Stettler
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stettler clear sky chart from 2005-11-06 to 2026-07-16.

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% 9% 3 8% 6% 5% 5% 4 6% 8% 37%	142423
	Night	7% 10% 4 10% 6% 5% 5% 4 6% 8% 34%	138990
Transparency	Day	44% 7% 16% 24% 9% 1	142120
	Night	46% 7% 15% 22% 9% 1	138877
Seeing	Day	13% 7% 26% 31% 18% 5%	17689
	Night	12% 6% 31% 35% 14% 2	26703

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	5% 12% 5% 14% 9% 6% 5% 4 5% 7% 27%	4125
	11th to 20th	Day	3 9% 4 12% 6% 7% 6% 6% 8% 8% 32%	4119
	21st to end	Day	3 10% 5% 11% 6% 5% 5% 3 6% 8% 37%	4924
February	1st to 10th	Day	7% 14% 4 12% 7% 7% 4 4 5% 9% 27%	1689
	11th to 20th	Day	6% 14% 5% 11% 7% 6% 7% 5% 7% 7% 26%	1845
	21st to end	Day	4 13% 4 12% 8% 7% 7% 5% 6% 8% 26%	1599
March	1st to 10th	Day	4 10% 4 11% 8% 7% 7% 4 6% 8% 32%	4654
	11th to 20th	Day	7% 11% 4 10% 7% 6% 4 3 5% 8% 35%	5109
	21st to end	Day	10% 15% 7% 14% 6% 4 5% 3 6% 7% 23%	5607
April	1st to 10th	Day	10% 12% 3 7% 7% 6% 6% 5% 6% 7% 31%	2625
	11th to 20th	Day	12% 12% 4 9% 5% 5% 5% 5% 7% 7% 30%	2700
	21st to end	Day	12% 10% 4 9% 5% 5% 5% 4 6% 8% 32%	2730
May	1st to 10th	Day	11% 8% 3 6% 5% 4 4 4 6% 8% 41%	8321
	11th to 20th	Day	14% 10% 3 8% 6% 6% 6% 5% 7% 8% 27%	8755
	21st to end	Day	11% 6% 3 8% 6% 5% 5% 4 6% 7% 37%	9649
June	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 5% 7% 8% 32%	3150
	11th to 20th	Day	18% 11% 3 8% 6% 6% 5% 5% 6% 7% 25%	3150
	21st to end	Day	12% 5% 2 6% 5% 5% 6% 5% 7% 9% 38%	3150
July	1st to 10th	Day	8% 5% 2 5% 4 4 5% 4 6% 8% 49%	6930
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 7% 9% 42%	6856
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 6% 8% 45%	7376
August	1st to 10th	Day	11% 6% 2 6% 4 5% 4 3 6% 8% 44%	4641
	11th to 20th	Day	7% 5% 2 6% 4 5% 5% 4 7% 11% 43%	4174
	21st to end	Day	10% 4 1 5% 3 4 4 5% 6% 9% 48%	4664
September	1st to 10th	Day	11% 6% 2 6% 4 5% 4 3 5% 8% 46%	2528
	11th to 20th	Day	14% 8% 2 5% 5% 4 4 2 5% 8% 44%	2200
	21st to end	Day	9% 7% 2 6% 3 4 4 3 6% 8% 47%	2200
October	1st to 10th	Day	7% 7% 3 6% 4 5% 6% 4 5% 7% 45%	3369
	11th to 20th	Day	6% 8% 3 7% 4 4 5% 4 7% 9% 42%	3067
	21st to end	Day	8% 9% 3 8% 5% 5% 5% 4 6% 7% 40%	3151
November	1st to 10th	Day	8% 15% 5% 10% 8% 6% 6% 3 6% 7% 26%	1648
	11th to 20th	Day	6% 12% 5% 12% 6% 5% 5% 4 6% 7% 32%	1601
	21st to end	Day	6% 9% 5% 12% 7% 7% 6% 4 6% 7% 31%	1470
December	1st to 10th	Day	11% 17% 4 11% 6% 6% 5% 4 5% 7% 24%	2360
	11th to 20th	Day	7% 11% 5% 14% 8% 7% 6% 5% 7% 6% 23%	2712
	21st to end	Day	3 7% 3 11% 7% 5% 5% 4 6% 7% 43%	3575
January	1st to 10th	Night	6% 12% 5% 14% 8% 7% 6% 5% 7% 7% 24%	8768
	11th to 20th	Night	3 9% 5% 10% 6% 5% 5% 5% 6% 8% 38%	8779
	21st to end	Night	4 10% 5% 11% 6% 5% 5% 4 6% 8% 35%	9312
February	1st to 10th	Night	5% 11% 5% 13% 7% 7% 5% 5% 6% 8% 28%	2930
	11th to 20th	Night	5% 13% 4 10% 7% 7% 6% 6% 7% 8% 27%	2662
