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 2024-01-14.

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% 3 5% 5% 3 5% 4 5% 7% 44%	74638
	Night	12% 7% 3 5% 4 3 4 4 5% 7% 48%	75129
Transparency	Day	40% 4 12% 25% 16% 3	74361
	Night	37% 4 11% 25% 19% 3	74926
Seeing	Day	15% 9% 26% 27% 18% 5%	14394
	Night	16% 9% 30% 31% 13% 1	24355

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	13% 9% 2 4 5% 2 4 3 3 6% 48%	1707
	11th to 20th	Day	15% 9% 5% 5% 5% 2 4 4 5% 6% 39%	1647
	21st to end	Day	13% 9% 4 6% 4 2 3 4 4 6% 44%	1782
February	1st to 10th	Day	16% 11% 4 6% 6% 2 5% 4 3 6% 38%	1620
	11th to 20th	Day	13% 9% 4 6% 6% 3 4 4 5% 5% 41%	1578
	21st to end	Day	16% 11% 3 6% 4 3 4 4 5% 8% 37%	1560
March	1st to 10th	Day	15% 9% 4 6% 4 3 3 3 4 6% 44%	1980
	11th to 20th	Day	22% 9% 4 6% 4 2 3 4 3 5% 37%	1980
	21st to end	Day	21% 11% 4 6% 4 3 5% 4 5% 6% 32%	2178
April	1st to 10th	Day	11% 8% 3 6% 4 2 5% 4 5% 7% 45%	2121
	11th to 20th	Day	16% 9% 3 5% 5% 3 4 4 5% 7% 40%	2134
	21st to end	Day	20% 7% 3 6% 6% 3 4 4 5% 6% 36%	2160
May	1st to 10th	Day	20% 6% 3 5% 5% 3 4 5% 5% 6% 38%	2326
	11th to 20th	Day	14% 6% 3 5% 6% 3 5% 5% 5% 7% 42%	2302
	21st to end	Day	11% 6% 3 6% 6% 4 7% 6% 7% 9% 35%	2598
June	1st to 10th	Day	7% 4 2 5% 4 3 5% 5% 7% 10% 47%	2520
	11th to 20th	Day	7% 4 2 6% 6% 3 5% 5% 7% 9% 47%	2520
	21st to end	Day	5% 2 1 3 3 3 5% 5% 6% 9% 56%	2510
July	1st to 10th	Day	9% 4 2 5% 6% 3 7% 7% 9% 9% 39%	2340
	11th to 20th	Day	5% 3 2 4 4 4 6% 6% 7% 9% 51%	2340
	21st to end	Day	8% 4 2 6% 5% 3 6% 6% 7% 10% 42%	2546
August	1st to 10th	Day	8% 4 2 6% 6% 4 6% 6% 7% 8% 43%	2328
	11th to 20th	Day	8% 5% 2 5% 6% 4 6% 6% 7% 8% 43%	2261
	21st to end	Day	7% 4 3 4 5% 3 5% 5% 5% 7% 51%	2376
September	1st to 10th	Day	12% 5% 2 4 5% 2 4 4 5% 7% 50%	2160
	11th to 20th	Day	11% 6% 2 5% 5% 3 4 5% 4 7% 48%	2080
	21st to end	Day	7% 4 2 4 5% 3 4 5% 6% 7% 52%	1919
October	1st to 10th	Day	11% 5% 1 4 4 2 4 4 5% 6% 54%	1800
	11th to 20th	Day	14% 6% 2 4 3 2 3 3 3 5% 54%	1800
	21st to end	Day	19% 6% 3 4 4 2 3 3 4 5% 47%	1980
November	1st to 10th	Day	12% 5% 2 4 3 2 3 3 3 5% 58%	1858
	11th to 20th	Day	14% 7% 3 4 4 2 3 4 4 6% 48%	1754
	21st to end	Day	16% 7% 3 4 4 2 3 2 4 6% 49%	1520
December	1st to 10th	Day	13% 9% 3 5% 5% 2 3 3 5% 7% 44%	1520
	11th to 20th	Day	13% 11% 4 7% 5% 3 4 3 3 5% 43%	1918
	21st to end	Day	15% 18% 5% 7% 5% 3 5% 4 4 6% 28%	2915
January	1st to 10th	Night	13% 8% 3 6% 5% 2 3 4 4 6% 46%	2458
	11th to 20th	Night	14% 8% 4 6% 4 2 3 3 4 7% 44%	2392
	21st to end	Night	13% 8% 4 6% 4 3 4 4 4 6% 44%	2574
February	1st to 10th	Night	15% 10% 3 6% 4 2 3 4 5% 6% 42%	2340
	11th to 20th	Night	14% 9% 4 5% 4 2 3 4 4 6% 44%	2268
