 20% 12% 4 1	2839
	21st to end	Night	28% 37% 14% 14% 8%	3267
September	1st to 10th	Night	15% 62% 8% 9% 5% 1	1900
	11th to 20th	Night	20% 62% 5% 5% 6% 1	1840
	21st to end	Night	17% 63% 5% 10% 5%	2061
October	1st to 10th	Night	18% 63% 6% 9% 3	2160
	11th to 20th	Night	23% 63% 4 6% 3	2160
	21st to end	Night	22% 62% 4 8% 4	2510
November	1st to 10th	Night	29% 59% 6% 5% 2	2590
	11th to 20th	Night	25% 60% 4 5% 3 2	2660
	21st to end	Night	27% 59% 4 4 5% 1	2660
December	1st to 10th	Night	26% 60% 3 6% 5%	2660
	11th to 20th	Night	41% 51% 3 2 2 1	3501
	21st to end	Night	45% 40% 5% 7% 2 1	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	45% 7% 18% 14% 9% 7%	180
	11th to 20th	Day	46% 11% 12% 13% 11% 7%	180
	21st to end	Day	50% 6% 13% 14% 14% 4	218
February	1st to 10th	Day	41% 8% 16% 20% 13% 2	370
	11th to 20th	Day	38% 7% 17% 21% 15% 2	365
	21st to end	Day	33% 10% 20% 24% 9% 3	319
March	1st to 10th	Day	34% 7% 21% 20% 14% 4	460
	11th to 20th	Day	32% 8% 16% 20% 19% 5%	460
	21st to end	Day	35% 9% 20% 21% 13% 2	506
April	1st to 10th	Day	30% 11% 19% 23% 15% 2	460
	11th to 20th	Day	24% 7% 26% 23% 15% 5%	452
	21st to end	Day	26% 7% 25% 23% 14% 4	460
May	1st to 10th	Day	17% 7% 20% 31% 21% 4	463
	11th to 20th	Day	20% 3 18% 28% 24% 7%	488
	21st to end	Day	20% 5% 24% 27% 18% 7%	554
June	1st to 10th	Day	22% 5% 23% 29% 18% 3	680
	11th to 20th	Day	20% 6% 26% 28% 18% 3	680
	21st to end	Day	14% 5% 21% 31% 25% 5%	680
July	1st to 10th	Day	13% 3 16% 35% 29% 5%	671
	11th to 20th	Day	8% 3 17% 36% 29% 6%	668
	21st to end	Day	9% 3 13% 33% 33% 9%	560
August	1st to 10th	Day	11% 3 13% 29% 31% 12%	487
	11th to 20th	Day	9% 4 9% 36% 31% 11%	477
	21st to end	Day	14% 5% 20% 29% 23% 9%	539
September	1st to 10th	Day	17% 4 17% 32% 22% 8%	490
	11th to 20th	Day	21% 5% 16% 25% 27% 5%	463
	21st to end	Day	25% 5% 19% 22% 22% 6%	450
October	1st to 10th	Day	27% 4 18% 21% 20% 8%	450
	11th to 20th	Day	35% 6% 12% 20% 19% 8%	450
	21st to end	Day	37% 11% 14% 19% 13% 6%	368
November	1st to 10th	Day	38% 8% 18% 21% 13% 3	180
	11th to 20th	Day	41% 12% 9% 11% 17% 11%	180
	21st to end	Day	42% 6% 18% 16% 8% 10%	180
December	1st to 10th	Day	47% 9% 14% 8% 10% 12%	180
	11th to 20th	Day	47% 9% 13% 16% 13% 2	180
	21st to end	Day	44% 11% 16% 17% 9% 3	198
January	1st to 10th	Night	49% 8% 16% 16% 9% 3	850
	11th to 20th	Night	45% 6% 12% 20% 15% 2	844
	21st to end	Night	45% 5% 13% 22% 13% 2	836
February	1st to 10th	Night	40% 6% 19% 22% 11% 2	760
	11th to 20th	Night	36% 7% 17% 25% 13% 1	744
	21st to end	Night	37% 7% 20% 21% 12% 2	628
March	1st to 10th	Night	35% 8% 17% 21% 18% 2	760
	11th to 20th	Night	36% 7% 16% 23% 15% 3	760
	21st to end	Night	38% 6% 14% 23% 16% 3	836
April	1st to 10th	Night	35% 6% 13% 28% 16% 3	760
	11th to 20th	Night	26% 7% 17% 29% 17% 5%	668
	21st to end	Night	28% 5% 17% 30% 17% 3	511
May	1st to 10th	Night	19% 4 12% 30% 33% 3	380
	11th to 20th	Night	18% 3 7% 29% 37% 6%	374
	21st to end	Night	19% 3 9% 32% 31% 5%	411
June	1st to 10th	Night	24% 4 12% 28% 28% 3	380
	11th to 20th	Night	17% 4 19% 31% 24% 4	380
	21st to end	Night	14% 4 11% 30% 35% 6%	380
July	1st to 10th	Night	12% 2 8% 31% 42% 5%	370
	11th to 20th	Night	10% 2 8% 30% 42% 8%	368
	21st to end	Night	5% 1 6% 28% 50% 9%	416
August	1st to 10th	Night	10% 2 5% 20% 45% 18%	392
	11th to 20th	Night	9% 1 4 22% 48% 15%	564
	21st to end	Night	13% 3 9% 25% 40% 10%	696
September	1st to 10th	Night	12% 2 6% 34% 38% 9%	760
	11th to 20th	Night	21% 3 13% 17% 34% 12%	736
	21st to end	Night	24% 3 12% 27% 28% 6%	720
October	1st to 10th	Night	24% 3 13% 24% 27% 8%	720
	11th to 20th	Night	34% 4 14% 23% 19% 6%	720
	21st to end	Night	38% 5% 15% 24% 14% 4	792
November	1st to 10th	Night	44% 7% 16% 23% 10%	740
	11th to 20th	Night	43% 6% 18% 19% 12% 3	760
	21st to end	Night	41% 6% 16% 21% 13% 4	760
December	1st to 10th	Night	36% 5% 16% 25% 15% 3	760
	11th to 20th	Night	51% 8% 15% 19% 7% 1	843
	21st to end	Night	49% 7% 19% 18% 7% 1	935

Page generated at 2024-09-11 07:00:03. Version ac07

Copyright © 2024 Attilla Danko.