Spirit River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spirit River Observatory clear sky chart from 2005-11-06 to 2026-05-17.

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% 3 8% 6% 5% 6% 5% 7% 8% 34%	135555
	Night	7% 11% 4 10% 6% 6% 6% 5% 7% 8% 32%	135943
Transparency	Day	45% 7% 16% 23% 9% 1	135228
	Night	49% 6% 14% 21% 9% 1	135849
Seeing	Day	13% 8% 21% 29% 21% 7%	18585
	Night	14% 7% 23% 34% 18% 3	26718

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% 16% 7% 12% 7% 7% 6% 4 6% 9% 19%	3527
	11th to 20th	Day	3 8% 4 11% 6% 8% 8% 5% 7% 8% 32%	3522
	21st to end	Day	7% 10% 4 10% 5% 5% 7% 5% 7% 10% 30%	4705
February	1st to 10th	Day	7% 13% 4 10% 8% 6% 6% 4 9% 8% 25%	1680
	11th to 20th	Day	4 15% 5% 11% 8% 6% 5% 5% 7% 9% 25%	1689
	21st to end	Day	6% 12% 4 10% 7% 8% 6% 6% 8% 6% 26%	1631
March	1st to 10th	Day	3 8% 4 12% 10% 10% 7% 5% 8% 8% 26%	4618
	11th to 20th	Day	4 11% 6% 14% 8% 6% 6% 4 6% 10% 25%	4778
	21st to end	Day	6% 13% 4 11% 6% 5% 5% 4 6% 7% 33%	6101
April	1st to 10th	Day	4 11% 3 10% 8% 7% 7% 5% 6% 6% 32%	2520
	11th to 20th	Day	8% 11% 4 8% 5% 5% 5% 5% 7% 10% 31%	2720
	21st to end	Day	10% 8% 3 8% 5% 6% 6% 5% 7% 9% 33%	2940
May	1st to 10th	Day	6% 8% 3 7% 5% 5% 6% 5% 8% 9% 39%	6548
	11th to 20th	Day	7% 9% 4 9% 7% 7% 6% 5% 8% 9% 29%	6935
	21st to end	Day	12% 7% 3 7% 5% 5% 6% 6% 9% 11% 30%	7907
June	1st to 10th	Day	12% 8% 3 6% 6% 6% 5% 5% 7% 8% 36%	3200
	11th to 20th	Day	18% 9% 3 9% 6% 6% 5% 5% 6% 8% 26%	3200
	21st to end	Day	9% 6% 2 8% 6% 5% 6% 5% 8% 9% 35%	3200
July	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 4 6% 9% 43%	7240
	11th to 20th	Day	6% 5% 2 7% 5% 5% 5% 4 7% 7% 46%	7240
	21st to end	Day	11% 6% 2 6% 5% 4 5% 4 6% 8% 43%	7712
August	1st to 10th	Day	9% 6% 2 5% 5% 4 5% 4 6% 8% 46%	4541
	11th to 20th	Day	10% 6% 3 7% 5% 4 5% 4 7% 8% 40%	4470
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	4797
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 7% 8% 43%	2400
	11th to 20th	Day	11% 7% 2 6% 5% 4 5% 4 6% 9% 41%	2370
	21st to end	Day	12% 6% 3 6% 4 4 5% 4 8% 9% 39%	2181
October	1st to 10th	Day	12% 10% 4 8% 5% 5% 4 4 6% 8% 34%	3280
	11th to 20th	Day	9% 9% 3 8% 5% 5% 6% 5% 7% 9% 35%	2975
	21st to end	Day	9% 11% 4 10% 5% 4 4 4 6% 7% 34%	3111
November	1st to 10th	Day	13% 13% 5% 9% 6% 6% 4 3 5% 6% 30%	1550
	11th to 20th	Day	8% 15% 4 10% 8% 6% 5% 4 6% 7% 27%	1470
	21st to end	Day	6% 15% 4 10% 8% 5% 4 4 6% 8% 29%	1397
December	1st to 10th	Day	12% 20% 4 9% 6% 5% 6% 5% 5% 7% 22%	2020
	11th to 20th	Day	9% 13% 4 11% 8% 8% 6% 5% 6% 8% 21%	2322
	21st to end	Day	3 7% 3 9% 6% 6% 7% 5% 8% 9% 36%	3058
January	1st to 10th	Night	5% 17% 7% 15% 7% 6% 6% 5% 6% 7% 21%	9366
	11th to 20th	Night	4 8% 3 10% 7% 6% 7% 6% 8% 9% 32%	9376
	21st to end	Night	7% 12% 4 9% 5% 6% 6% 5% 7% 8% 30%	9516
February	1st to 10th	Night	6% 14% 5% 10% 8% 7% 5% 5% 7% 7% 27%	2940
	11th to 20th	Night	5% 13% 6% 13% 7% 6% 5% 4 5% 9% 28%	2813
