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 2024-07-31.

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 5% 2 5% 4 4 4 3 5% 6% 60%	90022
	Night	2 5% 2 6% 4 4 4 4 5% 7% 57%	89945
Transparency	Day	21% 8% 10% 21% 25% 16%	89730
	Night	22% 9% 12% 22% 22% 12%	89758
Seeing	Day	9% 18% 27% 25% 17% 5%	14681
	Night	6% 13% 20% 30% 24% 6%	24015

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 6% 2 9% 5% 6% 7% 5% 6% 8% 43%	2539
	11th to 20th	Day	1 6% 3 8% 7% 7% 7% 6% 6% 7% 42%	2608
	21st to end	Day	4 10% 5% 10% 6% 5% 6% 4 6% 8% 35%	3146
February	1st to 10th	Day	2 7% 3 7% 5% 5% 5% 4 6% 7% 49%	1710
	11th to 20th	Day	1 7% 3 8% 6% 5% 4 4 6% 8% 47%	1850
	21st to end	Day	1 6% 3 8% 6% 5% 5% 5% 6% 7% 49%	1570
March	1st to 10th	Day	2 7% 5% 14% 8% 7% 8% 6% 7% 7% 29%	3138
	11th to 20th	Day	1 5% 2 6% 4 4 4 4 4 7% 59%	3445
	21st to end	Day	1 10% 4 7% 5% 5% 5% 5% 7% 8% 43%	4067
April	1st to 10th	Day	3 6% 3 8% 5% 4 5% 4 6% 7% 49%	2280
	11th to 20th	Day	2 6% 2 5% 5% 4 5% 5% 6% 8% 53%	2249
	21st to end	Day	3 6% 1 5% 4 3 3 3 4 8% 59%	2280
May	1st to 10th	Day	3 4 2 4 3 2 3 2 4 5% 68%	3981
	11th to 20th	Day	2 3 1 3 3 2 3 2 4 5% 72%	4308
	21st to end	Day	3 4 1 5% 3 3 4 3 5% 5% 63%	4813
June	1st to 10th	Day	3 3 1 5% 3 3 3 4 6% 8% 60%	2660
	11th to 20th	Day	1 2 1 3 2 2 2 2 4 5% 75%	2660
	21st to end	Day	2 2 1 2 2 2 2 2 3 5% 77%	2660
July	1st to 10th	Day	1 1 1 1 1 2 2 2 3 3 83%	2660
	11th to 20th	Day	1 2 1 2 2 2 2 2 4 4 79%	2660
	21st to end	Day	2 2 1 3 2 3 3 2 3 4 75%	2819
August	1st to 10th	Day	3 1 1 3 3 3 3 2 4 4 74%	2307
	11th to 20th	Day	1 1 2 2 2 2 2 3 5% 80%	2122
	21st to end	Day	1 1 1 1 1 2 1 3 3 85%	2376
September	1st to 10th	Day	1 1 1 1 1 2 2 2 3 4 82%	2160
	11th to 20th	Day	2 2 1 4 3 2 2 2 4 5% 74%	2133
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 76%	1980
October	1st to 10th	Day	3 6% 2 3 3 3 3 2 3 5% 67%	1830
	11th to 20th	Day	2 3 1 4 3 2 3 2 3 6% 70%	1800
	21st to end	Day	2 3 1 4 3 3 3 3 5% 7% 68%	1936
November	1st to 10th	Day	3 5% 3 6% 4 5% 4 3 5% 5% 57%	1674
	11th to 20th	Day	2 4 2 4 3 4 4 5% 7% 10% 56%	1710
	21st to end	Day	2 5% 2 6% 5% 5% 5% 4 6% 8% 52%	1649
December	1st to 10th	Day	4 6% 3 5% 5% 5% 6% 3 6% 8% 48%	1520
	11th to 20th	Day	5% 13% 4 9% 5% 6% 6% 5% 7% 6% 33%	1928
	21st to end	Day	2 8% 3 9% 5% 5% 5% 5% 8% 11% 39%	2794
January	1st to 10th	Night	2 5% 3 8% 5% 4 6% 5% 7% 10% 45%	4406
	11th to 20th	Night	1 7% 4 9% 7% 7% 7% 5% 7% 8% 37%	4349
	21st to end	Night	4 11% 4 11% 5% 5% 6% 5% 6% 7% 37%	4521
February	1st to 10th	Night	2 6% 3 8% 5% 5% 5% 4 6% 7% 49%	2467
	11th to 20th	Night	1 6% 2 5% 5% 4 5% 6% 8% 9% 49%	2218
	21st to end	Night	1 5% 3 9% 6% 3 4 4 6% 8% 50%	1884
March	1st to 10th	Night	1 7% 5% 11% 7% 7% 6% 5% 7% 9% 35%	3736
	11th to 20th	Night	1 6% 2 6% 4 4 4 4 5% 7% 58%	3533
