Stone Garden Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stone Garden Observatory clear sky chart from 2005-11-06 to 2024-10-25.

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	9% 10% 4 9% 6% 6% 6% 5% 6% 8% 33%	101917
	Night	10% 12% 4 9% 6% 5% 5% 4 6% 7% 31%	96926
Transparency	Day	48% 7% 16% 21% 8% 1	101653
	Night	52% 6% 14% 19% 8% 1	96836
Seeing	Day	14% 10% 24% 27% 19% 6%	16424
	Night	18% 7% 21% 32% 19% 3	24163

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	8% 16% 5% 14% 9% 7% 6% 5% 5% 6% 18%	2073
	11th to 20th	Day	10% 17% 5% 9% 5% 4 4 4 5% 6% 31%	2199
	21st to end	Day	11% 21% 5% 11% 7% 6% 6% 4 5% 7% 15%	2442
February	1st to 10th	Day	12% 17% 5% 10% 6% 5% 4 2 5% 8% 27%	1531
	11th to 20th	Day	9% 13% 4 10% 6% 6% 6% 4 6% 7% 27%	1665
	21st to end	Day	6% 15% 5% 10% 7% 6% 6% 5% 5% 7% 30%	1413
March	1st to 10th	Day	5% 13% 6% 12% 8% 6% 6% 4 6% 8% 28%	3107
	11th to 20th	Day	5% 12% 4 9% 6% 6% 6% 6% 8% 9% 29%	3490
	21st to end	Day	5% 11% 4 7% 6% 5% 5% 5% 6% 7% 39%	3967
April	1st to 10th	Day	7% 11% 5% 14% 8% 6% 6% 5% 6% 7% 26%	2280
	11th to 20th	Day	9% 13% 5% 10% 8% 7% 7% 5% 6% 6% 26%	2434
	21st to end	Day	12% 12% 4 9% 6% 6% 5% 4 6% 6% 30%	2643
May	1st to 10th	Day	7% 9% 4 10% 6% 5% 5% 5% 7% 9% 33%	4420
	11th to 20th	Day	9% 11% 4 10% 8% 7% 7% 5% 7% 7% 25%	4592
	21st to end	Day	12% 11% 4 11% 7% 7% 6% 5% 6% 7% 25%	5398
June	1st to 10th	Day	11% 8% 3 9% 7% 7% 6% 5% 6% 8% 29%	3040
	11th to 20th	Day	14% 7% 3 8% 7% 7% 6% 5% 7% 8% 26%	3040
	21st to end	Day	11% 8% 3 8% 7% 6% 6% 5% 7% 9% 31%	3040
July	1st to 10th	Day	8% 5% 2 5% 5% 4 5% 4 6% 7% 48%	5060
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 6% 9% 52%	4754
	21st to end	Day	8% 6% 3 8% 6% 6% 7% 5% 8% 9% 34%	5138
August	1st to 10th	Day	4 3 1 4 4 3 4 3 5% 8% 61%	4514
	11th to 20th	Day	9% 5% 2 7% 4 5% 5% 4 7% 9% 42%	4247
	21st to end	Day	12% 7% 3 8% 5% 5% 6% 5% 6% 8% 36%	4521
September	1st to 10th	Day	10% 7% 2 7% 5% 6% 5% 4 7% 8% 40%	2290
	11th to 20th	Day	10% 6% 2 7% 6% 6% 5% 4 6% 9% 38%	2280
	21st to end	Day	15% 8% 3 9% 7% 6% 6% 5% 6% 7% 29%	2001
October	1st to 10th	Day	13% 11% 4 7% 6% 5% 5% 5% 7% 8% 30%	1900
	11th to 20th	Day	14% 11% 3 9% 6% 6% 6% 5% 6% 8% 27%	1895
	21st to end	Day	14% 12% 4 8% 5% 4 4 4 4 8% 32%	1671
November	1st to 10th	Day	16% 15% 4 10% 6% 5% 5% 4 5% 4 26%	1488
	11th to 20th	Day	10% 16% 5% 12% 8% 7% 6% 4 7% 7% 19%	1517
	21st to end	Day	12% 17% 6% 10% 7% 6% 8% 5% 6% 6% 17%	1195
December	1st to 10th	Day	11% 14% 5% 12% 8% 6% 7% 4 6% 6% 22%	1140
	11th to 20th	Day	13% 22% 6% 8% 7% 5% 5% 5% 5% 5% 18%	1442
	21st to end	Day	6% 16% 4 11% 8% 8% 5% 4 7% 6% 25%	2090
January	1st to 10th	Night	10% 16% 4 11% 8% 6% 6% 5% 6% 7% 19%	4888
	11th to 20th	Night	10% 15% 5% 10% 7% 5% 5% 3 4 5% 30%	4699
	21st to end	Night	16% 22% 6% 11% 6% 6% 5% 4 5% 4 15%	5214
February	1st to 10th	Night	11% 19% 4 11% 7% 5% 5% 4 5% 5% 24%	2645
