Joes Universe
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joes Universe clear sky chart from 2005-11-06 to 2024-05-13.

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	18% 7% 2 6% 4 4 4 4 5% 7% 40%	83408
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 41%	86087
Transparency	Day	42% 7% 12% 22% 15% 2	83113
	Night	43% 6% 12% 22% 15% 2	85916
Seeing	Day	20% 16% 31% 22% 9% 2	14331
	Night	21% 13% 32% 25% 8% 1	23524

By Month

Percentage Cloud Cover NE (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	15% 7% 2 7% 3 4 3 3 5% 5% 45%	2517
	11th to 20th	Day	17% 9% 3 8% 4 5% 5% 4 4 5% 36%	2520
	21st to end	Day	22% 12% 4 7% 4 4 3 3 4 5% 32%	2868
February	1st to 10th	Day	17% 7% 2 6% 5% 5% 5% 3 5% 6% 37%	1767
	11th to 20th	Day	15% 7% 3 5% 3 4 4 4 7% 7% 41%	1848
	21st to end	Day	22% 8% 3 6% 4 3 3 4 5% 6% 37%	1570
March	1st to 10th	Day	27% 10% 3 6% 4 3 3 2 4 5% 34%	3116
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 5% 7% 8% 43%	3268
	21st to end	Day	21% 7% 3 6% 4 3 3 4 5% 6% 39%	4166
April	1st to 10th	Day	19% 9% 2 6% 5% 4 3 3 6% 7% 37%	2280
	11th to 20th	Day	20% 6% 2 5% 4 3 4 3 5% 7% 41%	2254
	21st to end	Day	22% 5% 2 5% 4 4 4 3 5% 5% 40%	2375
May	1st to 10th	Day	25% 7% 2 6% 4 4 3 4 5% 7% 33%	2470
	11th to 20th	Day	19% 7% 2 5% 4 4 4 4 5% 7% 39%	2438
	21st to end	Day	17% 6% 2 5% 3 4 4 4 6% 6% 43%	2725
June	1st to 10th	Day	19% 5% 2 6% 5% 4 5% 5% 6% 8% 35%	2520
	11th to 20th	Day	17% 7% 2 6% 4 4 4 5% 6% 9% 35%	2520
	21st to end	Day	13% 7% 2 6% 5% 4 5% 4 7% 9% 38%	2520
July	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 5% 6% 8% 40%	2520
	11th to 20th	Day	13% 5% 2 5% 4 4 6% 5% 7% 10% 40%	2520
	21st to end	Day	13% 6% 2 6% 5% 5% 6% 5% 6% 8% 38%	2744
August	1st to 10th	Day	13% 5% 2 7% 5% 5% 5% 5% 8% 9% 37%	2422
	11th to 20th	Day	13% 5% 3 6% 4 4 5% 4 6% 9% 41%	2128
	21st to end	Day	12% 7% 2 6% 4 5% 5% 4 6% 7% 42%	2376
September	1st to 10th	Day	14% 6% 2 6% 5% 4 4 4 5% 7% 43%	2160
	11th to 20th	Day	14% 4 2 5% 3 3 4 4 4 6% 50%	2041
	21st to end	Day	19% 6% 2 6% 4 3 3 3 5% 6% 43%	1980
October	1st to 10th	Day	23% 6% 2 5% 3 4 3 3 4 6% 40%	1944
	11th to 20th	Day	16% 5% 2 5% 4 4 3 3 5% 8% 45%	1793
	21st to end	Day	21% 6% 2 6% 3 4 4 4 4 6% 39%	1782
November	1st to 10th	Day	14% 6% 2 6% 4 4 3 2 5% 6% 48%	1671
	11th to 20th	Day	19% 6% 2 5% 2 3 3 3 5% 6% 46%	1710
	21st to end	Day	17% 6% 2 5% 4 4 4 3 6% 6% 43%	1677
December	1st to 10th	Day	20% 6% 2 6% 5% 4 4 4 5% 6% 37%	1520
	11th to 20th	Day	23% 6% 2 4 4 3 3 3 4 6% 44%	1906
	21st to end	Day	19% 12% 3 7% 5% 5% 3 3 5% 6% 33%	2772
January	1st to 10th	Night	17% 6% 2 5% 4 3 3 3 5% 6% 46%	4429
	11th to 20th	Night	17% 9% 3 7% 4 4 3 2 4 4 43%	4440
	21st to end	Night	25% 11% 3 7% 4 3 4 3 4 4 33%	4784
February	1st to 10th	Night	17% 10% 3 5% 4 3 4 3 4 6% 41%	2411
	11th to 20th	Night	16% 9% 2 6% 4 4 4 2 5% 7% 41%	2218
