MAS LaGrange site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MAS LaGrange site clear sky chart from 2005-11-06 to 2026-02-16.

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	12% 7% 2 6% 4 4 4 4 6% 7% 42%	130432
	Night	13% 7% 2 6% 4 4 4 3 5% 7% 46%	130560
Transparency	Day	26% 37% 7% 16% 12% 3	134122
	Night	25% 36% 7% 16% 13% 4	134947
Seeing	Day	16% 11% 24% 24% 18% 7%	16950
	Night	16% 10% 25% 29% 18% 3	26815

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	16% 11% 4 10% 4 3 3 2 3 5% 40%	4751
	11th to 20th	Day	13% 7% 2 7% 3 3 3 2 3 4 53%	5310
	21st to end	Day	19% 8% 2 6% 5% 3 3 3 4 5% 41%	5849
February	1st to 10th	Day	20% 11% 3 6% 5% 3 3 2 3 5% 39%	2100
	11th to 20th	Day	21% 10% 3 6% 4 4 3 3 4 5% 38%	1998
	21st to end	Day	22% 9% 2 7% 3 3 4 3 4 6% 37%	1650
March	1st to 10th	Day	17% 13% 4 8% 5% 4 4 3 4 4 34%	4480
	11th to 20th	Day	14% 7% 3 6% 4 3 4 3 4 6% 46%	4883
	21st to end	Day	12% 7% 3 7% 5% 4 4 3 4 7% 42%	5875
April	1st to 10th	Day	13% 7% 2 6% 4 5% 4 4 5% 7% 44%	2400
	11th to 20th	Day	15% 8% 2 5% 4 4 4 2 5% 6% 45%	2374
	21st to end	Day	12% 7% 3 7% 5% 5% 4 4 5% 7% 41%	2400
May	1st to 10th	Day	16% 8% 3 7% 4 6% 5% 4 7% 8% 32%	5405
	11th to 20th	Day	15% 7% 3 8% 5% 5% 5% 4 7% 8% 32%	5861
	21st to end	Day	17% 7% 2 7% 5% 4 5% 4 6% 8% 34%	6568
June	1st to 10th	Day	8% 6% 2 6% 6% 5% 6% 5% 6% 9% 41%	2800
	11th to 20th	Day	5% 4 1 6% 5% 5% 6% 5% 7% 11% 45%	2800
	21st to end	Day	5% 4 2 5% 6% 5% 6% 6% 8% 9% 45%	2800
July	1st to 10th	Day	6% 5% 2 7% 6% 6% 6% 5% 8% 10% 39%	6360
	11th to 20th	Day	6% 4 2 6% 5% 6% 7% 6% 9% 13% 36%	6272
	21st to end	Day	11% 6% 2 6% 5% 5% 6% 5% 8% 12% 33%	6300
August	1st to 10th	Day	3 3 1 4 4 4 5% 4 6% 9% 57%	3905
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 4 7% 10% 47%	3849
	21st to end	Day	6% 4 2 5% 4 4 4 4 6% 8% 53%	4312
September	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 8% 43%	2400
	11th to 20th	Day	12% 5% 2 6% 4 5% 4 3 6% 8% 45%	2303
	21st to end	Day	11% 6% 2 6% 4 4 3 3 4 7% 51%	2200
October	1st to 10th	Day	8% 4 2 5% 3 3 3 3 4 6% 59%	2141
	11th to 20th	Day	9% 4 2 4 3 3 3 3 4 7% 58%	2000
	21st to end	Day	18% 7% 1 4 3 3 3 3 3 3 52%	2200
November	1st to 10th	Day	12% 5% 2 5% 3 2 3 3 4 5% 56%	1852
	11th to 20th	Day	13% 6% 2 4 3 3 3 3 5% 7% 52%	1890
	21st to end	Day	17% 8% 2 5% 4 3 3 3 5% 6% 44%	1890
December	1st to 10th	Day	15% 10% 3 7% 3 3 3 2 4 5% 46%	3020
	11th to 20th	Day	19% 10% 3 6% 4 3 3 3 3 4 42%	3164
	21st to end	Day	13% 11% 3 8% 5% 4 5% 4 5% 6% 36%	4070
January	1st to 10th	Night	19% 9% 3 8% 3 3 3 3 4 5% 41%	8154
	11th to 20th	Night	13% 7% 3 6% 3 3 3 3 3 4 52%	7680
	21st to end	Night	21% 9% 3 6% 4 3 3 2 4 5% 40%	8360
February	1st to 10th	Night	19% 9% 3 7% 3 3 3 2 4 5% 40%	2520
	11th to 20th	Night	20% 9% 3 6% 4 4 3 3 3 5% 40%	2399
