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 2024-02-05.

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	10% 9% 4 8% 7% 4 6% 6% 6% 8% 32%	77344
	Night	8% 11% 5% 9% 8% 4 6% 6% 6% 7% 30%	81447
Transparency	Day	48% 9% 16% 20% 7%	77017
	Night	50% 8% 15% 19% 8% 1	81354
Seeing	Day	14% 10% 27% 28% 16% 5%	15830
	Night	13% 9% 28% 31% 16% 2	23857

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	6% 13% 7% 12% 11% 6% 8% 7% 5% 5% 18%	1899
	11th to 20th	Day	7% 11% 5% 11% 9% 4 5% 9% 6% 7% 26%	1882
	21st to end	Day	6% 15% 7% 12% 8% 5% 6% 4 5% 6% 25%	2254
February	1st to 10th	Day	7% 10% 5% 8% 9% 6% 7% 7% 6% 7% 26%	1389
	11th to 20th	Day	5% 12% 6% 10% 10% 3 6% 6% 7% 7% 27%	1400
	21st to end	Day	5% 13% 6% 11% 9% 5% 8% 5% 6% 7% 26%	1342
March	1st to 10th	Day	5% 10% 5% 11% 9% 5% 6% 6% 7% 7% 30%	1800
	11th to 20th	Day	9% 14% 8% 10% 8% 3 5% 5% 4 6% 27%	1852
	21st to end	Day	7% 13% 5% 10% 7% 4 5% 5% 6% 8% 31%	2364
April	1st to 10th	Day	7% 12% 5% 8% 7% 4 5% 6% 6% 9% 33%	2160
	11th to 20th	Day	6% 10% 5% 8% 9% 3 6% 6% 7% 8% 34%	2427
	21st to end	Day	12% 11% 5% 9% 6% 4 6% 5% 6% 7% 28%	2520
May	1st to 10th	Day	8% 9% 4 8% 6% 4 6% 6% 6% 7% 36%	2653
	11th to 20th	Day	10% 8% 4 5% 6% 3 5% 6% 6% 7% 41%	2833
	21st to end	Day	13% 7% 3 6% 6% 3 5% 5% 5% 8% 37%	3111
June	1st to 10th	Day	13% 8% 3 7% 7% 5% 6% 6% 6% 8% 31%	2929
	11th to 20th	Day	19% 8% 4 8% 7% 4 6% 6% 7% 8% 24%	3145
	21st to end	Day	13% 7% 3 7% 6% 4 6% 6% 6% 8% 33%	3203
July	1st to 10th	Day	16% 7% 3 7% 6% 4 6% 6% 8% 8% 31%	2912
	11th to 20th	Day	14% 8% 3 6% 6% 4 5% 6% 7% 10% 31%	2880
	21st to end	Day	13% 5% 3 6% 6% 4 6% 6% 7% 9% 37%	3135
August	1st to 10th	Day	13% 5% 3 6% 8% 4 6% 6% 7% 8% 36%	2690
	11th to 20th	Day	10% 6% 2 5% 6% 4 6% 7% 7% 9% 37%	2475
	21st to end	Day	15% 6% 3 6% 6% 3 6% 5% 6% 8% 37%	2746
September	1st to 10th	Day	15% 8% 3 7% 5% 3 4 4 6% 7% 39%	2160
	11th to 20th	Day	11% 7% 3 5% 6% 2 5% 5% 7% 9% 40%	2155
	21st to end	Day	11% 8% 4 7% 5% 4 5% 6% 6% 8% 37%	1931
October	1st to 10th	Day	12% 11% 4 8% 7% 2 5% 5% 6% 7% 33%	1800
	11th to 20th	Day	10% 10% 4 9% 6% 3 5% 4 5% 8% 35%	1633
	21st to end	Day	11% 14% 6% 7% 7% 4 5% 5% 6% 8% 27%	1648
November	1st to 10th	Day	10% 13% 6% 10% 9% 4 5% 4 4 7% 28%	1327
	11th to 20th	Day	11% 12% 6% 11% 10% 4 5% 5% 5% 5% 26%	1283
	21st to end	Day	7% 10% 5% 10% 8% 6% 7% 5% 7% 8% 27%	1140
December	1st to 10th	Day	8% 13% 6% 11% 9% 3 7% 5% 4 7% 27%	1070
	11th to 20th	Day	6% 14% 6% 10% 10% 4 7% 6% 5% 8% 25%	1199
	21st to end	Day	3 7% 5% 8% 6% 4 6% 5% 6% 9% 40%	1997
January	1st to 10th	Night	6% 14% 7% 14% 13% 6% 6% 7% 5% 6% 17%	5046
	11th to 20th	Night	6% 9% 4 8% 8% 5% 7% 9% 9% 8% 27%	5016
	21st to end	Night	6% 15% 7% 14% 10% 5% 6% 5% 5% 6% 21%	5432
February	1st to 10th	Night	6% 11% 5% 11% 8% 5% 6% 5% 6% 7% 29%	2664
	11th to 20th	Night	5% 13% 6% 11% 9% 5% 5% 5% 5% 6% 29%	2444
