MASIL Observatory East
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MASIL Observatory East clear sky chart from 2005-11-06 to 2024-12-09.

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	17% 7% 2 6% 4 4 4 4 5% 7% 38%	101567
	Night	17% 8% 2 6% 4 4 4 4 5% 6% 39%	98234
Transparency	Day	44% 6% 11% 22% 15% 2	105105
	Night	44% 6% 12% 22% 15% 2	102785
Seeing	Day	24% 17% 31% 19% 7% 2	15091
	Night	22% 15% 32% 24% 7% 1	24001

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% 8% 2 6% 4 4 4 3 4 6% 44%	2517
	11th to 20th	Day	17% 7% 3 8% 4 4 4 4 5% 6% 39%	2520
	21st to end	Day	20% 9% 3 7% 5% 4 4 3 5% 5% 35%	2772
February	1st to 10th	Day	18% 8% 3 6% 4 5% 6% 4 6% 6% 35%	1738
	11th to 20th	Day	13% 7% 3 7% 4 5% 4 3 5% 8% 40%	1848
	21st to end	Day	16% 11% 3 8% 5% 4 4 3 5% 5% 37%	1570
March	1st to 10th	Day	24% 13% 3 7% 4 4 4 3 4 5% 29%	3116
	11th to 20th	Day	15% 8% 2 6% 4 5% 5% 4 6% 7% 38%	3342
	21st to end	Day	21% 9% 3 7% 4 4 4 3 5% 6% 33%	4024
April	1st to 10th	Day	20% 10% 3 6% 5% 4 3 3 4 6% 37%	2280
	11th to 20th	Day	17% 7% 2 6% 5% 6% 5% 3 5% 7% 38%	2282
	21st to end	Day	20% 7% 3 7% 4 5% 4 3 5% 6% 35%	2470
May	1st to 10th	Day	22% 12% 3 8% 5% 4 4 4 5% 7% 27%	4106
	11th to 20th	Day	22% 7% 3 9% 5% 4 4 3 5% 7% 32%	4191
	21st to end	Day	15% 5% 2 5% 4 4 4 4 6% 9% 43%	4837
June	1st to 10th	Day	20% 7% 2 6% 5% 5% 5% 4 5% 8% 33%	2660
	11th to 20th	Day	17% 6% 2 6% 5% 4 5% 4 6% 8% 38%	2660
	21st to end	Day	19% 7% 3 7% 6% 5% 5% 4 5% 8% 32%	2660
July	1st to 10th	Day	13% 7% 2 7% 5% 5% 6% 5% 6% 9% 35%	4440
	11th to 20th	Day	10% 7% 2 7% 4 5% 5% 5% 7% 10% 39%	4440
	21st to end	Day	17% 8% 3 7% 5% 4 4 4 6% 7% 35%	4814
August	1st to 10th	Day	15% 6% 3 7% 6% 6% 5% 5% 7% 8% 34%	4174
	11th to 20th	Day	16% 8% 2 7% 5% 4 4 5% 6% 7% 34%	4027
	21st to end	Day	8% 4 2 6% 4 5% 5% 5% 7% 9% 44%	4180
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 5% 5% 6% 47%	2275
	11th to 20th	Day	15% 6% 2 5% 3 3 3 2 4 6% 52%	2090
	21st to end	Day	16% 6% 2 6% 4 4 4 3 4 6% 45%	2090
October	1st to 10th	Day	23% 6% 2 5% 4 4 3 3 4 5% 40%	2090
	11th to 20th	Day	15% 5% 2 6% 4 5% 3 3 6% 6% 46%	1840
	21st to end	Day	23% 7% 2 6% 4 3 4 4 4 6% 39%	1881
November	1st to 10th	Day	15% 6% 3 5% 4 3 2 3 5% 5% 49%	1761
	11th to 20th	Day	18% 5% 1 5% 3 3 3 3 4 6% 48%	1800
	21st to end	Day	20% 7% 2 5% 3 3 3 3 5% 6% 42%	1800
December	1st to 10th	Day	18% 8% 3 7% 5% 4 4 3 5% 7% 37%	1594
	11th to 20th	Day	22% 7% 2 5% 3 4 3 3 3 5% 42%	1906
	21st to end	Day	24% 9% 3 7% 4 4 3 3 5% 6% 32%	2772
January	1st to 10th	Night	18% 8% 2 5% 3 3 3 3 5% 5% 44%	4429
	11th to 20th	Night	14% 7% 3 8% 5% 4 4 4 5% 6% 38%	4440
	21st to end	Night	21% 13% 3 7% 5% 5% 4 3 4 5% 31%	4884
February	1st to 10th	Night	15% 10% 3 6% 5% 3 5% 4 5% 6% 37%	2439
	11th to 20th	Night	13% 9% 3 6% 5% 4 4 4 6% 6% 40%	2218
	21st to end	Night	17% 9% 2 5% 4 3 4 4 5% 6% 41%	1884
