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 2024-02-05.

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	10% 8% 4 7% 7% 4 6% 5% 6% 8% 35%	77625
	Night	8% 9% 4 8% 7% 4 6% 6% 6% 8% 34%	81189
Transparency	Day	45% 8% 16% 21% 8% 1	77327
	Night	45% 8% 15% 21% 9% 1	81067
Seeing	Day	13% 7% 25% 31% 18% 5%	14352
	Night	12% 6% 30% 35% 15% 2	23646

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	4 11% 6% 11% 11% 4 5% 5% 5% 9% 30%	2219
	11th to 20th	Day	4 8% 4 10% 7% 4 7% 9% 9% 9% 29%	2199
	21st to end	Day	5% 11% 5% 9% 7% 4 5% 5% 6% 8% 35%	2643
February	1st to 10th	Day	8% 13% 5% 10% 8% 6% 5% 4 6% 9% 27%	1479
	11th to 20th	Day	7% 14% 6% 10% 8% 4 7% 7% 7% 7% 23%	1575
	21st to end	Day	5% 11% 6% 11% 8% 4 7% 8% 6% 8% 26%	1368
March	1st to 10th	Day	8% 12% 5% 9% 10% 6% 8% 7% 6% 5% 24%	1809
	11th to 20th	Day	8% 10% 5% 7% 7% 4 7% 5% 6% 9% 32%	1979
	21st to end	Day	9% 12% 6% 11% 7% 5% 5% 5% 6% 8% 26%	2178
April	1st to 10th	Day	11% 9% 5% 7% 8% 5% 6% 7% 6% 7% 29%	2249
	11th to 20th	Day	13% 11% 4 9% 6% 3 6% 6% 6% 7% 30%	2310
	21st to end	Day	13% 9% 4 7% 7% 4 5% 5% 5% 8% 32%	2340
May	1st to 10th	Day	12% 11% 4 7% 7% 4 6% 7% 6% 8% 28%	2547
	11th to 20th	Day	9% 5% 3 6% 7% 4 7% 5% 6% 8% 39%	2654
	21st to end	Day	17% 8% 3 7% 6% 3 5% 5% 6% 8% 31%	2917
June	1st to 10th	Day	17% 7% 3 6% 6% 4 6% 5% 7% 9% 31%	2700
	11th to 20th	Day	20% 10% 4 7% 7% 5% 5% 6% 6% 8% 24%	2700
	21st to end	Day	11% 5% 2 5% 5% 4 6% 7% 7% 10% 38%	2700
July	1st to 10th	Day	11% 5% 2 5% 6% 3 6% 5% 6% 9% 43%	2700
	11th to 20th	Day	13% 4 2 5% 5% 3 5% 6% 7% 10% 41%	2700
	21st to end	Day	8% 4 2 4 5% 3 5% 6% 7% 9% 47%	2938
August	1st to 10th	Day	11% 6% 2 5% 5% 3 5% 5% 7% 10% 42%	2562
	11th to 20th	Day	10% 5% 1 5% 5% 3 5% 5% 5% 9% 46%	2314
	21st to end	Day	9% 5% 2 5% 4 3 5% 6% 7% 10% 45%	2574
September	1st to 10th	Day	12% 6% 2 5% 5% 4 4 5% 5% 8% 43%	2277
	11th to 20th	Day	15% 8% 3 4 6% 3 4 3 5% 8% 42%	1980
	21st to end	Day	9% 7% 3 6% 4 3 4 4 6% 9% 46%	1980
October	1st to 10th	Day	12% 10% 3 6% 5% 4 5% 4 4 6% 41%	1854
	11th to 20th	Day	9% 9% 5% 6% 5% 3 5% 5% 6% 7% 41%	1699
	21st to end	Day	8% 11% 5% 7% 7% 4 6% 7% 6% 7% 33%	1760
November	1st to 10th	Day	9% 14% 6% 9% 9% 4 6% 5% 6% 7% 25%	1488
	11th to 20th	Day	6% 11% 6% 10% 8% 4 5% 5% 6% 7% 31%	1449
