Blue Creek
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Creek clear sky chart from 2005-11-06 to 2024-11-04.

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	15% 9% 3 7% 5% 4 4 4 5% 7% 36%	101123
	Night	15% 10% 3 7% 4 4 4 3 5% 7% 37%	97866
Transparency	Day	46% 3 10% 24% 15% 2	104841
	Night	46% 3 9% 23% 16% 3	102286
Seeing	Day	21% 13% 27% 21% 13% 5%	14828
	Night	20% 11% 24% 28% 15% 2	24875

By Month

Percentage Cloud Cover SE (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	17% 18% 5% 10% 4 4 3 3 6% 6% 23%	2836
	11th to 20th	Day	16% 16% 7% 14% 6% 5% 3 2 3 3 25%	2840
	21st to end	Day	27% 19% 7% 7% 4 4 4 3 4 4 19%	3124
February	1st to 10th	Day	20% 14% 4 10% 5% 3 4 4 4 4 29%	1750
	11th to 20th	Day	17% 13% 5% 10% 4 4 5% 3 4 5% 29%	1848
	21st to end	Day	21% 14% 4 7% 5% 3 3 2 5% 5% 32%	1570
March	1st to 10th	Day	22% 16% 4 8% 5% 4 3 3 4 5% 27%	3243
	11th to 20th	Day	15% 7% 4 6% 4 4 4 4 5% 7% 40%	3480
	21st to end	Day	18% 9% 2 6% 5% 5% 4 3 5% 7% 35%	3815
April	1st to 10th	Day	15% 10% 3 7% 4 4 4 3 5% 8% 37%	2147
	11th to 20th	Day	18% 9% 3 6% 4 3 4 2 5% 7% 40%	2356
	21st to end	Day	18% 8% 3 7% 6% 5% 4 3 5% 7% 35%	2470
May	1st to 10th	Day	21% 10% 3 8% 5% 4 4 4 5% 6% 30%	4082
	11th to 20th	Day	21% 8% 3 7% 5% 4 4 4 5% 7% 33%	4081
	21st to end	Day	11% 7% 2 7% 5% 5% 6% 5% 7% 9% 35%	4476
June	1st to 10th	Day	12% 5% 2 5% 5% 5% 6% 5% 6% 9% 39%	2470
	11th to 20th	Day	10% 5% 2 6% 6% 5% 5% 5% 7% 9% 40%	2470
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 5% 6% 10% 39%	2470
July	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 4 6% 9% 40%	4120
	11th to 20th	Day	9% 6% 2 5% 4 5% 6% 5% 7% 10% 42%	4120
	21st to end	Day	13% 9% 4 9% 6% 6% 6% 4 7% 8% 28%	4466
August	1st to 10th	Day	8% 5% 2 7% 5% 5% 5% 4 8% 10% 40%	4104
	11th to 20th	Day	9% 6% 2 6% 4 5% 6% 5% 7% 10% 38%	4044
	21st to end	Day	6% 3 2 4 4 4 4 4 6% 9% 55%	4346
September	1st to 10th	Day	14% 5% 2 5% 3 4 4 3 5% 6% 48%	2104
	11th to 20th	Day	10% 4 2 6% 4 4 4 4 6% 7% 49%	2090
	21st to end	Day	19% 6% 2 6% 3 3 4 3 4 5% 44%	2090
October	1st to 10th	Day	12% 4 2 5% 4 4 4 3 6% 7% 49%	2067
	11th to 20th	Day	15% 7% 3 5% 3 4 4 3 4 5% 48%	1900
	21st to end	Day	21% 8% 3 6% 4 3 3 3 4 6% 40%	2038
November	1st to 10th	Day	12% 7% 2 4 3 3 4 3 4 6% 51%	1699
	11th to 20th	Day	15% 13% 3 6% 4 3 4 3 6% 6% 38%	1710
