Chimney Rock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chimney Rock clear sky chart from 2005-11-06 to 2024-11-28.

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% 6% 2 5% 4 4 4 4 6% 7% 54%	105168
	Night	6% 7% 2 6% 4 4 4 3 5% 6% 53%	103092
Transparency	Day	26% 6% 10% 21% 24% 12%	104929
	Night	29% 6% 10% 21% 24% 11%	102920
Seeing	Day	10% 11% 28% 30% 17% 4	15279
	Night	10% 4 19% 44% 21% 2	25450

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	3 9% 4 6% 4 3 4 4 7% 7% 49%	2804
	11th to 20th	Day	4 11% 3 5% 3 3 4 4 5% 6% 52%	2860
	21st to end	Day	6% 11% 3 6% 4 3 4 3 4 6% 50%	3146
February	1st to 10th	Day	4 10% 3 5% 5% 3 3 3 4 6% 53%	1710
	11th to 20th	Day	6% 10% 3 7% 4 4 4 3 5% 6% 49%	1750
	21st to end	Day	5% 13% 4 7% 4 4 3 3 4 6% 47%	1570
March	1st to 10th	Day	4 9% 2 6% 4 4 4 3 6% 8% 49%	3412
	11th to 20th	Day	6% 14% 3 7% 4 4 4 3 6% 7% 42%	3490
	21st to end	Day	5% 12% 4 10% 5% 4 4 4 5% 6% 41%	3869
April	1st to 10th	Day	5% 5% 2 4 4 5% 5% 4 6% 7% 53%	2280
	11th to 20th	Day	4 6% 2 4 5% 4 5% 4 6% 7% 53%	2251
	21st to end	Day	5% 5% 2 5% 4 4 4 4 6% 7% 54%	2280
May	1st to 10th	Day	5% 4 1 5% 3 3 4 3 5% 6% 60%	3912
	11th to 20th	Day	4 4 2 4 5% 5% 6% 6% 8% 9% 48%	4089
	21st to end	Day	3 2 1 3 3 3 4 3 5% 6% 66%	4825
June	1st to 10th	Day	4 2 1 3 3 3 4 4 7% 7% 63%	2660
	11th to 20th	Day	2 2 1 3 2 3 3 2 5% 6% 71%	2660
	21st to end	Day	2 2 1 4 4 4 5% 4 7% 8% 59%	2660
July	1st to 10th	Day	3 2 1 4 4 4 5% 4 6% 7% 61%	4348
	11th to 20th	Day	1 2 1 3 4 7% 8% 8% 11% 12% 42%	4110
	21st to end	Day	3 3 2 4 5% 6% 7% 7% 8% 9% 45%	4454
August	1st to 10th	Day	5% 4 2 6% 6% 8% 8% 6% 10% 10% 36%	4092
	11th to 20th	Day	3 3 1 5% 4 5% 6% 5% 8% 10% 50%	3824
	21st to end	Day	5% 3 2 6% 5% 6% 7% 6% 8% 11% 42%	4180
September	1st to 10th	Day	7% 4 2 5% 3 4 5% 4 6% 7% 53%	2280
	11th to 20th	Day	8% 3 1 4 3 3 5% 4 5% 7% 56%	2280
	21st to end	Day	8% 3 1 3 3 3 3 2 3 5% 65%	2010
October	1st to 10th	Day	5% 2 1 3 2 2 3 3 4 5% 70%	3170
	11th to 20th	Day	9% 5% 2 5% 4 4 4 3 3 5% 55%	3150
	21st to end	Day	6% 4 2 4 2 3 3 2 3 5% 67%	3438
November	1st to 10th	Day	5% 4 1 3 2 2 3 3 4 5% 68%	1938
	11th to 20th	Day	3 3 1 4 2 2 2 2 4 6% 70%	1800
	21st to end	Day	8% 7% 2 3 3 2 3 2 4 5% 61%	1626
December	1st to 10th	Day	7% 8% 3 4 3 2 3 3 5% 7% 57%	1520
	11th to 20th	Day	7% 10% 3 5% 4 4 4 4 5% 6% 48%	1926
	21st to end	Day	5% 11% 3 7% 3 3 3 3 5% 5% 52%	2794
January	1st to 10th	Night	4 9% 5% 8% 5% 4 4 3 5% 5% 47%	4179
	11th to 20th	Night	3 10% 4 5% 3 4 4 4 5% 5% 54%	4110
	21st to end	Night	6% 12% 3 8% 3 3 3 2 5% 5% 49%	4521
February	1st to 10th	Night	6% 10% 3 5% 2 2 3 3 3 5% 58%	2470
	11th to 20th	Night	7% 10% 2 6% 3 3 3 3 4 6% 55%	2316
	21st to end	Night	7% 12% 2 5% 3 3 3 2 4 5% 55%	1884
March	1st to 10th	Night	4 14% 2 6% 3 4 4 3 4 5% 50%	3448
