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 2026-09-14.

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% 8% 3 9% 6% 6% 6% 5% 8% 9% 32%	154166
	Night	4 8% 4 10% 6% 6% 6% 5% 8% 9% 34%	145623
Transparency	Day	47% 12% 15% 18% 8% 1	153863
	Night	46% 12% 17% 18% 7% 1	145509
Seeing	Day	19% 20% 31% 20% 8% 2	18686
	Night	13% 18% 35% 24% 9% 1	26778

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% 4 11% 8% 8% 8% 7% 10% 11% 27%	3527
	11th to 20th	Day	1 5% 2 8% 6% 6% 6% 5% 8% 9% 43%	4016
	21st to end	Day	1 6% 4 10% 6% 6% 8% 6% 10% 11% 33%	5186
February	1st to 10th	Day	1 8% 5% 11% 8% 7% 8% 7% 9% 9% 27%	1680
	11th to 20th	Day	1 11% 5% 11% 8% 7% 6% 6% 7% 9% 28%	1723
	21st to end	Day	1 8% 5% 12% 10% 8% 7% 8% 8% 7% 26%	1710
March	1st to 10th	Day	1 7% 4 10% 9% 8% 8% 6% 9% 10% 29%	4618
	11th to 20th	Day	2 9% 3 8% 5% 5% 7% 6% 9% 12% 34%	4772
	21st to end	Day	3 12% 6% 19% 8% 6% 5% 5% 6% 9% 21%	6101
April	1st to 10th	Day	3 12% 6% 13% 9% 9% 8% 6% 8% 8% 18%	2520
	11th to 20th	Day	4 14% 7% 13% 9% 6% 5% 5% 7% 8% 23%	2638
	21st to end	Day	7% 14% 4 12% 8% 6% 6% 5% 6% 8% 24%	2897
May	1st to 10th	Day	5% 12% 4 9% 6% 5% 5% 4 6% 8% 36%	8195
	11th to 20th	Day	8% 12% 4 10% 7% 7% 7% 5% 8% 9% 23%	8594
	21st to end	Day	12% 11% 4 10% 6% 6% 6% 5% 6% 8% 26%	9760
June	1st to 10th	Day	18% 11% 3 9% 7% 7% 5% 4 6% 7% 23%	3360
	11th to 20th	Day	20% 12% 4 9% 8% 7% 6% 5% 5% 6% 17%	3360
	21st to end	Day	13% 10% 4 9% 7% 7% 6% 5% 7% 7% 26%	3360
July	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 5% 8% 10% 38%	9420
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 4 7% 9% 41%	9420
	21st to end	Day	7% 5% 2 6% 5% 6% 7% 6% 10% 10% 36%	9049
August	1st to 10th	Day	10% 6% 2 6% 5% 5% 6% 5% 7% 8% 40%	6441
	11th to 20th	Day	9% 6% 3 7% 6% 6% 6% 6% 8% 9% 34%	6367
	21st to end	Day	9% 6% 2 6% 5% 6% 6% 4 7% 9% 40%	6511
September	1st to 10th	Day	11% 8% 3 8% 5% 5% 5% 4 7% 7% 38%	2520
	11th to 20th	Day	9% 9% 3 8% 4 5% 5% 5% 7% 7% 38%	2371
	21st to end	Day	9% 10% 4 9% 6% 6% 5% 5% 7% 7% 34%	2200
October	1st to 10th	Day	4 9% 3 8% 6% 6% 6% 5% 9% 10% 33%	3327
	11th to 20th	Day	5% 10% 3 8% 7% 7% 6% 6% 8% 9% 32%	2980
	21st to end	Day	2 9% 4 11% 6% 6% 6% 5% 7% 8% 37%	3200
November	1st to 10th	Day	3 10% 4 12% 7% 7% 8% 5% 8% 9% 28%	1692
	11th to 20th	Day	2 6% 4 8% 6% 6% 6% 6% 7% 12% 37%	1470
	21st to end	Day	2 9% 3 10% 7% 7% 5% 5% 9% 12% 30%	1470
December	1st to 10th	Day	2 7% 3 10% 9% 8% 8% 6% 9% 10% 29%	2331
	11th to 20th	Day	2 6% 4 9% 6% 7% 7% 6% 8% 10% 35%	2322
	21st to end	Day	6% 4 10% 7% 6% 6% 5% 7% 9% 41%	3058
January	1st to 10th	Night	1 6% 4 14% 8% 7% 7% 5% 9% 11% 28%	9366
	11th to 20th	Night	1 6% 3 10% 6% 6% 6% 5% 7% 10% 39%	8937
	21st to end	Night	1 7% 4 10% 6% 7% 7% 6% 8% 10% 34%	8994
February	1st to 10th	Night	2 9% 4 11% 10% 8% 7% 7% 7% 9% 26%	2940
	11th to 20th	Night	1 9% 4 11% 8% 7% 7% 5% 8% 9% 30%	2781
