Burley/Heyburn
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burley/Heyburn clear sky chart from 2005-11-06 to 2025-07-21.

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	5% 7% 2 6% 4 4 4 3 5% 7% 53%	123234
	Night	6% 7% 2 6% 4 4 4 4 6% 8% 49%	124743
Transparency	Day	31% 4 10% 23% 20% 13%	122985
	Night	33% 4 11% 23% 18% 10%	124580
Seeing	Day	10% 11% 24% 27% 21% 8%	15382
	Night	9% 8% 21% 37% 22% 3	25271

By Month

Percentage Cloud Cover SW (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	9% 17% 4 11% 7% 5% 5% 4 7% 7% 24%	3639
	11th to 20th	Day	6% 11% 7% 12% 6% 5% 4 4 4 6% 35%	3640
	21st to end	Day	7% 10% 3 7% 4 4 4 3 5% 7% 46%	4349
February	1st to 10th	Day	7% 13% 4 11% 6% 4 4 4 6% 7% 34%	1800
	11th to 20th	Day	8% 14% 4 8% 5% 5% 5% 3 6% 7% 36%	1895
	21st to end	Day	6% 12% 4 10% 6% 5% 4 3 6% 8% 37%	1650
March	1st to 10th	Day	8% 14% 4 8% 5% 4 4 3 5% 7% 38%	4595
	11th to 20th	Day	5% 9% 2 7% 4 4 4 4 6% 7% 47%	5000
	21st to end	Day	7% 10% 3 9% 6% 6% 6% 4 6% 8% 33%	5486
April	1st to 10th	Day	7% 9% 3 6% 5% 4 5% 4 7% 7% 42%	2334
	11th to 20th	Day	6% 9% 3 6% 5% 5% 4 4 6% 7% 46%	2516
	21st to end	Day	7% 6% 2 6% 5% 5% 4 4 6% 8% 47%	2600
May	1st to 10th	Day	5% 6% 2 5% 4 4 4 3 5% 8% 52%	5880
	11th to 20th	Day	6% 5% 2 5% 4 3 4 3 5% 7% 56%	5841
	21st to end	Day	4 4 1 4 3 3 4 3 5% 8% 60%	6500
June	1st to 10th	Day	5% 4 1 4 4 4 5% 4 7% 9% 54%	2800
	11th to 20th	Day	5% 3 1 4 3 4 4 3 4 8% 62%	2800
	21st to end	Day	2 2 1 2 2 2 3 3 5% 6% 74%	2800
July	1st to 10th	Day	1 1 2 2 2 2 2 4 5% 80%	4560
	11th to 20th	Day	2 2 1 3 2 3 4 4 5% 6% 68%	4560
	21st to end	Day	2 3 1 3 3 3 4 3 5% 6% 67%	4579
August	1st to 10th	Day	2 3 1 3 3 4 4 4 6% 8% 62%	4092
	11th to 20th	Day	2 1 1 2 2 2 3 2 4 6% 75%	4028
	21st to end	Day	1 2 1 3 2 2 3 3 4 5% 74%	4433
September	1st to 10th	Day	3 2 1 2 2 2 3 3 5% 7% 71%	2180
	11th to 20th	Day	3 3 2 3 2 2 3 3 5% 6% 67%	2090
	21st to end	Day	5% 4 1 4 3 3 3 2 4 4 67%	2090
October	1st to 10th	Day	5% 3 1 4 3 3 3 3 4 5% 67%	3458
	11th to 20th	Day	5% 5% 2 4 3 3 3 2 4 5% 65%	3150
	21st to end	Day	4 5% 2 5% 3 4 4 4 6% 8% 54%	3141
November	1st to 10th	Day	7% 9% 2 6% 5% 4 5% 4 5% 9% 45%	1764
	11th to 20th	Day	8% 6% 2 7% 5% 4 5% 5% 7% 8% 43%	1800
