Jasper House Viewpoint
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jasper House Viewpoint clear sky chart from 2005-11-06 to 2025-05-11.

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	7% 9% 4 10% 7% 6% 6% 5% 7% 8% 30%	116930
	Night	4 8% 4 10% 6% 6% 6% 5% 8% 9% 33%	120708
Transparency	Day	49% 12% 14% 16% 7% 1	116668
	Night	47% 13% 16% 17% 7% 1	120616
Seeing	Day	19% 21% 31% 20% 7% 1	16715
	Night	13% 18% 35% 24% 9% 1	25183

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	1 5% 5% 13% 8% 8% 7% 6% 9% 11% 28%	2719
	11th to 20th	Day	1 5% 2 10% 7% 7% 7% 6% 10% 10% 35%	3070
	21st to end	Day	2 7% 4 11% 7% 7% 7% 6% 8% 9% 32%	4004
February	1st to 10th	Day	1 9% 5% 12% 8% 7% 7% 7% 9% 9% 27%	1600
	11th to 20th	Day	1 10% 5% 11% 8% 7% 6% 5% 7% 9% 30%	1639
	21st to end	Day	1 7% 5% 12% 10% 8% 8% 8% 8% 7% 27%	1631
March	1st to 10th	Day	1 7% 3 10% 9% 8% 8% 6% 9% 10% 29%	4518
	11th to 20th	Day	2 9% 3 8% 5% 5% 6% 6% 9% 12% 35%	4671
	21st to end	Day	3 12% 6% 19% 8% 6% 5% 5% 6% 9% 21%	5969
April	1st to 10th	Day	3 12% 6% 13% 9% 9% 8% 6% 8% 8% 18%	2400
	11th to 20th	Day	4 14% 7% 13% 9% 7% 5% 5% 7% 8% 22%	2511
	21st to end	Day	7% 14% 5% 12% 8% 6% 6% 5% 6% 8% 23%	2759
May	1st to 10th	Day	8% 18% 5% 11% 7% 6% 5% 4 5% 6% 25%	4560
	11th to 20th	Day	9% 15% 5% 10% 7% 6% 6% 4 7% 8% 24%	4618
	21st to end	Day	16% 16% 5% 12% 7% 7% 6% 4 5% 6% 16%	5216
June	1st to 10th	Day	18% 11% 3 9% 7% 7% 5% 5% 6% 7% 21%	3040
	11th to 20th	Day	21% 13% 4 10% 8% 7% 6% 5% 5% 6% 16%	3040
	21st to end	Day	13% 9% 4 9% 7% 7% 6% 5% 7% 6% 26%	3040
July	1st to 10th	Day	12% 7% 3 7% 6% 4 5% 4 5% 6% 41%	5060
	11th to 20th	Day	8% 5% 1 6% 5% 5% 5% 4 6% 8% 46%	5060
	21st to end	Day	9% 6% 3 8% 7% 6% 8% 6% 9% 8% 32%	4868
August	1st to 10th	Day	12% 6% 2 6% 5% 5% 6% 5% 6% 8% 40%	4401
	11th to 20th	Day	11% 7% 3 6% 5% 6% 6% 5% 7% 9% 35%	4330
	21st to end	Day	12% 7% 3 8% 5% 6% 6% 4 7% 8% 34%	4478
September	1st to 10th	Day	11% 9% 3 8% 5% 5% 5% 4 6% 6% 37%	2280
	11th to 20th	Day	10% 9% 3 8% 4 5% 5% 5% 7% 7% 37%	2218
	21st to end	Day	9% 10% 4 9% 6% 6% 5% 5% 7% 7% 35%	2090
October	1st to 10th	Day	4 9% 3 8% 6% 6% 6% 5% 9% 11% 33%	3225
	11th to 20th	Day	5% 10% 3 8% 7% 7% 6% 6% 8% 9% 31%	2888
	21st to end	Day	3 9% 4 11% 6% 6% 6% 5% 6% 8% 37%	3101
November	1st to 10th	Day	2 10% 4 12% 7% 8% 7% 5% 7% 9% 28%	1610
	11th to 20th	Day	1 7% 4 8% 6% 6% 7% 6% 7% 12% 37%	1400
	21st to end	Day	2 10% 3 11% 7% 7% 5% 5% 9% 11% 30%	1400
December	1st to 10th	Day	2 7% 3 10% 9% 8% 7% 6% 9% 10% 30%	2262
	11th to 20th	Day	2 6% 4 9% 6% 7% 7% 6% 7% 9% 36%	2262
	21st to end	Day	6% 4 10% 7% 6% 6% 5% 7% 9% 41%	2992
January	1st to 10th	Night	1 6% 4 14% 7% 7% 7% 5% 8% 10% 30%	7226
	11th to 20th	Night	1 6% 3 11% 7% 7% 7% 6% 7% 11% 33%	6869
	21st to end	Night	1 7% 4 10% 6% 7% 7% 6% 8% 10% 34%	6952
February	1st to 10th	Night	2 9% 4 12% 10% 8% 7% 8% 7% 8% 25%	2800
	11th to 20th	Night	1 9% 4 11% 8% 7% 8% 6% 8% 9% 30%	2645