	21st to end	Night	1 8% 5% 12% 9% 7% 7% 6% 7% 9% 28%	2095
March	1st to 10th	Night	1 7% 4 10% 9% 8% 7% 5% 8% 9% 32%	5496
	11th to 20th	Night	2 6% 4 12% 8% 6% 7% 6% 9% 10% 32%	5446
	21st to end	Night	4 14% 7% 17% 6% 4 5% 4 6% 7% 26%	5116
April	1st to 10th	Night	1 13% 5% 12% 7% 6% 6% 7% 8% 8% 26%	2100
	11th to 20th	Night	5% 13% 4 11% 7% 5% 5% 4 7% 9% 30%	1932
	21st to end	Night	8% 12% 5% 10% 5% 6% 5% 4 6% 7% 33%	1722
May	1st to 10th	Night	6% 12% 3 8% 5% 4 4 4 6% 10% 38%	4724
	11th to 20th	Night	8% 9% 4 10% 7% 6% 7% 5% 7% 8% 28%	4265
	21st to end	Night	10% 10% 3 6% 4 4 5% 4 7% 9% 36%	4407
June	1st to 10th	Night	14% 10% 4 7% 5% 6% 5% 4 7% 6% 32%	1260
	11th to 20th	Night	18% 10% 2 9% 7% 6% 7% 5% 8% 7% 21%	1260
	21st to end	Night	10% 8% 2 7% 6% 7% 5% 5% 8% 7% 35%	1260
July	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 4 8% 10% 42%	3540
	11th to 20th	Night	10% 6% 2 5% 5% 5% 6% 5% 7% 7% 42%	3540
	21st to end	Night	9% 5% 2 5% 4 5% 4 4 7% 9% 47%	5002
August	1st to 10th	Night	9% 7% 3 6% 4 5% 4 4 7% 8% 42%	3709
	11th to 20th	Night	13% 8% 3 8% 4 4 4 4 6% 8% 38%	3677
	21st to end	Night	8% 6% 3 6% 5% 6% 6% 5% 7% 9% 39%	4624
September	1st to 10th	Night	11% 8% 2 7% 4 4 5% 4 5% 8% 40%	2100
	11th to 20th	Night	9% 9% 3 7% 5% 5% 5% 4 5% 7% 41%	2095
	21st to end	Night	8% 8% 3 6% 4 5% 5% 6% 7% 8% 39%	2200
October	1st to 10th	Night	5% 11% 4 8% 5% 7% 6% 5% 8% 9% 32%	3869
	11th to 20th	Night	4 7% 3 7% 6% 6% 7% 6% 9% 10% 35%	4169
	21st to end	Night	2 8% 4 11% 6% 6% 7% 4 7% 9% 36%	4600
November	1st to 10th	Night	3 11% 5% 11% 7% 6% 6% 6% 8% 8% 29%	2803
	11th to 20th	Night	2 9% 4 10% 6% 5% 6% 5% 9% 11% 34%	3150
	21st to end	Night	1 9% 4 10% 7% 7% 6% 5% 8% 11% 31%	3150
December	1st to 10th	Night	2 7% 4 10% 7% 7% 8% 6% 8% 9% 33%	5064
	11th to 20th	Night	1 8% 4 10% 8% 8% 7% 5% 8% 11% 29%	6090
	21st to end	Night	1 6% 4 11% 6% 6% 7% 6% 8% 10% 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	51% 16% 15% 12% 6% 1	3527
	11th to 20th	Day	40% 12% 12% 21% 12% 2	4036
	21st to end	Day	43% 19% 18% 13% 6%	5187
February	1st to 10th	Day	49% 14% 12% 11% 12% 2	1680
	11th to 20th	Day	54% 11% 12% 15% 8% 1	1731
	21st to end	Day	55% 12% 12% 14% 6% 2	1710
March	1st to 10th	Day	44% 16% 15% 13% 11%	4618
	11th to 20th	Day	38% 17% 13% 21% 11%	4772
	21st to end	Day	58% 13% 10% 11% 8%	6101
April	1st to 10th	Day	61% 14% 14% 9% 2	2520
	11th to 20th	Day	59% 10% 14% 13% 3	2638
	21st to end	Day	59% 12% 13% 14% 3	2897
May	1st to 10th	Day	47% 9% 19% 19% 7%	8195
	11th to 20th	Day	54% 14% 13% 14% 5%	8598
	21st to end	Day	55% 12% 16% 14% 3	9761
June	1st to 10th	Day	60% 10% 10% 13% 6% 1	3360
	11th to 20th	Day	67% 10% 10% 10% 3	3360
	21st to end	Day	56% 13% 12% 13% 5% 1	3360
July	1st to 10th	Day	41% 10% 11% 22% 14% 3	9341
	11th to 20th	Day	40% 10% 9% 22% 16% 2	9333
	21st to end	Day	40% 10% 17% 20% 12% 1	8852
August	1st to 10th	Day	39% 11% 16% 27% 8%	6424
