Ibis Observatoire
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ibis Observatoire 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	16% 11% 4 9% 6% 5% 5% 4 5% 6% 28%	101667
	Night	14% 12% 4 9% 6% 5% 5% 4 5% 6% 29%	97902
Transparency	Day	55% 7% 12% 18% 8% 1	105149
	Night	54% 8% 12% 18% 8% 1	102509
Seeing	Day	25% 20% 31% 16% 6% 1	15577
	Night	23% 18% 31% 21% 7% 1	23904

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	10% 15% 7% 14% 7% 5% 6% 5% 5% 7% 19%	2469
	11th to 20th	Day	8% 14% 6% 19% 8% 5% 4 3 3 3 25%	2520
	21st to end	Day	8% 10% 6% 18% 7% 6% 5% 4 5% 6% 25%	2772
February	1st to 10th	Day	10% 14% 5% 14% 9% 9% 6% 4 5% 5% 19%	1577
	11th to 20th	Day	11% 17% 6% 13% 8% 5% 6% 3 5% 4 21%	1787
	21st to end	Day	10% 15% 4 13% 7% 6% 5% 3 4 6% 26%	1570
March	1st to 10th	Day	16% 18% 5% 10% 5% 5% 4 4 3 5% 24%	3116
	11th to 20th	Day	14% 23% 5% 12% 5% 5% 4 3 4 3 22%	3399
	21st to end	Day	14% 15% 6% 10% 5% 4 4 3 3 4 32%	3959
April	1st to 10th	Day	20% 17% 5% 8% 5% 4 4 3 4 5% 25%	2280
	11th to 20th	Day	16% 12% 3 9% 5% 4 4 3 4 5% 34%	2390
	21st to end	Day	21% 14% 3 8% 5% 4 3 3 4 6% 29%	2470
May	1st to 10th	Day	18% 10% 4 9% 6% 5% 5% 4 5% 6% 29%	4106
	11th to 20th	Day	20% 10% 2 9% 6% 5% 5% 4 5% 7% 26%	4383
	21st to end	Day	15% 8% 3 8% 6% 6% 6% 5% 6% 7% 29%	5050
June	1st to 10th	Day	21% 10% 3 7% 5% 5% 6% 4 5% 8% 26%	2850
	11th to 20th	Day	20% 8% 3 5% 5% 5% 5% 4 6% 8% 31%	2850
	21st to end	Day	23% 10% 4 9% 6% 6% 4 3 5% 6% 24%	2850
July	1st to 10th	Day	14% 8% 4 8% 6% 6% 7% 5% 7% 7% 28%	4671
	11th to 20th	Day	15% 6% 2 7% 5% 6% 6% 6% 7% 9% 31%	4440
	21st to end	Day	14% 7% 3 6% 5% 4 5% 5% 6% 7% 38%	4814
August	1st to 10th	Day	15% 6% 3 8% 6% 5% 6% 4 8% 10% 28%	4303
	11th to 20th	Day	16% 8% 3 8% 7% 7% 7% 6% 7% 7% 24%	4045
	21st to end	Day	18% 7% 3 6% 5% 5% 5% 4 6% 7% 36%	4441
September	1st to 10th	Day	16% 7% 3 8% 5% 5% 4 3 5% 8% 36%	2258
	11th to 20th	Day	17% 7% 3 5% 3 4 3 3 6% 7% 42%	2090
	21st to end	Day	17% 9% 2 7% 5% 4 4 4 5% 7% 37%	2090
October	1st to 10th	Day	18% 10% 3 7% 5% 5% 5% 3 5% 6% 33%	2076
	11th to 20th	Day	20% 11% 4 9% 5% 5% 5% 4 5% 6% 26%	1768
	21st to end	Day	21% 16% 4 10% 5% 5% 4 3 4 5% 23%	1881
November	1st to 10th	Day	17% 15% 4 9% 6% 5% 4 3 4 5% 28%	1761
	11th to 20th	Day	16% 14% 4 10% 7% 6% 5% 3 5% 6% 24%	1749
	21st to end	Day	17% 18% 5% 10% 5% 5% 5% 4 4 4 22%	1453
December	1st to 10th	Day	17% 18% 8% 13% 7% 4 5% 2 4 3 18%	1330
	11th to 20th	Day	16% 17% 5% 11% 6% 4 4 3 5% 5% 24%	1668
	21st to end	Day	19% 16% 6% 10% 6% 6% 4 4 4 4 22%	2431
January	1st to 10th	Night	10% 14% 7% 15% 7% 7% 6% 5% 6% 5% 18%	4463
	11th to 20th	Night	8% 14% 5% 15% 10% 8% 6% 4 5% 5% 21%	4440
	21st to end	Night	7% 11% 7% 15% 6% 5% 5% 5% 6% 7% 24%	4884
February	1st to 10th	Night	7% 15% 5% 12% 9% 6% 5% 5% 6% 5% 25%	2601
	11th to 20th	Night	9% 13% 6% 14% 7% 6% 6% 3 6% 5% 23%	2279
