Montebello
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Montebello clear sky chart from 2005-11-06 to 2024-11-04.

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% 4 2 5% 3 3 3 3 5% 7% 60%	104982
	Night	6% 6% 2 5% 4 4 4 3 5% 7% 54%	102792
Transparency	Day	24% 3 9% 19% 24% 20%	104742
	Night	28% 4 10% 19% 20% 18%	102622
Seeing	Day	8% 12% 27% 31% 18% 5%	15463
	Night	9% 7% 17% 32% 29% 7%	24805

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	13% 8% 3 8% 5% 5% 5% 4 5% 6% 38%	2740
	11th to 20th	Day	12% 8% 5% 12% 6% 6% 5% 3 5% 6% 32%	2860
	21st to end	Day	14% 11% 4 10% 5% 5% 5% 4 6% 8% 28%	3146
February	1st to 10th	Day	12% 8% 2 6% 5% 4 4 4 5% 6% 43%	1710
	11th to 20th	Day	11% 8% 3 7% 4 4 4 3 5% 7% 43%	1755
	21st to end	Day	11% 7% 3 8% 5% 3 4 3 5% 5% 46%	1570
March	1st to 10th	Day	10% 10% 3 11% 9% 7% 7% 5% 6% 6% 27%	3399
	11th to 20th	Day	6% 5% 2 6% 4 4 4 3 6% 7% 52%	3490
	21st to end	Day	10% 8% 3 9% 6% 6% 6% 5% 7% 7% 32%	3876
April	1st to 10th	Day	11% 7% 3 6% 5% 4 3 3 6% 7% 44%	2280
	11th to 20th	Day	9% 5% 1 5% 3 3 4 4 5% 8% 52%	2249
	21st to end	Day	5% 5% 1 5% 4 4 3 3 5% 9% 56%	2280
May	1st to 10th	Day	5% 3 1 2 2 2 2 2 4 5% 71%	3908
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 7% 75%	4122
	21st to end	Day	3 4 2 4 3 3 4 3 4 6% 65%	4813
June	1st to 10th	Day	5% 4 1 3 2 3 4 4 5% 7% 62%	2660
	11th to 20th	Day	2 2 1 1 2 1 2 3 5% 7% 74%	2660
	21st to end	Day	1 2 1 2 2 2 3 2 3 5% 78%	2660
July	1st to 10th	Day	1 1 1 1 1 1 2 2 4 86%	4392
	11th to 20th	Day	1 1 1 1 2 2 2 4 7% 77%	4110
	21st to end	Day	1 1 1 1 1 2 2 5% 9% 78%	4455
August	1st to 10th	Day	1 2 1 2 1 2 4 4 6% 9% 70%	4091
	11th to 20th	Day	1 2 1 1 2 2 4 7% 81%	3817
	21st to end	Day	1 1 2 1 2 3 2 4 8% 76%	4180
September	1st to 10th	Day	1 1 1 2 1 2 2 2 3 7% 79%	2280
	11th to 20th	Day	2 3 1 4 3 3 3 3 5% 9% 64%	2280
	21st to end	Day	2 2 1 2 2 2 2 2 3 6% 76%	2014
October	1st to 10th	Day	2 2 1 3 2 2 3 2 4 6% 71%	3180
	11th to 20th	Day	3 3 1 3 3 2 3 4 6% 8% 64%	3161
	21st to end	Day	3 3 1 4 3 4 4 4 7% 8% 59%	3448
November	1st to 10th	Day	7% 6% 2 5% 4 4 4 3 4 8% 53%	1871
	11th to 20th	Day	7% 6% 3 5% 5% 5% 4 4 5% 6% 50%	1710
	21st to end	Day	8% 6% 2 5% 4 3 4 3 5% 8% 53%	1573
December	1st to 10th	Day	8% 6% 3 7% 6% 4 5% 5% 6% 8% 42%	1520
	11th to 20th	Day	16% 10% 4 10% 6% 5% 5% 4 6% 5% 30%	1928
	21st to end	Day	11% 11% 4 9% 6% 5% 5% 4 5% 7% 34%	2794
January	1st to 10th	Night	12% 10% 3 7% 4 4 4 3 6% 6% 41%	4207
	11th to 20th	Night	12% 10% 4 12% 6% 6% 5% 4 5% 5% 30%	4110
	21st to end	Night	14% 12% 4 10% 6% 5% 5% 3 4 6% 30%	4521
February	1st to 10th	Night	10% 9% 3 5% 5% 5% 4 3 4 5% 47%	2470
	11th to 20th	Night	10% 7% 2 7% 5% 5% 4 4 5% 8% 42%	2309
	21st to end	Night	10% 7% 2 6% 5% 4 4 3 6% 6% 48%	1884
March	1st to 10th	Night	10% 11% 4 10% 6% 6% 6% 5% 5% 5% 32%	3471