	21st to end	Night	16% 9% 3 5% 5% 2 4 3 4 5% 44%	1709
March	1st to 10th	Night	15% 7% 3 5% 4 2 3 3 3 7% 46%	1980
	11th to 20th	Night	19% 8% 3 5% 4 3 4 4 4 5% 40%	1980
	21st to end	Night	18% 9% 3 6% 5% 4 4 4 4 7% 36%	2178
April	1st to 10th	Night	11% 5% 2 4 3 2 4 4 4 6% 54%	1837
	11th to 20th	Night	13% 8% 2 4 5% 3 3 3 5% 8% 46%	1775
	21st to end	Night	17% 8% 3 5% 5% 3 4 3 5% 7% 40%	1800
May	1st to 10th	Night	15% 6% 3 5% 3 2 4 4 6% 8% 45%	1630
	11th to 20th	Night	14% 5% 2 5% 5% 2 4 4 5% 8% 47%	1593
	21st to end	Night	11% 5% 2 6% 6% 3 5% 5% 6% 10% 40%	1673
June	1st to 10th	Night	6% 3 2 3 5% 3 5% 5% 6% 9% 54%	1440
	11th to 20th	Night	5% 3 1 3 5% 2 5% 4 7% 10% 54%	1440
	21st to end	Night	3 2 1 2 2 2 4 4 6% 9% 64%	1444
July	1st to 10th	Night	8% 3 1 3 4 3 5% 5% 7% 9% 50%	1620
	11th to 20th	Night	4 2 1 2 4 2 4 4 7% 10% 59%	1620
	21st to end	Night	6% 4 1 4 4 3 5% 6% 8% 10% 49%	1772
August	1st to 10th	Night	6% 3 1 4 5% 3 6% 4 6% 9% 53%	1611
	11th to 20th	Night	6% 3 1 4 4 2 5% 4 5% 8% 57%	1637
	21st to end	Night	5% 3 2 4 4 3 4 4 6% 8% 57%	1980
September	1st to 10th	Night	9% 4 2 4 5% 3 3 3 4 7% 55%	1800
	11th to 20th	Night	9% 4 2 5% 4 3 4 4 4 7% 54%	1876
	21st to end	Night	8% 4 2 4 3 2 4 3 4 6% 59%	2021
October	1st to 10th	Night	8% 4 2 3 3 2 3 3 5% 7% 60%	2160
	11th to 20th	Night	15% 5% 1 3 3 2 3 3 5% 5% 55%	2160
	21st to end	Night	17% 6% 2 4 4 2 3 3 3 5% 51%	2376
November	1st to 10th	Night	12% 5% 2 3 2 2 3 2 3 5% 61%	2220
	11th to 20th	Night	13% 7% 2 4 4 3 3 3 4 5% 53%	2419
	21st to end	Night	15% 8% 3 5% 3 2 3 3 4 5% 50%	2660
December	1st to 10th	Night	14% 8% 4 5% 4 2 4 3 5% 7% 43%	2660
	11th to 20th	Night	14% 10% 4 6% 5% 2 4 3 4 5% 43%	3279
	21st to end	Night	17% 16% 5% 8% 4 3 3 4 4 5% 31%	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	40% 2 10% 27% 18% 2	1708
	11th to 20th	Day	46% 3 10% 23% 17% 1	1647
	21st to end	Day	42% 3 14% 28% 12% 3	1782
February	1st to 10th	Day	51% 3 10% 24% 11% 1	1620
	11th to 20th	Day	47% 3 11% 20% 16% 4	1587
	21st to end	Day	48% 3 7% 23% 13% 6%	1560
March	1st to 10th	Day	43% 4 9% 21% 19% 5%	1980
	11th to 20th	Day	51% 3 8% 21% 13% 3	1980
	21st to end	Day	54% 5% 12% 18% 9% 1	2178
April	1st to 10th	Day	40% 3 12% 25% 18% 2	2121
	11th to 20th	Day	45% 3 14% 20% 14% 3	2134
	21st to end	Day	49% 4 10% 24% 11% 1	2160
May	1st to 10th	Day	48% 5% 12% 21% 13% 1	2326
	11th to 20th	Day	42% 5% 14% 25% 13% 1	2306
	21st to end	Day	44% 8% 14% 23% 11% 1	2598
June	1st to 10th	Day	33% 5% 17% 28% 16% 1	2520
	11th to 20th	Day	33% 5% 15% 30% 14% 2	2520
	21st to end	Day	24% 5% 16% 32% 17% 4	2510
July	1st to 10th	Day	36% 8% 16% 24% 13% 2	2276
