Jasper
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jasper clear sky chart from 2005-11-06 to 2025-05-26.

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% 11% 4 11% 7% 7% 7% 5% 7% 8% 26%	117169
	Night	4 9% 4 11% 7% 7% 7% 6% 8% 10% 27%	120814
Transparency	Day	55% 9% 14% 15% 6% 1	116910
	Night	53% 10% 16% 15% 5% 1	120719
Seeing	Day	19% 15% 29% 23% 11% 3	16740
	Night	11% 11% 36% 30% 10% 1	25180

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 6% 7% 13% 10% 11% 8% 6% 9% 9% 20%	2719
	11th to 20th	Day	1 5% 4 12% 8% 7% 8% 8% 10% 8% 29%	3157
	21st to end	Day	1 12% 4 12% 8% 7% 8% 5% 7% 8% 28%	4004
February	1st to 10th	Day	2 9% 5% 15% 9% 7% 7% 5% 9% 9% 23%	1600
	11th to 20th	Day	1 9% 5% 16% 9% 7% 7% 6% 8% 8% 24%	1649
	21st to end	Day	1 8% 5% 16% 12% 8% 6% 6% 9% 7% 22%	1633
March	1st to 10th	Day	6% 4 14% 10% 10% 9% 7% 8% 10% 22%	4518
	11th to 20th	Day	2 9% 4 12% 7% 7% 7% 6% 10% 10% 26%	4658
	21st to end	Day	2 13% 6% 18% 10% 7% 6% 5% 7% 8% 18%	5969
April	1st to 10th	Day	3 15% 7% 17% 9% 10% 8% 5% 6% 6% 15%	2400
	11th to 20th	Day	3 14% 7% 17% 9% 7% 6% 5% 5% 7% 19%	2504
	21st to end	Day	6% 16% 6% 14% 7% 6% 6% 5% 7% 7% 21%	2755
May	1st to 10th	Day	8% 20% 6% 12% 6% 6% 4 4 5% 6% 23%	4560
	11th to 20th	Day	9% 15% 5% 11% 7% 7% 6% 5% 7% 7% 21%	4730
	21st to end	Day	14% 20% 6% 14% 8% 6% 6% 4 5% 5% 13%	5266
June	1st to 10th	Day	18% 13% 4 12% 7% 6% 5% 5% 7% 6% 18%	3040
	11th to 20th	Day	19% 17% 5% 12% 7% 6% 6% 4 5% 4 13%	3040
	21st to end	Day	12% 12% 5% 12% 8% 6% 6% 5% 6% 6% 21%	3040
July	1st to 10th	Day	10% 8% 2 7% 5% 5% 5% 4 5% 6% 43%	5060
	11th to 20th	Day	7% 6% 2 6% 5% 5% 5% 4 6% 7% 46%	5041
	21st to end	Day	9% 7% 3 8% 6% 7% 7% 6% 8% 8% 31%	4827
August	1st to 10th	Day	11% 7% 3 7% 5% 6% 5% 4 7% 8% 37%	4401
	11th to 20th	Day	11% 8% 3 8% 6% 6% 7% 5% 8% 9% 32%	4330
	21st to end	Day	12% 9% 3 7% 5% 6% 7% 5% 7% 9% 29%	4467
September	1st to 10th	Day	11% 10% 4 10% 6% 6% 5% 4 4 6% 34%	2280
	11th to 20th	Day	10% 10% 3 9% 5% 6% 6% 5% 7% 6% 34%	2218
	21st to end	Day	9% 12% 4 10% 7% 7% 6% 4 7% 6% 29%	2090
October	1st to 10th	Day	5% 11% 4 10% 7% 7% 7% 5% 8% 11% 26%	3225
	11th to 20th	Day	5% 12% 4 10% 7% 8% 7% 5% 6% 8% 27%	2908
	21st to end	Day	2 10% 5% 10% 7% 6% 7% 5% 7% 9% 31%	3101
November	1st to 10th	Day	3 12% 5% 14% 9% 8% 6% 5% 7% 9% 22%	1630