	21st to end	Day	18% 10% 3 7% 4 4 4 3 5% 6% 38%	1710
December	1st to 10th	Day	24% 14% 4 8% 5% 4 3 3 4 5% 26%	1710
	11th to 20th	Day	17% 16% 5% 9% 5% 4 4 3 4 5% 28%	2153
	21st to end	Day	19% 19% 5% 11% 5% 5% 4 3 5% 5% 19%	3124
January	1st to 10th	Night	16% 21% 5% 11% 5% 5% 4 4 5% 4 21%	4109
	11th to 20th	Night	17% 16% 6% 13% 6% 3 3 2 4 4 24%	4120
	21st to end	Night	25% 16% 5% 8% 5% 5% 3 2 3 5% 23%	4532
February	1st to 10th	Night	21% 14% 5% 8% 5% 4 3 3 4 6% 28%	2428
	11th to 20th	Night	20% 12% 4 9% 4 5% 4 3 4 5% 31%	2218
	21st to end	Night	23% 15% 4 8% 4 4 3 2 4 5% 28%	1884
March	1st to 10th	Night	20% 15% 3 6% 4 4 4 3 4 6% 32%	3610
	11th to 20th	Night	14% 9% 3 6% 4 3 4 4 5% 6% 42%	3480
	21st to end	Night	15% 9% 3 7% 4 5% 5% 3 6% 6% 38%	3817
April	1st to 10th	Night	15% 9% 2 6% 6% 3 4 4 5% 7% 39%	2048
	11th to 20th	Night	15% 8% 3 6% 4 4 4 5% 5% 7% 40%	1772
	21st to end	Night	17% 8% 3 6% 4 4 5% 5% 5% 7% 37%	1710
May	1st to 10th	Night	24% 12% 4 7% 4 4 3 3 5% 7% 29%	2813
	11th to 20th	Night	19% 7% 3 6% 4 4 3 3 6% 8% 38%	2812
	21st to end	Night	10% 6% 2 5% 3 5% 4 5% 7% 9% 44%	3079
June	1st to 10th	Night	8% 4 2 6% 5% 5% 5% 4 7% 9% 45%	1710
	11th to 20th	Night	7% 4 2 5% 5% 4 5% 4 6% 12% 46%	1710
	21st to end	Night	7% 5% 1 5% 5% 4 5% 5% 8% 10% 45%	1710
July	1st to 10th	Night	8% 6% 2 6% 4 5% 4 4 7% 9% 45%	2840
	11th to 20th	Night	7% 5% 2 6% 5% 5% 5% 3 7% 10% 46%	2840
	21st to end	Night	10% 9% 3 8% 5% 4 5% 5% 6% 8% 36%	3087
August	1st to 10th	Night	7% 6% 2 6% 4 5% 6% 4 7% 9% 44%	2825
	11th to 20th	Night	10% 7% 2 6% 4 6% 5% 3 6% 7% 42%	2785
	21st to end	Night	4 3 1 4 3 3 4 4 6% 9% 59%	3306
September	1st to 10th	Night	11% 5% 2 4 4 4 4 3 5% 7% 51%	2057
	11th to 20th	Night	10% 4 2 5% 4 4 4 2 4 7% 54%	2090
	21st to end	Night	13% 6% 3 6% 4 3 4 4 5% 6% 46%	2090
October	1st to 10th	Night	10% 5% 1 5% 4 4 4 3 5% 7% 53%	2111
	11th to 20th	Night	14% 6% 2 5% 2 4 4 3 7% 7% 45%	2280
	21st to end	Night	19% 8% 2 5% 4 4 4 3 4 5% 42%	2557
November	1st to 10th	Night	13% 7% 2 5% 4 3 3 3 4 5% 50%	2452
	11th to 20th	Night	16% 9% 3 7% 5% 4 4 3 4 6% 40%	2470
	21st to end	Night	19% 12% 3 6% 5% 4 4 3 4 6% 36%	2470
December	1st to 10th	Night	22% 14% 4 8% 5% 4 4 3 5% 6% 27%	2470
	11th to 20th	Night	18% 13% 6% 9% 4 3 3 3 4 6% 31%	3042
	21st to end	Night	19% 19% 6% 10% 6% 5% 4 3 4 5% 19%	4532

