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 2025-12-03.

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	13% 7% 2 7% 5% 5% 5% 4 5% 7% 41%	126743
	Night	14% 7% 2 6% 4 3 4 3 5% 7% 45%	124191
Transparency	Day	42% 5% 10% 19% 18% 7%	130349
	Night	38% 4 11% 19% 19% 9%	128661
Seeing	Day	14% 9% 22% 25% 21% 8%	16397
	Night	16% 8% 24% 31% 18% 3	26178

By Month

Percentage Cloud Cover SE (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	19% 9% 3 6% 3 3 3 2 4 5% 42%	4077
	11th to 20th	Day	16% 6% 2 5% 4 3 3 2 3 5% 50%	4080
	21st to end	Day	26% 10% 3 6% 2 3 3 2 3 6% 38%	4488
February	1st to 10th	Day	19% 8% 3 7% 4 5% 5% 3 4 5% 37%	1800
	11th to 20th	Day	23% 10% 3 6% 4 3 3 2 3 5% 39%	1989
	21st to end	Day	19% 9% 3 8% 4 3 3 4 5% 5% 36%	1815
March	1st to 10th	Day	21% 10% 3 8% 4 4 3 3 4 5% 36%	4936
	11th to 20th	Day	14% 6% 3 6% 4 4 4 3 4 6% 47%	4980
	21st to end	Day	17% 9% 3 7% 4 4 3 3 4 5% 40%	5462
April	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 4 5% 5% 38%	2266
	11th to 20th	Day	16% 6% 3 6% 5% 5% 5% 4 5% 6% 38%	2374
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 5% 6% 7% 41%	2400
May	1st to 10th	Day	19% 7% 2 8% 5% 5% 5% 4 6% 7% 30%	5405
	11th to 20th	Day	12% 6% 3 7% 4 5% 4 4 6% 7% 40%	5711
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 5% 8% 9% 35%	6434
June	1st to 10th	Day	9% 5% 2 7% 6% 7% 6% 5% 8% 11% 35%	2600
	11th to 20th	Day	6% 5% 2 6% 6% 7% 7% 6% 8% 10% 37%	2600
	21st to end	Day	8% 6% 2 7% 6% 7% 7% 5% 8% 11% 31%	2600
July	1st to 10th	Day	8% 5% 2 8% 6% 7% 6% 6% 8% 12% 32%	5900
	11th to 20th	Day	7% 6% 3 7% 6% 7% 7% 5% 8% 11% 33%	5900
	21st to end	Day	13% 7% 2 8% 5% 6% 5% 5% 7% 9% 34%	6422
August	1st to 10th	Day	3 2 1 4 3 4 4 4 5% 9% 61%	4234
	11th to 20th	Day	3 3 1 5% 4 5% 5% 5% 7% 12% 50%	3861
	21st to end	Day	9% 5% 2 7% 6% 6% 7% 5% 8% 8% 37%	4312
September	1st to 10th	Day	9% 5% 2 6% 5% 5% 6% 4 6% 10% 40%	2384
	11th to 20th	Day	13% 6% 3 7% 6% 6% 6% 4 6% 7% 38%	2200
	21st to end	Day	9% 5% 2 5% 4 5% 4 4 6% 8% 49%	2180
October	1st to 10th	Day	7% 4 2 5% 4 4 3 3 4 5% 61%	2000
	11th to 20th	Day	10% 5% 2 4 4 4 4 3 5% 6% 54%	2000
	21st to end	Day	14% 5% 1 5% 3 4 3 2 3 5% 54%	2200
November	1st to 10th	Day	11% 6% 3 5% 4 4 4 4 5% 6% 48%	2058
	11th to 20th	Day	12% 6% 2 5% 4 3 4 3 3 5% 52%	2100