	21st to end	Day	7% 8% 5% 10% 8% 5% 6% 5% 7% 7% 33%	1330
December	1st to 10th	Day	9% 12% 5% 10% 11% 6% 7% 5% 5% 5% 25%	1330
	11th to 20th	Day	6% 9% 5% 13% 9% 5% 7% 6% 7% 7% 26%	1682
	21st to end	Day	4 8% 3 8% 8% 3 5% 5% 5% 6% 45%	2442
January	1st to 10th	Night	4 11% 5% 12% 9% 5% 5% 7% 7% 8% 27%	4726
	11th to 20th	Night	4 7% 5% 10% 10% 5% 7% 8% 6% 8% 31%	4699
	21st to end	Night	5% 12% 4 10% 7% 4 5% 5% 6% 8% 34%	5041
February	1st to 10th	Night	6% 9% 6% 10% 9% 6% 6% 6% 6% 8% 29%	2574
	11th to 20th	Night	6% 14% 5% 9% 8% 5% 7% 6% 7% 8% 25%	2272
	21st to end	Night	6% 10% 5% 8% 7% 4 6% 7% 7% 8% 32%	1887
March	1st to 10th	Night	5% 11% 5% 9% 9% 4 7% 6% 7% 9% 27%	2150
	11th to 20th	Night	6% 10% 5% 8% 7% 4 7% 7% 6% 9% 30%	1980
	21st to end	Night	9% 11% 6% 9% 7% 5% 5% 7% 7% 9% 24%	2178
April	1st to 10th	Night	9% 9% 4 8% 7% 5% 5% 5% 7% 9% 33%	1710
	11th to 20th	Night	10% 11% 4 9% 7% 4 6% 7% 6% 8% 30%	1601
	21st to end	Night	13% 10% 3 7% 5% 4 5% 4 7% 8% 33%	1620
May	1st to 10th	Night	14% 11% 4 8% 5% 3 5% 5% 7% 7% 30%	1410
	11th to 20th	Night	11% 7% 3 8% 6% 4 5% 7% 6% 6% 36%	1239
	21st to end	Night	19% 8% 3 7% 6% 4 5% 4 6% 7% 33%	1358
June	1st to 10th	Night	15% 8% 4 7% 8% 4 5% 7% 7% 7% 29%	1260
	11th to 20th	Night	17% 9% 4 7% 6% 4 6% 5% 6% 8% 27%	1260
	21st to end	Night	7% 5% 2 5% 7% 5% 6% 7% 7% 10% 38%	1260
July	1st to 10th	Night	9% 5% 2 5% 5% 4 5% 6% 6% 11% 41%	1260
	11th to 20th	Night	12% 4 2 5% 5% 4 6% 6% 7% 11% 38%	1260
	21st to end	Night	8% 4 2 5% 5% 3 4 6% 7% 10% 47%	1379
August	1st to 10th	Night	9% 6% 3 6% 6% 4 6% 5% 7% 9% 40%	1373
	11th to 20th	Night	10% 6% 2 5% 6% 4 5% 5% 7% 9% 41%	1586
	21st to end	Night	9% 5% 2 5% 6% 3 5% 5% 6% 8% 46%	1782
September	1st to 10th	Night	10% 5% 3 6% 6% 4 5% 4 6% 8% 44%	1682
	11th to 20th	Night	14% 6% 2 5% 5% 3 3 5% 4 7% 44%	1980
	21st to end	Night	8% 7% 2 5% 5% 3 5% 6% 6% 8% 45%	1980
October	1st to 10th	Night	11% 8% 4 8% 6% 3 4 5% 5% 8% 39%	2106
	11th to 20th	Night	8% 9% 4 7% 6% 3 6% 6% 6% 8% 38%	2258
	21st to end	Night	7% 11% 4 7% 7% 4 6% 5% 7% 8% 33%	2578
November	1st to 10th	Night	9% 14% 6% 7% 6% 4 5% 6% 6% 7% 31%	2590
	11th to 20th	Night	7% 10% 6% 9% 7% 4 6% 5% 6% 9% 31%	2726
	21st to end	Night	5% 10% 5% 9% 8% 4 6% 5% 7% 8% 31%	2850
December	1st to 10th	Night	8% 12% 6% 10% 8% 4 6% 5% 6% 8% 28%	2850
