Taché Observation Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Taché Observation Point clear sky chart from 2005-11-06 to 2026-03-18.

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	11% 9% 4 9% 6% 5% 5% 4 6% 7% 34%	131280
	Night	9% 10% 4 10% 6% 6% 5% 4 6% 7% 32%	130540
Transparency	Day	47% 6% 15% 24% 8% 1	134703
	Night	51% 5% 13% 22% 9% 1	135204
Seeing	Day	14% 10% 31% 28% 13% 4	18050
	Night	15% 7% 31% 33% 13% 1	28166

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	6% 16% 7% 14% 9% 6% 8% 6% 5% 5% 19%	4124
	11th to 20th	Day	4 11% 5% 14% 11% 9% 10% 10% 8% 6% 11%	4112
	21st to end	Day	5% 13% 6% 14% 8% 9% 7% 4 6% 8% 19%	5160
February	1st to 10th	Day	7% 12% 7% 13% 8% 7% 8% 6% 8% 5% 19%	1827
	11th to 20th	Day	7% 10% 4 10% 7% 8% 7% 7% 8% 8% 25%	1844
	21st to end	Day	6% 11% 4 12% 9% 9% 8% 5% 6% 5% 24%	1624
March	1st to 10th	Day	8% 12% 4 9% 9% 5% 5% 5% 6% 8% 28%	4747
	11th to 20th	Day	8% 10% 4 15% 10% 7% 5% 4 6% 7% 23%	5057
	21st to end	Day	10% 13% 5% 10% 6% 6% 5% 4 6% 6% 28%	5464
April	1st to 10th	Day	10% 12% 4 8% 6% 6% 4 5% 5% 7% 35%	2428
	11th to 20th	Day	13% 10% 3 9% 6% 4 5% 4 5% 7% 34%	2572
	21st to end	Day	16% 10% 4 7% 5% 4 4 4 6% 7% 34%	2600
May	1st to 10th	Day	12% 8% 3 6% 4 4 4 4 5% 7% 45%	6114
	11th to 20th	Day	18% 9% 3 6% 5% 5% 4 4 6% 8% 33%	6569
	21st to end	Day	14% 7% 3 6% 3 4 4 3 5% 6% 46%	7428
June	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	3000
	11th to 20th	Day	15% 8% 2 6% 6% 5% 4 4 7% 8% 37%	3000
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 5% 8% 9% 35%	3000
July	1st to 10th	Day	8% 4 2 5% 4 5% 5% 5% 7% 10% 45%	6799
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 4 6% 9% 44%	6800
	21st to end	Day	8% 4 2 6% 5% 4 5% 4 7% 9% 46%	7364
August	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 4 6% 10% 46%	4362
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 3 6% 8% 46%	4171
	21st to end	Day	13% 5% 2 6% 4 3 4 3 6% 9% 45%	4675
September	1st to 10th	Day	11% 5% 2 6% 4 3 4 4 6% 8% 48%	2485
	11th to 20th	Day	14% 7% 3 7% 4 4 4 5% 6% 8% 38%	2200
	21st to end	Day	15% 8% 3 5% 4 3 4 3 5% 8% 42%	2200
October	1st to 10th	Day	17% 9% 3 7% 5% 4 5% 3 5% 7% 36%	2025
	11th to 20th	Day	15% 11% 3 8% 6% 4 5% 4 5% 6% 33%	1983
	21st to end	Day	16% 15% 4 8% 5% 4 6% 4 5% 6% 26%	1980
November	1st to 10th	Day	16% 14% 5% 11% 5% 4 5% 4 4 6% 27%	1662
	11th to 20th	Day	11% 17% 6% 13% 7% 4 4 3 5% 6% 25%	1680
	21st to end	Day	12% 13% 5% 15% 9% 6% 4 3 4 6% 22%	1580
December	1st to 10th	Day	10% 17% 7% 14% 8% 7% 6% 5% 5% 7% 15%	2360
	11th to 20th	Day	9% 14% 6% 14% 7% 5% 5% 5% 7% 10% 19%	2709
	21st to end	Day	8% 15% 7% 18% 8% 7% 6% 5% 6% 5% 14%	3575
January	1st to 10th	Night	5% 13% 7% 16% 8% 9% 7% 5% 6% 6% 18%	8800
	11th to 20th	Night	5% 14% 6% 14% 9% 8% 11% 9% 7% 5% 12%	8803
	21st to end	Night	6% 15% 6% 12% 6% 6% 7% 6% 7% 9% 22%	9049
