Pettis Rd Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pettis Rd Observatory clear sky chart from 2005-11-06 to 2024-12-24.

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	17% 12% 4 9% 5% 4 4 3 5% 7% 29%	101629
	Night	18% 14% 5% 9% 5% 4 4 3 5% 6% 29%	98438
Transparency	Day	53% 6% 11% 19% 10% 1	105273
	Night	55% 5% 11% 18% 10% 1	102933
Seeing	Day	24% 16% 29% 19% 9% 3	14709
	Night	24% 14% 27% 23% 10% 1	24387

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	18% 25% 11% 14% 5% 3 3 2 3 4 12%	2713
	11th to 20th	Day	13% 25% 9% 17% 8% 5% 3 2 3 4 14%	2840
	21st to end	Day	25% 21% 10% 17% 6% 3 3 2 2 3 8%	3124
February	1st to 10th	Day	17% 21% 6% 15% 9% 5% 3 2 2 4 17%	1710
	11th to 20th	Day	15% 16% 8% 17% 8% 4 3 3 5% 4 17%	1663
	21st to end	Day	18% 19% 3 13% 5% 5% 3 3 4 5% 22%	1540
March	1st to 10th	Day	22% 12% 7% 9% 4 4 3 3 5% 6% 25%	3435
	11th to 20th	Day	12% 19% 6% 11% 5% 4 4 2 4 4 29%	3480
	21st to end	Day	21% 13% 4 11% 4 3 3 2 4 5% 29%	3815
April	1st to 10th	Day	17% 15% 3 7% 4 5% 4 3 5% 7% 30%	2198
	11th to 20th	Day	21% 13% 3 6% 4 4 4 3 4 6% 32%	2317
	21st to end	Day	21% 12% 4 7% 4 4 4 3 4 5% 33%	2470
May	1st to 10th	Day	22% 9% 3 8% 5% 5% 4 4 5% 6% 29%	4082
	11th to 20th	Day	20% 10% 3 8% 5% 4 4 5% 6% 8% 28%	4107
	21st to end	Day	13% 6% 2 6% 5% 4 5% 4 6% 8% 40%	4823
June	1st to 10th	Day	17% 7% 3 7% 5% 5% 5% 4 6% 8% 35%	2660
	11th to 20th	Day	15% 7% 2 8% 5% 5% 5% 4 6% 8% 36%	2660
	21st to end	Day	16% 6% 2 6% 5% 5% 5% 4 6% 9% 37%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 5% 6% 10% 38%	4440
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 9% 41%	4132
	21st to end	Day	11% 6% 2 7% 6% 5% 6% 4 7% 8% 38%	4466
August	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 6% 8% 31%	4104
	11th to 20th	Day	15% 7% 3 8% 5% 6% 6% 5% 8% 8% 29%	4044
	21st to end	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 9% 38%	4349
September	1st to 10th	Day	17% 8% 2 6% 4 5% 4 3 5% 7% 39%	2280
	11th to 20th	Day	13% 6% 2 6% 5% 4 5% 3 6% 9% 40%	2104
	21st to end	Day	22% 8% 3 7% 5% 4 4 4 5% 7% 32%	2085
October	1st to 10th	Day	17% 8% 3 6% 5% 5% 5% 4 6% 8% 35%	1900
	11th to 20th	Day	21% 11% 3 8% 5% 4 4 3 4 5% 30%	1900
	21st to end	Day	25% 13% 3 8% 4 4 4 4 5% 6% 24%	2090
November	1st to 10th	Day	13% 13% 3 7% 5% 5% 5% 3 6% 6% 33%	1837
	11th to 20th	Day	18% 20% 3 8% 5% 4 4 4 5% 5% 25%	1615
	21st to end	Day	20% 23% 6% 10% 5% 4 4 3 5% 5% 16%	1600
December	1st to 10th	Day	20% 26% 9% 12% 5% 4 4 2 3 3 13%	1600
	11th to 20th	Day	20% 21% 8% 13% 5% 3 3 3 5% 4 14%	1990
	21st to end	Day	27% 25% 8% 11% 5% 3 3 2 2 3 11%	2796
January	1st to 10th	Night	17% 24% 11% 17% 5% 3 3 2 3 4 11%	4228
	11th to 20th	Night	16% 20% 10% 18% 5% 5% 5% 3 3 3 10%	4120
	21st to end	Night	27% 20% 9% 15% 5% 3 3 2 3 3 11%	4532
February	1st to 10th	Night	19% 18% 6% 13% 8% 5% 3 2 3 4 18%	2470