	21st to end	Night	4 12% 4 10% 7% 7% 6% 5% 6% 7% 30%	2174
March	1st to 10th	Night	2 9% 4 12% 8% 6% 6% 6% 7% 8% 32%	5496
	11th to 20th	Night	3 13% 6% 13% 7% 6% 5% 5% 7% 9% 27%	5438
	21st to end	Night	8% 9% 3 9% 5% 4 4 4 6% 9% 40%	5116
April	1st to 10th	Night	5% 10% 3 9% 8% 6% 7% 5% 8% 7% 33%	2100
	11th to 20th	Night	9% 11% 2 8% 7% 5% 7% 5% 6% 7% 32%	1846
	21st to end	Night	11% 9% 3 9% 6% 5% 5% 5% 7% 8% 33%	1680
May	1st to 10th	Night	6% 10% 4 9% 5% 4 5% 4 8% 9% 38%	3631
	11th to 20th	Night	8% 8% 3 9% 6% 7% 7% 5% 7% 9% 31%	3076
	21st to end	Night	10% 7% 4 8% 5% 6% 6% 6% 8% 11% 30%	2968
June	1st to 10th	Night	13% 8% 2 8% 7% 5% 6% 5% 6% 7% 34%	1200
	11th to 20th	Night	18% 8% 3 7% 5% 5% 6% 5% 8% 7% 29%	1200
	21st to end	Night	11% 6% 3 7% 6% 7% 5% 5% 7% 7% 37%	1200
July	1st to 10th	Night	11% 7% 3 7% 5% 4 5% 5% 7% 8% 38%	2720
	11th to 20th	Night	7% 5% 3 6% 5% 5% 6% 5% 6% 9% 43%	2720
	21st to end	Night	10% 5% 3 7% 4 4 4 5% 7% 11% 40%	3128
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 6% 8% 48%	2609
	11th to 20th	Night	11% 5% 2 7% 4 5% 5% 4 7% 8% 44%	2577
	21st to end	Night	8% 5% 2 7% 5% 6% 5% 5% 7% 8% 41%	3106
September	1st to 10th	Night	12% 6% 2 7% 5% 5% 4 4 7% 8% 40%	2000
	11th to 20th	Night	10% 6% 3 6% 4 5% 5% 4 6% 7% 44%	2030
	21st to end	Night	10% 8% 2 7% 5% 5% 6% 4 6% 8% 39%	2215
October	1st to 10th	Night	10% 11% 4 10% 5% 5% 5% 4 5% 6% 33%	3920
	11th to 20th	Night	7% 8% 3 6% 6% 5% 6% 4 6% 8% 41%	4174
	21st to end	Night	9% 10% 3 8% 6% 5% 6% 4 7% 7% 34%	4683
November	1st to 10th	Night	13% 14% 5% 9% 6% 5% 4 3 5% 7% 28%	2947
	11th to 20th	Night	7% 16% 5% 10% 7% 5% 5% 4 6% 7% 29%	3150
	21st to end	Night	7% 15% 5% 9% 8% 6% 5% 4 6% 6% 28%	3218
December	1st to 10th	Night	10% 14% 5% 10% 6% 7% 6% 5% 6% 6% 26%	5380
	11th to 20th	Night	9% 16% 5% 13% 7% 7% 7% 5% 6% 7% 19%	6090
	21st to end	Night	4 10% 4 11% 7% 7% 6% 4 7% 7% 34%	8140

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% 6% 9% 14% 9%	3527
	11th to 20th	Day	48% 5% 15% 19% 12% 2	3540
	21st to end	Day	47% 11% 20% 16% 6%	4706
February	1st to 10th	Day	54% 7% 12% 14% 13% 1	1680
	11th to 20th	Day	54% 8% 13% 16% 8%	1697
	21st to end	Day	55% 6% 13% 18% 8%	1631
March	1st to 10th	Day	54% 6% 13% 21% 6%	4618
	11th to 20th	Day	53% 8% 14% 18% 7%	4778
	21st to end	Day	48% 6% 13% 22% 10%	6101
April	1st to 10th	Day	49% 7% 13% 21% 9%	2520
	11th to 20th	Day	45% 7% 16% 21% 10% 1	2720
	21st to end	Day	45% 6% 14% 26% 8% 1	2940
May	1st to 10th	Day	39% 5% 12% 26% 15% 3	6548
	11th to 20th	Day	47% 6% 14% 23% 9% 1	6939
	21st to end	Day	43% 7% 18% 21% 10% 1	7908
June	1st to 10th	Day	45% 6% 15% 24% 9% 1	3200
	11th to 20th	Day	55% 7% 13% 19% 6%	3200
	21st to end	Day	41% 8% 17% 25% 8%	3200
July	1st to 10th	Day	37% 6% 19% 22% 15% 1	7161
	11th to 20th	Day	36% 6% 15% 32% 10% 2	7153
	21st to end	Day	38% 7% 20% 29% 6% 1	7493
August	1st to 10th	Day	35% 8% 18% 34% 6%	4524
