Stavely
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stavely clear sky chart from 2005-11-06 to 2024-11-28.

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	8% 8% 3 7% 5% 5% 5% 4 6% 8% 42%	105729
	Night	6% 8% 3 8% 5% 5% 5% 4 6% 8% 42%	102403
Transparency	Day	37% 8% 16% 25% 12% 3	105476
	Night	38% 8% 15% 24% 12% 2	102302
Seeing	Day	13% 15% 30% 26% 13% 4	15424
	Night	11% 12% 33% 31% 13% 2	24556

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	3 8% 6% 12% 6% 5% 4 5% 8% 10% 35%	2219
	11th to 20th	Day	3 9% 4 10% 8% 6% 5% 5% 7% 7% 35%	2295
	21st to end	Day	3 7% 4 9% 7% 6% 6% 4 6% 10% 39%	2794
February	1st to 10th	Day	4 11% 4 10% 6% 8% 6% 5% 6% 9% 30%	1549
	11th to 20th	Day	4 12% 4 10% 6% 6% 6% 5% 8% 8% 31%	1665
	21st to end	Day	4 12% 5% 11% 8% 5% 5% 4 7% 7% 33%	1532
March	1st to 10th	Day	2 10% 4 11% 8% 6% 6% 4 6% 8% 36%	3138
	11th to 20th	Day	6% 8% 3 6% 3 4 5% 4 6% 8% 48%	3479
	21st to end	Day	9% 17% 6% 12% 6% 5% 5% 3 5% 6% 26%	3845
April	1st to 10th	Day	8% 13% 5% 9% 7% 5% 5% 4 6% 8% 30%	2332
	11th to 20th	Day	10% 12% 4 9% 5% 5% 5% 5% 6% 7% 32%	2440
	21st to end	Day	10% 10% 3 7% 6% 5% 4 4 7% 9% 34%	2470
May	1st to 10th	Day	18% 15% 4 7% 4 4 5% 3 5% 6% 29%	4200
	11th to 20th	Day	9% 7% 3 8% 6% 6% 6% 5% 8% 8% 32%	4694
	21st to end	Day	15% 8% 3 9% 6% 6% 7% 5% 7% 8% 26%	5161
June	1st to 10th	Day	14% 8% 3 7% 6% 5% 5% 5% 7% 8% 32%	2850
	11th to 20th	Day	18% 8% 3 7% 6% 6% 6% 4 7% 8% 28%	2850
	21st to end	Day	8% 5% 2 5% 4 4 6% 4 8% 9% 45%	2850
July	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 6% 8% 53%	4740
	11th to 20th	Day	4 3 1 4 3 3 5% 4 7% 9% 57%	4740
	21st to end	Day	3 2 1 4 3 3 4 4 6% 8% 64%	4963
August	1st to 10th	Day	9% 5% 2 5% 4 4 4 4 7% 9% 46%	4378
	11th to 20th	Day	6% 4 2 4 4 4 5% 4 7% 9% 52%	4028
	21st to end	Day	8% 3 1 4 3 3 4 3 6% 8% 57%	4521
September	1st to 10th	Day	10% 5% 2 5% 3 4 4 3 5% 6% 53%	2341
	11th to 20th	Day	12% 7% 1 5% 4 4 4 4 5% 7% 47%	2090
	21st to end	Day	9% 7% 2 5% 4 4 4 4 5% 8% 49%	2090
October	1st to 10th	Day	7% 6% 2 6% 4 4 5% 5% 8% 8% 44%	3340
	11th to 20th	Day	5% 7% 2 5% 3 4 4 4 6% 11% 50%	2966
	21st to end	Day	6% 7% 2 6% 4 5% 5% 5% 6% 9% 45%	3101
November	1st to 10th	Day	9% 12% 4 8% 6% 5% 4 4 5% 7% 36%	1652
	11th to 20th	Day	4 10% 4 8% 5% 6% 4 4 6% 8% 42%	1583
	21st to end	Day	4 11% 4 9% 4 3 4 5% 6% 11% 37%	1379
December	1st to 10th	Day	3 9% 5% 10% 6% 6% 6% 4 6% 8% 39%	1330
	11th to 20th	Day	3 10% 5% 12% 7% 6% 6% 4 7% 6% 32%	1682
	21st to end	Day	3 9% 3 8% 4 4 5% 5% 5% 8% 46%	2442
January	1st to 10th	Night	3 12% 5% 10% 6% 5% 6% 5% 8% 9% 31%	4726
	11th to 20th	Night	3 9% 4 13% 6% 6% 6% 5% 6% 7% 34%	4634
	21st to end	Night	3 10% 4 9% 5% 5% 5% 5% 7% 8% 40%	4862
February	1st to 10th	Night	4 11% 4 11% 7% 6% 6% 4 5% 8% 33%	2629
	11th to 20th	Night	4 13% 5% 9% 6% 5% 6% 6% 7% 7% 31%	2402
	21st to end	Night	4 10% 5% 12% 8% 6% 5% 4 6% 6% 35%	1922
