Danville Conservation Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Danville Conservation Area clear sky chart from 2005-11-06 to 2024-11-02.

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	12% 8% 3 6% 4 4 4 4 5% 7% 42%	101232
	Night	13% 9% 3 6% 4 4 4 3 5% 6% 44%	97795
Transparency	Day	40% 6% 12% 25% 15% 2	101030
	Night	41% 5% 11% 24% 16% 2	97668
Seeing	Day	16% 13% 29% 26% 13% 3	15648
	Night	17% 13% 31% 27% 12% 1	25445

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	11% 14% 5% 11% 5% 4 4 3 5% 7% 31%	2527
	11th to 20th	Day	12% 12% 4 8% 6% 7% 4 3 4 5% 34%	2850
	21st to end	Day	19% 16% 7% 8% 4 4 3 3 4 4 29%	3135
February	1st to 10th	Day	16% 12% 4 8% 5% 4 4 3 4 6% 35%	1710
	11th to 20th	Day	14% 10% 3 6% 5% 4 3 3 5% 6% 40%	1760
	21st to end	Day	15% 12% 2 8% 4 4 4 4 4 5% 39%	1570
March	1st to 10th	Day	18% 12% 3 5% 4 3 3 3 3 5% 42%	3302
	11th to 20th	Day	12% 8% 3 5% 3 3 3 3 5% 6% 50%	3480
	21st to end	Day	17% 11% 3 8% 5% 4 4 4 5% 7% 32%	3933
April	1st to 10th	Day	12% 8% 2 6% 5% 4 5% 3 5% 6% 44%	2280
	11th to 20th	Day	18% 8% 2 6% 4 4 3 3 4 6% 42%	2254
	21st to end	Day	21% 7% 3 6% 5% 4 3 4 6% 7% 35%	2280
May	1st to 10th	Day	13% 8% 3 7% 5% 5% 5% 4 6% 9% 33%	3884
	11th to 20th	Day	17% 9% 3 7% 4 4 4 3 5% 7% 37%	4367
	21st to end	Day	11% 6% 2 6% 5% 4 5% 3 6% 6% 45%	4824
June	1st to 10th	Day	8% 5% 2 5% 4 3 5% 4 7% 11% 47%	2660
	11th to 20th	Day	8% 4 2 5% 4 4 4 4 6% 11% 49%	2660
	21st to end	Day	6% 4 2 4 4 5% 5% 5% 7% 11% 47%	2660
July	1st to 10th	Day	14% 6% 2 6% 4 4 4 5% 6% 10% 39%	4440
	11th to 20th	Day	5% 4 2 5% 4 4 5% 4 7% 10% 50%	4394
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 11% 38%	4465
August	1st to 10th	Day	6% 4 2 5% 4 4 5% 5% 7% 10% 49%	4104
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 4 6% 9% 44%	3828
	21st to end	Day	6% 4 2 5% 4 4 5% 4 6% 10% 51%	4180
September	1st to 10th	Day	11% 5% 1 5% 3 4 4 3 5% 7% 51%	2280
	11th to 20th	Day	10% 5% 2 5% 4 3 3 3 6% 8% 51%	2280
	21st to end	Day	8% 5% 2 6% 3 4 4 4 5% 7% 53%	2022
October	1st to 10th	Day	9% 5% 2 5% 3 3 3 3 4 5% 56%	1900
	11th to 20th	Day	16% 6% 2 5% 3 3 3 2 4 4 53%	1900
	21st to end	Day	18% 8% 2 5% 4 3 3 2 4 5% 46%	2090
November	1st to 10th	Day	12% 5% 2 4 3 3 3 3 4 6% 55%	1728
	11th to 20th	Day	14% 8% 3 4 4 3 3 3 6% 6% 46%	1710
	21st to end	Day	17% 10% 3 6% 4 3 3 3 4 5% 43%	1554
December	1st to 10th	Day	13% 12% 3 6% 4 4 3 2 5% 7% 41%	1520
	11th to 20th	Day	15% 10% 4 7% 5% 3 3 3 5% 7% 40%	1918
	21st to end	Day	19% 14% 6% 11% 4 4 5% 4 5% 4 24%	2783
January	1st to 10th	Night	12% 12% 8% 10% 4 4 4 3 4 4 34%	4424
	11th to 20th	Night	13% 12% 5% 11% 5% 6% 7% 4 5% 4 30%	4120
	21st to end	Night	21% 17% 6% 8% 4 3 3 2 4 4 28%	4532
February	1st to 10th	Night	15% 12% 4 8% 5% 5% 4 3 5% 5% 34%	2470
	11th to 20th	Night	15% 8% 3 8% 5% 4 3 3 5% 6% 40%	2305