	21st to end	Night	5% 11% 4 10% 7% 5% 7% 6% 7% 8% 31%	2205
March	1st to 10th	Night	3 9% 4 12% 7% 6% 6% 5% 8% 10% 29%	5459
	11th to 20th	Night	4 11% 5% 10% 7% 6% 6% 5% 7% 9% 31%	5110
	21st to end	Night	9% 15% 7% 16% 7% 6% 5% 4 6% 6% 20%	5610
April	1st to 10th	Night	9% 11% 3 9% 6% 6% 5% 4 7% 8% 32%	1993
	11th to 20th	Night	9% 11% 4 10% 7% 5% 6% 5% 6% 7% 29%	1871
	21st to end	Night	11% 11% 3 8% 5% 6% 4 4 6% 7% 33%	1890
May	1st to 10th	Night	15% 8% 3 7% 4 4 4 4 6% 7% 38%	4612
	11th to 20th	Night	11% 10% 4 10% 6% 5% 6% 6% 7% 7% 28%	4105
	21st to end	Night	12% 7% 3 8% 6% 6% 5% 5% 6% 8% 33%	4522
June	1st to 10th	Night	15% 9% 3 8% 7% 5% 4 6% 7% 7% 29%	1470
	11th to 20th	Night	16% 10% 3 8% 6% 7% 6% 5% 7% 7% 26%	1470
	21st to end	Night	9% 6% 2 6% 5% 5% 6% 5% 7% 9% 38%	1470
July	1st to 10th	Night	7% 5% 2 6% 4 4 4 4 6% 9% 47%	3250
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 4 7% 9% 42%	3215
	21st to end	Night	9% 4 2 7% 5% 4 5% 4 6% 10% 43%	3467
August	1st to 10th	Night	13% 7% 2 6% 3 4 4 4 6% 7% 44%	2505
	11th to 20th	Night	7% 5% 3 6% 5% 5% 5% 4 7% 11% 42%	2884
	21st to end	Night	10% 5% 2 7% 5% 5% 5% 4 7% 9% 43%	3245
September	1st to 10th	Night	9% 5% 2 7% 5% 4 4 3 6% 8% 45%	1870
	11th to 20th	Night	14% 6% 2 6% 4 4 3 4 5% 7% 45%	2200
	21st to end	Night	8% 7% 2 6% 4 4 5% 4 7% 9% 45%	2200
October	1st to 10th	Night	8% 7% 3 8% 4 5% 5% 4 6% 8% 42%	3824
	11th to 20th	Night	7% 8% 3 7% 4 4 6% 4 7% 9% 42%	4078
	21st to end	Night	7% 10% 3 8% 6% 6% 6% 4 6% 8% 36%	4617
November	1st to 10th	Night	9% 15% 5% 8% 5% 5% 5% 4 6% 7% 31%	2870
	11th to 20th	Night	6% 11% 5% 10% 6% 6% 6% 4 6% 9% 30%	3014
	21st to end	Night	5% 12% 4 11% 7% 7% 6% 4 7% 8% 29%	3150
December	1st to 10th	Night	10% 16% 5% 12% 7% 5% 5% 4 5% 7% 24%	5040
	11th to 20th	Night	6% 15% 4 14% 8% 6% 5% 4 6% 8% 23%	5700
	21st to end	Night	3 7% 3 10% 6% 5% 5% 4 6% 8% 42%	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	56% 5% 10% 17% 12%	4125
	11th to 20th	Day	46% 5% 14% 14% 19% 2	4140
	21st to end	Day	44% 6% 19% 26% 5%	4925
February	1st to 10th	Day	54% 6% 14% 15% 11% 1	1689
	11th to 20th	Day	53% 7% 13% 16% 10% 1	1854
	21st to end	Day	53% 6% 14% 18% 9%	1599
March	1st to 10th	Day	47% 7% 17% 20% 9%	4654
	11th to 20th	Day	47% 6% 14% 21% 12%	5110
	21st to end	Day	59% 6% 10% 19% 6%	5607
April	1st to 10th	Day	49% 8% 16% 18% 8% 1	2625
	11th to 20th	Day	50% 7% 13% 20% 9% 1	2700
	21st to end	Day	48% 8% 13% 23% 7% 2	2730
May	1st to 10th	Day	39% 6% 10% 31% 12% 2	8321
	11th to 20th	Day	50% 7% 10% 23% 9%	8759
	21st to end	Day	43% 8% 17% 24% 8% 1	9650
June	1st to 10th	Day	46% 8% 15% 22% 8% 1	3150
	11th to 20th	Day	55% 9% 13% 18% 4 1	3150
	21st to end	Day	39% 10% 23% 21% 6% 1	3150
July	1st to 10th	Day	32% 6% 18% 30% 12% 1	6856
	11th to 20th	Day	38% 6% 18% 28% 9%	6775
	21st to end	Day	36% 7% 18% 28% 11% 1	7169
August	1st to 10th	Day	37% 7% 17% 33% 6%	4623
