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 2026-08-30.

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% 32%	148521
	Night	9% 13% 4 9% 6% 5% 6% 4 6% 7% 30%	142368
Transparency	Day	49% 6% 16% 21% 8% 1	148213
	Night	53% 5% 15% 19% 8% 1	142259
Seeing	Day	14% 10% 24% 27% 19% 5%	18906
	Night	17% 7% 21% 33% 19% 3	26567

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	9% 18% 7% 15% 7% 6% 6% 4 5% 5% 18%	3869
	11th to 20th	Day	7% 11% 4 8% 4 5% 6% 6% 7% 7% 36%	4119
	21st to end	Day	8% 18% 4 10% 7% 6% 6% 5% 6% 8% 23%	4529
February	1st to 10th	Day	12% 16% 4 11% 7% 5% 4 3 5% 8% 26%	1693
	11th to 20th	Day	8% 13% 5% 11% 6% 7% 6% 4 7% 7% 26%	1845
	21st to end	Day	6% 15% 5% 11% 7% 6% 6% 4 5% 7% 28%	1557
March	1st to 10th	Day	5% 12% 5% 13% 9% 7% 6% 5% 7% 7% 25%	4571
	11th to 20th	Day	5% 11% 4 9% 6% 6% 7% 7% 9% 10% 26%	5110
	21st to end	Day	8% 13% 4 7% 6% 5% 5% 4 6% 6% 35%	5818
April	1st to 10th	Day	7% 11% 5% 14% 7% 6% 6% 5% 7% 7% 26%	2520
	11th to 20th	Day	9% 13% 5% 10% 7% 7% 6% 5% 6% 6% 27%	2694
	21st to end	Day	11% 11% 3 9% 5% 6% 6% 4 6% 7% 32%	2921
May	1st to 10th	Day	6% 9% 3 9% 5% 5% 5% 5% 6% 9% 38%	8195
	11th to 20th	Day	7% 10% 4 12% 8% 7% 7% 6% 7% 7% 24%	8571
	21st to end	Day	11% 9% 3 10% 7% 7% 7% 6% 8% 8% 24%	10082
June	1st to 10th	Day	11% 8% 3 9% 7% 7% 6% 5% 6% 8% 30%	3360
	11th to 20th	Day	14% 7% 3 8% 7% 7% 6% 5% 7% 9% 26%	3360
	21st to end	Day	10% 8% 3 8% 7% 6% 6% 5% 7% 9% 31%	3360
July	1st to 10th	Day	10% 7% 3 7% 6% 6% 6% 5% 6% 8% 37%	9420
	11th to 20th	Day	9% 6% 2 7% 5% 5% 5% 4 6% 8% 44%	8848
	21st to end	Day	7% 5% 3 8% 6% 5% 6% 5% 7% 9% 39%	9567
August	1st to 10th	Day	4 4 2 4 4 3 4 3 5% 8% 59%	4802
	11th to 20th	Day	8% 5% 2 7% 4 5% 5% 4 7% 9% 42%	4522
	21st to end	Day	11% 7% 3 8% 5% 5% 6% 4 6% 7% 38%	4782
September	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 7% 8% 41%	2410
	11th to 20th	Day	10% 6% 2 7% 6% 6% 5% 4 6% 9% 38%	2400
	21st to end	Day	15% 9% 3 9% 7% 6% 6% 5% 6% 7% 28%	2106
October	1st to 10th	Day	14% 13% 4 8% 6% 6% 6% 4 7% 7% 25%	3280
	11th to 20th	Day	15% 12% 3 8% 6% 5% 5% 4 6% 8% 28%	3244
	21st to end	Day	11% 11% 4 9% 5% 5% 5% 4 5% 8% 34%	2922
November	1st to 10th	Day	15% 15% 5% 11% 6% 5% 5% 4 5% 4 25%	1648
	11th to 20th	Day	10% 15% 5% 13% 7% 7% 6% 4 7% 7% 19%	1676
	21st to end	Day	12% 17% 6% 10% 8% 6% 8% 5% 6% 6% 18%	1320
December	1st to 10th	Day	18% 18% 5% 11% 6% 5% 6% 4 5% 5% 17%	2020
	11th to 20th	Day	11% 22% 8% 12% 8% 6% 5% 4 5% 4 15%	2322
	21st to end	Day	5% 18% 6% 13% 7% 7% 5% 4 6% 7% 23%	3058
January	1st to 10th	Night	9% 20% 6% 13% 8% 6% 6% 5% 6% 6% 16%	9068
	11th to 20th	Night	7% 11% 4 8% 5% 5% 6% 4 6% 8% 36%	8779
	21st to end	Night	11% 18% 6% 9% 5% 5% 5% 5% 7% 6% 23%	9651
February	1st to 10th	Night	10% 18% 4 11% 7% 5% 5% 4 6% 6% 24%	2923
	11th to 20th	Night	8% 13% 5% 11% 7% 5% 6% 4 6% 7% 29%	2662