	11th to 20th	Night	5% 10% 5% 11% 9% 4 6% 6% 7% 9% 29%	3510
	21st to end	Night	4 8% 4 7% 6% 4 5% 5% 6% 9% 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	51% 7% 12% 21% 9% 1	2219
	11th to 20th	Day	45% 7% 13% 15% 18% 2	2220
	21st to end	Day	45% 8% 16% 24% 6%	2643
February	1st to 10th	Day	53% 6% 14% 15% 10% 1	1479
	11th to 20th	Day	56% 7% 14% 15% 8%	1584
	21st to end	Day	53% 6% 14% 18% 9%	1368
March	1st to 10th	Day	58% 10% 14% 15% 4	1809
	11th to 20th	Day	46% 8% 13% 23% 10% 1	1980
	21st to end	Day	55% 8% 16% 15% 5%	2178
April	1st to 10th	Day	50% 9% 15% 17% 8% 1	2249
	11th to 20th	Day	51% 7% 13% 19% 9%	2310
	21st to end	Day	48% 8% 15% 21% 6% 2	2340
May	1st to 10th	Day	51% 9% 14% 19% 7%	2547
	11th to 20th	Day	40% 8% 14% 26% 11% 1	2658
	21st to end	Day	49% 9% 15% 19% 8%	2918
June	1st to 10th	Day	47% 8% 16% 21% 7%	2700
	11th to 20th	Day	56% 10% 14% 16% 4 1	2700
	21st to end	Day	37% 11% 24% 20% 6% 1	2700
July	1st to 10th	Day	37% 9% 22% 24% 6% 1	2626
	11th to 20th	Day	38% 11% 21% 26% 4	2619
	21st to end	Day	32% 11% 22% 29% 6%	2775
August	1st to 10th	Day	37% 10% 23% 25% 6%	2544
	11th to 20th	Day	32% 10% 25% 24% 9%	2314
	21st to end	Day	33% 9% 21% 26% 10% 1	2574
September	1st to 10th	Day	38% 7% 18% 26% 8% 2	2277
	11th to 20th	Day	42% 5% 16% 28% 8% 1	1980
	21st to end	Day	35% 8% 18% 26% 10% 2	1980
October	1st to 10th	Day	45% 6% 17% 21% 10% 1	1854
	11th to 20th	Day	41% 7% 19% 23% 9% 1	1699
	21st to end	Day	48% 9% 13% 21% 9%	1760
November	1st to 10th	Day	56% 7% 13% 16% 6% 1	1488
	11th to 20th	Day	51% 8% 15% 20% 6%	1449
	21st to end	Day	48% 9% 17% 18% 6% 1	1330
December	1st to 10th	Day	59% 7% 10% 16% 7% 2	1330
	11th to 20th	Day	52% 10% 15% 17% 5% 1	1684
	21st to end	Day	38% 6% 10% 27% 16% 3	2442
January	1st to 10th	Night	51% 9% 13% 19% 6% 2	4726
	11th to 20th	Night	49% 7% 13% 15% 13% 3	4740
	21st to end	Night	46% 7% 15% 23% 7% 1	5041
February	1st to 10th	Night	53% 6% 12% 19% 10%	2574
	11th to 20th	Night	53% 9% 13% 16% 8% 1	2273
	21st to end	Night	45% 9% 14% 19% 10% 2	1887
March	1st to 10th	Night	49% 10% 15% 19% 6%	2150
	11th to 20th	Night	49% 7% 13% 21% 10% 1	1980
	21st to end	Night	52% 9% 16% 15% 7% 1	2178
April	1st to 10th	Night	46% 7% 15% 19% 12% 1	1710
	11th to 20th	Night	49% 7% 14% 20% 8% 2	1601
	21st to end	Night	46% 7% 14% 21% 10% 2	1620
