Sand Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sand Point clear sky chart from 2005-11-06 to 2026-05-02.

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	2 4 2 5% 3 3 3 3 4 6% 65%	140357
	Night	2 4 2 5% 4 4 4 3 5% 7% 61%	139518
Transparency	Day	17% 7% 9% 19% 27% 21%	135331
	Night	18% 9% 11% 21% 25% 16%	135537
Seeing	Day	10% 18% 27% 24% 17% 5%	16928
	Night	6% 14% 21% 31% 24% 5%	26389

By Month

Percentage Cloud Cover SW (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% 3 8% 5% 5% 6% 4 6% 8% 49%	4722
	11th to 20th	Day	1 3 2 5% 4 4 4 4 4 6% 63%	4878
	21st to end	Day	3 6% 4 10% 4 4 5% 4 6% 10% 45%	5843
February	1st to 10th	Day	2 7% 3 7% 5% 5% 5% 4 6% 7% 49%	1891
	11th to 20th	Day	1 7% 3 8% 7% 6% 4 4 6% 8% 46%	2050
	21st to end	Day	1 6% 3 7% 5% 5% 5% 5% 6% 7% 50%	1730
March	1st to 10th	Day	2 9% 5% 12% 7% 6% 6% 5% 6% 8% 35%	4618
	11th to 20th	Day	1 4 2 6% 5% 5% 5% 5% 5% 8% 56%	5037
	21st to end	Day	1 8% 3 8% 6% 5% 6% 4 6% 7% 46%	5961
April	1st to 10th	Day	3 5% 3 8% 5% 5% 5% 4 6% 7% 49%	2520
	11th to 20th	Day	2 5% 2 6% 5% 4 5% 5% 6% 8% 53%	2489
	21st to end	Day	2 6% 2 6% 4 3 3 3 5% 8% 57%	2520
May	1st to 10th	Day	3 4 2 4 3 2 3 2 3 4 70%	5712
	11th to 20th	Day	1 3 1 3 3 3 4 3 5% 5% 69%	6182
	21st to end	Day	2 3 1 4 3 2 3 3 4 5% 71%	6902
June	1st to 10th	Day	3 3 1 5% 3 3 3 4 6% 8% 61%	2800
	11th to 20th	Day	1 2 1 3 2 2 2 2 4 5% 76%	2800
	21st to end	Day	2 2 1 2 2 2 2 2 3 5% 78%	2800
July	1st to 10th	Day	1 1 1 2 1 2 2 88%	6319
	11th to 20th	Day	1 2 1 2 2 1 2 2 3 3 81%	6320
	21st to end	Day	1 1 1 2 2 3 3 3 4 6% 75%	6717
August	1st to 10th	Day	2 1 1 2 1 2 2 1 3 3 83%	5706
	11th to 20th	Day	1 1 1 1 1 1 2 3 90%	5364
	21st to end	Day	1 2 1 3 2 3 2 2 3 4 77%	5984
September	1st to 10th	Day	1 1 1 1 1 2 2 2 4 4 81%	2400
	11th to 20th	Day	2 2 1 4 3 2 3 2 3 5% 73%	2369
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 77%	2200
October	1st to 10th	Day	2 3 1 3 3 2 2 2 4 6% 72%	3324
	11th to 20th	Day	2 4 1 5% 2 2 2 2 2 4 75%	3261
	21st to end	Day	1 2 4 3 3 4 3 5% 8% 64%	3472
November	1st to 10th	Day	3 4 3 6% 4 4 4 3 5% 6% 57%	1854
	11th to 20th	Day	3 5% 2 4 3 4 4 5% 7% 10% 54%	1890
