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 2026-09-29.

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	6% 10% 4 10% 7% 7% 7% 5% 8% 9% 28%	154274
	Night	4 8% 4 10% 7% 7% 7% 6% 8% 10% 29%	145846
Transparency	Day	52% 9% 15% 17% 6% 1	153974
	Night	51% 9% 18% 16% 5% 1	145729
Seeing	Day	19% 15% 30% 23% 11% 3	18694
	Night	11% 12% 36% 30% 10% 1	26802

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% 9% 11% 10% 8% 11% 10% 18%	3527
	11th to 20th	Day	1 4 3 10% 7% 7% 8% 7% 9% 9% 37%	4131
	21st to end	Day	1 9% 3 11% 7% 7% 8% 6% 8% 10% 29%	5186
February	1st to 10th	Day	2 9% 5% 14% 9% 7% 7% 6% 9% 10% 23%	1680
	11th to 20th	Day	1 9% 6% 16% 9% 7% 7% 6% 8% 8% 23%	1734
	21st to end	Day	1 7% 5% 16% 12% 8% 6% 7% 9% 7% 22%	1712
March	1st to 10th	Day	6% 4 14% 10% 10% 9% 7% 8% 10% 21%	4618
	11th to 20th	Day	2 9% 4 12% 7% 7% 7% 6% 10% 10% 25%	4760
	21st to end	Day	2 13% 6% 18% 10% 7% 6% 5% 7% 8% 17%	6101
April	1st to 10th	Day	3 14% 7% 17% 9% 9% 8% 5% 6% 6% 15%	2520
	11th to 20th	Day	3 14% 7% 16% 9% 7% 6% 5% 5% 7% 19%	2631
	21st to end	Day	6% 16% 6% 14% 8% 6% 6% 4 7% 7% 21%	2893
May	1st to 10th	Day	5% 13% 4 9% 5% 5% 5% 4 6% 9% 34%	8195
	11th to 20th	Day	8% 12% 4 11% 7% 7% 6% 6% 9% 10% 20%	8535
	21st to end	Day	13% 15% 4 11% 6% 6% 5% 4 7% 8% 22%	9704
June	1st to 10th	Day	17% 13% 4 11% 6% 6% 5% 4 7% 6% 20%	3360
	11th to 20th	Day	18% 16% 5% 12% 7% 7% 6% 4 5% 5% 14%	3360
	21st to end	Day	12% 12% 5% 12% 8% 6% 6% 5% 6% 7% 21%	3360
July	1st to 10th	Day	7% 6% 2 7% 6% 6% 7% 6% 8% 9% 37%	9420
	11th to 20th	Day	9% 6% 2 7% 5% 6% 6% 5% 7% 8% 39%	9387
	21st to end	Day	6% 6% 2 8% 6% 7% 7% 7% 9% 10% 33%	8981
August	1st to 10th	Day	9% 7% 2 6% 5% 5% 5% 5% 7% 8% 39%	6441
	11th to 20th	Day	9% 7% 3 7% 5% 6% 7% 5% 7% 9% 34%	6367
	21st to end	Day	10% 7% 2 7% 5% 6% 6% 5% 7% 9% 36%	6486
September	1st to 10th	Day	10% 9% 3 9% 6% 6% 5% 4 5% 7% 35%	2520
	11th to 20th	Day	10% 10% 3 8% 5% 5% 6% 5% 7% 7% 36%	2452
	21st to end	Day	9% 11% 4 10% 7% 6% 6% 4 7% 6% 29%	2289
October	1st to 10th	Day	5% 11% 4 11% 6% 7% 7% 6% 8% 10% 25%	3326
	11th to 20th	Day	5% 12% 4 10% 8% 8% 7% 5% 7% 8% 27%	3000
	21st to end	Day	2 10% 5% 10% 7% 6% 7% 5% 7% 9% 32%	3200
November	1st to 10th	Day	3 12% 5% 13% 9% 8% 7% 6% 8% 9% 22%	1713
	11th to 20th	Day	2 8% 4 10% 6% 7% 7% 6% 9% 12% 28%	1470
	21st to end	Day	1 10% 5% 12% 8% 7% 9% 5% 8% 10% 25%	1470
December	1st to 10th	Day	1 7% 3 13% 8% 7% 8% 7% 9% 10% 24%	2360
	11th to 20th	Day	1 9% 4 10% 8% 9% 9% 7% 9% 10% 24%	2327
	21st to end	Day	6% 3 10% 7% 7% 8% 5% 9% 12% 32%	3058
January	1st to 10th	Night	1 5% 4 15% 11% 10% 9% 7% 9% 10% 18%	9366
	11th to 20th	Night	5% 3 11% 8% 7% 7% 6% 8% 9% 35%	8821
	21st to end	Night	1 8% 4 12% 7% 7% 7% 6% 9% 10% 28%	8994
February	1st to 10th	Night	2 9% 4 12% 10% 7% 8% 7% 9% 9% 20%	2940
	11th to 20th	Night	1 9% 4 12% 8% 8% 8% 7% 7% 10% 26%	2769