	21st to end	Night	7% 15% 6% 10% 6% 5% 5% 4 6% 6% 30%	2249
March	1st to 10th	Night	5% 15% 6% 12% 6% 6% 6% 4 6% 7% 28%	5538
	11th to 20th	Night	5% 12% 5% 10% 6% 6% 6% 5% 7% 8% 30%	5109
	21st to end	Night	10% 10% 3 7% 4 4 6% 4 6% 7% 40%	5399
April	1st to 10th	Night	8% 13% 5% 9% 6% 6% 5% 4 6% 8% 30%	2100
	11th to 20th	Night	8% 12% 4 9% 6% 6% 6% 5% 7% 7% 30%	1871
	21st to end	Night	9% 11% 3 7% 6% 5% 6% 5% 6% 6% 36%	1699
May	1st to 10th	Night	9% 8% 3 7% 5% 5% 5% 5% 7% 9% 37%	4724
	11th to 20th	Night	9% 9% 4 9% 7% 7% 7% 5% 7% 9% 29%	4288
	21st to end	Night	11% 11% 4 12% 6% 6% 6% 4 6% 6% 28%	4086
June	1st to 10th	Night	13% 8% 3 8% 5% 6% 6% 5% 7% 7% 32%	1260
	11th to 20th	Night	14% 8% 3 10% 6% 6% 4 4 7% 8% 30%	1260
	21st to end	Night	10% 5% 3 10% 8% 7% 7% 5% 7% 9% 30%	1260
July	1st to 10th	Night	10% 9% 3 7% 5% 4 5% 3 6% 8% 40%	3540
	11th to 20th	Night	9% 5% 2 6% 3 4 4 3 6% 8% 49%	4096
	21st to end	Night	9% 8% 2 6% 4 5% 4 4 6% 8% 43%	4501
August	1st to 10th	Night	4 3 1 3 2 2 3 3 5% 6% 68%	2554
	11th to 20th	Night	7% 4 2 4 4 4 6% 5% 6% 9% 49%	2745
	21st to end	Night	13% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	3326
September	1st to 10th	Night	10% 7% 2 6% 5% 5% 5% 3 5% 8% 44%	1990
	11th to 20th	Night	9% 7% 2 6% 6% 4 5% 4 5% 7% 45%	2000
	21st to end	Night	16% 11% 4 7% 5% 5% 5% 4 5% 7% 32%	2293
October	1st to 10th	Night	14% 13% 4 10% 5% 5% 5% 4 7% 7% 26%	3920
	11th to 20th	Night	11% 10% 3 9% 5% 5% 6% 5% 7% 8% 30%	3912
	21st to end	Night	11% 10% 4 9% 6% 5% 6% 5% 6% 6% 32%	4867
November	1st to 10th	Night	14% 14% 3 9% 6% 6% 7% 5% 6% 6% 24%	2870
	11th to 20th	Night	10% 15% 5% 11% 7% 6% 6% 5% 6% 7% 22%	2940
	21st to end	Night	9% 18% 5% 12% 6% 6% 6% 4 6% 7% 22%	3278
December	1st to 10th	Night	13% 17% 4 10% 7% 7% 6% 4 6% 5% 20%	5380
	11th to 20th	Night	14% 19% 5% 12% 7% 5% 5% 4 6% 5% 17%	6090
	21st to end	Night	5% 17% 6% 13% 8% 7% 6% 4 6% 7% 22%	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	68% 5% 10% 12% 4	3869
	11th to 20th	Day	48% 5% 21% 13% 10% 2	4140
	21st to end	Day	60% 7% 16% 13% 3	4530
February	1st to 10th	Day	59% 5% 13% 12% 11% 1	1693
	11th to 20th	Day	58% 5% 15% 16% 5%	1854
	21st to end	Day	56% 5% 15% 14% 8% 2	1557
March	1st to 10th	Day	56% 5% 11% 18% 9%	4571
	11th to 20th	Day	48% 7% 15% 19% 9% 1	5110
	21st to end	Day	47% 6% 12% 23% 12% 1	5818
April	1st to 10th	Day	54% 7% 13% 19% 7% 1	2520
	11th to 20th	Day	55% 5% 11% 21% 8%	2694
	21st to end	Day	50% 5% 13% 21% 10%	2921
May	1st to 10th	Day	40% 6% 15% 28% 9% 2	8195
	11th to 20th	Day	52% 8% 11% 20% 9%	8574
	21st to end	Day	53% 6% 14% 20% 6% 1	10083
June	1st to 10th	Day	48% 7% 13% 21% 10% 1	3360
	11th to 20th	Day	51% 8% 14% 21% 6%	3360
	21st to end	Day	47% 7% 17% 22% 6%	3360
July	1st to 10th	Day	42% 6% 11% 23% 16% 1	9341
	11th to 20th	Day	38% 4 17% 29% 12%	8766
	21st to end	Day	39% 5% 21% 25% 11%	9360
August	1st to 10th	Day	24% 6% 18% 38% 13% 1	4784