	21st to end	Day	16% 7% 3 6% 4 4 3 2 4 5% 44%	2100
December	1st to 10th	Day	22% 8% 2 5% 3 3 3 3 4 4 44%	2996
	11th to 20th	Day	17% 10% 3 6% 4 4 4 3 4 5% 40%	3391
	21st to end	Day	17% 7% 2 6% 4 4 3 3 4 5% 46%	4488
January	1st to 10th	Night	18% 6% 2 5% 3 2 2 2 4 5% 50%	5888
	11th to 20th	Night	18% 8% 2 5% 3 3 3 2 2 4 50%	5900
	21st to end	Night	27% 11% 2 5% 3 3 3 2 3 5% 35%	6490
February	1st to 10th	Night	19% 8% 3 5% 4 3 3 3 5% 6% 41%	2600
	11th to 20th	Night	22% 10% 3 5% 4 3 2 2 4 5% 42%	2311
	21st to end	Night	21% 8% 3 7% 3 4 3 2 4 5% 39%	1815
March	1st to 10th	Night	22% 10% 2 6% 3 3 3 3 4 5% 38%	4919
	11th to 20th	Night	18% 8% 2 6% 4 3 3 3 4 5% 44%	4980
	21st to end	Night	19% 8% 2 6% 4 4 4 3 4 5% 42%	5467
April	1st to 10th	Night	15% 6% 2 6% 5% 4 5% 3 6% 7% 42%	2131
	11th to 20th	Night	15% 6% 2 5% 3 3 4 3 4 7% 45%	1975
	21st to end	Night	14% 6% 2 5% 4 4 4 3 5% 6% 46%	2000
May	1st to 10th	Night	21% 10% 3 7% 4 4 4 4 5% 8% 30%	4490
	11th to 20th	Night	16% 6% 3 8% 4 4 4 3 5% 8% 39%	4193
	21st to end	Night	12% 7% 3 7% 5% 4 5% 4 7% 11% 34%	4443
June	1st to 10th	Night	6% 5% 2 5% 5% 4 4 5% 6% 8% 51%	1800
	11th to 20th	Night	4 3 2 4 4 4 4 4 7% 11% 55%	1800
	21st to end	Night	6% 4 2 5% 5% 4 4 5% 8% 11% 46%	1800
July	1st to 10th	Night	6% 5% 2 7% 6% 5% 6% 5% 8% 13% 38%	4078
	11th to 20th	Night	5% 3 2 6% 4 5% 5% 5% 8% 13% 44%	4077
	21st to end	Night	10% 7% 3 8% 5% 4 4 4 6% 10% 40%	4449
August	1st to 10th	Night	2 1 1 2 2 2 3 3 5% 9% 70%	2926
	11th to 20th	Night	2 2 1 3 2 3 3 4 8% 12% 59%	3186
	21st to end	Night	7% 4 2 6% 5% 5% 6% 5% 8% 9% 42%	3586
September	1st to 10th	Night	7% 4 2 6% 4 4 4 5% 7% 9% 47%	2010
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 3 7% 8% 45%	2200
	21st to end	Night	8% 5% 2 5% 3 4 3 3 5% 7% 56%	2200
October	1st to 10th	Night	5% 3 1 4 4 3 5% 4 4 6% 61%	2398
	11th to 20th	Night	11% 3 2 4 3 2 3 3 5% 5% 59%	2400
	21st to end	Night	11% 5% 2 4 3 3 3 2 3 5% 58%	2640
November	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 4 5% 54%	2460
	11th to 20th	Night	11% 5% 2 5% 3 4 3 3 5% 6% 53%	2520
	21st to end	Night	16% 7% 3 5% 4 3 3 4 4 6% 45%	2520
December	1st to 10th	Night	22% 8% 3 7% 4 3 3 2 4 5% 40%	4233
	11th to 20th	Night	15% 11% 2 6% 3 4 4 3 4 4 44%	4816
	21st to end	Night	16% 9% 2 5% 3 3 3 2 4 4 49%	6490

