Rainbow Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rainbow Lake clear sky chart from 2005-11-06 to 2025-02-25.

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	9% 9% 4 9% 6% 5% 6% 5% 6% 8% 34%	111746
	Night	7% 11% 4 11% 6% 6% 6% 5% 6% 7% 31%	115545
Transparency	Day	45% 8% 16% 21% 9%	111461
	Night	48% 8% 15% 20% 8% 1	115476
Seeing	Day	14% 10% 27% 28% 16% 5%	17259
	Night	13% 9% 28% 31% 16% 2	25285

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	5% 13% 6% 14% 8% 8% 8% 5% 5% 5% 22%	2719
	11th to 20th	Day	5% 10% 4 11% 6% 5% 8% 6% 7% 8% 32%	2702
	21st to end	Day	4 15% 6% 14% 6% 6% 5% 3 5% 7% 29%	3240
February	1st to 10th	Day	6% 12% 4 10% 7% 8% 6% 6% 6% 7% 28%	1512
	11th to 20th	Day	4 12% 4 11% 8% 5% 6% 5% 7% 6% 30%	1560
	21st to end	Day	4 14% 5% 13% 8% 8% 6% 4 6% 7% 26%	1461
March	1st to 10th	Day	3 8% 3 14% 9% 7% 6% 6% 8% 7% 27%	3138
	11th to 20th	Day	6% 14% 5% 13% 7% 6% 6% 4 5% 7% 28%	3271
	21st to end	Day	3 10% 4 10% 6% 6% 5% 4 6% 7% 37%	4153
April	1st to 10th	Day	7% 13% 4 9% 6% 5% 5% 5% 6% 8% 33%	2280
	11th to 20th	Day	6% 10% 4 8% 8% 4 5% 5% 7% 7% 35%	2565
	21st to end	Day	11% 12% 5% 10% 6% 6% 6% 4 6% 7% 28%	2660
May	1st to 10th	Day	6% 7% 2 7% 5% 5% 6% 5% 7% 10% 39%	4665
	11th to 20th	Day	9% 9% 3 7% 5% 5% 5% 5% 7% 8% 38%	5013
	21st to end	Day	11% 9% 3 9% 6% 5% 6% 5% 6% 7% 33%	5509
June	1st to 10th	Day	13% 9% 3 8% 7% 6% 6% 5% 6% 7% 30%	3092
	11th to 20th	Day	18% 9% 3 9% 6% 6% 6% 5% 7% 8% 23%	3320
	21st to end	Day	12% 8% 3 7% 5% 5% 6% 5% 7% 8% 34%	3380
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 6% 5% 8% 9% 38%	5106
	11th to 20th	Day	11% 7% 3 7% 5% 5% 5% 4 6% 8% 39%	5060
	21st to end	Day	10% 6% 2 8% 5% 5% 6% 5% 7% 9% 38%	5486
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 5% 6% 7% 46%	4709
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 8% 43%	4330
	21st to end	Day	14% 6% 3 7% 5% 5% 5% 5% 7% 9% 35%	4797
September	1st to 10th	Day	15% 8% 2 8% 4 4 5% 3 6% 7% 39%	2280
	11th to 20th	Day	11% 8% 3 6% 5% 3 5% 4 7% 9% 39%	2274
	21st to end	Day	11% 9% 3 8% 4 5% 4 5% 6% 8% 36%	2038
October	1st to 10th	Day	10% 12% 4 8% 4 3 4 4 6% 7% 37%	3180
	11th to 20th	Day	7% 12% 4 10% 5% 4 5% 4 6% 8% 35%	2855
	21st to end	Day	9% 17% 7% 10% 6% 5% 5% 3 5% 7% 26%	2859
November	1st to 10th	Day	10% 14% 5% 12% 8% 5% 5% 3 4 7% 27%	1398
	11th to 20th	Day	11% 13% 6% 13% 9% 6% 4 3 5% 5% 25%	1350
	21st to end	Day	6% 11% 4 11% 8% 8% 7% 4 7% 8% 26%	1200
December	1st to 10th	Day	7% 14% 7% 15% 9% 8% 6% 4 5% 6% 19%	1834
	11th to 20th	Day	4 14% 5% 13% 7% 5% 6% 7% 8% 7% 24%	1879
	21st to end	Day	3 8% 5% 11% 6% 6% 8% 4 6% 8% 35%	2871
January	1st to 10th	Night	5% 12% 6% 14% 9% 7% 6% 6% 5% 6% 23%	7226
	11th to 20th	Night	4 9% 3 9% 7% 6% 7% 7% 8% 8% 31%	7196
	21st to end	Night	4 13% 6% 15% 7% 5% 5% 4 5% 6% 30%	7760
February	1st to 10th	Night	5% 12% 4 13% 7% 7% 6% 4 6% 6% 30%	2887