	11th to 20th	Night	9% 14% 5% 11% 7% 5% 5% 4 6% 7% 28%	2402
	21st to end	Night	7% 14% 6% 10% 6% 5% 5% 4 7% 6% 31%	2041
March	1st to 10th	Night	5% 15% 5% 11% 6% 6% 6% 4 7% 7% 29%	3764
	11th to 20th	Night	7% 12% 4 9% 6% 6% 6% 5% 7% 9% 30%	3489
	21st to end	Night	6% 9% 3 6% 4 4 6% 4 6% 7% 46%	3686
April	1st to 10th	Night	9% 13% 5% 9% 6% 6% 5% 4 6% 7% 30%	1900
	11th to 20th	Night	8% 12% 4 9% 6% 6% 6% 6% 7% 7% 29%	1691
	21st to end	Night	9% 12% 4 7% 6% 5% 6% 5% 6% 6% 35%	1537
May	1st to 10th	Night	10% 10% 3 9% 6% 5% 6% 5% 7% 7% 34%	2540
	11th to 20th	Night	11% 10% 4 7% 7% 7% 6% 4 6% 9% 28%	2300
	21st to end	Night	13% 13% 5% 11% 6% 5% 4 4 6% 6% 27%	2174
June	1st to 10th	Night	14% 9% 3 7% 5% 6% 6% 5% 7% 8% 29%	1140
	11th to 20th	Night	14% 8% 2 10% 6% 6% 5% 4 8% 8% 29%	1140
	21st to end	Night	10% 5% 3 9% 8% 7% 7% 5% 6% 9% 32%	1140
July	1st to 10th	Night	7% 6% 2 5% 5% 4 3 3 6% 7% 51%	1900
	11th to 20th	Night	6% 4 2 4 4 3 4 3 5% 7% 58%	2204
	21st to end	Night	12% 8% 2 5% 4 4 4 4 7% 9% 41%	2414
August	1st to 10th	Night	4 3 1 3 2 2 3 3 4 5% 70%	2402
	11th to 20th	Night	7% 4 1 4 4 4 5% 5% 6% 9% 49%	2580
	21st to end	Night	14% 8% 3 8% 5% 5% 5% 4 6% 8% 35%	3146
September	1st to 10th	Night	10% 7% 2 7% 5% 5% 5% 3 5% 8% 41%	1890
	11th to 20th	Night	10% 7% 2 6% 6% 4 5% 4 5% 7% 45%	1900
	21st to end	Night	15% 10% 3 7% 5% 5% 5% 4 5% 7% 33%	2178
October	1st to 10th	Night	12% 11% 4 9% 5% 5% 5% 4 7% 8% 31%	2280
	11th to 20th	Night	15% 11% 3 9% 5% 5% 6% 4 7% 7% 29%	2284
	21st to end	Night	13% 11% 4 9% 6% 5% 6% 4 6% 7% 30%	2787
November	1st to 10th	Night	14% 15% 3 9% 6% 5% 7% 5% 6% 5% 24%	2590
	11th to 20th	Night	10% 15% 5% 10% 7% 6% 6% 5% 6% 7% 23%	2660
	21st to end	Night	9% 18% 5% 12% 6% 6% 5% 5% 6% 7% 21%	2965
December	1st to 10th	Night	9% 13% 5% 11% 7% 7% 6% 5% 5% 6% 26%	3040
	11th to 20th	Night	14% 18% 5% 11% 7% 5% 5% 4 6% 6% 19%	3750
	21st to end	Night	6% 14% 4 11% 9% 7% 6% 5% 7% 7% 23%	5566

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	65% 8% 11% 13% 3	2073
	11th to 20th	Day	55% 7% 15% 8% 11% 5%	2220
	21st to end	Day	67% 9% 12% 8% 3 1	2442
February	1st to 10th	Day	59% 5% 14% 11% 11% 1	1531
	11th to 20th	Day	58% 6% 16% 16% 5%	1674
	21st to end	Day	54% 5% 16% 15% 9% 2	1413
March	1st to 10th	Day	51% 7% 10% 21% 10% 1	3107
	11th to 20th	Day	47% 8% 18% 21% 5%	3490
	21st to end	Day	42% 7% 15% 23% 11% 1	3967
April	1st to 10th	Day	55% 8% 12% 18% 7% 1	2280
	11th to 20th	Day	56% 5% 10% 21% 8%	2434
	21st to end	Day	53% 5% 13% 19% 9%	2643
May	1st to 10th	Day	43% 8% 15% 24% 8% 2	4420
	11th to 20th	Day	51% 9% 12% 18% 9% 1	4595
	21st to end	Day	53% 7% 13% 21% 5% 1	5399
June	1st to 10th	Day	49% 7% 13% 20% 9% 1	3040
	11th to 20th	Day	52% 8% 13% 21% 6%	3040
	21st to end	Day	47% 8% 17% 21% 7%	3040
July	1st to 10th	Day	32% 7% 10% 26% 23% 2	4981
	11th to 20th	Day	29% 6% 20% 33% 13%	4672
	21st to end	Day	41% 7% 18% 21% 12% 1	4976
