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 2026-07-01.

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% 9% 4 9% 6% 6% 6% 5% 7% 8% 33%	142684
	Night	6% 11% 4 11% 7% 6% 6% 5% 6% 8% 31%	138338
Transparency	Day	45% 8% 16% 22% 9%	142352
	Night	48% 8% 15% 21% 8% 1	138253
Seeing	Day	14% 11% 27% 28% 16% 5%	19251
	Night	13% 9% 28% 31% 16% 2	26970

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	4 13% 7% 15% 9% 9% 8% 5% 6% 5% 19%	3527
	11th to 20th	Day	4 8% 3 10% 6% 5% 7% 6% 7% 8% 35%	3522
	21st to end	Day	4 15% 6% 15% 7% 6% 6% 4 6% 7% 25%	4190
February	1st to 10th	Day	6% 12% 4 11% 8% 8% 6% 6% 6% 6% 27%	1588
	11th to 20th	Day	4 12% 5% 12% 8% 5% 6% 5% 7% 6% 30%	1640
	21st to end	Day	4 14% 5% 13% 8% 8% 6% 4 6% 7% 24%	1570
March	1st to 10th	Day	2 7% 4 15% 8% 7% 6% 5% 7% 8% 31%	4618
	11th to 20th	Day	4 14% 6% 15% 9% 6% 5% 4 5% 6% 24%	4793
	21st to end	Day	3 9% 4 10% 6% 5% 5% 4 6% 8% 39%	6088
April	1st to 10th	Day	6% 13% 4 9% 6% 5% 5% 4 6% 8% 33%	2520
	11th to 20th	Day	6% 10% 5% 9% 8% 4 5% 5% 7% 7% 33%	2838
	21st to end	Day	10% 12% 4 10% 6% 6% 6% 4 6% 7% 30%	2940
May	1st to 10th	Day	4 5% 2 7% 5% 6% 6% 5% 8% 10% 42%	8647
	11th to 20th	Day	10% 10% 4 8% 5% 5% 6% 5% 7% 8% 31%	9352
	21st to end	Day	10% 9% 3 9% 6% 6% 7% 5% 7% 8% 29%	10305
June	1st to 10th	Day	12% 9% 3 8% 7% 6% 6% 5% 7% 8% 30%	3418
	11th to 20th	Day	18% 9% 3 9% 6% 6% 6% 5% 7% 8% 24%	3670
	21st to end	Day	11% 7% 3 7% 5% 5% 6% 5% 7% 8% 34%	3736
July	1st to 10th	Day	11% 6% 3 8% 6% 6% 7% 6% 8% 9% 31%	7315
	11th to 20th	Day	10% 6% 3 8% 5% 5% 6% 5% 6% 8% 39%	7240
	21st to end	Day	10% 5% 2 7% 5% 5% 5% 4 7% 8% 42%	7877
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 6% 5% 6% 7% 45%	4859
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 8% 43%	4470
	21st to end	Day	14% 6% 3 7% 5% 5% 5% 4 7% 8% 36%	4949
September	1st to 10th	Day	14% 8% 2 7% 4 4 5% 3 6% 8% 40%	2400
	11th to 20th	Day	11% 8% 2 6% 5% 3 5% 4 7% 9% 39%	2393
	21st to end	Day	11% 9% 3 8% 4 5% 4 5% 6% 8% 37%	2145
October	1st to 10th	Day	10% 12% 4 8% 4 4 4 4 6% 7% 37%	3280
	11th to 20th	Day	7% 12% 4 10% 5% 4 5% 4 6% 7% 35%	2945
	21st to end	Day	9% 17% 7% 10% 6% 5% 5% 3 5% 7% 26%	2950
November	1st to 10th	Day	10% 14% 5% 12% 8% 5% 5% 3 4 7% 28%	1469
	11th to 20th	Day	10% 14% 5% 13% 9% 6% 5% 3 5% 5% 25%	1417
	21st to end	Day	6% 11% 4 11% 7% 8% 7% 4 7% 8% 27%	1260
December	1st to 10th	Day	7% 14% 7% 15% 9% 7% 6% 4 5% 6% 19%	1890
	11th to 20th	Day	4 14% 5% 13% 7% 5% 6% 7% 8% 8% 24%	1929
	21st to end	Day	4 8% 5% 11% 6% 6% 8% 4 6% 8% 34%	2934
January	1st to 10th	Night	4 13% 7% 17% 9% 7% 6% 6% 6% 6% 20%	9366
	11th to 20th	Night	4 8% 3 9% 7% 6% 6% 6% 8% 9% 34%	9376
	21st to end	Night	4 12% 6% 16% 8% 6% 5% 4 5% 6% 27%	10035
February	1st to 10th	Night	5% 12% 4 14% 7% 6% 5% 4 6% 6% 29%	3031
	11th to 20th	Night	4 13% 5% 13% 8% 6% 5% 4 5% 6% 31%	2863