	21st to end	Night	1 8% 5% 11% 9% 7% 7% 6% 8% 9% 29%	1998
March	1st to 10th	Night	1 7% 4 10% 9% 8% 7% 5% 8% 9% 32%	5376
	11th to 20th	Night	2 6% 4 12% 7% 6% 7% 6% 9% 10% 32%	5327
	21st to end	Night	4 14% 7% 18% 6% 4 5% 4 6% 7% 26%	5006
April	1st to 10th	Night	2 13% 5% 12% 7% 6% 6% 7% 8% 7% 27%	2000
	11th to 20th	Night	5% 13% 4 10% 7% 6% 5% 4 7% 9% 30%	1839
	21st to end	Night	8% 13% 5% 10% 5% 5% 5% 4 6% 7% 32%	1640
May	1st to 10th	Night	8% 17% 4 9% 6% 5% 5% 4 6% 8% 28%	2620
	11th to 20th	Night	9% 12% 4 10% 7% 6% 5% 4 6% 7% 30%	2280
	21st to end	Night	16% 15% 4 8% 5% 4 5% 5% 7% 7% 23%	2355
June	1st to 10th	Night	15% 10% 4 7% 5% 5% 5% 4 7% 6% 32%	1140
	11th to 20th	Night	18% 10% 3 9% 7% 6% 7% 5% 8% 7% 21%	1140
	21st to end	Night	10% 8% 2 7% 6% 6% 6% 5% 7% 6% 36%	1140
July	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 6% 8% 45%	1900
	11th to 20th	Night	8% 5% 2 4 4 3 4 4 7% 7% 53%	1900
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 5% 7% 8% 42%	2680
August	1st to 10th	Night	11% 8% 3 6% 4 5% 4 3 7% 8% 41%	2529
	11th to 20th	Night	14% 8% 2 7% 4 4 4 5% 7% 8% 36%	2497
	21st to end	Night	11% 6% 3 6% 5% 5% 6% 5% 7% 8% 38%	3175
September	1st to 10th	Night	11% 9% 2 7% 5% 4 5% 4 5% 8% 40%	1900
	11th to 20th	Night	10% 9% 3 7% 5% 5% 5% 4 5% 7% 40%	1962
	21st to end	Night	8% 8% 3 6% 4 5% 5% 6% 7% 8% 39%	2090
October	1st to 10th	Night	5% 11% 4 8% 5% 7% 6% 5% 8% 9% 31%	3751
	11th to 20th	Night	4 7% 3 7% 6% 6% 7% 7% 9% 10% 35%	4041
	21st to end	Night	2 9% 5% 11% 6% 6% 7% 4 7% 9% 35%	4457
November	1st to 10th	Night	3 11% 5% 11% 7% 6% 6% 6% 8% 8% 29%	2666
	11th to 20th	Night	2 9% 4 10% 6% 5% 6% 5% 9% 11% 34%	3000
	21st to end	Night	1 10% 3 10% 8% 7% 6% 5% 8% 11% 31%	3000
December	1st to 10th	Night	2 7% 4 10% 7% 7% 8% 6% 8% 8% 33%	4913
	11th to 20th	Night	1 8% 4 10% 8% 9% 7% 5% 8% 11% 29%	5930
	21st to end	Night	1 7% 4 11% 6% 6% 7% 5% 8% 10% 35%	7964

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	49% 15% 17% 13% 6% 1	2719
	11th to 20th	Day	47% 12% 9% 16% 13% 3	3090
	21st to end	Day	42% 20% 20% 12% 6%	4004
February	1st to 10th	Day	49% 14% 12% 10% 12% 3	1600
	11th to 20th	Day	54% 11% 12% 15% 7% 1	1647
	21st to end	Day	54% 12% 12% 14% 7% 2	1631
March	1st to 10th	Day	44% 16% 15% 13% 12%	4518
	11th to 20th	Day	38% 17% 13% 21% 11%	4671
	21st to end	Day	58% 13% 10% 11% 8%	5969
April	1st to 10th	Day	61% 14% 14% 9% 2	2400
	11th to 20th	Day	60% 10% 13% 13% 3	2511
	21st to end	Day	59% 12% 13% 13% 3	2759
May	1st to 10th	Day	58% 9% 13% 14% 5%	4560
	11th to 20th	Day	53% 15% 15% 12% 6%	4622
	21st to end	Day	65% 13% 11% 8% 3	5217
June	1st to 10th	Day	62% 11% 10% 12% 4 1	3040
	11th to 20th	Day	68% 10% 10% 9% 3	3040
	21st to end	Day	57% 13% 12% 12% 5% 1	3040
July	1st to 10th	Day	41% 8% 9% 18% 18% 6%	4981
	11th to 20th	Day	35% 10% 11% 24% 17% 3	4973
	21st to end	Day	46% 9% 16% 16% 12% 1	4713