March	1st to 10th	Night	2 8% 4 14% 9% 6% 6% 4 6% 8% 33%	3736
	11th to 20th	Night	4 8% 3 6% 5% 4 4 4 7% 9% 46%	3500
	21st to end	Night	11% 19% 6% 11% 6% 5% 4 3 5% 7% 23%	3806
April	1st to 10th	Night	8% 14% 5% 8% 5% 4 4 3 6% 7% 36%	1847
	11th to 20th	Night	10% 11% 4 10% 5% 5% 5% 5% 6% 6% 33%	1691
	21st to end	Night	11% 9% 3 8% 6% 5% 6% 5% 6% 7% 36%	1710
May	1st to 10th	Night	16% 14% 4 9% 5% 4 5% 4 4 6% 30%	2764
	11th to 20th	Night	10% 7% 2 7% 4 5% 6% 5% 7% 9% 39%	2199
	21st to end	Night	13% 7% 3 7% 6% 7% 7% 5% 6% 8% 31%	2414
June	1st to 10th	Night	14% 6% 2 6% 5% 5% 5% 3 7% 7% 40%	1330
	11th to 20th	Night	17% 8% 3 6% 5% 4 6% 3 5% 9% 35%	1330
	21st to end	Night	7% 4 1 4 5% 4 4 5% 7% 9% 49%	1330
July	1st to 10th	Night	4 3 1 5% 5% 5% 5% 4 7% 8% 51%	2220
	11th to 20th	Night	5% 3 1 5% 4 3 5% 5% 6% 8% 55%	2220
	21st to end	Night	3 3 1 4 3 2 3 3 4 7% 66%	2585
August	1st to 10th	Night	8% 5% 2 6% 4 4 5% 4 6% 7% 49%	2552
	11th to 20th	Night	5% 5% 2 6% 5% 5% 5% 5% 7% 10% 46%	2811
	21st to end	Night	6% 3 1 4 3 3 4 4 5% 8% 60%	3146
September	1st to 10th	Night	9% 4 2 5% 4 3 4 3 6% 6% 55%	1837
	11th to 20th	Night	12% 7% 1 4 3 3 3 2 4 7% 53%	2090
	21st to end	Night	9% 6% 2 5% 3 3 3 4 6% 7% 51%	2090
October	1st to 10th	Night	7% 5% 2 5% 3 3 4 4 5% 7% 56%	3635
	11th to 20th	Night	5% 5% 2 5% 4 4 5% 4 6% 8% 52%	3958
	21st to end	Night	5% 6% 2 5% 5% 5% 5% 4 7% 8% 48%	4457
November	1st to 10th	Night	7% 13% 4 7% 5% 5% 5% 4 6% 7% 37%	2625
	11th to 20th	Night	3 8% 3 8% 5% 5% 5% 4 7% 9% 43%	2815
	21st to end	Night	4 10% 4 8% 5% 4 4 4 7% 10% 40%	2956
December	1st to 10th	Night	4 10% 3 10% 6% 6% 6% 4 7% 7% 37%	2850
	11th to 20th	Night	2 9% 4 10% 6% 5% 6% 5% 7% 9% 36%	3510
	21st to end	Night	4 9% 3 9% 5% 4 4 5% 6% 8% 44%	5214

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	40% 11% 16% 23% 8% 2	2219
	11th to 20th	Day	45% 8% 11% 17% 16% 3	2316
	21st to end	Day	35% 12% 17% 28% 7% 1	2794
February	1st to 10th	Day	50% 8% 14% 18% 8% 2	1549
	11th to 20th	Day	46% 8% 17% 19% 8% 2	1674
	21st to end	Day	49% 8% 12% 18% 12% 1	1532
March	1st to 10th	Day	41% 11% 15% 21% 11% 1	3138
	11th to 20th	Day	32% 7% 20% 28% 12% 1	3480
	21st to end	Day	55% 9% 14% 18% 4	3845
April	1st to 10th	Day	49% 9% 15% 20% 7% 1	2332
	11th to 20th	Day	47% 7% 14% 21% 9% 2	2440
	21st to end	Day	44% 9% 15% 22% 10% 1	2470
May	1st to 10th	Day	53% 7% 11% 24% 5%	4200
	11th to 20th	Day	40% 11% 17% 23% 8%	4698
	21st to end	Day	48% 11% 18% 15% 8% 1	5162
June	1st to 10th	Day	45% 8% 17% 18% 10% 1	2850
	11th to 20th	Day	49% 8% 15% 18% 8% 2	2850
	21st to end	Day	31% 9% 19% 27% 12% 3	2850
July	1st to 10th	Day	26% 7% 14% 30% 17% 5%	4666
	11th to 20th	Day	22% 7% 18% 33% 17% 3	4659
	21st to end	Day	17% 5% 11% 27% 24% 16%	4806
August	1st to 10th	Day	30% 8% 17% 31% 12% 2	4361
	11th to 20th	Day	27% 7% 22% 32% 10% 2	4067
