Joseph
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joseph clear sky chart from 2005-11-06 to 2024-01-12.

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	5% 8% 3 6% 6% 4 6% 6% 6% 8% 42%	74810
	Night	4 6% 3 6% 6% 4 6% 6% 7% 9% 43%	74923
Transparency	Day	40% 9% 14% 19% 14% 5%	74514
	Night	38% 11% 14% 21% 13% 4	74740
Seeing	Day	9% 12% 29% 29% 16% 5%	13258
	Night	7% 7% 26% 36% 19% 3	22572

By Month

Percentage Cloud Cover SW (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	2 8% 4 10% 8% 5% 8% 8% 9% 11% 27%	1519
	11th to 20th	Day	2 7% 5% 10% 8% 5% 7% 8% 6% 7% 34%	1448
	21st to end	Day	2 9% 4 8% 8% 5% 7% 6% 8% 10% 33%	1584
February	1st to 10th	Day	2 10% 7% 8% 8% 5% 6% 7% 7% 9% 31%	1496
	11th to 20th	Day	2 12% 7% 10% 8% 5% 7% 7% 7% 8% 27%	1742
	21st to end	Day	3 8% 6% 13% 10% 6% 9% 8% 7% 8% 24%	1480
March	1st to 10th	Day	3 11% 6% 10% 9% 5% 7% 8% 8% 8% 24%	1800
	11th to 20th	Day	2 13% 5% 7% 8% 5% 8% 8% 7% 8% 28%	1857
	21st to end	Day	6% 16% 6% 11% 10% 5% 8% 7% 6% 7% 18%	2341
April	1st to 10th	Day	6% 13% 6% 10% 9% 4 7% 7% 7% 7% 24%	2160
	11th to 20th	Day	7% 12% 5% 8% 7% 4 6% 6% 6% 7% 32%	2155
	21st to end	Day	10% 15% 4 7% 7% 4 4 5% 6% 7% 31%	2340
May	1st to 10th	Day	7% 12% 4 7% 7% 3 5% 5% 5% 8% 37%	2373
	11th to 20th	Day	13% 10% 4 7% 6% 4 6% 6% 6% 8% 31%	2477
	21st to end	Day	17% 12% 4 8% 8% 4 6% 5% 5% 7% 25%	2723
June	1st to 10th	Day	12% 9% 4 7% 7% 4 6% 6% 7% 9% 31%	2520
	11th to 20th	Day	12% 8% 3 6% 6% 4 5% 4 5% 8% 39%	2520
	21st to end	Day	5% 3 1 3 4 2 4 5% 6% 8% 58%	2520
July	1st to 10th	Day	2 2 1 3 3 2 4 5% 7% 8% 63%	2520
	11th to 20th	Day	1 1 1 2 2 2 4 4 5% 6% 71%	2520
	21st to end	Day	1 1 2 3 1 4 4 5% 6% 73%	2741
August	1st to 10th	Day	3 2 1 3 4 3 5% 5% 6% 9% 60%	2507
	11th to 20th	Day	3 2 1 2 3 2 4 4 5% 7% 68%	2304
	21st to end	Day	3 3 1 3 3 2 5% 5% 5% 6% 64%	2376
September	1st to 10th	Day	3 3 1 3 3 2 3 4 4 6% 68%	2160
	11th to 20th	Day	5% 5% 2 4 4 3 5% 5% 6% 8% 54%	2044
	21st to end	Day	7% 6% 2 4 5% 3 5% 5% 5% 5% 53%	1980
October	1st to 10th	Day	9% 9% 4 6% 6% 3 5% 4 5% 6% 45%	1942
	11th to 20th	Day	5% 7% 3 6% 6% 4 5% 5% 5% 8% 46%	1718
	21st to end	Day	5% 8% 5% 8% 8% 5% 6% 5% 6% 7% 38%	1782
November	1st to 10th	Day	5% 10% 4 7% 7% 6% 7% 6% 7% 8% 33%	1674
	11th to 20th	Day	3 7% 4 7% 8% 4 7% 8% 9% 12% 31%	1710
	21st to end	Day	2 6% 5% 7% 7% 5% 7% 7% 9% 8% 37%	1535
December	1st to 10th	Day	2 8% 3 10% 8% 4 7% 8% 7% 8% 36%	1520
	11th to 20th	Day	2 8% 4 9% 8% 6% 7% 8% 8% 10% 30%	1928
	21st to end	Day	4 8% 4 7% 8% 5% 8% 6% 7% 9% 33%	2794
January	1st to 10th	Night	3 8% 4 8% 8% 5% 8% 8% 8% 10% 29%	2646
	11th to 20th	Night	3 8% 4 8% 7% 5% 7% 8% 7% 9% 34%	2540
	21st to end	Night	3 9% 5% 8% 9% 5% 6% 7% 8% 10% 32%	2772
February	1st to 10th	Night	3 9% 5% 9% 9% 5% 7% 8% 8% 8% 30%	2462
	11th to 20th	Night	2 8% 5% 10% 7% 5% 8% 7% 8% 10% 30%	2104
