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 2025-02-25.

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% 9% 3 9% 6% 5% 5% 4 6% 8% 36%	112120
	Night	7% 10% 4 10% 6% 5% 5% 4 6% 8% 34%	115205
Transparency	Day	44% 7% 16% 23% 9% 1	111861
	Night	46% 7% 15% 21% 9% 1	115110
Seeing	Day	13% 7% 26% 31% 18% 5%	15731
	Night	12% 6% 30% 35% 15% 2	25022

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% 10% 5% 14% 10% 6% 5% 4 5% 8% 28%	3179
	11th to 20th	Day	4 11% 4 11% 7% 7% 6% 6% 9% 9% 27%	3159
	21st to end	Day	4 11% 5% 10% 6% 6% 5% 3 6% 8% 37%	3797
February	1st to 10th	Day	7% 14% 5% 12% 7% 7% 4 3 5% 9% 25%	1608
	11th to 20th	Day	6% 14% 5% 12% 7% 6% 7% 5% 6% 7% 25%	1755
	21st to end	Day	4 13% 4 12% 7% 7% 7% 5% 6% 8% 26%	1487
March	1st to 10th	Day	5% 13% 5% 13% 8% 8% 8% 4 5% 6% 25%	3160
	11th to 20th	Day	8% 10% 3 6% 5% 5% 4 3 6% 10% 39%	3489
	21st to end	Day	7% 16% 7% 16% 7% 5% 4 3 5% 6% 25%	3825
April	1st to 10th	Day	10% 12% 3 7% 7% 6% 6% 5% 6% 7% 30%	2375
	11th to 20th	Day	12% 12% 5% 9% 5% 5% 5% 5% 6% 6% 30%	2440
	21st to end	Day	13% 10% 3 8% 6% 5% 5% 4 6% 8% 32%	2470
May	1st to 10th	Day	18% 12% 4 9% 6% 5% 5% 4 5% 6% 28%	4494
	11th to 20th	Day	12% 10% 3 8% 6% 6% 6% 5% 6% 8% 30%	4694
	21st to end	Day	14% 9% 4 10% 7% 5% 5% 4 6% 8% 28%	5161
June	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 5% 7% 9% 31%	2850
	11th to 20th	Day	19% 11% 3 8% 6% 6% 5% 5% 6% 7% 25%	2850
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 5% 7% 10% 38%	2850
July	1st to 10th	Day	8% 5% 2 5% 4 4 4 3 6% 9% 50%	4740
	11th to 20th	Day	9% 4 2 5% 4 5% 4 4 7% 10% 47%	4740
	21st to end	Day	7% 5% 2 5% 4 4 5% 4 6% 9% 50%	5138
August	1st to 10th	Day	11% 6% 2 6% 4 5% 4 3 6% 8% 45%	4498
	11th to 20th	Day	7% 5% 2 6% 4 5% 5% 4 7% 11% 44%	4043
	21st to end	Day	10% 4 2 5% 3 4 5% 5% 6% 9% 47%	4521
September	1st to 10th	Day	11% 6% 2 6% 4 5% 4 3 5% 8% 45%	2402
	11th to 20th	Day	15% 8% 2 6% 5% 4 4 2 5% 8% 42%	2090
	21st to end	Day	9% 7% 2 7% 3 4 4 3 6% 8% 46%	2090
October	1st to 10th	Day	8% 7% 3 6% 4 5% 6% 4 5% 7% 45%	3266
	11th to 20th	Day	6% 8% 3 7% 4 4 6% 4 7% 9% 41%	2973
	21st to end	Day	9% 9% 3 8% 5% 6% 5% 4 6% 7% 40%	3053
November	1st to 10th	Day	8% 15% 5% 11% 7% 6% 6% 3 6% 7% 25%	1568
	11th to 20th	Day	6% 13% 5% 12% 6% 5% 5% 4 6% 7% 31%	1525
	21st to end	Day	7% 9% 5% 12% 7% 7% 6% 4 6% 7% 31%	1400
December	1st to 10th	Day	11% 16% 4 11% 6% 6% 5% 4 5% 7% 24%	2290
	11th to 20th	Day	7% 11% 5% 14% 8% 7% 6% 5% 7% 7% 23%	2642
	21st to end	Day	3 7% 3 11% 7% 4 4 4 6% 7% 44%	3498
January	1st to 10th	Night	3 11% 5% 15% 8% 7% 6% 5% 7% 7% 26%	6766
	11th to 20th	Night	3 10% 5% 11% 7% 6% 6% 5% 5% 7% 34%	6739
	21st to end	Night	4 12% 5% 11% 5% 5% 5% 4 5% 8% 36%	7201
February	1st to 10th	Night	6% 11% 5% 13% 8% 7% 5% 5% 6% 7% 27%	2791
	11th to 20th	Night	5% 14% 4 10% 7% 7% 6% 6% 7% 8% 27%	2532
