Journey's End Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Journey's End Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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 3 5% 7% 45%	101156
	Night	12% 7% 2 6% 4 3 4 3 5% 6% 48%	98455
Transparency	Day	38% 4 12% 26% 17% 3	104807
	Night	36% 4 11% 26% 19% 4	102944
Seeing	Day	15% 9% 26% 27% 18% 5%	15626
	Night	16% 9% 30% 31% 13% 1	25460

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	16% 12% 3 5% 4 3 3 3 3 5% 44%	2847
	11th to 20th	Day	11% 11% 4 8% 4 4 4 3 4 5% 42%	2850
	21st to end	Day	20% 12% 4 7% 3 3 3 2 3 4 39%	3135
February	1st to 10th	Day	16% 12% 3 7% 5% 3 5% 4 4 5% 37%	1710
	11th to 20th	Day	13% 10% 2 7% 5% 4 3 3 4 5% 42%	1668
	21st to end	Day	15% 11% 2 6% 4 4 4 3 5% 7% 38%	1655
March	1st to 10th	Day	16% 9% 2 6% 3 2 3 2 4 6% 47%	3436
	11th to 20th	Day	14% 7% 2 4 3 3 3 3 4 6% 51%	3480
	21st to end	Day	18% 11% 3 6% 4 4 3 4 5% 6% 35%	3814
April	1st to 10th	Day	12% 9% 2 7% 3 3 5% 4 5% 7% 45%	2239
	11th to 20th	Day	16% 9% 2 6% 4 3 4 3 5% 7% 40%	2254
	21st to end	Day	20% 8% 3 7% 5% 4 4 3 5% 6% 36%	2280
May	1st to 10th	Day	20% 8% 3 6% 5% 4 4 4 6% 6% 36%	4068
	11th to 20th	Day	14% 7% 3 6% 5% 4 5% 4 5% 7% 42%	4082
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 7% 8% 39%	4599
June	1st to 10th	Day	8% 5% 3 5% 4 4 5% 4 7% 10% 46%	2660
	11th to 20th	Day	7% 4 2 6% 5% 4 4 4 6% 9% 48%	2660
	21st to end	Day	6% 3 1 4 3 5% 5% 4 6% 9% 55%	2649
July	1st to 10th	Day	11% 5% 2 6% 5% 4 6% 5% 7% 8% 41%	4120
	11th to 20th	Day	5% 4 2 6% 4 5% 5% 5% 7% 10% 48%	4120
	21st to end	Day	6% 4 2 7% 5% 5% 5% 5% 8% 11% 42%	4465
August	1st to 10th	Day	5% 3 2 5% 4 4 4 4 6% 8% 56%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 8% 44%	3959
	21st to end	Day	5% 4 2 4 4 4 4 4 5% 8% 56%	4180
September	1st to 10th	Day	11% 6% 2 5% 4 3 4 3 5% 6% 51%	2280
	11th to 20th	Day	10% 6% 2 6% 4 5% 4 3 5% 7% 47%	2195
	21st to end	Day	7% 5% 1 5% 5% 5% 4 4 6% 6% 52%	2025
October	1st to 10th	Day	10% 5% 1 4 3 3 4 3 5% 6% 56%	1900
	11th to 20th	Day	14% 6% 2 5% 3 3 3 2 3 5% 55%	1900
	21st to end	Day	18% 6% 3 5% 3 2 3 2 4 5% 48%	2090
November	1st to 10th	Day	12% 5% 2 4 3 3 3 3 4 5% 56%	1958
	11th to 20th	Day	14% 8% 3 5% 3 3 3 3 4 7% 48%	1845
	21st to end	Day	15% 7% 3 5% 4 3 2 2 4 5% 49%	1576
December	1st to 10th	Day	13% 9% 3 7% 4 3 3 3 6% 6% 44%	1520
	11th to 20th	Day	12% 12% 4 8% 4 4 3 2 3 5% 43%	1918
	21st to end	Day	15% 18% 5% 8% 4 4 5% 3 5% 5% 28%	2915
January	1st to 10th	Night	11% 11% 4 10% 5% 3 3 2 4 5% 42%	4108
	11th to 20th	Night	11% 7% 3 8% 7% 6% 5% 4 4 6% 39%	4120
	21st to end	Night	21% 13% 4 6% 3 3 2 3 3 4 38%	4532
February	1st to 10th	Night	15% 11% 3 6% 4 3 3 3 5% 6% 42%	2470
	11th to 20th	Night	14% 10% 3 7% 3 3 3 3 4 6% 45%	2398
	21st to end	Night	15% 9% 3 6% 4 3 3 2 5% 5% 44%	1813
