Jefferson College Observatory
Clear Sky Chart
History

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

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% 7% 2 6% 4 4 4 4 5% 7% 43%	101432
	Night	13% 8% 3 6% 4 4 4 3 5% 6% 44%	98311
Transparency	Day	38% 5% 11% 26% 18% 3	105065
	Night	39% 4 11% 25% 18% 3	102820
Seeing	Day	16% 10% 26% 26% 16% 5%	15700
	Night	17% 10% 28% 30% 14% 2	25533

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% 11% 6% 9% 5% 4 5% 4 6% 6% 34%	2527
	11th to 20th	Day	12% 10% 4 7% 5% 4 4 3 4 6% 41%	2768
	21st to end	Day	21% 14% 4 7% 4 3 3 3 4 5% 32%	3135
February	1st to 10th	Day	16% 12% 3 7% 4 4 4 4 5% 6% 35%	1710
	11th to 20th	Day	15% 8% 3 8% 5% 4 4 3 5% 7% 38%	1832
	21st to end	Day	15% 9% 3 6% 4 4 4 4 5% 6% 39%	1570
March	1st to 10th	Day	18% 13% 2 6% 3 3 3 2 4 4 42%	3184
	11th to 20th	Day	13% 7% 2 5% 3 3 3 3 4 6% 50%	3480
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 4 5% 7% 38%	4005
April	1st to 10th	Day	11% 5% 2 7% 5% 4 4 4 6% 8% 44%	2280
	11th to 20th	Day	17% 8% 3 6% 4 3 4 3 5% 7% 41%	2254
	21st to end	Day	18% 7% 3 6% 5% 4 4 4 6% 6% 37%	2280
May	1st to 10th	Day	14% 7% 2 7% 5% 5% 6% 5% 7% 10% 32%	3819
	11th to 20th	Day	19% 7% 3 6% 4 4 4 3 5% 7% 38%	4335
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 6% 7% 43%	4824
June	1st to 10th	Day	8% 5% 2 6% 4 5% 5% 4 5% 8% 46%	2660
	11th to 20th	Day	7% 4 1 5% 4 4 4 4 7% 10% 50%	2660
	21st to end	Day	5% 3 1 5% 5% 5% 6% 5% 7% 10% 48%	2660
July	1st to 10th	Day	13% 4 2 6% 4 5% 5% 4 7% 9% 42%	4440
	11th to 20th	Day	4 4 2 5% 4 5% 5% 4 7% 12% 49%	4440
	21st to end	Day	7% 5% 2 6% 5% 6% 6% 5% 7% 10% 39%	4512
August	1st to 10th	Day	6% 3 1 5% 3 4 4 4 7% 9% 52%	4079
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 4 5% 8% 44%	3729
	21st to end	Day	8% 4 2 4 3 4 4 4 5% 9% 53%	4180
September	1st to 10th	Day	13% 5% 2 4 3 4 4 3 5% 7% 49%	2280
	11th to 20th	Day	10% 5% 2 6% 4 4 4 3 5% 7% 50%	2261
	21st to end	Day	9% 5% 2 4 3 5% 4 3 5% 7% 53%	2079
October	1st to 10th	Day	9% 4 1 5% 3 3 4 3 4 6% 56%	1900
	11th to 20th	Day	14% 5% 2 4 3 3 3 2 4 6% 53%	1900
	21st to end	Day	16% 7% 2 5% 3 4 3 3 4 5% 47%	2090
November	1st to 10th	Day	12% 5% 1 5% 4 4 3 3 4 5% 54%	1762
	11th to 20th	Day	14% 7% 2 6% 4 3 3 2 5% 7% 47%	1800
	21st to end	Day	15% 10% 3 7% 3 3 3 3 4 5% 43%	1736
December	1st to 10th	Day	13% 10% 2 6% 4 3 4 3 6% 7% 41%	1560
	11th to 20th	Day	13% 12% 4 7% 4 4 4 3 5% 5% 39%	1918
	21st to end	Day	18% 14% 5% 7% 4 5% 4 3 4 5% 29%	2783
January	1st to 10th	Night	15% 9% 5% 8% 5% 4 4 3 5% 6% 36%	4428
	11th to 20th	Night	13% 10% 4 12% 6% 7% 6% 3 4 5% 31%	4184
	21st to end	Night	23% 15% 4 8% 4 3 3 2 4 4 30%	4532
February	1st to 10th	Night	18% 11% 4 8% 5% 4 3 3 4 5% 35%	2470
	11th to 20th	Night	14% 8% 4 7% 5% 4 3 3 4 6% 42%	2233
	21st to end	Night	16% 9% 3 8% 5% 4 3 3 4 5% 40%	1884