	21st to end	Night	18% 9% 2 6% 4 4 4 3 4 5% 40%	1980
March	1st to 10th	Night	18% 9% 3 6% 4 4 3 3 4 5% 39%	5373
	11th to 20th	Night	13% 7% 2 5% 3 3 4 3 5% 7% 50%	5119
	21st to end	Night	13% 7% 3 7% 4 4 4 3 5% 6% 44%	5040
April	1st to 10th	Night	13% 6% 2 6% 3 3 3 3 6% 7% 46%	2000
	11th to 20th	Night	15% 6% 2 4 3 3 3 4 5% 7% 49%	1975
	21st to end	Night	11% 7% 2 5% 5% 4 4 4 5% 7% 47%	2000
May	1st to 10th	Night	18% 10% 3 7% 4 4 4 3 5% 7% 36%	4475
	11th to 20th	Night	16% 10% 3 8% 4 4 4 3 5% 6% 36%	4032
	21st to end	Night	13% 8% 3 8% 4 4 4 5% 6% 8% 37%	4274
June	1st to 10th	Night	7% 5% 2 7% 3 4 6% 4 5% 11% 45%	1600
	11th to 20th	Night	4 3 2 3 4 3 4 4 6% 10% 58%	1600
	21st to end	Night	3 4 1 4 3 4 4 4 7% 11% 55%	1600
July	1st to 10th	Night	5% 4 2 6% 4 5% 5% 5% 8% 11% 45%	3618
	11th to 20th	Night	4 3 1 4 3 4 4 4 7% 16% 48%	3700
	21st to end	Night	7% 6% 2 7% 4 5% 5% 5% 7% 12% 39%	4552
August	1st to 10th	Night	2 2 1 3 2 3 4 3 5% 7% 68%	3244
	11th to 20th	Night	4 2 1 4 4 4 4 4 7% 11% 54%	3200
	21st to end	Night	4 3 1 4 3 4 4 4 6% 10% 56%	3586
September	1st to 10th	Night	6% 5% 2 6% 4 4 5% 4 6% 7% 51%	2000
	11th to 20th	Night	9% 6% 3 5% 3 3 4 3 5% 8% 51%	2075
	21st to end	Night	9% 5% 2 5% 3 3 3 3 5% 6% 57%	2200
October	1st to 10th	Night	7% 4 2 4 2 3 3 2 4 6% 62%	2255
	11th to 20th	Night	11% 4 2 5% 2 3 3 3 3 6% 59%	2400
	21st to end	Night	16% 6% 2 6% 3 2 3 2 3 5% 52%	2640
November	1st to 10th	Night	11% 4 2 4 4 3 4 3 5% 5% 56%	2664
	11th to 20th	Night	11% 5% 2 4 3 3 4 3 6% 6% 53%	2730
	21st to end	Night	15% 7% 1 5% 3 3 4 3 4 5% 48%	2730
December	1st to 10th	Night	19% 8% 2 4 3 3 3 2 4 6% 47%	4380
	11th to 20th	Night	20% 8% 3 5% 4 3 3 3 4 4 44%	5255
	21st to end	Night	17% 8% 3 7% 4 5% 5% 4 5% 6% 36%	7150

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% 20% 7% 21% 10% 1	4752
	11th to 20th	Day	27% 21% 3 18% 28% 3	5310
	21st to end	Day	38% 22% 3 14% 16% 6%	5849
February	1st to 10th	Day	23% 58% 2 11% 6% 1	2100
	11th to 20th	Day	21% 60% 3 11% 5% 1	2008
	21st to end	Day	18% 62% 3 6% 8% 4	1650
March	1st to 10th	Day	42% 30% 2 11% 8% 8%	4480
	11th to 20th	Day	25% 30% 5% 15% 18% 8%	4883
	21st to end	Day	29% 29% 6% 18% 17% 1	5877
April	1st to 10th	Day	18% 62% 3 10% 7% 1	2400
	11th to 20th	Day	18% 63% 3 9% 6% 2	2374
	21st to end	Day	17% 62% 4 10% 6% 1	2400
May	1st to 10th	Day	35% 31% 9% 17% 7%	5440
	11th to 20th	Day	37% 31% 13% 14% 5%	5865
	21st to end	Day	36% 31% 7% 15% 9% 2	6582
June	1st to 10th	Day	16% 64% 5% 6% 8% 1	2800
	11th to 20th	Day	15% 63% 7% 9% 6%	2800
	21st to end	Day	16% 62% 6% 11% 4	2800
July	1st to 10th	Day	28% 27% 12% 22% 10%	6291
	11th to 20th	Day	29% 27% 16% 26% 3	6197
	21st to end	Day	35% 26% 16% 20% 3	6119
August	1st to 10th	Day	12% 36% 11% 21% 18% 2	3893
	11th to 20th	Day	20% 36% 12% 19% 12% 1	3885
	21st to end	Day	17% 36% 8% 17% 21% 1	4311