	11th to 20th	Day	40% 7% 18% 23% 12%	4512
	21st to end	Day	42% 6% 23% 24% 5%	4796
September	1st to 10th	Day	38% 6% 25% 25% 6% 1	2400
	11th to 20th	Day	40% 6% 21% 26% 7%	2370
	21st to end	Day	40% 7% 19% 24% 9% 1	2181
October	1st to 10th	Day	47% 5% 19% 23% 5% 1	3280
	11th to 20th	Day	44% 6% 18% 27% 5%	2975
	21st to end	Day	49% 4 22% 22% 4	3111
November	1st to 10th	Day	55% 5% 12% 22% 5%	1550
	11th to 20th	Day	56% 8% 14% 16% 6%	1470
	21st to end	Day	55% 7% 11% 18% 7% 2	1397
December	1st to 10th	Day	64% 8% 12% 9% 6% 1	2020
	11th to 20th	Day	62% 7% 14% 13% 4	2324
	21st to end	Day	42% 9% 14% 24% 9% 1	3058
January	1st to 10th	Night	63% 6% 7% 14% 9%	9367
	11th to 20th	Night	46% 6% 16% 17% 13% 1	9420
	21st to end	Night	50% 9% 17% 17% 6%	9516
February	1st to 10th	Night	55% 5% 12% 16% 11%	2940
	11th to 20th	Night	55% 6% 12% 17% 9% 1	2815
	21st to end	Night	51% 4 14% 21% 9% 1	2174
March	1st to 10th	Night	48% 5% 13% 20% 13%	5496
	11th to 20th	Night	50% 8% 14% 21% 7%	5439
	21st to end	Night	40% 5% 11% 27% 16%	5116
April	1st to 10th	Night	47% 7% 10% 21% 14% 1	2100
	11th to 20th	Night	49% 5% 12% 20% 12% 2	1846
	21st to end	Night	47% 6% 9% 26% 10% 1	1680
May	1st to 10th	Night	41% 5% 10% 25% 16% 3	3628
	11th to 20th	Night	45% 7% 12% 25% 10% 1	3076
	21st to end	Night	43% 10% 17% 19% 9% 3	2968
June	1st to 10th	Night	47% 7% 9% 25% 12% 1	1200
	11th to 20th	Night	50% 7% 14% 21% 7%	1200
	21st to end	Night	43% 8% 15% 23% 11%	1200
July	1st to 10th	Night	41% 6% 16% 23% 14% 1	2690
	11th to 20th	Night	38% 6% 14% 30% 12%	2684
	21st to end	Night	37% 6% 20% 28% 8%	3042
August	1st to 10th	Night	35% 6% 18% 36% 5%	2601
	11th to 20th	Night	37% 6% 15% 27% 14% 1	2601
	21st to end	Night	39% 7% 25% 22% 6% 1	3106
September	1st to 10th	Night	39% 7% 20% 27% 7% 1	2000
	11th to 20th	Night	39% 6% 17% 31% 7%	2030
	21st to end	Night	41% 8% 15% 24% 12% 1	2215
October	1st to 10th	Night	51% 6% 15% 19% 9% 1	3920
	11th to 20th	Night	41% 5% 15% 30% 8%	4174
	21st to end	Night	48% 5% 17% 24% 6%	4683
November	1st to 10th	Night	56% 6% 12% 21% 6%	2947
	11th to 20th	Night	55% 8% 13% 18% 6%	3150
	21st to end	Night	56% 7% 11% 18% 6% 1	3218
December	1st to 10th	Night	59% 7% 11% 16% 6%	5380
	11th to 20th	Night	64% 8% 12% 11% 5%	6087
	21st to end	Night	48% 6% 14% 24% 6% 1	8140

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% 10% 17% 35% 17% 7%	220
	11th to 20th	Day	12% 14% 22% 31% 16% 5%	220
	21st to end	Day	13% 10% 28% 28% 17% 4	242
February	1st to 10th	Day	14% 6% 23% 33% 18% 6%	220
	11th to 20th	Day	10% 7% 20% 30% 26% 6%	269
	21st to end	Day	9% 7% 22% 35% 23% 4	395
March	1st to 10th	Day	9% 7% 21% 34% 23% 7%	540
	11th to 20th	Day	10% 6% 19% 35% 23% 7%	540
	21st to end	Day	15% 6% 21% 28% 21% 8%	594
April	1st to 10th	Day	9% 11% 25% 32% 15% 8%	540
	11th to 20th	Day	14% 8% 21% 29% 21% 7%	532
	21st to end	Day	13% 8% 21% 29% 22% 7%	540