	21st to end	Night	5% 11% 6% 12% 10% 5% 6% 5% 6% 6% 28%	1914
March	1st to 10th	Night	5% 11% 4 9% 7% 4 5% 7% 7% 7% 35%	2160
	11th to 20th	Night	8% 15% 6% 9% 8% 4 6% 5% 4 8% 28%	2105
	21st to end	Night	5% 11% 6% 8% 7% 3 6% 4 7% 8% 34%	1991
April	1st to 10th	Night	5% 10% 5% 8% 7% 5% 7% 7% 6% 8% 33%	1800
	11th to 20th	Night	5% 9% 5% 10% 8% 4 5% 7% 7% 8% 32%	1481
	21st to end	Night	12% 10% 4 8% 7% 4 7% 6% 6% 8% 29%	1440
May	1st to 10th	Night	9% 9% 5% 7% 6% 4 7% 7% 7% 8% 32%	1306
	11th to 20th	Night	9% 7% 3 5% 6% 3 4 6% 6% 7% 43%	1062
	21st to end	Night	15% 5% 3 5% 6% 2 5% 5% 5% 9% 40%	1164
June	1st to 10th	Night	12% 8% 3 6% 6% 4 6% 7% 6% 8% 34%	1027
	11th to 20th	Night	13% 6% 3 7% 6% 4 6% 7% 8% 9% 30%	810
	21st to end	Night	10% 5% 4 8% 6% 4 6% 5% 6% 10% 35%	754
July	1st to 10th	Night	14% 5% 2 5% 7% 3 6% 8% 7% 10% 33%	1044
	11th to 20th	Night	13% 5% 4 7% 6% 4 5% 6% 6% 9% 34%	1080
	21st to end	Night	10% 6% 2 3 6% 4 6% 6% 8% 10% 38%	1182
August	1st to 10th	Night	10% 5% 2 6% 6% 3 5% 6% 6% 9% 42%	1247
	11th to 20th	Night	9% 5% 2 5% 5% 3 6% 7% 8% 10% 39%	1424
	21st to end	Night	13% 5% 2 6% 6% 5% 5% 6% 6% 8% 36%	1607
September	1st to 10th	Night	12% 8% 3 5% 5% 3 4 5% 6% 9% 41%	1800
	11th to 20th	Night	8% 7% 3 7% 6% 4 6% 6% 7% 9% 37%	1804
	21st to end	Night	9% 9% 3 7% 7% 4 6% 6% 7% 8% 33%	2025
October	1st to 10th	Night	10% 11% 4 7% 7% 5% 6% 5% 7% 7% 32%	2160
	11th to 20th	Night	11% 10% 4 7% 6% 4 5% 6% 6% 8% 33%	2327
	21st to end	Night	8% 15% 5% 8% 7% 4 6% 5% 6% 7% 29%	2708
November	1st to 10th	Night	14% 14% 5% 10% 8% 4 4 4 4 6% 28%	2732
	11th to 20th	Night	9% 14% 7% 12% 10% 5% 6% 5% 5% 5% 23%	2897
	21st to end	Night	8% 11% 5% 9% 8% 5% 7% 5% 6% 7% 30%	3040
December	1st to 10th	Night	8% 14% 6% 11% 9% 4 6% 5% 6% 7% 25%	3106
	11th to 20th	Night	6% 13% 6% 11% 9% 5% 7% 6% 5% 6% 28%	3993
	21st to end	Night	3 10% 5% 8% 6% 4 6% 6% 6% 9% 37%	5655

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	65% 8% 11% 13% 3	1899
	11th to 20th	Day	53% 10% 10% 11% 15% 2	1900
	21st to end	Day	59% 8% 13% 15% 5%	2254
February	1st to 10th	Day	52% 9% 12% 18% 9% 1	1389
	11th to 20th	Day	53% 9% 16% 18% 4	1408
	21st to end	Day	55% 7% 13% 16% 8%	1342
March	1st to 10th	Day	52% 6% 15% 20% 6%	1800
	11th to 20th	Day	57% 6% 13% 19% 6%	1852
	21st to end	Day	51% 7% 16% 22% 5%	2364
April	1st to 10th	Day	46% 8% 16% 20% 9%	2160
	11th to 20th	Day	46% 6% 14% 22% 11% 1	2427
	21st to end	Day	52% 8% 14% 17% 8%	2520
May	1st to 10th	Day	43% 8% 15% 23% 10% 1	2653
	11th to 20th	Day	39% 6% 12% 24% 17% 2	2837
	21st to end	Day	43% 6% 11% 26% 13%	3112
June	1st to 10th	Day	48% 9% 14% 19% 9% 1	2929
	11th to 20th	Day	56% 10% 14% 16% 5%	3145
	21st to end	Day	45% 9% 18% 22% 6%	3203
July	1st to 10th	Day	46% 11% 19% 21% 3	2833
	11th to 20th	Day	46% 12% 21% 19% 2	2793
	21st to end	Day	39% 11% 24% 23% 3	2961
August	1st to 10th	Day	42% 12% 22% 19% 4	2671
	11th to 20th	Day	40% 11% 25% 21% 3	2475