	21st to end	Day	2 5% 2 6% 5% 5% 5% 5% 6% 8% 53%	1822
December	1st to 10th	Day	2 4 2 3 4 4 4 2 5% 9% 61%	2700
	11th to 20th	Day	3 9% 4 9% 6% 6% 6% 4 7% 8% 37%	3108
	21st to end	Day	1 7% 3 12% 8% 6% 5% 5% 7% 11% 35%	4092
January	1st to 10th	Night	2 5% 2 7% 6% 5% 6% 5% 7% 10% 47%	8172
	11th to 20th	Night	1 4 2 5% 4 4 4 3 5% 7% 61%	8071
	21st to end	Night	2 8% 4 9% 5% 5% 5% 4 5% 7% 49%	8371
February	1st to 10th	Night	2 6% 2 8% 5% 5% 5% 4 6% 7% 50%	2726
	11th to 20th	Night	1 5% 2 6% 6% 5% 6% 6% 8% 9% 47%	2458
	21st to end	Night	1 5% 3 9% 6% 3 5% 4 6% 8% 51%	2076
March	1st to 10th	Night	2 7% 5% 11% 6% 6% 5% 5% 6% 8% 40%	5496
	11th to 20th	Night	4 2 8% 6% 5% 5% 4 5% 7% 53%	5168
	21st to end	Night	1 8% 3 9% 7% 5% 7% 5% 6% 8% 40%	5255
April	1st to 10th	Night	2 4 2 6% 5% 5% 5% 5% 7% 9% 50%	2100
	11th to 20th	Night	2 5% 2 6% 4 4 4 5% 6% 7% 55%	2079
	21st to end	Night	3 5% 2 4 4 3 4 4 5% 7% 60%	2100
May	1st to 10th	Night	2 3 1 4 3 2 2 3 4 5% 72%	4296
	11th to 20th	Night	1 2 1 4 3 2 3 2 3 6% 71%	3711
	21st to end	Night	2 2 1 3 2 2 2 2 4 6% 73%	3972
June	1st to 10th	Night	3 4 2 4 3 3 3 4 4 7% 64%	1600
	11th to 20th	Night	1 1 2 1 2 2 3 3 5% 79%	1600
	21st to end	Night	3 2 1 2 2 2 2 2 3 4 78%	1600
July	1st to 10th	Night	1 1 1 1 1 2 3 90%	3640
	11th to 20th	Night	2 3 1 3 1 2 1 1 3 3 79%	3640
	21st to end	Night	2 3 1 3 2 3 3 3 4 6% 71%	4123
August	1st to 10th	Night	2 2 1 1 1 2 2 2 3 4 80%	4097
	11th to 20th	Night	1 1 2 1 1 2 1 2 4 85%	4506
	21st to end	Night	2 2 1 4 2 2 2 2 3 3 76%	5015
September	1st to 10th	Night	1 1 1 1 1 1 2 2 4 85%	2000
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 5% 76%	2030
	21st to end	Night	1 2 1 3 2 3 2 2 3 5% 76%	2200
October	1st to 10th	Night	2 2 1 2 2 2 3 2 4 4 77%	3873
	11th to 20th	Night	2 2 1 3 2 2 2 2 2 4 79%	3897
	21st to end	Night	1 3 1 5% 3 3 3 4 5% 7% 65%	4336
November	1st to 10th	Night	2 5% 2 5% 4 3 4 3 6% 8% 59%	2665
	11th to 20th	Night	2 4 1 4 4 3 4 4 5% 9% 59%	2730
	21st to end	Night	2 4 2 6% 5% 4 3 4 6% 8% 56%	2793
December	1st to 10th	Night	2 4 2 4 3 3 4 3 5% 7% 63%	4700
	11th to 20th	Night	3 7% 2 8% 8% 6% 7% 5% 8% 11% 37%	5316
	21st to end	Night	1 7% 4 12% 8% 7% 7% 5% 8% 9% 33%	7106