	21st to end	Night	16% 11% 3 7% 3 4 3 3 4 5% 42%	1884
March	1st to 10th	Night	21% 12% 2 5% 3 3 2 2 3 4 44%	3580
	11th to 20th	Night	14% 7% 2 4 4 3 4 2 4 6% 50%	3480
	21st to end	Night	18% 13% 4 10% 5% 4 4 3 4 5% 30%	3696
April	1st to 10th	Night	11% 7% 3 8% 3 4 4 3 4 6% 47%	1900
	11th to 20th	Night	14% 8% 3 6% 3 4 3 3 5% 6% 46%	1875
	21st to end	Night	20% 6% 2 5% 4 4 4 3 4 7% 42%	1900
May	1st to 10th	Night	16% 8% 3 6% 4 4 3 3 6% 9% 38%	3011
	11th to 20th	Night	14% 8% 2 7% 4 4 4 4 5% 7% 41%	2524
	21st to end	Night	10% 5% 2 6% 4 5% 4 4 6% 9% 46%	2743
June	1st to 10th	Night	8% 4 2 5% 4 4 4 4 7% 8% 51%	1520
	11th to 20th	Night	6% 5% 1 6% 4 4 5% 3 5% 10% 51%	1520
	21st to end	Night	4 4 2 3 4 5% 5% 5% 5% 11% 54%	1520
July	1st to 10th	Night	12% 6% 2 7% 4 4 4 4 6% 9% 44%	2530
	11th to 20th	Night	4 3 1 3 3 3 3 4 6% 10% 59%	2558
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 4 7% 9% 45%	3098
August	1st to 10th	Night	5% 3 1 5% 3 3 4 3 5% 8% 61%	2836
	11th to 20th	Night	11% 6% 2 5% 3 4 3 3 5% 7% 50%	3003
	21st to end	Night	5% 3 1 3 3 3 3 3 6% 9% 59%	3476
September	1st to 10th	Night	12% 4 1 3 3 3 3 3 4 7% 56%	1900
	11th to 20th	Night	9% 5% 2 4 3 3 4 4 6% 7% 52%	1900
	21st to end	Night	7% 5% 2 6% 4 3 3 3 5% 6% 56%	2132
October	1st to 10th	Night	9% 3 2 4 3 3 3 3 4 6% 60%	2280
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 6% 53%	2280
	21st to end	Night	18% 7% 2 5% 3 4 3 3 4 5% 47%	2508
November	1st to 10th	Night	10% 6% 2 4 3 3 4 3 4 5% 56%	2373
	11th to 20th	Night	12% 7% 3 5% 4 3 3 3 4 7% 49%	2470
	21st to end	Night	17% 10% 2 5% 4 3 3 3 4 5% 44%	2624
December	1st to 10th	Night	14% 12% 4 7% 5% 4 4 3 4 7% 37%	2660
	11th to 20th	Night	15% 11% 4 7% 4 3 3 3 5% 5% 39%	3279
	21st to end	Night	19% 20% 6% 9% 5% 4 3 3 3 4 23%	4884

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	52% 6% 10% 22% 9% 1	2528
	11th to 20th	Day	51% 5% 12% 20% 12%	2850
	21st to end	Day	57% 5% 10% 14% 13% 1	3135
February	1st to 10th	Day	52% 4 11% 22% 10% 1	1710
	11th to 20th	Day	46% 5% 11% 20% 15% 4	1769
	21st to end	Day	47% 5% 9% 22% 13% 4	1570
March	1st to 10th	Day	46% 4 7% 22% 17% 4	3302
	11th to 20th	Day	35% 5% 12% 26% 17% 5%	3480
	21st to end	Day	50% 7% 15% 20% 7%	3933
April	1st to 10th	Day	41% 5% 10% 25% 17% 1	2280
	11th to 20th	Day	44% 5% 9% 23% 15% 3	2254
	21st to end	Day	48% 5% 12% 20% 14% 1	2280
May	1st to 10th	Day	44% 9% 14% 21% 11% 1	3919
	11th to 20th	Day	46% 7% 10% 24% 12% 1	4371
	21st to end	Day	36% 8% 10% 23% 21% 1	4837
June	1st to 10th	Day	31% 8% 15% 28% 15% 2	2660
	11th to 20th	Day	29% 8% 13% 27% 19% 4	2660
	21st to end	Day	29% 8% 17% 26% 15% 4	2660
July	1st to 10th	Day	40% 6% 13% 26% 13% 2	4371
	11th to 20th	Day	27% 7% 15% 32% 18% 2	4319
	21st to end	Day	36% 7% 20% 26% 10% 1	4325
August	1st to 10th	Day	27% 7% 16% 37% 13% 1	4090
	11th to 20th	Day	38% 6% 13% 25% 17% 2	3866
