Malhotra Observatory
Clear Sky Chart
History

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

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	7% 5% 2 7% 6% 6% 7% 6% 9% 12% 34%	100622
	Night	7% 5% 2 7% 5% 6% 6% 5% 8% 11% 38%	98504
Transparency	Day	36% 13% 22% 19% 9% 2	104319
	Night	36% 11% 20% 20% 10% 2	102946
Seeing	Day	7% 3 13% 30% 32% 15%	16093
	Night	8% 3 13% 30% 32% 14%	26220

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	10% 7% 3 7% 5% 6% 5% 4 7% 9% 36%	2836
	11th to 20th	Day	15% 8% 3 8% 7% 7% 6% 5% 7% 8% 26%	2840
	21st to end	Day	6% 7% 2 10% 7% 6% 7% 5% 7% 7% 36%	3157
February	1st to 10th	Day	8% 6% 3 6% 6% 5% 5% 4 7% 10% 40%	1900
	11th to 20th	Day	7% 4 2 5% 4 4 4 5% 7% 10% 49%	1988
	21st to end	Day	5% 4 2 5% 5% 5% 6% 6% 8% 9% 47%	1727
March	1st to 10th	Day	5% 5% 2 7% 6% 6% 7% 6% 9% 12% 34%	3435
	11th to 20th	Day	4 2 1 4 4 4 4 4 9% 11% 52%	3480
	21st to end	Day	8% 5% 2 5% 4 4 5% 5% 7% 10% 45%	3815
April	1st to 10th	Day	3 3 1 4 4 4 6% 5% 9% 13% 47%	2090
	11th to 20th	Day	5% 4 2 6% 4 5% 6% 5% 8% 13% 41%	2166
	21st to end	Day	6% 3 2 5% 5% 5% 5% 7% 9% 10% 43%	2280
May	1st to 10th	Day	2 2 1 3 3 4 5% 4 7% 13% 57%	3765
	11th to 20th	Day	6% 4 2 6% 4 6% 7% 7% 10% 12% 35%	3764
	21st to end	Day	5% 4 2 5% 5% 6% 7% 6% 8% 12% 39%	4437
June	1st to 10th	Day	11% 9% 4 10% 7% 8% 8% 7% 8% 10% 18%	2470
	11th to 20th	Day	7% 7% 3 9% 9% 9% 8% 8% 10% 12% 20%	2470
	21st to end	Day	6% 6% 2 9% 8% 9% 8% 7% 10% 12% 23%	2470
July	1st to 10th	Day	4 5% 2 7% 5% 5% 7% 6% 10% 15% 33%	4120
	11th to 20th	Day	4 5% 2 8% 6% 7% 8% 7% 12% 15% 27%	4120
	21st to end	Day	2 2 2 6% 5% 6% 7% 7% 11% 15% 37%	4466
August	1st to 10th	Day	3 4 2 10% 8% 9% 10% 7% 12% 12% 22%	3978
	11th to 20th	Day	4 5% 2 7% 6% 6% 8% 7% 10% 15% 30%	3730
	21st to end	Day	5% 3 2 7% 7% 8% 10% 8% 12% 17% 22%	3928
September	1st to 10th	Day	6% 5% 2 7% 8% 8% 9% 8% 9% 14% 22%	2090
	11th to 20th	Day	4 7% 3 9% 8% 8% 9% 7% 10% 13% 22%	2090
	21st to end	Day	9% 8% 3 10% 8% 7% 8% 6% 10% 11% 23%	2090
October	1st to 10th	Day	9% 7% 3 9% 7% 7% 8% 6% 10% 12% 23%	1986
	11th to 20th	Day	10% 6% 3 7% 6% 7% 7% 7% 9% 11% 28%	1900
	21st to end	Day	11% 7% 2 8% 5% 6% 6% 5% 7% 9% 35%	2090
November	1st to 10th	Day	8% 7% 3 7% 6% 6% 6% 5% 8% 9% 36%	1957
	11th to 20th	Day	11% 7% 2 7% 7% 6% 7% 5% 7% 9% 31%	1900
	21st to end	Day	9% 5% 2 7% 6% 6% 6% 5% 8% 10% 35%	1900
December	1st to 10th	Day	8% 5% 2 6% 5% 6% 6% 6% 7% 8% 40%	1900
	11th to 20th	Day	10% 6% 2 7% 6% 5% 6% 4 7% 9% 39%	2163
	21st to end	Day	13% 6% 2 8% 6% 6% 7% 5% 7% 9% 30%	3124
January	1st to 10th	Night	9% 6% 2 8% 5% 7% 6% 5% 8% 10% 34%	4109
	11th to 20th	Night	17% 9% 3 9% 6% 6% 6% 5% 6% 7% 27%	4120
	21st to end	Night	7% 8% 3 8% 6% 6% 6% 5% 7% 8% 35%	4495
February	1st to 10th	Night	8% 6% 2 6% 5% 5% 5% 4 7% 10% 42%	2280
	11th to 20th	Night	6% 4 1 5% 3 3 4 4 7% 9% 54%	2075
