Ashton Observatory at Johnson Farms
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashton Observatory at Johnson Farms clear sky chart from 2005-11-06 to 2024-11-01.

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% 6% 2 6% 4 4 5% 4 6% 8% 41%	101215
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 43%	97693
Transparency	Day	40% 7% 12% 23% 15% 3	101015
	Night	40% 6% 12% 23% 15% 3	97564
Seeing	Day	19% 13% 28% 24% 13% 4	14975
	Night	17% 11% 30% 29% 11% 1	24436

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% 4 2 5% 3 3 4 3 5% 6% 47%	2551
	11th to 20th	Day	15% 11% 3 6% 5% 4 4 2 4 4 41%	2840
	21st to end	Day	19% 9% 3 7% 5% 5% 4 3 4 5% 36%	3124
February	1st to 10th	Day	14% 7% 2 7% 5% 5% 5% 4 6% 7% 38%	1710
	11th to 20th	Day	18% 7% 2 5% 4 5% 4 4 6% 6% 40%	1724
	21st to end	Day	18% 8% 2 6% 4 5% 5% 2 4 5% 40%	1570
March	1st to 10th	Day	23% 6% 2 5% 3 4 4 4 5% 6% 37%	3358
	11th to 20th	Day	10% 4 2 5% 5% 4 5% 4 5% 7% 49%	3480
	21st to end	Day	20% 7% 2 5% 4 4 3 3 5% 6% 41%	3898
April	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 6% 8% 42%	2280
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 3 4 6% 47%	2254
	21st to end	Day	19% 6% 2 4 4 4 3 4 5% 7% 41%	2280
May	1st to 10th	Day	25% 7% 2 7% 4 4 5% 4 6% 7% 30%	4004
	11th to 20th	Day	23% 7% 3 7% 4 4 5% 4 6% 8% 30%	4324
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 9% 45%	4823
June	1st to 10th	Day	12% 5% 2 5% 5% 4 5% 4 7% 8% 43%	2660
	11th to 20th	Day	12% 5% 2 6% 5% 5% 4 4 7% 9% 41%	2660
	21st to end	Day	10% 4 1 4 4 4 5% 5% 8% 10% 43%	2660
July	1st to 10th	Day	6% 4 2 6% 5% 6% 6% 5% 8% 11% 42%	4440
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 5% 8% 11% 39%	4353
	21st to end	Day	11% 6% 3 7% 5% 5% 6% 5% 6% 9% 35%	4466
August	1st to 10th	Day	17% 6% 2 7% 4 6% 6% 4 7% 9% 32%	4104
	11th to 20th	Day	11% 5% 2 6% 5% 5% 6% 5% 8% 8% 38%	3860
	21st to end	Day	11% 5% 2 6% 4 4 5% 5% 6% 8% 46%	4180
September	1st to 10th	Day	14% 6% 2 5% 3 5% 4 4 5% 6% 46%	2280
	11th to 20th	Day	12% 5% 1 5% 3 4 5% 3 5% 8% 47%	2280
	21st to end	Day	20% 8% 2 6% 4 4 4 3 5% 6% 37%	2005
October	1st to 10th	Day	17% 5% 3 5% 3 3 4 3 5% 7% 46%	1900
	11th to 20th	Day	18% 3 2 4 3 3 3 3 5% 6% 49%	1900
	21st to end	Day	14% 5% 2 5% 4 3 4 3 5% 6% 49%	2090
November	1st to 10th	Day	13% 5% 2 5% 3 3 4 3 5% 7% 51%	1739
	11th to 20th	Day	15% 6% 2 4 3 3 4 4 6% 5% 49%	1696
	21st to end	Day	15% 5% 2 5% 5% 3 4 3 5% 5% 47%	1520
December	1st to 10th	Day	16% 6% 2 5% 4 4 5% 4 6% 7% 40%	1520
	11th to 20th	Day	17% 5% 2 6% 3 3 3 4 6% 8% 44%	1910
	21st to end	Day	17% 7% 2 7% 4 4 5% 4 5% 8% 37%	2772
January	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 5% 7% 44%	4393
	11th to 20th	Night	19% 8% 2 4 3 3 3 3 4 5% 46%	4120
	21st to end	Night	21% 9% 2 5% 3 3 3 3 4 5% 41%	4532
February	1st to 10th	Night	15% 7% 2 6% 4 5% 4 4 6% 6% 41%	2470