	21st to end	Day	29% 5% 16% 32% 14% 3	4179
September	1st to 10th	Day	33% 6% 10% 24% 22% 5%	2280
	11th to 20th	Day	32% 5% 9% 28% 23% 4	2280
	21st to end	Day	31% 6% 9% 27% 24% 3	2022
October	1st to 10th	Day	31% 4 9% 25% 26% 5%	1900
	11th to 20th	Day	35% 4 7% 25% 24% 5%	1900
	21st to end	Day	42% 3 9% 24% 19% 3	2090
November	1st to 10th	Day	31% 5% 12% 25% 22% 5%	1728
	11th to 20th	Day	38% 3 9% 24% 21% 4	1710
	21st to end	Day	44% 5% 9% 27% 15%	1554
December	1st to 10th	Day	44% 4 12% 27% 12% 1	1520
	11th to 20th	Day	45% 4 11% 24% 13% 2	1915
	21st to end	Day	62% 6% 8% 15% 8% 1	2783
January	1st to 10th	Night	53% 4 10% 23% 10% 1	4424
	11th to 20th	Night	58% 4 9% 19% 9% 1	4120
	21st to end	Night	60% 5% 9% 19% 7% 1	4532
February	1st to 10th	Night	52% 5% 10% 19% 12% 2	2470
	11th to 20th	Night	45% 4 11% 21% 16% 3	2306
	21st to end	Night	47% 4 10% 21% 15% 3	1884
March	1st to 10th	Night	46% 4 8% 22% 17% 3	3580
	11th to 20th	Night	36% 5% 10% 24% 22% 4	3480
	21st to end	Night	55% 6% 10% 24% 5%	3696
April	1st to 10th	Night	37% 6% 10% 26% 18% 3	1900
	11th to 20th	Night	39% 5% 10% 24% 17% 5%	1875
	21st to end	Night	44% 4 10% 23% 18% 1	1900
May	1st to 10th	Night	41% 9% 17% 18% 14% 1	3041
	11th to 20th	Night	41% 8% 12% 27% 11% 1	2525
	21st to end	Night	33% 9% 15% 22% 20% 2	2751
June	1st to 10th	Night	29% 7% 16% 28% 18% 3	1520
	11th to 20th	Night	28% 6% 11% 27% 24% 3	1520
	21st to end	Night	24% 8% 16% 28% 19% 6%	1520
July	1st to 10th	Night	38% 5% 11% 30% 14% 2	2490
	11th to 20th	Night	19% 6% 13% 39% 20% 2	2510
	21st to end	Night	34% 6% 21% 26% 13% 1	2999
August	1st to 10th	Night	21% 6% 17% 35% 19% 2	2826
	11th to 20th	Night	34% 5% 13% 27% 19% 3	3031
	21st to end	Night	22% 5% 19% 35% 16% 3	3476
September	1st to 10th	Night	29% 5% 11% 25% 24% 6%	1900
	11th to 20th	Night	30% 7% 10% 24% 26% 4	1900
	21st to end	Night	30% 5% 9% 25% 27% 4	2132
October	1st to 10th	Night	26% 5% 10% 25% 29% 5%	2280
	11th to 20th	Night	34% 4 7% 28% 22% 6%	2280
	21st to end	Night	41% 3 9% 21% 22% 4	2508
November	1st to 10th	Night	31% 5% 12% 26% 20% 6%	2373
	11th to 20th	Night	37% 4 8% 26% 22% 4	2470
	21st to end	Night	43% 4 11% 25% 16% 2	2624
December	1st to 10th	Night	48% 5% 11% 23% 13% 1	2660
	11th to 20th	Night	47% 4 9% 24% 15% 1	3281
	21st to end	Night	66% 5% 9% 13% 7% 1	4884

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	27% 21% 34% 16% 2	270
	11th to 20th	Day	29% 26% 35% 10% 1	270
	21st to end	Day	21% 24% 40% 13% 2	297
February	1st to 10th	Day	30% 23% 33% 13% 2	270
	11th to 20th	Day	25% 29% 31% 12% 3	270
	21st to end	Day	32% 24% 34% 9% 2	225
March	1st to 10th	Day	21% 27% 41% 10% 1	270
	11th to 20th	Day	29% 23% 34% 12% 1	270
	21st to end	Day	33% 24% 30% 10% 3	365
April	1st to 10th	Day	21% 17% 39% 18% 5%	460
	11th to 20th	Day	27% 19% 30% 19% 5%	452