February	1st to 10th	Night	8% 13% 5% 12% 7% 7% 7% 6% 6% 6% 24%	2793
	11th to 20th	Night	6% 10% 4 8% 6% 7% 6% 6% 7% 7% 33%	2663
	21st to end	Night	6% 12% 5% 13% 7% 6% 6% 4 5% 6% 29%	2202
March	1st to 10th	Night	9% 11% 4 11% 7% 6% 5% 4 6% 7% 32%	5326
	11th to 20th	Night	7% 10% 4 10% 6% 5% 5% 5% 5% 7% 37%	5056
	21st to end	Night	12% 12% 4 10% 5% 5% 4 3 5% 5% 34%	5467
April	1st to 10th	Night	12% 9% 3 6% 5% 4 4 4 7% 7% 40%	1969
	11th to 20th	Night	14% 10% 4 8% 5% 5% 3 4 4 6% 36%	1779
	21st to end	Night	13% 9% 3 7% 7% 5% 5% 4 6% 7% 36%	1800
May	1st to 10th	Night	13% 7% 3 6% 4 4 3 3 5% 7% 45%	3846
	11th to 20th	Night	17% 7% 3 7% 4 4 4 4 7% 7% 37%	3344
	21st to end	Night	13% 6% 3 5% 3 3 3 4 4 6% 50%	3470
June	1st to 10th	Night	11% 6% 2 6% 5% 4 5% 3 7% 9% 42%	1400
	11th to 20th	Night	13% 5% 2 7% 5% 4 4 4 5% 7% 44%	1400
	21st to end	Night	11% 4 2 6% 5% 5% 5% 4 6% 9% 43%	1400
July	1st to 10th	Night	7% 3 2 5% 4 4 5% 4 7% 9% 50%	3180
	11th to 20th	Night	7% 3 2 5% 4 4 5% 4 7% 9% 51%	3180
	21st to end	Night	6% 4 2 5% 4 5% 5% 4 6% 11% 47%	3508
August	1st to 10th	Night	6% 4 2 5% 5% 4 5% 5% 8% 8% 49%	2796
	11th to 20th	Night	10% 4 1 5% 4 4 5% 4 5% 9% 51%	2888
	21st to end	Night	10% 5% 2 6% 4 4 5% 3 6% 8% 47%	3234
September	1st to 10th	Night	9% 4 2 5% 4 4 4 3 5% 8% 53%	1912
	11th to 20th	Night	15% 6% 2 5% 3 4 4 3 6% 7% 44%	2200
	21st to end	Night	15% 7% 2 6% 5% 3 4 3 4 8% 43%	2200
October	1st to 10th	Night	16% 8% 3 6% 5% 4 5% 4 5% 7% 38%	2355
	11th to 20th	Night	15% 12% 4 7% 5% 4 5% 4 5% 6% 34%	2415
	21st to end	Night	15% 12% 4 8% 5% 5% 4 3 6% 6% 31%	2860
November	1st to 10th	Night	13% 14% 5% 11% 6% 5% 5% 3 4 5% 29%	2856
	11th to 20th	Night	11% 16% 5% 11% 7% 5% 5% 4 5% 5% 27%	2940
	21st to end	Night	11% 13% 6% 14% 8% 6% 5% 3 4 5% 24%	3036
December	1st to 10th	Night	9% 17% 6% 17% 13% 7% 5% 4 4 4 14%	5050
	11th to 20th	Night	8% 15% 6% 14% 7% 5% 5% 5% 6% 7% 23%	5718
	21st to end	Night	8% 12% 6% 19% 9% 7% 6% 4 6% 5% 18%	7645

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	65% 3 9% 16% 6%	4125
	11th to 20th	Day	69% 5% 9% 13% 5%	4140
	21st to end	Day	63% 4 8% 21% 5%	5160
February	1st to 10th	Day	62% 5% 13% 12% 7% 1	1827
	11th to 20th	Day	53% 6% 13% 21% 7%	1853
	21st to end	Day	60% 5% 12% 14% 9%	1624
March	1st to 10th	Day	53% 6% 16% 15% 10%	4749
	11th to 20th	Day	59% 5% 14% 16% 6%	5057
	21st to end	Day	54% 6% 11% 22% 7%	5464
April	1st to 10th	Day	49% 5% 10% 25% 11%	2428
	11th to 20th	Day	49% 5% 11% 22% 11% 1	2572
	21st to end	Day	49% 5% 15% 22% 8% 2	2600
May	1st to 10th	Day	38% 5% 11% 27% 18%	6125
	11th to 20th	Day	48% 5% 10% 27% 10%	6573
	21st to end	Day	39% 4 8% 24% 21% 4	7428
June	1st to 10th	Day	44% 6% 15% 24% 10% 1	3000
	11th to 20th	Day	45% 6% 15% 24% 9% 1	3000
	21st to end	Day	43% 9% 19% 22% 7%	3000
July	1st to 10th	Day	32% 8% 25% 28% 6%	6726
	11th to 20th	Day	35% 7% 20% 33% 5%	6719
	21st to end	Day	34% 7% 22% 31% 6%	7151