March	1st to 10th	Night	17% 9% 2 5% 4 3 3 3 3 5% 47%	3419
	11th to 20th	Night	13% 6% 1 4 3 3 4 3 5% 5% 52%	3480
	21st to end	Night	14% 8% 3 7% 5% 5% 5% 3 5% 6% 39%	3817
April	1st to 10th	Night	11% 6% 2 5% 3 3 4 3 5% 6% 54%	1939
	11th to 20th	Night	13% 8% 2 5% 3 4 3 3 5% 7% 46%	1875
	21st to end	Night	17% 8% 3 6% 4 4 3 3 5% 7% 40%	1900
May	1st to 10th	Night	14% 7% 2 6% 3 3 4 3 6% 8% 43%	2833
	11th to 20th	Night	13% 8% 3 7% 4 3 4 3 5% 8% 41%	2823
	21st to end	Night	11% 6% 2 6% 5% 4 5% 4 6% 9% 44%	2963
June	1st to 10th	Night	7% 3 2 4 4 3 5% 4 7% 9% 53%	1520
	11th to 20th	Night	5% 3 1 3 4 3 4 3 8% 10% 54%	1520
	21st to end	Night	3 3 1 2 2 3 4 3 6% 10% 63%	1525
July	1st to 10th	Night	11% 5% 2 6% 3 4 4 4 6% 7% 48%	2850
	11th to 20th	Night	4 3 2 4 3 4 4 4 6% 9% 59%	2850
	21st to end	Night	6% 4 1 5% 3 4 4 4 7% 10% 52%	3098
August	1st to 10th	Night	4 2 1 4 4 4 4 3 5% 8% 63%	2836
	11th to 20th	Night	8% 4 2 6% 4 4 5% 4 5% 8% 49%	2874
	21st to end	Night	4 3 1 4 3 3 4 2 6% 8% 62%	3476
September	1st to 10th	Night	9% 5% 2 5% 3 3 3 3 4 7% 56%	1900
	11th to 20th	Night	10% 4 2 6% 4 3 4 3 4 7% 54%	1981
	21st to end	Night	8% 5% 2 5% 3 3 4 3 4 6% 57%	2134
October	1st to 10th	Night	8% 4 1 4 3 3 2 3 4 7% 62%	2280
	11th to 20th	Night	15% 5% 1 3 2 2 3 2 5% 5% 57%	2280
	21st to end	Night	16% 6% 2 4 3 3 3 3 4 5% 51%	2508
November	1st to 10th	Night	12% 7% 1 3 2 3 2 2 3 5% 60%	2340
	11th to 20th	Night	12% 7% 1 4 3 3 3 3 4 5% 53%	2548
	21st to end	Night	14% 9% 2 5% 3 3 3 2 4 5% 51%	2759
December	1st to 10th	Night	14% 9% 4 6% 3 4 3 2 5% 7% 43%	2660
	11th to 20th	Night	14% 10% 4 7% 4 3 3 3 4 5% 43%	3279
	21st to end	Night	17% 16% 5% 9% 4 4 3 3 4 5% 30%	4747

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	44% 3 7% 28% 17% 1	2848
	11th to 20th	Day	45% 4 9% 27% 12% 3	2850
	21st to end	Day	50% 3 9% 19% 16% 4	3135
February	1st to 10th	Day	51% 3 9% 23% 12% 2	1710
	11th to 20th	Day	46% 3 10% 21% 16% 4	1677
	21st to end	Day	47% 3 7% 23% 14% 7%	1655
March	1st to 10th	Day	40% 4 8% 22% 20% 7%	3436
	11th to 20th	Day	36% 3 11% 30% 15% 6%	3480
	21st to end	Day	50% 5% 16% 20% 8% 1	3814
April	1st to 10th	Day	40% 4 12% 24% 18% 2	2239
	11th to 20th	Day	44% 3 14% 20% 15% 3	2254
	21st to end	Day	49% 4 10% 24% 11% 1	2280
May	1st to 10th	Day	48% 6% 11% 20% 14% 1	4106
	11th to 20th	Day	42% 6% 14% 25% 12%	4086
	21st to end	Day	41% 7% 14% 25% 13% 1	4612
June	1st to 10th	Day	33% 5% 17% 27% 16% 1	2660
	11th to 20th	Day	32% 5% 15% 31% 15% 2	2660
	21st to end	Day	25% 5% 17% 32% 17% 4	2649
July	1st to 10th	Day	37% 7% 15% 23% 15% 2	4056
	11th to 20th	Day	30% 6% 13% 33% 17% 2	4051
	21st to end	Day	33% 7% 22% 28% 10%	4325
August	1st to 10th	Day	26% 4 19% 28% 22% 1	4090
	11th to 20th	Day	36% 6% 15% 28% 14% 1	3998
	21st to end	Day	27% 5% 11% 36% 17% 4	4179
