Observatoire Laforge-1
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Laforge-1 clear sky chart from 2005-11-06 to 2025-10-04.

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	15% 15% 5% 12% 7% 6% 6% 4 6% 5% 18%	127363
	Night	13% 16% 6% 14% 9% 7% 7% 5% 5% 5% 15%	122296
Transparency	Day	66% 6% 9% 14% 4	130652
	Night	70% 6% 8% 12% 4	127099
Seeing	Day	23% 10% 25% 25% 13% 5%	17781
	Night	21% 8% 26% 28% 14% 3	25380

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	9% 20% 7% 19% 11% 9% 8% 3 7% 4 4	2718
	11th to 20th	Day	4 12% 8% 23% 12% 9% 11% 6% 8% 4 3	2767
	21st to end	Day	2 10% 4 14% 10% 13% 11% 7% 13% 4 12%	3942
February	1st to 10th	Day	2 10% 5% 13% 12% 12% 13% 10% 11% 6% 5%	1600
	11th to 20th	Day	3 12% 4 16% 13% 11% 11% 8% 10% 5% 6%	1615
	21st to end	Day	4 12% 5% 16% 10% 10% 10% 9% 8% 8% 7%	1624
March	1st to 10th	Day	11% 14% 5% 13% 8% 10% 10% 9% 9% 4 7%	4476
	11th to 20th	Day	11% 20% 8% 18% 8% 6% 8% 5% 5% 4 7%	4646
	21st to end	Day	7% 16% 6% 15% 7% 9% 12% 8% 7% 4 11%	5970
April	1st to 10th	Day	12% 19% 6% 14% 9% 7% 6% 3 5% 5% 14%	2400
	11th to 20th	Day	10% 14% 6% 15% 7% 6% 5% 3 5% 5% 25%	2542
	21st to end	Day	13% 18% 7% 13% 7% 4 4 3 4 4 23%	2790
May	1st to 10th	Day	12% 19% 7% 14% 5% 4 3 3 3 4 27%	6382
	11th to 20th	Day	16% 17% 6% 11% 5% 4 5% 4 5% 7% 21%	6775
	21st to end	Day	18% 17% 5% 9% 5% 4 3 3 4 6% 25%	7671
June	1st to 10th	Day	20% 13% 4 7% 6% 4 4 4 5% 6% 29%	3200
	11th to 20th	Day	20% 12% 3 8% 6% 5% 4 4 5% 6% 28%	3200
	21st to end	Day	21% 11% 3 8% 5% 5% 4 4 6% 6% 27%	3200
July	1st to 10th	Day	18% 8% 3 8% 5% 5% 5% 4 5% 6% 32%	7279
	11th to 20th	Day	21% 12% 4 10% 6% 5% 5% 4 5% 6% 20%	7280
	21st to end	Day	20% 12% 4 11% 6% 6% 6% 4 6% 6% 19%	7350
August	1st to 10th	Day	23% 12% 4 9% 6% 5% 5% 4 6% 7% 19%	4563
	11th to 20th	Day	16% 10% 3 8% 5% 5% 5% 4 6% 9% 30%	4499
	21st to end	Day	19% 11% 4 9% 5% 5% 5% 4 5% 7% 27%	4689
September	1st to 10th	Day	30% 16% 5% 10% 6% 4 3 3 4 4 15%	2400
	11th to 20th	Day	24% 18% 5% 10% 5% 5% 4 3 4 6% 15%	2309
	21st to end	Day	27% 18% 5% 9% 5% 5% 3 2 5% 5% 16%	2200
October	1st to 10th	Day	22% 24% 6% 11% 6% 5% 3 3 4 4 13%	1971
	11th to 20th	Day	26% 24% 8% 9% 4 4 3 4 3 3 12%	1710
	21st to end	Day	25% 22% 8% 16% 6% 3 3 2 3 3 9%	1881
November	1st to 10th	Day	19% 28% 10% 17% 7% 4 3 2 3 3 6%	1533
	11th to 20th	Day	18% 26% 11% 20% 7% 5% 2 2 2 2 4	1400
	21st to end	Day	11% 25% 8% 19% 10% 7% 4 2 4 3 6%	1400
December	1st to 10th	Day	5% 16% 8% 18% 14% 8% 8% 5% 7% 6% 7%	2136
	11th to 20th	Day	11% 23% 8% 17% 12% 9% 7% 4 3 2 5%	2253
	21st to end	Day	16% 19% 7% 13% 13% 8% 9% 6% 5% 2 3	2992
January	1st to 10th	Night	7% 20% 8% 23% 10% 9% 8% 4 5% 4 3	7267
	11th to 20th	Night	6% 13% 7% 21% 13% 12% 10% 6% 5% 4 2	7154
	21st to end	Night	3 11% 6% 12% 10% 12% 14% 8% 9% 5% 10%	7014
February	1st to 10th	Night	3 11% 5% 13% 12% 12% 13% 9% 9% 6% 7%	2800