	21st to end	Night	5% 11% 4 9% 7% 5% 7% 6% 7% 8% 31%	2059
March	1st to 10th	Night	3 10% 5% 16% 9% 6% 5% 4 8% 9% 26%	3713
	11th to 20th	Night	5% 10% 3 8% 6% 5% 5% 5% 6% 9% 37%	3490
	21st to end	Night	6% 14% 7% 17% 8% 7% 5% 5% 7% 7% 20%	3828
April	1st to 10th	Night	9% 11% 3 9% 6% 6% 5% 4 7% 9% 32%	1804
	11th to 20th	Night	10% 11% 4 10% 7% 5% 6% 5% 6% 7% 29%	1691
	21st to end	Night	12% 10% 3 8% 5% 6% 4 4 7% 8% 32%	1710
May	1st to 10th	Night	24% 12% 4 9% 4 4 4 3 4 5% 27%	2468
	11th to 20th	Night	10% 9% 3 11% 6% 6% 6% 6% 7% 8% 30%	2199
	21st to end	Night	15% 9% 4 10% 6% 7% 5% 5% 7% 7% 25%	2414
June	1st to 10th	Night	14% 9% 3 8% 7% 5% 5% 6% 7% 7% 29%	1330
	11th to 20th	Night	16% 10% 3 8% 5% 6% 5% 4 7% 7% 27%	1330
	21st to end	Night	7% 5% 2 7% 5% 6% 6% 6% 7% 10% 39%	1330
July	1st to 10th	Night	8% 6% 3 7% 5% 5% 5% 4 6% 8% 44%	2220
	11th to 20th	Night	8% 4 2 5% 4 4 5% 4 8% 10% 46%	2220
	21st to end	Night	7% 5% 2 6% 4 4 4 4 7% 11% 47%	2414
August	1st to 10th	Night	12% 7% 2 6% 3 4 4 4 6% 7% 45%	2428
	11th to 20th	Night	7% 5% 3 6% 5% 5% 5% 4 7% 10% 42%	2795
	21st to end	Night	10% 5% 2 7% 5% 5% 5% 4 7% 9% 42%	3146
September	1st to 10th	Night	10% 5% 3 7% 5% 4 5% 3 5% 8% 44%	1776
	11th to 20th	Night	15% 7% 2 6% 4 4 3 4 4 7% 43%	2090
	21st to end	Night	8% 7% 2 6% 4 4 5% 4 7% 8% 44%	2090
October	1st to 10th	Night	9% 7% 3 8% 4 5% 5% 4 6% 8% 42%	3707
	11th to 20th	Night	7% 8% 3 7% 4 4 6% 4 8% 9% 41%	3952
	21st to end	Night	7% 10% 3 8% 6% 6% 6% 4 7% 8% 36%	4474
November	1st to 10th	Night	9% 15% 5% 8% 5% 5% 5% 4 6% 7% 31%	2730
	11th to 20th	Night	6% 12% 5% 11% 6% 6% 5% 4 6% 9% 30%	2870
	21st to end	Night	5% 12% 4 11% 7% 7% 5% 4 7% 8% 30%	3000
December	1st to 10th	Night	11% 16% 5% 12% 7% 5% 5% 4 5% 7% 24%	4890
	11th to 20th	Night	6% 15% 4 14% 8% 6% 5% 4 6% 8% 23%	5550
	21st to end	Night	3 7% 3 10% 6% 5% 5% 5% 6% 8% 42%	7458

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	54% 5% 11% 20% 9% 1	3179
	11th to 20th	Day	49% 6% 11% 13% 19% 2	3180
	21st to end	Day	44% 7% 19% 25% 6%	3797
February	1st to 10th	Day	55% 6% 13% 14% 10% 1	1608
	11th to 20th	Day	55% 7% 14% 15% 10% 1	1764
	21st to end	Day	52% 7% 14% 18% 9% 1	1487
March	1st to 10th	Day	55% 8% 13% 16% 8%	3160
	11th to 20th	Day	39% 8% 19% 21% 13%	3490
	21st to end	Day	58% 8% 11% 18% 4	3825
April	1st to 10th	Day	50% 9% 15% 17% 8% 1	2375
	11th to 20th	Day	50% 7% 13% 20% 9%	2440
	21st to end	Day	48% 8% 15% 21% 7% 2	2470
May	1st to 10th	Day	54% 8% 10% 23% 5%	4494
	11th to 20th	Day	47% 10% 12% 22% 8%	4698
	21st to end	Day	49% 11% 15% 17% 7% 1	5162
June	1st to 10th	Day	46% 8% 16% 22% 7% 1	2850
	11th to 20th	Day	55% 9% 14% 17% 4 1	2850
	21st to end	Day	37% 11% 23% 21% 7% 1	2850
July	1st to 10th	Day	31% 8% 17% 28% 15% 2	4666
	11th to 20th	Day	32% 8% 17% 33% 11%	4659
	21st to end	Day	30% 8% 17% 29% 15% 1	4976
August	1st to 10th	Day	37% 7% 16% 33% 6%	4480
	11th to 20th	Day	32% 7% 26% 28% 6%	4082