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	45% 2 4 23% 20% 5%	4078
	11th to 20th	Day	40% 2 3 16% 28% 11%	4080
	21st to end	Day	51% 2 3 13% 17% 13%	4488
February	1st to 10th	Day	50% 4 5% 12% 18% 10%	1800
	11th to 20th	Day	50% 4 5% 15% 17% 9%	1998
	21st to end	Day	50% 5% 7% 12% 16% 11%	1815
March	1st to 10th	Day	53% 3 5% 10% 19% 11%	4936
	11th to 20th	Day	40% 3 5% 15% 21% 16%	4980
	21st to end	Day	48% 3 8% 20% 17% 5%	5464
April	1st to 10th	Day	47% 6% 6% 16% 17% 8%	2266
	11th to 20th	Day	45% 5% 9% 14% 17% 10%	2374
	21st to end	Day	40% 6% 9% 18% 22% 5%	2400
May	1st to 10th	Day	52% 5% 9% 22% 10% 3	5440
	11th to 20th	Day	42% 4 15% 18% 19% 2	5715
	21st to end	Day	43% 7% 12% 23% 13% 2	6447
June	1st to 10th	Day	41% 9% 15% 20% 15% 1	2600
	11th to 20th	Day	40% 9% 14% 22% 15% 2	2600
	21st to end	Day	43% 10% 16% 19% 10% 1	2600
July	1st to 10th	Day	45% 5% 26% 20% 4	5836
	11th to 20th	Day	44% 5% 22% 24% 5%	5831
	21st to end	Day	47% 6% 14% 25% 7%	6240
August	1st to 10th	Day	21% 6% 13% 34% 25% 1	4220
	11th to 20th	Day	26% 6% 25% 36% 6% 1	3897
	21st to end	Day	44% 7% 14% 18% 17% 1	4311
September	1st to 10th	Day	38% 9% 14% 17% 15% 6%	2384
	11th to 20th	Day	43% 7% 12% 16% 15% 6%	2200
	21st to end	Day	34% 6% 11% 20% 19% 11%	2180
October	1st to 10th	Day	19% 3 6% 12% 24% 36%	3260
	11th to 20th	Day	21% 3 4 19% 31% 23%	3240
	21st to end	Day	29% 2 4 11% 41% 14%	3538
November	1st to 10th	Day	37% 5% 8% 18% 22% 11%	2058
	11th to 20th	Day	36% 3 5% 16% 26% 13%	2100
	21st to end	Day	44% 3 6% 18% 21% 8%	2100
December	1st to 10th	Day	45% 3 5% 15% 26% 5%	2996
	11th to 20th	Day	48% 3 5% 11% 23% 10%	3389
	21st to end	Day	42% 2 6% 15% 28% 8%	4488
January	1st to 10th	Night	38% 2 6% 24% 25% 6%	5888
	11th to 20th	Night	42% 2 3 16% 29% 8%	5900
	21st to end	Night	55% 2 4 13% 15% 12%	6490
February	1st to 10th	Night	45% 4 6% 15% 17% 13%	2600
	11th to 20th	Night	48% 3 5% 15% 19% 10%	2312
	21st to end	Night	49% 4 6% 12% 16% 13%	1815
March	1st to 10th	Night	49% 3 5% 12% 19% 12%	4919
	11th to 20th	Night	44% 4 6% 14% 16% 17%	4980
	21st to end	Night	46% 4 8% 15% 20% 7%	5467
April	1st to 10th	Night	42% 6% 8% 19% 16% 10%	2131
	11th to 20th	Night	39% 5% 9% 19% 16% 12%	1975
	21st to end	Night	39% 5% 10% 18% 23% 6%	2000
May	1st to 10th	Night	53% 6% 10% 18% 11% 3	4520
	11th to 20th	Night	44% 4 13% 18% 19% 2	4194
	21st to end	Night	43% 7% 15% 23% 11% 1	4452
June	1st to 10th	Night	30% 8% 17% 28% 16% 1	1800
	11th to 20th	Night	23% 8% 18% 33% 16% 3	1800
	21st to end	Night	30% 10% 22% 26% 12% 1	1800
July	1st to 10th	Night	36% 7% 35% 19% 3	4035
	11th to 20th	Night	31% 8% 30% 27% 5%	4026
	21st to end	Night	40% 7% 19% 26% 7%	4320
August	1st to 10th	Night	13% 5% 19% 35% 28% 1	2916
	11th to 20th	Night	17% 6% 31% 38% 7% 1	3216
	21st to end	Night	37% 10% 16% 20% 15% 2	3586
September	1st to 10th	Night	31% 10% 18% 19% 14% 8%	2010
	11th to 20th	Night	37% 7% 14% 20% 16% 6%	2200
	21st to end	Night	29% 4 12% 23% 19% 13%	2200
October	1st to 10th	Night	17% 3 6% 16% 20% 38%	3918
	11th to 20th	Night	17% 3 4 22% 31% 24%	3899
	21st to end	Night	25% 2 4 13% 38% 18%	4252
November	1st to 10th	Night	33% 4 9% 18% 23% 12%	2460
	11th to 20th	Night	32% 4 8% 17% 24% 13%	2520
	21st to end	Night	40% 5% 7% 16% 22% 10%	2520
December	1st to 10th	Night	50% 2 4 16% 22% 5%	4233
	11th to 20th	Night	45% 2 7% 12% 22% 12%	4817
	21st to end	Night	40% 3 6% 15% 28% 8%	6490