	11th to 20th	Day	2 8% 4 10% 6% 7% 8% 6% 9% 12% 28%	1400
	21st to end	Day	1 11% 5% 12% 8% 7% 8% 5% 8% 10% 25%	1400
December	1st to 10th	Day	1 7% 3 13% 9% 7% 8% 7% 9% 10% 25%	2290
	11th to 20th	Day	1 9% 4 10% 8% 9% 8% 7% 9% 11% 24%	2267
	21st to end	Day	6% 3 10% 7% 6% 8% 5% 9% 12% 32%	2992
January	1st to 10th	Night	1 6% 5% 16% 11% 9% 8% 6% 8% 10% 22%	7226
	11th to 20th	Night	1 6% 4 12% 8% 8% 8% 7% 9% 9% 29%	6781
	21st to end	Night	2 10% 4 13% 7% 7% 7% 6% 8% 10% 27%	6952
February	1st to 10th	Night	3 10% 4 13% 11% 7% 8% 7% 8% 9% 20%	2800
	11th to 20th	Night	1 9% 4 12% 8% 8% 8% 7% 7% 10% 26%	2634
	21st to end	Night	1 10% 5% 12% 9% 8% 7% 7% 8% 10% 24%	1996
March	1st to 10th	Night	7% 4 12% 10% 9% 7% 6% 9% 9% 25%	5376
	11th to 20th	Night	2 6% 4 12% 9% 8% 8% 7% 11% 11% 22%	5339
	21st to end	Night	3 15% 6% 17% 7% 6% 6% 5% 8% 10% 17%	5006
April	1st to 10th	Night	2 12% 6% 13% 9% 9% 7% 6% 8% 9% 22%	2000
	11th to 20th	Night	3 10% 5% 12% 8% 6% 6% 4 7% 9% 29%	1846
	21st to end	Night	5% 12% 5% 11% 6% 5% 7% 6% 7% 9% 29%	1643
May	1st to 10th	Night	5% 16% 5% 11% 6% 6% 5% 5% 6% 8% 26%	2620
	11th to 20th	Night	8% 12% 4 11% 7% 6% 6% 5% 6% 7% 27%	2383
	21st to end	Night	11% 16% 6% 12% 7% 7% 6% 5% 5% 7% 20%	2422
June	1st to 10th	Night	13% 11% 4 9% 6% 6% 6% 5% 6% 5% 29%	1140
	11th to 20th	Night	17% 12% 5% 9% 8% 6% 6% 5% 7% 7% 19%	1140
	21st to end	Night	9% 6% 2 9% 7% 6% 7% 5% 7% 9% 32%	1140
July	1st to 10th	Night	9% 6% 2 5% 3 4 5% 4 5% 7% 51%	1900
	11th to 20th	Night	6% 4 2 5% 3 4 5% 4 7% 8% 52%	1918
	21st to end	Night	8% 6% 3 7% 5% 4 5% 5% 7% 9% 40%	2722
August	1st to 10th	Night	9% 9% 3 8% 5% 4 5% 4 8% 9% 36%	2529
	11th to 20th	Night	12% 9% 3 6% 4 4 6% 5% 8% 9% 35%	2497
	21st to end	Night	12% 8% 2 7% 5% 5% 6% 5% 7% 8% 35%	3200
September	1st to 10th	Night	11% 9% 2 7% 5% 5% 5% 5% 5% 6% 39%	1900
	11th to 20th	Night	9% 11% 3 10% 5% 5% 4 5% 6% 7% 36%	1961
	21st to end	Night	8% 9% 4 8% 5% 5% 6% 5% 8% 9% 33%	2090
October	1st to 10th	Night	4 9% 4 10% 6% 7% 7% 6% 10% 11% 26%	3754
	11th to 20th	Night	4 9% 3 8% 7% 7% 7% 7% 9% 10% 29%	4021
	21st to end	Night	3 9% 3 9% 6% 7% 7% 6% 9% 10% 30%	4457
November	1st to 10th	Night	3 12% 5% 12% 9% 8% 6% 5% 8% 9% 22%	2663
	11th to 20th	Night	1 10% 5% 10% 7% 8% 7% 7% 9% 11% 28%	2984
	21st to end	Night	1 10% 5% 10% 10% 7% 7% 5% 9% 11% 24%	3000