May	1st to 10th	Night	49% 8% 13% 21% 8% 1	1410
	11th to 20th	Night	45% 8% 11% 22% 13% 1	1239
	21st to end	Night	49% 8% 11% 21% 8% 2	1358
June	1st to 10th	Night	50% 10% 13% 20% 7%	1260
	11th to 20th	Night	52% 10% 15% 15% 6% 1	1260
	21st to end	Night	37% 12% 21% 23% 6% 1	1260
July	1st to 10th	Night	35% 12% 21% 24% 7% 1	1225
	11th to 20th	Night	36% 13% 22% 21% 7%	1218
	21st to end	Night	29% 10% 23% 28% 9%	1302
August	1st to 10th	Night	39% 10% 20% 23% 7%	1366
	11th to 20th	Night	36% 9% 20% 26% 8% 2	1586
	21st to end	Night	35% 8% 18% 28% 10% 2	1782
September	1st to 10th	Night	37% 8% 16% 22% 13% 4	1682
	11th to 20th	Night	38% 7% 14% 27% 10% 3	1980
	21st to end	Night	34% 8% 16% 25% 14% 3	1980
October	1st to 10th	Night	42% 7% 16% 23% 11% 1	2106
	11th to 20th	Night	41% 8% 16% 23% 10% 1	2258
	21st to end	Night	46% 8% 16% 21% 7% 1	2578
November	1st to 10th	Night	50% 8% 13% 21% 7% 1	2590
	11th to 20th	Night	49% 8% 15% 18% 9% 1	2726
	21st to end	Night	48% 8% 18% 19% 7% 1	2850
December	1st to 10th	Night	54% 7% 10% 19% 8% 2	2850
	11th to 20th	Night	49% 10% 18% 17% 6%	3507
	21st to end	Night	36% 6% 14% 22% 16% 5%	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	5% 8% 27% 36% 19% 5%	180
	11th to 20th	Day	6% 6% 34% 31% 21% 3	180
	21st to end	Day	9% 8% 34% 28% 13% 8%	198
February	1st to 10th	Day	14% 9% 28% 33% 11% 5%	172
	11th to 20th	Day	14% 8% 30% 33% 13% 1	240
	21st to end	Day	8% 5% 32% 33% 17% 6%	234
March	1st to 10th	Day	12% 8% 32% 29% 17% 2	420
	11th to 20th	Day	10% 5% 34% 30% 15% 5%	420
	21st to end	Day	15% 7% 29% 29% 16% 4	462
April	1st to 10th	Day	11% 12% 31% 30% 12% 3	420
	11th to 20th	Day	16% 9% 25% 29% 16% 5%	412
	21st to end	Day	18% 7% 25% 35% 12% 2	420
May	1st to 10th	Day	14% 8% 25% 29% 18% 6%	557
	11th to 20th	Day	10% 6% 23% 35% 20% 5%	625
	21st to end	Day	19% 5% 20% 30% 18% 9%	679
June	1st to 10th	Day	17% 6% 22% 35% 15% 4	630
	11th to 20th	Day	20% 9% 24% 26% 17% 4	630
	21st to end	Day	12% 4 22% 32% 22% 8%	630
July	1st to 10th	Day	11% 4 18% 34% 25% 8%	621
	11th to 20th	Day	15% 4 18% 34% 23% 5%	618
	21st to end	Day	7% 4 18% 34% 28% 9%	684
August	1st to 10th	Day	12% 4 20% 31% 23% 10%	502
	11th to 20th	Day	10% 5% 21% 30% 26% 8%	437
	21st to end	Day	10% 7% 16% 32% 26% 8%	495
September	1st to 10th	Day	14% 8% 28% 29% 18% 4	450