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	23% 21% 37% 12% 5% 1	300
	11th to 20th	Day	30% 16% 32% 18% 4 1	300
	21st to end	Day	27% 23% 31% 16% 2	330
February	1st to 10th	Day	25% 20% 35% 16% 3 1	300
	11th to 20th	Day	39% 15% 30% 15% 1	300
	21st to end	Day	31% 27% 31% 9% 2	249
March	1st to 10th	Day	26% 20% 34% 14% 5%	300
	11th to 20th	Day	20% 28% 37% 11% 3 1	300
	21st to end	Day	22% 18% 43% 13% 3 1	330
April	1st to 10th	Day	18% 18% 39% 20% 4 1	366
	11th to 20th	Day	22% 19% 28% 21% 9% 1	492
	21st to end	Day	17% 13% 35% 25% 8% 2	500
May	1st to 10th	Day	20% 9% 35% 23% 12%	503
	11th to 20th	Day	13% 8% 27% 32% 16% 4	652
	21st to end	Day	9% 7% 29% 32% 18% 5%	789
June	1st to 10th	Day	9% 3 20% 32% 27% 10%	730
	11th to 20th	Day	9% 2 18% 36% 29% 7%	730
	21st to end	Day	10% 2 11% 28% 34% 15%	730
July	1st to 10th	Day	9% 1 10% 27% 38% 15%	721
	11th to 20th	Day	8% 1 6% 28% 41% 17%	718
	21st to end	Day	9% 1 5% 28% 42% 16%	794
August	1st to 10th	Day	4 1 4 27% 43% 21%	726
	11th to 20th	Day	4 1 4 19% 47% 26%	531
	21st to end	Day	12% 2 8% 22% 33% 22%	583
September	1st to 10th	Day	8% 2 10% 26% 36% 18%	514
	11th to 20th	Day	9% 2 15% 26% 34% 13%	330
	21st to end	Day	13% 4 15% 29% 28% 11%	330
October	1st to 10th	Day	7% 2 23% 41% 20% 6%	330
	11th to 20th	Day	9% 5% 23% 38% 18% 7%	330
	21st to end	Day	19% 10% 26% 26% 13% 6%	363
November	1st to 10th	Day	14% 12% 23% 29% 18% 3	330
	11th to 20th	Day	15% 11% 33% 32% 8% 1	330
	21st to end	Day	23% 16% 33% 20% 6% 2	330
December	1st to 10th	Day	20% 12% 37% 22% 6% 3	306
	11th to 20th	Day	24% 16% 36% 19% 5%	300
	21st to end	Day	25% 20% 30% 20% 4 1	330
January	1st to 10th	Night	24% 14% 30% 27% 5%	1000
	11th to 20th	Night	26% 12% 29% 25% 7%	1000
	21st to end	Night	25% 12% 33% 27% 4	1100
February	1st to 10th	Night	25% 14% 33% 25% 4	1000
	11th to 20th	Night	29% 14% 32% 21% 4	756
	21st to end	Night	25% 17% 34% 23% 1	495
March	1st to 10th	Night	27% 11% 31% 26% 5%	600
	11th to 20th	Night	23% 13% 34% 25% 5% 1	600
	21st to end	Night	20% 10% 37% 25% 8%	660
April	1st to 10th	Night	18% 11% 40% 24% 7%	600
	11th to 20th	Night	18% 14% 31% 27% 10%	593
	21st to end	Night	18% 8% 34% 29% 10% 1	600
May	1st to 10th	Night	17% 10% 31% 32% 9%	600
	11th to 20th	Night	14% 7% 28% 36% 14% 1	591
	21st to end	Night	8% 5% 25% 36% 22% 3	650
June	1st to 10th	Night	5% 4 15% 39% 33% 5%	600
	11th to 20th	Night	5% 2 18% 46% 25% 5%	600
	21st to end	Night	7% 2 11% 33% 40% 7%	600
July	1st to 10th	Night	5% 1 6% 37% 41% 10%	585
	11th to 20th	Night	5% 1 6% 39% 41% 8%	582
	21st to end	Night	5% 1 7% 35% 46% 6%	657
August	1st to 10th	Night	4 5% 39% 45% 8%	597
	11th to 20th	Night	4 4 38% 44% 9%	594
	21st to end	Night	10% 1 7% 28% 43% 10%	660
September	1st to 10th	Night	8% 1 8% 33% 42% 9%	600
	11th to 20th	Night	13% 9% 31% 40% 8%	600
	21st to end	Night	11% 2 10% 36% 35% 7%	600
October	1st to 10th	Night	6% 2 14% 38% 35% 5%	798
	11th to 20th	Night	12% 4 23% 39% 19% 3	800
	21st to end	Night	14% 7% 25% 32% 19% 2	880
November	1st to 10th	Night	13% 6% 26% 33% 20% 2	820
	11th to 20th	Night	13% 10% 25% 39% 12%	840
	21st to end	Night	19% 10% 31% 28% 11% 1	840
December	1st to 10th	Night	27% 9% 26% 29% 8% 1	980
	11th to 20th	Night	26% 11% 29% 29% 6%	1000
	21st to end	Night	24% 11% 31% 28% 6%	1100

Page generated at 2025-11-30 00:00:55. Version ac07

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