Johnson East Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Johnson East Observatory clear sky chart from 2005-11-06 to 2024-10-25.

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% 11% 4 8% 5% 4 4 3 5% 7% 31%	101012
	Night	18% 13% 4 8% 5% 4 4 3 5% 6% 31%	97740
Transparency	Day	52% 7% 10% 20% 10% 1	100822
	Night	53% 6% 9% 20% 10% 1	97600
Seeing	Day	25% 16% 25% 19% 10% 4	14742
	Night	25% 14% 24% 25% 11% 1	24402

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% 21% 9% 14% 5% 4 2 2 3 3 19%	2810
	11th to 20th	Day	12% 23% 11% 16% 9% 3 3 2 2 3 15%	2840
	21st to end	Day	23% 20% 9% 11% 7% 4 4 2 3 4 13%	3124
February	1st to 10th	Day	19% 19% 5% 11% 6% 4 3 3 4 5% 20%	1710
	11th to 20th	Day	17% 16% 8% 12% 4 4 3 3 5% 5% 21%	1663
	21st to end	Day	21% 17% 5% 10% 4 3 3 3 4 4 24%	1583
March	1st to 10th	Day	18% 15% 6% 8% 4 4 4 3 5% 5% 29%	3435
	11th to 20th	Day	16% 13% 6% 9% 5% 4 4 3 4 6% 31%	3480
	21st to end	Day	20% 13% 3 8% 4 4 4 3 4 6% 30%	3815
April	1st to 10th	Day	17% 16% 4 6% 4 4 5% 4 5% 7% 28%	2209
	11th to 20th	Day	17% 14% 3 7% 5% 4 4 4 5% 6% 33%	2254
	21st to end	Day	23% 11% 2 6% 4 4 4 4 5% 6% 31%	2456
May	1st to 10th	Day	25% 9% 3 8% 5% 4 4 3 5% 6% 27%	4082
	11th to 20th	Day	22% 8% 3 8% 5% 5% 5% 4 5% 7% 29%	4081
	21st to end	Day	15% 6% 2 6% 5% 5% 6% 4 6% 9% 35%	4756
June	1st to 10th	Day	17% 6% 2 7% 5% 5% 5% 4 7% 8% 33%	2660
	11th to 20th	Day	15% 7% 2 7% 6% 5% 6% 4 6% 9% 34%	2660
	21st to end	Day	17% 6% 2 6% 5% 4 5% 5% 6% 9% 34%	2660
July	1st to 10th	Day	12% 6% 2 7% 5% 5% 6% 5% 6% 8% 39%	4322
	11th to 20th	Day	12% 7% 2 7% 5% 5% 5% 4 7% 9% 38%	4120
	21st to end	Day	14% 8% 3 8% 5% 5% 5% 4 6% 7% 34%	4466
August	1st to 10th	Day	16% 7% 3 8% 5% 5% 6% 4 7% 9% 29%	4104
	11th to 20th	Day	15% 6% 3 7% 5% 5% 5% 4 7% 8% 35%	4044
	21st to end	Day	9% 5% 2 6% 4 5% 5% 4 7% 9% 43%	4257
September	1st to 10th	Day	17% 6% 2 5% 4 3 4 4 4 7% 44%	2280
	11th to 20th	Day	14% 6% 2 4 4 4 4 3 5% 7% 45%	2128
	21st to end	Day	20% 9% 3 7% 5% 4 4 3 5% 6% 34%	2067
October	1st to 10th	Day	18% 7% 2 6% 4 4 4 3 5% 7% 40%	1900
	11th to 20th	Day	21% 9% 3 7% 4 4 4 3 4 5% 36%	1900
	21st to end	Day	25% 13% 2 5% 3 3 3 2 3 5% 35%	2027
November	1st to 10th	Day	13% 13% 3 6% 4 4 4 3 3 6% 41%	1829
	11th to 20th	Day	16% 15% 4 7% 4 4 5% 3 5% 5% 31%	1568
	21st to end	Day	20% 19% 5% 7% 3 4 3 3 4 5% 27%	1520
December	1st to 10th	Day	21% 20% 9% 11% 5% 4 3 4 4 4 17%	1520
	11th to 20th	Day	19% 20% 8% 11% 4 2 3 2 5% 5% 21%	1910
	21st to end	Day	22% 22% 7% 10% 4 3 3 2 4 5% 16%	2772
January	1st to 10th	Night	17% 24% 8% 12% 4 4 3 3 3 4 17%	4131
	11th to 20th	Night	17% 20% 9% 14% 5% 6% 4 3 4 3 15%	4120
	21st to end	Night	25% 20% 8% 11% 7% 4 2 2 2 2 17%	4532
February	1st to 10th	Night	20% 17% 5% 11% 5% 3 3 3 4 4 25%	2470
	11th to 20th	Night	19% 17% 5% 13% 4 4 4 3 4 4 22%	2403