	21st to end	Day	44% 9% 20% 23% 4	2746
September	1st to 10th	Day	44% 8% 21% 20% 7%	2160
	11th to 20th	Day	38% 9% 23% 26% 3	2155
	21st to end	Day	42% 8% 20% 22% 8%	1931
October	1st to 10th	Day	48% 7% 19% 20% 6%	1800
	11th to 20th	Day	46% 8% 20% 21% 5%	1633
	21st to end	Day	53% 9% 16% 19% 3	1648
November	1st to 10th	Day	55% 8% 13% 20% 4 1	1327
	11th to 20th	Day	60% 6% 15% 15% 4	1283
	21st to end	Day	52% 9% 16% 17% 5% 1	1140
December	1st to 10th	Day	56% 9% 14% 13% 7%	1070
	11th to 20th	Day	57% 6% 13% 20% 4	1200
	21st to end	Day	38% 7% 18% 26% 9% 1	1997
January	1st to 10th	Night	66% 7% 10% 11% 4 1	5046
	11th to 20th	Night	46% 10% 10% 16% 16% 2	5060
	21st to end	Night	63% 8% 11% 13% 5%	5432
February	1st to 10th	Night	54% 6% 12% 18% 9% 1	2664
	11th to 20th	Night	55% 8% 14% 18% 5%	2446
	21st to end	Night	54% 9% 11% 17% 9%	1914
March	1st to 10th	Night	45% 7% 17% 22% 9%	2160
	11th to 20th	Night	54% 6% 12% 22% 6%	2106
	21st to end	Night	45% 7% 15% 24% 8% 1	1991
April	1st to 10th	Night	45% 9% 14% 21% 10% 1	1800
	11th to 20th	Night	44% 7% 14% 21% 12% 1	1481
	21st to end	Night	51% 7% 10% 20% 11% 2	1440
May	1st to 10th	Night	44% 9% 16% 19% 11% 1	1306
	11th to 20th	Night	37% 7% 13% 25% 14% 4	1062
	21st to end	Night	41% 7% 11% 26% 16%	1164
June	1st to 10th	Night	44% 9% 19% 19% 8% 2	1027
	11th to 20th	Night	44% 12% 19% 20% 5%	810
	21st to end	Night	43% 8% 18% 24% 6%	754
July	1st to 10th	Night	42% 10% 21% 23% 4	1014
	11th to 20th	Night	45% 11% 19% 23% 3	1044
	21st to end	Night	39% 12% 22% 24% 4	1116
August	1st to 10th	Night	37% 8% 25% 23% 6%	1241
	11th to 20th	Night	35% 13% 23% 25% 4	1424
	21st to end	Night	42% 10% 21% 22% 6%	1607
September	1st to 10th	Night	39% 9% 21% 23% 8%	1800
	11th to 20th	Night	40% 9% 19% 27% 5%	1804
	21st to end	Night	44% 9% 19% 20% 8% 1	2025
October	1st to 10th	Night	48% 8% 15% 21% 7% 1	2160
	11th to 20th	Night	46% 8% 19% 22% 5%	2327
	21st to end	Night	51% 10% 16% 18% 5%	2708
November	1st to 10th	Night	58% 7% 11% 20% 3 1	2732
	11th to 20th	Night	63% 6% 11% 15% 5%	2897
	21st to end	Night	53% 8% 14% 17% 7% 1	3040
December	1st to 10th	Night	56% 8% 14% 15% 7%	3106
	11th to 20th	Night	54% 9% 13% 18% 6%	3991
	21st to end	Night	41% 8% 18% 21% 11% 1	5655

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	13% 7% 24% 35% 18% 3	180
	11th to 20th	Day	18% 16% 23% 24% 17% 2	180
	21st to end	Day	15% 18% 28% 24% 15% 1	198
February	1st to 10th	Day	10% 12% 33% 32% 10% 4	168
	11th to 20th	Day	13% 10% 38% 26% 9% 4	160
	21st to end	Day	9% 10% 35% 31% 11% 4	286
March	1st to 10th	Day	6% 10% 32% 30% 17% 5%	420
	11th to 20th	Day	14% 10% 32% 27% 13% 4	420
	21st to end	Day	13% 16% 29% 30% 10% 3	462
April	1st to 10th	Day	15% 13% 35% 24% 10% 4	420
	11th to 20th	Day	10% 15% 32% 26% 14% 4	412
	21st to end	Day	16% 16% 30% 25% 10% 2	420
May	1st to 10th	Day	13% 15% 30% 27% 11% 4	556