September	1st to 10th	Day	35% 4 11% 26% 15% 9%	2280
	11th to 20th	Day	36% 5% 8% 22% 26% 2	2195
	21st to end	Day	31% 5% 9% 27% 23% 4	2025
October	1st to 10th	Day	18% 2 6% 19% 36% 20%	3160
	11th to 20th	Day	21% 2 4 24% 35% 14%	3140
	21st to end	Day	29% 3 7% 32% 25% 4	3428
November	1st to 10th	Day	32% 3 9% 28% 23% 5%	1958
	11th to 20th	Day	37% 3 8% 22% 23% 7%	1845
	21st to end	Day	39% 3 9% 25% 22% 2	1576
December	1st to 10th	Day	41% 3 9% 31% 14% 1	1520
	11th to 20th	Day	46% 3 7% 20% 22% 2	1915
	21st to end	Day	58% 4 8% 17% 11% 1	2915
January	1st to 10th	Night	46% 4 10% 25% 14% 1	4108
	11th to 20th	Night	44% 6% 10% 26% 13% 1	4120
	21st to end	Night	52% 2 9% 21% 15% 2	4532
February	1st to 10th	Night	44% 3 12% 23% 15% 3	2470
	11th to 20th	Night	43% 3 10% 23% 17% 4	2399
	21st to end	Night	43% 2 9% 22% 18% 6%	1813
March	1st to 10th	Night	42% 2 11% 19% 20% 6%	3419
	11th to 20th	Night	35% 4 10% 26% 22% 3	3480
	21st to end	Night	43% 7% 15% 24% 10% 1	3817
April	1st to 10th	Night	32% 4 12% 25% 22% 5%	1939
	11th to 20th	Night	37% 3 11% 23% 19% 5%	1875
	21st to end	Night	45% 3 12% 22% 17% 1	1900
May	1st to 10th	Night	39% 5% 14% 23% 15% 4	2860
	11th to 20th	Night	42% 5% 13% 27% 12% 1	2824
	21st to end	Night	36% 8% 14% 29% 12% 1	2971
June	1st to 10th	Night	28% 6% 15% 30% 19% 3	1520
	11th to 20th	Night	23% 6% 17% 30% 21% 3	1520
	21st to end	Night	18% 5% 18% 33% 22% 5%	1525
July	1st to 10th	Night	34% 5% 15% 25% 16% 4	2805
	11th to 20th	Night	22% 4 11% 38% 24% 2	2796
	21st to end	Night	25% 6% 21% 34% 13% 1	2999
August	1st to 10th	Night	20% 4 15% 35% 23% 2	2826
	11th to 20th	Night	33% 5% 13% 29% 18% 1	2901
	21st to end	Night	21% 4 14% 37% 20% 4	3476
September	1st to 10th	Night	29% 4 11% 27% 20% 8%	1900
	11th to 20th	Night	31% 4 10% 25% 26% 4	1981
	21st to end	Night	28% 4 7% 27% 30% 4	2134
October	1st to 10th	Night	14% 2 6% 17% 42% 18%	3800
	11th to 20th	Night	22% 2 5% 22% 31% 19%	3779
	21st to end	Night	30% 3 6% 32% 25% 5%	4120
November	1st to 10th	Night	29% 2 9% 27% 25% 8%	2340
	11th to 20th	Night	34% 2 6% 25% 26% 6%	2548
	21st to end	Night	38% 3 8% 24% 23% 3	2759
December	1st to 10th	Night	41% 4 11% 24% 18% 1	2660
	11th to 20th	Night	45% 3 7% 23% 20% 2	3281
	21st to end	Night	57% 4 10% 18% 9% 2	4747

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	22% 16% 36% 22% 4	270
	11th to 20th	Day	26% 19% 38% 15% 2	270
	21st to end	Day	19% 16% 46% 16% 4	297
February	1st to 10th	Day	24% 17% 41% 16% 2	270
	11th to 20th	Day	25% 23% 33% 17% 3	270
	21st to end	Day	30% 20% 36% 12% 1	225
March	1st to 10th	Day	22% 20% 34% 21% 3	270
	11th to 20th	Day	28% 16% 32% 21% 4	270
	21st to end	Day	29% 20% 35% 12% 3	297
April	1st to 10th	Day	21% 15% 36% 22% 5%	419
	11th to 20th	Day	20% 17% 37% 19% 6%	452
	21st to end	Day	21% 17% 31% 25% 6% 1	460