September	1st to 10th	Day	13% 59% 4 14% 8% 2	2400
	11th to 20th	Day	13% 58% 6% 11% 10% 2	2303
	21st to end	Day	17% 57% 5% 11% 8% 2	2200
October	1st to 10th	Day	8% 36% 3 8% 27% 18%	3492
	11th to 20th	Day	8% 35% 2 14% 27% 13%	3240
	21st to end	Day	16% 35% 2 19% 22% 7%	3538
November	1st to 10th	Day	21% 54% 3 8% 12% 3	1852
	11th to 20th	Day	15% 55% 4 10% 13% 4	1890
	21st to end	Day	21% 54% 3 9% 12% 1	1890
December	1st to 10th	Day	28% 34% 2 19% 16% 1	3020
	11th to 20th	Day	34% 30% 3 16% 14% 4	3161
	21st to end	Day	37% 27% 7% 19% 9% 1	4070
January	1st to 10th	Night	40% 20% 8% 19% 11% 2	8155
	11th to 20th	Night	28% 21% 4 15% 27% 5%	7680
	21st to end	Night	40% 21% 4 16% 14% 5%	8360
February	1st to 10th	Night	21% 58% 3 9% 7% 1	2520
	11th to 20th	Night	22% 59% 3 8% 6% 1	2400
	21st to end	Night	17% 62% 2 7% 7% 4	1980
March	1st to 10th	Night	38% 30% 4 10% 13% 6%	5373
	11th to 20th	Night	22% 29% 4 17% 14% 15%	5119
	21st to end	Night	28% 30% 6% 15% 18% 3	5040
April	1st to 10th	Night	16% 62% 4 9% 8% 1	2000
	11th to 20th	Night	17% 62% 3 10% 6% 2	1975
	21st to end	Night	14% 62% 5% 9% 8% 2	2000
May	1st to 10th	Night	37% 30% 9% 15% 8%	4505
	11th to 20th	Night	38% 30% 10% 17% 4	4033
	21st to end	Night	35% 32% 8% 15% 8% 2	4282
June	1st to 10th	Night	13% 64% 5% 8% 9% 1	1600
	11th to 20th	Night	10% 63% 8% 10% 9% 1	1600
	21st to end	Night	10% 62% 8% 14% 7%	1600
July	1st to 10th	Night	25% 28% 15% 20% 10% 1	3580
	11th to 20th	Night	18% 26% 19% 32% 4 1	3655
	21st to end	Night	32% 26% 17% 20% 6%	4421
August	1st to 10th	Night	8% 36% 5% 30% 19% 1	3232
	11th to 20th	Night	13% 37% 17% 20% 12%	3230
	21st to end	Night	13% 36% 9% 19% 21% 2	3586
September	1st to 10th	Night	11% 57% 5% 14% 11% 3	2000
	11th to 20th	Night	11% 59% 5% 12% 12% 2	2075
	21st to end	Night	12% 57% 6% 14% 8% 3	2200
October	1st to 10th	Night	8% 36% 3 9% 25% 19%	3684
	11th to 20th	Night	8% 35% 2 10% 27% 19%	3899
	21st to end	Night	15% 35% 3 21% 15% 12%	4252
November	1st to 10th	Night	19% 53% 3 9% 13% 2	2664
	11th to 20th	Night	14% 54% 4 11% 13% 4	2730
	21st to end	Night	18% 54% 4 11% 11% 2	2730
December	1st to 10th	Night	27% 34% 4 19% 15% 1	4380
	11th to 20th	Night	32% 30% 3 16% 16% 2	5257
	21st to end	Night	35% 28% 8% 18% 9% 2	7150

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	26% 24% 34% 14% 3	330
	11th to 20th	Day	29% 25% 34% 10% 2 1	330
	21st to end	Day	28% 27% 34% 9% 2	363
February	1st to 10th	Day	29% 22% 33% 13% 2 1	330
	11th to 20th	Day	37% 24% 29% 8% 1	315
	21st to end	Day	34% 29% 29% 8% 2	249
March	1st to 10th	Day	28% 21% 34% 13% 3	300
	11th to 20th	Day	27% 27% 32% 13%	300
	21st to end	Day	27% 18% 35% 13% 6%	510
April	1st to 10th	Day	25% 17% 32% 19% 6% 1	500
	11th to 20th	Day	21% 20% 32% 20% 7% 1	492
	21st to end	Day	21% 14% 31% 23% 10% 1	500
