Tmakwa Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tmakwa Observatory clear sky chart from 2005-11-06 to 2026-08-30.

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% 13% 5% 11% 6% 5% 5% 4 5% 6% 25%	143885
	Night	14% 14% 5% 13% 7% 6% 5% 3 4 5% 23%	138363
Transparency	Day	54% 9% 11% 16% 8% 1	147368
	Night	58% 9% 11% 14% 7% 1	142956
Seeing	Day	27% 21% 27% 17% 7% 2	17128
	Night	25% 17% 25% 24% 8% 1	25913

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	8% 15% 8% 22% 12% 9% 5% 3 3 3 12%	4661
	11th to 20th	Day	6% 13% 6% 21% 15% 8% 5% 4 4 4 15%	4650
	21st to end	Day	6% 12% 6% 15% 10% 10% 8% 4 4 4 19%	5124
February	1st to 10th	Day	12% 14% 7% 14% 11% 6% 5% 2 5% 5% 20%	1825
	11th to 20th	Day	8% 14% 8% 15% 10% 7% 6% 4 4 4 19%	2048
	21st to end	Day	9% 16% 6% 15% 9% 6% 4 3 5% 5% 22%	1730
March	1st to 10th	Day	13% 15% 6% 16% 7% 6% 5% 3 4 4 20%	4576
	11th to 20th	Day	11% 13% 9% 12% 6% 5% 4 3 4 5% 28%	4845
	21st to end	Day	18% 14% 6% 12% 6% 4 4 3 4 6% 23%	5956
April	1st to 10th	Day	16% 20% 6% 10% 4 4 3 3 3 5% 26%	2520
	11th to 20th	Day	15% 17% 5% 9% 4 4 4 4 4 5% 28%	2535
	21st to end	Day	20% 16% 3 9% 5% 4 4 4 5% 5% 26%	2730
May	1st to 10th	Day	24% 17% 5% 10% 6% 5% 5% 3 4 4 17%	7639
	11th to 20th	Day	16% 13% 4 9% 7% 6% 6% 4 5% 7% 23%	8099
	21st to end	Day	21% 13% 3 7% 5% 4 5% 4 6% 7% 26%	9060
June	1st to 10th	Day	25% 11% 3 8% 5% 4 5% 3 6% 6% 24%	2940
	11th to 20th	Day	18% 8% 3 7% 5% 4 5% 4 6% 8% 30%	2940
	21st to end	Day	21% 10% 3 8% 6% 5% 5% 5% 6% 6% 25%	2940
July	1st to 10th	Day	15% 9% 3 8% 5% 6% 6% 5% 8% 10% 26%	8280
	11th to 20th	Day	12% 7% 3 7% 5% 5% 6% 5% 8% 9% 35%	8280
	21st to end	Day	15% 8% 3 8% 5% 5% 5% 4 7% 8% 32%	8993
August	1st to 10th	Day	16% 11% 3 9% 6% 5% 6% 4 5% 7% 28%	4552
	11th to 20th	Day	17% 9% 3 9% 6% 5% 6% 5% 7% 9% 24%	4305
	21st to end	Day	14% 8% 2 7% 5% 5% 5% 5% 7% 9% 34%	4431
September	1st to 10th	Day	15% 7% 2 6% 4 4 4 4 4 8% 42%	2400
	11th to 20th	Day	16% 7% 2 5% 3 4 4 3 4 6% 45%	2217
	21st to end	Day	15% 11% 2 7% 4 4 4 3 6% 8% 36%	2200
October	1st to 10th	Day	20% 12% 4 6% 4 4 4 3 5% 7% 31%	2200
	11th to 20th	Day	15% 16% 4 7% 4 4 4 3 5% 6% 32%	1893
	21st to end	Day	18% 21% 5% 7% 4 5% 4 3 4 5% 25%	1980
November	1st to 10th	Day	14% 18% 5% 9% 4 4 3 4 5% 5% 29%	1851
	11th to 20th	Day	13% 17% 8% 12% 7% 5% 3 3 5% 6% 22%	1890
	21st to end	Day	14% 17% 6% 16% 7% 4 3 4 5% 5% 20%	1801
December	1st to 10th	Day	9% 18% 7% 24% 11% 5% 4 3 3 3 13%	2680
	11th to 20th	Day	8% 18% 9% 16% 8% 4 4 3 4 4 21%	3066
	21st to end	Day	13% 16% 6% 12% 8% 5% 5% 4 5% 4 21%	4048
January	1st to 10th	Night	7% 18% 8% 22% 12% 8% 5% 3 3 3 11%	8234
	11th to 20th	Night	7% 15% 10% 25% 14% 7% 5% 3 3 3 9%	8235
	21st to end	Night	8% 11% 5% 15% 11% 13% 8% 4 5% 4 16%	9057
February	1st to 10th	Night	11% 15% 6% 17% 10% 7% 5% 3 4 5% 17%	2790
	11th to 20th	Night	8% 14% 7% 18% 11% 8% 6% 3 3 3 17%	2458