	11th to 20th	Night	17% 16% 6% 15% 7% 5% 4 3 5% 4 17%	2403
	21st to end	Night	20% 14% 5% 14% 7% 4 4 3 4 4 21%	1912
March	1st to 10th	Night	22% 16% 4 8% 5% 4 2 3 4 5% 28%	3418
	11th to 20th	Night	17% 17% 8% 8% 4 4 3 2 4 6% 27%	3480
	21st to end	Night	18% 13% 4 9% 4 4 3 2 4 4 34%	3817
April	1st to 10th	Night	18% 16% 3 7% 4 4 4 3 4 6% 29%	1981
	11th to 20th	Night	19% 11% 3 6% 5% 4 5% 3 5% 6% 33%	1829
	21st to end	Night	15% 11% 3 6% 5% 4 5% 3 6% 7% 33%	1710
May	1st to 10th	Night	26% 9% 3 6% 5% 4 4 3 4 7% 30%	2813
	11th to 20th	Night	16% 11% 3 8% 4 4 4 3 5% 7% 34%	2785
	21st to end	Night	13% 6% 2 5% 4 3 4 4 6% 11% 44%	2732
June	1st to 10th	Night	11% 7% 2 6% 6% 4 5% 5% 8% 8% 40%	1520
	11th to 20th	Night	11% 6% 3 7% 6% 4 4 4 6% 7% 42%	1520
	21st to end	Night	13% 6% 3 6% 4 5% 5% 4 6% 9% 40%	1520
July	1st to 10th	Night	13% 8% 3 7% 4 3 4 3 5% 8% 42%	2520
	11th to 20th	Night	13% 5% 2 5% 4 4 5% 4 6% 10% 44%	2824
	21st to end	Night	10% 6% 2 7% 5% 4 5% 4 6% 8% 43%	3087
August	1st to 10th	Night	13% 8% 3 8% 5% 4 5% 3 6% 7% 38%	2825
	11th to 20th	Night	17% 7% 2 6% 4 4 4 4 6% 7% 39%	2785
	21st to end	Night	10% 5% 2 7% 4 5% 6% 4 6% 8% 43%	3274
September	1st to 10th	Night	14% 6% 2 6% 3 4 4 4 5% 6% 46%	1900
	11th to 20th	Night	12% 5% 2 5% 3 3 5% 4 5% 7% 50%	2073
	21st to end	Night	20% 7% 2 7% 5% 4 4 3 5% 7% 36%	2094
October	1st to 10th	Night	17% 7% 3 5% 3 4 4 3 5% 7% 41%	2280
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 4 6% 6% 33%	2280
	21st to end	Night	25% 12% 3 7% 3 4 4 3 4 7% 29%	2508
November	1st to 10th	Night	14% 12% 3 7% 4 4 4 3 6% 6% 36%	2458
	11th to 20th	Night	20% 17% 4 9% 5% 4 5% 3 5% 6% 24%	2782
	21st to end	Night	21% 22% 5% 8% 5% 4 4 3 4 6% 20%	2800
December	1st to 10th	Night	21% 24% 8% 11% 6% 4 4 3 3 4 13%	2800
	11th to 20th	Night	18% 23% 8% 13% 5% 4 3 2 4 4 16%	3425
	21st to end	Night	25% 24% 8% 11% 5% 5% 4 3 3 3 9%	4933

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	77% 3 7% 8% 4	2714
	11th to 20th	Day	77% 3 8% 10% 3	2840
	21st to end	Day	85% 3 6% 5% 1	3124
February	1st to 10th	Day	73% 3 7% 11% 5%	1710
	11th to 20th	Day	70% 5% 7% 12% 6%	1672
	21st to end	Day	65% 4 10% 14% 5% 2	1540
March	1st to 10th	Day	60% 5% 9% 23% 4	3435
	11th to 20th	Day	58% 5% 15% 16% 5% 1	3480
	21st to end	Day	57% 4 8% 19% 11% 1	3815
April	1st to 10th	Day	54% 6% 12% 16% 12% 1	2198
	11th to 20th	Day	53% 4 11% 18% 12% 2	2317
	21st to end	Day	54% 5% 9% 19% 11% 2	2470
May	1st to 10th	Day	54% 6% 8% 23% 8% 1	4120
	11th to 20th	Day	51% 8% 11% 21% 8% 1	4111
	21st to end	Day	40% 8% 12% 22% 14% 3	4837
June	1st to 10th	Day	46% 8% 11% 23% 11% 1	2660
	11th to 20th	Day	46% 7% 12% 20% 14% 1	2660
	21st to end	Day	43% 7% 11% 25% 13% 1	2660
July	1st to 10th	Day	39% 8% 13% 23% 15% 2	4370
	11th to 20th	Day	38% 7% 11% 26% 17% 1	4062
	21st to end	Day	41% 8% 13% 21% 16% 1	4324