	21st to end	Night	1 10% 5% 12% 10% 8% 8% 7% 8% 10% 23%	2093
March	1st to 10th	Night	7% 4 12% 9% 9% 8% 7% 9% 10% 25%	5496
	11th to 20th	Night	2 6% 4 12% 9% 8% 9% 7% 11% 11% 22%	5457
	21st to end	Night	3 15% 6% 17% 7% 6% 6% 5% 8% 10% 17%	5116
April	1st to 10th	Night	2 12% 6% 13% 8% 8% 7% 6% 8% 9% 22%	2100
	11th to 20th	Night	3 10% 5% 12% 8% 6% 6% 5% 7% 9% 29%	1939
	21st to end	Night	5% 11% 5% 11% 6% 5% 7% 6% 7% 9% 29%	1725
May	1st to 10th	Night	4 11% 4 9% 5% 5% 5% 4 6% 10% 37%	4724
	11th to 20th	Night	6% 10% 4 11% 8% 7% 7% 5% 7% 11% 24%	4325
	21st to end	Night	7% 11% 4 8% 5% 5% 6% 5% 7% 9% 34%	4464
June	1st to 10th	Night	12% 10% 4 9% 5% 6% 6% 5% 6% 6% 29%	1260
	11th to 20th	Night	16% 11% 5% 9% 8% 6% 6% 5% 6% 7% 20%	1260
	21st to end	Night	10% 7% 2 9% 7% 7% 7% 5% 7% 9% 31%	1260
July	1st to 10th	Night	7% 5% 2 5% 3 4 5% 5% 7% 9% 45%	3540
	11th to 20th	Night	8% 5% 2 6% 4 5% 7% 4 7% 8% 43%	3558
	21st to end	Night	8% 5% 2 5% 4 4 5% 5% 7% 10% 42%	5084
August	1st to 10th	Night	8% 7% 3 7% 5% 5% 6% 5% 8% 9% 40%	3709
	11th to 20th	Night	9% 8% 3 6% 4 4 6% 4 8% 10% 36%	3677
	21st to end	Night	8% 7% 2 7% 5% 5% 7% 5% 8% 10% 35%	4650
September	1st to 10th	Night	11% 8% 2 7% 5% 5% 6% 4 5% 7% 39%	2100
	11th to 20th	Night	8% 10% 3 9% 5% 5% 4 5% 6% 7% 39%	2167
	21st to end	Night	8% 9% 4 8% 5% 5% 6% 5% 8% 10% 34%	2288
October	1st to 10th	Night	4 9% 4 10% 6% 7% 7% 6% 10% 11% 26%	3872
	11th to 20th	Night	4 9% 3 8% 6% 7% 7% 7% 9% 10% 29%	4149
	21st to end	Night	3 8% 3 9% 6% 7% 8% 6% 10% 10% 31%	4600
November	1st to 10th	Night	3 11% 5% 12% 9% 8% 7% 6% 8% 10% 23%	2800
	11th to 20th	Night	1 9% 4 10% 7% 8% 7% 7% 9% 11% 27%	3133
	21st to end	Night	1 10% 5% 10% 9% 7% 7% 6% 9% 11% 25%	3150
December	1st to 10th	Night	2 6% 4 11% 8% 7% 7% 7% 10% 11% 27%	5040
	11th to 20th	Night	1 7% 4 12% 9% 10% 9% 6% 10% 11% 21%	6080
	21st to end	Night	7% 4 11% 7% 7% 9% 7% 9% 11% 27%	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	60% 12% 15% 10% 2	3527
	11th to 20th	Day	45% 9% 16% 19% 10% 2	4152
	21st to end	Day	50% 14% 19% 14% 2	5187
February	1st to 10th	Day	56% 8% 12% 12% 10% 2	1680
	11th to 20th	Day	59% 8% 11% 16% 7%	1742
	21st to end	Day	60% 7% 13% 13% 6% 1	1712
March	1st to 10th	Day	55% 10% 13% 14% 8%	4618
	11th to 20th	Day	51% 11% 13% 20% 5%	4760
	21st to end	Day	64% 8% 10% 11% 7%	6101
April	1st to 10th	Day	69% 8% 12% 10% 2	2520
	11th to 20th	Day	64% 7% 12% 14% 2	2631
	21st to end	Day	63% 8% 13% 13% 3	2893
May	1st to 10th	Day	48% 7% 21% 18% 5%	8195
	11th to 20th	Day	59% 9% 15% 14% 4	8539
	21st to end	Day	59% 9% 17% 13% 2	9705
June	1st to 10th	Day	63% 7% 11% 12% 6% 2	3360
	11th to 20th	Day	70% 7% 10% 9% 3	3360
	21st to end	Day	61% 8% 13% 13% 4 1	3360
July	1st to 10th	Day	43% 9% 12% 21% 11% 4	9341
	11th to 20th	Day	41% 7% 10% 22% 16% 2	9300
	21st to end	Day	44% 11% 15% 18% 11% 2	8786
August	1st to 10th	Day	40% 8% 15% 27% 10%	6424