	11th to 20th	Night	4 14% 5% 12% 7% 6% 5% 4 5% 6% 32%	2723
	21st to end	Night	4 13% 5% 13% 9% 6% 6% 4 6% 6% 28%	2087
March	1st to 10th	Night	4 10% 3 12% 7% 6% 8% 6% 7% 7% 30%	3736
	11th to 20th	Night	5% 14% 4 11% 7% 8% 7% 6% 7% 8% 24%	3706
	21st to end	Night	3 9% 4 8% 5% 4 4 3 7% 8% 44%	3499
April	1st to 10th	Night	5% 12% 4 9% 6% 6% 7% 5% 6% 8% 33%	1900
	11th to 20th	Night	5% 10% 4 10% 7% 6% 5% 5% 7% 8% 33%	1563
	21st to end	Night	12% 11% 3 9% 6% 6% 7% 3 6% 7% 30%	1520
May	1st to 10th	Night	7% 7% 2 6% 4 5% 6% 5% 8% 10% 41%	2294
	11th to 20th	Night	8% 8% 4 8% 5% 5% 5% 4 7% 6% 40%	1882
	21st to end	Night	13% 7% 3 8% 6% 5% 5% 5% 6% 7% 37%	2066
June	1st to 10th	Night	12% 8% 3 6% 6% 6% 6% 6% 6% 8% 33%	1084
	11th to 20th	Night	12% 7% 3 9% 6% 5% 7% 6% 8% 8% 30%	855
	21st to end	Night	10% 6% 4 9% 5% 6% 6% 4 8% 8% 35%	796
July	1st to 10th	Night	9% 4 2 6% 5% 4 6% 6% 7% 10% 41%	1850
	11th to 20th	Night	12% 7% 3 7% 6% 5% 5% 4 6% 6% 37%	1900
	21st to end	Night	9% 6% 3 6% 5% 5% 5% 5% 8% 10% 37%	2066
August	1st to 10th	Night	7% 4 2 5% 4 4 5% 4 5% 7% 53%	2219
	11th to 20th	Night	8% 5% 2 6% 4 4 5% 5% 7% 9% 44%	2497
	21st to end	Night	10% 6% 2 6% 5% 5% 5% 5% 8% 10% 37%	2859
September	1st to 10th	Night	12% 8% 3 6% 4 4 4 4 6% 9% 40%	1900
	11th to 20th	Night	7% 8% 3 8% 5% 5% 6% 5% 7% 9% 36%	1905
	21st to end	Night	9% 9% 3 8% 6% 6% 6% 4 8% 8% 33%	2138
October	1st to 10th	Night	8% 10% 4 10% 6% 6% 6% 5% 7% 9% 30%	3800
	11th to 20th	Night	10% 12% 4 8% 5% 4 5% 4 6% 8% 34%	4073
	21st to end	Night	6% 15% 6% 12% 6% 5% 5% 3 6% 7% 30%	4692
November	1st to 10th	Night	13% 15% 5% 11% 7% 5% 4 3 4 5% 28%	2880
	11th to 20th	Night	8% 16% 6% 14% 8% 7% 4 4 5% 5% 23%	3050
	21st to end	Night	7% 12% 4 11% 7% 8% 6% 4 6% 6% 29%	3200
December	1st to 10th	Night	8% 17% 5% 12% 8% 6% 6% 4 6% 6% 22%	5342
	11th to 20th	Night	6% 14% 5% 13% 7% 6% 7% 6% 6% 7% 23%	6313
	21st to end	Night	2 9% 5% 12% 7% 8% 6% 5% 6% 8% 31%	8081

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	62% 7% 11% 13% 7%	2719
	11th to 20th	Day	45% 9% 14% 16% 13% 2	2720
	21st to end	Day	54% 7% 18% 15% 6%	3240
February	1st to 10th	Day	51% 9% 12% 18% 9% 1	1512
	11th to 20th	Day	50% 9% 16% 19% 6%	1568
	21st to end	Day	55% 7% 14% 15% 8%	1461
March	1st to 10th	Day	50% 8% 13% 21% 7%	3138
	11th to 20th	Day	52% 9% 16% 16% 7%	3271
	21st to end	Day	42% 9% 14% 24% 11%	4153
April	1st to 10th	Day	46% 8% 15% 20% 10%	2280
	11th to 20th	Day	45% 6% 13% 22% 13% 1	2565
	21st to end	Day	52% 8% 14% 17% 8% 1	2660
May	1st to 10th	Day	34% 8% 13% 26% 16% 2	4665
	11th to 20th	Day	38% 9% 11% 24% 16% 2	5017
	21st to end	Day	43% 10% 12% 23% 12%	5510
June	1st to 10th	Day	48% 10% 14% 19% 8%	3092
	11th to 20th	Day	55% 10% 13% 17% 5%	3320
	21st to end	Day	45% 9% 17% 22% 7%	3380
July	1st to 10th	Day	37% 10% 19% 25% 8%	5027
	11th to 20th	Day	41% 9% 16% 26% 7%	4973
	21st to end	Day	39% 9% 20% 28% 5%	5313
August	1st to 10th	Day	33% 10% 18% 23% 16%	4690