	21st to end	Night	8% 17% 6% 13% 9% 6% 5% 3 5% 5% 24%	2076
March	1st to 10th	Night	13% 15% 6% 16% 7% 7% 6% 3 3 5% 18%	5484
	11th to 20th	Night	12% 18% 7% 12% 6% 5% 5% 3 4 5% 23%	5332
	21st to end	Night	17% 18% 7% 13% 7% 4 3 3 3 4 23%	5216
April	1st to 10th	Night	18% 18% 6% 10% 5% 5% 3 2 4 5% 24%	2100
	11th to 20th	Night	18% 17% 4 8% 6% 5% 4 3 4 5% 27%	2034
	21st to end	Night	19% 14% 4 9% 4 4 4 3 5% 6% 30%	1890
May	1st to 10th	Night	26% 15% 4 8% 4 4 4 4 4 5% 22%	5259
	11th to 20th	Night	18% 13% 3 8% 5% 4 5% 4 5% 7% 28%	4817
	21st to end	Night	19% 12% 3 7% 4 4 5% 4 6% 8% 29%	5114
June	1st to 10th	Night	27% 11% 3 6% 4 4 4 3 4 8% 27%	1680
	11th to 20th	Night	19% 8% 2 8% 5% 5% 4 4 5% 7% 33%	1680
	21st to end	Night	20% 9% 2 7% 5% 5% 4 6% 6% 6% 30%	1680
July	1st to 10th	Night	18% 9% 3 8% 5% 6% 5% 4 5% 8% 28%	4680
	11th to 20th	Night	16% 8% 3 8% 4 4 5% 4 6% 7% 36%	4680
	21st to end	Night	15% 8% 3 7% 5% 4 5% 4 5% 8% 36%	5084
August	1st to 10th	Night	22% 11% 4 7% 4 4 4 4 4 6% 30%	2782
	11th to 20th	Night	17% 9% 4 8% 5% 4 5% 4 6% 7% 30%	2962
	21st to end	Night	15% 11% 2 5% 4 4 5% 3 6% 7% 38%	3662
September	1st to 10th	Night	17% 8% 2 5% 3 2 3 3 5% 6% 44%	2000
	11th to 20th	Night	16% 8% 2 5% 3 3 3 2 5% 6% 46%	2181
	21st to end	Night	18% 8% 2 5% 4 4 5% 3 6% 7% 38%	2200
October	1st to 10th	Night	19% 12% 3 6% 5% 4 4 4 5% 6% 32%	2200
	11th to 20th	Night	17% 16% 3 7% 5% 4 4 3 5% 6% 29%	2504
	21st to end	Night	20% 19% 4 7% 5% 5% 5% 4 5% 5% 23%	2860
November	1st to 10th	Night	17% 17% 5% 10% 4 4 4 2 4 5% 28%	2667
	11th to 20th	Night	13% 17% 7% 13% 6% 4 3 3 4 6% 24%	2730
	21st to end	Night	14% 17% 8% 15% 8% 5% 3 3 4 5% 19%	2817
December	1st to 10th	Night	11% 17% 10% 24% 10% 6% 4 3 4 3 10%	4720
	11th to 20th	Night	13% 19% 8% 16% 10% 5% 4 4 4 3 15%	5348
	21st to end	Night	13% 16% 6% 16% 7% 5% 6% 3 4 4 20%	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	69% 11% 9% 9% 2	4662
	11th to 20th	Day	63% 13% 9% 9% 4 2	4680
	21st to end	Day	62% 10% 8% 11% 9% 1	5124
February	1st to 10th	Day	65% 7% 7% 13% 6% 2	1825
	11th to 20th	Day	62% 9% 10% 10% 6% 2	2057
	21st to end	Day	61% 7% 9% 12% 8% 2	1730
March	1st to 10th	Day	63% 8% 9% 8% 8% 4	4579
	11th to 20th	Day	48% 13% 13% 13% 9% 3	4845
	21st to end	Day	57% 9% 8% 12% 13% 1	5956
April	1st to 10th	Day	61% 5% 8% 14% 9% 2	2520
	11th to 20th	Day	54% 8% 9% 17% 11% 1	2535
	21st to end	Day	58% 6% 8% 16% 9% 2	2730
May	1st to 10th	Day	66% 8% 8% 12% 4 1	7651
	11th to 20th	Day	56% 10% 13% 14% 6% 1	8103
	21st to end	Day	53% 9% 11% 20% 6%	9061
June	1st to 10th	Day	59% 6% 11% 17% 7%	2940
	11th to 20th	Day	49% 8% 12% 19% 11% 1	2940
	21st to end	Day	57% 9% 10% 16% 7% 1	2940
July	1st to 10th	Day	49% 8% 16% 19% 7%	8210
	11th to 20th	Day	40% 10% 16% 26% 7%	8205
	21st to end	Day	45% 8% 14% 26% 6%	8795
August	1st to 10th	Day	54% 8% 14% 17% 6%	4538