	11th to 20th	Night	9% 13% 3 7% 4 3 3 4 5% 6% 43%	3490
	21st to end	Night	8% 8% 3 7% 6% 5% 5% 4 5% 5% 45%	3780
April	1st to 10th	Night	6% 7% 2 4 4 4 4 3 5% 6% 55%	1900
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 4 5% 55%	1877
	21st to end	Night	6% 7% 2 4 3 3 4 3 4 5% 58%	1900
May	1st to 10th	Night	6% 5% 1 4 3 3 3 3 4 6% 61%	3055
	11th to 20th	Night	6% 4 1 4 4 4 4 4 6% 8% 54%	2812
	21st to end	Night	6% 3 1 4 3 3 3 2 4 6% 65%	2762
June	1st to 10th	Night	3 3 2 3 3 3 4 4 4 6% 66%	1520
	11th to 20th	Night	3 3 1 3 3 2 3 3 4 5% 69%	1520
	21st to end	Night	4 2 1 3 4 5% 5% 4 7% 7% 57%	1520
July	1st to 10th	Night	4 4 1 5% 3 4 5% 3 5% 6% 59%	2604
	11th to 20th	Night	2 3 2 6% 5% 6% 6% 6% 10% 13% 41%	2860
	21st to end	Night	5% 5% 2 7% 5% 6% 6% 6% 9% 10% 38%	3109
August	1st to 10th	Night	5% 6% 3 10% 7% 7% 7% 6% 9% 11% 31%	2847
	11th to 20th	Night	4 3 2 6% 5% 5% 6% 5% 9% 12% 42%	3012
	21st to end	Night	5% 5% 3 9% 6% 7% 7% 5% 9% 11% 33%	3487
September	1st to 10th	Night	6% 3 1 8% 5% 5% 5% 5% 8% 9% 46%	1900
	11th to 20th	Night	6% 3 1 6% 4 4 4 3 5% 7% 57%	1900
	21st to end	Night	8% 3 1 4 2 3 3 2 4 6% 64%	2164
October	1st to 10th	Night	7% 3 1 3 2 2 3 2 3 5% 69%	3800
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 5% 6% 54%	3778
	21st to end	Night	7% 4 2 4 2 2 2 2 3 4 67%	4120
November	1st to 10th	Night	5% 5% 1 3 2 2 3 3 5% 6% 66%	2340
	11th to 20th	Night	3 3 1 2 2 2 2 3 3 4 74%	2599
	21st to end	Night	8% 9% 2 4 2 2 3 2 3 4 60%	2704
December	1st to 10th	Night	7% 8% 2 5% 3 3 2 2 4 6% 58%	2660
	11th to 20th	Night	7% 9% 3 6% 4 3 4 3 5% 7% 49%	3271
	21st to end	Night	7% 10% 3 8% 4 3 3 2 4 5% 50%	4873

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	30% 5% 17% 28% 18% 2	2805
	11th to 20th	Day	30% 6% 20% 28% 14% 1	2860
	21st to end	Day	35% 5% 10% 30% 17% 2	3146
February	1st to 10th	Day	32% 5% 14% 25% 20% 4	1710
	11th to 20th	Day	36% 4 8% 27% 21% 3	1759
	21st to end	Day	39% 4 7% 17% 28% 6%	1570
March	1st to 10th	Day	29% 7% 8% 24% 28% 4	3412
	11th to 20th	Day	37% 8% 8% 28% 16% 3	3490
	21st to end	Day	38% 9% 7% 21% 21% 3	3869
April	1st to 10th	Day	28% 5% 8% 22% 26% 12%	2280
	11th to 20th	Day	27% 5% 6% 21% 27% 13%	2254
	21st to end	Day	27% 6% 7% 22% 30% 9%	2280
May	1st to 10th	Day	22% 6% 7% 16% 30% 19%	3912
	11th to 20th	Day	25% 10% 11% 23% 23% 9%	4092
	21st to end	Day	15% 5% 7% 12% 42% 19%	4825
June	1st to 10th	Day	17% 6% 7% 21% 28% 21%	2660
	11th to 20th	Day	14% 4 5% 13% 28% 37%	2660
	21st to end	Day	20% 6% 7% 16% 26% 26%	2660
July	1st to 10th	Day	20% 7% 8% 11% 20% 34%	4281
	11th to 20th	Day	24% 10% 15% 29% 16% 5%	4041
	21st to end	Day	26% 10% 18% 22% 15% 9%	4314
August	1st to 10th	Day	35% 10% 19% 17% 12% 7%	4078
	11th to 20th	Day	25% 9% 14% 18% 19% 15%	3862
	21st to end	Day	30% 9% 14% 19% 20% 7%	4179
September	1st to 10th	Day	27% 7% 10% 18% 25% 14%	2280