	21st to end	Night	4 13% 5% 13% 9% 7% 6% 4 6% 6% 27%	2236
March	1st to 10th	Night	3 10% 4 12% 7% 6% 7% 6% 7% 8% 31%	5496
	11th to 20th	Night	4 13% 5% 16% 8% 8% 6% 5% 7% 8% 20%	5424
	21st to end	Night	4 9% 4 8% 5% 4 5% 4 7% 8% 43%	5128
April	1st to 10th	Night	5% 11% 4 8% 6% 6% 6% 5% 7% 9% 33%	2100
	11th to 20th	Night	5% 11% 4 10% 7% 6% 5% 5% 7% 8% 32%	1728
	21st to end	Night	11% 11% 3 9% 6% 6% 7% 4 6% 7% 31%	1680
May	1st to 10th	Night	5% 5% 2 6% 4 5% 6% 6% 8% 10% 42%	4271
	11th to 20th	Night	9% 10% 3 9% 5% 5% 5% 5% 6% 7% 35%	3510
	21st to end	Night	12% 7% 3 8% 6% 6% 6% 5% 7% 7% 33%	3866
June	1st to 10th	Night	11% 9% 3 7% 6% 6% 7% 6% 7% 8% 32%	1198
	11th to 20th	Night	12% 8% 3 9% 5% 5% 7% 6% 8% 8% 29%	945
	21st to end	Night	9% 5% 4 8% 5% 5% 6% 5% 8% 8% 35%	880
July	1st to 10th	Night	10% 6% 2 7% 6% 6% 7% 6% 8% 10% 32%	2642
	11th to 20th	Night	10% 6% 3 8% 6% 5% 5% 5% 7% 8% 38%	2720
	21st to end	Night	9% 6% 2 6% 5% 5% 5% 5% 8% 9% 41%	2966
August	1st to 10th	Night	7% 4 2 6% 4 4 5% 4 5% 7% 52%	2289
	11th to 20th	Night	9% 6% 2 6% 4 4 5% 5% 7% 9% 43%	2577
	21st to end	Night	10% 6% 2 6% 5% 5% 5% 5% 8% 10% 38%	2949
September	1st to 10th	Night	12% 8% 3 6% 4 4 4 4 6% 9% 40%	2000
	11th to 20th	Night	8% 8% 3 8% 5% 5% 6% 5% 7% 9% 36%	2006
	21st to end	Night	9% 10% 3 8% 6% 6% 6% 4 7% 8% 34%	2251
October	1st to 10th	Night	8% 10% 3 10% 6% 6% 6% 5% 7% 9% 30%	3920
	11th to 20th	Night	10% 12% 4 8% 5% 4 5% 4 6% 8% 34%	4203
	21st to end	Night	6% 15% 5% 12% 6% 5% 5% 3 6% 7% 30%	4843
November	1st to 10th	Night	12% 15% 5% 11% 7% 5% 4 3 4 5% 28%	3028
	11th to 20th	Night	8% 16% 6% 14% 8% 6% 4 4 5% 5% 23%	3203
	21st to end	Night	7% 12% 4 10% 7% 8% 6% 4 5% 6% 30%	3360
December	1st to 10th	Night	8% 17% 6% 13% 8% 6% 6% 4 6% 6% 21%	5506
	11th to 20th	Night	6% 14% 5% 13% 8% 6% 7% 6% 6% 7% 23%	6483
	21st to end	Night	3 9% 5% 12% 7% 8% 6% 5% 6% 8% 31%	8259

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% 7% 10% 13% 6%	3527
	11th to 20th	Day	41% 9% 18% 19% 12% 2	3540
	21st to end	Day	58% 7% 16% 15% 4	4191
February	1st to 10th	Day	52% 9% 12% 18% 9% 1	1588
	11th to 20th	Day	51% 8% 16% 18% 7%	1648
	21st to end	Day	57% 7% 13% 15% 8%	1570
March	1st to 10th	Day	48% 6% 14% 22% 10%	4618
	11th to 20th	Day	57% 7% 14% 16% 6%	4793
	21st to end	Day	40% 7% 12% 22% 17% 1	6088
April	1st to 10th	Day	46% 8% 15% 20% 11%	2520
	11th to 20th	Day	46% 6% 13% 22% 12% 1	2838
	21st to end	Day	50% 8% 14% 19% 9% 1	2940
May	1st to 10th	Day	31% 7% 16% 29% 16% 1	8647
	11th to 20th	Day	46% 8% 12% 22% 12% 1	9356
	21st to end	Day	46% 9% 13% 23% 10%	10306
June	1st to 10th	Day	48% 9% 13% 20% 9%	3418
	11th to 20th	Day	55% 9% 13% 18% 5%	3670
	21st to end	Day	44% 9% 17% 23% 7%	3736
July	1st to 10th	Day	44% 10% 19% 21% 6%	7236
	11th to 20th	Day	40% 9% 15% 30% 6%	7153
	21st to end	Day	36% 8% 19% 33% 4	7656
August	1st to 10th	Day	33% 10% 18% 23% 16%	4840
	11th to 20th	Day	37% 8% 17% 20% 17% 1	4512