	11th to 20th	Night	18% 7% 2 6% 4 3 3 3 5% 5% 44%	2342
	21st to end	Night	17% 7% 2 6% 4 4 3 3 4 6% 42%	1884
March	1st to 10th	Night	22% 7% 2 5% 4 4 4 3 4 6% 39%	3493
	11th to 20th	Night	11% 4 2 5% 4 4 4 4 6% 7% 50%	3480
	21st to end	Night	15% 9% 3 5% 4 3 3 3 3 5% 47%	3732
April	1st to 10th	Night	15% 8% 2 6% 3 3 5% 4 6% 7% 41%	1900
	11th to 20th	Night	14% 5% 2 7% 4 3 5% 3 5% 7% 45%	1875
	21st to end	Night	17% 5% 2 5% 4 3 4 4 7% 7% 42%	1900
May	1st to 10th	Night	25% 8% 2 6% 4 4 4 3 6% 6% 32%	2919
	11th to 20th	Night	24% 9% 2 6% 5% 4 4 4 5% 7% 31%	2566
	21st to end	Night	11% 4 1 6% 3 5% 4 4 8% 10% 43%	2732
June	1st to 10th	Night	11% 4 2 6% 4 4 4 4 7% 10% 45%	1520
	11th to 20th	Night	11% 6% 2 6% 5% 4 5% 4 7% 9% 42%	1520
	21st to end	Night	9% 4 2 5% 6% 5% 6% 4 6% 11% 42%	1520
July	1st to 10th	Night	7% 5% 2 6% 6% 6% 7% 4 7% 10% 40%	2520
	11th to 20th	Night	8% 6% 2 7% 5% 5% 7% 5% 7% 10% 37%	2603
	21st to end	Night	12% 7% 3 6% 4 5% 5% 4 7% 8% 38%	3087
August	1st to 10th	Night	18% 6% 3 7% 4 5% 5% 5% 6% 9% 33%	2825
	11th to 20th	Night	10% 8% 3 9% 6% 5% 6% 4 7% 8% 35%	2935
	21st to end	Night	11% 5% 1 6% 4 3 5% 4 5% 8% 48%	3476
September	1st to 10th	Night	15% 6% 2 5% 4 3 4 3 6% 7% 45%	1900
	11th to 20th	Night	11% 5% 3 5% 4 4 3 4 4 7% 50%	1900
	21st to end	Night	20% 6% 3 6% 4 4 4 3 4 7% 38%	2170
October	1st to 10th	Night	20% 6% 2 5% 3 3 4 3 4 5% 46%	2280
	11th to 20th	Night	15% 4 1 4 3 3 4 2 4 5% 53%	2280
	21st to end	Night	15% 5% 2 4 3 3 4 3 5% 7% 50%	2508
November	1st to 10th	Night	12% 5% 1 6% 3 3 4 2 4 6% 54%	2343
	11th to 20th	Night	14% 6% 2 5% 4 3 3 2 5% 6% 50%	2479
	21st to end	Night	14% 4 2 4 4 5% 4 3 6% 7% 47%	2660
December	1st to 10th	Night	17% 7% 3 6% 4 4 3 4 6% 6% 41%	2660
	11th to 20th	Night	17% 6% 2 5% 4 4 4 3 5% 6% 43%	3285
	21st to end	Night	16% 7% 2 6% 5% 5% 5% 4 6% 7% 37%	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	37% 5% 9% 31% 14% 4	2552
	11th to 20th	Day	46% 5% 11% 20% 15% 4	2840
	21st to end	Day	48% 6% 11% 22% 11% 2	3124
February	1st to 10th	Day	43% 7% 13% 24% 12% 2	1710
	11th to 20th	Day	43% 5% 10% 24% 15% 3	1733
	21st to end	Day	47% 5% 10% 20% 15% 4	1570
March	1st to 10th	Day	44% 6% 12% 22% 13% 3	3358
	11th to 20th	Day	32% 6% 10% 28% 20% 4	3480
	21st to end	Day	45% 5% 10% 20% 17% 3	3898
April	1st to 10th	Day	39% 7% 12% 20% 17% 5%	2280
	11th to 20th	Day	37% 5% 11% 22% 19% 5%	2254
	21st to end	Day	41% 5% 12% 20% 18% 3	2280
May	1st to 10th	Day	51% 7% 11% 19% 11% 1	4041
	11th to 20th	Day	48% 10% 14% 18% 8% 1	4328
	21st to end	Day	34% 8% 15% 24% 17% 3	4837
June	1st to 10th	Day	36% 9% 14% 25% 15% 1	2660
	11th to 20th	Day	38% 10% 12% 24% 14% 2	2660
	21st to end	Day	33% 9% 15% 24% 17% 2	2660
July	1st to 10th	Day	33% 11% 19% 20% 12% 5%	4370
	11th to 20th	Day	36% 8% 16% 27% 11% 2	4278
	21st to end	Day	43% 8% 12% 19% 17% 1	4324
August	1st to 10th	Day	45% 9% 15% 23% 8% 1	4091