August	1st to 10th	Day	22% 6% 18% 40% 14% 1	4496
	11th to 20th	Day	36% 7% 20% 29% 7%	4289
	21st to end	Day	47% 5% 26% 19% 3	4520
September	1st to 10th	Day	40% 8% 25% 22% 5%	2290
	11th to 20th	Day	43% 7% 19% 25% 6%	2280
	21st to end	Day	53% 8% 16% 18% 4 1	2001
October	1st to 10th	Day	52% 6% 22% 17% 4	1900
	11th to 20th	Day	54% 6% 18% 20% 2	1895
	21st to end	Day	52% 6% 18% 19% 5%	1671
November	1st to 10th	Day	61% 6% 13% 13% 6%	1488
	11th to 20th	Day	64% 6% 14% 11% 4	1517
	21st to end	Day	68% 6% 12% 12% 2	1195
December	1st to 10th	Day	63% 6% 14% 14% 4	1140
	11th to 20th	Day	69% 6% 11% 9% 4	1444
	21st to end	Day	57% 7% 16% 14% 6%	2090
January	1st to 10th	Night	62% 8% 15% 14% 2	4888
	11th to 20th	Night	57% 6% 11% 7% 12% 7%	4740
	21st to end	Night	71% 8% 9% 8% 3	5214
February	1st to 10th	Night	62% 5% 12% 11% 9% 1	2645
	11th to 20th	Night	57% 4 18% 16% 6%	2404
	21st to end	Night	52% 4 15% 18% 9% 2	2041
March	1st to 10th	Night	51% 7% 11% 20% 10% 1	3764
	11th to 20th	Night	48% 8% 12% 25% 7%	3490
	21st to end	Night	37% 7% 12% 26% 18%	3686
April	1st to 10th	Night	51% 6% 11% 22% 10% 1	1900
	11th to 20th	Night	52% 6% 11% 23% 9%	1691
	21st to end	Night	48% 6% 12% 21% 12% 1	1537
May	1st to 10th	Night	45% 7% 14% 25% 8% 1	2540
	11th to 20th	Night	49% 8% 15% 21% 7% 1	2300
	21st to end	Night	55% 7% 12% 21% 5%	2174
June	1st to 10th	Night	50% 7% 12% 19% 11% 1	1140
	11th to 20th	Night	52% 6% 13% 22% 6%	1140
	21st to end	Night	47% 6% 18% 24% 5%	1140
July	1st to 10th	Night	33% 5% 10% 27% 24% 1	1870
	11th to 20th	Night	27% 4 18% 39% 12%	2163
	21st to end	Night	39% 5% 23% 18% 14% 1	2337
August	1st to 10th	Night	18% 3 15% 43% 20% 1	2395
	11th to 20th	Night	31% 6% 18% 36% 9%	2604
	21st to end	Night	48% 4 25% 19% 3	3146
September	1st to 10th	Night	41% 6% 20% 27% 7% 1	1890
	11th to 20th	Night	38% 6% 15% 31% 9%	1900
	21st to end	Night	50% 7% 15% 19% 9%	2178
October	1st to 10th	Night	50% 7% 19% 19% 5%	2280
	11th to 20th	Night	53% 5% 19% 18% 4	2284
	21st to end	Night	53% 6% 16% 19% 5%	2787
November	1st to 10th	Night	59% 7% 14% 14% 5%	2590
	11th to 20th	Night	60% 8% 14% 13% 6%	2660
	21st to end	Night	62% 6% 15% 13% 4	2965
December	1st to 10th	Night	59% 7% 13% 15% 5%	3040
	11th to 20th	Night	67% 8% 12% 10% 4	3747
	21st to end	Night	57% 8% 16% 13% 6%	5566

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	14% 7% 21% 35% 17% 6%	180
	11th to 20th	Day	17% 12% 20% 29% 16% 6%	180
	21st to end	Day	21% 11% 26% 21% 17% 4	198
February	1st to 10th	Day	22% 18% 25% 20% 11% 3	232
	11th to 20th	Day	17% 11% 28% 26% 15% 3	365
	21st to end	Day	12% 18% 29% 23% 12% 5%	307
March	1st to 10th	Day	11% 14% 28% 25% 17% 5%	442
	11th to 20th	Day	12% 15% 29% 25% 16% 3	460
	21st to end	Day	16% 16% 25% 20% 17% 5%	506
April	1st to 10th	Day	12% 17% 29% 26% 14% 3	460
	11th to 20th	Day	14% 15% 27% 22% 15% 6%	452
	21st to end	Day	13% 16% 27% 27% 13% 3	460