	21st to end	Day	27% 17% 34% 17% 5%	460
May	1st to 10th	Day	18% 18% 38% 19% 6% 1	530
	11th to 20th	Day	17% 16% 27% 27% 10% 1	675
	21st to end	Day	14% 13% 31% 27% 11% 4	734
June	1st to 10th	Day	9% 7% 28% 34% 18% 5%	680
	11th to 20th	Day	9% 4 29% 41% 14% 3	680
	21st to end	Day	7% 10% 33% 35% 12% 3	680
July	1st to 10th	Day	13% 3 20% 31% 27% 7%	671
	11th to 20th	Day	7% 6% 24% 37% 23% 4	668
	21st to end	Day	10% 4 21% 32% 29% 5%	739
August	1st to 10th	Day	8% 4 21% 40% 22% 5%	676
	11th to 20th	Day	10% 5% 23% 35% 21% 6%	542
	21st to end	Day	8% 3 20% 32% 29% 8%	539
September	1st to 10th	Day	12% 3 18% 35% 25% 6%	490
	11th to 20th	Day	10% 3 20% 32% 25% 10%	490
	21st to end	Day	10% 12% 25% 27% 21% 5%	395
October	1st to 10th	Day	10% 12% 32% 28% 13% 4	300
	11th to 20th	Day	20% 26% 27% 22% 6%	300
	21st to end	Day	29% 24% 29% 15% 2	330
November	1st to 10th	Day	14% 15% 40% 20% 10% 2	273
	11th to 20th	Day	22% 20% 29% 22% 4 2	270
	21st to end	Day	27% 17% 30% 22% 3	270
December	1st to 10th	Day	17% 21% 39% 14% 8% 1	270
	11th to 20th	Day	23% 18% 38% 18% 3	270
	21st to end	Day	25% 28% 35% 11% 1	297
January	1st to 10th	Night	19% 20% 39% 17% 5%	950
	11th to 20th	Night	24% 19% 36% 17% 3	950
	21st to end	Night	19% 21% 38% 21% 1	1045
February	1st to 10th	Night	22% 20% 35% 20% 3	950
	11th to 20th	Night	22% 20% 35% 20% 2	831
	21st to end	Night	26% 21% 34% 18% 2	628
March	1st to 10th	Night	24% 17% 40% 18% 2	672
	11th to 20th	Night	23% 16% 35% 22% 4	570
	21st to end	Night	27% 17% 36% 17% 4	627
April	1st to 10th	Night	18% 19% 37% 23% 4	570
	11th to 20th	Night	20% 15% 35% 25% 6%	563
	21st to end	Night	21% 11% 40% 22% 5%	570
May	1st to 10th	Night	15% 11% 34% 32% 7%	570
	11th to 20th	Night	18% 8% 29% 34% 10% 1	561
	21st to end	Night	12% 7% 31% 31% 17% 2	617
June	1st to 10th	Night	8% 4 24% 39% 23% 1	570
	11th to 20th	Night	8% 3 27% 41% 19% 1	570
	21st to end	Night	5% 4 30% 43% 17% 1	570
July	1st to 10th	Night	10% 3 14% 37% 31% 4	555
	11th to 20th	Night	5% 2 18% 42% 30% 2	552
	21st to end	Night	8% 2 18% 40% 31% 2	624
August	1st to 10th	Night	7% 3 13% 45% 31% 1	567
	11th to 20th	Night	9% 2 15% 40% 31% 3	564
	21st to end	Night	6% 2 18% 38% 33% 3	627
September	1st to 10th	Night	13% 4 18% 35% 24% 6%	570
	11th to 20th	Night	11% 3 19% 35% 28% 5%	570
	21st to end	Night	9% 8% 24% 34% 21% 4	712
October	1st to 10th	Night	10% 8% 29% 29% 22% 3	760
	11th to 20th	Night	18% 12% 33% 28% 9% 1	760
	21st to end	Night	23% 13% 35% 23% 6%	836
November	1st to 10th	Night	12% 13% 37% 28% 9%	745
	11th to 20th	Night	17% 17% 34% 24% 7%	760
	21st to end	Night	22% 16% 34% 22% 5%	914
December	1st to 10th	Night	21% 19% 34% 20% 5% 1	950
	11th to 20th	Night	25% 14% 32% 25% 4	950
	21st to end	Night	24% 22% 34% 18% 2	1045

Page generated at 2024-10-30 00:22:59. Version ac07

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