	11th to 20th	Day	39% 8% 14% 25% 14% 1	3899
	21st to end	Day	35% 7% 12% 27% 16% 2	4180
September	1st to 10th	Day	38% 8% 12% 19% 19% 4	2280
	11th to 20th	Day	34% 6% 11% 24% 21% 3	2280
	21st to end	Day	46% 6% 9% 19% 18% 2	2005
October	1st to 10th	Day	39% 6% 10% 23% 20% 3	1900
	11th to 20th	Day	35% 6% 10% 24% 22% 4	1900
	21st to end	Day	36% 5% 9% 26% 22% 2	2090
November	1st to 10th	Day	32% 6% 12% 26% 20% 4	1739
	11th to 20th	Day	34% 6% 10% 23% 22% 4	1696
	21st to end	Day	38% 5% 11% 28% 17% 2	1520
December	1st to 10th	Day	41% 7% 14% 24% 12% 2	1520
	11th to 20th	Day	38% 4 13% 31% 11% 2	1906
	21st to end	Day	45% 6% 15% 22% 11% 1	2772
January	1st to 10th	Night	39% 5% 11% 26% 15% 3	4393
	11th to 20th	Night	41% 4 11% 24% 17% 3	4120
	21st to end	Night	45% 4 8% 27% 14% 1	4532
February	1st to 10th	Night	42% 6% 12% 24% 14% 1	2470
	11th to 20th	Night	43% 4 9% 22% 17% 4	2344
	21st to end	Night	43% 5% 11% 22% 15% 5%	1884
March	1st to 10th	Night	46% 5% 9% 26% 12% 2	3493
	11th to 20th	Night	31% 7% 11% 30% 18% 3	3480
	21st to end	Night	41% 5% 9% 21% 19% 5%	3732
April	1st to 10th	Night	41% 7% 10% 19% 19% 4	1900
	11th to 20th	Night	38% 5% 13% 20% 18% 6%	1875
	21st to end	Night	38% 7% 11% 23% 15% 5%	1900
May	1st to 10th	Night	52% 6% 10% 19% 10% 2	2948
	11th to 20th	Night	50% 9% 11% 18% 10% 1	2567
	21st to end	Night	33% 9% 18% 25% 12% 3	2739
June	1st to 10th	Night	33% 8% 13% 27% 17% 2	1520
	11th to 20th	Night	37% 9% 13% 25% 14% 3	1520
	21st to end	Night	36% 8% 13% 23% 18% 3	1520
July	1st to 10th	Night	38% 9% 20% 17% 12% 4	2480
	11th to 20th	Night	39% 8% 18% 24% 10% 1	2555
	21st to end	Night	41% 8% 14% 20% 16% 1	2988
August	1st to 10th	Night	45% 9% 17% 20% 8% 1	2814
	11th to 20th	Night	43% 8% 12% 25% 11% 1	2962
	21st to end	Night	34% 6% 12% 30% 16% 2	3476
September	1st to 10th	Night	39% 5% 11% 21% 18% 5%	1900
	11th to 20th	Night	34% 5% 9% 26% 22% 4	1900
	21st to end	Night	46% 6% 10% 17% 17% 4	2170
October	1st to 10th	Night	41% 5% 11% 22% 18% 3	2280
	11th to 20th	Night	34% 4 10% 27% 21% 4	2280
	21st to end	Night	35% 5% 10% 26% 21% 4	2508
November	1st to 10th	Night	33% 5% 10% 26% 21% 5%	2343
	11th to 20th	Night	36% 5% 9% 23% 22% 5%	2479
	21st to end	Night	35% 5% 12% 25% 19% 3	2660
December	1st to 10th	Night	43% 6% 12% 24% 14% 2	2660
	11th to 20th	Night	41% 5% 11% 22% 18% 3	3288
	21st to end	Night	43% 7% 16% 22% 11% 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	29% 23% 30% 14% 4 1	191
	11th to 20th	Day	30% 24% 31% 13% 2	270
	21st to end	Day	23% 24% 36% 13% 3	297
February	1st to 10th	Day	24% 23% 39% 10% 4	270
	11th to 20th	Day	31% 21% 39% 6% 2	331
	21st to end	Day	29% 20% 33% 17% 2	382
March	1st to 10th	Day	25% 22% 30% 19% 4	460
	11th to 20th	Day	25% 22% 32% 17% 3 2	460
	21st to end	Day	23% 20% 32% 19% 5% 1	506
April	1st to 10th	Day	21% 23% 32% 17% 5% 2	460
	11th to 20th	Day	18% 18% 33% 19% 10% 2	452