	21st to end	Night	2 7% 4 10% 9% 5% 8% 8% 10% 9% 27%	1776
March	1st to 10th	Night	3 7% 5% 8% 6% 4 7% 8% 9% 11% 31%	2160
	11th to 20th	Night	2 9% 3 6% 6% 4 9% 8% 8% 10% 34%	2102
	21st to end	Night	5% 10% 5% 8% 8% 5% 8% 6% 9% 10% 25%	2012
April	1st to 10th	Night	4 9% 5% 7% 7% 6% 7% 6% 8% 9% 33%	1800
	11th to 20th	Night	6% 9% 3 7% 7% 5% 6% 6% 5% 7% 40%	1752
	21st to end	Night	7% 9% 3 5% 7% 4 6% 5% 6% 8% 39%	1620
May	1st to 10th	Night	7% 7% 3 4 5% 4 6% 6% 6% 8% 45%	1584
	11th to 20th	Night	9% 6% 2 5% 5% 3 7% 6% 8% 9% 39%	1416
	21st to end	Night	14% 8% 3 6% 5% 3 5% 5% 6% 7% 38%	1552
June	1st to 10th	Night	9% 6% 3 5% 6% 3 4 7% 7% 9% 41%	1440
	11th to 20th	Night	10% 5% 2 4 4 3 5% 4 5% 8% 49%	1440
	21st to end	Night	4 3 1 3 4 2 4 5% 5% 6% 64%	1440
July	1st to 10th	Night	1 1 1 1 3 2 3 4 4 8% 72%	1440
	11th to 20th	Night	1 1 1 1 2 2 3 4 7% 77%	1440
	21st to end	Night	1 1 1 1 2 2 2 3 5% 5% 78%	1576
August	1st to 10th	Night	3 2 1 3 2 2 3 4 6% 7% 67%	1432
	11th to 20th	Night	1 1 1 2 2 2 3 5% 4 6% 73%	1593
	21st to end	Night	3 3 1 3 2 2 3 4 5% 8% 68%	1980
September	1st to 10th	Night	4 2 1 2 3 2 2 4 4 6% 70%	1800
	11th to 20th	Night	3 3 2 4 4 3 5% 6% 5% 7% 60%	1916
	21st to end	Night	6% 5% 2 4 5% 3 3 4 4 6% 58%	1980
October	1st to 10th	Night	9% 8% 2 6% 5% 2 6% 4 5% 7% 48%	2016
	11th to 20th	Night	4 5% 3 5% 6% 4 5% 6% 6% 9% 47%	2241
	21st to end	Night	4 7% 3 7% 7% 4 5% 7% 7% 7% 41%	2574
November	1st to 10th	Night	4 9% 3 7% 8% 4 6% 7% 7% 9% 36%	2405
	11th to 20th	Night	4 7% 3 7% 7% 5% 7% 8% 8% 11% 34%	2470
	21st to end	Night	3 6% 3 6% 7% 5% 7% 6% 8% 9% 41%	2644
December	1st to 10th	Night	2 5% 3 7% 7% 5% 8% 8% 8% 10% 38%	2660
	11th to 20th	Night	2 7% 3 6% 8% 4 7% 8% 9% 12% 34%	3276
	21st to end	Night	2 9% 4 8% 7% 4 7% 7% 7% 9% 36%	4862

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	49% 16% 18% 13% 3 1	1519
	11th to 20th	Day	48% 11% 14% 15% 9% 3	1448
	21st to end	Day	47% 11% 18% 15% 8% 1	1584
February	1st to 10th	Day	51% 14% 14% 17% 4 1	1496
	11th to 20th	Day	54% 12% 14% 13% 7% 1	1752
	21st to end	Day	56% 11% 14% 12% 6% 1	1480
March	1st to 10th	Day	57% 10% 16% 12% 5% 1	1800
	11th to 20th	Day	52% 11% 13% 18% 6%	1857
	21st to end	Day	64% 10% 13% 11% 2	2341
April	1st to 10th	Day	56% 8% 16% 14% 4	2160
	11th to 20th	Day	49% 8% 15% 15% 11% 2	2158
	21st to end	Day	51% 9% 12% 19% 10%	2340
May	1st to 10th	Day	42% 9% 16% 24% 9% 1	2373
	11th to 20th	Day	49% 9% 15% 19% 7% 1	2480
	21st to end	Day	58% 8% 13% 16% 4	2724
June	1st to 10th	Day	49% 10% 13% 22% 6%	2520
	11th to 20th	Day	43% 8% 13% 21% 11% 3	2520
	21st to end	Day	22% 7% 13% 31% 22% 5%	2520
July	1st to 10th	Day	17% 5% 14% 22% 28% 14%	2451
	11th to 20th	Day	14% 5% 10% 18% 29% 24%	2445
	21st to end	Day	11% 4 6% 17% 41% 22%	2589
August	1st to 10th	Day	20% 5% 10% 22% 31% 12%	2490
	11th to 20th	Day	17% 5% 9% 25% 32% 14%	2304