	21st to end	Day	25% 5% 13% 39% 15% 2	4520
September	1st to 10th	Day	31% 5% 14% 25% 17% 8%	2341
	11th to 20th	Day	35% 6% 15% 27% 13% 3	2090
	21st to end	Day	33% 6% 14% 30% 14% 3	2090
October	1st to 10th	Day	33% 8% 13% 34% 11% 1	3340
	11th to 20th	Day	29% 5% 22% 26% 16% 2	2966
	21st to end	Day	34% 7% 12% 31% 12% 4	3101
November	1st to 10th	Day	47% 7% 13% 22% 11%	1652
	11th to 20th	Day	40% 8% 18% 24% 10% 1	1583
	21st to end	Day	39% 7% 21% 21% 10% 2	1379
December	1st to 10th	Day	43% 8% 16% 18% 11% 4	1330
	11th to 20th	Day	49% 9% 16% 20% 6% 1	1684
	21st to end	Day	33% 8% 14% 23% 20% 2	2442
January	1st to 10th	Night	45% 11% 15% 21% 7% 2	4726
	11th to 20th	Night	47% 8% 13% 15% 15% 2	4675
	21st to end	Night	38% 11% 17% 24% 10% 1	4862
February	1st to 10th	Night	47% 9% 13% 17% 12% 2	2629
	11th to 20th	Night	48% 8% 14% 20% 10% 1	2403
	21st to end	Night	48% 6% 14% 20% 10% 2	1922
March	1st to 10th	Night	44% 10% 14% 23% 9%	3736
	11th to 20th	Night	31% 10% 21% 24% 12%	3500
	21st to end	Night	60% 8% 13% 15% 4	3806
April	1st to 10th	Night	46% 8% 13% 21% 11% 1	1847
	11th to 20th	Night	47% 10% 12% 21% 9% 1	1691
	21st to end	Night	45% 9% 13% 23% 8% 2	1710
May	1st to 10th	Night	53% 8% 11% 23% 5%	2764
	11th to 20th	Night	36% 11% 14% 31% 8% 1	2199
	21st to end	Night	45% 14% 16% 17% 7% 1	2414
June	1st to 10th	Night	42% 8% 14% 24% 10% 1	1330
	11th to 20th	Night	46% 8% 15% 21% 9% 2	1330
	21st to end	Night	28% 9% 21% 26% 15% 2	1330
July	1st to 10th	Night	27% 9% 19% 23% 18% 5%	2185
	11th to 20th	Night	23% 10% 17% 30% 15% 6%	2178
	21st to end	Night	19% 5% 10% 29% 22% 15%	2503
August	1st to 10th	Night	33% 7% 16% 26% 16% 3	2544
	11th to 20th	Night	31% 8% 18% 28% 13% 2	2838
	21st to end	Night	22% 5% 14% 37% 18% 4	3146
September	1st to 10th	Night	29% 5% 15% 26% 18% 6%	1837
	11th to 20th	Night	31% 6% 14% 27% 17% 5%	2090
	21st to end	Night	31% 7% 16% 27% 15% 4	2090
October	1st to 10th	Night	27% 5% 11% 31% 22% 3	3635
	11th to 20th	Night	30% 6% 18% 25% 18% 3	3958
	21st to end	Night	32% 6% 14% 31% 16% 1	4457
November	1st to 10th	Night	44% 8% 14% 22% 11% 1	2625
	11th to 20th	Night	37% 9% 17% 21% 15% 1	2815
	21st to end	Night	38% 8% 19% 20% 11% 4	2956
December	1st to 10th	Night	42% 9% 16% 19% 10% 3	2850
	11th to 20th	Night	41% 10% 21% 21% 6% 1	3507
	21st to end	Night	36% 9% 13% 24% 13% 4	5214

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	7% 15% 33% 25% 12% 8%	180
	11th to 20th	Day	10% 15% 36% 23% 13% 4	180
	21st to end	Day	7% 19% 35% 28% 8% 3	198
February	1st to 10th	Day	14% 22% 35% 19% 7% 3	194
	11th to 20th	Day	10% 16% 34% 26% 11% 2	270
	21st to end	Day	12% 18% 34% 24% 11% 1	344
March	1st to 10th	Day	10% 25% 35% 20% 8% 3	460
	11th to 20th	Day	9% 21% 29% 28% 11% 3	460
	21st to end	Day	12% 22% 35% 20% 9% 2	506
April	1st to 10th	Day	14% 23% 35% 21% 5% 1	460
	11th to 20th	Day	16% 16% 34% 21% 12% 1	452