	11th to 20th	Day	32% 7% 26% 28% 6%	4213
	21st to end	Day	32% 6% 23% 30% 9%	4663
September	1st to 10th	Day	36% 6% 18% 27% 10% 3	2528
	11th to 20th	Day	40% 5% 16% 30% 9% 1	2200
	21st to end	Day	34% 7% 18% 27% 11% 3	2200
October	1st to 10th	Day	38% 5% 19% 30% 7% 1	3369
	11th to 20th	Day	38% 5% 17% 29% 11% 1	3067
	21st to end	Day	42% 6% 13% 33% 6%	3151
November	1st to 10th	Day	56% 7% 13% 17% 6% 1	1648
	11th to 20th	Day	50% 7% 16% 20% 7% 1	1601
	21st to end	Day	50% 8% 16% 18% 6% 1	1470
December	1st to 10th	Day	60% 6% 16% 13% 4 1	2360
	11th to 20th	Day	58% 8% 16% 14% 3	2714
	21st to end	Day	39% 5% 10% 28% 16% 2	3575
January	1st to 10th	Night	57% 6% 12% 15% 9% 1	8769
	11th to 20th	Night	43% 5% 17% 18% 15% 2	8820
	21st to end	Night	46% 6% 19% 21% 7%	9312
February	1st to 10th	Night	53% 6% 12% 18% 11%	2930
	11th to 20th	Night	51% 8% 12% 16% 12% 1	2663
	21st to end	Night	46% 9% 13% 21% 10% 2	2205
March	1st to 10th	Night	46% 7% 18% 21% 8%	5459
	11th to 20th	Night	47% 6% 15% 22% 9% 1	5110
	21st to end	Night	61% 8% 9% 15% 6%	5610
April	1st to 10th	Night	47% 7% 15% 19% 12% 1	1993
	11th to 20th	Night	50% 7% 13% 20% 8% 2	1871
	21st to end	Night	46% 7% 13% 21% 11% 2	1890
May	1st to 10th	Night	43% 5% 9% 27% 15% 1	4610
	11th to 20th	Night	49% 8% 13% 22% 7% 1	4105
	21st to end	Night	44% 10% 17% 23% 7%	4526
June	1st to 10th	Night	49% 9% 13% 20% 8% 1	1470
	11th to 20th	Night	53% 10% 15% 16% 6% 1	1470
	21st to end	Night	39% 11% 20% 24% 6% 1	1470
July	1st to 10th	Night	33% 7% 24% 23% 13% 1	3215
	11th to 20th	Night	38% 7% 15% 31% 7% 2	3173
	21st to end	Night	36% 7% 20% 26% 10% 1	3369
August	1st to 10th	Night	37% 7% 18% 32% 6%	2498
	11th to 20th	Night	35% 7% 22% 28% 7% 1	2911
	21st to end	Night	37% 6% 19% 29% 8% 1	3245
September	1st to 10th	Night	36% 7% 15% 24% 14% 4	1870
	11th to 20th	Night	38% 7% 14% 28% 10% 3	2200
	21st to end	Night	33% 8% 16% 26% 14% 2	2200
October	1st to 10th	Night	40% 6% 19% 26% 10% 1	3824
	11th to 20th	Night	37% 6% 15% 31% 9% 1	4078
	21st to end	Night	44% 6% 16% 28% 5%	4617
November	1st to 10th	Night	50% 8% 13% 21% 7% 1	2870
	11th to 20th	Night	49% 8% 15% 18% 9% 1	3014
	21st to end	Night	50% 7% 16% 18% 7% 1	3150
December	1st to 10th	Night	61% 5% 14% 14% 5% 1	5040
	11th to 20th	Night	57% 7% 17% 13% 5%	5697
	21st to end	Night	39% 5% 13% 24% 16% 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% 7% 31% 35% 17% 4	220
	11th to 20th	Day	6% 8% 36% 30% 18% 2	220
	21st to end	Day	10% 8% 37% 26% 13% 6%	242
February	1st to 10th	Day	12% 9% 28% 32% 12% 6%	226
	11th to 20th	Day	11% 8% 28% 37% 13% 3	330
	21st to end	Day	6% 8% 35% 32% 16% 4	315
March	1st to 10th	Day	11% 7% 33% 30% 16% 2	540
	11th to 20th	Day	11% 5% 34% 30% 15% 5%	540
	21st to end	Day	15% 8% 30% 28% 15% 3	594
April	1st to 10th	Day	12% 12% 31% 29% 12% 4	540
	11th to 20th	Day	14% 11% 28% 28% 15% 4	532
	21st to end	Day	17% 8% 24% 32% 14% 4	540
