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 2025-02-06.

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	21% 8% 3 6% 4 4 4 3 5% 6% 36%	112036
	Night	25% 9% 3 7% 4 4 4 3 5% 6% 30%	114878
Transparency	Day	28% 44% 9% 12% 5% 1	111786
	Night	33% 42% 8% 11% 5% 1	114774
Seeing	Day	25% 6% 18% 25% 20% 6%	15530
	Night	32% 5% 14% 24% 21% 5%	23930

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	38% 12% 4 9% 5% 5% 5% 3 4 5% 10%	3179
	11th to 20th	Day	20% 11% 3 8% 5% 4 4 3 4 8% 29%	3183
	21st to end	Day	40% 10% 3 6% 4 3 3 2 4 4 21%	4065
February	1st to 10th	Day	32% 13% 3 9% 5% 4 4 3 5% 5% 17%	1756
	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	15% 8% 2 7% 4 4 4 3 4 7% 40%	2280
	21st to end	Day	23% 8% 2 6% 4 3 4 3 5% 7% 36%	2000
October	1st to 10th	Day	19% 7% 2 7% 5% 5% 5% 4 6% 9% 31%	3180
	11th to 20th	Day	33% 7% 2 6% 4 4 4 3 5% 7% 25%	3161
	21st to end	Day	28% 10% 4 10% 6% 5% 5% 3 5% 6% 19%	3189
November	1st to 10th	Day	37% 9% 3 7% 4 5% 4 4 5% 5% 18%	1568
	11th to 20th	Day	34% 11% 3 8% 4 3 3 3 4 5% 22%	1600
	21st to end	Day	34% 12% 3 7% 5% 5% 4 3 4 5% 18%	1600
December	1st to 10th	Day	24% 11% 3 8% 6% 5% 5% 4 6% 7% 20%	2620
	11th to 20th	Day	38% 14% 4 8% 4 5% 4 3 4 4 13%	2656
	21st to end	Day	33% 15% 5% 10% 6% 5% 4 3 4 4 11%	3498
January	1st to 10th	Night	37% 14% 4 9% 5% 4 4 3 4 5% 12%	6766
	11th to 20th	Night	22% 8% 2 5% 4 4 4 4 7% 9% 30%	6712
	21st to end	Night	37% 9% 3 6% 3 3 2 2 4 6% 23%	6891
February	1st to 10th	Night	33% 12% 3 8% 4 4 3 3 5% 5% 20%	2535
	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	18% 6% 2 6% 5% 3 3 2 6% 5% 43%	1900
	21st to end	Night	20% 5% 2 7% 5% 3 4 3 5% 7% 40%	2177
October	1st to 10th	Night	18% 7% 2 7% 5% 5% 5% 4 6% 7% 34%	3800
	11th to 20th	Night	29% 7% 3 6% 3 4 4 3 5% 7% 28%	3777
	21st to end	Night	29% 9% 3 8% 4 4 4 3 4 6% 26%	4367
November	1st to 10th	Night	38% 9% 3 7% 5% 5% 4 3 4 5% 17%	2730
	11th to 20th	Night	36% 10% 3 6% 4 4 4 3 4 6% 21%	2800
	21st to end	Night	34% 12% 3 9% 5% 4 4 3 4 5% 18%	2800
December	1st to 10th	Night	26% 9% 3 6% 5% 5% 7% 5% 7% 7% 19%	4560
	11th to 20th	Night	41% 13% 4 9% 4 4 4 3 4 4 11%	5545
	21st to end	Night	34% 14% 4 9% 5% 5% 4 3 4 4 15%	7458