	11th to 20th	Day	53% 9% 17% 16% 5%	4344
	21st to end	Day	42% 10% 16% 17% 11% 3	4431
September	1st to 10th	Day	40% 8% 13% 27% 12% 1	2400
	11th to 20th	Day	39% 6% 10% 29% 15% 2	2217
	21st to end	Day	44% 8% 13% 22% 12% 1	2200
October	1st to 10th	Day	49% 6% 11% 20% 13% 1	3590
	11th to 20th	Day	49% 7% 10% 22% 11% 1	3044
	21st to end	Day	48% 7% 12% 21% 10% 1	3180
November	1st to 10th	Day	54% 8% 11% 16% 10% 1	1851
	11th to 20th	Day	59% 9% 9% 10% 10% 2	1890
	21st to end	Day	64% 8% 12% 13% 3	1801
December	1st to 10th	Day	74% 6% 8% 8% 3	2680
	11th to 20th	Day	63% 8% 7% 12% 10% 1	3066
	21st to end	Day	58% 11% 9% 9% 9% 4	4048
January	1st to 10th	Night	72% 9% 9% 7% 2	8234
	11th to 20th	Night	73% 10% 8% 5% 3 1	8280
	21st to end	Night	65% 10% 8% 9% 7% 1	9057
February	1st to 10th	Night	65% 9% 8% 10% 6% 1	2790
	11th to 20th	Night	65% 9% 8% 10% 6% 1	2460
	21st to end	Night	57% 9% 10% 15% 8% 2	2076
March	1st to 10th	Night	65% 8% 10% 10% 6% 1	5494
	11th to 20th	Night	54% 12% 14% 12% 8% 1	5333
	21st to end	Night	60% 7% 7% 10% 14% 1	5216
April	1st to 10th	Night	60% 8% 7% 14% 9% 1	2100
	11th to 20th	Night	57% 8% 8% 18% 10%	2034
	21st to end	Night	54% 7% 9% 16% 12% 2	1890
May	1st to 10th	Night	61% 8% 11% 13% 6%	5265
	11th to 20th	Night	52% 11% 11% 20% 5% 1	4818
	21st to end	Night	49% 10% 12% 21% 8%	5115
June	1st to 10th	Night	55% 7% 11% 18% 9%	1680
	11th to 20th	Night	48% 10% 12% 20% 8% 2	1680
	21st to end	Night	52% 9% 13% 19% 8%	1680
July	1st to 10th	Night	53% 7% 14% 19% 7%	4640
	11th to 20th	Night	44% 9% 13% 24% 9%	4632
	21st to end	Night	44% 8% 16% 25% 7%	4967
August	1st to 10th	Night	55% 7% 14% 18% 6%	2772
	11th to 20th	Night	48% 13% 16% 16% 7%	2989
	21st to end	Night	42% 8% 17% 20% 12% 2	3662
September	1st to 10th	Night	38% 8% 15% 28% 11%	2000
	11th to 20th	Night	38% 6% 11% 30% 14% 1	2181
	21st to end	Night	43% 9% 12% 22% 13% 2	2200
October	1st to 10th	Night	48% 8% 16% 17% 10% 1	3590
	11th to 20th	Night	53% 7% 10% 16% 12% 2	4079
	21st to end	Night	53% 6% 13% 18% 9% 1	4610
November	1st to 10th	Night	58% 7% 10% 16% 8% 1	2667
	11th to 20th	Night	59% 9% 10% 12% 8% 3	2730
	21st to end	Night	64% 9% 11% 11% 5%	2817
December	1st to 10th	Night	78% 7% 6% 6% 2	4720
	11th to 20th	Night	68% 12% 5% 8% 8%	5348
	21st to end	Night	61% 11% 8% 10% 6% 4	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	23% 34% 25% 16% 2	220
	11th to 20th	Day	31% 29% 24% 13% 2 1	220
	21st to end	Day	26% 29% 29% 14% 3	242
February	1st to 10th	Day	35% 28% 24% 13% 1	327
	11th to 20th	Day	31% 27% 29% 11% 2	536
	21st to end	Day	29% 25% 30% 14% 2	446
March	1st to 10th	Day	31% 24% 27% 14% 3	540
	11th to 20th	Day	31% 28% 26% 12% 3 1	540
	21st to end	Day	35% 24% 23% 12% 5% 2	594
April	1st to 10th	Day	36% 23% 24% 12% 4 1	540
	11th to 20th	Day	32% 27% 22% 13% 5% 2	532
	21st to end	Day	34% 22% 26% 12% 4 2	540