	21st to end	Day	26% 15% 32% 19% 7% 2	460
May	1st to 10th	Day	23% 19% 29% 18% 8% 3	463
	11th to 20th	Day	21% 13% 28% 25% 11% 3	487
	21st to end	Day	17% 7% 26% 27% 20% 4	529
June	1st to 10th	Day	13% 10% 29% 25% 18% 6%	490
	11th to 20th	Day	16% 6% 28% 28% 18% 4	490
	21st to end	Day	9% 7% 30% 33% 17% 4	490
July	1st to 10th	Day	10% 5% 19% 36% 20% 10%	485
	11th to 20th	Day	5% 3 23% 35% 27% 8%	484
	21st to end	Day	13% 3 23% 34% 21% 6%	532
August	1st to 10th	Day	12% 5% 21% 28% 24% 10%	486
	11th to 20th	Day	12% 4 20% 31% 24% 9%	479
	21st to end	Day	9% 3 22% 32% 22% 12%	539
September	1st to 10th	Day	16% 7% 21% 25% 20% 12%	490
	11th to 20th	Day	14% 4 22% 32% 18% 10%	490
	21st to end	Day	26% 10% 23% 26% 11% 4	490
October	1st to 10th	Day	22% 8% 23% 23% 18% 5%	490
	11th to 20th	Day	17% 15% 26% 27% 12% 3	490
	21st to end	Day	16% 13% 33% 26% 9% 2	539
November	1st to 10th	Day	16% 12% 33% 23% 12% 3	399
	11th to 20th	Day	18% 14% 35% 22% 10% 1	356
	21st to end	Day	24% 17% 32% 17% 8% 1	180
December	1st to 10th	Day	19% 23% 37% 16% 3 2	180
	11th to 20th	Day	24% 22% 29% 18% 7%	180
	21st to end	Day	25% 16% 33% 19% 6%	198
January	1st to 10th	Night	18% 18% 43% 18% 3	760
	11th to 20th	Night	22% 17% 34% 24% 3	760
	21st to end	Night	20% 18% 38% 22% 2	836
February	1st to 10th	Night	18% 17% 36% 27% 2	760
	11th to 20th	Night	25% 21% 37% 16% 1	743
	21st to end	Night	24% 18% 37% 18% 3	628
March	1st to 10th	Night	19% 16% 38% 24% 3	760
	11th to 20th	Night	22% 18% 35% 19% 4 1	760
	21st to end	Night	18% 16% 41% 20% 4 1	836
April	1st to 10th	Night	19% 21% 35% 21% 4	760
	11th to 20th	Night	15% 15% 36% 27% 7%	751
	21st to end	Night	20% 11% 34% 27% 7%	760
May	1st to 10th	Night	21% 9% 30% 28% 11%	639
	11th to 20th	Night	21% 7% 28% 35% 9%	419
	21st to end	Night	15% 6% 21% 39% 17% 2	411
June	1st to 10th	Night	11% 3 28% 36% 20% 1	380
	11th to 20th	Night	11% 4 26% 42% 16% 1	380
	21st to end	Night	11% 2 26% 46% 15%	380
July	1st to 10th	Night	8% 2 20% 43% 24% 3	370
	11th to 20th	Night	6% 2 16% 42% 32% 2	412
	21st to end	Night	8% 3 18% 42% 26% 3	624
August	1st to 10th	Night	12% 2 12% 42% 30% 2	567
	11th to 20th	Night	11% 4 15% 43% 24% 3	649
	21st to end	Night	11% 3 17% 39% 26% 4	836
September	1st to 10th	Night	16% 3 21% 31% 24% 4	760
	11th to 20th	Night	11% 4 17% 37% 28% 4	760
	21st to end	Night	23% 4 23% 30% 18% 1	760
October	1st to 10th	Night	20% 6% 23% 28% 19% 4	760
	11th to 20th	Night	17% 9% 28% 31% 14% 1	760
	21st to end	Night	17% 11% 32% 27% 12%	836
November	1st to 10th	Night	15% 8% 34% 31% 9% 2	743
	11th to 20th	Night	17% 17% 32% 27% 7% 1	760
	21st to end	Night	17% 15% 32% 28% 8% 1	760
December	1st to 10th	Night	20% 17% 35% 20% 7% 1	760
	11th to 20th	Night	18% 13% 40% 24% 5%	760
	21st to end	Night	19% 15% 35% 29% 3	836

Page generated at 2024-10-29 11:20:50. Version ac07

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