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	21% 15% 20% 26% 17% 1	4723
	11th to 20th	Day	19% 7% 9% 18% 28% 19%	4878
	21st to end	Day	30% 10% 8% 20% 23% 10%	5843
February	1st to 10th	Day	28% 10% 12% 23% 18% 8%	1891
	11th to 20th	Day	30% 10% 11% 25% 19% 5%	2060
	21st to end	Day	25% 13% 15% 24% 17% 6%	1730
March	1st to 10th	Day	33% 15% 13% 15% 19% 5%	4618
	11th to 20th	Day	15% 10% 16% 35% 20% 3	5037
	21st to end	Day	25% 14% 17% 23% 19% 2	5961
April	1st to 10th	Day	28% 10% 15% 22% 20% 4	2520
	11th to 20th	Day	23% 9% 13% 26% 22% 6%	2492
	21st to end	Day	22% 8% 14% 28% 24% 3	2520
May	1st to 10th	Day	15% 6% 7% 27% 38% 6%	5712
	11th to 20th	Day	13% 5% 10% 23% 40% 9%	6185
	21st to end	Day	14% 5% 6% 21% 45% 9%	6904
June	1st to 10th	Day	19% 7% 9% 24% 32% 10%	2800
	11th to 20th	Day	11% 4 7% 20% 36% 23%	2800
	21st to end	Day	10% 3 4 12% 34% 37%	2800
July	1st to 10th	Day	5% 1 2 5% 18% 68%	6251
	11th to 20th	Day	9% 2 2 7% 12% 68%	6245
	21st to end	Day	9% 4 5% 13% 30% 40%	6521
August	1st to 10th	Day	12% 2 3 8% 25% 50%	4157
	11th to 20th	Day	5% 2 2 6% 26% 59%	3880
	21st to end	Day	7% 1 2 9% 41% 40%	4311
September	1st to 10th	Day	8% 2 3 10% 34% 42%	2400
	11th to 20th	Day	13% 5% 5% 19% 36% 22%	2369
	21st to end	Day	13% 3 4 18% 37% 25%	2200
October	1st to 10th	Day	13% 4 5% 12% 38% 29%	3324
	11th to 20th	Day	13% 4 5% 20% 46% 12%	3261
	21st to end	Day	12% 7% 9% 28% 33% 11%	3472
November	1st to 10th	Day	23% 9% 10% 24% 25% 9%	1854
	11th to 20th	Day	20% 10% 16% 24% 26% 5%	1890
	21st to end	Day	24% 9% 11% 24% 24% 8%	1822
December	1st to 10th	Day	19% 7% 9% 28% 29% 8%	2700
	11th to 20th	Day	33% 15% 14% 17% 16% 6%	3108
	21st to end	Day	27% 18% 19% 21% 13% 2	4092
January	1st to 10th	Night	20% 15% 22% 26% 16% 1	8172
	11th to 20th	Night	19% 7% 10% 16% 28% 19%	8071
	21st to end	Night	30% 10% 10% 16% 27% 8%	8371
February	1st to 10th	Night	28% 11% 12% 22% 20% 7%	2726
	11th to 20th	Night	24% 12% 15% 27% 19% 4	2459
	21st to end	Night	25% 11% 15% 26% 16% 7%	2076
March	1st to 10th	Night	28% 14% 12% 20% 20% 5%	5496
	11th to 20th	Night	18% 14% 13% 38% 13% 3	5168
	21st to end	Night	25% 19% 21% 24% 9% 2	5255
April	1st to 10th	Night	23% 13% 15% 26% 17% 5%	2100
	11th to 20th	Night	23% 9% 15% 29% 18% 6%	2079
	21st to end	Night	20% 10% 15% 33% 19% 3	2100
May	1st to 10th	Night	12% 6% 10% 32% 36% 4	4293
	11th to 20th	Night	11% 6% 11% 28% 36% 8%	3711
	21st to end	Night	11% 5% 9% 26% 43% 6%	3972
June	1st to 10th	Night	18% 7% 11% 25% 30% 9%	1600
	11th to 20th	Night	9% 4 7% 21% 37% 22%	1600
	21st to end	Night	11% 2 4 14% 35% 33%	1600
July	1st to 10th	Night	4 1 2 4 23% 67%	3600
	11th to 20th	Night	12% 2 2 6% 15% 63%	3592
	21st to end	Night	13% 4 5% 14% 25% 40%	4007
August	1st to 10th	Night	13% 3 3 9% 30% 42%	2979
	11th to 20th	Night	6% 2 2 7% 28% 55%	3256
	21st to end	Night	8% 2 2 10% 42% 36%	3608
September	1st to 10th	Night	6% 2 3 10% 38% 41%	2000
	11th to 20th	Night	11% 4 6% 22% 36% 21%	2030
	21st to end	Night	12% 3 5% 20% 36% 24%	2200
October	1st to 10th	Night	12% 3 5% 13% 36% 30%	3873
	11th to 20th	Night	9% 4 5% 20% 48% 13%	3897
	21st to end	Night	13% 7% 9% 26% 34% 11%	4336
November	1st to 10th	Night	19% 10% 12% 25% 23% 11%	2665
	11th to 20th	Night	19% 9% 12% 28% 25% 6%	2730
	21st to end	Night	22% 9% 10% 26% 24% 9%	2793
December	1st to 10th	Night	19% 7% 10% 26% 26% 11%	4700
	11th to 20th	Night	26% 18% 14% 19% 19% 4	5316
	21st to end	Night	32% 17% 17% 20% 12% 3	7106