May	1st to 10th	Day	14% 9% 27% 29% 16% 5%	700
	11th to 20th	Day	12% 8% 24% 32% 18% 5%	775
	21st to end	Day	17% 5% 19% 31% 20% 8%	844
June	1st to 10th	Day	17% 9% 23% 33% 14% 4	780
	11th to 20th	Day	18% 10% 24% 27% 17% 4	780
	21st to end	Day	13% 4 22% 32% 22% 8%	780
July	1st to 10th	Day	11% 4 18% 35% 25% 8%	771
	11th to 20th	Day	14% 4 20% 33% 22% 7%	744
	21st to end	Day	8% 5% 17% 34% 27% 10%	794
August	1st to 10th	Day	11% 4 21% 29% 24% 10%	588
	11th to 20th	Day	10% 5% 22% 32% 24% 8%	517
	21st to end	Day	10% 7% 17% 32% 26% 9%	583
September	1st to 10th	Day	12% 8% 26% 28% 20% 6%	530
	11th to 20th	Day	17% 5% 24% 26% 22% 5%	530
	21st to end	Day	11% 10% 32% 29% 15% 3	530
October	1st to 10th	Day	15% 6% 31% 25% 17% 6%	390
	11th to 20th	Day	11% 8% 32% 31% 15% 2	330
	21st to end	Day	12% 10% 37% 28% 12% 2	363
November	1st to 10th	Day	15% 8% 35% 30% 9% 3	330
	11th to 20th	Day	12% 7% 39% 30% 10% 1	289
	21st to end	Day	8% 8% 32% 28% 19% 5%	220
December	1st to 10th	Day	10% 8% 35% 31% 11% 4	220
	11th to 20th	Day	10% 11% 30% 35% 12% 2	220
	21st to end	Day	7% 6% 27% 40% 15% 4	242
January	1st to 10th	Night	10% 8% 36% 31% 14% 1	1050
	11th to 20th	Night	11% 8% 36% 32% 11% 1	1050
	21st to end	Night	13% 11% 33% 32% 9% 2	1035
February	1st to 10th	Night	9% 9% 28% 37% 15% 2	840
	11th to 20th	Night	11% 6% 35% 34% 14% 1	824
	21st to end	Night	9% 5% 30% 36% 17% 3	692
March	1st to 10th	Night	8% 5% 29% 40% 16% 2	840
	11th to 20th	Night	10% 5% 36% 35% 12% 3	840
	21st to end	Night	14% 5% 30% 37% 13% 2	924
April	1st to 10th	Night	10% 8% 32% 30% 17% 2	719
	11th to 20th	Night	14% 8% 32% 37% 9% 1	623
	21st to end	Night	17% 7% 26% 37% 13% 1	630
May	1st to 10th	Night	17% 7% 27% 35% 12% 2	541
	11th to 20th	Night	13% 5% 25% 38% 18% 1	414
	21st to end	Night	20% 5% 22% 31% 20% 2	455
June	1st to 10th	Night	19% 9% 25% 34% 11% 2	420
	11th to 20th	Night	20% 5% 25% 31% 17% 1	420
	21st to end	Night	14% 2 23% 37% 22% 2	420
July	1st to 10th	Night	10% 3 18% 44% 23% 1	410
	11th to 20th	Night	13% 3 22% 44% 16% 1	398
	21st to end	Night	10% 4 18% 40% 27% 2	438
August	1st to 10th	Night	13% 3 21% 33% 27% 4	398
	11th to 20th	Night	11% 4 16% 44% 24% 2	577
	21st to end	Night	11% 4 19% 42% 23% 1	660
September	1st to 10th	Night	12% 4 24% 41% 18% 2	620
	11th to 20th	Night	16% 4 20% 41% 18% 1	800
	21st to end	Night	11% 5% 32% 38% 13% 2	800
October	1st to 10th	Night	15% 4 31% 35% 14% 1	800
	11th to 20th	Night	12% 6% 36% 33% 13% 2	800
	21st to end	Night	13% 8% 34% 34% 10%	885
November	1st to 10th	Night	16% 6% 36% 32% 9% 1	1025
	11th to 20th	Night	12% 8% 38% 31% 8% 3	1050
	21st to end	Night	9% 5% 40% 34% 10% 1	1050
December	1st to 10th	Night	14% 7% 36% 28% 12% 2	1050
	11th to 20th	Night	11% 7% 38% 31% 11% 2	1050
	21st to end	Night	13% 3 35% 34% 13% 2	1155

Page generated at 2026-07-13 01:14:47. Version ac07

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