March	1st to 10th	Night	26% 11% 2 5% 4 3 3 3 5% 5% 31%	3724
	11th to 20th	Night	13% 9% 3 8% 5% 5% 6% 4 6% 6% 36%	3617
	21st to end	Night	24% 9% 2 5% 3 3 4 4 6% 6% 33%	3604
April	1st to 10th	Night	19% 9% 2 7% 5% 4 4 3 5% 7% 36%	1900
	11th to 20th	Night	21% 9% 2 5% 5% 3 4 3 4 6% 39%	1847
	21st to end	Night	21% 6% 3 6% 4 3 4 3 5% 6% 39%	1710
May	1st to 10th	Night	24% 11% 3 8% 5% 4 4 3 5% 7% 25%	2834
	11th to 20th	Night	18% 8% 3 8% 6% 6% 6% 4 7% 6% 27%	2731
	21st to end	Night	16% 6% 3 6% 4 4 4 4 5% 7% 40%	2738
June	1st to 10th	Night	19% 8% 3 6% 5% 5% 4 3 5% 7% 36%	1520
	11th to 20th	Night	19% 6% 3 6% 4 3 5% 4 5% 9% 37%	1520
	21st to end	Night	18% 8% 2 6% 4 5% 4 4 6% 9% 36%	1520
July	1st to 10th	Night	12% 5% 3 7% 6% 6% 6% 6% 7% 9% 34%	2520
	11th to 20th	Night	11% 6% 2 7% 5% 5% 5% 4 6% 9% 39%	2520
	21st to end	Night	15% 7% 3 6% 4 4 4 4 5% 7% 39%	2739
August	1st to 10th	Night	20% 7% 3 7% 5% 4 5% 4 6% 7% 34%	2722
	11th to 20th	Night	12% 8% 3 8% 5% 5% 6% 4 6% 8% 35%	2798
	21st to end	Night	9% 4 2 5% 3 3 4 4 6% 9% 52%	3476
September	1st to 10th	Night	12% 6% 1 5% 3 3 3 4 6% 6% 49%	1905
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 5% 7% 51%	2090
	21st to end	Night	15% 6% 3 5% 3 3 3 2 4 7% 47%	2090
October	1st to 10th	Night	21% 7% 2 6% 4 4 3 4 4 6% 40%	2090
	11th to 20th	Night	15% 5% 2 5% 4 4 4 3 6% 6% 46%	2335
	21st to end	Night	21% 7% 3 5% 4 4 3 3 4 6% 39%	2717
November	1st to 10th	Night	15% 6% 2 5% 3 4 4 4 4 5% 47%	2537
	11th to 20th	Night	17% 6% 2 6% 3 4 4 2 4 6% 47%	2600
	21st to end	Night	16% 7% 2 6% 4 4 3 3 5% 7% 43%	2600
December	1st to 10th	Night	18% 10% 3 6% 5% 3 4 4 5% 6% 37%	2764
	11th to 20th	Night	20% 6% 2 5% 4 4 4 4 5% 7% 40%	3288
	21st to end	Night	22% 10% 3 7% 4 4 4 3 4 6% 35%	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	41% 5% 10% 32% 11% 1	2518
	11th to 20th	Day	45% 6% 12% 24% 12% 2	2520
	21st to end	Day	51% 6% 10% 22% 9% 2	2772
February	1st to 10th	Day	47% 6% 12% 21% 11% 2	1738
	11th to 20th	Day	43% 5% 12% 20% 15% 4	1857
	21st to end	Day	49% 4 10% 20% 13% 3	1570
March	1st to 10th	Day	59% 4 9% 14% 11% 3	3119
	11th to 20th	Day	41% 7% 15% 19% 15% 3	3342
	21st to end	Day	50% 4 6% 16% 16% 7%	4024
April	1st to 10th	Day	49% 4 8% 18% 17% 4	2280
	11th to 20th	Day	45% 5% 10% 19% 17% 3	2282
	21st to end	Day	49% 5% 8% 16% 18% 3	2470
May	1st to 10th	Day	55% 8% 11% 14% 11% 1	4120
	11th to 20th	Day	50% 8% 15% 16% 10% 2	4195
	21st to end	Day	36% 8% 13% 23% 19% 2	4837
June	1st to 10th	Day	48% 7% 12% 21% 12% 1	2660
	11th to 20th	Day	42% 8% 12% 20% 16% 3	2660
	21st to end	Day	48% 8% 11% 20% 12% 1	2660
July	1st to 10th	Day	44% 6% 12% 22% 15% 1	4370
	11th to 20th	Day	37% 7% 15% 26% 13% 1	4365
	21st to end	Day	47% 6% 11% 20% 14% 2	4661
August	1st to 10th	Day	46% 8% 14% 21% 10% 1	4160
	11th to 20th	Day	45% 7% 12% 25% 9% 1	4066