	11th to 20th	Day	36% 7% 20% 29% 7%	4564
	21st to end	Day	45% 4 25% 21% 4	4781
September	1st to 10th	Day	38% 7% 25% 23% 6%	2410
	11th to 20th	Day	43% 7% 20% 25% 6%	2400
	21st to end	Day	54% 8% 15% 18% 4 1	2106
October	1st to 10th	Day	57% 5% 19% 13% 6%	3280
	11th to 20th	Day	55% 5% 20% 18% 2	3244
	21st to end	Day	50% 6% 24% 14% 5%	2922
November	1st to 10th	Day	61% 5% 14% 13% 6%	1648
	11th to 20th	Day	64% 6% 14% 12% 4	1676
	21st to end	Day	67% 6% 12% 13% 2	1320
December	1st to 10th	Day	71% 5% 12% 10% 2	2020
	11th to 20th	Day	74% 4 11% 6% 4	2324
	21st to end	Day	61% 6% 15% 14% 4	3058
January	1st to 10th	Night	70% 5% 11% 10% 5%	9069
	11th to 20th	Night	48% 4 20% 15% 9% 4	8820
	21st to end	Night	63% 5% 15% 13% 3	9651
February	1st to 10th	Night	62% 5% 12% 10% 10% 1	2923
	11th to 20th	Night	56% 4 18% 16% 6%	2664
	21st to end	Night	54% 4 15% 17% 9% 1	2249
March	1st to 10th	Night	54% 5% 11% 18% 11% 1	5538
	11th to 20th	Night	49% 7% 10% 23% 11%	5110
	21st to end	Night	42% 5% 11% 25% 16%	5399
April	1st to 10th	Night	51% 5% 12% 22% 9% 1	2100
	11th to 20th	Night	50% 5% 12% 23% 9%	1871
	21st to end	Night	46% 6% 13% 23% 12% 1	1699
May	1st to 10th	Night	42% 5% 16% 29% 9% 1	4721
	11th to 20th	Night	50% 5% 12% 26% 6%	4288
	21st to end	Night	56% 5% 10% 20% 8% 1	4090
June	1st to 10th	Night	48% 6% 12% 21% 11% 1	1260
	11th to 20th	Night	52% 6% 14% 22% 7%	1260
	21st to end	Night	49% 6% 18% 23% 5%	1260
July	1st to 10th	Night	43% 4 13% 23% 17% 1	3510
	11th to 20th	Night	35% 3 18% 31% 12%	4055
	21st to end	Night	38% 4 23% 22% 13%	4403
August	1st to 10th	Night	19% 3 16% 42% 19% 1	2547
	11th to 20th	Night	31% 6% 19% 35% 9%	2769
	21st to end	Night	46% 4 25% 20% 5%	3326
September	1st to 10th	Night	39% 5% 20% 28% 7% 1	1990
	11th to 20th	Night	38% 6% 16% 31% 9%	2000
	21st to end	Night	51% 6% 15% 18% 9%	2293
October	1st to 10th	Night	56% 5% 17% 17% 5%	3920
	11th to 20th	Night	51% 4 21% 20% 5%	3912
	21st to end	Night	53% 5% 21% 18% 4	4867
November	1st to 10th	Night	59% 7% 14% 15% 6%	2870
	11th to 20th	Night	61% 7% 14% 13% 6%	2940
	21st to end	Night	62% 6% 15% 13% 4	3278
December	1st to 10th	Night	67% 5% 12% 12% 3	5380
	11th to 20th	Night	70% 6% 13% 8% 3	6087
	21st to end	Night	61% 6% 16% 12% 4	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	15% 6% 22% 34% 16% 6%	220
	11th to 20th	Day	15% 11% 20% 34% 16% 5%	220
	21st to end	Day	20% 10% 24% 23% 21% 3	242
February	1st to 10th	Day	20% 15% 26% 22% 13% 4	278
	11th to 20th	Day	16% 11% 26% 27% 17% 3	425
	21st to end	Day	15% 18% 30% 23% 11% 4	355
March	1st to 10th	Day	12% 15% 28% 24% 17% 4	518
	11th to 20th	Day	12% 16% 28% 26% 15% 3	540
	21st to end	Day	15% 16% 26% 21% 16% 5%	594
April	1st to 10th	Day	12% 16% 28% 26% 14% 3	540
	11th to 20th	Day	15% 15% 28% 21% 14% 6%	532
	21st to end	Day	13% 15% 28% 26% 14% 4	540
May	1st to 10th	Day	13% 13% 30% 27% 15% 3	543