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	56% 29% 6% 7% 1	3179
	11th to 20th	Day	37% 27% 10% 18% 6% 2	3204
	21st to end	Day	50% 28% 5% 14% 4	4065
February	1st to 10th	Day	28% 63% 3 2 2 2	1756
	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	22% 60% 6% 7% 5% 1	2280
	21st to end	Day	20% 60% 7% 9% 4	2000
October	1st to 10th	Day	36% 38% 11% 13% 2	3180
	11th to 20th	Day	41% 37% 7% 9% 6%	3161
	21st to end	Day	45% 37% 7% 8% 3	3189
November	1st to 10th	Day	31% 57% 6% 5% 1	1568
	11th to 20th	Day	26% 58% 5% 7% 2 2	1600
	21st to end	Day	27% 57% 6% 5% 4 1	1600
December	1st to 10th	Day	39% 37% 6% 14% 4	2620
	11th to 20th	Day	55% 33% 6% 5% 1	2659
	21st to end	Day	58% 30% 7% 4 1	3498
January	1st to 10th	Night	56% 29% 5% 7% 2	6766
	11th to 20th	Night	34% 29% 13% 17% 7% 1	6753
	21st to end	Night	47% 29% 8% 13% 4	6891
February	1st to 10th	Night	25% 64% 3 3 3 2	2535
	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	21% 60% 6% 6% 6% 1	1900
	21st to end	Night	19% 60% 6% 10% 4	2177
October	1st to 10th	Night	34% 39% 14% 10% 2	3800
	11th to 20th	Night	39% 37% 7% 12% 4	3777
	21st to end	Night	41% 37% 10% 9% 3	4367
November	1st to 10th	Night	31% 56% 6% 5% 2	2730
	11th to 20th	Night	28% 57% 5% 6% 3 2	2800
	21st to end	Night	30% 56% 4 4 5% 1	2800
December	1st to 10th	Night	41% 39% 8% 9% 3	4560
	11th to 20th	Night	55% 33% 5% 5% 1	5541
	21st to end	Night	55% 29% 6% 8% 1	7458

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	44% 7% 17% 17% 9% 7%	200
	11th to 20th	Day	42% 10% 12% 17% 13% 7%	200
	21st to end	Day	47% 6% 13% 14% 14% 6%	242
February	1st to 10th	Day	41% 9% 17% 19% 12% 2	386
	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% 6% 16% 26% 26% 6%	490
	21st to end	Day	26% 6% 18% 23% 21% 6%	490
October	1st to 10th	Day	27% 4 18% 22% 20% 8%	490
	11th to 20th	Day	36% 6% 11% 20% 18% 7%	490
	21st to end	Day	36% 12% 15% 20% 12% 5%	403
November	1st to 10th	Day	38% 9% 18% 20% 14% 3	200
	11th to 20th	Day	40% 15% 9% 12% 16% 10%	200
	21st to end	Day	42% 8% 17% 15% 9% 11%	200
December	1st to 10th	Day	43% 9% 14% 9% 12% 14%	200
	11th to 20th	Day	48% 11% 14% 14% 13% 2	200
	21st to end	Day	45% 11% 16% 16% 9% 2	220
January	1st to 10th	Night	48% 7% 15% 17% 10% 3	900
	11th to 20th	Night	43% 6% 12% 21% 16% 2	893
	21st to end	Night	43% 5% 13% 22% 14% 3	880
February	1st to 10th	Night	39% 7% 20% 21% 11% 2	780
	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 12% 18% 33% 12%	760
	21st to end	Night	24% 3 12% 26% 28% 6%	760
October	1st to 10th	Night	24% 4 13% 25% 27% 8%	760
	11th to 20th	Night	34% 4 14% 23% 19% 5%	760
	21st to end	Night	38% 6% 15% 24% 13% 4	836
November	1st to 10th	Night	44% 7% 16% 23% 10%	780
	11th to 20th	Night	44% 6% 18% 18% 12% 3	800
	21st to end	Night	41% 6% 15% 21% 14% 4	800
December	1st to 10th	Night	35% 5% 15% 25% 16% 4	800
	11th to 20th	Night	50% 9% 15% 18% 7% 1	893
	21st to end	Night	49% 7% 19% 17% 7% 1	990

Page generated at 2025-02-03 00:05:52. Version ac07

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