	21st to end	Night	5% 5% 1 5% 4 4 4 4 7% 10% 50%	1727
March	1st to 10th	Night	4 5% 2 9% 5% 6% 7% 6% 8% 9% 37%	3418
	11th to 20th	Night	4 3 1 4 4 4 3 4 7% 11% 54%	3480
	21st to end	Night	7% 4 1 5% 4 4 5% 4 6% 9% 52%	3817
April	1st to 10th	Night	3 3 1 4 3 4 4 4 7% 10% 54%	2090
	11th to 20th	Night	5% 4 2 4 4 5% 5% 5% 8% 10% 49%	1961
	21st to end	Night	6% 4 2 5% 4 4 4 4 8% 11% 46%	1900
May	1st to 10th	Night	3 2 1 3 2 3 4 3 6% 10% 62%	3130
	11th to 20th	Night	5% 4 1 6% 4 4 5% 4 7% 10% 49%	3130
	21st to end	Night	6% 6% 2 6% 6% 5% 6% 5% 7% 11% 40%	3142
June	1st to 10th	Night	11% 8% 4 9% 7% 7% 7% 7% 9% 10% 21%	1710
	11th to 20th	Night	8% 6% 2 8% 6% 6% 6% 5% 9% 11% 32%	1710
	21st to end	Night	4 6% 3 7% 6% 6% 6% 7% 11% 15% 29%	1710
July	1st to 10th	Night	3 4 2 7% 6% 5% 6% 5% 9% 14% 38%	2840
	11th to 20th	Night	3 4 2 6% 5% 5% 6% 6% 12% 13% 36%	2840
	21st to end	Night	2 3 2 6% 5% 6% 7% 6% 8% 15% 42%	3087
August	1st to 10th	Night	3 4 2 8% 7% 7% 8% 7% 10% 14% 31%	2918
	11th to 20th	Night	2 3 2 6% 5% 6% 7% 6% 10% 15% 38%	3097
	21st to end	Night	4 4 2 7% 6% 7% 9% 8% 13% 16% 25%	3721
September	1st to 10th	Night	6% 5% 2 7% 6% 7% 8% 6% 9% 13% 30%	2090
	11th to 20th	Night	7% 8% 3 9% 7% 7% 8% 7% 8% 12% 25%	2090
	21st to end	Night	8% 7% 3 10% 7% 8% 8% 6% 8% 12% 23%	2090
October	1st to 10th	Night	9% 7% 2 9% 7% 7% 7% 7% 9% 12% 24%	2192
	11th to 20th	Night	9% 7% 2 9% 5% 6% 7% 5% 9% 11% 31%	2280
	21st to end	Night	12% 6% 3 8% 5% 5% 5% 4 6% 9% 36%	2508
November	1st to 10th	Night	8% 7% 2 7% 6% 5% 5% 4 7% 11% 37%	2341
	11th to 20th	Night	10% 9% 3 8% 6% 6% 6% 5% 7% 8% 32%	2287
	21st to end	Night	9% 6% 2 7% 5% 6% 5% 6% 6% 12% 36%	2280
December	1st to 10th	Night	8% 5% 2 6% 5% 5% 6% 5% 8% 10% 40%	2280
	11th to 20th	Night	10% 6% 2 8% 5% 5% 5% 3 6% 9% 40%	3027
	21st to end	Night	9% 8% 3 10% 6% 6% 6% 5% 7% 10% 30%	4532

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% 8% 12% 23% 13% 3	2837
	11th to 20th	Day	50% 12% 15% 14% 7% 2	2840
	21st to end	Day	40% 10% 12% 18% 15% 6%	3157
February	1st to 10th	Day	35% 9% 14% 25% 14% 3	1900
	11th to 20th	Day	27% 7% 14% 27% 20% 4	1998
	21st to end	Day	24% 10% 15% 21% 23% 7%	1727
March	1st to 10th	Day	33% 14% 19% 21% 11% 2	3435
	11th to 20th	Day	19% 10% 25% 34% 9% 2	3480
	21st to end	Day	28% 8% 14% 30% 16% 4	3815
April	1st to 10th	Day	22% 10% 22% 32% 12% 2	2090
	11th to 20th	Day	28% 12% 21% 22% 16% 2	2166
	21st to end	Day	27% 10% 17% 25% 19% 3	2280
May	1st to 10th	Day	14% 9% 18% 37% 19% 3	3800
	11th to 20th	Day	29% 15% 28% 24% 4	3768
	21st to end	Day	29% 13% 18% 31% 8%	4450
June	1st to 10th	Day	53% 17% 18% 9% 2	2470
	11th to 20th	Day	46% 20% 21% 11% 1	2470
	21st to end	Day	43% 20% 27% 9%	2470
July	1st to 10th	Day	32% 17% 34% 17%	4055
	11th to 20th	Day	37% 16% 38% 9%	4051
	21st to end	Day	28% 17% 40% 15%	4324