August	1st to 10th	Day	49% 8% 12% 22% 8%	4091
	11th to 20th	Day	46% 9% 12% 25% 7% 1	4083
	21st to end	Day	39% 8% 13% 27% 12% 1	4349
September	1st to 10th	Day	44% 6% 12% 21% 14% 2	2280
	11th to 20th	Day	40% 8% 12% 24% 15% 1	2104
	21st to end	Day	51% 7% 11% 21% 11%	2085
October	1st to 10th	Day	37% 7% 14% 24% 17% 1	3160
	11th to 20th	Day	47% 6% 12% 19% 12% 4	3140
	21st to end	Day	46% 5% 14% 24% 11% 1	3428
November	1st to 10th	Day	50% 6% 11% 19% 13% 2	1837
	11th to 20th	Day	61% 5% 11% 14% 7% 2	1615
	21st to end	Day	70% 4 10% 11% 4 1	1600
December	1st to 10th	Day	77% 4 8% 9% 2	1600
	11th to 20th	Day	73% 4 9% 11% 2	1986
	21st to end	Day	82% 3 7% 7% 1	2796
January	1st to 10th	Night	79% 3 8% 8% 3	4228
	11th to 20th	Night	79% 5% 7% 7% 2	4120
	21st to end	Night	81% 3 6% 8% 2	4532
February	1st to 10th	Night	70% 4 9% 12% 5%	2470
	11th to 20th	Night	69% 5% 8% 13% 5%	2405
	21st to end	Night	67% 4 8% 13% 8% 1	1912
March	1st to 10th	Night	59% 4 9% 22% 6%	3418
	11th to 20th	Night	58% 5% 14% 15% 7% 1	3480
	21st to end	Night	53% 3 8% 20% 14% 2	3817
April	1st to 10th	Night	56% 5% 10% 16% 11% 1	1981
	11th to 20th	Night	51% 5% 11% 18% 13% 2	1829
	21st to end	Night	48% 6% 12% 20% 10% 3	1710
May	1st to 10th	Night	54% 5% 9% 19% 10% 2	2840
	11th to 20th	Night	47% 9% 11% 22% 10% 2	2786
	21st to end	Night	34% 8% 14% 24% 16% 3	2739
June	1st to 10th	Night	39% 8% 12% 25% 15% 2	1520
	11th to 20th	Night	39% 7% 14% 23% 15% 2	1520
	21st to end	Night	39% 9% 14% 21% 17% 1	1520
July	1st to 10th	Night	42% 6% 11% 22% 18% 2	2480
	11th to 20th	Night	35% 7% 12% 29% 16% 2	2771
	21st to end	Night	37% 9% 12% 18% 24% 1	2988
August	1st to 10th	Night	45% 8% 10% 25% 11% 1	2814
	11th to 20th	Night	41% 8% 13% 30% 8%	2812
	21st to end	Night	36% 8% 15% 27% 12% 2	3274
September	1st to 10th	Night	36% 7% 13% 26% 16% 3	1900
	11th to 20th	Night	32% 6% 14% 25% 21% 1	2073
	21st to end	Night	47% 7% 11% 20% 15% 1	2094
October	1st to 10th	Night	38% 5% 10% 24% 22% 1	3800
	11th to 20th	Night	44% 6% 12% 18% 14% 5%	3779
	21st to end	Night	42% 4 15% 22% 16% 1	4120
November	1st to 10th	Night	47% 5% 13% 21% 11% 3	2458
	11th to 20th	Night	60% 5% 10% 15% 7% 3	2782
	21st to end	Night	65% 5% 11% 14% 3 1	2800
December	1st to 10th	Night	75% 4 10% 8% 3	2800
	11th to 20th	Night	72% 4 10% 11% 2	3428
	21st to end	Night	79% 4 9% 7% 1	4933

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	36% 25% 28% 7% 3	236
	11th to 20th	Day	37% 28% 25% 6% 3 1	270
	21st to end	Day	34% 32% 26% 7% 1	297
February	1st to 10th	Day	34% 24% 35% 6%	270
	11th to 20th	Day	37% 28% 27% 7% 1	270
	21st to end	Day	41% 25% 29% 5%	239
March	1st to 10th	Day	33% 22% 28% 14% 2	460
	11th to 20th	Day	31% 22% 32% 11% 2 2	460
	21st to end	Day	36% 22% 25% 13% 3 1	506
April	1st to 10th	Day	29% 22% 29% 14% 5% 1	460
	11th to 20th	Day	31% 20% 25% 14% 7% 2	452
	21st to end	Day	29% 19% 32% 15% 4 1	460