May	1st to 10th	Day	22% 10% 33% 25% 9% 1	639
	11th to 20th	Day	17% 8% 31% 27% 13% 4	675
	21st to end	Day	14% 7% 32% 25% 16% 6%	734
June	1st to 10th	Day	9% 4 18% 32% 27% 9%	680
	11th to 20th	Day	8% 2 18% 39% 27% 6%	680
	21st to end	Day	6% 3 26% 37% 22% 5%	680
July	1st to 10th	Day	11% 2 15% 30% 31% 11%	671
	11th to 20th	Day	5% 2 14% 37% 32% 10%	668
	21st to end	Day	9% 1 11% 33% 33% 14%	739
August	1st to 10th	Day	10% 2 13% 37% 32% 7%	676
	11th to 20th	Day	9% 3 14% 33% 33% 8%	622
	21st to end	Day	11% 2 10% 26% 39% 12%	539
September	1st to 10th	Day	11% 1 11% 34% 32% 11%	490
	11th to 20th	Day	9% 2 16% 38% 25% 9%	405
	21st to end	Day	12% 6% 22% 32% 19% 8%	300
October	1st to 10th	Day	10% 9% 24% 31% 20% 6%	300
	11th to 20th	Day	16% 16% 31% 27% 9% 2	300
	21st to end	Day	26% 13% 32% 23% 5%	330
November	1st to 10th	Day	15% 12% 37% 24% 10% 3	300
	11th to 20th	Day	19% 16% 34% 21% 8% 1	300
	21st to end	Day	21% 16% 34% 21% 7% 1	291
December	1st to 10th	Day	18% 13% 43% 17% 8% 2	270
	11th to 20th	Day	22% 16% 38% 17% 7% 1	270
	21st to end	Day	21% 23% 37% 16% 2	297
January	1st to 10th	Night	17% 17% 35% 25% 6%	950
	11th to 20th	Night	20% 17% 39% 20% 4 1	950
	21st to end	Night	18% 15% 41% 23% 2	1045
February	1st to 10th	Night	22% 14% 41% 20% 3	950
	11th to 20th	Night	20% 15% 39% 23% 3	924
	21st to end	Night	23% 20% 35% 19% 2	557
March	1st to 10th	Night	19% 13% 38% 26% 4	570
	11th to 20th	Night	24% 12% 33% 25% 5%	570
	21st to end	Night	22% 15% 35% 24% 4	627
April	1st to 10th	Night	15% 13% 40% 27% 5%	570
	11th to 20th	Night	17% 13% 36% 28% 6%	563
	21st to end	Night	21% 11% 37% 24% 7%	570
May	1st to 10th	Night	18% 4 34% 34% 9%	570
	11th to 20th	Night	16% 4 28% 34% 17% 1	561
	21st to end	Night	12% 4 29% 33% 20% 1	617
June	1st to 10th	Night	9% 4 15% 44% 28% 1	570
	11th to 20th	Night	5% 1 23% 45% 25% 1	570
	21st to end	Night	4 1 22% 49% 23% 1	570
July	1st to 10th	Night	10% 2 10% 43% 31% 5%	555
	11th to 20th	Night	3 1 10% 42% 39% 4	552
	21st to end	Night	7% 2 8% 45% 35% 4	624
August	1st to 10th	Night	7% 2 7% 50% 31% 3	567
	11th to 20th	Night	7% 2 12% 51% 25% 4	564
	21st to end	Night	5% 2 10% 40% 39% 5%	627
September	1st to 10th	Night	10% 2 11% 42% 32% 3	570
	11th to 20th	Night	11% 2 12% 42% 29% 4	570
	21st to end	Night	11% 3 22% 43% 19% 3	614
October	1st to 10th	Night	9% 4 26% 37% 22% 3	760
	11th to 20th	Night	17% 6% 34% 32% 10%	760
	21st to end	Night	20% 10% 31% 29% 9% 1	836
November	1st to 10th	Night	16% 9% 36% 29% 11%	780
	11th to 20th	Night	15% 13% 37% 27% 7%	846
	21st to end	Night	21% 11% 36% 23% 8%	986
December	1st to 10th	Night	21% 12% 37% 25% 6%	950
	11th to 20th	Night	22% 13% 35% 26% 4	950
	21st to end	Night	21% 14% 38% 24% 3	1045

Page generated at 2024-11-24 23:22:19. Version ac07

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