	21st to end	Day	33% 7% 12% 29% 18% 2	4180
September	1st to 10th	Day	35% 7% 12% 24% 20% 2	2275
	11th to 20th	Day	35% 4 8% 26% 23% 3	2090
	21st to end	Day	40% 5% 9% 22% 21% 2	2090
October	1st to 10th	Day	45% 5% 8% 22% 18% 2	3480
	11th to 20th	Day	33% 4 8% 29% 24% 3	3030
	21st to end	Day	34% 4 7% 30% 21% 3	3081
November	1st to 10th	Day	38% 4 13% 26% 17% 2	1761
	11th to 20th	Day	39% 4 8% 23% 23% 3	1800
	21st to end	Day	43% 5% 15% 22% 13% 2	1800
December	1st to 10th	Day	46% 5% 14% 19% 14% 2	1594
	11th to 20th	Day	45% 4 12% 18% 16% 5%	1906
	21st to end	Day	53% 6% 11% 19% 10% 1	2772
January	1st to 10th	Night	40% 5% 13% 28% 11% 3	4429
	11th to 20th	Night	45% 5% 12% 22% 12% 3	4440
	21st to end	Night	55% 6% 10% 17% 11% 2	4884
February	1st to 10th	Night	45% 7% 13% 19% 13% 3	2439
	11th to 20th	Night	43% 5% 12% 21% 17% 3	2220
	21st to end	Night	43% 5% 11% 23% 14% 4	1884
March	1st to 10th	Night	53% 5% 10% 18% 11% 3	3734
	11th to 20th	Night	44% 8% 13% 17% 15% 2	3618
	21st to end	Night	49% 4 8% 13% 19% 7%	3604
April	1st to 10th	Night	47% 5% 11% 18% 16% 3	1900
	11th to 20th	Night	46% 5% 8% 20% 18% 2	1847
	21st to end	Night	46% 7% 10% 18% 16% 4	1710
May	1st to 10th	Night	57% 8% 10% 15% 8% 2	2840
	11th to 20th	Night	52% 8% 15% 14% 8% 2	2732
	21st to end	Night	40% 8% 16% 20% 14% 2	2739
June	1st to 10th	Night	48% 6% 11% 22% 12% 1	1520
	11th to 20th	Night	44% 8% 12% 20% 13% 2	1520
	21st to end	Night	43% 9% 13% 21% 12% 1	1520
July	1st to 10th	Night	44% 8% 13% 22% 14% 1	2480
	11th to 20th	Night	39% 7% 15% 23% 15%	2472
	21st to end	Night	44% 7% 11% 22% 15% 1	2651
August	1st to 10th	Night	49% 8% 13% 19% 11% 1	2712
	11th to 20th	Night	44% 9% 14% 21% 11%	2825
	21st to end	Night	28% 6% 16% 28% 22% 1	3476
September	1st to 10th	Night	34% 6% 13% 26% 20% 1	1905
	11th to 20th	Night	33% 6% 10% 24% 25% 2	2090
	21st to end	Night	38% 5% 10% 26% 18% 2	2090
October	1st to 10th	Night	42% 5% 15% 22% 15% 2	3480
	11th to 20th	Night	28% 4 11% 27% 27% 3	3884
	21st to end	Night	36% 4 11% 31% 17% 2	4467
November	1st to 10th	Night	38% 6% 11% 23% 20% 3	2537
	11th to 20th	Night	40% 3 10% 22% 21% 3	2600
	21st to end	Night	41% 4 14% 25% 14% 1	2600
December	1st to 10th	Night	47% 5% 12% 23% 12% 1	2764
	11th to 20th	Night	43% 6% 15% 17% 18% 1	3288
	21st to end	Night	51% 5% 10% 23% 10% 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	32% 21% 28% 16% 2	180
	11th to 20th	Day	33% 22% 31% 11% 2 1	180
	21st to end	Day	26% 24% 35% 12% 3 1	198
February	1st to 10th	Day	30% 25% 31% 12% 2	348
	11th to 20th	Day	32% 27% 29% 11% 2	456
	21st to end	Day	29% 23% 31% 14% 3	382
March	1st to 10th	Day	32% 17% 36% 12% 3	460
	11th to 20th	Day	30% 26% 30% 11% 3 1	460
	21st to end	Day	31% 22% 31% 9% 4 2	506
April	1st to 10th	Day	33% 22% 26% 12% 5% 1	460
	11th to 20th	Day	29% 26% 27% 13% 6% 1	452
	21st to end	Day	28% 17% 34% 15% 5% 1	460