	21st to end	Day	43% 8% 24% 21% 4	4948
September	1st to 10th	Day	42% 8% 21% 22% 7%	2400
	11th to 20th	Day	39% 9% 23% 26% 4	2393
	21st to end	Day	43% 8% 18% 21% 10%	2145
October	1st to 10th	Day	44% 5% 19% 28% 3	3280
	11th to 20th	Day	45% 6% 21% 23% 4	2945
	21st to end	Day	56% 9% 15% 17% 3	2950
November	1st to 10th	Day	55% 8% 13% 19% 5%	1469
	11th to 20th	Day	61% 6% 14% 14% 5%	1417
	21st to end	Day	51% 9% 16% 16% 6% 1	1260
December	1st to 10th	Day	64% 9% 12% 11% 4	1890
	11th to 20th	Day	55% 5% 15% 21% 3	1930
	21st to end	Day	45% 7% 16% 25% 7%	2934
January	1st to 10th	Night	62% 5% 10% 13% 9%	9367
	11th to 20th	Night	41% 9% 16% 20% 13% 1	9420
	21st to end	Night	56% 7% 15% 18% 5%	10035
February	1st to 10th	Night	54% 6% 11% 18% 10% 1	3031
	11th to 20th	Night	53% 7% 13% 19% 8%	2865
	21st to end	Night	56% 8% 10% 18% 8%	2236
March	1st to 10th	Night	47% 6% 13% 25% 9%	5496
	11th to 20th	Night	57% 9% 14% 16% 5%	5425
	21st to end	Night	35% 7% 14% 25% 17% 2	5128
April	1st to 10th	Night	45% 9% 13% 21% 11% 1	2100
	11th to 20th	Night	45% 7% 14% 21% 12% 2	1728
	21st to end	Night	50% 6% 10% 21% 11% 2	1680
May	1st to 10th	Night	30% 8% 18% 26% 14% 3	4268
	11th to 20th	Night	43% 8% 13% 21% 13% 2	3510
	21st to end	Night	43% 9% 12% 23% 11% 1	3870
June	1st to 10th	Night	44% 9% 18% 19% 10% 1	1198
	11th to 20th	Night	46% 11% 17% 21% 5%	945
	21st to end	Night	41% 8% 18% 24% 8%	880
July	1st to 10th	Night	42% 9% 20% 22% 6%	2612
	11th to 20th	Night	41% 8% 14% 30% 6%	2684
	21st to end	Night	36% 9% 19% 32% 4 1	2882
August	1st to 10th	Night	29% 8% 18% 30% 16%	2283
	11th to 20th	Night	33% 10% 16% 26% 13% 1	2601
	21st to end	Night	37% 9% 23% 26% 5%	2949
September	1st to 10th	Night	39% 9% 21% 24% 7%	2000
	11th to 20th	Night	40% 9% 19% 27% 5%	2006
	21st to end	Night	44% 9% 18% 20% 9% 1	2251
October	1st to 10th	Night	47% 8% 15% 24% 5% 1	3920
	11th to 20th	Night	46% 6% 17% 27% 4	4203
	21st to end	Night	52% 7% 17% 22% 3	4843
November	1st to 10th	Night	58% 6% 11% 19% 4 1	3028
	11th to 20th	Night	63% 6% 10% 15% 6%	3203
	21st to end	Night	53% 8% 13% 18% 7% 1	3360
December	1st to 10th	Night	62% 7% 13% 13% 6%	5506
	11th to 20th	Night	58% 7% 14% 17% 5%	6481
	21st to end	Night	48% 8% 16% 20% 8% 1	8259

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% 8% 25% 32% 18% 3	220
	11th to 20th	Day	19% 17% 26% 23% 14% 1	220
	21st to end	Day	16% 17% 33% 21% 12% 1	242
February	1st to 10th	Day	8% 12% 34% 32% 10% 4	220
	11th to 20th	Day	10% 10% 39% 27% 12% 3	220
	21st to end	Day	9% 10% 38% 30% 10% 3	364
March	1st to 10th	Day	5% 11% 34% 29% 15% 5%	540
	11th to 20th	Day	13% 11% 32% 26% 14% 4	540
	21st to end	Day	11% 14% 30% 32% 10% 4	594
April	1st to 10th	Day	14% 13% 35% 25% 9% 4	540
	11th to 20th	Day	11% 15% 30% 27% 13% 3	532
	21st to end	Day	14% 17% 30% 26% 11% 3	540
May	1st to 10th	Day	14% 15% 31% 26% 11% 4	699