	21st to end	Night	20% 8% 3 6% 3 4 4 3 4 6% 40%	1884
March	1st to 10th	Night	25% 12% 3 5% 3 3 3 2 4 4 35%	3724
	11th to 20th	Night	12% 7% 2 7% 4 4 4 4 5% 7% 44%	3689
	21st to end	Night	21% 8% 3 6% 3 3 3 3 5% 5% 41%	3466
April	1st to 10th	Night	19% 8% 2 6% 4 4 4 4 5% 7% 37%	1900
	11th to 20th	Night	20% 6% 2 5% 4 3 4 3 6% 6% 41%	1875
	21st to end	Night	20% 7% 2 6% 5% 3 3 3 4 5% 42%	1804
May	1st to 10th	Night	23% 8% 2 7% 5% 4 4 4 5% 6% 32%	1710
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 4 6% 38%	1526
	21st to end	Night	18% 7% 3 5% 4 3 3 4 6% 7% 40%	1550
June	1st to 10th	Night	19% 6% 3 6% 5% 4 4 3 5% 6% 39%	1440
	11th to 20th	Night	17% 7% 2 6% 4 3 4 3 6% 9% 40%	1440
	21st to end	Night	13% 8% 2 6% 4 4 4 4 5% 9% 43%	1440
July	1st to 10th	Night	14% 5% 3 5% 5% 5% 4 5% 7% 9% 39%	1440
	11th to 20th	Night	14% 6% 2 6% 5% 4 6% 4 7% 8% 38%	1440
	21st to end	Night	13% 5% 2 6% 5% 4 5% 5% 7% 8% 40%	1574
August	1st to 10th	Night	9% 6% 2 6% 5% 5% 6% 5% 7% 7% 43%	1497
	11th to 20th	Night	12% 7% 2 8% 6% 5% 6% 4 7% 6% 38%	1769
	21st to end	Night	14% 6% 2 4 4 4 4 3 5% 8% 45%	1980
September	1st to 10th	Night	14% 7% 2 7% 4 4 5% 3 4 7% 43%	1800
	11th to 20th	Night	15% 5% 2 5% 3 3 3 2 4 6% 52%	1917
	21st to end	Night	17% 6% 3 6% 3 4 4 3 4 5% 45%	1980
October	1st to 10th	Night	21% 7% 2 6% 4 4 3 3 4 6% 41%	2012
	11th to 20th	Night	16% 5% 2 6% 3 3 4 3 4 5% 47%	2166
	21st to end	Night	23% 8% 2 5% 3 3 4 3 4 5% 41%	2574
November	1st to 10th	Night	12% 6% 2 5% 5% 4 3 3 5% 6% 48%	2407
	11th to 20th	Night	20% 6% 2 5% 3 3 3 3 4 6% 46%	2470
	21st to end	Night	17% 6% 2 4 5% 3 3 4 4 6% 46%	2499
December	1st to 10th	Night	21% 7% 3 5% 4 4 4 4 4 5% 40%	2660
	11th to 20th	Night	21% 7% 1 4 4 4 4 3 4 6% 41%	3288
	21st to end	Night	22% 11% 3 7% 4 3 3 3 4 5% 36%	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	38% 5% 10% 32% 11% 2	2518
	11th to 20th	Day	47% 6% 11% 23% 11% 1	2520
	21st to end	Day	51% 9% 8% 20% 10% 2	2868
February	1st to 10th	Day	45% 5% 14% 20% 13% 2	1767
	11th to 20th	Day	39% 6% 12% 23% 17% 3	1857
	21st to end	Day	47% 6% 11% 20% 13% 3	1570
March	1st to 10th	Day	52% 5% 12% 18% 11% 2	3119
	11th to 20th	Day	31% 8% 16% 30% 13% 1	3268
	21st to end	Day	45% 5% 7% 17% 21% 5%	4166
April	1st to 10th	Day	46% 5% 10% 20% 15% 3	2280
	11th to 20th	Day	43% 6% 11% 20% 18% 3	2254
	21st to end	Day	44% 6% 10% 20% 16% 4	2375
May	1st to 10th	Day	48% 7% 10% 19% 13% 2	2470
	11th to 20th	Day	43% 6% 11% 20% 17% 3	2442
	21st to end	Day	39% 9% 17% 20% 14% 2	2725
June	1st to 10th	Day	44% 8% 12% 23% 11% 1	2520
	11th to 20th	Day	43% 9% 13% 22% 12% 1	2520
	21st to end	Day	40% 9% 14% 24% 13% 1	2520
July	1st to 10th	Day	39% 10% 12% 21% 17% 1	2450
	11th to 20th	Day	37% 9% 15% 24% 13% 2	2445
	21st to end	Day	39% 9% 13% 20% 16% 2	2591
August	1st to 10th	Day	38% 10% 16% 23% 13% 1	2408
	11th to 20th	Day	39% 8% 17% 23% 13% 1	2128