	21st to end	Night	20% 16% 6% 9% 5% 4 4 3 4 5% 23%	1868
March	1st to 10th	Night	22% 13% 4 7% 5% 3 3 3 3 6% 30%	3418
	11th to 20th	Night	18% 17% 6% 8% 3 3 3 2 4 5% 31%	3480
	21st to end	Night	18% 13% 3 7% 4 4 3 3 4 5% 37%	3817
April	1st to 10th	Night	19% 16% 3 6% 5% 4 4 3 4 5% 32%	1971
	11th to 20th	Night	17% 10% 2 7% 4 4 4 3 5% 7% 36%	1875
	21st to end	Night	17% 11% 3 7% 3 4 4 4 5% 7% 36%	1741
May	1st to 10th	Night	28% 11% 3 8% 4 4 4 3 4 6% 25%	2813
	11th to 20th	Night	20% 10% 4 7% 4 4 4 3 5% 6% 33%	2812
	21st to end	Night	15% 9% 3 7% 5% 4 4 4 6% 8% 36%	2794
June	1st to 10th	Night	13% 6% 2 7% 3 4 5% 4 5% 7% 43%	1520
	11th to 20th	Night	13% 6% 2 7% 5% 4 4 4 7% 10% 38%	1520
	21st to end	Night	13% 6% 3 5% 4 4 4 5% 6% 10% 40%	1520
July	1st to 10th	Night	13% 8% 3 7% 5% 4 4 4 6% 8% 38%	2633
	11th to 20th	Night	13% 7% 3 7% 5% 4 5% 4 6% 8% 39%	2840
	21st to end	Night	15% 8% 2 7% 5% 5% 5% 4 7% 6% 37%	3087
August	1st to 10th	Night	14% 9% 3 7% 5% 5% 6% 4 7% 8% 33%	2825
	11th to 20th	Night	18% 7% 3 7% 4 3 4 3 5% 7% 40%	2785
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 6% 9% 45%	3366
September	1st to 10th	Night	14% 5% 2 6% 3 5% 4 3 5% 6% 45%	1900
	11th to 20th	Night	13% 4 2 4 3 3 4 3 6% 7% 52%	2047
	21st to end	Night	18% 8% 3 6% 5% 4 4 3 5% 6% 40%	2111
October	1st to 10th	Night	17% 6% 2 6% 4 4 4 4 5% 6% 43%	2280
	11th to 20th	Night	18% 8% 2 6% 4 4 4 3 6% 6% 39%	2280
	21st to end	Night	26% 9% 2 5% 3 3 3 3 4 4 36%	2435
November	1st to 10th	Night	14% 10% 2 6% 5% 3 3 3 4 6% 44%	2247
	11th to 20th	Night	19% 16% 4 7% 5% 4 3 3 4 5% 31%	2610
	21st to end	Night	19% 15% 5% 8% 5% 4 3 3 4 5% 28%	2660
December	1st to 10th	Night	23% 20% 8% 10% 4 4 3 2 3 4 19%	2660
	11th to 20th	Night	20% 19% 7% 11% 5% 4 3 2 3 5% 22%	3285
	21st to end	Night	21% 22% 8% 10% 5% 4 3 3 4 5% 15%	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	71% 5% 8% 12% 4	2811
	11th to 20th	Day	75% 4 6% 9% 5% 1	2840
	21st to end	Day	76% 4 7% 11% 3	3124
February	1st to 10th	Day	67% 4 9% 13% 7%	1710
	11th to 20th	Day	64% 6% 8% 14% 8%	1672
	21st to end	Day	63% 5% 9% 12% 8% 2	1583
March	1st to 10th	Day	56% 5% 9% 22% 7%	3435
	11th to 20th	Day	53% 6% 9% 23% 7% 1	3480
	21st to end	Day	54% 6% 9% 19% 11% 1	3815
April	1st to 10th	Day	54% 6% 9% 18% 11% 2	2209
	11th to 20th	Day	50% 7% 10% 15% 16% 2	2254
	21st to end	Day	52% 6% 9% 21% 9% 2	2456
May	1st to 10th	Day	57% 8% 8% 20% 7% 1	4120
	11th to 20th	Day	52% 9% 9% 22% 7% 1	4085
	21st to end	Day	42% 10% 13% 21% 11% 2	4770
June	1st to 10th	Day	46% 9% 12% 23% 10% 1	2660
	11th to 20th	Day	45% 9% 12% 23% 11% 1	2660
	21st to end	Day	44% 8% 11% 25% 11% 1	2660
July	1st to 10th	Day	41% 8% 12% 22% 14% 2	4255
	11th to 20th	Day	40% 7% 13% 26% 13%	4051
	21st to end	Day	48% 6% 9% 21% 15% 1	4324
August	1st to 10th	Day	48% 9% 13% 22% 8%	4091