August	1st to 10th	Day	44% 18% 27% 9% 2	3965
	11th to 20th	Day	35% 16% 34% 15%	3766
	21st to end	Day	39% 17% 37% 6%	3928
September	1st to 10th	Day	41% 23% 24% 11% 1	2090
	11th to 20th	Day	44% 21% 24% 9% 2	2090
	21st to end	Day	47% 19% 17% 13% 5%	2090
October	1st to 10th	Day	43% 14% 22% 16% 5% 1	3298
	11th to 20th	Day	47% 11% 16% 17% 8% 1	3140
	21st to end	Day	36% 7% 13% 28% 13% 3	3428
November	1st to 10th	Day	38% 10% 14% 16% 16% 5%	1957
	11th to 20th	Day	43% 11% 14% 16% 13% 3	1900
	21st to end	Day	37% 9% 17% 16% 19% 2	1900
December	1st to 10th	Day	34% 11% 15% 23% 16% 2	1900
	11th to 20th	Day	38% 9% 11% 19% 18% 4	2160
	21st to end	Day	45% 10% 15% 15% 14% 2	3124
January	1st to 10th	Night	39% 10% 15% 19% 14% 2	4109
	11th to 20th	Night	53% 10% 13% 15% 7% 2	4120
	21st to end	Night	42% 9% 12% 18% 14% 5%	4495
February	1st to 10th	Night	34% 8% 13% 25% 17% 3	2280
	11th to 20th	Night	25% 7% 14% 26% 21% 7%	2076
	21st to end	Night	25% 7% 14% 23% 26% 6%	1727
March	1st to 10th	Night	36% 12% 16% 21% 12% 3	3418
	11th to 20th	Night	21% 10% 25% 32% 11% 2	3480
	21st to end	Night	25% 8% 13% 26% 24% 4	3817
April	1st to 10th	Night	21% 7% 19% 35% 15% 3	2090
	11th to 20th	Night	27% 9% 20% 24% 18% 2	1961
	21st to end	Night	28% 8% 17% 26% 18% 4	1900
May	1st to 10th	Night	14% 8% 19% 41% 15% 3	3160
	11th to 20th	Night	25% 10% 22% 34% 9%	3131
	21st to end	Night	30% 12% 20% 30% 8%	3150
June	1st to 10th	Night	50% 15% 20% 12% 2	1710
	11th to 20th	Night	42% 14% 24% 18% 2	1710
	21st to end	Night	37% 18% 34% 10%	1710
July	1st to 10th	Night	33% 13% 36% 19%	2795
	11th to 20th	Night	32% 12% 44% 11%	2786
	21st to end	Night	29% 14% 40% 16% 1	2988
August	1st to 10th	Night	38% 16% 31% 14% 2	2907
	11th to 20th	Night	30% 17% 35% 18% 1	3127
	21st to end	Night	39% 17% 36% 7% 1	3721
September	1st to 10th	Night	38% 20% 27% 13% 2	2090
	11th to 20th	Night	47% 19% 23% 10% 2	2090
	21st to end	Night	49% 16% 17% 12% 6%	2090
October	1st to 10th	Night	46% 14% 20% 16% 3 1	3660
	11th to 20th	Night	50% 9% 18% 14% 9% 1	3779
	21st to end	Night	41% 6% 11% 25% 14% 3	4120
November	1st to 10th	Night	38% 8% 14% 20% 16% 4	2341
	11th to 20th	Night	47% 10% 9% 20% 12% 3	2287
	21st to end	Night	39% 9% 15% 20% 15% 3	2280
December	1st to 10th	Night	35% 11% 14% 23% 16% 2	2280
	11th to 20th	Night	38% 7% 11% 20% 17% 7%	3029
	21st to end	Night	44% 11% 15% 14% 14% 2	4532

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	7% 8% 24% 44% 16%	270
	11th to 20th	Day	11% 7% 27% 40% 13% 1	270
	21st to end	Day	7% 9% 32% 44% 8% 1	297
February	1st to 10th	Day	7% 8% 23% 43% 19% 1	270
	11th to 20th	Day	7% 5% 19% 42% 25% 2	411
	21st to end	Day	5% 3 20% 42% 30% 1	382
March	1st to 10th	Day	5% 5% 28% 45% 16% 2	460
	11th to 20th	Day	5% 3 26% 43% 22% 2	460
	21st to end	Day	5% 4 19% 46% 23% 2	506
April	1st to 10th	Day	4 1 23% 50% 19% 3	460