	21st to end	Night	12% 13% 4 10% 6% 6% 5% 4 5% 6% 31%	1884
March	1st to 10th	Night	16% 17% 5% 8% 4 4 5% 3 4 6% 27%	3724
	11th to 20th	Night	11% 15% 5% 11% 7% 6% 6% 4 6% 5% 24%	3559
	21st to end	Night	16% 16% 4 9% 6% 5% 3 3 4 5% 29%	3672
April	1st to 10th	Night	16% 16% 5% 7% 5% 5% 4 4 4 5% 29%	1900
	11th to 20th	Night	16% 13% 3 6% 4 3 4 4 7% 8% 32%	1739
	21st to end	Night	19% 13% 3 9% 4 4 4 4 4 5% 31%	1710
May	1st to 10th	Night	19% 10% 3 6% 4 4 5% 5% 5% 7% 33%	2834
	11th to 20th	Night	18% 10% 4 8% 5% 5% 5% 3 5% 5% 33%	2540
	21st to end	Night	16% 6% 2 6% 4 5% 5% 5% 6% 9% 36%	2530
June	1st to 10th	Night	21% 11% 2 6% 6% 4 6% 4 7% 7% 27%	1330
	11th to 20th	Night	14% 8% 3 7% 4 4 5% 4 5% 8% 38%	1330
	21st to end	Night	19% 10% 3 7% 5% 5% 5% 4 6% 6% 30%	1330
July	1st to 10th	Night	10% 7% 3 7% 6% 5% 7% 5% 7% 9% 35%	2292
	11th to 20th	Night	18% 6% 2 6% 4 5% 5% 5% 6% 8% 36%	2520
	21st to end	Night	11% 5% 2 6% 5% 5% 4 4 6% 8% 44%	2739
August	1st to 10th	Night	18% 7% 3 7% 5% 4 5% 4 6% 7% 34%	2594
	11th to 20th	Night	14% 6% 3 9% 6% 5% 6% 5% 6% 8% 32%	2782
	21st to end	Night	15% 6% 2 6% 5% 5% 5% 3 5% 7% 40%	3211
September	1st to 10th	Night	15% 7% 2 5% 4 5% 4 4 5% 7% 41%	1921
	11th to 20th	Night	16% 6% 2 5% 5% 4 4 4 5% 6% 43%	2090
	21st to end	Night	16% 7% 3 6% 4 5% 5% 4 5% 6% 41%	2090
October	1st to 10th	Night	16% 9% 3 6% 4 4 4 4 5% 6% 39%	2104
	11th to 20th	Night	20% 10% 3 7% 5% 5% 5% 3 5% 6% 31%	2408
	21st to end	Night	18% 12% 4 8% 5% 5% 4 4 5% 6% 28%	2717
November	1st to 10th	Night	15% 11% 4 9% 4 6% 6% 4 6% 7% 28%	2537
	11th to 20th	Night	14% 11% 4 10% 6% 5% 5% 4 6% 7% 30%	2650
	21st to end	Night	15% 15% 5% 10% 6% 5% 5% 4 5% 7% 23%	2881
December	1st to 10th	Night	17% 15% 5% 12% 7% 6% 5% 4 5% 5% 19%	2850
	11th to 20th	Night	16% 14% 5% 12% 7% 6% 5% 3 5% 5% 22%	3531
	21st to end	Night	17% 19% 5% 10% 5% 4 4 3 4 4 25%	5236

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	67% 7% 10% 12% 4	2470
	11th to 20th	Day	68% 4 5% 14% 8% 1	2520
	21st to end	Day	60% 7% 7% 14% 11% 1	2772
February	1st to 10th	Day	66% 7% 7% 10% 8% 2	1577
	11th to 20th	Day	65% 6% 8% 11% 8% 1	1795
	21st to end	Day	59% 6% 7% 18% 8% 3	1570
March	1st to 10th	Day	63% 5% 8% 13% 9% 2	3119
	11th to 20th	Day	67% 7% 8% 12% 6% 1	3399
	21st to end	Day	58% 3 7% 17% 12% 3	3959
April	1st to 10th	Day	62% 5% 9% 13% 9% 2	2280
	11th to 20th	Day	52% 6% 9% 19% 12% 2	2390
	21st to end	Day	57% 5% 8% 16% 11% 3	2470
May	1st to 10th	Day	55% 7% 9% 16% 11% 1	4120
	11th to 20th	Day	53% 9% 16% 16% 6%	4387
	21st to end	Day	50% 10% 11% 18% 10%	5050
June	1st to 10th	Day	56% 8% 11% 18% 7% 1	2850
	11th to 20th	Day	49% 8% 13% 20% 8% 1	2850
	21st to end	Day	60% 8% 9% 15% 7%	2850
July	1st to 10th	Day	51% 9% 14% 18% 7%	4598
	11th to 20th	Day	45% 11% 17% 23% 4	4365
	21st to end	Day	44% 9% 13% 26% 8%	4661
