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 2026-02-01.

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	7% 8% 3 7% 5% 5% 5% 4 6% 8% 42%	131621
	Night	6% 9% 3 8% 5% 5% 5% 4 6% 8% 41%	129120
Transparency	Day	37% 7% 15% 25% 13% 2	131324
	Night	39% 8% 15% 23% 12% 2	128994
Seeing	Day	12% 15% 30% 26% 14% 4	16871
	Night	11% 12% 33% 31% 13% 1	26156

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	2 11% 7% 14% 6% 5% 4 4 6% 8% 32%	3249
	11th to 20th	Day	3 9% 3 9% 7% 6% 4 5% 7% 7% 40%	3370
	21st to end	Day	2 5% 3 9% 5% 5% 5% 4 6% 11% 44%	4092
February	1st to 10th	Day	4 10% 5% 11% 6% 8% 6% 5% 6% 8% 30%	1631
	11th to 20th	Day	4 12% 4 10% 7% 5% 6% 5% 8% 8% 30%	1755
	21st to end	Day	4 11% 4 10% 8% 5% 5% 4 7% 8% 34%	1610
March	1st to 10th	Day	3 10% 3 9% 6% 5% 4 3 6% 11% 39%	4518
	11th to 20th	Day	4 8% 3 8% 4 5% 6% 5% 6% 8% 42%	4989
	21st to end	Day	7% 17% 6% 11% 6% 5% 5% 4 6% 8% 24%	5519
April	1st to 10th	Day	8% 13% 5% 9% 7% 5% 5% 4 6% 8% 31%	2455
	11th to 20th	Day	10% 12% 4 9% 5% 5% 5% 5% 6% 7% 32%	2570
	21st to end	Day	10% 10% 3 8% 6% 5% 4 4 7% 9% 34%	2600
May	1st to 10th	Day	14% 11% 3 6% 4 4 4 3 5% 7% 40%	6010
	11th to 20th	Day	12% 7% 3 9% 6% 7% 6% 6% 7% 9% 28%	6734
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 5% 6% 8% 38%	7405
June	1st to 10th	Day	13% 8% 3 7% 6% 5% 5% 5% 7% 8% 33%	3000
	11th to 20th	Day	17% 8% 3 6% 5% 6% 6% 4 7% 9% 29%	3000
	21st to end	Day	8% 5% 2 5% 4 4 6% 4 8% 9% 45%	3000
July	1st to 10th	Day	7% 4 2 5% 4 4 4 3 6% 8% 53%	6780
	11th to 20th	Day	8% 4 2 5% 3 4 4 4 6% 9% 51%	6780
	21st to end	Day	7% 4 1 5% 3 3 4 4 5% 8% 56%	7131
August	1st to 10th	Day	8% 5% 2 5% 4 4 4 4 7% 9% 46%	4517
	11th to 20th	Day	6% 4 2 4 4 4 5% 4 7% 9% 51%	4158
	21st to end	Day	8% 3 1 4 3 3 4 3 6% 8% 57%	4664
September	1st to 10th	Day	10% 5% 2 5% 3 4 4 3 5% 6% 53%	2464
	11th to 20th	Day	12% 6% 1 5% 4 4 4 4 5% 7% 49%	2200
	21st to end	Day	8% 7% 2 5% 4 3 4 4 5% 8% 50%	2200
October	1st to 10th	Day	7% 6% 2 6% 4 4 4 5% 8% 8% 45%	3445
	11th to 20th	Day	5% 7% 2 5% 3 4 4 4 6% 11% 50%	3060
	21st to end	Day	6% 7% 2 6% 4 4 5% 5% 6% 9% 46%	3200
November	1st to 10th	Day	9% 12% 4 8% 5% 5% 4 4 5% 7% 37%	1736
	11th to 20th	Day	5% 10% 4 8% 5% 6% 4 4 5% 8% 43%	1662
	21st to end	Day	4 10% 4 10% 4 4 5% 5% 7% 11% 36%	1470
December	1st to 10th	Day	2 9% 4 11% 6% 6% 6% 4 6% 8% 39%	2360
	11th to 20th	Day	3 9% 4 11% 7% 7% 6% 4 7% 8% 34%	2712
	21st to end	Day	3 9% 4 11% 5% 4 5% 4 5% 8% 42%	3575
January	1st to 10th	Night	3 15% 6% 13% 6% 6% 6% 4 6% 7% 28%	6916
	11th to 20th	Night	2 9% 4 11% 6% 6% 6% 5% 6% 8% 36%	6780
	21st to end	Night	2 8% 5% 9% 5% 5% 5% 4 6% 8% 41%	7106
February	1st to 10th	Night	4 11% 4 11% 7% 7% 6% 4 5% 8% 33%	2767
	11th to 20th	Night	4 13% 6% 10% 6% 5% 6% 5% 6% 7% 31%	2532
	21st to end	Night	4 10% 5% 11% 8% 6% 5% 4 6% 6% 35%	2019
March	1st to 10th	Night	2 7% 4 12% 7% 5% 5% 4 6% 10% 37%	5376