	11th to 20th	Day	37% 8% 17% 20% 17% 1	4372
	21st to end	Day	43% 8% 25% 21% 3	4796
September	1st to 10th	Day	44% 8% 21% 21% 7%	2280
	11th to 20th	Day	39% 9% 22% 26% 3	2274
	21st to end	Day	43% 8% 19% 22% 9%	2038
October	1st to 10th	Day	44% 6% 19% 28% 3	3180
	11th to 20th	Day	45% 7% 21% 23% 3	2855
	21st to end	Day	56% 9% 15% 17% 3	2859
November	1st to 10th	Day	55% 8% 13% 20% 4 1	1398
	11th to 20th	Day	61% 6% 15% 14% 4	1350
	21st to end	Day	52% 9% 17% 16% 5% 1	1200
December	1st to 10th	Day	64% 9% 12% 11% 4	1834
	11th to 20th	Day	55% 6% 16% 21% 3	1880
	21st to end	Day	45% 7% 16% 25% 7%	2871
January	1st to 10th	Night	59% 6% 11% 13% 11%	7226
	11th to 20th	Night	44% 9% 13% 19% 14% 1	7240
	21st to end	Night	54% 7% 16% 17% 6%	7760
February	1st to 10th	Night	53% 6% 12% 19% 10% 1	2887
	11th to 20th	Night	52% 7% 14% 19% 8%	2725
	21st to end	Night	55% 8% 11% 18% 9%	2087
March	1st to 10th	Night	49% 7% 14% 23% 7%	3736
	11th to 20th	Night	50% 12% 17% 18% 4	3707
	21st to end	Night	35% 8% 16% 26% 15%	3499
April	1st to 10th	Night	45% 9% 14% 21% 10% 1	1900
	11th to 20th	Night	44% 7% 14% 21% 12% 2	1563
	21st to end	Night	51% 7% 10% 20% 11% 2	1520
May	1st to 10th	Night	32% 9% 13% 26% 16% 4	2294
	11th to 20th	Night	38% 9% 12% 21% 17% 3	1882
	21st to end	Night	41% 10% 11% 25% 14%	2066
June	1st to 10th	Night	44% 10% 18% 19% 8% 1	1084
	11th to 20th	Night	45% 12% 18% 20% 5%	855
	21st to end	Night	42% 8% 18% 24% 7%	796
July	1st to 10th	Night	34% 9% 20% 27% 9%	1820
	11th to 20th	Night	44% 9% 15% 25% 6% 1	1864
	21st to end	Night	38% 10% 17% 28% 6% 1	2000
August	1st to 10th	Night	28% 8% 18% 30% 16%	2213
	11th to 20th	Night	32% 10% 16% 27% 14% 2	2521
	21st to end	Night	38% 9% 23% 26% 3	2859
September	1st to 10th	Night	40% 8% 21% 24% 8%	1900
	11th to 20th	Night	40% 9% 19% 27% 5%	1905
	21st to end	Night	44% 9% 19% 20% 8% 1	2138
October	1st to 10th	Night	47% 8% 16% 24% 5% 1	3800
	11th to 20th	Night	46% 6% 17% 27% 4	4073
	21st to end	Night	52% 8% 17% 21% 3	4692
November	1st to 10th	Night	58% 7% 11% 19% 4 1	2880
	11th to 20th	Night	64% 6% 10% 15% 5%	3050
	21st to end	Night	54% 8% 13% 18% 6% 1	3200
December	1st to 10th	Night	61% 7% 13% 13% 6%	5342
	11th to 20th	Night	57% 8% 14% 17% 4	6311
	21st to end	Night	47% 8% 17% 20% 8% 1	8081

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	15% 7% 24% 33% 19% 3	200
	11th to 20th	Day	19% 17% 25% 24% 15% 2	200
	21st to end	Day	16% 18% 30% 22% 13% 1	220
February	1st to 10th	Day	9% 12% 34% 32% 11% 4	200
	11th to 20th	Day	11% 9% 39% 26% 12% 4	200
	21st to end	Day	9% 9% 36% 31% 10% 4	327
March	1st to 10th	Day	5% 9% 32% 30% 17% 6%	460
	11th to 20th	Day	14% 10% 34% 26% 13% 3	460
	21st to end	Day	12% 15% 28% 32% 10% 3	506
April	1st to 10th	Day	16% 13% 34% 24% 9% 3	460
	11th to 20th	Day	10% 14% 30% 28% 14% 4	452
	21st to end	Day	15% 17% 29% 26% 11% 2	460
May	1st to 10th	Day	13% 16% 29% 26% 12% 4	604