August	1st to 10th	Day	48% 10% 17% 19% 6%	4289
	11th to 20th	Day	54% 11% 16% 15% 4	4084
	21st to end	Day	45% 9% 15% 19% 11% 1	4441
September	1st to 10th	Day	45% 9% 14% 21% 11% 1	2258
	11th to 20th	Day	42% 6% 13% 27% 12%	2090
	21st to end	Day	46% 8% 12% 24% 11%	2090
October	1st to 10th	Day	53% 6% 11% 23% 6%	3453
	11th to 20th	Day	49% 8% 14% 23% 5%	2919
	21st to end	Day	50% 6% 16% 18% 10%	3081
November	1st to 10th	Day	57% 7% 12% 17% 7%	1761
	11th to 20th	Day	61% 8% 9% 14% 7% 1	1749
	21st to end	Day	65% 9% 9% 13% 5%	1453
December	1st to 10th	Day	70% 6% 8% 11% 5%	1330
	11th to 20th	Day	63% 6% 8% 14% 9% 1	1668
	21st to end	Day	66% 6% 9% 11% 6% 2	2431
January	1st to 10th	Night	68% 7% 9% 11% 5%	4463
	11th to 20th	Night	67% 6% 9% 13% 5%	4440
	21st to end	Night	58% 7% 9% 13% 10% 2	4884
February	1st to 10th	Night	59% 8% 9% 13% 10% 1	2601
	11th to 20th	Night	62% 7% 9% 13% 8% 1	2281
	21st to end	Night	55% 6% 9% 16% 12% 2	1884
March	1st to 10th	Night	59% 6% 9% 15% 8% 1	3734
	11th to 20th	Night	60% 8% 12% 13% 6% 1	3560
	21st to end	Night	59% 4 7% 19% 10% 2	3672
April	1st to 10th	Night	56% 7% 8% 14% 12% 3	1900
	11th to 20th	Night	49% 8% 10% 20% 12% 1	1739
	21st to end	Night	55% 6% 8% 17% 11% 2	1710
May	1st to 10th	Night	49% 8% 13% 20% 10% 1	2840
	11th to 20th	Night	51% 8% 14% 18% 9%	2541
	21st to end	Night	43% 9% 16% 19% 13%	2531
June	1st to 10th	Night	54% 8% 13% 20% 5%	1330
	11th to 20th	Night	44% 8% 14% 22% 11% 2	1330
	21st to end	Night	53% 9% 14% 16% 9%	1330
July	1st to 10th	Night	42% 10% 21% 21% 5%	2255
	11th to 20th	Night	44% 9% 21% 21% 4	2472
	21st to end	Night	37% 10% 23% 24% 7%	2651
August	1st to 10th	Night	47% 9% 16% 25% 3	2584
	11th to 20th	Night	48% 10% 19% 16% 6%	2809
	21st to end	Night	42% 9% 14% 22% 13% 1	3211
September	1st to 10th	Night	40% 10% 14% 25% 10% 1	1921
	11th to 20th	Night	40% 8% 17% 26% 9%	2090
	21st to end	Night	44% 9% 11% 24% 12% 1	2090
October	1st to 10th	Night	44% 6% 12% 29% 8%	3507
	11th to 20th	Night	47% 7% 11% 28% 6%	3996
	21st to end	Night	46% 7% 18% 17% 12% 1	4467
November	1st to 10th	Night	53% 10% 12% 18% 6%	2537
	11th to 20th	Night	54% 9% 11% 16% 10% 1	2650
	21st to end	Night	61% 9% 11% 13% 5%	2881
December	1st to 10th	Night	67% 8% 10% 12% 4	2850
	11th to 20th	Night	64% 7% 7% 14% 8%	3532
	21st to end	Night	63% 6% 8% 14% 9% 1	5236

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	25% 32% 33% 8% 1 1	180
	11th to 20th	Day	31% 26% 33% 7% 3 1	180
	21st to end	Day	20% 25% 38% 13% 4 1	198
February	1st to 10th	Day	28% 30% 28% 11% 3	237
	11th to 20th	Day	26% 28% 36% 8% 2	426
	21st to end	Day	25% 28% 31% 13% 3	382
March	1st to 10th	Day	28% 23% 32% 14% 3	460
	11th to 20th	Day	28% 26% 29% 11% 7%	460
	21st to end	Day	29% 24% 27% 14% 6% 1	506
April	1st to 10th	Day	34% 25% 23% 13% 5% 1	460
	11th to 20th	Day	29% 25% 27% 14% 4 1	452