	11th to 20th	Day	12% 9% 24% 31% 19% 5%	704
	21st to end	Day	15% 8% 23% 27% 22% 5%	992
June	1st to 10th	Day	15% 9% 24% 30% 18% 3	990
	11th to 20th	Day	15% 8% 24% 30% 18% 5%	990
	21st to end	Day	12% 6% 23% 28% 25% 6%	990
July	1st to 10th	Day	13% 7% 19% 30% 25% 7%	976
	11th to 20th	Day	13% 7% 20% 27% 26% 7%	782
	21st to end	Day	9% 6% 18% 32% 27% 7%	849
August	1st to 10th	Day	9% 5% 16% 33% 28% 10%	650
	11th to 20th	Day	8% 7% 25% 27% 22% 11%	557
	21st to end	Day	12% 7% 23% 30% 18% 10%	620
September	1st to 10th	Day	12% 7% 23% 25% 24% 8%	530
	11th to 20th	Day	12% 8% 22% 27% 22% 8%	530
	21st to end	Day	20% 11% 31% 22% 13% 3	530
October	1st to 10th	Day	22% 9% 23% 25% 16% 5%	530
	11th to 20th	Day	20% 11% 28% 23% 17% 2	525
	21st to end	Day	20% 12% 24% 28% 13% 3	272
November	1st to 10th	Day	28% 12% 23% 25% 7% 5%	220
	11th to 20th	Day	20% 8% 25% 23% 16% 9%	220
	21st to end	Day	19% 9% 25% 28% 15% 4	220
December	1st to 10th	Day	17% 6% 20% 30% 24% 4	220
	11th to 20th	Day	15% 9% 21% 31% 20% 4	220
	21st to end	Day	22% 7% 14% 37% 12% 7%	242
January	1st to 10th	Night	23% 9% 23% 33% 11% 2	1057
	11th to 20th	Night	21% 6% 27% 30% 15% 1	950
	21st to end	Night	20% 10% 24% 31% 13% 2	1045
February	1st to 10th	Night	21% 10% 20% 31% 15% 3	862
	11th to 20th	Night	17% 6% 25% 35% 15% 2	824
	21st to end	Night	17% 9% 24% 32% 16% 2	692
March	1st to 10th	Night	15% 11% 23% 32% 16% 3	840
	11th to 20th	Night	13% 11% 24% 35% 15% 1	840
	21st to end	Night	13% 8% 19% 30% 25% 4	924
April	1st to 10th	Night	16% 9% 18% 33% 21% 3	840
	11th to 20th	Night	14% 6% 21% 35% 19% 5%	623
	21st to end	Night	14% 5% 27% 33% 20% 1	439
May	1st to 10th	Night	16% 5% 22% 38% 16% 3	420
	11th to 20th	Night	14% 4 18% 40% 22% 2	414
	21st to end	Night	16% 9% 16% 33% 24% 2	455
June	1st to 10th	Night	15% 5% 24% 32% 21% 2	420
	11th to 20th	Night	16% 4 21% 31% 24% 3	420
	21st to end	Night	11% 3 16% 38% 30% 2	420
July	1st to 10th	Night	11% 4 14% 39% 31% 1	410
	11th to 20th	Night	12% 4 14% 37% 30% 3	408
	21st to end	Night	12% 3 13% 37% 30% 6%	460
August	1st to 10th	Night	8% 2 11% 36% 36% 7%	418
	11th to 20th	Night	9% 1 15% 37% 33% 5%	465
	21st to end	Night	16% 3 15% 34% 28% 4	687
September	1st to 10th	Night	14% 3 16% 33% 31% 3	790
	11th to 20th	Night	12% 4 13% 33% 31% 7%	800
	21st to end	Night	21% 7% 22% 32% 17% 2	800
October	1st to 10th	Night	19% 5% 19% 33% 19% 4	800
	11th to 20th	Night	21% 5% 23% 31% 18% 2	800
	21st to end	Night	21% 10% 25% 31% 12% 1	880
November	1st to 10th	Night	24% 10% 24% 30% 11% 2	820
	11th to 20th	Night	20% 10% 25% 32% 11% 2	840
	21st to end	Night	20% 10% 27% 30% 11% 2	1108
December	1st to 10th	Night	18% 6% 22% 35% 17% 2	1160
	11th to 20th	Night	21% 8% 25% 31% 13% 2	1160
	21st to end	Night	18% 7% 25% 33% 15% 2	1276

Page generated at 2026-08-27 01:07:16. Version ac07

Copyright © 2026 Attilla Danko.