	11th to 20th	Day	43% 9% 18% 24% 5%	6409
	21st to end	Day	46% 9% 15% 23% 7% 1	6485
September	1st to 10th	Day	50% 6% 16% 22% 5% 1	2520
	11th to 20th	Day	47% 7% 16% 20% 9% 1	2452
	21st to end	Day	55% 8% 14% 15% 6% 1	2289
October	1st to 10th	Day	56% 9% 17% 15% 3	3326
	11th to 20th	Day	58% 8% 17% 15% 2	3000
	21st to end	Day	54% 8% 21% 14% 3	3200
November	1st to 10th	Day	59% 10% 14% 13% 4 1	1713
	11th to 20th	Day	49% 11% 22% 13% 5% 1	1470
	21st to end	Day	55% 11% 17% 10% 5% 2	1470
December	1st to 10th	Day	60% 14% 14% 8% 4	2360
	11th to 20th	Day	54% 12% 18% 12% 4 1	2329
	21st to end	Day	45% 11% 21% 15% 7%	3058
January	1st to 10th	Night	62% 10% 14% 11% 3	9367
	11th to 20th	Night	47% 9% 15% 16% 12% 1	8862
	21st to end	Night	54% 11% 17% 15% 3	8994
February	1st to 10th	Night	60% 8% 11% 11% 8% 1	2940
	11th to 20th	Night	54% 8% 15% 15% 7% 1	2771
	21st to end	Night	56% 6% 12% 19% 7% 1	2093
March	1st to 10th	Night	52% 11% 13% 16% 8%	5496
	11th to 20th	Night	55% 8% 16% 17% 4	5458
	21st to end	Night	60% 10% 12% 13% 5%	5116
April	1st to 10th	Night	59% 9% 16% 13% 2	2100
	11th to 20th	Night	52% 8% 17% 18% 5%	1939
	21st to end	Night	52% 10% 14% 19% 5%	1725
May	1st to 10th	Night	44% 7% 29% 18% 2	4721
	11th to 20th	Night	56% 9% 15% 16% 5%	4325
	21st to end	Night	48% 10% 24% 15% 3	4468
June	1st to 10th	Night	55% 7% 14% 16% 7% 2	1260
	11th to 20th	Night	61% 8% 15% 12% 4	1260
	21st to end	Night	48% 10% 18% 18% 5% 1	1260
July	1st to 10th	Night	37% 7% 18% 22% 13% 2	3510
	11th to 20th	Night	39% 7% 12% 24% 16% 2	3522
	21st to end	Night	37% 8% 21% 24% 8% 3	4974
August	1st to 10th	Night	39% 9% 20% 27% 4	3701
	11th to 20th	Night	40% 10% 27% 20% 3	3701
	21st to end	Night	45% 8% 23% 20% 3	4650
September	1st to 10th	Night	43% 7% 20% 23% 7% 1	2100
	11th to 20th	Night	45% 6% 20% 22% 7% 1	2167
	21st to end	Night	45% 10% 20% 19% 5%	2288
October	1st to 10th	Night	57% 10% 18% 13% 2	3872
	11th to 20th	Night	53% 9% 20% 16% 2	4149
	21st to end	Night	52% 10% 23% 11% 3	4600
November	1st to 10th	Night	60% 8% 16% 13% 3	2800
	11th to 20th	Night	51% 12% 19% 12% 6%	3133
	21st to end	Night	54% 12% 16% 12% 5% 1	3150
December	1st to 10th	Night	55% 12% 17% 11% 4	5040
	11th to 20th	Night	58% 14% 14% 10% 3	6077
	21st to end	Night	52% 9% 18% 16% 4	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	10% 10% 25% 37% 15% 3	220
	11th to 20th	Day	11% 7% 36% 32% 10% 4	220
	21st to end	Day	14% 10% 38% 26% 9% 3	242
February	1st to 10th	Day	15% 14% 36% 21% 11% 3	220
	11th to 20th	Day	14% 15% 32% 25% 12% 4	314
	21st to end	Day	16% 20% 37% 16% 10% 2	438
March	1st to 10th	Day	18% 22% 30% 18% 10% 3	540
	11th to 20th	Day	16% 20% 34% 19% 9% 2	540
	21st to end	Day	19% 20% 29% 20% 8% 5%	594
April	1st to 10th	Day	18% 20% 32% 22% 7% 1	540
	11th to 20th	Day	17% 19% 29% 23% 8% 4	532
	21st to end	Day	19% 19% 28% 21% 11% 3	540