March	1st to 10th	Night	22% 10% 2 4 4 3 3 2 3 4 42%	3683
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 4 5% 51%	3480
	21st to end	Night	17% 10% 3 7% 5% 5% 4 4 5% 6% 34%	3626
April	1st to 10th	Night	11% 6% 2 6% 5% 4 4 3 4 7% 49%	1900
	11th to 20th	Night	13% 8% 2 6% 4 3 4 2 5% 6% 45%	1875
	21st to end	Night	20% 6% 2 6% 3 4 4 2 5% 6% 41%	1900
May	1st to 10th	Night	17% 7% 3 5% 4 4 4 3 5% 7% 40%	3073
	11th to 20th	Night	16% 7% 2 5% 4 3 4 3 5% 7% 45%	2552
	21st to end	Night	10% 5% 3 7% 5% 4 5% 4 7% 9% 41%	2743
June	1st to 10th	Night	9% 3 1 5% 4 4 4 4 7% 10% 47%	1520
	11th to 20th	Night	4 4 1 4 4 3 3 5% 7% 9% 56%	1520
	21st to end	Night	4 3 1 4 4 5% 5% 4 7% 10% 54%	1520
July	1st to 10th	Night	12% 4 2 5% 4 3 4 3 6% 10% 47%	2530
	11th to 20th	Night	5% 4 2 5% 3 4 4 4 5% 8% 57%	2530
	21st to end	Night	7% 5% 2 7% 6% 4 5% 4 8% 9% 43%	3033
August	1st to 10th	Night	5% 3 1 4 3 3 3 4 5% 9% 59%	2857
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 4 5% 8% 48%	3100
	21st to end	Night	6% 4 1 4 3 3 3 3 5% 9% 58%	3476
September	1st to 10th	Night	12% 5% 2 4 3 3 4 2 5% 5% 53%	1900
	11th to 20th	Night	9% 5% 2 4 4 4 4 4 5% 7% 53%	1900
	21st to end	Night	10% 4 1 4 4 3 4 3 5% 6% 55%	2098
October	1st to 10th	Night	7% 4 2 4 3 3 3 2 4 7% 62%	2280
	11th to 20th	Night	13% 5% 2 5% 3 2 3 2 4 6% 55%	2280
	21st to end	Night	18% 7% 2 4 3 3 3 2 4 5% 48%	2508
November	1st to 10th	Night	12% 5% 2 4 2 3 3 3 4 5% 57%	2536
	11th to 20th	Night	14% 6% 3 5% 3 3 4 3 5% 5% 49%	2600
	21st to end	Night	17% 10% 3 5% 4 2 3 2 4 5% 45%	2660
December	1st to 10th	Night	16% 11% 3 6% 4 3 4 3 5% 7% 38%	2737
	11th to 20th	Night	15% 10% 4 7% 5% 4 3 3 4 5% 41%	3279
	21st to end	Night	16% 17% 5% 9% 5% 5% 4 4 5% 5% 25%	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	50% 3 12% 25% 9% 2	2528
	11th to 20th	Day	46% 3 11% 24% 17% 1	2768
	21st to end	Day	56% 3 9% 17% 13% 2	3135
February	1st to 10th	Day	49% 3 11% 23% 12% 1	1710
	11th to 20th	Day	47% 4 11% 20% 15% 4	1842
	21st to end	Day	45% 4 10% 23% 14% 5%	1570
March	1st to 10th	Day	48% 3 6% 20% 16% 6%	3184
	11th to 20th	Day	36% 3 10% 27% 17% 6%	3480
	21st to end	Day	45% 4 17% 22% 11% 1	4005
April	1st to 10th	Day	38% 4 11% 27% 18% 1	2280
	11th to 20th	Day	42% 4 10% 24% 16% 4	2254
	21st to end	Day	47% 5% 11% 23% 14% 1	2280
May	1st to 10th	Day	45% 7% 13% 23% 11% 1	3854
	11th to 20th	Day	45% 5% 11% 26% 12% 1	4339
	21st to end	Day	38% 7% 10% 22% 22% 1	4837
June	1st to 10th	Day	35% 6% 13% 26% 18% 2	2660
	11th to 20th	Day	28% 6% 13% 28% 23% 3	2660
	21st to end	Day	28% 7% 18% 26% 16% 5%	2660
July	1st to 10th	Day	39% 5% 12% 30% 13% 2	4371
	11th to 20th	Day	27% 7% 14% 33% 17% 2	4365
	21st to end	Day	37% 8% 16% 27% 11% 1	4370
August	1st to 10th	Day	26% 6% 16% 35% 17%	4065
	11th to 20th	Day	38% 5% 13% 24% 18% 2	3765