	11th to 20th	Day	27% 7% 16% 27% 21% 3	2271
	21st to end	Day	36% 6% 15% 32% 11% 1	2405
August	1st to 10th	Day	36% 6% 19% 24% 14% 1	2314
	11th to 20th	Day	37% 7% 13% 29% 15% 1	2261
	21st to end	Day	33% 4 12% 24% 21% 7%	2376
September	1st to 10th	Day	36% 4 12% 27% 14% 7%	2160
	11th to 20th	Day	36% 5% 8% 22% 27% 2	2080
	21st to end	Day	30% 5% 10% 28% 23% 4	1919
October	1st to 10th	Day	31% 4 10% 26% 25% 5%	1800
	11th to 20th	Day	35% 3 6% 27% 22% 6%	1800
	21st to end	Day	41% 3 8% 24% 18% 6%	1980
November	1st to 10th	Day	31% 3 9% 29% 23% 5%	1858
	11th to 20th	Day	38% 3 9% 22% 23% 6%	1754
	21st to end	Day	40% 3 9% 24% 22% 2	1520
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	41% 3 11% 25% 18% 2	2458
	11th to 20th	Night	42% 3 10% 27% 16% 1	2392
	21st to end	Night	42% 3 11% 26% 16% 3	2574
February	1st to 10th	Night	45% 3 12% 23% 15% 2	2340
	11th to 20th	Night	43% 3 11% 23% 16% 3	2269
	21st to end	Night	44% 2 9% 23% 16% 6%	1709
March	1st to 10th	Night	41% 3 9% 21% 20% 7%	1980
	11th to 20th	Night	48% 4 9% 19% 17% 3	1980
	21st to end	Night	48% 5% 10% 22% 13% 1	2178
April	1st to 10th	Night	32% 4 13% 26% 21% 4	1837
	11th to 20th	Night	37% 4 12% 24% 18% 5%	1775
	21st to end	Night	45% 3 12% 22% 17% 1	1800
May	1st to 10th	Night	38% 5% 14% 24% 17% 2	1630
	11th to 20th	Night	37% 6% 14% 26% 15% 2	1594
	21st to end	Night	39% 7% 15% 27% 10% 1	1674
June	1st to 10th	Night	27% 6% 15% 31% 19% 2	1440
	11th to 20th	Night	24% 6% 17% 30% 21% 3	1440
	21st to end	Night	17% 5% 18% 34% 22% 5%	1444
July	1st to 10th	Night	27% 5% 18% 28% 17% 3	1575
	11th to 20th	Night	21% 4 14% 31% 27% 3	1566
	21st to end	Night	26% 6% 15% 35% 17% 1	1673
August	1st to 10th	Night	27% 6% 16% 35% 14% 1	1601
	11th to 20th	Night	26% 5% 12% 32% 25% 1	1637
	21st to end	Night	25% 4 15% 25% 24% 7%	1980
September	1st to 10th	Night	30% 4 12% 28% 20% 7%	1800
	11th to 20th	Night	31% 4 10% 24% 26% 5%	1876
	21st to end	Night	27% 4 8% 27% 30% 4	2021
October	1st to 10th	Night	25% 3 11% 27% 27% 6%	2160
	11th to 20th	Night	32% 3 7% 27% 25% 6%	2160
	21st to end	Night	38% 3 7% 23% 22% 6%	2376
November	1st to 10th	Night	29% 2 10% 27% 25% 8%	2220
	11th to 20th	Night	34% 2 6% 26% 26% 5%	2419
	21st to end	Night	39% 3 8% 24% 23% 3	2660
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	27% 17% 39% 15% 2	249
	21st to end	Day	17% 17% 47% 16% 4	264
February	1st to 10th	Day	23% 17% 44% 14% 2	240
	11th to 20th	Day	26% 24% 33% 15% 3	240
	21st to end	Day	32% 19% 34% 14% 2	198
March	1st to 10th	Day	23% 20% 34% 20% 3	240
	11th to 20th	Day	31% 12% 31% 22% 4	240
	21st to end	Day	30% 20% 34% 13% 3	264
April	1st to 10th	Day	20% 14% 37% 23% 6% 1	381