August	1st to 10th	Day	42% 11% 12% 28% 7%	4384
	11th to 20th	Day	43% 12% 16% 22% 7%	4372
	21st to end	Day	47% 10% 16% 21% 5%	4477
September	1st to 10th	Day	46% 10% 16% 21% 5% 2	2280
	11th to 20th	Day	45% 11% 15% 19% 9% 1	2218
	21st to end	Day	49% 11% 16% 15% 8% 2	2090
October	1st to 10th	Day	45% 12% 22% 18% 4	3225
	11th to 20th	Day	51% 11% 17% 18% 2	2888
	21st to end	Day	45% 10% 23% 18% 3	3101
November	1st to 10th	Day	52% 12% 16% 14% 5% 1	1610
	11th to 20th	Day	42% 15% 21% 16% 6% 1	1400
	21st to end	Day	48% 16% 17% 12% 4 4	1400
December	1st to 10th	Day	55% 13% 17% 10% 4	2262
	11th to 20th	Day	44% 12% 20% 17% 6% 1	2264
	21st to end	Day	38% 12% 17% 22% 9% 1	2992
January	1st to 10th	Night	51% 12% 14% 16% 6% 1	7226
	11th to 20th	Night	46% 12% 11% 14% 15% 2	6911
	21st to end	Night	43% 19% 18% 12% 7%	6952
February	1st to 10th	Night	55% 12% 12% 12% 9% 1	2800
	11th to 20th	Night	50% 12% 15% 15% 7% 1	2647
	21st to end	Night	49% 11% 13% 18% 7% 1	1998
March	1st to 10th	Night	44% 16% 14% 16% 10% 1	5376
	11th to 20th	Night	43% 15% 16% 19% 7%	5328
	21st to end	Night	54% 10% 13% 15% 9%	5006
April	1st to 10th	Night	52% 15% 17% 14% 3	2000
	11th to 20th	Night	51% 11% 15% 16% 6%	1839
	21st to end	Night	49% 13% 15% 18% 5% 1	1640
May	1st to 10th	Night	51% 12% 16% 18% 3	2620
	11th to 20th	Night	49% 13% 15% 14% 8%	2280
	21st to end	Night	54% 18% 14% 12% 3	2355
June	1st to 10th	Night	51% 10% 15% 15% 7% 1	1140
	11th to 20th	Night	59% 14% 13% 10% 4	1140
	21st to end	Night	47% 12% 19% 15% 6% 1	1140
July	1st to 10th	Night	35% 10% 11% 24% 17% 3	1870
	11th to 20th	Night	30% 10% 16% 26% 18% 1	1864
	21st to end	Night	39% 9% 20% 21% 9% 3	2596
August	1st to 10th	Night	40% 9% 17% 32% 2	2521
	11th to 20th	Night	43% 12% 18% 23% 5%	2521
	21st to end	Night	43% 10% 23% 19% 4	3175
September	1st to 10th	Night	43% 10% 15% 23% 7% 2	1900
	11th to 20th	Night	43% 10% 18% 20% 8% 1	1962
	21st to end	Night	42% 13% 18% 18% 8%	2090
October	1st to 10th	Night	49% 12% 19% 16% 3	3751
	11th to 20th	Night	44% 13% 19% 19% 4	4041
	21st to end	Night	47% 11% 22% 16% 5%	4457
November	1st to 10th	Night	51% 11% 18% 15% 4 1	2666
	11th to 20th	Night	46% 14% 18% 15% 7% 1	3000
	21st to end	Night	49% 14% 15% 14% 6% 2	3000
December	1st to 10th	Night	51% 12% 18% 13% 5% 1	4913
	11th to 20th	Night	52% 15% 15% 14% 5%	5927
	21st to end	Night	42% 14% 17% 19% 7% 1	7964

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	9% 26% 35% 23% 5% 3	200
	11th to 20th	Day	15% 24% 35% 19% 6% 3	200
	21st to end	Day	16% 30% 37% 11% 5% 1	220
February	1st to 10th	Day	18% 25% 33% 15% 8% 3	200
	11th to 20th	Day	13% 20% 43% 18% 5% 1	279
	21st to end	Day	17% 25% 36% 18% 4 1	405
March	1st to 10th	Day	18% 26% 31% 17% 6% 1	500
	11th to 20th	Day	17% 26% 35% 16% 4 2	500
	21st to end	Day	14% 29% 30% 18% 6% 2	550
April	1st to 10th	Day	24% 20% 33% 18% 6%	500
	11th to 20th	Day	17% 21% 35% 18% 8% 1	492