December	1st to 10th	Night	2 6% 4 11% 8% 7% 7% 7% 10% 11% 28%	4890
	11th to 20th	Night	1 7% 4 12% 9% 10% 9% 6% 10% 11% 21%	5920
	21st to end	Night	7% 4 11% 7% 7% 9% 7% 9% 11% 27%	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	57% 13% 15% 12% 3	2719
	11th to 20th	Day	52% 9% 11% 14% 12% 2	3178
	21st to end	Day	51% 13% 20% 13% 3	4004
February	1st to 10th	Day	57% 8% 12% 12% 10% 2	1600
	11th to 20th	Day	58% 7% 11% 16% 7%	1657
	21st to end	Day	59% 6% 13% 14% 7% 1	1633
March	1st to 10th	Day	55% 9% 13% 14% 8%	4518
	11th to 20th	Day	51% 11% 13% 20% 5%	4658
	21st to end	Day	64% 8% 10% 11% 7%	5969
April	1st to 10th	Day	69% 7% 12% 10% 2	2400
	11th to 20th	Day	64% 7% 12% 14% 2	2504
	21st to end	Day	63% 8% 13% 13% 2	2755
May	1st to 10th	Day	62% 6% 14% 14% 5%	4560
	11th to 20th	Day	60% 6% 14% 14% 5%	4734
	21st to end	Day	72% 8% 9% 8% 3	5267
June	1st to 10th	Day	65% 7% 11% 11% 5% 1	3040
	11th to 20th	Day	72% 7% 10% 8% 3	3040
	21st to end	Day	62% 8% 12% 13% 5% 1	3040
July	1st to 10th	Day	43% 7% 8% 20% 15% 7%	4981
	11th to 20th	Day	37% 7% 11% 24% 19% 3	4954
	21st to end	Day	50% 9% 11% 15% 11% 3	4674
August	1st to 10th	Day	42% 8% 13% 27% 10%	4384
	11th to 20th	Day	46% 9% 17% 21% 6% 1	4372
	21st to end	Day	52% 9% 13% 22% 5%	4466
September	1st to 10th	Day	52% 6% 14% 21% 5% 2	2280
	11th to 20th	Day	49% 7% 16% 19% 8% 1	2218
	21st to end	Day	56% 8% 13% 14% 7% 1	2090
October	1st to 10th	Day	56% 9% 17% 15% 3	3225
	11th to 20th	Day	58% 8% 17% 15% 2	2908
	21st to end	Day	54% 8% 21% 14% 3	3101
November	1st to 10th	Day	59% 10% 14% 13% 4 1	1630
	11th to 20th	Day	49% 10% 23% 13% 5% 1	1400
	21st to end	Day	55% 11% 17% 10% 5% 2	1400
December	1st to 10th	Day	59% 14% 14% 8% 4	2290
	11th to 20th	Day	53% 12% 18% 12% 4 1	2269
	21st to end	Day	45% 11% 21% 15% 7%	2992
January	1st to 10th	Night	58% 10% 15% 13% 3 1	7226
	11th to 20th	Night	51% 10% 11% 14% 13% 1	6822
	21st to end	Night	55% 11% 17% 14% 3	6952
February	1st to 10th	Night	61% 8% 11% 11% 8% 1	2800
	11th to 20th	Night	54% 8% 16% 15% 6% 1	2636
	21st to end	Night	54% 6% 12% 20% 8% 1	1996
March	1st to 10th	Night	52% 10% 13% 17% 8%	5376
	11th to 20th	Night	54% 8% 16% 18% 4	5340
	21st to end	Night	60% 10% 12% 13% 5%	5006
April	1st to 10th	Night	60% 9% 16% 14% 2	2000