	11th to 20th	Night	8% 7% 2 5% 4 4 3 3 4 7% 53%	3490
	21st to end	Night	9% 14% 3 9% 6% 6% 6% 4 4 5% 33%	3775
April	1st to 10th	Night	9% 7% 3 6% 4 4 4 4 6% 7% 45%	1900
	11th to 20th	Night	8% 6% 2 5% 4 3 4 4 4 8% 51%	1879
	21st to end	Night	4 4 1 3 3 4 4 4 6% 10% 57%	1900
May	1st to 10th	Night	2 5% 2 4 3 3 3 3 5% 6% 65%	3065
	11th to 20th	Night	1 2 1 3 3 3 3 3 6% 7% 67%	2775
	21st to end	Night	2 2 1 3 2 3 5% 4 8% 7% 63%	2762
June	1st to 10th	Night	3 4 1 5% 3 2 3 4 7% 9% 59%	1520
	11th to 20th	Night	1 1 1 2 2 2 2 3 6% 8% 72%	1520
	21st to end	Night	1 2 1 3 2 3 2 2 4 7% 74%	1520
July	1st to 10th	Night	1 1 1 1 2 1 3 5% 84%	2563
	11th to 20th	Night	1 1 2 3 4 3 3 5% 7% 71%	2860
	21st to end	Night	1 1 3 2 3 4 6% 11% 11% 59%	3109
August	1st to 10th	Night	2 3 1 2 2 3 5% 5% 8% 11% 58%	2848
	11th to 20th	Night	1 1 2 2 2 3 2 5% 8% 74%	3026
	21st to end	Night	1 2 1 2 2 3 4 3 5% 7% 72%	3498
September	1st to 10th	Night	1 2 2 2 2 2 2 5% 10% 73%	1900
	11th to 20th	Night	2 3 1 4 2 3 3 4 6% 9% 62%	1900
	21st to end	Night	2 2 1 2 2 2 2 2 4 7% 74%	2162
October	1st to 10th	Night	2 2 1 2 3 2 3 2 5% 6% 73%	3800
	11th to 20th	Night	3 4 1 4 3 3 3 3 8% 7% 61%	3777
	21st to end	Night	3 4 2 5% 3 3 3 3 6% 6% 62%	4121
November	1st to 10th	Night	6% 5% 2 5% 4 3 4 3 5% 9% 55%	2278
	11th to 20th	Night	7% 6% 2 6% 4 4 4 4 6% 8% 50%	2470
	21st to end	Night	7% 5% 2 4 4 4 4 4 5% 7% 56%	2604
December	1st to 10th	Night	9% 6% 3 7% 4 5% 4 3 5% 7% 46%	2660
	11th to 20th	Night	16% 10% 4 9% 6% 5% 4 4 5% 7% 29%	3276
	21st to end	Night	12% 9% 3 9% 6% 5% 6% 4 6% 6% 34%	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	43% 8% 12% 25% 8% 3	2740
	11th to 20th	Day	51% 6% 11% 14% 10% 8%	2860
	21st to end	Day	52% 6% 9% 14% 13% 5%	3146
February	1st to 10th	Day	40% 4 8% 20% 17% 11%	1710
	11th to 20th	Day	39% 4 10% 18% 21% 7%	1764
	21st to end	Day	40% 4 8% 23% 18% 7%	1570
March	1st to 10th	Day	52% 8% 11% 14% 13% 3	3399
	11th to 20th	Day	30% 5% 13% 26% 16% 10%	3490
	21st to end	Day	46% 7% 17% 18% 10% 2	3876
April	1st to 10th	Day	38% 4 13% 21% 19% 4	2280
	11th to 20th	Day	30% 5% 15% 25% 21% 5%	2252
	21st to end	Day	25% 4 15% 28% 23% 5%	2280
May	1st to 10th	Day	17% 3 10% 30% 27% 13%	3908
	11th to 20th	Day	11% 2 11% 31% 32% 14%	4125
	21st to end	Day	17% 3 18% 27% 30% 4	4814
June	1st to 10th	Day	21% 5% 14% 25% 26% 9%	2660
	11th to 20th	Day	9% 3 11% 25% 35% 17%	2660
	21st to end	Day	10% 1 6% 18% 30% 34%	2660
July	1st to 10th	Day	5% 1 3 9% 15% 67%	4323
	11th to 20th	Day	7% 1 5% 11% 17% 58%	4041
	21st to end	Day	5% 1 3 11% 33% 47%	4315
August	1st to 10th	Day	11% 1 5% 14% 32% 37%	4076
	11th to 20th	Day	5% 1 4 12% 40% 38%	3855
	21st to end	Day	9% 2 5% 16% 36% 33%	4179
September	1st to 10th	Day	8% 2 3 14% 31% 42%	2280
	11th to 20th	Day	17% 4 8% 26% 28% 17%	2280