	11th to 20th	Day	42% 11% 17% 25% 5%	6409
	21st to end	Day	40% 10% 18% 25% 7%	6510
September	1st to 10th	Day	45% 10% 17% 21% 5% 2	2520
	11th to 20th	Day	44% 11% 15% 21% 8% 1	2371
	21st to end	Day	49% 11% 16% 14% 7% 2	2200
October	1st to 10th	Day	45% 12% 21% 18% 4	3327
	11th to 20th	Day	51% 11% 17% 18% 3	2980
	21st to end	Day	45% 10% 23% 18% 3	3200
November	1st to 10th	Day	52% 12% 16% 15% 5% 1	1692
	11th to 20th	Day	42% 15% 21% 16% 6% 1	1470
	21st to end	Day	47% 16% 16% 12% 5% 3	1470
December	1st to 10th	Day	56% 13% 17% 10% 4	2331
	11th to 20th	Day	45% 12% 19% 17% 6% 1	2324
	21st to end	Day	38% 12% 17% 22% 9% 1	3058
January	1st to 10th	Night	54% 13% 12% 13% 6% 1	9367
	11th to 20th	Night	42% 11% 14% 16% 15% 2	8979
	21st to end	Night	44% 18% 17% 14% 7%	8994
February	1st to 10th	Night	54% 12% 12% 12% 9% 1	2940
	11th to 20th	Night	50% 12% 14% 15% 8% 1	2783
	21st to end	Night	51% 11% 12% 18% 7% 1	2095
March	1st to 10th	Night	44% 16% 14% 16% 10% 1	5496
	11th to 20th	Night	43% 14% 16% 19% 7%	5447
	21st to end	Night	54% 10% 13% 15% 9%	5116
April	1st to 10th	Night	53% 15% 16% 14% 3	2100
	11th to 20th	Night	51% 11% 16% 16% 6%	1932
	21st to end	Night	49% 12% 14% 19% 5% 1	1722
May	1st to 10th	Night	42% 11% 21% 22% 3	4721
	11th to 20th	Night	51% 13% 12% 19% 6%	4265
	21st to end	Night	41% 14% 22% 19% 3	4411
June	1st to 10th	Night	51% 10% 14% 16% 8% 1	1260
	11th to 20th	Night	58% 14% 12% 12% 4	1260
	21st to end	Night	47% 12% 19% 16% 6% 1	1260
July	1st to 10th	Night	38% 10% 15% 23% 12% 2	3510
	11th to 20th	Night	39% 9% 13% 23% 15% 1	3504
	21st to end	Night	33% 9% 23% 23% 9% 2	4894
August	1st to 10th	Night	39% 10% 20% 29% 3	3701
	11th to 20th	Night	40% 10% 24% 22% 3	3701
	21st to end	Night	40% 11% 24% 22% 4	4624
September	1st to 10th	Night	42% 10% 17% 23% 7% 1	2100
	11th to 20th	Night	42% 10% 18% 22% 8% 1	2095
	21st to end	Night	42% 13% 19% 18% 8%	2200
October	1st to 10th	Night	49% 12% 18% 17% 3	3869
	11th to 20th	Night	44% 13% 19% 19% 5%	4169
	21st to end	Night	46% 11% 22% 16% 5%	4600
November	1st to 10th	Night	51% 11% 17% 16% 4 1	2803
	11th to 20th	Night	46% 14% 18% 14% 7% 1	3150
	21st to end	Night	49% 14% 15% 15% 6% 2	3150
December	1st to 10th	Night	51% 12% 18% 13% 5% 1	5064
	11th to 20th	Night	52% 15% 14% 14% 5%	6087
	21st to end	Night	42% 14% 17% 19% 7% 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	9% 26% 34% 24% 5% 3	220
	11th to 20th	Day	13% 25% 37% 18% 5% 2	220
	21st to end	Day	15% 29% 39% 12% 4 1	242
February	1st to 10th	Day	17% 25% 34% 15% 7% 2	220
	11th to 20th	Day	13% 20% 44% 18% 5% 1	303
	21st to end	Day	17% 25% 35% 18% 4 1	436
March	1st to 10th	Day	19% 26% 31% 16% 6% 1	540
	11th to 20th	Day	18% 27% 34% 16% 4 2	540
	21st to end	Day	14% 29% 31% 17% 7% 2	594
April	1st to 10th	Day	23% 19% 34% 17% 6% 1	540
	11th to 20th	Day	17% 21% 35% 18% 8% 2	532
	21st to end	Day	19% 26% 30% 16% 8% 2	540