May	1st to 10th	Day	37% 24% 22% 12% 3 2	543
	11th to 20th	Day	30% 18% 29% 16% 5% 2	567
	21st to end	Day	24% 22% 30% 19% 6%	617
June	1st to 10th	Day	31% 17% 32% 13% 6% 1	570
	11th to 20th	Day	23% 18% 33% 19% 7% 1	570
	21st to end	Day	27% 21% 29% 16% 6% 2	570
July	1st to 10th	Day	21% 18% 30% 21% 9% 1	565
	11th to 20th	Day	16% 15% 37% 23% 8% 2	564
	21st to end	Day	21% 14% 33% 23% 6% 2	620
August	1st to 10th	Day	16% 14% 30% 26% 12% 3	566
	11th to 20th	Day	20% 16% 29% 18% 13% 5%	559
	21st to end	Day	17% 16% 29% 22% 10% 5%	619
September	1st to 10th	Day	18% 16% 27% 21% 13% 4	530
	11th to 20th	Day	19% 13% 24% 22% 16% 7%	530
	21st to end	Day	18% 16% 28% 20% 12% 5%	530
October	1st to 10th	Day	27% 17% 22% 19% 12% 4	530
	11th to 20th	Day	28% 18% 25% 17% 11% 1	461
	21st to end	Day	31% 21% 26% 17% 5%	462
November	1st to 10th	Day	33% 20% 19% 22% 5% 1	425
	11th to 20th	Day	30% 20% 28% 16% 5% 2	430
	21st to end	Day	31% 24% 26% 14% 4 1	341
December	1st to 10th	Day	27% 30% 21% 15% 7%	220
	11th to 20th	Day	36% 26% 26% 8% 3	220
	21st to end	Day	33% 23% 26% 15% 2	242
January	1st to 10th	Night	26% 24% 26% 19% 4	840
	11th to 20th	Night	24% 25% 29% 19% 3	840
	21st to end	Night	19% 24% 35% 18% 4	924
February	1st to 10th	Night	23% 23% 33% 18% 3	840
	11th to 20th	Night	24% 26% 32% 16% 3	823
	21st to end	Night	24% 23% 32% 19% 3	692
March	1st to 10th	Night	28% 22% 29% 19% 3	840
	11th to 20th	Night	26% 22% 27% 19% 5%	840
	21st to end	Night	29% 22% 24% 19% 5% 1	924
April	1st to 10th	Night	31% 22% 24% 18% 4	840
	11th to 20th	Night	27% 21% 24% 23% 5% 1	790
	21st to end	Night	28% 17% 30% 18% 6%	630
May	1st to 10th	Night	30% 15% 25% 21% 7% 1	630
	11th to 20th	Night	20% 15% 31% 25% 8% 1	477
	21st to end	Night	21% 13% 20% 35% 10%	455
June	1st to 10th	Night	29% 10% 22% 30% 9%	420
	11th to 20th	Night	21% 12% 20% 34% 13%	420
	21st to end	Night	23% 10% 22% 36% 10%	420
July	1st to 10th	Night	16% 5% 24% 40% 13%	410
	11th to 20th	Night	18% 6% 20% 39% 15% 2	408
	21st to end	Night	18% 5% 21% 40% 15% 1	460
August	1st to 10th	Night	17% 5% 17% 43% 17% 1	482
	11th to 20th	Night	18% 8% 24% 31% 17% 2	622
	21st to end	Night	19% 7% 22% 32% 18% 3	902
September	1st to 10th	Night	19% 9% 21% 32% 17% 2	800
	11th to 20th	Night	20% 8% 16% 32% 20% 4	800
	21st to end	Night	21% 11% 21% 29% 15% 3	800
October	1st to 10th	Night	25% 11% 22% 27% 13% 2	800
	11th to 20th	Night	26% 14% 25% 24% 9% 2	800
	21st to end	Night	31% 16% 26% 21% 5%	880
November	1st to 10th	Night	30% 17% 21% 24% 7% 1	820
	11th to 20th	Night	25% 20% 26% 20% 7% 1	840
	21st to end	Night	26% 23% 25% 20% 5% 1	840
December	1st to 10th	Night	28% 24% 26% 18% 4	840
	11th to 20th	Night	29% 22% 27% 19% 4	840
	21st to end	Night	30% 21% 28% 18% 3	924

Page generated at 2026-08-27 04:07:09. Version ac07

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