	11th to 20th	Day	21% 16% 35% 20% 7%	412
	21st to end	Day	21% 15% 32% 25% 6% 1	420
May	1st to 10th	Day	22% 10% 32% 25% 9% 1	589
	11th to 20th	Day	17% 8% 32% 26% 13% 4	625
	21st to end	Day	13% 7% 31% 25% 17% 7%	679
June	1st to 10th	Day	9% 4 17% 31% 29% 10%	630
	11th to 20th	Day	8% 2 18% 39% 27% 6%	630
	21st to end	Day	6% 3 26% 37% 22% 6%	630
July	1st to 10th	Day	11% 2 14% 29% 32% 12%	621
	11th to 20th	Day	5% 2 15% 35% 33% 10%	618
	21st to end	Day	9% 1 10% 34% 32% 14%	684
August	1st to 10th	Day	10% 2 13% 37% 32% 6%	626
	11th to 20th	Day	9% 3 14% 32% 34% 9%	575
	21st to end	Day	11% 2 10% 26% 39% 12%	495
September	1st to 10th	Day	12% 1 11% 34% 32% 10%	450
	11th to 20th	Day	10% 2 14% 38% 26% 10%	370
	21st to end	Day	11% 6% 21% 32% 21% 8%	270
October	1st to 10th	Day	11% 10% 26% 30% 17% 6%	270
	11th to 20th	Day	17% 16% 33% 27% 6% 1	270
	21st to end	Day	29% 13% 30% 23% 5%	297
November	1st to 10th	Day	14% 11% 39% 23% 10% 3	270
	11th to 20th	Day	17% 17% 34% 23% 8% 1	270
	21st to end	Day	23% 16% 33% 21% 6% 1	270
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% 38% 20% 4 1	920
	21st to end	Night	17% 15% 42% 23% 2	990
February	1st to 10th	Night	22% 14% 40% 20% 3	900
	11th to 20th	Night	21% 15% 39% 23% 3	874
	21st to end	Night	24% 19% 35% 20% 2	525
March	1st to 10th	Night	19% 12% 39% 26% 4	540
	11th to 20th	Night	25% 12% 33% 24% 5%	540
	21st to end	Night	22% 14% 35% 24% 4 1	594
April	1st to 10th	Night	15% 12% 39% 28% 5%	540
	11th to 20th	Night	17% 12% 36% 29% 7%	533
	21st to end	Night	21% 10% 38% 24% 7%	540
May	1st to 10th	Night	19% 4 34% 34% 9%	540
	11th to 20th	Night	16% 4 28% 34% 16% 1	531
	21st to end	Night	12% 4 28% 33% 21% 1	584
June	1st to 10th	Night	8% 3 14% 44% 29% 1	540
	11th to 20th	Night	6% 1 24% 44% 25% 1	540
	21st to end	Night	3 1 22% 49% 24% 1	540
July	1st to 10th	Night	9% 2 9% 43% 32% 5%	525
	11th to 20th	Night	3 1 10% 41% 40% 4	522
	21st to end	Night	7% 2 8% 45% 35% 4	591
August	1st to 10th	Night	8% 1 7% 50% 31% 3	537
	11th to 20th	Night	7% 1 12% 51% 26% 4	534
	21st to end	Night	5% 2 10% 39% 40% 5%	594
September	1st to 10th	Night	10% 2 11% 42% 31% 3	540
	11th to 20th	Night	10% 2 12% 41% 30% 4	540
	21st to end	Night	10% 3 21% 43% 20% 3	581
October	1st to 10th	Night	9% 4 27% 35% 21% 3	720
	11th to 20th	Night	18% 7% 35% 30% 9%	720
	21st to end	Night	22% 10% 29% 29% 10% 1	792
November	1st to 10th	Night	15% 9% 36% 29% 11%	740
	11th to 20th	Night	15% 12% 37% 27% 7%	803
	21st to end	Night	22% 11% 35% 24% 8%	950
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 2024-01-11 12:32:02. Version ac07

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