	21st to end	Day	20% 5% 11% 26% 28% 10%	2376
September	1st to 10th	Day	17% 5% 11% 24% 29% 14%	2160
	11th to 20th	Day	28% 5% 13% 21% 25% 9%	2044
	21st to end	Day	31% 6% 12% 27% 20% 4	1980
October	1st to 10th	Day	39% 7% 11% 21% 19% 3	1942
	11th to 20th	Day	36% 7% 13% 26% 16% 2	1718
	21st to end	Day	44% 9% 13% 20% 13% 1	1782
November	1st to 10th	Day	47% 9% 17% 18% 8% 1	1674
	11th to 20th	Day	44% 13% 18% 18% 6%	1710
	21st to end	Day	42% 12% 17% 15% 12% 2	1535
December	1st to 10th	Day	46% 14% 18% 10% 10% 2	1520
	11th to 20th	Day	50% 18% 14% 12% 4	1928
	21st to end	Day	46% 10% 18% 19% 6% 1	2794
January	1st to 10th	Night	50% 13% 15% 16% 4 1	2646
	11th to 20th	Night	48% 11% 12% 16% 11% 3	2540
	21st to end	Night	47% 12% 15% 17% 8% 1	2772
February	1st to 10th	Night	52% 13% 15% 15% 5% 1	2462
	11th to 20th	Night	48% 14% 14% 16% 8% 1	2105
	21st to end	Night	52% 13% 14% 12% 7% 2	1776
March	1st to 10th	Night	45% 12% 19% 15% 8% 1	2160
	11th to 20th	Night	44% 14% 15% 20% 7%	2102
	21st to end	Night	53% 13% 17% 14% 3	2012
April	1st to 10th	Night	46% 11% 18% 19% 6%	1800
	11th to 20th	Night	43% 8% 15% 22% 10% 2	1752
	21st to end	Night	43% 12% 14% 19% 12%	1620
May	1st to 10th	Night	36% 11% 13% 28% 11%	1584
	11th to 20th	Night	39% 11% 15% 26% 8% 1	1416
	21st to end	Night	44% 9% 17% 23% 7%	1552
June	1st to 10th	Night	39% 13% 15% 27% 7%	1440
	11th to 20th	Night	34% 9% 17% 25% 13% 2	1440
	21st to end	Night	22% 7% 14% 29% 24% 4	1440
July	1st to 10th	Night	13% 5% 12% 25% 31% 14%	1400
	11th to 20th	Night	9% 5% 11% 27% 25% 23%	1392
	21st to end	Night	8% 2 8% 21% 39% 22%	1488
August	1st to 10th	Night	15% 5% 12% 25% 30% 12%	1424
	11th to 20th	Night	13% 7% 9% 24% 33% 15%	1593
	21st to end	Night	16% 4 11% 29% 29% 11%	1980
September	1st to 10th	Night	16% 4 10% 26% 27% 17%	1800
	11th to 20th	Night	23% 7% 12% 24% 24% 11%	1916
	21st to end	Night	28% 7% 11% 27% 20% 8%	1980
October	1st to 10th	Night	37% 6% 11% 26% 17% 3	2016
	11th to 20th	Night	33% 9% 14% 24% 18% 2	2241
	21st to end	Night	40% 12% 14% 20% 13% 2	2574
November	1st to 10th	Night	43% 11% 15% 18% 10% 2	2405
	11th to 20th	Night	43% 13% 16% 21% 7%	2470
	21st to end	Night	40% 11% 13% 19% 14% 2	2644
December	1st to 10th	Night	41% 15% 19% 16% 8% 2	2660
	11th to 20th	Night	44% 20% 14% 17% 4 1	3276
	21st to end	Night	43% 12% 18% 19% 8% 1	4862

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	4 16% 36% 24% 16% 3	180
	11th to 20th	Day	8% 12% 34% 28% 10% 8%	162
	21st to end	Day	10% 12% 36% 24% 16% 2	176
February	1st to 10th	Day	11% 18% 40% 23% 7% 1	216
	11th to 20th	Day	7% 22% 38% 23% 10% 1	412
	21st to end	Day	8% 23% 29% 29% 9% 1	346
March	1st to 10th	Day	8% 20% 40% 25% 6% 1	420
	11th to 20th	Day	10% 19% 30% 30% 10% 1	420
	21st to end	Day	16% 20% 31% 26% 5% 1	462
April	1st to 10th	Day	12% 21% 30% 23% 11% 2	420
	11th to 20th	Day	12% 21% 33% 22% 8% 4	412