	21st to end	Day	20% 25% 30% 15% 8% 2	500
May	1st to 10th	Day	18% 21% 34% 21% 6% 1	503
	11th to 20th	Day	18% 15% 30% 27% 9% 2	623
	21st to end	Day	24% 13% 25% 23% 12% 2	763
June	1st to 10th	Day	23% 21% 30% 20% 6%	870
	11th to 20th	Day	26% 19% 29% 19% 7% 1	870
	21st to end	Day	18% 16% 27% 24% 13% 2	870
July	1st to 10th	Day	21% 14% 29% 27% 8% 1	856
	11th to 20th	Day	17% 17% 31% 22% 11% 1	852
	21st to end	Day	15% 16% 31% 26% 9% 3	583
August	1st to 10th	Day	17% 13% 29% 27% 10% 4	487
	11th to 20th	Day	14% 21% 34% 22% 7% 2	477
	21st to end	Day	17% 21% 34% 20% 8% 1	539
September	1st to 10th	Day	19% 23% 31% 21% 6% 1	490
	11th to 20th	Day	18% 20% 34% 21% 6% 1	490
	21st to end	Day	28% 26% 26% 15% 4 1	490
October	1st to 10th	Day	22% 22% 31% 17% 7% 1	490
	11th to 20th	Day	20% 27% 31% 17% 5% 1	333
	21st to end	Day	16% 25% 35% 19% 4 1	330
November	1st to 10th	Day	24% 31% 28% 15% 3	233
	11th to 20th	Day	19% 29% 33% 15% 4 1	200
	21st to end	Day	22% 24% 26% 19% 8% 2	200
December	1st to 10th	Day	14% 27% 30% 16% 11% 3	200
	11th to 20th	Day	13% 25% 38% 17% 7% 1	200
	21st to end	Day	13% 21% 42% 15% 6% 4	220
January	1st to 10th	Night	12% 21% 45% 16% 5% 1	1100
	11th to 20th	Night	11% 26% 41% 16% 5% 1	980
	21st to end	Night	12% 29% 37% 16% 5%	880
February	1st to 10th	Night	14% 22% 30% 25% 8% 1	800
	11th to 20th	Night	11% 17% 38% 29% 5%	784
	21st to end	Night	10% 16% 39% 24% 10% 1	660
March	1st to 10th	Night	9% 20% 36% 25% 9% 2	800
	11th to 20th	Night	8% 21% 40% 23% 8% 1	800
	21st to end	Night	10% 16% 35% 27% 10% 1	880
April	1st to 10th	Night	11% 17% 31% 31% 9% 1	800
	11th to 20th	Night	11% 15% 37% 26% 10%	651
	21st to end	Night	14% 17% 29% 29% 9% 1	440
May	1st to 10th	Night	16% 8% 26% 40% 11%	400
	11th to 20th	Night	12% 9% 29% 34% 15% 1	375
	21st to end	Night	21% 11% 25% 25% 17%	411
June	1st to 10th	Night	22% 11% 29% 26% 13% 1	380
	11th to 20th	Night	23% 9% 23% 29% 14% 1	380
	21st to end	Night	14% 11% 27% 29% 18% 1	380
July	1st to 10th	Night	18% 6% 22% 37% 16% 1	370
	11th to 20th	Night	18% 11% 18% 32% 20% 1	368
	21st to end	Night	12% 8% 21% 34% 25% 1	416
August	1st to 10th	Night	15% 6% 19% 34% 23% 3	378
	11th to 20th	Night	15% 7% 23% 32% 21% 2	376
	21st to end	Night	16% 10% 31% 31% 10% 1	643
September	1st to 10th	Night	18% 12% 27% 31% 11% 1	760
	11th to 20th	Night	18% 11% 27% 29% 14% 2	760
	21st to end	Night	17% 23% 29% 22% 9% 1	760
October	1st to 10th	Night	17% 16% 33% 25% 8% 1	760
	11th to 20th	Night	15% 17% 39% 24% 4 1	760
	21st to end	Night	14% 21% 38% 20% 6% 1	836
November	1st to 10th	Night	14% 25% 38% 20% 3	780
	11th to 20th	Night	13% 28% 39% 16% 3	1000
	21st to end	Night	11% 27% 39% 16% 6% 1	1000
December	1st to 10th	Night	12% 24% 37% 21% 5%	1005
	11th to 20th	Night	9% 24% 43% 18% 5% 1	1100
	21st to end	Night	10% 22% 43% 17% 6% 1	1210

Page generated at 2025-05-08 07:33:55. Version ac07

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