May	1st to 10th	Day	14% 13% 28% 27% 15% 3	463
	11th to 20th	Day	12% 9% 24% 31% 19% 5%	610
	21st to end	Day	13% 8% 22% 27% 24% 6%	868
June	1st to 10th	Day	15% 10% 23% 30% 19% 3	870
	11th to 20th	Day	15% 7% 24% 29% 19% 5%	870
	21st to end	Day	13% 6% 24% 28% 24% 6%	870
July	1st to 10th	Day	13% 6% 18% 30% 26% 7%	856
	11th to 20th	Day	13% 6% 20% 26% 28% 7%	681
	21st to end	Day	9% 6% 18% 32% 27% 7%	739
August	1st to 10th	Day	8% 4 17% 32% 28% 10%	562
	11th to 20th	Day	8% 7% 25% 27% 21% 11%	477
	21st to end	Day	14% 8% 25% 30% 16% 7%	539
September	1st to 10th	Day	13% 8% 25% 26% 22% 7%	490
	11th to 20th	Day	12% 8% 23% 26% 23% 9%	490
	21st to end	Day	18% 11% 32% 23% 13% 3	490
October	1st to 10th	Day	22% 9% 23% 25% 15% 6%	490
	11th to 20th	Day	20% 10% 29% 24% 17% 1	485
	21st to end	Day	18% 13% 26% 26% 13% 4	234
November	1st to 10th	Day	31% 12% 22% 23% 8% 6%	180
	11th to 20th	Day	19% 9% 23% 23% 15% 10%	180
	21st to end	Day	21% 10% 26% 27% 12% 4	180
December	1st to 10th	Day	16% 5% 18% 31% 26% 5%	180
	11th to 20th	Day	13% 9% 18% 32% 23% 4	180
	21st to end	Day	21% 5% 14% 37% 15% 8%	198
January	1st to 10th	Night	23% 9% 22% 33% 11% 2	947
	11th to 20th	Night	22% 7% 26% 28% 16% 1	850
	21st to end	Night	21% 10% 25% 29% 13% 2	935
February	1st to 10th	Night	22% 11% 20% 30% 15% 2	778
	11th to 20th	Night	18% 6% 25% 34% 15% 1	744
	21st to end	Night	16% 10% 23% 32% 17% 2	628
March	1st to 10th	Night	15% 11% 23% 32% 16% 3	760
	11th to 20th	Night	13% 10% 24% 36% 16% 1	760
	21st to end	Night	13% 9% 19% 30% 26% 4	836
April	1st to 10th	Night	17% 9% 17% 34% 21% 3	760
	11th to 20th	Night	14% 6% 21% 34% 19% 5%	563
	21st to end	Night	15% 5% 27% 31% 20% 1	397
May	1st to 10th	Night	16% 6% 22% 37% 16% 3	380
	11th to 20th	Night	13% 4 18% 40% 23% 3	374
	21st to end	Night	15% 8% 16% 33% 26% 2	411
June	1st to 10th	Night	16% 6% 22% 32% 21% 2	380
	11th to 20th	Night	17% 4 21% 30% 25% 3	380
	21st to end	Night	11% 3 17% 38% 29% 2	380
July	1st to 10th	Night	12% 4 14% 37% 32% 1	370
	11th to 20th	Night	12% 3 14% 37% 30% 3	368
	21st to end	Night	12% 3 13% 36% 30% 6%	416
August	1st to 10th	Night	8% 2 11% 34% 37% 8%	378
	11th to 20th	Night	9% 1 15% 37% 34% 5%	420
	21st to end	Night	17% 4 16% 34% 26% 4	627
September	1st to 10th	Night	14% 4 17% 34% 29% 3	750
	11th to 20th	Night	13% 4 14% 32% 30% 7%	760
	21st to end	Night	21% 7% 21% 33% 17% 2	760
October	1st to 10th	Night	20% 5% 19% 32% 19% 4	760
	11th to 20th	Night	22% 5% 23% 30% 18% 2	760
	21st to end	Night	21% 10% 25% 30% 13% 1	812
November	1st to 10th	Night	24% 10% 24% 29% 11% 2	740
	11th to 20th	Night	21% 11% 26% 30% 11% 1	760
	21st to end	Night	20% 10% 29% 29% 10% 2	995
December	1st to 10th	Night	18% 6% 21% 36% 18% 2	1040
	11th to 20th	Night	21% 8% 24% 32% 13% 2	1040
	21st to end	Night	18% 7% 25% 33% 15% 2	1144

Page generated at 2024-10-22 17:21:02. Version ac07

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