	11th to 20th	Day	24% 7% 8% 17% 26% 17%	2280
	21st to end	Day	22% 4 4 19% 37% 14%	2010
October	1st to 10th	Day	17% 4 4 16% 32% 27%	3170
	11th to 20th	Day	30% 4 4 22% 29% 11%	3150
	21st to end	Day	21% 3 5% 23% 42% 6%	3438
November	1st to 10th	Day	19% 3 7% 30% 34% 7%	1938
	11th to 20th	Day	16% 3 8% 32% 35% 7%	1800
	21st to end	Day	27% 3 5% 30% 26% 10%	1626
December	1st to 10th	Day	28% 4 16% 27% 19% 7%	1520
	11th to 20th	Day	36% 7% 9% 28% 18% 3	1924
	21st to end	Day	32% 5% 11% 18% 27% 7%	2794
January	1st to 10th	Night	37% 5% 10% 27% 19% 2	4179
	11th to 20th	Night	30% 6% 17% 27% 16% 3	4110
	21st to end	Night	35% 7% 9% 31% 15% 3	4521
February	1st to 10th	Night	30% 3 12% 28% 19% 7%	2470
	11th to 20th	Night	33% 4 9% 27% 23% 5%	2317
	21st to end	Night	33% 3 8% 18% 31% 7%	1884
March	1st to 10th	Night	32% 7% 6% 22% 28% 5%	3448
	11th to 20th	Night	39% 7% 8% 24% 17% 5%	3490
	21st to end	Night	34% 10% 8% 23% 21% 4	3780
April	1st to 10th	Night	30% 3 7% 18% 28% 13%	1900
	11th to 20th	Night	29% 5% 6% 17% 28% 14%	1877
	21st to end	Night	29% 4 6% 21% 30% 10%	1900
May	1st to 10th	Night	22% 6% 6% 15% 36% 15%	3055
	11th to 20th	Night	25% 7% 12% 27% 19% 11%	2813
	21st to end	Night	19% 5% 8% 13% 33% 24%	2762
June	1st to 10th	Night	19% 5% 8% 17% 25% 26%	1520
	11th to 20th	Night	17% 3 5% 13% 20% 41%	1520
	21st to end	Night	21% 6% 9% 14% 23% 27%	1520
July	1st to 10th	Night	25% 5% 9% 9% 16% 35%	2562
	11th to 20th	Night	28% 9% 15% 31% 8% 8%	2806
	21st to end	Night	34% 11% 17% 17% 12% 8%	3011
August	1st to 10th	Night	41% 10% 19% 11% 11% 8%	2838
	11th to 20th	Night	32% 8% 19% 12% 15% 14%	3040
	21st to end	Night	39% 9% 14% 19% 14% 6%	3487
September	1st to 10th	Night	30% 7% 13% 17% 17% 16%	1900
	11th to 20th	Night	27% 6% 9% 15% 23% 21%	1900
	21st to end	Night	22% 5% 5% 16% 36% 16%	2164
October	1st to 10th	Night	18% 4 5% 12% 37% 24%	3800
	11th to 20th	Night	31% 4 5% 17% 32% 12%	3778
	21st to end	Night	21% 3 5% 22% 41% 8%	4120
November	1st to 10th	Night	20% 3 6% 28% 34% 9%	2340
	11th to 20th	Night	15% 3 6% 32% 36% 8%	2599
	21st to end	Night	30% 2 5% 25% 30% 7%	2704
December	1st to 10th	Night	29% 2 13% 28% 22% 5%	2660
	11th to 20th	Night	35% 5% 11% 26% 21% 3	3272
	21st to end	Night	36% 5% 9% 20% 25% 5%	4873

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	19% 5% 31% 28% 15% 3	270
	11th to 20th	Day	21% 7% 32% 30% 8% 1	270
	21st to end	Day	7% 8% 32% 38% 11% 4	297
February	1st to 10th	Day	9% 12% 35% 35% 7% 2	270
	11th to 20th	Day	16% 13% 36% 29% 6% 1	270
	21st to end	Day	19% 19% 34% 21% 7%	225
March	1st to 10th	Day	16% 21% 28% 26% 10%	439
	11th to 20th	Day	17% 17% 33% 23% 8% 3	460
	21st to end	Day	18% 26% 31% 20% 4	506
April	1st to 10th	Day	12% 25% 37% 19% 7% 1	460
	11th to 20th	Day	16% 31% 31% 16% 6%	452
	21st to end	Day	12% 27% 35% 18% 6% 1	460