	21st to end	Night	1 11% 4 9% 6% 6% 6% 6% 7% 8% 36%	3585
April	1st to 10th	Night	2 5% 2 5% 5% 6% 5% 5% 8% 9% 49%	1900
	11th to 20th	Night	2 6% 2 5% 4 4 4 5% 6% 7% 55%	1879
	21st to end	Night	3 5% 2 4 3 3 4 4 5% 7% 61%	1900
May	1st to 10th	Night	2 3 2 5% 3 2 3 3 4 5% 68%	2990
	11th to 20th	Night	1 3 1 3 2 2 3 3 4 6% 73%	2583
	21st to end	Night	3 3 1 5% 3 3 3 3 5% 7% 66%	2762
June	1st to 10th	Night	3 4 2 4 3 3 3 4 4 7% 63%	1520
	11th to 20th	Night	1 1 2 1 2 2 3 3 5% 78%	1520
	21st to end	Night	3 2 1 2 2 2 2 2 3 4 77%	1520
July	1st to 10th	Night	1 1 1 2 1 2 2 1 3 5% 82%	1520
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 3 77%	1520
	21st to end	Night	2 3 1 3 2 2 2 2 3 6% 74%	1726
August	1st to 10th	Night	4 3 1 2 3 3 3 3 4 4 72%	1632
	11th to 20th	Night	2 1 1 3 2 2 3 2 3 4 78%	1780
	21st to end	Night	2 2 1 2 1 1 2 1 2 3 83%	1980
September	1st to 10th	Night	1 1 2 1 1 1 2 2 3 86%	1800
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 5% 78%	1826
	21st to end	Night	1 2 1 4 2 3 2 2 3 5% 75%	1980
October	1st to 10th	Night	3 4 1 4 2 3 3 2 4 4 70%	2128
	11th to 20th	Night	2 2 1 3 2 2 3 2 3 5% 74%	2160
	21st to end	Night	2 4 1 3 2 2 2 3 4 6% 71%	2420
November	1st to 10th	Night	2 5% 2 5% 4 3 4 3 6% 8% 57%	2405
	11th to 20th	Night	2 5% 1 4 3 3 4 4 5% 9% 61%	2470
	21st to end	Night	2 4 2 6% 5% 5% 4 4 6% 8% 54%	2527
December	1st to 10th	Night	3 7% 3 5% 4 4 5% 4 5% 9% 50%	2660
	11th to 20th	Night	4 10% 3 9% 7% 5% 6% 4 7% 8% 36%	3276
	21st to end	Night	1 8% 4 10% 7% 6% 7% 5% 8% 8% 34%	4862

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	26% 16% 17% 25% 14% 1	2539
	11th to 20th	Day	33% 12% 16% 23% 11% 5%	2608
	21st to end	Day	40% 12% 12% 22% 12% 2	3146
February	1st to 10th	Day	30% 10% 13% 24% 18% 7%	1710
	11th to 20th	Day	31% 9% 11% 25% 20% 5%	1860
	21st to end	Day	27% 12% 14% 25% 17% 4	1570
March	1st to 10th	Day	36% 19% 15% 16% 11% 3	3138
	11th to 20th	Day	18% 10% 13% 34% 22% 3	3445
	21st to end	Day	29% 13% 19% 21% 16% 2	4067
April	1st to 10th	Day	29% 10% 15% 22% 18% 5%	2280
	11th to 20th	Day	24% 9% 14% 27% 21% 6%	2252
	21st to end	Day	21% 7% 15% 30% 23% 3	2280
May	1st to 10th	Day	15% 7% 9% 33% 30% 6%	3981
	11th to 20th	Day	14% 4 8% 21% 41% 11%	4311
	21st to end	Day	19% 7% 8% 27% 33% 5%	4814
June	1st to 10th	Day	20% 7% 9% 24% 31% 10%	2660
	11th to 20th	Day	11% 4 7% 21% 37% 21%	2660
	21st to end	Day	11% 3 4 13% 32% 37%	2660
July	1st to 10th	Day	8% 2 3 11% 25% 52%	2591
	11th to 20th	Day	10% 3 3 13% 23% 48%	2585
	21st to end	Day	14% 3 3 9% 24% 46%	2670
August	1st to 10th	Day	14% 3 4 11% 25% 43%	2291
	11th to 20th	Day	8% 4 3 8% 31% 45%	2122
	21st to end	Day	7% 1 2 10% 37% 43%	2376
September	1st to 10th	Day	8% 2 3 9% 34% 44%	2160
	11th to 20th	Day	13% 5% 5% 19% 35% 24%	2133
	21st to end	Day	13% 3 4 18% 37% 24%	1980
October	1st to 10th	Day	20% 4 7% 18% 30% 21%	1830