	21st to end	Day	33% 6% 24% 30% 7%	4520
September	1st to 10th	Day	37% 7% 18% 26% 10% 3	2402
	11th to 20th	Day	42% 5% 16% 28% 8% 1	2090
	21st to end	Day	35% 8% 18% 26% 11% 3	2090
October	1st to 10th	Day	39% 5% 19% 29% 7% 1	3266
	11th to 20th	Day	39% 5% 17% 28% 10% 1	2973
	21st to end	Day	42% 6% 13% 33% 6%	3053
November	1st to 10th	Day	56% 7% 13% 17% 6% 1	1568
	11th to 20th	Day	51% 7% 15% 19% 7% 1	1525
	21st to end	Day	50% 9% 17% 18% 6% 1	1400
December	1st to 10th	Day	60% 6% 17% 13% 4 1	2290
	11th to 20th	Day	58% 8% 16% 14% 3	2644
	21st to end	Day	39% 5% 10% 28% 16% 2	3498
January	1st to 10th	Night	54% 7% 13% 17% 7% 1	6766
	11th to 20th	Night	48% 6% 13% 15% 16% 2	6780
	21st to end	Night	46% 6% 17% 24% 6%	7201
February	1st to 10th	Night	54% 6% 12% 18% 10%	2791
	11th to 20th	Night	51% 8% 13% 16% 11% 1	2533
	21st to end	Night	46% 9% 14% 20% 10% 2	2059
March	1st to 10th	Night	50% 9% 14% 21% 6%	3713
	11th to 20th	Night	41% 8% 19% 21% 10% 1	3490
	21st to end	Night	58% 11% 12% 13% 6%	3828
April	1st to 10th	Night	47% 7% 15% 19% 11% 1	1804
	11th to 20th	Night	49% 7% 13% 20% 9% 2	1691
	21st to end	Night	46% 8% 14% 20% 10% 2	1710
May	1st to 10th	Night	57% 6% 10% 20% 6%	2468
	11th to 20th	Night	45% 11% 14% 22% 8% 1	2199
	21st to end	Night	50% 14% 13% 16% 6% 1	2414
June	1st to 10th	Night	48% 10% 13% 20% 7% 1	1330
	11th to 20th	Night	52% 10% 15% 16% 6% 1	1330
	21st to end	Night	37% 12% 20% 24% 7% 1	1330
July	1st to 10th	Night	36% 8% 19% 19% 17% 1	2185
	11th to 20th	Night	30% 9% 15% 34% 9% 2	2178
	21st to end	Night	30% 7% 20% 28% 13% 2	2337
August	1st to 10th	Night	37% 7% 17% 32% 6%	2421
	11th to 20th	Night	35% 7% 22% 28% 7% 1	2822
	21st to end	Night	38% 7% 20% 29% 7% 1	3146
September	1st to 10th	Night	37% 7% 16% 22% 14% 4	1776
	11th to 20th	Night	39% 7% 14% 27% 10% 3	2090
	21st to end	Night	34% 8% 16% 25% 14% 3	2090
October	1st to 10th	Night	40% 6% 18% 26% 10% 1	3707
	11th to 20th	Night	38% 6% 16% 31% 8% 1	3952
	21st to end	Night	44% 6% 16% 28% 5%	4474
November	1st to 10th	Night	50% 8% 13% 21% 7% 1	2730
	11th to 20th	Night	50% 8% 15% 18% 9% 1	2870
	21st to end	Night	50% 8% 17% 18% 6% 1	3000
December	1st to 10th	Night	60% 6% 14% 14% 5% 1	4890
	11th to 20th	Night	57% 7% 17% 12% 5%	5547
	21st to end	Night	38% 5% 13% 24% 16% 3	7458

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	6% 7% 29% 36% 18% 5%	200
	11th to 20th	Day	6% 7% 35% 31% 20% 3	200
	21st to end	Day	10% 9% 36% 26% 12% 7%	220
February	1st to 10th	Day	13% 10% 27% 33% 12% 5%	205
	11th to 20th	Day	11% 7% 29% 36% 13% 3	300
	21st to end	Day	7% 8% 31% 34% 16% 5%	275
March	1st to 10th	Day	12% 7% 33% 29% 17% 2	460
	11th to 20th	Day	10% 5% 34% 29% 16% 5%	460
	21st to end	Day	14% 8% 30% 29% 16% 4	506
April	1st to 10th	Day	12% 13% 31% 29% 11% 3	460
	11th to 20th	Day	15% 9% 27% 29% 16% 5%	452
	21st to end	Day	17% 8% 26% 34% 12% 3	460