	21st to end	Day	12% 2 7% 21% 35% 23%	2014
October	1st to 10th	Day	16% 2 5% 11% 27% 39%	3180
	11th to 20th	Day	16% 4 8% 24% 32% 16%	3161
	21st to end	Day	21% 2 9% 23% 29% 17%	3448
November	1st to 10th	Day	30% 5% 9% 22% 22% 12%	1871
	11th to 20th	Day	32% 6% 10% 22% 22% 8%	1710
	21st to end	Day	31% 4 8% 17% 29% 10%	1573
December	1st to 10th	Day	39% 5% 11% 18% 16% 11%	1520
	11th to 20th	Day	54% 5% 9% 13% 13% 5%	1928
	21st to end	Day	48% 6% 12% 19% 11% 3	2794
January	1st to 10th	Night	40% 7% 18% 22% 10% 3	4207
	11th to 20th	Night	52% 6% 14% 11% 9% 8%	4110
	21st to end	Night	54% 6% 10% 11% 12% 7%	4521
February	1st to 10th	Night	38% 3 9% 19% 19% 12%	2470
	11th to 20th	Night	37% 4 11% 19% 22% 7%	2311
	21st to end	Night	35% 5% 11% 29% 16% 5%	1884
March	1st to 10th	Night	50% 7% 14% 14% 13% 3	3471
	11th to 20th	Night	32% 5% 12% 21% 20% 10%	3490
	21st to end	Night	50% 6% 14% 18% 10% 3	3775
April	1st to 10th	Night	36% 5% 16% 21% 17% 5%	1900
	11th to 20th	Night	31% 4 13% 26% 18% 7%	1879
	21st to end	Night	22% 5% 16% 29% 23% 7%	1900
May	1st to 10th	Night	19% 3 14% 25% 25% 13%	3065
	11th to 20th	Night	13% 2 12% 34% 28% 11%	2776
	21st to end	Night	14% 3 22% 26% 30% 5%	2762
June	1st to 10th	Night	18% 5% 16% 26% 26% 9%	1520
	11th to 20th	Night	10% 3 9% 24% 32% 22%	1520
	21st to end	Night	12% 1 6% 18% 30% 32%	1520
July	1st to 10th	Night	5% 1 3 10% 17% 65%	2523
	11th to 20th	Night	9% 1 8% 15% 13% 53%	2806
	21st to end	Night	9% 1 5% 17% 20% 47%	3011
August	1st to 10th	Night	14% 1 8% 15% 27% 34%	2839
	11th to 20th	Night	9% 1 3 12% 33% 42%	3054
	21st to end	Night	10% 2 5% 16% 33% 34%	3498
September	1st to 10th	Night	9% 2 5% 16% 24% 44%	1900
	11th to 20th	Night	17% 4 7% 25% 30% 17%	1900
	21st to end	Night	13% 2 8% 19% 32% 28%	2162
October	1st to 10th	Night	14% 2 6% 11% 20% 48%	3800
	11th to 20th	Night	18% 3 8% 23% 27% 20%	3777
	21st to end	Night	22% 3 7% 20% 26% 22%	4121
November	1st to 10th	Night	27% 4 10% 24% 19% 15%	2278
	11th to 20th	Night	30% 5% 10% 24% 22% 9%	2470
	21st to end	Night	28% 4 10% 20% 24% 14%	2604
December	1st to 10th	Night	37% 6% 9% 18% 17% 13%	2660
	11th to 20th	Night	53% 4 10% 14% 15% 5%	3276
	21st to end	Night	48% 7% 15% 15% 11% 4	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	24% 18% 23% 21% 12% 2	303
	11th to 20th	Day	16% 16% 25% 29% 12% 3	370
	21st to end	Day	15% 13% 28% 25% 16% 3	407
February	1st to 10th	Day	17% 18% 23% 24% 13% 4	370
	11th to 20th	Day	17% 22% 26% 24% 9% 1	408
	21st to end	Day	13% 19% 31% 25% 10% 1	382
March	1st to 10th	Day	18% 21% 31% 22% 7% 1	460
	11th to 20th	Day	17% 20% 28% 19% 13% 3	460
	21st to end	Day	14% 21% 34% 23% 7% 1	506
April	1st to 10th	Day	15% 18% 34% 21% 10% 2	460
	11th to 20th	Day	13% 19% 31% 24% 9% 3	452
	21st to end	Day	7% 22% 30% 26% 10% 5%	460
May	1st to 10th	Day	7% 14% 37% 27% 12% 2	463