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	63% 1 11% 15% 9%	2837
	11th to 20th	Day	67% 2 7% 17% 7% 1	2840
	21st to end	Day	70% 1 6% 17% 4 1	3124
February	1st to 10th	Day	59% 3 9% 17% 10% 1	1750
	11th to 20th	Day	58% 2 8% 19% 11% 1	1858
	21st to end	Day	56% 2 7% 22% 11% 2	1570
March	1st to 10th	Day	61% 1 5% 22% 8% 2	3243
	11th to 20th	Day	45% 1 9% 27% 16% 1	3480
	21st to end	Day	49% 2 9% 26% 14% 1	3815
April	1st to 10th	Day	48% 2 9% 25% 13% 3	2147
	11th to 20th	Day	47% 2 8% 22% 17% 4	2356
	21st to end	Day	50% 3 11% 21% 12% 3	2470
May	1st to 10th	Day	56% 2 9% 22% 10% 1	4120
	11th to 20th	Day	52% 2 10% 21% 13% 1	4085
	21st to end	Day	44% 3 13% 20% 17% 3	4489
June	1st to 10th	Day	42% 4 11% 26% 16% 2	2470
	11th to 20th	Day	40% 5% 14% 23% 17% 2	2470
	21st to end	Day	39% 5% 14% 23% 14% 4	2470
July	1st to 10th	Day	42% 5% 11% 23% 17% 2	4055
	11th to 20th	Day	35% 5% 12% 32% 15% 1	4051
	21st to end	Day	51% 5% 11% 17% 14% 2	4324
August	1st to 10th	Day	36% 5% 13% 33% 11% 1	4091
	11th to 20th	Day	38% 5% 9% 30% 16% 1	4083
	21st to end	Day	26% 4 15% 31% 21% 3	4345
September	1st to 10th	Day	37% 3 10% 23% 20% 6%	2104
	11th to 20th	Day	35% 2 10% 25% 25% 2	2090
	21st to end	Day	43% 3 6% 25% 21% 2	2090
October	1st to 10th	Day	24% 2 7% 31% 34% 2	3431
	11th to 20th	Day	30% 2 8% 31% 27% 2	3140
	21st to end	Day	34% 2 10% 28% 23% 3	3340
November	1st to 10th	Day	36% 2 9% 28% 21% 3	1699
	11th to 20th	Day	47% 2 7% 22% 18% 4	1710
	21st to end	Day	49% 2 9% 23% 16% 2	1710
December	1st to 10th	Day	62% 2 9% 19% 7% 1	1710
	11th to 20th	Day	60% 2 8% 18% 12% 1	2150
	21st to end	Day	69% 2 8% 14% 6% 1	3124
January	1st to 10th	Night	67% 2 7% 16% 8%	4109
	11th to 20th	Night	66% 1 8% 16% 8% 1	4120
	21st to end	Night	67% 1 6% 19% 6% 1	4532
February	1st to 10th	Night	60% 3 8% 19% 9% 1	2428
	11th to 20th	Night	58% 2 7% 20% 12% 1	2219
	21st to end	Night	59% 2 9% 16% 10% 3	1884
March	1st to 10th	Night	56% 1 4 25% 12% 1	3610
	11th to 20th	Night	44% 1 8% 29% 17% 1	3480
	21st to end	Night	48% 2 7% 27% 15% 1	3817
April	1st to 10th	Night	46% 3 9% 24% 17% 2	2048
	11th to 20th	Night	44% 3 9% 21% 17% 6%	1772
	21st to end	Night	47% 4 10% 22% 15% 2	1710
May	1st to 10th	Night	57% 3 9% 20% 10% 2	2840
	11th to 20th	Night	47% 4 13% 24% 12% 1	2813
	21st to end	Night	37% 3 12% 28% 16% 4	3087
June	1st to 10th	Night	35% 4 14% 25% 19% 3	1710
	11th to 20th	Night	32% 5% 16% 22% 22% 3	1710
	21st to end	Night	32% 5% 17% 26% 17% 3	1710
July	1st to 10th	Night	36% 5% 12% 25% 17% 5%	2795
	11th to 20th	Night	33% 4 14% 28% 19% 2	2786
	21st to end	Night	45% 5% 11% 22% 13% 4	2988
August	1st to 10th	Night	35% 6% 13% 33% 12% 1	2814
	11th to 20th	Night	40% 5% 10% 25% 19% 1	2812
	21st to end	Night	22% 4 16% 32% 22% 4	3306
September	1st to 10th	Night	33% 3 13% 24% 19% 7%	2057
	11th to 20th	Night	33% 3 9% 25% 27% 3	2090
	21st to end	Night	39% 3 7% 22% 26% 2	2090
October	1st to 10th	Night	26% 2 7% 25% 37% 3	3527
	11th to 20th	Night	27% 3 7% 27% 30% 6%	3779
	21st to end	Night	33% 2 8% 23% 26% 8%	4205
November	1st to 10th	Night	38% 3 8% 24% 24% 4	2452
	11th to 20th	Night	48% 2 6% 20% 20% 4	2470
	21st to end	Night	51% 2 9% 23% 14% 2	2470
December	1st to 10th	Night	60% 2 8% 20% 9% 1	2470
	11th to 20th	Night	57% 1 9% 23% 9% 1	3044
	21st to end	Night	69% 2 7% 16% 7%	4532