	21st to end	Day	38% 7% 13% 22% 18% 2	2376
September	1st to 10th	Day	40% 8% 12% 21% 18% 2	2160
	11th to 20th	Day	34% 6% 11% 23% 24% 2	2041
	21st to end	Day	42% 6% 10% 21% 19% 3	1980
October	1st to 10th	Day	45% 7% 9% 21% 16% 3	1944
	11th to 20th	Day	36% 6% 14% 26% 16% 2	1793
	21st to end	Day	45% 6% 10% 21% 16% 3	1782
November	1st to 10th	Day	38% 5% 12% 23% 19% 3	1671
	11th to 20th	Day	39% 4 11% 22% 20% 3	1710
	21st to end	Day	40% 4 14% 26% 12% 3	1677
December	1st to 10th	Day	46% 6% 16% 17% 14% 1	1520
	11th to 20th	Day	42% 3 17% 19% 17% 2	1906
	21st to end	Day	51% 6% 11% 22% 9% 1	2772
January	1st to 10th	Night	39% 4 11% 30% 11% 4	4429
	11th to 20th	Night	44% 5% 12% 24% 13% 3	4440
	21st to end	Night	54% 4 9% 20% 11% 2	4784
February	1st to 10th	Night	45% 5% 12% 23% 13% 2	2411
	11th to 20th	Night	43% 4 11% 20% 18% 4	2220
	21st to end	Night	45% 4 9% 23% 14% 5%	1884
March	1st to 10th	Night	52% 4 10% 19% 12% 2	3734
	11th to 20th	Night	37% 8% 15% 23% 15% 3	3690
	21st to end	Night	45% 4 8% 13% 24% 6%	3466
April	1st to 10th	Night	45% 6% 11% 20% 15% 3	1900
	11th to 20th	Night	44% 5% 11% 19% 20% 1	1875
	21st to end	Night	45% 5% 9% 22% 16% 4	1804
May	1st to 10th	Night	51% 8% 10% 15% 14% 2	1710
	11th to 20th	Night	47% 6% 10% 17% 17% 2	1527
	21st to end	Night	44% 7% 16% 20% 12% 1	1551
June	1st to 10th	Night	45% 7% 11% 19% 17% 2	1440
	11th to 20th	Night	41% 8% 15% 24% 11% 1	1440
	21st to end	Night	38% 8% 13% 25% 15% 1	1440
July	1st to 10th	Night	39% 10% 14% 20% 14% 2	1400
	11th to 20th	Night	40% 9% 15% 26% 9% 1	1392
	21st to end	Night	36% 9% 16% 22% 14% 3	1486
August	1st to 10th	Night	35% 10% 15% 23% 14% 1	1487
	11th to 20th	Night	43% 9% 14% 23% 10% 1	1769
	21st to end	Night	35% 8% 15% 22% 18% 1	1980
September	1st to 10th	Night	41% 6% 10% 25% 16% 2	1800
	11th to 20th	Night	34% 6% 10% 22% 25% 3	1917
	21st to end	Night	42% 7% 7% 21% 21% 3	1980
October	1st to 10th	Night	45% 6% 11% 21% 14% 3	2012
	11th to 20th	Night	38% 6% 12% 28% 15% 1	2166
	21st to end	Night	46% 5% 12% 20% 15% 1	2574
November	1st to 10th	Night	37% 5% 12% 22% 20% 4	2407
	11th to 20th	Night	41% 4 10% 23% 18% 4	2470
	21st to end	Night	39% 4 13% 29% 12% 2	2499
December	1st to 10th	Night	45% 5% 13% 21% 14% 1	2660
	11th to 20th	Night	44% 5% 13% 18% 17% 2	3288
	21st to end	Night	49% 5% 12% 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	23% 28% 28% 19% 2	180
	11th to 20th	Day	19% 34% 31% 14% 1 1	180
	21st to end	Day	19% 28% 36% 11% 5% 1	225
February	1st to 10th	Day	26% 25% 35% 13% 1	327
	11th to 20th	Day	22% 28% 37% 12% 1	456
	21st to end	Day	27% 25% 31% 13% 3	382
March	1st to 10th	Day	21% 23% 37% 15% 3	460
	11th to 20th	Day	18% 28% 35% 14% 3 1	460
	21st to end	Day	25% 23% 37% 11% 4 1	506
April	1st to 10th	Day	23% 26% 31% 13% 6% 1	460
	11th to 20th	Day	26% 21% 32% 15% 6% 1	452
	21st to end	Day	26% 18% 34% 15% 5% 1	460