	11th to 20th	Day	9% 14% 35% 25% 14% 2	488
	21st to end	Day	7% 14% 32% 29% 13% 5%	529
June	1st to 10th	Day	6% 11% 33% 30% 16% 4	490
	11th to 20th	Day	2 12% 32% 36% 15% 3	490
	21st to end	Day	1 4 31% 38% 22% 4	490
July	1st to 10th	Day	2 4 21% 47% 22% 4	486
	11th to 20th	Day	1 1 19% 46% 29% 5%	484
	21st to end	Day	1 1 19% 47% 25% 8%	531
August	1st to 10th	Day	2 2 26% 43% 20% 7%	487
	11th to 20th	Day	1 2 26% 38% 25% 8%	477
	21st to end	Day	1 3 21% 42% 26% 8%	539
September	1st to 10th	Day	2 4 18% 42% 26% 8%	490
	11th to 20th	Day	4 10% 26% 35% 19% 6%	490
	21st to end	Day	3 9% 20% 35% 27% 6%	490
October	1st to 10th	Day	2 9% 23% 34% 23% 8%	490
	11th to 20th	Day	6% 9% 22% 29% 26% 9%	490
	21st to end	Day	7% 9% 26% 31% 22% 6%	539
November	1st to 10th	Day	9% 13% 22% 26% 23% 7%	449
	11th to 20th	Day	5% 10% 20% 30% 26% 10%	270
	21st to end	Day	7% 9% 26% 29% 25% 4	205
December	1st to 10th	Day	8% 19% 21% 23% 24% 6%	180
	11th to 20th	Day	14% 17% 24% 21% 18% 7%	180
	21st to end	Day	19% 20% 25% 20% 14% 3	198
January	1st to 10th	Night	19% 8% 16% 29% 22% 6%	760
	11th to 20th	Night	15% 8% 15% 31% 23% 7%	760
	21st to end	Night	17% 7% 15% 32% 23% 5%	836
February	1st to 10th	Night	14% 9% 18% 32% 22% 4	760
	11th to 20th	Night	14% 11% 19% 31% 21% 5%	744
	21st to end	Night	14% 11% 22% 32% 18% 3	628
March	1st to 10th	Night	17% 11% 20% 28% 20% 3	760
	11th to 20th	Night	15% 11% 17% 30% 22% 5%	760
	21st to end	Night	13% 11% 25% 32% 17% 2	836
April	1st to 10th	Night	12% 10% 25% 29% 20% 3	760
	11th to 20th	Night	11% 14% 21% 29% 19% 5%	751
	21st to end	Night	6% 10% 29% 26% 22% 6%	760
May	1st to 10th	Night	6% 7% 26% 33% 24% 5%	697
	11th to 20th	Night	5% 5% 22% 32% 30% 6%	529
	21st to end	Night	4 9% 24% 32% 26% 4	411
June	1st to 10th	Night	5% 4 24% 35% 27% 4	380
	11th to 20th	Night	1 4 19% 43% 30% 1	380
	21st to end	Night	2 3 14% 38% 39% 5%	380
July	1st to 10th	Night	1 2 12% 35% 47% 4	380
	11th to 20th	Night	1 5% 36% 45% 13%	552
	21st to end	Night	1 8% 29% 51% 11%	624
August	1st to 10th	Night	4 2 11% 31% 44% 8%	567
	11th to 20th	Night	1 2 14% 34% 42% 7%	688
	21st to end	Night	1 1 11% 31% 46% 10%	836
September	1st to 10th	Night	2 2 9% 33% 43% 11%	760
	11th to 20th	Night	5% 3 13% 36% 36% 7%	760
	21st to end	Night	2 4 12% 30% 41% 11%	760
October	1st to 10th	Night	5% 3 13% 33% 36% 10%	760
	11th to 20th	Night	6% 4 13% 29% 39% 9%	760
	21st to end	Night	6% 6% 12% 31% 32% 13%	836
November	1st to 10th	Night	7% 6% 17% 27% 34% 9%	754
	11th to 20th	Night	9% 4 14% 33% 32% 7%	760
	21st to end	Night	10% 5% 15% 38% 26% 7%	760
December	1st to 10th	Night	13% 8% 19% 31% 24% 6%	760
	11th to 20th	Night	18% 9% 18% 30% 21% 4	760
	21st to end	Night	17% 14% 20% 29% 18% 3	836

Page generated at 2024-11-01 19:47:49. Version ac07

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