May	1st to 10th	Day	14% 22% 40% 17% 6% 1	463
	11th to 20th	Day	10% 15% 35% 25% 13% 2	493
	21st to end	Day	9% 14% 30% 30% 16% 1	734
June	1st to 10th	Day	5% 7% 23% 38% 23% 4	680
	11th to 20th	Day	4 9% 33% 31% 19% 4	680
	21st to end	Day	3 10% 26% 33% 23% 5%	680
July	1st to 10th	Day	3 5% 19% 36% 31% 6%	630
	11th to 20th	Day	4 2 18% 35% 29% 12%	484
	21st to end	Day	7% 3 12% 36% 33% 9%	531
August	1st to 10th	Day	6% 6% 16% 37% 27% 8%	487
	11th to 20th	Day	5% 3 23% 37% 25% 7%	477
	21st to end	Day	7% 3 23% 36% 25% 6%	539
September	1st to 10th	Day	7% 3 22% 34% 25% 9%	490
	11th to 20th	Day	6% 5% 27% 40% 19% 3	490
	21st to end	Day	11% 7% 24% 33% 20% 6%	384
October	1st to 10th	Day	11% 8% 20% 30% 22% 9%	300
	11th to 20th	Day	11% 10% 27% 28% 18% 6%	300
	21st to end	Day	12% 9% 26% 30% 19% 4	330
November	1st to 10th	Day	10% 13% 27% 32% 15% 2	300
	11th to 20th	Day	5% 7% 33% 34% 17% 4	300
	21st to end	Day	17% 5% 29% 26% 20% 3	291
December	1st to 10th	Day	14% 9% 30% 32% 10% 5%	270
	11th to 20th	Day	11% 8% 30% 35% 13% 2	270
	21st to end	Day	19% 10% 29% 31% 10% 1	297
January	1st to 10th	Night	12% 3 24% 43% 16% 3	803
	11th to 20th	Night	10% 3 25% 45% 14% 3	760
	21st to end	Night	11% 3 22% 45% 16% 3	836
February	1st to 10th	Night	13% 3 27% 44% 11% 2	760
	11th to 20th	Night	12% 4 29% 43% 11% 1	744
	21st to end	Night	15% 3 32% 43% 6%	628
March	1st to 10th	Night	10% 6% 27% 45% 12%	760
	11th to 20th	Night	11% 5% 22% 44% 18% 1	760
	21st to end	Night	11% 9% 25% 43% 12% 1	813
April	1st to 10th	Night	11% 8% 31% 43% 7%	570
	11th to 20th	Night	12% 9% 24% 43% 12%	563
	21st to end	Night	10% 10% 24% 43% 13%	570
May	1st to 10th	Night	8% 7% 26% 44% 15%	570
	11th to 20th	Night	10% 2 22% 45% 19% 1	561
	21st to end	Night	10% 7% 19% 44% 19% 2	617
June	1st to 10th	Night	4 3 16% 49% 27% 1	570
	11th to 20th	Night	4 3 18% 50% 25% 1	570
	21st to end	Night	5% 2 12% 48% 32% 1	570
July	1st to 10th	Night	4 2 9% 48% 37% 1	555
	11th to 20th	Night	4 2 6% 36% 45% 7%	552
	21st to end	Night	7% 2 6% 33% 45% 8%	624
August	1st to 10th	Night	5% 1 5% 32% 50% 6%	567
	11th to 20th	Night	6% 2 6% 39% 42% 4	564
	21st to end	Night	6% 2 6% 40% 41% 4	627
September	1st to 10th	Night	7% 1 6% 43% 39% 4	570
	11th to 20th	Night	7% 2 12% 46% 31% 2	570
	21st to end	Night	9% 2 11% 44% 31% 3	730
October	1st to 10th	Night	12% 3 14% 47% 23% 2	760
	11th to 20th	Night	8% 2 15% 51% 21% 3	760
	21st to end	Night	8% 3 16% 49% 20% 5%	836
November	1st to 10th	Night	7% 2 16% 51% 20% 3	780
	11th to 20th	Night	5% 4 22% 47% 18% 3	999
	21st to end	Night	14% 4 19% 37% 22% 3	986
December	1st to 10th	Night	12% 5% 23% 45% 13% 2	950
	11th to 20th	Night	14% 5% 21% 44% 14% 1	950
	21st to end	Night	14% 5% 24% 45% 11% 1	1045

Page generated at 2024-11-24 22:22:19. Version ac07

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