May	1st to 10th	Day	18% 19% 34% 22% 6% 1	543
	11th to 20th	Day	18% 14% 31% 26% 9% 2	716
	21st to end	Day	24% 13% 25% 23% 12% 2	877
June	1st to 10th	Day	23% 20% 31% 20% 5% 1	990
	11th to 20th	Day	25% 18% 28% 21% 8% 1	990
	21st to end	Day	18% 15% 27% 24% 14% 2	990
July	1st to 10th	Day	21% 14% 30% 26% 9% 1	976
	11th to 20th	Day	19% 16% 31% 23% 11% 1	972
	21st to end	Day	14% 16% 31% 26% 9% 4	675
August	1st to 10th	Day	17% 12% 29% 26% 12% 4	567
	11th to 20th	Day	15% 20% 34% 21% 8% 3	557
	21st to end	Day	15% 19% 32% 21% 9% 4	627
September	1st to 10th	Day	18% 20% 30% 22% 7% 3	570
	11th to 20th	Day	17% 18% 32% 23% 8% 2	543
	21st to end	Day	29% 25% 26% 15% 4 1	530
October	1st to 10th	Day	22% 21% 32% 16% 7% 1	530
	11th to 20th	Day	20% 25% 32% 18% 5% 1	365
	21st to end	Day	17% 23% 36% 19% 3 1	363
November	1st to 10th	Day	23% 29% 31% 14% 2	256
	11th to 20th	Day	18% 28% 33% 16% 3 1	220
	21st to end	Day	20% 23% 27% 19% 10% 2	220
December	1st to 10th	Day	14% 26% 31% 17% 10% 2	220
	11th to 20th	Day	13% 25% 38% 18% 6% 1	220
	21st to end	Day	13% 21% 42% 15% 6% 3	242
January	1st to 10th	Night	12% 21% 46% 16% 4 1	1160
	11th to 20th	Night	11% 27% 42% 16% 5% 1	1032
	21st to end	Night	12% 27% 38% 17% 5%	924
February	1st to 10th	Night	14% 21% 32% 25% 8% 1	840
	11th to 20th	Night	10% 17% 38% 29% 5%	824
	21st to end	Night	10% 16% 39% 24% 10% 1	692
March	1st to 10th	Night	9% 19% 37% 25% 8% 1	840
	11th to 20th	Night	9% 20% 40% 22% 8% 1	840
	21st to end	Night	10% 16% 36% 27% 10% 1	924
April	1st to 10th	Night	11% 16% 31% 32% 9% 1	840
	11th to 20th	Night	11% 14% 37% 28% 10%	684
	21st to end	Night	14% 16% 29% 30% 10% 1	462
May	1st to 10th	Night	15% 7% 25% 41% 11%	420
	11th to 20th	Night	12% 8% 29% 35% 16% 1	414
	21st to end	Night	20% 10% 25% 28% 17%	455
June	1st to 10th	Night	20% 10% 29% 28% 13% 1	420
	11th to 20th	Night	23% 9% 23% 29% 15% 1	420
	21st to end	Night	14% 10% 25% 30% 20% 1	420
July	1st to 10th	Night	18% 7% 21% 38% 17%	410
	11th to 20th	Night	19% 11% 18% 32% 19% 1	408
	21st to end	Night	11% 7% 20% 35% 25% 1	460
August	1st to 10th	Night	15% 6% 18% 33% 25% 3	418
	11th to 20th	Night	15% 7% 22% 33% 21% 2	416
	21st to end	Night	15% 9% 30% 32% 13% 1	711
September	1st to 10th	Night	17% 11% 26% 32% 13% 1	840
	11th to 20th	Night	17% 10% 26% 30% 16% 2	812
	21st to end	Night	17% 22% 30% 22% 8% 1	800
October	1st to 10th	Night	17% 16% 33% 26% 8% 1	800
	11th to 20th	Night	15% 16% 39% 25% 5% 1	800
	21st to end	Night	14% 20% 39% 20% 6% 1	880
November	1st to 10th	Night	14% 24% 39% 20% 3	820
	11th to 20th	Night	13% 27% 40% 17% 4	1050
	21st to end	Night	11% 26% 39% 18% 6% 1	1050
December	1st to 10th	Night	12% 23% 39% 20% 5%	1056
	11th to 20th	Night	9% 24% 44% 17% 5% 1	1160
	21st to end	Night	10% 22% 44% 17% 6% 1	1276

Page generated at 2026-09-11 02:11:51. Version ac07

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