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% 23% 24% 17% 11% 3	220
	11th to 20th	Day	9% 23% 28% 20% 14% 5%	267
	21st to end	Day	9% 18% 28% 24% 16% 4	473
February	1st to 10th	Day	16% 19% 27% 22% 13% 3	431
	11th to 20th	Day	13% 24% 28% 23% 10% 1	535
	21st to end	Day	13% 20% 31% 26% 9%	446
March	1st to 10th	Day	18% 31% 23% 17% 9% 2	540
	11th to 20th	Day	14% 25% 26% 19% 13% 2	540
	21st to end	Day	16% 28% 27% 20% 8% 1	594
April	1st to 10th	Day	13% 24% 29% 19% 11% 3	540
	11th to 20th	Day	15% 27% 28% 16% 11% 3	532
	21st to end	Day	13% 23% 27% 20% 13% 4	540
May	1st to 10th	Day	16% 21% 29% 21% 10% 4	508
	11th to 20th	Day	13% 22% 23% 22% 13% 5%	528
	21st to end	Day	11% 16% 24% 25% 18% 6%	573
June	1st to 10th	Day	7% 17% 26% 26% 19% 5%	530
	11th to 20th	Day	9% 21% 31% 22% 12% 5%	530
	21st to end	Day	3 13% 26% 32% 20% 6%	530
July	1st to 10th	Day	2 10% 35% 31% 17% 5%	526
	11th to 20th	Day	2 8% 33% 31% 19% 7%	524
	21st to end	Day	3 7% 32% 29% 23% 6%	575
August	1st to 10th	Day	4 11% 31% 30% 20% 5%	527
	11th to 20th	Day	3 11% 25% 30% 21% 10%	517
	21st to end	Day	3 8% 31% 30% 23% 4	583
September	1st to 10th	Day	3 10% 30% 28% 24% 5%	530
	11th to 20th	Day	8% 15% 25% 26% 21% 5%	530
	21st to end	Day	5% 12% 28% 31% 20% 3	530
October	1st to 10th	Day	6% 16% 25% 25% 21% 7%	530
	11th to 20th	Day	10% 14% 21% 26% 24% 5%	530
	21st to end	Day	11% 16% 26% 19% 24% 5%	533
November	1st to 10th	Day	13% 18% 21% 20% 20% 9%	330
	11th to 20th	Day	9% 21% 21% 26% 16% 8%	330
	21st to end	Day	10% 17% 22% 26% 19% 5%	294
December	1st to 10th	Day	11% 18% 20% 23% 18% 10%	220
	11th to 20th	Day	13% 23% 25% 15% 16% 8%	220
	21st to end	Day	24% 17% 22% 23% 12% 3	242
January	1st to 10th	Night	8% 20% 22% 24% 19% 7%	840
	11th to 20th	Night	6% 17% 21% 33% 18% 5%	840
	21st to end	Night	6% 14% 25% 30% 19% 5%	924
February	1st to 10th	Night	10% 14% 22% 31% 19% 3	840
	11th to 20th	Night	6% 17% 25% 29% 18% 5%	824
	21st to end	Night	9% 20% 22% 33% 13% 3	692
March	1st to 10th	Night	9% 23% 27% 24% 15% 3	840
	11th to 20th	Night	7% 22% 21% 24% 23% 3	840
	21st to end	Night	7% 25% 27% 25% 14% 2	924
April	1st to 10th	Night	6% 21% 26% 28% 18% 1	840
	11th to 20th	Night	10% 19% 23% 27% 17% 4	831
	21st to end	Night	8% 16% 23% 27% 22% 4	840
May	1st to 10th	Night	9% 16% 25% 27% 21% 4	686
	11th to 20th	Night	5% 11% 23% 33% 24% 4	437
	21st to end	Night	6% 8% 18% 34% 29% 4	433
June	1st to 10th	Night	6% 8% 18% 35% 27% 6%	400
	11th to 20th	Night	2 8% 22% 37% 30% 2	400
	21st to end	Night	3 5% 19% 38% 33% 3	400
July	1st to 10th	Night	1 3 17% 45% 31% 3	390
	11th to 20th	Night	1 2 18% 44% 34% 2	388
	21st to end	Night	3 3 10% 40% 38% 6%	503
August	1st to 10th	Night	4 2 14% 38% 38% 5%	621
	11th to 20th	Night	3 5% 18% 37% 32% 5%	792
	21st to end	Night	3 4 17% 43% 30% 4	880
September	1st to 10th	Night	2 3 19% 34% 36% 6%	800
	11th to 20th	Night	4 7% 18% 30% 33% 8%	800
	21st to end	Night	3 9% 20% 31% 30% 8%	800
October	1st to 10th	Night	5% 11% 18% 32% 27% 8%	800
	11th to 20th	Night	7% 10% 14% 32% 30% 8%	800
	21st to end	Night	7% 12% 16% 27% 28% 10%	880
November	1st to 10th	Night	6% 16% 18% 23% 29% 8%	820
	11th to 20th	Night	8% 16% 21% 31% 18% 6%	840
	21st to end	Night	8% 16% 20% 27% 24% 6%	840
December	1st to 10th	Night	9% 16% 21% 30% 18% 7%	840
	11th to 20th	Night	11% 19% 20% 28% 17% 6%	840
	21st to end	Night	11% 22% 25% 27% 13% 2	924

Page generated at 2026-04-28 23:21:46. Version ac07

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