	11th to 20th	Night	52% 8% 16% 18% 5%	1846
	21st to end	Night	52% 10% 15% 19% 5%	1643
May	1st to 10th	Night	55% 8% 19% 17% 2	2620
	11th to 20th	Night	54% 9% 14% 15% 8%	2383
	21st to end	Night	63% 10% 12% 12% 3	2422
June	1st to 10th	Night	56% 6% 15% 16% 6% 1	1140
	11th to 20th	Night	62% 8% 16% 11% 4	1140
	21st to end	Night	47% 10% 19% 18% 6% 1	1140
July	1st to 10th	Night	34% 7% 13% 23% 21% 2	1870
	11th to 20th	Night	31% 7% 14% 28% 20% 1	1882
	21st to end	Night	41% 8% 16% 21% 9% 5%	2636
August	1st to 10th	Night	42% 9% 18% 28% 3	2521
	11th to 20th	Night	43% 10% 22% 20% 5%	2521
	21st to end	Night	47% 8% 23% 18% 4	3200
September	1st to 10th	Night	44% 7% 18% 23% 7% 1	1900
	11th to 20th	Night	47% 6% 19% 19% 7% 1	1961
	21st to end	Night	45% 11% 19% 19% 6% 1	2090
October	1st to 10th	Night	57% 10% 18% 13% 2	3754
	11th to 20th	Night	53% 9% 21% 15% 2	4021
	21st to end	Night	52% 10% 23% 11% 3	4457
November	1st to 10th	Night	60% 8% 16% 13% 3	2663
	11th to 20th	Night	51% 12% 19% 12% 6%	2984
	21st to end	Night	54% 12% 16% 12% 5% 2	3000
December	1st to 10th	Night	55% 12% 17% 11% 4	4890
	11th to 20th	Night	58% 14% 14% 10% 3	5917
	21st to end	Night	52% 9% 18% 16% 4	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% 9% 24% 40% 16% 3	200
	11th to 20th	Day	11% 7% 33% 35% 11% 4	200
	21st to end	Day	15% 9% 35% 27% 10% 4	220
February	1st to 10th	Day	15% 12% 35% 23% 12% 4	200
	11th to 20th	Day	14% 13% 30% 26% 13% 4	289
	21st to end	Day	14% 19% 37% 17% 11% 2	407
March	1st to 10th	Day	16% 21% 31% 19% 11% 3	500
	11th to 20th	Day	14% 19% 35% 20% 9% 3	500
	21st to end	Day	17% 20% 29% 20% 9% 5%	550
April	1st to 10th	Day	19% 20% 32% 22% 7% 1	500
	11th to 20th	Day	17% 18% 30% 22% 9% 4	492
	21st to end	Day	20% 18% 27% 21% 10% 3	500
May	1st to 10th	Day	23% 16% 30% 21% 7% 2	503
	11th to 20th	Day	18% 11% 26% 29% 13% 2	650
	21st to end	Day	23% 10% 24% 23% 17% 3	774
June	1st to 10th	Day	25% 15% 30% 21% 8%	870
	11th to 20th	Day	29% 14% 28% 20% 8% 1	870
	21st to end	Day	19% 15% 24% 24% 15% 3	870
July	1st to 10th	Day	19% 12% 29% 27% 11% 2	856
	11th to 20th	Day	18% 11% 31% 25% 12% 2	846
	21st to end	Day	16% 13% 27% 25% 15% 4	555
August	1st to 10th	Day	17% 10% 25% 28% 14% 5%	487
	11th to 20th	Day	15% 14% 34% 22% 11% 3	477
	21st to end	Day	19% 14% 32% 20% 11% 3	539