May	1st to 10th	Day	11% 10% 23% 35% 17% 5%	579
	11th to 20th	Day	12% 6% 21% 27% 28% 7%	800
	21st to end	Day	14% 6% 19% 29% 23% 8%	1006
June	1st to 10th	Day	15% 8% 25% 30% 17% 5%	930
	11th to 20th	Day	21% 6% 18% 26% 23% 6%	930
	21st to end	Day	11% 5% 18% 28% 26% 12%	930
July	1st to 10th	Day	14% 5% 17% 30% 26% 9%	916
	11th to 20th	Day	11% 5% 18% 30% 24% 12%	912
	21st to end	Day	13% 6% 17% 30% 25% 9%	948
August	1st to 10th	Day	15% 8% 14% 26% 23% 13%	527
	11th to 20th	Day	9% 9% 27% 27% 20% 7%	517
	21st to end	Day	15% 9% 22% 23% 19% 12%	583
September	1st to 10th	Day	17% 7% 23% 25% 19% 9%	530
	11th to 20th	Day	15% 7% 22% 26% 22% 7%	530
	21st to end	Day	15% 14% 30% 22% 15% 4	530
October	1st to 10th	Day	17% 13% 22% 27% 17% 4	530
	11th to 20th	Day	17% 13% 23% 28% 15% 3	360
	21st to end	Day	17% 10% 26% 27% 16% 5%	333
November	1st to 10th	Day	18% 9% 20% 32% 16% 5%	220
	11th to 20th	Day	15% 7% 23% 37% 15% 4	220
	21st to end	Day	11% 12% 23% 32% 17% 5%	220
December	1st to 10th	Day	12% 17% 21% 31% 14% 4	220
	11th to 20th	Day	15% 10% 21% 37% 14% 3	220
	21st to end	Day	11% 5% 23% 33% 24% 6%	242
January	1st to 10th	Night	14% 8% 21% 36% 19% 3	1160
	11th to 20th	Night	13% 12% 24% 34% 15% 2	1160
	21st to end	Night	19% 13% 25% 30% 12% 1	1029
February	1st to 10th	Night	14% 7% 20% 35% 19% 6%	840
	11th to 20th	Night	11% 9% 24% 36% 17% 3	824
	21st to end	Night	8% 7% 23% 36% 22% 4	692
March	1st to 10th	Night	9% 7% 26% 32% 22% 4	840
	11th to 20th	Night	13% 5% 22% 41% 18% 2	840
	21st to end	Night	15% 5% 18% 34% 24% 3	924
April	1st to 10th	Night	9% 6% 24% 38% 22% 2	840
	11th to 20th	Night	14% 6% 22% 34% 22% 2	598
	21st to end	Night	14% 7% 23% 32% 22% 3	420
May	1st to 10th	Night	11% 8% 25% 38% 16% 2	420
	11th to 20th	Night	11% 6% 23% 33% 24% 2	406
	21st to end	Night	17% 4 16% 36% 24% 3	433
June	1st to 10th	Night	15% 7% 24% 33% 21% 1	400
	11th to 20th	Night	21% 5% 18% 31% 23% 4	400
	21st to end	Night	13% 4 18% 34% 28% 3	400
July	1st to 10th	Night	12% 5% 19% 35% 27% 2	390
	11th to 20th	Night	13% 2 18% 36% 26% 5%	388
	21st to end	Night	8% 4 17% 37% 29% 4	438
August	1st to 10th	Night	10% 2 17% 34% 32% 6%	398
	11th to 20th	Night	9% 5% 26% 37% 21% 3	396
	21st to end	Night	11% 5% 23% 38% 22% 2	573
September	1st to 10th	Night	15% 4 19% 38% 21% 3	800
	11th to 20th	Night	12% 7% 19% 37% 23% 3	800
	21st to end	Night	14% 8% 32% 29% 15% 2	800
October	1st to 10th	Night	16% 9% 26% 33% 14% 2	800
	11th to 20th	Night	16% 8% 26% 34% 13% 2	800
	21st to end	Night	19% 10% 29% 30% 11% 1	880
November	1st to 10th	Night	20% 7% 26% 29% 16% 3	897
	11th to 20th	Night	18% 8% 26% 35% 12% 1	1050
	21st to end	Night	15% 10% 25% 36% 13% 2	1086
December	1st to 10th	Night	14% 10% 27% 35% 12% 2	1160
	11th to 20th	Night	15% 10% 23% 34% 16% 3	1160
	21st to end	Night	12% 6% 23% 36% 20% 3	1276

Page generated at 2026-05-13 23:58:58. Version ac07

Copyright © 2026 Attilla Danko.