	21st to end	Day	16% 16% 29% 27% 9% 2	420
May	1st to 10th	Day	12% 13% 27% 32% 12% 4	423
	11th to 20th	Day	21% 12% 23% 25% 14% 5%	448
	21st to end	Day	20% 9% 20% 25% 19% 6%	485
June	1st to 10th	Day	12% 12% 25% 26% 18% 7%	450
	11th to 20th	Day	13% 17% 32% 24% 11% 3	450
	21st to end	Day	6% 7% 27% 32% 22% 5%	450
July	1st to 10th	Day	3 7% 27% 36% 22% 5%	446
	11th to 20th	Day	1 8% 31% 36% 20% 4	444
	21st to end	Day	1 4 29% 35% 24% 7%	487
August	1st to 10th	Day	4 6% 23% 36% 23% 8%	447
	11th to 20th	Day	2 5% 21% 36% 25% 11%	437
	21st to end	Day	4 9% 23% 36% 21% 8%	495
September	1st to 10th	Day	6% 7% 24% 31% 24% 8%	450
	11th to 20th	Day	8% 8% 25% 32% 19% 8%	450
	21st to end	Day	10% 9% 25% 34% 18% 5%	450
October	1st to 10th	Day	13% 11% 26% 28% 17% 6%	450
	11th to 20th	Day	6% 13% 29% 29% 18% 6%	368
	21st to end	Day	11% 11% 32% 25% 16% 4	297
November	1st to 10th	Day	10% 14% 32% 33% 11%	270
	11th to 20th	Day	6% 11% 33% 33% 14% 3	270
	21st to end	Day	5% 9% 31% 37% 16% 2	187
December	1st to 10th	Day	6% 12% 27% 32% 14% 8%	180
	11th to 20th	Day	8% 11% 44% 26% 10% 1	180
	21st to end	Day	7% 14% 38% 27% 12% 3	198
January	1st to 10th	Night	8% 12% 35% 28% 15% 2	760
	11th to 20th	Night	7% 12% 33% 30% 15% 3	726
	21st to end	Night	7% 8% 30% 35% 19% 2	792
February	1st to 10th	Night	7% 11% 37% 34% 9% 2	720
	11th to 20th	Night	7% 8% 38% 31% 14% 2	704
	21st to end	Night	7% 13% 34% 31% 12% 3	592
March	1st to 10th	Night	6% 9% 37% 31% 14% 2	720
	11th to 20th	Night	8% 8% 33% 33% 15% 3	720
	21st to end	Night	10% 11% 31% 34% 12% 1	792
April	1st to 10th	Night	9% 8% 31% 35% 15% 3	720
	11th to 20th	Night	10% 9% 32% 30% 17% 3	684
	21st to end	Night	12% 8% 24% 37% 17% 2	540
May	1st to 10th	Night	11% 7% 23% 40% 17% 2	504
	11th to 20th	Night	11% 5% 17% 34% 28% 5%	354
	21st to end	Night	13% 6% 13% 34% 28% 5%	389
June	1st to 10th	Night	10% 6% 18% 40% 22% 3	360
	11th to 20th	Night	13% 6% 19% 41% 19% 3	360
	21st to end	Night	6% 1 11% 46% 34% 1	360
July	1st to 10th	Night	1 2 11% 48% 35% 3	350
	11th to 20th	Night	2 1 10% 57% 28% 1	348
	21st to end	Night	2 1 8% 54% 32% 3	394
August	1st to 10th	Night	3 1 8% 47% 37% 4	358
	11th to 20th	Night	1 1 10% 45% 35% 7%	525
	21st to end	Night	4 1 15% 41% 34% 6%	792
September	1st to 10th	Night	4 2 13% 43% 32% 7%	720
	11th to 20th	Night	4 2 14% 36% 35% 9%	720
	21st to end	Night	10% 3 19% 36% 25% 8%	720
October	1st to 10th	Night	11% 4 19% 38% 22% 5%	720
	11th to 20th	Night	6% 6% 25% 36% 20% 7%	720
	21st to end	Night	8% 6% 28% 38% 15% 5%	792
November	1st to 10th	Night	10% 6% 31% 40% 11% 1	740
	11th to 20th	Night	8% 11% 34% 34% 12% 2	760
	21st to end	Night	6% 9% 31% 34% 16% 4	760
December	1st to 10th	Night	8% 8% 33% 34% 15% 2	760
	11th to 20th	Night	7% 8% 36% 35% 11% 2	760
	21st to end	Night	7% 12% 39% 33% 8% 1	836

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