	21st to end	Day	17% 22% 29% 21% 9% 2	460
May	1st to 10th	Day	17% 13% 28% 26% 11% 5%	482
	11th to 20th	Day	19% 11% 23% 25% 18% 4	675
	21st to end	Day	19% 11% 21% 27% 19% 4	734
June	1st to 10th	Day	15% 14% 30% 26% 11% 3	680
	11th to 20th	Day	20% 16% 28% 24% 11% 2	680
	21st to end	Day	11% 9% 25% 31% 19% 5%	680
July	1st to 10th	Day	8% 6% 28% 34% 20% 4	671
	11th to 20th	Day	7% 10% 30% 31% 19% 4	668
	21st to end	Day	5% 8% 31% 34% 18% 4	639
August	1st to 10th	Day	10% 8% 28% 35% 15% 4	487
	11th to 20th	Day	7% 10% 25% 32% 20% 5%	477
	21st to end	Day	9% 11% 32% 26% 16% 6%	539
September	1st to 10th	Day	11% 13% 30% 29% 12% 6%	490
	11th to 20th	Day	16% 13% 28% 24% 15% 4	490
	21st to end	Day	15% 21% 29% 25% 7% 2	490
October	1st to 10th	Day	14% 14% 27% 26% 17% 3	405
	11th to 20th	Day	12% 17% 31% 19% 15% 6%	300
	21st to end	Day	15% 20% 31% 22% 8% 3	330
November	1st to 10th	Day	18% 16% 32% 24% 8% 2	300
	11th to 20th	Day	13% 21% 37% 20% 8% 1	291
	21st to end	Day	10% 22% 29% 21% 10% 9%	194
December	1st to 10th	Day	7% 20% 31% 27% 12% 4	180
	11th to 20th	Day	7% 25% 38% 18% 9% 3	180
	21st to end	Day	10% 13% 27% 31% 16% 4	198
January	1st to 10th	Night	8% 20% 35% 26% 9% 1	950
	11th to 20th	Night	8% 14% 41% 28% 9% 1	911
	21st to end	Night	8% 14% 40% 28% 9% 1	836
February	1st to 10th	Night	9% 16% 32% 27% 12% 3	760
	11th to 20th	Night	10% 11% 38% 29% 11% 1	744
	21st to end	Night	8% 11% 35% 29% 15% 2	628
March	1st to 10th	Night	8% 14% 37% 29% 11% 2	760
	11th to 20th	Night	8% 16% 35% 31% 9% 2	760
	21st to end	Night	12% 11% 34% 31% 10% 3	836
April	1st to 10th	Night	13% 15% 34% 27% 10% 1	707
	11th to 20th	Night	16% 11% 33% 29% 10% 1	563
	21st to end	Night	17% 11% 29% 32% 10% 1	570
May	1st to 10th	Night	16% 11% 27% 31% 14%	532
	11th to 20th	Night	12% 7% 23% 35% 21% 1	374
	21st to end	Night	18% 7% 24% 30% 19% 1	411
June	1st to 10th	Night	16% 9% 27% 32% 14% 2	380
	11th to 20th	Night	22% 9% 29% 26% 14%	380
	21st to end	Night	9% 4 24% 39% 23% 1	380
July	1st to 10th	Night	7% 6% 17% 44% 26% 1	370
	11th to 20th	Night	7% 3 26% 42% 21% 1	368
	21st to end	Night	5% 4 24% 44% 21% 2	416
August	1st to 10th	Night	9% 4 16% 41% 29% 1	388
	11th to 20th	Night	8% 3 22% 44% 21% 2	564
	21st to end	Night	9% 7% 26% 38% 19% 1	627
September	1st to 10th	Night	11% 5% 26% 36% 20% 3	664
	11th to 20th	Night	17% 5% 23% 33% 20% 3	760
	21st to end	Night	13% 8% 32% 31% 12% 4	760
October	1st to 10th	Night	15% 8% 28% 33% 15% 2	760
	11th to 20th	Night	11% 10% 33% 28% 16% 2	760
	21st to end	Night	10% 14% 37% 28% 10% 1	836
November	1st to 10th	Night	13% 17% 39% 23% 8%	870
	11th to 20th	Night	10% 20% 40% 23% 5% 1	1000
	21st to end	Night	10% 16% 38% 25% 9% 2	986
December	1st to 10th	Night	8% 14% 37% 29% 11% 2	950
	11th to 20th	Night	7% 16% 38% 31% 7% 1	950
	21st to end	Night	10% 13% 37% 29% 10% 2	1045

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