May	1st to 10th	Day	20% 18% 28% 24% 8% 2	503
	11th to 20th	Day	15% 9% 28% 28% 15% 5%	527
	21st to end	Day	11% 8% 26% 30% 17% 8%	630
June	1st to 10th	Day	12% 5% 21% 28% 24% 10%	730
	11th to 20th	Day	6% 3 18% 36% 27% 11%	730
	21st to end	Day	6% 4 19% 34% 25% 12%	730
July	1st to 10th	Day	7% 2 13% 33% 31% 14%	721
	11th to 20th	Day	7% 2 12% 27% 36% 16%	718
	21st to end	Day	8% 2 10% 31% 33% 15%	747
August	1st to 10th	Day	5% 3 12% 32% 36% 12%	526
	11th to 20th	Day	9% 3 14% 30% 33% 11%	519
	21st to end	Day	11% 2 11% 25% 33% 18%	583
September	1st to 10th	Day	8% 3 13% 33% 34% 8%	530
	11th to 20th	Day	11% 3 15% 25% 33% 13%	530
	21st to end	Day	17% 6% 16% 30% 21% 9%	530
October	1st to 10th	Day	11% 2 24% 31% 28% 5%	471
	11th to 20th	Day	11% 11% 39% 28% 8% 2	330
	21st to end	Day	24% 14% 32% 22% 6% 1	363
November	1st to 10th	Day	20% 11% 28% 30% 9% 1	330
	11th to 20th	Day	13% 18% 39% 25% 5%	330
	21st to end	Day	25% 17% 29% 18% 10% 2	330
December	1st to 10th	Day	28% 21% 30% 17% 3 1	330
	11th to 20th	Day	27% 18% 33% 16% 5%	330
	21st to end	Day	26% 20% 39% 13% 3	363
January	1st to 10th	Night	23% 18% 33% 22% 4	1050
	11th to 20th	Night	23% 18% 35% 20% 3	1050
	21st to end	Night	22% 17% 37% 23% 2	1139
February	1st to 10th	Night	23% 17% 35% 22% 3	840
	11th to 20th	Night	25% 20% 32% 21% 2	804
	21st to end	Night	23% 22% 31% 21% 3	660
March	1st to 10th	Night	21% 16% 31% 28% 4	800
	11th to 20th	Night	23% 13% 35% 25% 4 1	661
	21st to end	Night	20% 14% 33% 23% 10%	660
April	1st to 10th	Night	16% 16% 34% 26% 8% 1	600
	11th to 20th	Night	18% 12% 33% 27% 10% 1	593
	21st to end	Night	15% 10% 34% 30% 10% 1	600
May	1st to 10th	Night	17% 8% 27% 34% 13% 2	600
	11th to 20th	Night	14% 6% 26% 33% 17% 4	591
	21st to end	Night	10% 2 24% 35% 25% 4	650
June	1st to 10th	Night	8% 3 16% 37% 30% 6%	600
	11th to 20th	Night	5% 2 14% 36% 40% 3	600
	21st to end	Night	5% 2 13% 37% 38% 6%	600
July	1st to 10th	Night	5% 2 12% 28% 45% 10%	585
	11th to 20th	Night	6% 2 11% 28% 42% 12%	582
	21st to end	Night	6% 1 9% 30% 44% 11%	657
August	1st to 10th	Night	5% 1 7% 30% 48% 9%	597
	11th to 20th	Night	6% 2 6% 39% 42% 6%	594
	21st to end	Night	7% 1 10% 29% 43% 9%	660
September	1st to 10th	Night	7% 2 9% 39% 39% 5%	600
	11th to 20th	Night	11% 2 13% 32% 35% 7%	675
	21st to end	Night	11% 3 17% 35% 29% 4	800
October	1st to 10th	Night	9% 4 19% 34% 31% 4	800
	11th to 20th	Night	13% 8% 25% 35% 18% 2	800
	21st to end	Night	21% 9% 25% 31% 13% 1	880
November	1st to 10th	Night	13% 9% 25% 35% 17% 1	820
	11th to 20th	Night	13% 11% 34% 30% 12%	840
	21st to end	Night	21% 11% 31% 26% 10% 1	840
December	1st to 10th	Night	25% 12% 32% 26% 6%	840
	11th to 20th	Night	23% 14% 32% 25% 6%	992
	21st to end	Night	24% 16% 32% 23% 4	1155

Page generated at 2026-02-13 00:42:13. Version ac07

Copyright © 2026 Attilla Danko.