	11th to 20th	Night	3 8% 3 9% 6% 5% 5% 4 7% 9% 40%	5010
	21st to end	Night	10% 18% 6% 10% 5% 5% 4 4 6% 8% 24%	5454
April	1st to 10th	Night	7% 14% 4 8% 5% 4 4 3 7% 7% 36%	1944
	11th to 20th	Night	10% 10% 4 9% 5% 5% 5% 5% 6% 6% 34%	1781
	21st to end	Night	11% 10% 3 8% 6% 5% 5% 5% 6% 7% 36%	1800
May	1st to 10th	Night	13% 11% 3 7% 5% 4 4 3 4 7% 38%	3962
	11th to 20th	Night	11% 8% 3 9% 5% 5% 6% 5% 6% 8% 34%	3159
	21st to end	Night	10% 6% 3 6% 5% 6% 6% 4 5% 7% 43%	3470
June	1st to 10th	Night	13% 6% 2 6% 5% 5% 5% 3 7% 7% 41%	1400
	11th to 20th	Night	17% 8% 3 6% 5% 4 6% 3 5% 9% 35%	1400
	21st to end	Night	7% 5% 1 4 4 4 4 5% 7% 9% 50%	1400
July	1st to 10th	Night	5% 3 1 4 4 4 5% 4 7% 8% 54%	3180
	11th to 20th	Night	7% 3 1 6% 3 3 5% 5% 6% 8% 53%	3180
	21st to end	Night	8% 4 2 5% 3 3 4 3 4 7% 56%	3708
August	1st to 10th	Night	8% 5% 2 6% 4 5% 5% 4 6% 8% 48%	2633
	11th to 20th	Night	5% 5% 2 6% 5% 4 5% 5% 7% 10% 46%	2901
	21st to end	Night	6% 3 1 4 3 3 4 4 5% 8% 60%	3245
September	1st to 10th	Night	8% 4 2 5% 4 3 4 3 6% 6% 55%	1934
	11th to 20th	Night	12% 7% 1 5% 3 3 3 2 4 7% 54%	2200
	21st to end	Night	9% 6% 2 5% 3 3 3 4 6% 7% 51%	2200
October	1st to 10th	Night	7% 5% 2 5% 3 3 4 4 5% 7% 56%	3750
	11th to 20th	Night	6% 5% 2 5% 4 4 5% 4 6% 8% 52%	4084
	21st to end	Night	5% 6% 2 5% 5% 5% 5% 4 7% 8% 48%	4600
November	1st to 10th	Night	7% 13% 3 7% 5% 5% 5% 4 6% 8% 37%	2760
	11th to 20th	Night	3 8% 3 8% 5% 5% 5% 4 7% 9% 42%	2956
	21st to end	Night	4 10% 4 7% 5% 4 4 4 7% 10% 40%	3150
December	1st to 10th	Night	3 8% 3 9% 5% 6% 6% 5% 7% 9% 38%	5040
	11th to 20th	Night	3 10% 4 10% 6% 6% 6% 5% 7% 9% 33%	5700
	21st to end	Night	4 9% 4 9% 5% 4 4 5% 6% 8% 40%	7623

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	48% 9% 12% 22% 8% 2	3249
	11th to 20th	Day	42% 7% 12% 20% 17% 3	3391
	21st to end	Day	31% 9% 13% 33% 13% 2	4092
February	1st to 10th	Day	51% 8% 13% 17% 9% 2	1631
	11th to 20th	Day	47% 8% 16% 19% 8% 2	1764
	21st to end	Day	47% 8% 12% 18% 12% 2	1610
March	1st to 10th	Day	37% 8% 13% 25% 16% 1	4518
	11th to 20th	Day	38% 7% 16% 24% 15% 1	4990
	21st to end	Day	55% 9% 16% 15% 5%	5519
April	1st to 10th	Day	48% 8% 15% 20% 8% 1	2455
	11th to 20th	Day	47% 7% 14% 21% 9% 2	2570
	21st to end	Day	44% 8% 15% 22% 10% 1	2600
May	1st to 10th	Day	43% 6% 10% 22% 17% 3	6010
	11th to 20th	Day	45% 10% 16% 22% 7% 1	6738
	21st to end	Day	39% 9% 17% 22% 12% 1	7406
June	1st to 10th	Day	44% 8% 17% 19% 11% 1	3000
	11th to 20th	Day	48% 8% 15% 18% 9% 2	3000
	21st to end	Day	31% 9% 19% 27% 11% 3	3000
July	1st to 10th	Day	27% 6% 16% 26% 20% 5%	6706
	11th to 20th	Day	28% 7% 19% 30% 13% 2	6699
	21st to end	Day	26% 6% 14% 26% 17% 11%	6930
August	1st to 10th	Day	30% 8% 17% 31% 12% 2	4500
	11th to 20th	Day	27% 7% 22% 32% 10% 2	4197
	21st to end	Day	24% 5% 13% 39% 16% 2	4663