	11th to 20th	Day	42% 7% 11% 28% 11%	4083
	21st to end	Day	35% 8% 14% 27% 14% 2	4257
September	1st to 10th	Day	39% 7% 11% 20% 19% 3	2280
	11th to 20th	Day	38% 5% 12% 28% 15% 2	2128
	21st to end	Day	50% 6% 10% 20% 13% 1	2067
October	1st to 10th	Day	44% 6% 12% 21% 15% 2	1900
	11th to 20th	Day	49% 6% 10% 24% 10% 1	1900
	21st to end	Day	53% 4 8% 20% 13% 1	2027
November	1st to 10th	Day	45% 6% 9% 20% 15% 4	1829
	11th to 20th	Day	54% 5% 9% 17% 12% 3	1568
	21st to end	Day	60% 5% 11% 15% 9% 1	1520
December	1st to 10th	Day	71% 6% 7% 11% 4	1520
	11th to 20th	Day	66% 3 7% 18% 4 1	1906
	21st to end	Day	71% 4 9% 12% 4	2772
January	1st to 10th	Night	70% 5% 7% 12% 5% 1	4131
	11th to 20th	Night	73% 6% 8% 11% 2	4120
	21st to end	Night	75% 3 5% 13% 4 1	4532
February	1st to 10th	Night	63% 5% 8% 16% 7%	2470
	11th to 20th	Night	65% 5% 8% 15% 8%	2405
	21st to end	Night	63% 4 8% 15% 8% 1	1868
March	1st to 10th	Night	56% 5% 7% 25% 7% 1	3418
	11th to 20th	Night	53% 9% 8% 24% 6% 1	3480
	21st to end	Night	48% 6% 7% 24% 13% 2	3817
April	1st to 10th	Night	55% 5% 8% 17% 13% 2	1971
	11th to 20th	Night	46% 8% 11% 18% 15% 3	1875
	21st to end	Night	46% 8% 9% 25% 9% 3	1741
May	1st to 10th	Night	59% 6% 8% 16% 9% 2	2840
	11th to 20th	Night	50% 9% 9% 22% 8% 1	2813
	21st to end	Night	41% 10% 13% 22% 9% 4	2801
June	1st to 10th	Night	40% 8% 11% 26% 14% 1	1520
	11th to 20th	Night	41% 8% 13% 26% 11% 1	1520
	21st to end	Night	38% 9% 13% 24% 14% 2	1520
July	1st to 10th	Night	43% 6% 11% 23% 14% 4	2590
	11th to 20th	Night	41% 8% 13% 24% 14% 1	2786
	21st to end	Night	45% 8% 10% 18% 17% 2	2988
August	1st to 10th	Night	46% 10% 15% 21% 8%	2814
	11th to 20th	Night	44% 6% 9% 23% 17% 1	2812
	21st to end	Night	34% 7% 12% 33% 12% 2	3366
September	1st to 10th	Night	38% 7% 9% 23% 18% 4	1900
	11th to 20th	Night	30% 7% 13% 28% 22% 1	2047
	21st to end	Night	43% 8% 9% 22% 17% 1	2111
October	1st to 10th	Night	42% 6% 10% 25% 14% 2	2280
	11th to 20th	Night	45% 6% 9% 25% 13% 2	2280
	21st to end	Night	51% 5% 8% 20% 14% 2	2435
November	1st to 10th	Night	43% 5% 10% 21% 17% 5%	2247
	11th to 20th	Night	56% 5% 7% 18% 12% 2	2610
	21st to end	Night	58% 5% 8% 19% 8% 1	2660
December	1st to 10th	Night	70% 5% 8% 13% 4 1	2660
	11th to 20th	Night	66% 5% 8% 16% 4 1	3288
	21st to end	Night	71% 6% 8% 11% 4	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	33% 33% 19% 11% 4	265
	11th to 20th	Day	41% 28% 25% 5% 1	270
	21st to end	Day	34% 33% 26% 4 3	297
February	1st to 10th	Day	39% 27% 27% 6% 1	270
	11th to 20th	Day	39% 33% 24% 3 1	270
	21st to end	Day	41% 25% 28% 6% 1	286
March	1st to 10th	Day	30% 27% 26% 14% 3	460
	11th to 20th	Day	37% 23% 25% 11% 3 1	460
	21st to end	Day	33% 21% 28% 14% 4	506
April	1st to 10th	Day	30% 25% 25% 13% 7%	460
	11th to 20th	Day	28% 19% 29% 15% 5% 4	452
	21st to end	Day	32% 19% 27% 14% 6% 1	460