	21st to end	Day	33% 20% 31% 10% 3 2	460
May	1st to 10th	Day	29% 16% 38% 14% 3 1	463
	11th to 20th	Day	25% 18% 32% 18% 6% 1	487
	21st to end	Day	23% 20% 34% 17% 5%	651
June	1st to 10th	Day	24% 17% 35% 16% 7% 1	680
	11th to 20th	Day	21% 19% 28% 23% 9% 1	680
	21st to end	Day	28% 14% 30% 21% 6% 1	680
July	1st to 10th	Day	20% 16% 36% 20% 8%	622
	11th to 20th	Day	19% 14% 42% 18% 6%	484
	21st to end	Day	19% 14% 36% 23% 7% 1	532
August	1st to 10th	Day	19% 17% 32% 22% 8% 2	486
	11th to 20th	Day	18% 12% 35% 24% 10% 1	479
	21st to end	Day	20% 17% 29% 21% 9% 4	539
September	1st to 10th	Day	17% 20% 30% 20% 10% 3	490
	11th to 20th	Day	23% 13% 30% 20% 10% 3	490
	21st to end	Day	20% 17% 32% 17% 10% 5%	490
October	1st to 10th	Day	23% 19% 25% 20% 11% 2	483
	11th to 20th	Day	29% 20% 28% 15% 7% 1	390
	21st to end	Day	34% 24% 27% 12% 3	429
November	1st to 10th	Day	34% 18% 32% 14% 3	395
	11th to 20th	Day	26% 24% 28% 15% 7% 1	400
	21st to end	Day	31% 26% 29% 10% 3	268
December	1st to 10th	Day	32% 17% 32% 16% 3 1	180
	11th to 20th	Day	36% 24% 31% 8% 1 1	180
	21st to end	Day	36% 25% 25% 13% 1	198
January	1st to 10th	Night	23% 26% 36% 12% 2	769
	11th to 20th	Night	23% 24% 34% 16% 2	760
	21st to end	Night	15% 23% 38% 20% 4	836
February	1st to 10th	Night	16% 29% 36% 14% 4	760
	11th to 20th	Night	22% 26% 36% 13% 3	743
	21st to end	Night	22% 21% 37% 16% 3	628
March	1st to 10th	Night	23% 21% 36% 17% 3	760
	11th to 20th	Night	22% 23% 34% 15% 5% 1	760
	21st to end	Night	22% 20% 31% 21% 6%	836
April	1st to 10th	Night	28% 20% 31% 15% 5%	760
	11th to 20th	Night	25% 18% 30% 20% 6%	615
	21st to end	Night	32% 13% 27% 20% 7% 1	570
May	1st to 10th	Night	24% 13% 32% 23% 7%	570
	11th to 20th	Night	22% 11% 29% 28% 8% 1	406
	21st to end	Night	23% 13% 33% 24% 7% 1	411
June	1st to 10th	Night	24% 9% 33% 25% 8%	380
	11th to 20th	Night	17% 12% 27% 33% 10% 1	380
	21st to end	Night	23% 9% 31% 29% 8% 1	380
July	1st to 10th	Night	15% 11% 34% 30% 10%	370
	11th to 20th	Night	17% 7% 34% 31% 10% 1	368
	21st to end	Night	16% 6% 30% 37% 11%	416
August	1st to 10th	Night	16% 6% 32% 31% 15% 1	427
	11th to 20th	Night	18% 7% 29% 33% 13% 1	562
	21st to end	Night	15% 9% 30% 31% 13% 2	675
September	1st to 10th	Night	18% 11% 32% 29% 10% 1	760
	11th to 20th	Night	20% 10% 28% 26% 14% 2	760
	21st to end	Night	20% 12% 29% 24% 14% 1	760
October	1st to 10th	Night	21% 17% 29% 23% 10% 1	760
	11th to 20th	Night	28% 15% 29% 19% 8% 1	760
	21st to end	Night	28% 21% 31% 16% 5%	836
November	1st to 10th	Night	27% 21% 29% 18% 4	780
	11th to 20th	Night	24% 23% 27% 19% 6% 1	825
	21st to end	Night	27% 23% 31% 14% 4 1	886
December	1st to 10th	Night	27% 23% 31% 14% 5% 1	850
	11th to 20th	Night	25% 26% 27% 17% 5%	850
	21st to end	Night	28% 26% 27% 16% 3	935

Page generated at 2024-11-25 00:22:20. Version ac07

Copyright © 2024 Attilla Danko.