September	1st to 10th	Day	30% 5% 14% 26% 17% 8%	2464
	11th to 20th	Day	34% 6% 14% 29% 14% 3	2200
	21st to end	Day	32% 6% 15% 31% 14% 3	2200
October	1st to 10th	Day	33% 7% 13% 35% 11% 1	3445
	11th to 20th	Day	29% 5% 21% 26% 16% 2	3060
	21st to end	Day	34% 7% 12% 31% 13% 4	3200
November	1st to 10th	Day	47% 7% 13% 22% 11% 1	1736
	11th to 20th	Day	39% 8% 18% 24% 10% 1	1662
	21st to end	Day	41% 7% 20% 21% 9% 2	1470
December	1st to 10th	Day	45% 6% 15% 25% 8% 2	2360
	11th to 20th	Day	46% 7% 20% 19% 7% 1	2714
	21st to end	Day	39% 7% 12% 23% 19% 1	3575
January	1st to 10th	Night	52% 8% 12% 20% 6% 2	6916
	11th to 20th	Night	44% 6% 14% 19% 14% 3	6821
	21st to end	Night	37% 8% 15% 25% 13% 1	7106
February	1st to 10th	Night	48% 9% 12% 17% 12% 2	2767
	11th to 20th	Night	49% 8% 13% 20% 9% 1	2533
	21st to end	Night	48% 6% 14% 20% 10% 2	2019
March	1st to 10th	Night	39% 8% 18% 22% 11% 2	5376
	11th to 20th	Night	37% 9% 16% 25% 13%	5010
	21st to end	Night	57% 7% 16% 14% 6% 1	5454
April	1st to 10th	Night	45% 8% 13% 22% 12% 1	1944
	11th to 20th	Night	46% 9% 12% 22% 9% 1	1781
	21st to end	Night	45% 9% 13% 23% 8% 2	1800
May	1st to 10th	Night	46% 6% 10% 22% 12% 3	3959
	11th to 20th	Night	43% 10% 12% 28% 6% 1	3159
	21st to end	Night	37% 10% 15% 25% 11% 1	3470
June	1st to 10th	Night	42% 8% 13% 25% 11% 1	1400
	11th to 20th	Night	46% 7% 15% 21% 8% 2	1400
	21st to end	Night	28% 9% 20% 27% 14% 2	1400
July	1st to 10th	Night	26% 8% 19% 22% 21% 5%	3145
	11th to 20th	Night	27% 8% 19% 30% 12% 4	3138
	21st to end	Night	28% 6% 14% 26% 15% 10%	3604
August	1st to 10th	Night	33% 7% 16% 26% 15% 3	2625
	11th to 20th	Night	31% 8% 18% 28% 13% 2	2928
	21st to end	Night	22% 5% 14% 37% 18% 4	3245
September	1st to 10th	Night	29% 5% 15% 27% 18% 6%	1934
	11th to 20th	Night	30% 6% 14% 27% 17% 5%	2200
	21st to end	Night	31% 6% 16% 28% 15% 4	2200
October	1st to 10th	Night	27% 5% 11% 32% 22% 3	3750
	11th to 20th	Night	30% 6% 18% 25% 18% 3	4084
	21st to end	Night	32% 6% 14% 31% 16% 1	4600
November	1st to 10th	Night	44% 8% 14% 22% 11% 1	2760
	11th to 20th	Night	37% 9% 17% 21% 15% 1	2956
	21st to end	Night	38% 8% 20% 20% 11% 3	3150
December	1st to 10th	Night	42% 9% 19% 19% 9% 2	5040
	11th to 20th	Night	46% 9% 21% 18% 6% 1	5697
	21st to end	Night	39% 7% 12% 24% 14% 3	7623

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% 35% 25% 12% 7%	220
	11th to 20th	Day	11% 15% 35% 23% 13% 3	220
	21st to end	Day	7% 18% 36% 28% 9% 3	242
February	1st to 10th	Day	13% 20% 36% 20% 7% 3	216
	11th to 20th	Day	9% 14% 34% 29% 12% 2	300
	21st to end	Day	12% 19% 34% 24% 10% 1	374
March	1st to 10th	Day	11% 24% 34% 20% 8% 4	500
	11th to 20th	Day	9% 20% 31% 28% 10% 2	500
	21st to end	Day	13% 22% 35% 19% 9% 2	550
April	1st to 10th	Day	13% 23% 35% 21% 6% 2	500
	11th to 20th	Day	16% 18% 32% 21% 12% 1	492
	21st to end	Day	17% 21% 28% 23% 9% 3	500
May	1st to 10th	Day	16% 14% 28% 27% 11% 5%	523