	11th to 20th	Day	11% 12% 27% 31% 15% 4	982
	21st to end	Day	13% 10% 25% 30% 18% 4	1072
June	1st to 10th	Day	16% 11% 28% 29% 13% 4	990
	11th to 20th	Day	20% 7% 21% 28% 19% 5%	990
	21st to end	Day	11% 6% 20% 30% 24% 8%	990
July	1st to 10th	Day	15% 6% 22% 31% 21% 6%	917
	11th to 20th	Day	14% 6% 20% 28% 24% 8%	912
	21st to end	Day	12% 5% 20% 31% 22% 9%	1013
August	1st to 10th	Day	13% 7% 18% 26% 25% 10%	729
	11th to 20th	Day	11% 12% 34% 29% 11% 3	517
	21st to end	Day	18% 9% 23% 27% 17% 6%	583
September	1st to 10th	Day	18% 11% 29% 23% 12% 6%	530
	11th to 20th	Day	12% 12% 24% 29% 18% 5%	530
	21st to end	Day	16% 17% 30% 23% 10% 3	530
October	1st to 10th	Day	19% 15% 32% 22% 9% 2	530
	11th to 20th	Day	17% 13% 32% 27% 10% 1	343
	21st to end	Day	15% 13% 29% 25% 14% 4	280
November	1st to 10th	Day	13% 10% 34% 27% 12% 3	220
	11th to 20th	Day	13% 10% 32% 33% 12% 1	220
	21st to end	Day	13% 11% 38% 23% 12% 3	220
December	1st to 10th	Day	11% 13% 35% 29% 10% 2	220
	11th to 20th	Day	12% 12% 35% 27% 12% 2	220
	21st to end	Day	7% 9% 23% 34% 21% 5%	242
January	1st to 10th	Night	14% 9% 26% 34% 15% 2	1160
	11th to 20th	Night	15% 12% 29% 31% 11% 2	1160
	21st to end	Night	15% 16% 31% 26% 11% 1	1184
February	1st to 10th	Night	10% 10% 31% 32% 14% 2	887
	11th to 20th	Night	10% 10% 36% 30% 13% 1	824
	21st to end	Night	9% 10% 30% 32% 16% 2	692
March	1st to 10th	Night	10% 9% 31% 29% 17% 4	840
	11th to 20th	Night	13% 9% 30% 31% 16% 1	840
	21st to end	Night	9% 7% 28% 35% 18% 2	924
April	1st to 10th	Night	10% 10% 32% 30% 16% 2	840
	11th to 20th	Night	10% 8% 30% 35% 14% 2	480
	21st to end	Night	15% 10% 27% 35% 14% 1	420
May	1st to 10th	Night	13% 8% 31% 30% 15% 2	420
	11th to 20th	Night	12% 10% 25% 33% 19% 1	414
	21st to end	Night	16% 7% 21% 33% 21% 2	455
June	1st to 10th	Night	15% 7% 23% 31% 24% 1	420
	11th to 20th	Night	14% 4 15% 37% 27% 3	420
	21st to end	Night	11% 3 18% 36% 27% 5%	420
July	1st to 10th	Night	16% 3 19% 33% 25% 3	390
	11th to 20th	Night	14% 4 19% 31% 27% 4	388
	21st to end	Night	12% 3 16% 36% 25% 8%	438
August	1st to 10th	Night	11% 4 17% 32% 30% 6%	398
	11th to 20th	Night	12% 3 25% 39% 18% 3	396
	21st to end	Night	15% 4 21% 32% 26% 2	468
September	1st to 10th	Night	15% 8% 24% 30% 21% 4	800
	11th to 20th	Night	11% 7% 26% 35% 17% 3	800
	21st to end	Night	14% 11% 29% 30% 13% 3	800
October	1st to 10th	Night	15% 12% 30% 28% 14% 2	800
	11th to 20th	Night	16% 10% 35% 27% 11% 2	800
	21st to end	Night	16% 13% 31% 26% 12% 2	880
November	1st to 10th	Night	21% 11% 28% 24% 14% 1	978
	11th to 20th	Night	15% 10% 29% 34% 11% 1	1078
	21st to end	Night	12% 10% 35% 28% 14% 2	1160
December	1st to 10th	Night	15% 12% 31% 29% 12% 1	1160
	11th to 20th	Night	13% 11% 29% 31% 14% 2	1160
	21st to end	Night	10% 7% 27% 35% 18% 3	1276

Page generated at 2026-06-28 00:10:45. Version ac07

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