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	30% 22% 31% 14% 3	270
	11th to 20th	Day	38% 23% 31% 7% 1	270
	21st to end	Day	33% 27% 27% 12% 2	297
February	1st to 10th	Day	33% 24% 29% 11% 3	270
	11th to 20th	Day	38% 27% 29% 4 2	270
	21st to end	Day	38% 23% 34% 5%	225
March	1st to 10th	Day	33% 21% 31% 11% 4	341
	11th to 20th	Day	28% 21% 32% 14% 5%	460
	21st to end	Day	35% 18% 28% 16% 4	506
April	1st to 10th	Day	26% 20% 27% 18% 8% 1	460
	11th to 20th	Day	28% 19% 25% 17% 8% 3	452
	21st to end	Day	26% 18% 34% 14% 6% 2	460
May	1st to 10th	Day	26% 17% 31% 16% 8% 2	463
	11th to 20th	Day	23% 10% 31% 21% 9% 5%	487
	21st to end	Day	13% 11% 26% 28% 15% 7%	529
June	1st to 10th	Day	15% 8% 23% 32% 15% 7%	490
	11th to 20th	Day	13% 7% 27% 30% 16% 7%	490
	21st to end	Day	13% 8% 31% 23% 16% 9%	490
July	1st to 10th	Day	16% 4 19% 23% 19% 20%	485
	11th to 20th	Day	10% 6% 24% 29% 21% 11%	484
	21st to end	Day	14% 4 21% 28% 22% 11%	532
August	1st to 10th	Day	12% 6% 19% 27% 23% 13%	486
	11th to 20th	Day	11% 5% 21% 33% 22% 8%	479
	21st to end	Day	8% 5% 19% 31% 25% 12%	539
September	1st to 10th	Day	14% 5% 19% 27% 26% 10%	490
	11th to 20th	Day	9% 3 19% 27% 31% 11%	490
	21st to end	Day	22% 10% 19% 25% 20% 4	490
October	1st to 10th	Day	12% 7% 26% 31% 18% 6%	490
	11th to 20th	Day	17% 16% 29% 21% 12% 5%	490
	21st to end	Day	26% 12% 32% 22% 8%	487
November	1st to 10th	Day	17% 18% 30% 26% 7% 1	279
	11th to 20th	Day	29% 17% 29% 17% 6% 1	270
	21st to end	Day	24% 21% 34% 15% 4 1	270
December	1st to 10th	Day	31% 22% 30% 13% 5%	270
	11th to 20th	Day	28% 20% 33% 13% 4 1	270
	21st to end	Day	32% 22% 32% 10% 4	297
January	1st to 10th	Night	31% 19% 28% 18% 5%	760
	11th to 20th	Night	32% 18% 30% 17% 2	760
	21st to end	Night	26% 21% 30% 21% 2	836
February	1st to 10th	Night	31% 16% 28% 23% 2	760
	11th to 20th	Night	32% 19% 28% 20% 1	743
	21st to end	Night	31% 18% 31% 18% 1	628
March	1st to 10th	Night	25% 18% 28% 23% 5%	760
	11th to 20th	Night	26% 18% 31% 18% 7%	760
	21st to end	Night	25% 13% 30% 25% 7%	836
April	1st to 10th	Night	22% 15% 31% 24% 8%	718
	11th to 20th	Night	19% 12% 31% 25% 11% 1	563
	21st to end	Night	22% 9% 33% 30% 6%	570
May	1st to 10th	Night	20% 10% 28% 29% 12% 1	570
	11th to 20th	Night	18% 7% 25% 32% 17% 1	561
	21st to end	Night	9% 6% 21% 32% 28% 5%	617
June	1st to 10th	Night	9% 4 21% 42% 23% 2	570
	11th to 20th	Night	9% 3 19% 38% 27% 4	570
	21st to end	Night	8% 4 23% 34% 28% 3	570
July	1st to 10th	Night	13% 3 14% 31% 30% 9%	555
	11th to 20th	Night	7% 2 14% 37% 37% 4	552
	21st to end	Night	10% 3 12% 38% 33% 4	624
August	1st to 10th	Night	8% 3 10% 37% 37% 5%	567
	11th to 20th	Night	8% 2 12% 38% 32% 7%	564
	21st to end	Night	8% 2 13% 33% 37% 7%	627
September	1st to 10th	Night	13% 2 12% 33% 33% 6%	727
	11th to 20th	Night	10% 4 15% 30% 33% 8%	760
	21st to end	Night	15% 6% 20% 33% 23% 3	760
October	1st to 10th	Night	12% 6% 22% 32% 25% 4	760
	11th to 20th	Night	18% 11% 26% 30% 15% 1	760
	21st to end	Night	23% 12% 26% 27% 12% 1	836
November	1st to 10th	Night	18% 10% 24% 29% 18% 1	755
	11th to 20th	Night	23% 15% 27% 23% 11% 1	760
	21st to end	Night	27% 12% 23% 29% 8% 1	760
December	1st to 10th	Night	31% 16% 25% 21% 6%	760
	11th to 20th	Night	27% 13% 31% 23% 6% 1	760
	21st to end	Night	30% 16% 28% 23% 4	836

Page generated at 2024-11-01 22:47:39. Version ac07

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