	11th to 20th	Night	4 14% 6% 16% 12% 8% 9% 8% 10% 6% 9%	2668
	21st to end	Night	4 12% 5% 13% 10% 10% 10% 7% 9% 8% 11%	2006
March	1st to 10th	Night	8% 13% 4 11% 10% 13% 10% 6% 9% 5% 12%	5364
	11th to 20th	Night	14% 17% 7% 14% 9% 8% 6% 5% 5% 4 10%	5310
	21st to end	Night	6% 16% 7% 13% 7% 8% 13% 8% 6% 5% 11%	4962
April	1st to 10th	Night	12% 17% 6% 13% 8% 7% 6% 4 5% 4 19%	2000
	11th to 20th	Night	11% 14% 6% 12% 6% 4 4 3 4 4 32%	1807
	21st to end	Night	14% 14% 6% 12% 8% 5% 4 3 5% 5% 27%	1629
May	1st to 10th	Night	16% 19% 6% 10% 5% 3 4 3 3 4 28%	3560
	11th to 20th	Night	13% 14% 7% 11% 6% 4 4 3 4 5% 29%	3138
	21st to end	Night	16% 14% 6% 10% 5% 5% 4 3 4 5% 29%	3234
June	1st to 10th	Night	18% 12% 3 7% 5% 4 4 4 5% 5% 34%	1200
	11th to 20th	Night	21% 8% 2 6% 6% 4 3 4 5% 8% 32%	1200
	21st to end	Night	22% 11% 3 6% 4 4 4 4 5% 7% 31%	1200
July	1st to 10th	Night	17% 9% 3 8% 5% 5% 4 4 5% 6% 34%	2720
	11th to 20th	Night	18% 11% 4 9% 5% 5% 4 4 5% 7% 28%	2720
	21st to end	Night	20% 12% 4 9% 5% 5% 5% 4 6% 6% 26%	3505
August	1st to 10th	Night	19% 11% 5% 9% 6% 5% 5% 4 5% 6% 25%	2586
	11th to 20th	Night	13% 9% 4 8% 4 4 4 4 7% 8% 35%	2550
	21st to end	Night	20% 9% 3 9% 5% 4 4 3 4 5% 33%	3172
September	1st to 10th	Night	26% 13% 4 11% 5% 4 5% 3 4 5% 21%	2000
	11th to 20th	Night	21% 16% 4 10% 6% 5% 5% 3 4 5% 21%	2090
	21st to end	Night	26% 16% 4 9% 5% 3 4 3 4 6% 21%	2200
October	1st to 10th	Night	24% 21% 4 8% 5% 4 3 3 4 6% 18%	2273
	11th to 20th	Night	25% 23% 6% 9% 6% 4 4 2 4 4 13%	2470
	21st to end	Night	23% 24% 7% 15% 6% 4 4 2 3 3 10%	2717
November	1st to 10th	Night	20% 24% 9% 17% 6% 5% 4 2 3 3 7%	2761
	11th to 20th	Night	19% 23% 10% 21% 9% 5% 3 2 3 2 4	3000
	21st to end	Night	12% 23% 8% 18% 11% 6% 5% 3 3 3 7%	3000
December	1st to 10th	Night	5% 17% 7% 17% 13% 12% 8% 5% 5% 4 6%	5042
	11th to 20th	Night	12% 20% 9% 20% 12% 8% 6% 4 3 2 5%	5969
	21st to end	Night	12% 20% 8% 13% 12% 11% 8% 4 4 2 4	8008

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	80% 5% 6% 8% 2	2719
	11th to 20th	Day	79% 5% 5% 8% 2	2790
	21st to end	Day	66% 5% 7% 13% 8% 1	3942
February	1st to 10th	Day	67% 8% 8% 12% 5%	1600
	11th to 20th	Day	72% 7% 6% 11% 4	1623
	21st to end	Day	69% 6% 9% 9% 5% 1	1624
March	1st to 10th	Day	73% 5% 5% 10% 6%	4479
	11th to 20th	Day	78% 5% 5% 8% 5%	4646
	21st to end	Day	72% 4 5% 9% 8% 1	5970
April	1st to 10th	Day	71% 6% 7% 11% 5%	2400
	11th to 20th	Day	60% 6% 7% 19% 8%	2542
	21st to end	Day	66% 5% 9% 14% 6%	2790
May	1st to 10th	Day	62% 6% 8% 17% 8%	6393
	11th to 20th	Day	61% 7% 9% 18% 5%	6779
	21st to end	Day	59% 5% 9% 21% 7%	7671
June	1st to 10th	Day	55% 7% 11% 18% 8% 1	3200
	11th to 20th	Day	55% 7% 11% 18% 9%	3200
	21st to end	Day	56% 8% 11% 18% 7%	3200
July	1st to 10th	Day	52% 6% 11% 26% 5%	7201
	11th to 20th	Day	63% 6% 10% 17% 4	7193
