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 2025-01-07.

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% 4 3 4 3 5% 6% 63%	108800
	Night	2 5% 2 6% 4 4 4 4 5% 7% 59%	108964
Transparency	Day	18% 7% 9% 19% 26% 21%	108545
	Night	20% 9% 11% 21% 24% 16%	108808
Seeing	Day	9% 18% 27% 24% 17% 5%	15209
	Night	6% 14% 20% 30% 24% 5%	24643

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%	2587
	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 1 1 2 2 89%	4420
	11th to 20th	Day	2 3 1 3 2 2 2 2 3 4 75%	4420
	21st to end	Day	1 1 2 1 2 2 2 3 4 82%	4679
August	1st to 10th	Day	2 2 1 2 2 2 2 2 4 4 76%	4044
	11th to 20th	Day	1 1 1 1 1 2 1 2 3 86%	3724
	21st to end	Day	1 1 1 2 1 1 2 1 2 2 87%	4180
September	1st to 10th	Day	1 1 1 1 1 2 2 2 3 4 82%	2280
	11th to 20th	Day	2 2 1 4 3 2 3 2 3 5% 73%	2251
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 78%	2090
October	1st to 10th	Day	2 3 1 3 3 2 2 2 4 6% 73%	3223
	11th to 20th	Day	2 3 1 4 2 2 2 2 2 4 75%	3161
	21st to end	Day	1 2 4 3 3 4 3 5% 8% 64%	3365
November	1st to 10th	Day	3 5% 3 6% 4 5% 4 3 5% 6% 57%	1764
	11th to 20th	Day	2 4 2 4 3 4 4 5% 7% 10% 56%	1800
	21st to end	Day	2 5% 2 6% 5% 5% 5% 4 6% 8% 52%	1735
December	1st to 10th	Day	2 4 2 4 4 4 5% 2 5% 8% 61%	2620
	11th to 20th	Day	3 10% 4 9% 6% 6% 7% 4 7% 8% 36%	3028
	21st to end	Day	1 7% 3 11% 8% 7% 5% 5% 7% 11% 35%	4004
January	1st to 10th	Night	2 5% 3 7% 5% 4 6% 5% 7% 10% 45%	4490
	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 1 1 1 2 3 89%	2540
	11th to 20th	Night	3 3 2 4 2 2 2 2 3 3 73%	2540
	21st to end	Night	2 2 1 2 2 2 2 2 2 5% 79%	2872
August	1st to 10th	Night	3 2 1 2 2 2 3 2 4 5% 74%	2897
	11th to 20th	Night	1 1 2 1 1 2 1 2 3 86%	3126
	21st to end	Night	1 2 1 2 1 1 1 1 2 2 86%	3498
September	1st to 10th	Night	1 1 1 1 1 1 2 2 3 86%	1900
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 5% 77%	1928
	21st to end	Night	1 2 1 3 2 3 2 2 3 5% 76%	2090
October	1st to 10th	Night	2 2 1 2 2 2 3 2 4 4 77%	3755
	11th to 20th	Night	2 2 1 3 2 2 2 2 2 4 79%	3777
	21st to end	Night	1 3 1 5% 3 3 3 3 5% 7% 65%	4201
November	1st to 10th	Night	2 5% 2 5% 4 3 4 3 7% 8% 58%	2535
	11th to 20th	Night	2 4 1 4 3 3 4 3 5% 10% 61%	2600
	21st to end	Night	2 4 2 6% 5% 5% 4 4 6% 8% 55%	2660
December	1st to 10th	Night	2 4 2 4 3 3 4 3 5% 7% 63%	4560
	11th to 20th	Night	3 7% 2 8% 8% 6% 7% 5% 8% 11% 36%	5176
	21st to end	Night	1 7% 4 12% 8% 7% 7% 5% 8% 9% 33%	6952