May	1st to 10th	Day	30% 21% 25% 15% 7% 3	463
	11th to 20th	Day	26% 16% 29% 17% 9% 3	487
	21st to end	Day	18% 11% 26% 26% 13% 6%	529
June	1st to 10th	Day	18% 11% 29% 24% 13% 4	490
	11th to 20th	Day	18% 13% 24% 23% 17% 4	490
	21st to end	Day	17% 13% 29% 25% 13% 2	490
July	1st to 10th	Day	17% 8% 21% 26% 17% 11%	485
	11th to 20th	Day	13% 8% 26% 30% 16% 7%	484
	21st to end	Day	18% 8% 24% 28% 17% 5%	532
August	1st to 10th	Day	15% 6% 25% 29% 18% 7%	486
	11th to 20th	Day	16% 8% 22% 28% 18% 8%	479
	21st to end	Day	15% 6% 23% 28% 19% 9%	539
September	1st to 10th	Day	19% 10% 18% 27% 17% 9%	490
	11th to 20th	Day	15% 4 22% 26% 25% 8%	490
	21st to end	Day	26% 14% 24% 20% 12% 4	490
October	1st to 10th	Day	20% 10% 25% 26% 15% 4	490
	11th to 20th	Day	26% 15% 26% 22% 9% 2	490
	21st to end	Day	33% 18% 24% 16% 8%	514
November	1st to 10th	Day	21% 16% 27% 23% 11% 2	427
	11th to 20th	Day	36% 20% 24% 14% 5% 1	203
	21st to end	Day	32% 23% 34% 9% 2	180
December	1st to 10th	Day	34% 32% 22% 8% 3 1	180
	11th to 20th	Day	36% 26% 27% 12% 1	180
	21st to end	Day	34% 32% 17% 14% 2 1	198
January	1st to 10th	Night	34% 25% 26% 12% 4	760
	11th to 20th	Night	36% 21% 27% 14% 1	760
	21st to end	Night	32% 26% 26% 15% 1	836
February	1st to 10th	Night	31% 21% 26% 20% 2	760
	11th to 20th	Night	34% 27% 26% 12% 1	743
	21st to end	Night	33% 22% 29% 14% 1	628
March	1st to 10th	Night	28% 20% 28% 21% 4	760
	11th to 20th	Night	31% 22% 21% 19% 6% 1	760
	21st to end	Night	27% 20% 28% 20% 3 1	836
April	1st to 10th	Night	28% 20% 29% 19% 5%	760
	11th to 20th	Night	23% 15% 28% 23% 9% 1	751
	21st to end	Night	24% 12% 31% 26% 7%	601
May	1st to 10th	Night	26% 9% 24% 31% 9% 1	570
	11th to 20th	Night	24% 10% 24% 31% 10% 1	561
	21st to end	Night	11% 5% 26% 33% 22% 2	448
June	1st to 10th	Night	14% 5% 22% 39% 19%	380
	11th to 20th	Night	14% 5% 24% 37% 18% 1	380
	21st to end	Night	14% 4 24% 37% 19%	380
July	1st to 10th	Night	13% 4 18% 37% 24% 4	428
	11th to 20th	Night	12% 4 16% 36% 28% 4	552
	21st to end	Night	15% 5% 15% 38% 26% 1	624
August	1st to 10th	Night	10% 4 13% 45% 27% 2	567
	11th to 20th	Night	14% 4 13% 37% 28% 3	564
	21st to end	Night	14% 3 16% 36% 27% 3	765
September	1st to 10th	Night	16% 6% 18% 31% 25% 4	760
	11th to 20th	Night	14% 5% 17% 35% 26% 3	760
	21st to end	Night	21% 9% 21% 29% 19% 2	760
October	1st to 10th	Night	19% 9% 21% 29% 19% 2	760
	11th to 20th	Night	23% 12% 26% 28% 10% 1	760
	21st to end	Night	31% 12% 25% 24% 7%	812
November	1st to 10th	Night	21% 11% 24% 32% 10% 1	740
	11th to 20th	Night	29% 18% 23% 22% 7% 1	760
	21st to end	Night	30% 17% 27% 20% 5% 1	760
December	1st to 10th	Night	35% 21% 24% 15% 5%	760
	11th to 20th	Night	30% 24% 25% 18% 3	760
	21st to end	Night	32% 21% 26% 20% 1	836

Page generated at 2024-10-22 20:21:01. Version ac07

Copyright © 2024 Attilla Danko.