	21st to end	Day	63% 7% 15% 14% 1	7141
August	1st to 10th	Day	63% 8% 14% 13% 1	4549
	11th to 20th	Day	50% 6% 21% 20% 3	4541
	21st to end	Day	56% 7% 18% 15% 4	4689
September	1st to 10th	Day	74% 6% 11% 8% 2	2400
	11th to 20th	Day	70% 7% 9% 11% 2	2309
	21st to end	Day	72% 5% 11% 12% 1	2200
October	1st to 10th	Day	70% 5% 11% 13% 1	3244
	11th to 20th	Day	77% 4 9% 9% 1	2822
	21st to end	Day	83% 4 6% 5% 1 1	3081
November	1st to 10th	Day	86% 5% 5% 3 1	1533
	11th to 20th	Day	88% 5% 3 2 1	1400
	21st to end	Day	84% 4 5% 5% 1	1400
December	1st to 10th	Day	76% 6% 8% 8% 2	2136
	11th to 20th	Day	86% 4 4 3 2	2253
	21st to end	Day	83% 6% 5% 4 2	2992
January	1st to 10th	Night	83% 5% 7% 5% 1	7267
	11th to 20th	Night	83% 5% 5% 6% 1	7206
	21st to end	Night	70% 5% 5% 8% 10% 1	7014
February	1st to 10th	Night	70% 7% 6% 13% 5%	2800
	11th to 20th	Night	67% 8% 9% 11% 5%	2671
	21st to end	Night	65% 7% 9% 11% 8%	2006
March	1st to 10th	Night	68% 5% 7% 13% 7%	5374
	11th to 20th	Night	74% 5% 5% 10% 5%	5311
	21st to end	Night	72% 6% 6% 10% 6%	4962
April	1st to 10th	Night	68% 6% 8% 12% 5% 1	2000
	11th to 20th	Night	55% 5% 8% 19% 12% 1	1807
	21st to end	Night	60% 5% 9% 16% 9% 1	1629
May	1st to 10th	Night	61% 4 6% 22% 7%	3566
	11th to 20th	Night	57% 6% 11% 20% 6%	3139
	21st to end	Night	56% 6% 12% 19% 8%	3235
June	1st to 10th	Night	51% 6% 11% 22% 9% 2	1200
	11th to 20th	Night	51% 7% 12% 20% 11%	1200
	21st to end	Night	52% 7% 10% 22% 9%	1200
July	1st to 10th	Night	50% 5% 10% 31% 3	2690
	11th to 20th	Night	56% 6% 12% 22% 5%	2684
	21st to end	Night	58% 7% 14% 18% 2	3402
August	1st to 10th	Night	59% 9% 14% 17% 1	2576
	11th to 20th	Night	47% 6% 18% 26% 3	2574
	21st to end	Night	54% 6% 15% 21% 3	3172
September	1st to 10th	Night	66% 7% 11% 12% 3	2000
	11th to 20th	Night	65% 8% 12% 13% 2	2090
	21st to end	Night	66% 5% 14% 12% 3	2200
October	1st to 10th	Night	63% 6% 17% 14% 1	3780
	11th to 20th	Night	71% 8% 10% 10% 1	4097
	21st to end	Night	79% 6% 6% 7% 2	4467
November	1st to 10th	Night	84% 5% 6% 4 1	2761
	11th to 20th	Night	88% 5% 4 2 1	3000
	21st to end	Night	82% 7% 6% 4 1	3000
December	1st to 10th	Night	80% 5% 7% 7% 1	5042
	11th to 20th	Night	86% 5% 5% 4 1	5969
	21st to end	Night	84% 5% 5% 5% 2	8008

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	14% 6% 31% 27% 20% 4	200
	11th to 20th	Day	10% 10% 30% 36% 10% 5%	200
	21st to end	Day	6% 6% 29% 33% 19% 7%	220
February	1st to 10th	Day	5% 8% 23% 42% 18% 5%	200
	11th to 20th	Day	3 5% 35% 28% 20% 9%	229
	21st to end	Day	6% 11% 32% 31% 16% 3	388
March	1st to 10th	Day	12% 8% 21% 31% 21% 7%	500
	11th to 20th	Day	13% 9% 31% 27% 16% 4	500
	21st to end	Day	13% 10% 32% 28% 13% 3	550
April	1st to 10th	Day	16% 7% 28% 29% 15% 4	500
	11th to 20th	Day	14% 11% 30% 24% 14% 7%	492
	21st to end	Day	20% 10% 25% 26% 14% 5%	500