	11th to 20th	Day	16% 4 7% 24% 31% 18%	1800
	21st to end	Day	15% 6% 9% 27% 29% 15%	1936
November	1st to 10th	Day	25% 8% 10% 22% 25% 10%	1674
	11th to 20th	Day	18% 10% 16% 23% 28% 5%	1710
	21st to end	Day	26% 8% 11% 24% 24% 7%	1649
December	1st to 10th	Day	29% 11% 11% 24% 20% 5%	1520
	11th to 20th	Day	42% 13% 10% 17% 13% 5%	1928
	21st to end	Day	32% 10% 18% 22% 16% 2	2794
January	1st to 10th	Night	26% 13% 21% 26% 14% 1	4406
	11th to 20th	Night	34% 13% 18% 19% 12% 5%	4349
	21st to end	Night	38% 13% 14% 21% 11% 3	4521
February	1st to 10th	Night	30% 11% 12% 23% 19% 6%	2467
	11th to 20th	Night	24% 11% 14% 27% 19% 4	2219
	21st to end	Night	27% 11% 15% 26% 17% 5%	1884
March	1st to 10th	Night	29% 18% 15% 21% 14% 2	3736
	11th to 20th	Night	20% 11% 11% 39% 16% 3	3533
	21st to end	Night	31% 19% 18% 20% 10% 2	3585
April	1st to 10th	Night	25% 13% 15% 27% 15% 5%	1900
	11th to 20th	Night	23% 9% 16% 29% 17% 6%	1879
	21st to end	Night	20% 10% 15% 32% 19% 3	1900
May	1st to 10th	Night	13% 8% 11% 33% 29% 5%	2990
	11th to 20th	Night	12% 4 9% 24% 39% 12%	2583
	21st to end	Night	15% 6% 13% 35% 28% 3	2762
June	1st to 10th	Night	19% 7% 11% 24% 29% 10%	1520
	11th to 20th	Night	9% 4 7% 22% 37% 20%	1520
	21st to end	Night	12% 3 5% 14% 34% 33%	1520
July	1st to 10th	Night	7% 2 3 8% 30% 49%	1480
	11th to 20th	Night	11% 3 4 11% 24% 46%	1472
	21st to end	Night	14% 3 5% 8% 26% 45%	1635
August	1st to 10th	Night	16% 5% 4 13% 24% 38%	1623
	11th to 20th	Night	11% 4 3 11% 31% 41%	1780
	21st to end	Night	9% 2 2 10% 36% 41%	1980
September	1st to 10th	Night	6% 2 3 9% 36% 43%	1800
	11th to 20th	Night	10% 3 6% 22% 35% 23%	1826
	21st to end	Night	13% 3 5% 20% 35% 23%	1980
October	1st to 10th	Night	19% 4 7% 21% 29% 20%	2128
	11th to 20th	Night	12% 5% 8% 22% 35% 18%	2160
	21st to end	Night	14% 5% 10% 25% 34% 13%	2420
November	1st to 10th	Night	21% 10% 11% 23% 24% 11%	2405
	11th to 20th	Night	19% 9% 12% 27% 27% 6%	2470
	21st to end	Night	23% 9% 10% 26% 23% 8%	2527
December	1st to 10th	Night	28% 11% 13% 23% 19% 6%	2660
	11th to 20th	Night	37% 14% 11% 18% 16% 4	3276
	21st to end	Night	34% 14% 16% 18% 14% 3	4862

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	22% 24% 23% 17% 12% 3	180
	11th to 20th	Day	11% 26% 26% 17% 14% 5%	222
	21st to end	Day	10% 18% 29% 23% 15% 4	407
February	1st to 10th	Day	13% 20% 28% 23% 14% 3	370
	11th to 20th	Day	11% 24% 27% 25% 12% 1	455
	21st to end	Day	13% 20% 30% 26% 10%	382
March	1st to 10th	Day	18% 31% 23% 17% 9% 2	460
	11th to 20th	Day	12% 27% 27% 18% 13% 3	460
	21st to end	Day	15% 28% 28% 21% 7% 1	506
April	1st to 10th	Day	13% 26% 29% 19% 11% 3	460
	11th to 20th	Day	17% 25% 26% 17% 11% 3	452
	21st to end	Day	12% 22% 27% 21% 13% 5%	460
May	1st to 10th	Day	16% 21% 28% 21% 10% 3	463
	11th to 20th	Day	12% 22% 24% 23% 14% 6%	488