May	1st to 10th	Day	34% 21% 30% 10% 5% 2	463
	11th to 20th	Day	22% 17% 39% 16% 4 2	487
	21st to end	Day	19% 16% 35% 23% 6% 1	529
June	1st to 10th	Day	20% 14% 38% 18% 8% 1	490
	11th to 20th	Day	17% 18% 34% 24% 6% 2	490
	21st to end	Day	18% 17% 37% 18% 7% 2	490
July	1st to 10th	Day	17% 7% 36% 26% 11% 3	485
	11th to 20th	Day	15% 10% 32% 29% 11% 3	484
	21st to end	Day	14% 9% 35% 31% 8% 2	532
August	1st to 10th	Day	14% 10% 30% 30% 14% 2	486
	11th to 20th	Day	18% 10% 29% 27% 13% 4	479
	21st to end	Day	12% 11% 32% 27% 12% 5%	539
September	1st to 10th	Day	17% 12% 28% 23% 14% 6%	490
	11th to 20th	Day	19% 12% 28% 19% 13% 9%	490
	21st to end	Day	20% 12% 31% 22% 9% 6%	490
October	1st to 10th	Day	27% 15% 24% 22% 10% 3	490
	11th to 20th	Day	21% 15% 30% 21% 10% 2	427
	21st to end	Day	30% 14% 31% 18% 6%	429
November	1st to 10th	Day	21% 19% 31% 20% 8% 2	395
	11th to 20th	Day	31% 20% 28% 16% 5% 1	400
	21st to end	Day	32% 21% 28% 14% 6% 1	400
December	1st to 10th	Day	20% 29% 30% 15% 6%	206
	11th to 20th	Day	34% 22% 30% 13% 1	180
	21st to end	Day	29% 25% 27% 14% 5% 1	198
January	1st to 10th	Night	22% 22% 35% 18% 3	760
	11th to 20th	Night	28% 19% 33% 18% 2	760
	21st to end	Night	22% 22% 36% 17% 3	836
February	1st to 10th	Night	25% 18% 37% 20% 1	760
	11th to 20th	Night	23% 21% 38% 15% 3	743
	21st to end	Night	25% 20% 34% 18% 4	628
March	1st to 10th	Night	26% 19% 36% 16% 3	760
	11th to 20th	Night	23% 22% 34% 15% 6%	760
	21st to end	Night	27% 19% 32% 18% 4	836
April	1st to 10th	Night	26% 17% 34% 20% 3	760
	11th to 20th	Night	25% 20% 33% 17% 6%	723
	21st to end	Night	24% 18% 34% 21% 3	570
May	1st to 10th	Night	25% 15% 33% 22% 5%	570
	11th to 20th	Night	20% 16% 34% 25% 5% 1	519
	21st to end	Night	20% 9% 32% 32% 7%	411
June	1st to 10th	Night	21% 9% 33% 28% 8% 1	380
	11th to 20th	Night	21% 8% 31% 31% 8% 1	380
	21st to end	Night	19% 7% 34% 34% 7%	380
July	1st to 10th	Night	15% 6% 26% 41% 10% 1	370
	11th to 20th	Night	13% 5% 25% 43% 13% 1	368
	21st to end	Night	16% 4 28% 40% 12%	416
August	1st to 10th	Night	13% 4 27% 42% 13% 1	503
	11th to 20th	Night	14% 7% 30% 34% 14% 1	565
	21st to end	Night	14% 5% 27% 36% 17% 2	836
September	1st to 10th	Night	15% 7% 33% 29% 16% 1	760
	11th to 20th	Night	16% 8% 27% 29% 17% 2	760
	21st to end	Night	18% 9% 29% 28% 14% 2	760
October	1st to 10th	Night	24% 10% 27% 25% 12% 1	760
	11th to 20th	Night	19% 13% 31% 25% 10% 1	760
	21st to end	Night	27% 16% 28% 23% 6%	836
November	1st to 10th	Night	19% 14% 34% 24% 7% 1	780
	11th to 20th	Night	24% 17% 33% 20% 6% 1	800
	21st to end	Night	24% 20% 33% 19% 5%	800
December	1st to 10th	Night	24% 16% 37% 19% 4	795
	11th to 20th	Night	24% 21% 30% 22% 3	760
	21st to end	Night	26% 18% 35% 19% 1	836

Page generated at 2024-12-06 03:54:47. Version ac07

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