	21st to end	Day	6% 11% 3 6% 5% 5% 4 4 6% 9% 42%	1756
December	1st to 10th	Day	5% 7% 3 7% 4 3 3 2 4 8% 53%	2620
	11th to 20th	Day	9% 11% 3 7% 4 6% 7% 6% 8% 10% 28%	2804
	21st to end	Day	10% 14% 5% 9% 4 4 5% 4 6% 7% 31%	4004
January	1st to 10th	Night	9% 13% 4 11% 6% 6% 6% 4 7% 9% 27%	6306
	11th to 20th	Night	8% 13% 5% 12% 6% 5% 5% 4 5% 7% 29%	6320
	21st to end	Night	7% 10% 3 7% 4 4 4 4 6% 7% 46%	6619
February	1st to 10th	Night	9% 11% 4 8% 6% 5% 5% 5% 7% 8% 33%	2600
	11th to 20th	Night	7% 11% 3 8% 5% 4 5% 3 5% 8% 42%	2389
	21st to end	Night	4 9% 4 8% 5% 4 5% 5% 8% 10% 39%	1980
March	1st to 10th	Night	8% 12% 3 7% 4 4 5% 4 6% 7% 40%	5299
	11th to 20th	Night	3 8% 2 7% 5% 5% 4 5% 6% 8% 46%	5000
	21st to end	Night	6% 8% 3 7% 5% 5% 5% 4 7% 10% 42%	5489
April	1st to 10th	Night	6% 9% 2 6% 6% 5% 4 4 5% 7% 46%	2063
	11th to 20th	Night	7% 8% 2 6% 5% 4 5% 4 5% 6% 49%	1831
	21st to end	Night	7% 5% 2 6% 4 3 4 4 6% 8% 52%	1800
May	1st to 10th	Night	8% 6% 2 5% 3 4 3 3 5% 7% 55%	4100
	11th to 20th	Night	5% 4 1 5% 3 4 5% 4 6% 7% 55%	4074
	21st to end	Night	4 4 1 4 3 4 4 4 5% 7% 59%	4389
June	1st to 10th	Night	4 3 1 5% 3 4 4 5% 7% 10% 54%	1600
	11th to 20th	Night	4 4 1 5% 2 3 3 3 5% 8% 62%	1600
	21st to end	Night	3 2 1 2 3 2 4 2 4 6% 72%	1600
July	1st to 10th	Night	1 1 1 2 2 2 3 2 4 6% 75%	2620
	11th to 20th	Night	1 2 1 3 2 2 3 2 6% 6% 72%	2620
	21st to end	Night	1 2 1 4 3 4 4 4 5% 8% 64%	2977
August	1st to 10th	Night	2 2 1 4 3 3 4 4 5% 8% 64%	2847
	11th to 20th	Night	2 2 1 3 2 3 3 3 5% 7% 68%	2811
	21st to end	Night	2 2 1 3 2 2 2 3 3 4 76%	3233
September	1st to 10th	Night	2 2 1 2 2 2 3 2 4 7% 73%	1998
	11th to 20th	Night	4 3 1 5% 2 3 3 3 4 7% 65%	2090
	21st to end	Night	5% 3 1 3 3 3 3 2 3 5% 69%	2090
October	1st to 10th	Night	4 3 1 3 2 2 3 2 3 5% 71%	3521
	11th to 20th	Night	6% 6% 2 5% 3 3 4 3 4 6% 58%	3778
	21st to end	Night	5% 6% 2 5% 3 4 5% 4 7% 9% 51%	4413
November	1st to 10th	Night	9% 7% 2 5% 4 4 4 4 6% 7% 47%	2535
	11th to 20th	Night	9% 7% 2 6% 5% 5% 4 4 6% 9% 44%	2600
	21st to end	Night	6% 8% 3 6% 4 5% 5% 4 7% 8% 44%	2617
December	1st to 10th	Night	6% 7% 3 5% 4 3 4 3 5% 11% 51%	4570
	11th to 20th	Night	9% 12% 5% 9% 5% 4 5% 4 6% 10% 31%	5412
	21st to end	Night	11% 11% 5% 10% 5% 5% 5% 5% 7% 9% 29%	6952