May	1st to 10th	Day	22% 17% 30% 22% 7% 2	543
	11th to 20th	Day	18% 12% 27% 29% 13% 2	696
	21st to end	Day	24% 12% 25% 22% 15% 3	860
June	1st to 10th	Day	25% 16% 30% 21% 7%	990
	11th to 20th	Day	27% 15% 29% 20% 8% 1	990
	21st to end	Day	18% 15% 25% 24% 15% 3	990
July	1st to 10th	Day	20% 13% 29% 26% 10% 2	976
	11th to 20th	Day	19% 12% 32% 24% 11% 2	965
	21st to end	Day	15% 14% 28% 23% 15% 4	645
August	1st to 10th	Day	17% 12% 26% 27% 14% 4	567
	11th to 20th	Day	15% 15% 34% 22% 11% 3	557
	21st to end	Day	17% 14% 31% 20% 14% 4	627
September	1st to 10th	Day	21% 16% 27% 21% 12% 3	570
	11th to 20th	Day	16% 14% 29% 26% 13% 2	570
	21st to end	Day	29% 22% 27% 13% 7% 2	563
October	1st to 10th	Day	22% 19% 28% 18% 9% 4	530
	11th to 20th	Day	21% 15% 31% 22% 9% 2	372
	21st to end	Day	17% 15% 29% 31% 6% 1	363
November	1st to 10th	Day	20% 13% 39% 20% 5% 3	258
	11th to 20th	Day	15% 13% 34% 25% 9% 4	220
	21st to end	Day	15% 15% 28% 25% 11% 5%	220
December	1st to 10th	Day	12% 10% 33% 26% 13% 5%	220
	11th to 20th	Day	10% 10% 33% 30% 12% 5%	220
	21st to end	Day	8% 11% 28% 33% 14% 6%	242
January	1st to 10th	Night	9% 14% 41% 30% 5% 1	1160
	11th to 20th	Night	8% 16% 41% 26% 6% 2	1001
	21st to end	Night	9% 18% 45% 22% 6% 1	924
February	1st to 10th	Night	10% 15% 36% 28% 10%	840
	11th to 20th	Night	8% 11% 42% 31% 8% 1	824
	21st to end	Night	8% 15% 39% 26% 10% 2	692
March	1st to 10th	Night	6% 16% 40% 26% 11% 1	840
	11th to 20th	Night	6% 13% 44% 27% 9% 1	840
	21st to end	Night	8% 12% 37% 29% 11% 2	924
April	1st to 10th	Night	8% 13% 31% 35% 11% 1	840
	11th to 20th	Night	10% 11% 36% 29% 13% 1	691
	21st to end	Night	13% 8% 32% 36% 10%	465
May	1st to 10th	Night	12% 7% 28% 42% 10%	420
	11th to 20th	Night	12% 4 29% 38% 16% 1	414
	21st to end	Night	16% 9% 28% 29% 18%	455
June	1st to 10th	Night	19% 4 33% 31% 13% 1	420
	11th to 20th	Night	22% 8% 24% 32% 13% 1	420
	21st to end	Night	14% 8% 23% 35% 19% 2	420
July	1st to 10th	Night	18% 5% 20% 40% 15% 1	410
	11th to 20th	Night	15% 8% 24% 34% 19%	408
	21st to end	Night	9% 6% 20% 42% 22% 1	460
August	1st to 10th	Night	13% 5% 15% 39% 27% 1	418
	11th to 20th	Night	14% 5% 21% 40% 19% 1	416
	21st to end	Night	15% 7% 26% 39% 12% 1	724
September	1st to 10th	Night	17% 8% 24% 37% 13% 1	840
	11th to 20th	Night	14% 6% 25% 35% 17% 1	840
	21st to end	Night	17% 15% 32% 25% 10% 1	832
October	1st to 10th	Night	16% 11% 33% 31% 9% 1	800
	11th to 20th	Night	14% 11% 40% 27% 7% 1	800
	21st to end	Night	12% 15% 42% 24% 6% 1	880
November	1st to 10th	Night	12% 15% 43% 25% 5% 1	820
	11th to 20th	Night	10% 17% 43% 25% 4	1033
	21st to end	Night	10% 13% 47% 24% 6% 1	1050
December	1st to 10th	Night	9% 14% 44% 25% 8% 1	1050
	11th to 20th	Night	9% 12% 45% 26% 7% 1	1155
	21st to end	Night	6% 12% 45% 27% 9% 1	1276

Page generated at 2026-09-26 02:18:42. Version ac07

Copyright © 2026 Attilla Danko.