May	1st to 10th	Day	16% 8% 25% 29% 17% 5%	605
	11th to 20th	Day	11% 7% 24% 34% 19% 5%	675
	21st to end	Day	18% 5% 20% 29% 19% 9%	734
June	1st to 10th	Day	17% 8% 23% 34% 15% 4	680
	11th to 20th	Day	19% 9% 25% 27% 16% 4	680
	21st to end	Day	12% 4 22% 32% 22% 8%	680
July	1st to 10th	Day	11% 3 18% 34% 25% 8%	671
	11th to 20th	Day	14% 4 18% 34% 24% 7%	668
	21st to end	Day	7% 4 18% 33% 28% 9%	739
August	1st to 10th	Day	11% 4 21% 30% 23% 10%	545
	11th to 20th	Day	9% 5% 21% 31% 26% 8%	477
	21st to end	Day	10% 8% 17% 32% 25% 8%	539
September	1st to 10th	Day	13% 8% 27% 28% 20% 5%	490
	11th to 20th	Day	18% 6% 26% 27% 19% 4	490
	21st to end	Day	12% 10% 31% 29% 15% 3	490
October	1st to 10th	Day	16% 6% 32% 23% 17% 6%	357
	11th to 20th	Day	11% 8% 30% 33% 16% 2	300
	21st to end	Day	12% 9% 34% 29% 13% 2	330
November	1st to 10th	Day	15% 8% 33% 31% 10% 3	300
	11th to 20th	Day	13% 8% 38% 31% 10% 1	263
	21st to end	Day	9% 8% 32% 28% 20% 5%	200
December	1st to 10th	Day	10% 8% 33% 33% 12% 5%	200
	11th to 20th	Day	10% 9% 30% 37% 13% 2	200
	21st to end	Day	6% 5% 25% 42% 17% 4	220
January	1st to 10th	Night	9% 8% 36% 31% 15% 1	1000
	11th to 20th	Night	12% 8% 35% 33% 12% 1	1000
	21st to end	Night	13% 11% 33% 32% 9% 2	986
February	1st to 10th	Night	9% 9% 26% 37% 16% 3	800
	11th to 20th	Night	11% 6% 35% 34% 14% 1	784
	21st to end	Night	9% 4 29% 37% 18% 3	646
March	1st to 10th	Night	8% 6% 29% 39% 17% 2	760
	11th to 20th	Night	9% 5% 34% 35% 13% 3	760
	21st to end	Night	13% 4 29% 38% 14% 2	836
April	1st to 10th	Night	10% 8% 32% 30% 18% 3	651
	11th to 20th	Night	14% 7% 31% 37% 9% 1	563
	21st to end	Night	16% 8% 26% 36% 13% 1	570
May	1st to 10th	Night	18% 7% 25% 35% 13% 2	489
	11th to 20th	Night	13% 5% 24% 39% 18% 1	374
	21st to end	Night	21% 5% 22% 31% 18% 2	411
June	1st to 10th	Night	18% 8% 24% 36% 11% 2	380
	11th to 20th	Night	21% 6% 25% 30% 18% 1	380
	21st to end	Night	12% 2 24% 37% 23% 2	380
July	1st to 10th	Night	11% 4 17% 43% 25% 1	370
	11th to 20th	Night	12% 3 22% 44% 17% 1	368
	21st to end	Night	9% 4 18% 40% 27% 2	416
August	1st to 10th	Night	13% 2 21% 33% 27% 4	378
	11th to 20th	Night	11% 4 15% 43% 24% 2	548
	21st to end	Night	12% 4 19% 42% 22% 1	627
September	1st to 10th	Night	12% 3 24% 40% 18% 2	589
	11th to 20th	Night	17% 4 21% 41% 17% 1	760
	21st to end	Night	11% 5% 31% 38% 13% 2	760
October	1st to 10th	Night	15% 4 31% 35% 14% 1	760
	11th to 20th	Night	11% 5% 35% 33% 13% 2	760
	21st to end	Night	13% 8% 33% 35% 11%	841
November	1st to 10th	Night	16% 5% 36% 32% 9% 1	975
	11th to 20th	Night	12% 9% 38% 30% 8% 3	1000
	21st to end	Night	9% 6% 40% 34% 10% 1	1000
December	1st to 10th	Night	14% 7% 35% 29% 13% 2	1000
	11th to 20th	Night	11% 7% 37% 32% 11% 3	1000
	21st to end	Night	12% 3 35% 34% 14% 2	1100

Page generated at 2025-02-22 04:51:38. Version ac07

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