August	1st to 10th	Day	33% 6% 19% 31% 10%	4346
	11th to 20th	Day	35% 6% 21% 33% 5%	4210
	21st to end	Day	36% 5% 22% 30% 6%	4674
September	1st to 10th	Day	33% 6% 18% 32% 9% 1	2485
	11th to 20th	Day	43% 7% 20% 26% 5%	2200
	21st to end	Day	41% 5% 15% 32% 7%	2200
October	1st to 10th	Day	39% 4 16% 30% 11%	3298
	11th to 20th	Day	43% 4 12% 26% 14%	3212
	21st to end	Day	51% 5% 16% 23% 5%	3190
November	1st to 10th	Day	58% 6% 14% 17% 5% 1	1662
	11th to 20th	Day	61% 6% 14% 13% 5% 1	1680
	21st to end	Day	64% 5% 14% 13% 3	1580
December	1st to 10th	Day	69% 8% 11% 7% 6%	2360
	11th to 20th	Day	59% 4 15% 15% 7%	2710
	21st to end	Day	71% 6% 7% 13% 4	3575
January	1st to 10th	Night	66% 4 11% 12% 7%	8800
	11th to 20th	Night	70% 4 7% 15% 4	8850
	21st to end	Night	58% 5% 11% 20% 6%	9049
February	1st to 10th	Night	58% 5% 12% 15% 8%	2793
	11th to 20th	Night	48% 6% 15% 22% 9%	2664
	21st to end	Night	55% 4 12% 18% 10%	2202
March	1st to 10th	Night	52% 5% 14% 16% 10% 3	5337
	11th to 20th	Night	45% 6% 15% 22% 12%	5057
	21st to end	Night	51% 5% 8% 23% 11%	5467
April	1st to 10th	Night	42% 5% 11% 24% 16% 2	1969
	11th to 20th	Night	49% 4 8% 22% 15% 2	1779
	21st to end	Night	47% 5% 12% 24% 11% 2	1800
May	1st to 10th	Night	39% 4 10% 27% 20%	3855
	11th to 20th	Night	44% 5% 10% 26% 13% 2	3345
	21st to end	Night	35% 4 9% 23% 23% 5%	3470
June	1st to 10th	Night	37% 7% 16% 25% 14% 1	1400
	11th to 20th	Night	39% 6% 18% 24% 12% 2	1400
	21st to end	Night	37% 8% 20% 26% 8% 1	1400
July	1st to 10th	Night	29% 8% 24% 30% 8% 1	3145
	11th to 20th	Night	28% 6% 20% 38% 8%	3138
	21st to end	Night	29% 7% 25% 33% 6%	3407
August	1st to 10th	Night	30% 6% 17% 34% 13% 1	2788
	11th to 20th	Night	30% 5% 25% 30% 9%	2915
	21st to end	Night	35% 5% 19% 32% 9%	3234
September	1st to 10th	Night	30% 5% 17% 34% 13% 1	1912
	11th to 20th	Night	39% 6% 18% 26% 10% 1	2200
	21st to end	Night	41% 5% 13% 29% 11% 1	2200
October	1st to 10th	Night	40% 4 11% 34% 12%	3849
	11th to 20th	Night	44% 4 13% 30% 10%	3926
	21st to end	Night	47% 4 14% 29% 6%	4610
November	1st to 10th	Night	56% 5% 15% 16% 6% 1	2856
	11th to 20th	Night	59% 6% 15% 14% 5% 1	2940
	21st to end	Night	64% 5% 14% 12% 5%	3036
December	1st to 10th	Night	73% 5% 11% 8% 3	5050
	11th to 20th	Night	60% 5% 12% 11% 11%	5716
	21st to end	Night	67% 5% 9% 15% 4	7645

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	10% 9% 34% 30% 15% 2	330
	11th to 20th	Day	11% 8% 31% 36% 13% 1	330
	21st to end	Day	12% 10% 31% 31% 12% 4	363
February	1st to 10th	Day	13% 12% 32% 32% 9% 2	330
	11th to 20th	Day	10% 10% 33% 29% 13% 5%	330
	21st to end	Day	10% 6% 45% 27% 11% 1	273
March	1st to 10th	Day	13% 8% 36% 29% 13% 1	330
	11th to 20th	Day	11% 13% 35% 24% 14% 2	321
	21st to end	Day	13% 11% 33% 27% 13% 2	330
April	1st to 10th	Day	14% 8% 33% 31% 11% 3	528
	11th to 20th	Day	18% 12% 32% 25% 12% 1	690
	21st to end	Day	18% 10% 32% 26% 12% 2	700