	11th to 20th	Day	10% 11% 27% 32% 16% 4	802
	21st to end	Day	14% 7% 23% 31% 21% 4	874
June	1st to 10th	Day	15% 9% 29% 29% 14% 4	810
	11th to 20th	Day	22% 7% 21% 28% 18% 4	810
	21st to end	Day	13% 7% 21% 29% 23% 8%	810
July	1st to 10th	Day	16% 5% 21% 30% 22% 7%	796
	11th to 20th	Day	15% 6% 20% 28% 24% 8%	792
	21st to end	Day	12% 5% 20% 31% 22% 10%	881
August	1st to 10th	Day	14% 7% 17% 28% 24% 11%	630
	11th to 20th	Day	10% 12% 35% 29% 12% 2	437
	21st to end	Day	19% 9% 23% 26% 17% 6%	495
September	1st to 10th	Day	20% 11% 29% 22% 12% 7%	450
	11th to 20th	Day	12% 12% 23% 28% 18% 6%	450
	21st to end	Day	15% 15% 30% 25% 11% 4	450
October	1st to 10th	Day	20% 14% 33% 22% 9% 2	450
	11th to 20th	Day	16% 11% 29% 31% 11% 1	283
	21st to end	Day	15% 11% 28% 26% 17% 4	230
November	1st to 10th	Day	13% 10% 32% 28% 13% 3	180
	11th to 20th	Day	13% 8% 31% 33% 14% 1	180
	21st to end	Day	15% 12% 39% 23% 8% 2	180
December	1st to 10th	Day	11% 12% 31% 31% 12% 3	180
	11th to 20th	Day	12% 13% 33% 27% 12% 2	180
	21st to end	Day	7% 10% 22% 31% 25% 6%	198
January	1st to 10th	Night	14% 9% 25% 35% 15% 2	1040
	11th to 20th	Night	15% 11% 28% 33% 12% 2	1040
	21st to end	Night	15% 14% 31% 27% 12% 1	1062
February	1st to 10th	Night	10% 10% 31% 33% 13% 2	776
	11th to 20th	Night	11% 10% 35% 31% 13% 1	704
	21st to end	Night	9% 8% 29% 33% 19% 3	592
March	1st to 10th	Night	10% 7% 30% 30% 18% 4	720
	11th to 20th	Night	14% 9% 29% 31% 16% 1	720
	21st to end	Night	10% 7% 27% 35% 18% 3	792
April	1st to 10th	Night	10% 10% 32% 29% 17% 2	720
	11th to 20th	Night	9% 8% 32% 34% 15% 2	413
	21st to end	Night	15% 9% 28% 33% 14% 1	360
May	1st to 10th	Night	14% 6% 31% 31% 15% 3	360
	11th to 20th	Night	12% 9% 27% 32% 19% 1	354
	21st to end	Night	16% 6% 21% 32% 23% 2	389
June	1st to 10th	Night	15% 6% 22% 31% 26% 1	360
	11th to 20th	Night	16% 4 14% 37% 26% 3	360
	21st to end	Night	12% 3 19% 36% 25% 5%	360
July	1st to 10th	Night	16% 3 18% 32% 27% 4	350
	11th to 20th	Night	15% 3 20% 31% 27% 4	348
	21st to end	Night	11% 3 16% 36% 25% 9%	394
August	1st to 10th	Night	11% 4 17% 31% 30% 6%	358
	11th to 20th	Night	11% 3 25% 39% 19% 3	356
	21st to end	Night	16% 4 21% 32% 25% 2	419
September	1st to 10th	Night	15% 8% 24% 29% 21% 4	720
	11th to 20th	Night	11% 7% 27% 34% 17% 3	720
	21st to end	Night	13% 10% 29% 31% 13% 3	720
October	1st to 10th	Night	15% 11% 30% 28% 14% 2	720
	11th to 20th	Night	16% 9% 34% 27% 11% 2	720
	21st to end	Night	16% 13% 30% 25% 13% 2	792
November	1st to 10th	Night	21% 10% 27% 26% 15% 1	882
	11th to 20th	Night	15% 10% 28% 34% 12% 1	972
	21st to end	Night	13% 11% 36% 27% 11% 2	1040
December	1st to 10th	Night	15% 10% 30% 30% 13% 2	1040
	11th to 20th	Night	14% 11% 28% 31% 15% 2	1040
	21st to end	Night	10% 7% 27% 34% 18% 3	1144

Page generated at 2024-02-02 03:20:31. Version ac07

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