	11th to 20th	Day	5% 2 23% 47% 21% 2	452
	21st to end	Day	4 2 16% 47% 30% 2	460
May	1st to 10th	Day	3 1 10% 46% 32% 7%	463
	11th to 20th	Day	8% 3 14% 34% 34% 7%	487
	21st to end	Day	8% 2 8% 24% 43% 16%	529
June	1st to 10th	Day	10% 3 8% 22% 42% 15%	490
	11th to 20th	Day	9% 1 6% 18% 39% 27%	490
	21st to end	Day	3 2 3 11% 40% 41%	490
July	1st to 10th	Day	3 1 2 8% 43% 44%	485
	11th to 20th	Day	4 1 1 9% 43% 40%	484
	21st to end	Day	3 1 3 10% 42% 42%	532
August	1st to 10th	Day	5% 1 5% 11% 42% 36%	486
	11th to 20th	Day	2 2 1 11% 45% 39%	479
	21st to end	Day	8% 2 4 19% 39% 29%	539
September	1st to 10th	Day	8% 1 4 10% 41% 36%	490
	11th to 20th	Day	6% 1 3 13% 41% 36%	490
	21st to end	Day	7% 1 7% 16% 40% 28%	490
October	1st to 10th	Day	11% 3 7% 30% 39% 11%	490
	11th to 20th	Day	10% 2 9% 34% 34% 10%	490
	21st to end	Day	12% 3 15% 35% 30% 6%	539
November	1st to 10th	Day	6% 5% 17% 36% 30% 6%	495
	11th to 20th	Day	13% 4 17% 35% 27% 4	460
	21st to end	Day	10% 3 18% 40% 26% 3	460
December	1st to 10th	Day	9% 1 19% 41% 27% 2	460
	11th to 20th	Day	9% 5% 16% 38% 30% 2	280
	21st to end	Day	9% 7% 20% 38% 24% 1	297
January	1st to 10th	Night	7% 6% 21% 37% 26% 3	760
	11th to 20th	Night	11% 5% 24% 40% 19% 1	760
	21st to end	Night	8% 8% 24% 42% 17% 1	836
February	1st to 10th	Night	10% 5% 19% 42% 23% 1	760
	11th to 20th	Night	7% 4 24% 38% 24% 2	743
	21st to end	Night	6% 3 19% 45% 26% 1	628
March	1st to 10th	Night	5% 5% 26% 44% 19% 2	760
	11th to 20th	Night	7% 2 19% 46% 23% 3	760
	21st to end	Night	5% 4 21% 43% 25% 1	836
April	1st to 10th	Night	4 2 15% 50% 29% 1	760
	11th to 20th	Night	5% 3 17% 47% 27% 2	751
	21st to end	Night	6% 2 15% 46% 29% 2	760
May	1st to 10th	Night	4 1 10% 41% 39% 4	760
	11th to 20th	Night	9% 2 10% 41% 36% 3	749
	21st to end	Night	9% 2 8% 22% 48% 11%	654
June	1st to 10th	Night	13% 2 5% 22% 41% 16%	570
	11th to 20th	Night	9% 1 4 12% 42% 32%	570
	21st to end	Night	4 1 3 10% 37% 45%	570
July	1st to 10th	Night	4 1 4 5% 41% 45%	555
	11th to 20th	Night	6% 1 1 8% 38% 47%	552
	21st to end	Night	3 1 2 9% 34% 51%	624
August	1st to 10th	Night	7% 2 12% 41% 38%	621
	11th to 20th	Night	4 2 9% 43% 42%	750
	21st to end	Night	9% 1 5% 16% 38% 32%	836
September	1st to 10th	Night	8% 1 4 10% 39% 38%	760
	11th to 20th	Night	9% 3 5% 13% 34% 37%	760
	21st to end	Night	11% 1 6% 16% 36% 29%	760
October	1st to 10th	Night	11% 2 7% 28% 39% 12%	760
	11th to 20th	Night	12% 1 11% 27% 36% 13%	760
	21st to end	Night	15% 2 15% 31% 31% 6%	836
November	1st to 10th	Night	11% 4 19% 33% 28% 5%	780
	11th to 20th	Night	12% 4 17% 32% 30% 5%	763
	21st to end	Night	11% 4 19% 35% 28% 3	760
December	1st to 10th	Night	9% 4 17% 36% 33% 2	760
	11th to 20th	Night	12% 5% 17% 34% 29% 4	760
	21st to end	Night	9% 4 20% 36% 27% 4	836

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