May	1st to 10th	Day	28% 20% 32% 14% 6% 1	463
	11th to 20th	Day	20% 14% 38% 20% 6% 1	456
	21st to end	Day	19% 10% 28% 29% 11% 3	485
June	1st to 10th	Day	19% 12% 29% 27% 11% 3	450
	11th to 20th	Day	16% 12% 32% 28% 11% 1	450
	21st to end	Day	14% 8% 36% 29% 12% 2	450
July	1st to 10th	Day	15% 5% 29% 30% 18% 3	445
	11th to 20th	Day	14% 5% 26% 32% 20% 3	444
	21st to end	Day	12% 7% 32% 36% 11% 1	488
August	1st to 10th	Day	13% 6% 25% 38% 12% 5%	446
	11th to 20th	Day	15% 4 25% 33% 16% 6%	439
	21st to end	Day	11% 9% 31% 26% 16% 6%	495
September	1st to 10th	Day	16% 10% 27% 24% 19% 4	450
	11th to 20th	Day	16% 8% 30% 26% 13% 8%	450
	21st to end	Day	20% 11% 32% 24% 11% 3	450
October	1st to 10th	Day	27% 10% 26% 21% 13% 4	450
	11th to 20th	Day	16% 19% 29% 25% 10% 1	446
	21st to end	Day	25% 16% 32% 19% 7% 1	396
November	1st to 10th	Day	16% 14% 30% 25% 12% 2	365
	11th to 20th	Day	23% 23% 28% 21% 5%	370
	21st to end	Day	20% 20% 32% 21% 6%	337
December	1st to 10th	Day	24% 18% 36% 17% 5%	180
	11th to 20th	Day	29% 26% 29% 14% 2	180
	21st to end	Day	21% 23% 34% 17% 5% 1	198
January	1st to 10th	Night	21% 20% 37% 19% 3	760
	11th to 20th	Night	26% 19% 33% 19% 3	760
	21st to end	Night	21% 19% 39% 18% 2	836
February	1st to 10th	Night	22% 19% 36% 21% 2	760
	11th to 20th	Night	23% 21% 38% 16% 2	743
	21st to end	Night	24% 20% 35% 17% 3	628
March	1st to 10th	Night	23% 19% 34% 20% 3	760
	11th to 20th	Night	21% 17% 38% 20% 3 1	760
	21st to end	Night	22% 19% 37% 17% 4	836
April	1st to 10th	Night	23% 18% 35% 21% 4	760
	11th to 20th	Night	22% 15% 36% 23% 4	751
	21st to end	Night	21% 16% 36% 21% 5% 1	664
May	1st to 10th	Night	26% 11% 33% 23% 6%	570
	11th to 20th	Night	22% 12% 38% 24% 4	447
	21st to end	Night	22% 6% 23% 38% 10% 1	389
June	1st to 10th	Night	20% 6% 31% 32% 11% 1	360
	11th to 20th	Night	18% 6% 28% 36% 13%	360
	21st to end	Night	16% 3 26% 44% 11%	360
July	1st to 10th	Night	14% 4 23% 40% 19% 1	350
	11th to 20th	Night	14% 3 20% 45% 17% 2	348
	21st to end	Night	13% 3 24% 45% 14% 1	394
August	1st to 10th	Night	9% 3 30% 41% 16% 1	423
	11th to 20th	Night	16% 3 20% 39% 19% 2	705
	21st to end	Night	14% 5% 22% 37% 19% 3	792
September	1st to 10th	Night	18% 5% 27% 34% 15% 2	720
	11th to 20th	Night	18% 6% 24% 31% 17% 3	720
	21st to end	Night	20% 7% 25% 31% 15% 1	720
October	1st to 10th	Night	23% 10% 29% 25% 13% 2	720
	11th to 20th	Night	18% 12% 32% 28% 9%	720
	21st to end	Night	27% 12% 35% 20% 7%	792
November	1st to 10th	Night	16% 13% 33% 26% 10% 1	740
	11th to 20th	Night	22% 16% 35% 20% 6% 1	760
	21st to end	Night	21% 18% 33% 24% 5% 1	760
December	1st to 10th	Night	26% 16% 33% 19% 5% 1	760
	11th to 20th	Night	23% 19% 33% 21% 3	760
	21st to end	Night	25% 18% 35% 19% 2	836

Page generated at 2024-05-10 12:39:04. Version ac07

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