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% 18% 25% 14% 1	2587
	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	5% 1 2 6% 15% 72%	4351
	11th to 20th	Day	13% 3 3 9% 16% 56%	4345
	21st to end	Day	9% 2 3 8% 27% 52%	4531
August	1st to 10th	Day	12% 2 3 7% 25% 50%	4029
	11th to 20th	Day	6% 2 2 5% 26% 59%	3760
	21st to end	Day	6% 1 2 9% 41% 41%	4179
September	1st to 10th	Day	7% 2 3 9% 34% 44%	2280
	11th to 20th	Day	13% 5% 5% 19% 35% 23%	2251
	21st to end	Day	13% 3 4 18% 37% 26%	2090
October	1st to 10th	Day	13% 3 5% 11% 38% 29%	3223
	11th to 20th	Day	13% 4 5% 19% 47% 12%	3161
	21st to end	Day	12% 7% 9% 28% 33% 11%	3365
November	1st to 10th	Day	24% 8% 10% 23% 25% 10%	1764
	11th to 20th	Day	18% 10% 16% 24% 27% 5%	1800
	21st to end	Day	25% 9% 11% 23% 24% 8%	1735
December	1st to 10th	Day	20% 7% 9% 27% 29% 8%	2620
	11th to 20th	Day	34% 15% 14% 17% 16% 5%	3028
	21st to end	Day	27% 18% 19% 21% 13% 2	4004
January	1st to 10th	Night	26% 13% 21% 26% 13% 1	4490
	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	4 1 2 5% 18% 70%	2500
	11th to 20th	Night	16% 2 3 8% 16% 55%	2492
	21st to end	Night	10% 2 3 8% 26% 51%	2782
August	1st to 10th	Night	13% 3 3 9% 29% 42%	2888
	11th to 20th	Night	6% 2 2 6% 28% 56%	3156
	21st to end	Night	8% 2 1 10% 42% 37%	3498
September	1st to 10th	Night	6% 2 3 9% 38% 43%	1900
	11th to 20th	Night	11% 4 6% 21% 36% 23%	1928
	21st to end	Night	12% 3 5% 20% 35% 24%	2090
October	1st to 10th	Night	12% 3 5% 13% 37% 31%	3755
	11th to 20th	Night	9% 4 6% 19% 48% 14%	3777
	21st to end	Night	13% 8% 9% 25% 34% 11%	4201
November	1st to 10th	Night	20% 10% 12% 24% 24% 11%	2535
	11th to 20th	Night	18% 9% 12% 29% 26% 6%	2600
	21st to end	Night	23% 9% 10% 26% 23% 9%	2660
December	1st to 10th	Night	20% 8% 10% 25% 27% 12%	4560
	11th to 20th	Night	27% 18% 14% 18% 19% 3	5176
	21st to end	Night	32% 17% 17% 20% 12% 3	6952

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% 22% 23% 17% 12% 3	192
	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%	531
August	1st to 10th	Day	4 10% 31% 30% 20% 5%	487
	11th to 20th	Day	3 11% 24% 31% 22% 10%	477
	21st to end	Day	4 8% 32% 30% 22% 4	539
September	1st to 10th	Day	3 9% 31% 28% 24% 5%	490
	11th to 20th	Day	8% 15% 25% 26% 21% 5%	490
	21st to end	Day	5% 12% 28% 32% 19% 3	490
October	1st to 10th	Day	6% 15% 25% 26% 20% 7%	490
	11th to 20th	Day	9% 14% 21% 27% 24% 6%	490
	21st to end	Day	10% 17% 27% 19% 23% 5%	492
November	1st to 10th	Day	13% 17% 21% 20% 19% 9%	300
	11th to 20th	Day	7% 20% 19% 27% 17% 8%	300
	21st to end	Day	11% 17% 23% 24% 19% 6%	267
December	1st to 10th	Day	13% 19% 19% 21% 20% 10%	200
	11th to 20th	Day	11% 25% 27% 16% 16% 7%	200
	21st to end	Day	22% 17% 23% 24% 12% 3	220
January	1st to 10th	Night	8% 19% 21% 25% 20% 7%	784
	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% 41% 39% 6%	478
August	1st to 10th	Night	4 2 14% 37% 38% 5%	590
	11th to 20th	Night	3 5% 18% 37% 32% 6%	752
	21st to end	Night	2 4 18% 42% 30% 5%	836
September	1st to 10th	Night	1 3 18% 34% 37% 6%	760
	11th to 20th	Night	4 8% 18% 29% 33% 8%	760
	21st to end	Night	3 9% 19% 30% 31% 8%	760
October	1st to 10th	Night	5% 10% 17% 32% 28% 9%	760
	11th to 20th	Night	7% 9% 13% 33% 31% 8%	760
	21st to end	Night	7% 12% 17% 26% 28% 11%	836
November	1st to 10th	Night	6% 16% 18% 24% 28% 8%	780
	11th to 20th	Night	7% 16% 21% 31% 19% 6%	800
	21st to end	Night	8% 17% 20% 26% 24% 6%	800
December	1st to 10th	Night	10% 16% 21% 29% 18% 7%	800
	11th to 20th	Night	10% 20% 20% 28% 16% 6%	800
	21st to end	Night	10% 22% 26% 27% 13% 2	880

Page generated at 2025-01-04 00:23:58. Version ac07

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