	21st to end	Day	12% 16% 22% 26% 19% 6%	529
June	1st to 10th	Day	8% 18% 27% 24% 19% 5%	490
	11th to 20th	Day	9% 20% 32% 23% 12% 5%	490
	21st to end	Day	3 14% 27% 31% 20% 6%	490
July	1st to 10th	Day	2 9% 36% 32% 16% 5%	486
	11th to 20th	Day	2 9% 32% 30% 19% 7%	484
	21st to end	Day	3 7% 33% 29% 23% 6%	528
August	1st to 10th	Day	4 9% 30% 31% 20% 5%	447
	11th to 20th	Day	2 8% 25% 32% 23% 11%	437
	21st to end	Day	3 8% 34% 30% 23% 3	495
September	1st to 10th	Day	3 8% 30% 29% 25% 6%	450
	11th to 20th	Day	7% 14% 25% 27% 22% 5%	450
	21st to end	Day	6% 13% 28% 32% 18% 3	450
October	1st to 10th	Day	6% 16% 24% 26% 21% 7%	450
	11th to 20th	Day	8% 13% 22% 27% 25% 5%	450
	21st to end	Day	9% 16% 26% 20% 25% 5%	451
November	1st to 10th	Day	14% 17% 20% 20% 20% 10%	270
	11th to 20th	Day	5% 20% 18% 29% 19% 9%	270
	21st to end	Day	7% 18% 24% 24% 20% 6%	241
December	1st to 10th	Day	14% 20% 19% 21% 18% 8%	180
	11th to 20th	Day	9% 26% 29% 13% 15% 7%	180
	21st to end	Day	18% 18% 22% 25% 14% 3	198
January	1st to 10th	Night	8% 18% 21% 25% 20% 8%	760
	11th to 20th	Night	7% 18% 21% 32% 17% 6%	760
	21st to end	Night	7% 14% 25% 28% 19% 6%	836
February	1st to 10th	Night	8% 15% 23% 31% 20% 4	760
	11th to 20th	Night	5% 17% 24% 29% 20% 6%	744
	21st to end	Night	9% 21% 21% 32% 14% 3	628
March	1st to 10th	Night	9% 23% 26% 23% 16% 3	760
	11th to 20th	Night	7% 21% 21% 23% 24% 4	760
	21st to end	Night	7% 25% 27% 24% 14% 2	836
April	1st to 10th	Night	6% 21% 26% 28% 18% 2	760
	11th to 20th	Night	10% 19% 22% 27% 17% 4	751
	21st to end	Night	7% 15% 24% 27% 22% 5%	760
May	1st to 10th	Night	9% 16% 24% 26% 21% 4	648
	11th to 20th	Night	5% 10% 21% 35% 25% 4	415
	21st to end	Night	6% 8% 17% 34% 30% 5%	411
June	1st to 10th	Night	7% 8% 18% 33% 27% 6%	380
	11th to 20th	Night	2 8% 20% 37% 31% 2	380
	21st to end	Night	3 4 19% 37% 34% 3	380
July	1st to 10th	Night	1 2 15% 46% 32% 3	370
	11th to 20th	Night	1 2 18% 43% 34% 2	368
	21st to end	Night	3 3 9% 40% 39% 6%	478
August	1st to 10th	Night	4 2 13% 36% 40% 5%	558
	11th to 20th	Night	3 4 16% 38% 34% 6%	712
	21st to end	Night	2 3 18% 43% 30% 5%	792
September	1st to 10th	Night	2 3 17% 33% 38% 7%	720
	11th to 20th	Night	3 7% 17% 30% 34% 9%	720
	21st to end	Night	3 9% 19% 29% 31% 9%	720
October	1st to 10th	Night	5% 10% 17% 32% 27% 9%	720
	11th to 20th	Night	7% 8% 13% 33% 31% 9%	720
	21st to end	Night	6% 12% 16% 26% 29% 11%	792
November	1st to 10th	Night	6% 16% 17% 24% 29% 8%	740
	11th to 20th	Night	6% 16% 20% 32% 20% 7%	760
	21st to end	Night	7% 16% 20% 26% 24% 6%	760
December	1st to 10th	Night	10% 17% 20% 29% 16% 7%	760
	11th to 20th	Night	10% 19% 21% 28% 16% 6%	760
	21st to end	Night	9% 21% 26% 28% 13% 2	836

Page generated at 2024-07-28 06:52:08. Version ac07

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