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	59% 4 16% 19% 2 1	3639
	11th to 20th	Day	51% 5% 18% 19% 5% 2	3640
	21st to end	Day	39% 4 16% 27% 13% 1	4349
February	1st to 10th	Day	51% 5% 18% 20% 5% 1	1800
	11th to 20th	Day	49% 4 16% 21% 9% 1	1905
	21st to end	Day	47% 5% 13% 22% 10% 2	1650
March	1st to 10th	Day	46% 5% 8% 30% 8% 5%	4595
	11th to 20th	Day	35% 5% 10% 33% 17% 1	5000
	21st to end	Day	48% 5% 20% 20% 6%	5486
April	1st to 10th	Day	40% 5% 13% 23% 15% 4	2334
	11th to 20th	Day	38% 4 10% 27% 17% 4	2519
	21st to end	Day	35% 3 12% 27% 20% 2	2600
May	1st to 10th	Day	30% 5% 6% 27% 28% 4	5880
	11th to 20th	Day	27% 3 7% 28% 29% 5%	5844
	21st to end	Day	23% 3 10% 31% 26% 7%	6501
June	1st to 10th	Day	27% 4 13% 31% 22% 3	2800
	11th to 20th	Day	23% 3 8% 25% 31% 10%	2800
	21st to end	Day	12% 3 4 23% 36% 22%	2800
July	1st to 10th	Day	9% 2 2 12% 22% 54%	4491
	11th to 20th	Day	15% 3 3 8% 25% 47%	4485
	21st to end	Day	18% 2 3 10% 27% 40%	4434
August	1st to 10th	Day	19% 3 4 15% 25% 34%	4078
	11th to 20th	Day	12% 3 3 14% 39% 30%	4067
	21st to end	Day	14% 2 3 14% 35% 32%	4432
September	1st to 10th	Day	15% 3 6% 15% 33% 29%	2180
	11th to 20th	Day	18% 2 7% 27% 27% 19%	2090
	21st to end	Day	22% 2 4 24% 35% 13%	2090
October	1st to 10th	Day	21% 2 6% 19% 31% 21%	3458
	11th to 20th	Day	24% 2 6% 30% 33% 6%	3150
	21st to end	Day	28% 4 10% 34% 20% 5%	3141
November	1st to 10th	Day	38% 5% 12% 27% 16% 3	1764
	11th to 20th	Day	39% 4 17% 30% 9% 1	1800
	21st to end	Day	41% 4 15% 27% 12% 1	1756
December	1st to 10th	Day	32% 5% 14% 41% 7% 2	2620
	11th to 20th	Day	48% 4 22% 23% 2	2803
	21st to end	Day	51% 4 17% 19% 8%	4004
January	1st to 10th	Night	53% 6% 17% 22% 3	6306
	11th to 20th	Night	54% 4 16% 22% 3 1	6320
	21st to end	Night	38% 4 15% 27% 15% 1	6619
February	1st to 10th	Night	48% 6% 17% 22% 6% 1	2600
	11th to 20th	Night	42% 4 18% 23% 12% 1	2390
	21st to end	Night	40% 5% 16% 27% 11% 1	1980
March	1st to 10th	Night	41% 6% 9% 25% 14% 5%	5299
	11th to 20th	Night	35% 4 12% 29% 19% 1	5000
	21st to end	Night	37% 4 20% 26% 12% 1	5489
April	1st to 10th	Night	38% 4 11% 26% 16% 6%	2063
	11th to 20th	Night	36% 5% 10% 26% 21% 3	1831
	21st to end	Night	31% 4 11% 29% 24% 2	1800
May	1st to 10th	Night	29% 4 9% 23% 29% 6%	4097
	11th to 20th	Night	25% 5% 8% 26% 29% 8%	4075
	21st to end	Night	23% 4 8% 25% 33% 7%	4389
June	1st to 10th	Night	25% 3 15% 27% 25% 6%	1600
	11th to 20th	Night	22% 3 7% 23% 32% 14%	1600
	21st to end	Night	16% 2 4 15% 33% 31%	1600
July	1st to 10th	Night	12% 2 1 9% 20% 56%	2580
	11th to 20th	Night	13% 2 2 6% 20% 57%	2572
	21st to end	Night	18% 3 3 9% 28% 40%	2884
August	1st to 10th	Night	18% 3 3 13% 21% 42%	2838
	11th to 20th	Night	16% 3 2 14% 34% 31%	2838
	21st to end	Night	13% 3 2 12% 32% 38%	3233
September	1st to 10th	Night	14% 2 3 14% 32% 34%	1998
	11th to 20th	Night	19% 3 5% 22% 29% 22%	2090
	21st to end	Night	21% 2 3 20% 37% 17%	2090
October	1st to 10th	Night	18% 2 5% 15% 37% 24%	3521
	11th to 20th	Night	29% 3 5% 25% 30% 8%	3778
	21st to end	Night	28% 3 11% 33% 20% 5%	4413
November	1st to 10th	Night	36% 4 13% 23% 19% 4	2535
	11th to 20th	Night	38% 3 15% 29% 14% 1	2600
	21st to end	Night	37% 4 16% 31% 12% 1	2617
December	1st to 10th	Night	30% 4 15% 42% 7% 1	4570
	11th to 20th	Night	49% 4 20% 24% 3	5413
	21st to end	Night	50% 5% 17% 19% 9%	6952