May	1st to 10th	Day	16% 15% 31% 25% 12% 2	703
	11th to 20th	Day	21% 11% 27% 25% 13% 2	725
	21st to end	Day	19% 9% 24% 28% 15% 4	789
June	1st to 10th	Day	15% 13% 29% 25% 12% 6%	730
	11th to 20th	Day	14% 13% 33% 29% 9% 3	730
	21st to end	Day	12% 9% 29% 29% 16% 5%	730
July	1st to 10th	Day	9% 6% 29% 28% 19% 9%	721
	11th to 20th	Day	11% 7% 31% 29% 17% 5%	718
	21st to end	Day	7% 6% 28% 31% 19% 8%	794
August	1st to 10th	Day	7% 8% 27% 30% 22% 6%	726
	11th to 20th	Day	10% 6% 25% 34% 17% 9%	715
	21st to end	Day	14% 7% 31% 27% 18% 4	803
September	1st to 10th	Day	10% 8% 31% 33% 15% 3	615
	11th to 20th	Day	14% 12% 37% 27% 8% 2	330
	21st to end	Day	19% 9% 32% 28% 10% 2	330
October	1st to 10th	Day	18% 13% 25% 32% 8% 4	330
	11th to 20th	Day	15% 12% 37% 28% 7% 1	330
	21st to end	Day	28% 9% 30% 23% 9% 1	363
November	1st to 10th	Day	24% 10% 29% 24% 11% 2	330
	11th to 20th	Day	18% 10% 40% 21% 9% 1	330
	21st to end	Day	15% 12% 40% 26% 6%	330
December	1st to 10th	Day	15% 8% 35% 28% 12% 2	330
	11th to 20th	Day	15% 10% 43% 25% 7% 1	330
	21st to end	Day	13% 9% 31% 30% 14% 4	363
January	1st to 10th	Night	11% 7% 34% 31% 14% 2	1050
	11th to 20th	Night	14% 8% 32% 35% 10%	1050
	21st to end	Night	13% 8% 35% 33% 11% 1	1155
February	1st to 10th	Night	13% 8% 28% 37% 13% 1	1050
	11th to 20th	Night	11% 6% 30% 36% 15% 3	1029
	21st to end	Night	10% 8% 36% 31% 13% 1	818
March	1st to 10th	Night	15% 8% 32% 31% 13% 2	774
	11th to 20th	Night	12% 8% 38% 29% 12% 1	621
	21st to end	Night	18% 8% 28% 30% 13% 3	660
April	1st to 10th	Night	14% 8% 29% 37% 11% 2	600
	11th to 20th	Night	18% 7% 31% 34% 10% 1	593
	21st to end	Night	16% 8% 31% 34% 12%	600
May	1st to 10th	Night	18% 7% 36% 29% 10%	600
	11th to 20th	Night	17% 8% 31% 29% 13% 1	591
	21st to end	Night	16% 7% 33% 32% 11% 1	650
June	1st to 10th	Night	14% 5% 33% 32% 16%	600
	11th to 20th	Night	15% 6% 31% 34% 14%	600
	21st to end	Night	11% 7% 21% 41% 18% 2	600
July	1st to 10th	Night	5% 5% 24% 42% 22% 1	585
	11th to 20th	Night	9% 4 24% 42% 19% 2	582
	21st to end	Night	7% 3 23% 43% 21% 3	657
August	1st to 10th	Night	8% 4 21% 47% 18% 2	597
	11th to 20th	Night	10% 4 21% 40% 23% 3	594
	21st to end	Night	12% 5% 26% 39% 19%	660
September	1st to 10th	Night	12% 5% 28% 37% 17% 2	600
	11th to 20th	Night	16% 6% 28% 37% 13%	600
	21st to end	Night	19% 6% 32% 31% 12% 1	600
October	1st to 10th	Night	19% 9% 34% 30% 8%	755
	11th to 20th	Night	20% 8% 33% 29% 9% 1	815
	21st to end	Night	22% 9% 30% 30% 8% 1	1100
November	1st to 10th	Night	18% 9% 37% 27% 9%	1025
	11th to 20th	Night	19% 8% 34% 28% 9% 2	1050
	21st to end	Night	18% 10% 40% 25% 7% 1	1050
December	1st to 10th	Night	12% 6% 34% 34% 12% 2	1050
	11th to 20th	Night	16% 8% 36% 31% 8% 1	1050
	21st to end	Night	19% 8% 32% 28% 12% 1	1155

Page generated at 2026-03-15 01:23:52. Version ac07

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