	11th to 20th	Day	10% 12% 26% 32% 16% 3	862
	21st to end	Day	13% 8% 24% 32% 20% 4	940
June	1st to 10th	Day	16% 10% 28% 29% 13% 4	870
	11th to 20th	Day	20% 7% 21% 28% 18% 4	870
	21st to end	Day	13% 6% 20% 29% 24% 8%	870
July	1st to 10th	Day	15% 5% 21% 31% 21% 7%	856
	11th to 20th	Day	14% 6% 21% 28% 23% 8%	852
	21st to end	Day	13% 5% 21% 31% 21% 9%	947
August	1st to 10th	Day	13% 7% 17% 27% 25% 11%	679
	11th to 20th	Day	10% 12% 34% 30% 12% 2	477
	21st to end	Day	19% 10% 24% 26% 16% 5%	539
September	1st to 10th	Day	20% 12% 29% 22% 11% 6%	490
	11th to 20th	Day	12% 12% 23% 29% 18% 6%	490
	21st to end	Day	16% 16% 30% 24% 11% 3	490
October	1st to 10th	Day	19% 14% 33% 22% 9% 2	490
	11th to 20th	Day	16% 12% 30% 29% 11% 1	313
	21st to end	Day	15% 12% 29% 25% 15% 4	255
November	1st to 10th	Day	13% 10% 33% 29% 14% 3	200
	11th to 20th	Day	13% 9% 31% 34% 14% 1	200
	21st to end	Day	14% 12% 38% 22% 12% 3	200
December	1st to 10th	Day	11% 13% 33% 31% 11% 3	200
	11th to 20th	Day	12% 13% 35% 27% 12% 2	200
	21st to end	Day	6% 9% 22% 34% 23% 5%	220
January	1st to 10th	Night	14% 9% 25% 34% 15% 2	1100
	11th to 20th	Night	15% 11% 29% 32% 12% 2	1100
	21st to end	Night	15% 16% 31% 26% 11% 1	1123
February	1st to 10th	Night	9% 9% 31% 33% 15% 2	843
	11th to 20th	Night	10% 10% 36% 30% 13% 1	784
	21st to end	Night	9% 10% 30% 32% 17% 3	646
March	1st to 10th	Night	10% 7% 30% 30% 19% 4	760
	11th to 20th	Night	14% 9% 31% 30% 16% 1	760
	21st to end	Night	9% 7% 28% 36% 17% 2	836
April	1st to 10th	Night	10% 10% 33% 28% 17% 2	760
	11th to 20th	Night	9% 9% 31% 34% 15% 2	435
	21st to end	Night	15% 9% 27% 34% 13% 1	380
May	1st to 10th	Night	14% 7% 30% 31% 16% 2	380
	11th to 20th	Night	13% 9% 25% 33% 19% 1	374
	21st to end	Night	15% 6% 21% 33% 22% 2	411
June	1st to 10th	Night	15% 6% 22% 31% 25% 1	380
	11th to 20th	Night	15% 4 15% 37% 27% 3	380
	21st to end	Night	11% 3 18% 36% 26% 5%	380
July	1st to 10th	Night	16% 3 18% 33% 26% 4	370
	11th to 20th	Night	15% 3 19% 32% 27% 4	368
	21st to end	Night	12% 3 17% 36% 25% 8%	416
August	1st to 10th	Night	11% 4 17% 32% 31% 6%	378
	11th to 20th	Night	11% 3 25% 40% 19% 3	376
	21st to end	Night	15% 4 22% 32% 24% 2	444
September	1st to 10th	Night	15% 8% 24% 29% 20% 4	760
	11th to 20th	Night	11% 7% 26% 34% 18% 3	760
	21st to end	Night	13% 10% 29% 31% 13% 3	760
October	1st to 10th	Night	15% 11% 30% 28% 13% 2	760
	11th to 20th	Night	16% 10% 35% 27% 11% 2	760
	21st to end	Night	16% 13% 31% 25% 13% 2	836
November	1st to 10th	Night	21% 11% 28% 25% 14% 1	930
	11th to 20th	Night	15% 10% 28% 35% 11% 1	1025
	21st to end	Night	12% 10% 35% 28% 13% 2	1100
December	1st to 10th	Night	15% 11% 30% 29% 13% 1	1100
	11th to 20th	Night	14% 11% 28% 31% 14% 2	1100
	21st to end	Night	10% 7% 27% 35% 18% 3	1210

Page generated at 2025-02-22 04:51:40. Version ac07

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