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	20% 14% 23% 30% 13% 1	200
	11th to 20th	Day	12% 14% 23% 32% 15% 6%	200
	21st to end	Day	13% 11% 28% 25% 22% 1	295
February	1st to 10th	Day	21% 15% 30% 23% 11%	300
	11th to 20th	Day	16% 20% 32% 18% 12% 2	441
	21st to end	Day	15% 19% 28% 28% 9%	414
March	1st to 10th	Day	15% 18% 29% 26% 12%	500
	11th to 20th	Day	12% 16% 30% 26% 15% 2	500
	21st to end	Day	17% 20% 30% 23% 8% 2	550
April	1st to 10th	Day	15% 17% 28% 19% 15% 6%	500
	11th to 20th	Day	14% 19% 27% 24% 12% 4	492
	21st to end	Day	11% 16% 32% 21% 15% 5%	500
May	1st to 10th	Day	8% 17% 26% 27% 17% 6%	503
	11th to 20th	Day	14% 11% 25% 24% 18% 8%	528
	21st to end	Day	9% 9% 21% 23% 22% 15%	573
June	1st to 10th	Day	5% 8% 25% 26% 23% 12%	530
	11th to 20th	Day	7% 11% 31% 27% 19% 5%	530
	21st to end	Day	3 5% 25% 35% 22% 10%	530
July	1st to 10th	Day	2 3 20% 35% 30% 10%	526
	11th to 20th	Day	2 2 21% 36% 31% 8%	524
	21st to end	Day	2 2 14% 34% 34% 13%	532
August	1st to 10th	Day	5% 2 20% 32% 29% 11%	487
	11th to 20th	Day	3 4 17% 29% 32% 15%	477
	21st to end	Day	3 5% 21% 24% 35% 14%	539
September	1st to 10th	Day	4 4 15% 29% 30% 18%	490
	11th to 20th	Day	5% 6% 19% 31% 26% 14%	490
	21st to end	Day	6% 8% 19% 29% 26% 12%	490
October	1st to 10th	Day	8% 7% 22% 26% 25% 12%	471
	11th to 20th	Day	7% 13% 19% 17% 32% 12%	300
	21st to end	Day	11% 9% 27% 29% 19% 5%	330
November	1st to 10th	Day	13% 12% 26% 24% 21% 3	300
	11th to 20th	Day	10% 11% 22% 34% 18% 5%	300
	21st to end	Day	14% 10% 18% 32% 21% 4	300
December	1st to 10th	Day	18% 8% 23% 28% 16% 6%	300
	11th to 20th	Day	19% 16% 23% 26% 14% 2	220
	21st to end	Day	21% 16% 24% 25% 10% 4	220
January	1st to 10th	Night	14% 12% 22% 32% 19% 2	800
	11th to 20th	Night	12% 13% 20% 34% 19% 2	800
	21st to end	Night	15% 9% 18% 35% 21% 2	880
February	1st to 10th	Night	14% 11% 29% 31% 14% 1	800
	11th to 20th	Night	13% 9% 29% 32% 14% 1	784
	21st to end	Night	7% 13% 28% 37% 13% 1	660
March	1st to 10th	Night	10% 11% 27% 38% 14% 1	800
	11th to 20th	Night	8% 10% 25% 37% 18% 2	800
	21st to end	Night	11% 12% 28% 34% 14%	880
April	1st to 10th	Night	9% 12% 24% 37% 17% 2	800
	11th to 20th	Night	9% 13% 33% 32% 12% 2	643
	21st to end	Night	8% 10% 31% 34% 16% 2	600
May	1st to 10th	Night	8% 10% 27% 35% 19% 1	600
	11th to 20th	Night	8% 6% 22% 35% 25% 3	591
	21st to end	Night	12% 5% 20% 32% 27% 4	617
June	1st to 10th	Night	5% 7% 17% 43% 25% 3	400
	11th to 20th	Night	6% 7% 21% 46% 20% 1	400
	21st to end	Night	4 2 18% 47% 25% 4	400
July	1st to 10th	Night	2 2 11% 51% 32% 2	390
	11th to 20th	Night	1 1 13% 54% 30% 1	388
	21st to end	Night	1 1 10% 47% 38% 3	544
August	1st to 10th	Night	3 2 13% 48% 33% 2	567
	11th to 20th	Night	3 1 15% 46% 32% 3	564
	21st to end	Night	4 2 16% 44% 31% 3	675
September	1st to 10th	Night	3 2 14% 41% 35% 6%	760
	11th to 20th	Night	5% 2 15% 38% 33% 7%	760
	21st to end	Night	6% 3 17% 36% 28% 9%	760
October	1st to 10th	Night	8% 6% 18% 36% 29% 4	760
	11th to 20th	Night	9% 6% 19% 33% 29% 4	760
	21st to end	Night	8% 8% 22% 36% 24% 3	836
November	1st to 10th	Night	12% 8% 23% 31% 23% 3	780
	11th to 20th	Night	12% 9% 22% 38% 17% 2	800
	21st to end	Night	10% 8% 23% 33% 23% 4	817
December	1st to 10th	Night	14% 9% 23% 35% 17% 1	1000
	11th to 20th	Night	17% 9% 19% 39% 14% 2	975
	21st to end	Night	19% 12% 24% 33% 11% 2	880

Page generated at 2025-07-17 23:10:00. Version ac07

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