	11th to 20th	Day	19% 11% 23% 25% 17% 5%	725
	21st to end	Day	17% 10% 21% 28% 20% 5%	789
June	1st to 10th	Day	14% 14% 30% 27% 12% 3	730
	11th to 20th	Day	19% 15% 28% 24% 11% 2	730
	21st to end	Day	11% 8% 25% 32% 19% 5%	730
July	1st to 10th	Day	9% 7% 28% 33% 20% 4	721
	11th to 20th	Day	8% 9% 29% 32% 18% 4	718
	21st to end	Day	6% 8% 30% 33% 19% 4	689
August	1st to 10th	Day	10% 8% 26% 35% 17% 4	527
	11th to 20th	Day	7% 10% 27% 32% 20% 5%	517
	21st to end	Day	9% 10% 30% 26% 16% 8%	583
September	1st to 10th	Day	10% 13% 28% 29% 13% 7%	530
	11th to 20th	Day	15% 12% 26% 24% 17% 6%	530
	21st to end	Day	14% 20% 31% 25% 8% 2	530
October	1st to 10th	Day	14% 14% 26% 27% 16% 3	440
	11th to 20th	Day	11% 17% 33% 19% 15% 5%	330
	21st to end	Day	14% 21% 31% 22% 9% 3	363
November	1st to 10th	Day	18% 17% 32% 24% 8% 2	330
	11th to 20th	Day	14% 20% 36% 21% 8% 2	320
	21st to end	Day	9% 21% 30% 21% 11% 7%	220
December	1st to 10th	Day	6% 18% 33% 28% 11% 4	220
	11th to 20th	Day	8% 25% 36% 19% 9% 3	220
	21st to end	Day	9% 13% 30% 31% 14% 3	242
January	1st to 10th	Night	8% 20% 36% 26% 9% 1	1050
	11th to 20th	Night	8% 14% 42% 28% 8% 1	1006
	21st to end	Night	7% 13% 40% 30% 9% 1	924
February	1st to 10th	Night	9% 16% 33% 28% 12% 3	800
	11th to 20th	Night	9% 10% 38% 30% 11% 1	784
	21st to end	Night	8% 11% 36% 29% 15% 2	660
March	1st to 10th	Night	8% 13% 36% 29% 12% 2	800
	11th to 20th	Night	8% 15% 36% 31% 9% 2	800
	21st to end	Night	11% 11% 35% 30% 10% 3	880
April	1st to 10th	Night	12% 15% 34% 27% 11% 1	744
	11th to 20th	Night	15% 11% 34% 29% 9% 1	593
	21st to end	Night	17% 11% 30% 32% 11% 1	600
May	1st to 10th	Night	16% 11% 26% 32% 14%	560
	11th to 20th	Night	13% 7% 22% 35% 22% 1	394
	21st to end	Night	18% 7% 24% 31% 19% 1	433
June	1st to 10th	Night	16% 10% 26% 32% 14% 2	400
	11th to 20th	Night	21% 9% 30% 27% 13%	400
	21st to end	Night	10% 4 23% 39% 23% 1	400
July	1st to 10th	Night	8% 5% 17% 44% 26% 1	390
	11th to 20th	Night	7% 3 25% 43% 20% 1	388
	21st to end	Night	6% 4 23% 43% 21% 2	438
August	1st to 10th	Night	9% 4 16% 40% 29% 1	409
	11th to 20th	Night	8% 4 22% 44% 21% 2	594
	21st to end	Night	9% 7% 26% 39% 19% 1	660
September	1st to 10th	Night	10% 4 25% 36% 21% 3	699
	11th to 20th	Night	16% 5% 22% 33% 21% 3	800
	21st to end	Night	13% 8% 32% 31% 12% 4	800
October	1st to 10th	Night	15% 8% 28% 32% 15% 3	800
	11th to 20th	Night	11% 11% 33% 29% 15% 2	800
	21st to end	Night	10% 14% 38% 28% 10% 1	880
November	1st to 10th	Night	13% 17% 39% 24% 7%	915
	11th to 20th	Night	10% 20% 40% 23% 6% 1	1050
	21st to end	Night	9% 16% 37% 27% 9% 2	1050
December	1st to 10th	Night	8% 13% 37% 30% 10% 2	1050
	11th to 20th	Night	7% 16% 39% 31% 7% 1	1050
	21st to end	Night	10% 12% 39% 28% 9% 2	1155

Page generated at 2026-01-28 23:21:43. Version ac07

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