September	1st to 10th	Day	22% 17% 27% 21% 11% 2	490
	11th to 20th	Day	18% 15% 29% 25% 11% 2	490
	21st to end	Day	28% 21% 27% 14% 7% 2	490
October	1st to 10th	Day	22% 18% 28% 18% 9% 4	490
	11th to 20th	Day	21% 15% 29% 22% 10% 3	340
	21st to end	Day	16% 14% 30% 32% 6% 2	330
November	1st to 10th	Day	19% 13% 38% 21% 6% 3	235
	11th to 20th	Day	14% 13% 33% 27% 10% 5%	200
	21st to end	Day	16% 15% 28% 26% 11% 6%	200
December	1st to 10th	Day	11% 8% 33% 29% 14% 6%	200
	11th to 20th	Day	9% 8% 32% 33% 14% 6%	200
	21st to end	Day	8% 8% 26% 35% 15% 6%	220
January	1st to 10th	Night	9% 12% 41% 31% 5% 1	1100
	11th to 20th	Night	8% 15% 41% 27% 7% 2	951
	21st to end	Night	9% 17% 44% 23% 6% 1	880
February	1st to 10th	Night	11% 14% 36% 29% 11% 1	800
	11th to 20th	Night	8% 10% 41% 31% 8% 1	784
	21st to end	Night	8% 14% 39% 27% 10% 3	660
March	1st to 10th	Night	6% 15% 40% 27% 12% 1	800
	11th to 20th	Night	6% 12% 44% 28% 10% 1	800
	21st to end	Night	8% 12% 36% 30% 11% 2	880
April	1st to 10th	Night	9% 13% 31% 35% 11% 1	800
	11th to 20th	Night	10% 11% 36% 28% 14% 1	658
	21st to end	Night	14% 8% 32% 36% 11%	443
May	1st to 10th	Night	13% 8% 26% 43% 11%	400
	11th to 20th	Night	12% 4 29% 38% 16% 1	394
	21st to end	Night	16% 8% 26% 30% 20%	422
June	1st to 10th	Night	20% 3 31% 32% 13% 1	380
	11th to 20th	Night	23% 8% 24% 32% 13% 1	380
	21st to end	Night	13% 8% 23% 34% 19% 2	380
July	1st to 10th	Night	19% 5% 19% 40% 16% 1	370
	11th to 20th	Night	15% 8% 23% 33% 21% 1	368
	21st to end	Night	9% 6% 20% 41% 22% 1	416
August	1st to 10th	Night	14% 4 15% 39% 27% 1	378
	11th to 20th	Night	14% 5% 20% 40% 19% 2	376
	21st to end	Night	16% 7% 27% 38% 11% 1	655
September	1st to 10th	Night	17% 8% 25% 37% 13% 1	760
	11th to 20th	Night	16% 7% 26% 33% 17% 1	760
	21st to end	Night	18% 13% 32% 26% 11% 1	760
October	1st to 10th	Night	16% 11% 33% 31% 9% 1	760
	11th to 20th	Night	14% 11% 39% 27% 7% 1	760
	21st to end	Night	13% 14% 42% 25% 6% 1	836
November	1st to 10th	Night	12% 14% 43% 26% 5% 1	780
	11th to 20th	Night	11% 16% 42% 26% 4 1	984
	21st to end	Night	10% 13% 47% 23% 6% 1	1000
December	1st to 10th	Night	9% 13% 43% 26% 8% 1	1000
	11th to 20th	Night	9% 11% 45% 27% 8% 1	1095
	21st to end	Night	6% 10% 45% 28% 10% 1	1210

Page generated at 2025-05-23 07:20:56. Version ac07

Copyright © 2025 Attilla Danko.