	21st to end	Day	29% 5% 13% 35% 15% 3	4179
September	1st to 10th	Day	34% 5% 10% 26% 20% 5%	2280
	11th to 20th	Day	34% 4 9% 27% 23% 2	2261
	21st to end	Day	30% 6% 7% 29% 24% 3	2079
October	1st to 10th	Day	18% 3 6% 20% 45% 9%	3160
	11th to 20th	Day	23% 2 6% 22% 37% 10%	3140
	21st to end	Day	32% 3 7% 28% 28% 3	3428
November	1st to 10th	Day	33% 3 12% 26% 20% 6%	1762
	11th to 20th	Day	39% 3 8% 24% 22% 5%	1800
	21st to end	Day	44% 3 9% 27% 16%	1736
December	1st to 10th	Day	44% 3 12% 28% 12% 1	1560
	11th to 20th	Day	47% 4 9% 23% 15% 2	1915
	21st to end	Day	58% 3 11% 16% 9% 2	2783
January	1st to 10th	Night	50% 3 11% 24% 11% 1	4428
	11th to 20th	Night	57% 3 8% 21% 9% 1	4184
	21st to end	Night	58% 3 9% 21% 8% 1	4532
February	1st to 10th	Night	52% 4 9% 21% 13% 1	2470
	11th to 20th	Night	45% 3 9% 22% 17% 3	2234
	21st to end	Night	48% 3 10% 20% 15% 4	1884
March	1st to 10th	Night	48% 3 7% 24% 16% 3	3683
	11th to 20th	Night	36% 3 11% 25% 20% 4	3480
	21st to end	Night	51% 4 12% 25% 7% 1	3626
April	1st to 10th	Night	36% 3 11% 28% 18% 4	1900
	11th to 20th	Night	40% 3 10% 25% 18% 5%	1875
	21st to end	Night	45% 4 9% 24% 16% 2	1900
May	1st to 10th	Night	43% 6% 15% 20% 14% 2	3103
	11th to 20th	Night	39% 5% 14% 27% 14% 1	2553
	21st to end	Night	37% 8% 12% 24% 17% 2	2751
June	1st to 10th	Night	31% 5% 15% 27% 18% 4	1520
	11th to 20th	Night	23% 7% 12% 29% 25% 4	1520
	21st to end	Night	24% 5% 16% 29% 20% 7%	1520
July	1st to 10th	Night	34% 5% 13% 29% 15% 3	2490
	11th to 20th	Night	25% 5% 11% 37% 20% 3	2482
	21st to end	Night	35% 8% 17% 24% 14% 2	2937
August	1st to 10th	Night	22% 6% 18% 33% 20% 1	2847
	11th to 20th	Night	35% 6% 13% 25% 18% 3	3130
	21st to end	Night	24% 5% 14% 36% 18% 3	3476
September	1st to 10th	Night	32% 4 9% 26% 22% 6%	1900
	11th to 20th	Night	30% 6% 9% 26% 26% 4	1900
	21st to end	Night	30% 5% 9% 24% 27% 4	2098
October	1st to 10th	Night	15% 2 7% 17% 50% 10%	3800
	11th to 20th	Night	22% 3 6% 22% 37% 11%	3779
	21st to end	Night	31% 3 8% 26% 27% 5%	4120
November	1st to 10th	Night	31% 3 12% 26% 23% 6%	2536
	11th to 20th	Night	37% 3 8% 24% 24% 5%	2600
	21st to end	Night	42% 3 10% 25% 19% 2	2660
December	1st to 10th	Night	46% 4 11% 26% 13% 1	2737
	11th to 20th	Night	47% 2 9% 24% 16% 1	3281
	21st to end	Night	61% 4 10% 16% 8% 2	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	25% 17% 35% 17% 4 1	270
	11th to 20th	Day	28% 20% 36% 16% 1	270
	21st to end	Day	19% 25% 38% 14% 4	297
February	1st to 10th	Day	27% 19% 35% 16% 2	270
	11th to 20th	Day	26% 24% 30% 15% 4 1	270
	21st to end	Day	26% 24% 37% 12% 1	225
March	1st to 10th	Day	22% 20% 41% 13% 4	270
	11th to 20th	Day	30% 19% 35% 11% 4 1	270
	21st to end	Day	30% 17% 34% 14% 4	411
April	1st to 10th	Day	19% 16% 36% 21% 7%	460
	11th to 20th	Day	25% 15% 31% 21% 7% 1	452
	21st to end	Day	25% 13% 34% 21% 7% 1	460