	11th to 20th	Day	19% 6% 25% 27% 19% 4	450
	21st to end	Day	13% 10% 30% 29% 15% 4	450
October	1st to 10th	Day	17% 7% 30% 23% 18% 6%	324
	11th to 20th	Day	13% 7% 30% 33% 16% 2	270
	21st to end	Day	12% 10% 35% 29% 12% 2	297
November	1st to 10th	Day	16% 8% 33% 30% 9% 3	270
	11th to 20th	Day	14% 8% 37% 31% 9% 1	237
	21st to end	Day	7% 9% 33% 26% 19% 6%	180
December	1st to 10th	Day	8% 7% 34% 32% 13% 5%	180
	11th to 20th	Day	10% 9% 29% 38% 13% 2	180
	21st to end	Day	7% 6% 26% 43% 16% 4	198
January	1st to 10th	Night	9% 9% 35% 31% 15% 1	950
	11th to 20th	Night	11% 7% 34% 34% 12% 1	950
	21st to end	Night	13% 11% 31% 33% 10% 2	937
February	1st to 10th	Night	10% 9% 26% 36% 16% 3	738
	11th to 20th	Night	12% 6% 36% 32% 13% 1	704
	21st to end	Night	9% 3 27% 39% 18% 3	592
March	1st to 10th	Night	8% 5% 28% 39% 17% 2	720
	11th to 20th	Night	10% 4 34% 36% 13% 3	720
	21st to end	Night	14% 4 28% 37% 14% 2	792
April	1st to 10th	Night	9% 7% 31% 31% 19% 3	617
	11th to 20th	Night	14% 7% 31% 38% 9% 2	533
	21st to end	Night	16% 8% 26% 36% 13% 1	540
May	1st to 10th	Night	18% 6% 25% 35% 14% 2	464
	11th to 20th	Night	13% 4 23% 39% 19% 1	354
	21st to end	Night	22% 5% 22% 31% 18% 3	389
June	1st to 10th	Night	19% 7% 23% 37% 12% 2	360
	11th to 20th	Night	22% 6% 23% 30% 18% 1	360
	21st to end	Night	11% 2 23% 38% 23% 3	360
July	1st to 10th	Night	12% 4 17% 42% 25% 1	350
	11th to 20th	Night	13% 3 23% 44% 17% 1	348
	21st to end	Night	10% 3 18% 41% 27% 2	394
August	1st to 10th	Night	12% 2 21% 34% 27% 4	358
	11th to 20th	Night	12% 4 15% 44% 24% 2	518
	21st to end	Night	11% 4 20% 42% 23% 1	594
September	1st to 10th	Night	13% 4 24% 40% 18% 2	558
	11th to 20th	Night	16% 4 21% 41% 17% 1	720
	21st to end	Night	12% 4 30% 39% 14% 2	720
October	1st to 10th	Night	15% 3 30% 35% 15% 2	720
	11th to 20th	Night	12% 5% 35% 32% 14% 2	720
	21st to end	Night	13% 8% 34% 34% 11%	796
November	1st to 10th	Night	16% 6% 36% 32% 10% 1	925
	11th to 20th	Night	12% 9% 38% 30% 8% 3	950
	21st to end	Night	8% 5% 41% 34% 10% 1	950
December	1st to 10th	Night	13% 7% 34% 30% 14% 3	950
	11th to 20th	Night	10% 7% 37% 32% 11% 3	950
	21st to end	Night	13% 3 35% 33% 14% 2	1045

Page generated at 2024-02-02 03:20:30. Version ac07

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