May	1st to 10th	Day	19% 9% 26% 26% 12% 7%	513
	11th to 20th	Day	20% 10% 24% 25% 15% 5%	724
	21st to end	Day	25% 11% 26% 26% 11% 2	880
June	1st to 10th	Day	28% 6% 25% 22% 14% 5%	930
	11th to 20th	Day	26% 12% 20% 28% 11% 4	930
	21st to end	Day	24% 10% 25% 23% 16% 3	930
July	1st to 10th	Day	26% 8% 21% 26% 13% 7%	916
	11th to 20th	Day	29% 8% 21% 27% 11% 2	912
	21st to end	Day	30% 8% 17% 20% 16% 8%	766
August	1st to 10th	Day	29% 9% 16% 22% 17% 8%	526
	11th to 20th	Day	24% 8% 24% 18% 15% 10%	519
	21st to end	Day	28% 8% 20% 23% 13% 8%	583
September	1st to 10th	Day	40% 12% 21% 16% 8% 3	530
	11th to 20th	Day	28% 14% 25% 20% 10% 3	530
	21st to end	Day	33% 12% 23% 18% 9% 4	530
October	1st to 10th	Day	31% 14% 25% 20% 8% 2	498
	11th to 20th	Day	35% 13% 21% 20% 7% 4	390
	21st to end	Day	31% 13% 23% 19% 10% 4	429
November	1st to 10th	Day	32% 18% 27% 16% 4 2	246
	11th to 20th	Day	24% 11% 33% 23% 9% 2	200
	21st to end	Day	13% 16% 30% 25% 14% 4	200
December	1st to 10th	Day	12% 13% 23% 20% 24% 10%	200
	11th to 20th	Day	21% 9% 36% 23% 11% 2	200
	21st to end	Day	16% 6% 29% 32% 11% 5%	220
January	1st to 10th	Night	16% 7% 26% 30% 17% 4	1100
	11th to 20th	Night	12% 8% 31% 28% 17% 4	1083
	21st to end	Night	9% 5% 25% 36% 19% 5%	885
February	1st to 10th	Night	7% 7% 26% 38% 18% 5%	800
	11th to 20th	Night	11% 3 26% 36% 20% 5%	783
	21st to end	Night	9% 4 29% 35% 19% 4	660
March	1st to 10th	Night	7% 7% 27% 33% 23% 4	800
	11th to 20th	Night	14% 9% 28% 30% 17% 3	800
	21st to end	Night	13% 8% 33% 33% 11% 3	880
April	1st to 10th	Night	19% 7% 31% 28% 13% 2	800
	11th to 20th	Night	16% 7% 26% 34% 16% 2	623
	21st to end	Night	16% 10% 29% 32% 12% 2	429
May	1st to 10th	Night	25% 9% 22% 31% 12% 2	400
	11th to 20th	Night	19% 8% 26% 31% 14% 2	394
	21st to end	Night	19% 10% 30% 32% 8%	433
June	1st to 10th	Night	24% 4 25% 32% 14% 1	400
	11th to 20th	Night	23% 10% 21% 34% 12% 1	400
	21st to end	Night	25% 7% 23% 30% 14% 1	400
July	1st to 10th	Night	25% 5% 22% 32% 14% 3	390
	11th to 20th	Night	24% 7% 23% 31% 13% 1	388
	21st to end	Night	22% 6% 20% 26% 22% 4	438
August	1st to 10th	Night	26% 4 18% 29% 20% 3	398
	11th to 20th	Night	25% 5% 20% 25% 22% 2	396
	21st to end	Night	27% 5% 20% 31% 15% 2	622
September	1st to 10th	Night	33% 9% 26% 22% 9% 1	800
	11th to 20th	Night	29% 11% 25% 27% 9%	800
	21st to end	Night	34% 10% 24% 22% 8% 2	800
October	1st to 10th	Night	35% 11% 29% 18% 6% 1	773
	11th to 20th	Night	36% 9% 22% 23% 8% 1	760
	21st to end	Night	34% 10% 26% 17% 11% 3	836
November	1st to 10th	Night	32% 13% 25% 21% 8% 2	819
	11th to 20th	Night	29% 12% 27% 20% 10% 3	900
	21st to end	Night	21% 10% 30% 25% 10% 4	900
December	1st to 10th	Night	16% 11% 28% 26% 16% 3	980
	11th to 20th	Night	16% 9% 30% 29% 14% 2	1100
	21st to end	Night	17% 7% 25% 32% 16% 3	1210

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