May	1st to 10th	Day	21% 14% 32% 24% 8% 1	463
	11th to 20th	Day	21% 9% 28% 25% 14% 4	637
	21st to end	Day	12% 7% 32% 29% 14% 6%	734
June	1st to 10th	Day	11% 6% 23% 30% 24% 6%	680
	11th to 20th	Day	9% 3 23% 40% 19% 7%	680
	21st to end	Day	5% 6% 28% 37% 17% 6%	680
July	1st to 10th	Day	12% 4 14% 28% 30% 13%	671
	11th to 20th	Day	5% 4 18% 38% 27% 8%	668
	21st to end	Day	9% 2 17% 33% 31% 8%	739
August	1st to 10th	Day	9% 3 14% 36% 30% 8%	664
	11th to 20th	Day	11% 5% 17% 28% 29% 10%	479
	21st to end	Day	10% 3 12% 30% 31% 14%	539
September	1st to 10th	Day	13% 3 15% 26% 33% 9%	490
	11th to 20th	Day	9% 3 12% 31% 30% 14%	490
	21st to end	Day	11% 9% 20% 31% 21% 9%	479
October	1st to 10th	Day	12% 9% 21% 38% 15% 5%	300
	11th to 20th	Day	16% 14% 35% 24% 10% 1	300
	21st to end	Day	28% 17% 29% 21% 5%	330
November	1st to 10th	Day	17% 10% 40% 20% 8% 4	300
	11th to 20th	Day	20% 19% 32% 17% 10% 2	300
	21st to end	Day	28% 16% 30% 18% 7% 1	300
December	1st to 10th	Day	18% 20% 36% 16% 7% 3	285
	11th to 20th	Day	24% 16% 34% 21% 4 1	270
	21st to end	Day	26% 21% 31% 17% 4	297
January	1st to 10th	Night	20% 19% 33% 23% 4	950
	11th to 20th	Night	22% 20% 35% 18% 4	950
	21st to end	Night	19% 17% 38% 23% 2	1045
February	1st to 10th	Night	23% 17% 34% 23% 2	950
	11th to 20th	Night	19% 20% 37% 21% 1	758
	21st to end	Night	21% 20% 36% 21% 2	628
March	1st to 10th	Night	24% 15% 36% 22% 3	736
	11th to 20th	Night	22% 13% 33% 27% 5%	570
	21st to end	Night	27% 10% 33% 25% 5%	627
April	1st to 10th	Night	16% 14% 36% 27% 7%	570
	11th to 20th	Night	19% 12% 32% 27% 9% 1	563
	21st to end	Night	25% 7% 37% 25% 6%	570
May	1st to 10th	Night	17% 9% 30% 35% 9% 1	570
	11th to 20th	Night	20% 6% 24% 32% 17% 1	561
	21st to end	Night	11% 5% 25% 37% 19% 4	617
June	1st to 10th	Night	10% 3 18% 40% 27% 1	570
	11th to 20th	Night	6% 2 21% 48% 21% 2	570
	21st to end	Night	4 2 23% 44% 24% 2	570
July	1st to 10th	Night	10% 2 9% 38% 34% 7%	555
	11th to 20th	Night	5% 3 13% 43% 33% 4	552
	21st to end	Night	7% 2 14% 41% 33% 4	624
August	1st to 10th	Night	8% 2 11% 39% 38% 3	567
	11th to 20th	Night	8% 1 12% 40% 35% 4	564
	21st to end	Night	6% 3 11% 33% 42% 5%	627
September	1st to 10th	Night	12% 3 13% 35% 31% 6%	570
	11th to 20th	Night	11% 4 11% 35% 34% 6%	570
	21st to end	Night	11% 5% 21% 33% 26% 4	760
October	1st to 10th	Night	8% 5% 25% 34% 24% 4	760
	11th to 20th	Night	16% 12% 28% 29% 14% 1	760
	21st to end	Night	23% 13% 30% 27% 7%	836
November	1st to 10th	Night	13% 9% 36% 31% 10% 1	780
	11th to 20th	Night	18% 15% 31% 27% 8%	800
	21st to end	Night	24% 12% 32% 27% 6%	860
December	1st to 10th	Night	23% 13% 33% 26% 5% 1	978
	11th to 20th	Night	24% 11% 31% 28% 5%	950
	21st to end	Night	23% 16% 34% 23% 3	1045

Page generated at 2024-12-03 05:45:09. Version ac07

Copyright © 2024 Attilla Danko.