May	1st to 10th	Day	29% 20% 27% 18% 6% 2	463
	11th to 20th	Day	25% 15% 28% 21% 9% 2	487
	21st to end	Day	17% 11% 30% 24% 12% 5%	529
June	1st to 10th	Day	19% 14% 31% 25% 8% 3	490
	11th to 20th	Day	20% 12% 28% 25% 13% 2	490
	21st to end	Day	18% 13% 33% 24% 9% 3	490
July	1st to 10th	Day	12% 8% 25% 28% 21% 7%	485
	11th to 20th	Day	14% 8% 29% 30% 13% 7%	484
	21st to end	Day	13% 8% 32% 27% 15% 5%	532
August	1st to 10th	Day	13% 8% 27% 25% 19% 7%	486
	11th to 20th	Day	17% 8% 24% 28% 14% 9%	479
	21st to end	Day	11% 9% 26% 31% 17% 6%	539
September	1st to 10th	Day	17% 10% 26% 26% 17% 5%	490
	11th to 20th	Day	11% 7% 23% 30% 21% 8%	490
	21st to end	Day	24% 13% 29% 18% 12% 4	490
October	1st to 10th	Day	19% 13% 28% 22% 15% 3	490
	11th to 20th	Day	26% 17% 33% 15% 6% 2	490
	21st to end	Day	34% 18% 29% 15% 4	539
November	1st to 10th	Day	23% 20% 33% 15% 7% 2	375
	11th to 20th	Day	36% 22% 29% 10% 3	207
	21st to end	Day	32% 24% 36% 9% 1	200
December	1st to 10th	Day	38% 30% 24% 5% 3 1	200
	11th to 20th	Day	40% 22% 31% 7% 1	200
	21st to end	Day	33% 27% 30% 8%	204
January	1st to 10th	Night	32% 23% 32% 11% 2	760
	11th to 20th	Night	35% 21% 29% 13% 2	760
	21st to end	Night	28% 22% 34% 14% 2	836
February	1st to 10th	Night	33% 20% 28% 18% 1	760
	11th to 20th	Night	29% 24% 32% 13% 1	743
	21st to end	Night	31% 22% 31% 14% 2	628
March	1st to 10th	Night	27% 18% 34% 17% 3	760
	11th to 20th	Night	29% 21% 27% 19% 4 1	760
	21st to end	Night	28% 17% 31% 18% 5% 1	836
April	1st to 10th	Night	27% 17% 30% 20% 5%	760
	11th to 20th	Night	27% 14% 30% 21% 8% 1	705
	21st to end	Night	22% 10% 35% 28% 4 1	570
May	1st to 10th	Night	22% 11% 26% 30% 11%	570
	11th to 20th	Night	19% 10% 29% 32% 9% 1	547
	21st to end	Night	13% 6% 28% 30% 20% 2	411
June	1st to 10th	Night	11% 6% 32% 36% 14% 1	380
	11th to 20th	Night	14% 8% 22% 42% 14%	380
	21st to end	Night	11% 5% 29% 38% 16% 1	380
July	1st to 10th	Night	8% 4 22% 41% 20% 5%	370
	11th to 20th	Night	13% 3 21% 35% 25% 4	537
	21st to end	Night	13% 4 14% 43% 25% 1	624
August	1st to 10th	Night	12% 3 19% 37% 26% 3	567
	11th to 20th	Night	14% 3 15% 38% 27% 4	564
	21st to end	Night	14% 5% 22% 30% 26% 4	712
September	1st to 10th	Night	16% 6% 21% 29% 25% 3	760
	11th to 20th	Night	13% 5% 17% 35% 26% 4	760
	21st to end	Night	22% 10% 23% 26% 16% 4	760
October	1st to 10th	Night	19% 9% 28% 25% 18% 2	760
	11th to 20th	Night	23% 15% 29% 24% 8% 1	760
	21st to end	Night	32% 14% 31% 21% 3	836
November	1st to 10th	Night	22% 15% 29% 25% 9% 1	780
	11th to 20th	Night	30% 19% 29% 16% 6% 1	800
	21st to end	Night	34% 17% 31% 15% 3	800
December	1st to 10th	Night	34% 23% 27% 13% 4	800
	11th to 20th	Night	32% 25% 26% 14% 3	800
	21st to end	Night	33% 21% 30% 15% 1	851

Page generated at 2024-12-21 04:13:50. Version ac07

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