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 2025-04-26.

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%	113384
	Night	14% 14% 6% 13% 7% 5% 5% 3 4 5% 23%	115231
Transparency	Day	54% 9% 11% 16% 8% 1	116913
	Night	58% 9% 10% 14% 8% 1	119853
Seeing	Day	27% 20% 27% 17% 7% 2	15352
	Night	24% 17% 25% 24% 8% 1	24365

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% 16% 9% 23% 11% 7% 4 3 3 3 12%	3597
	11th to 20th	Day	6% 12% 5% 20% 15% 7% 5% 4 4 4 17%	3570
	21st to end	Day	8% 15% 7% 16% 8% 7% 7% 4 4 4 21%	3960
February	1st to 10th	Day	12% 15% 7% 14% 11% 6% 4 2 5% 4 19%	1738
	11th to 20th	Day	9% 14% 8% 15% 11% 8% 6% 4 4 4 18%	1948
	21st to end	Day	10% 16% 6% 14% 8% 6% 4 3 5% 5% 22%	1650
March	1st to 10th	Day	13% 15% 6% 16% 7% 6% 5% 3 4 4 20%	4476
	11th to 20th	Day	11% 13% 9% 12% 6% 5% 4 3 4 5% 29%	4740
	21st to end	Day	18% 14% 6% 12% 6% 4 4 3 4 6% 23%	5827
April	1st to 10th	Day	16% 20% 5% 10% 4 4 3 3 3 5% 26%	2400
	11th to 20th	Day	14% 18% 5% 8% 4 4 4 4 4 5% 29%	2413
	21st to end	Day	20% 16% 3 9% 5% 4 4 4 5% 4 25%	2535
May	1st to 10th	Day	25% 16% 4 8% 5% 4 5% 3 3 4 23%	4106
	11th to 20th	Day	17% 12% 4 9% 6% 5% 6% 3 5% 7% 25%	4331
	21st to end	Day	13% 9% 3 8% 5% 5% 5% 5% 7% 9% 32%	4837
June	1st to 10th	Day	26% 11% 3 8% 5% 4 5% 3 6% 6% 23%	2660
	11th to 20th	Day	19% 8% 3 7% 5% 4 5% 4 6% 8% 31%	2660
	21st to end	Day	21% 11% 3 9% 6% 5% 5% 5% 5% 6% 24%	2660
July	1st to 10th	Day	15% 8% 2 7% 5% 6% 6% 5% 8% 10% 27%	4440
	11th to 20th	Day	11% 8% 3 8% 6% 6% 7% 5% 9% 9% 27%	4440
	21st to end	Day	17% 8% 3 8% 6% 5% 5% 4 6% 7% 30%	4814
August	1st to 10th	Day	17% 11% 3 9% 6% 5% 6% 4 5% 7% 26%	4280
	11th to 20th	Day	17% 9% 3 9% 7% 5% 6% 5% 7% 9% 23%	4045
	21st to end	Day	15% 8% 2 7% 5% 5% 5% 5% 7% 9% 34%	4190
September	1st to 10th	Day	15% 7% 2 6% 4 4 4 4 4 8% 41%	2280
	11th to 20th	Day	16% 8% 2 5% 3 4 4 3 4 6% 45%	2106
	21st to end	Day	15% 11% 2 7% 4 5% 4 3 6% 8% 36%	2090
October	1st to 10th	Day	21% 12% 4 6% 4 5% 4 3 5% 7% 29%	2090
	11th to 20th	Day	14% 16% 4 7% 4 4 4 3 5% 5% 32%	1798
	21st to end	Day	19% 20% 4 7% 4 5% 4 3 4 5% 26%	1881
November	1st to 10th	Day	15% 16% 4 9% 4 4 3 4 6% 6% 30%	1761
	11th to 20th	Day	14% 16% 7% 12% 7% 5% 4 4 5% 6% 23%	1800
	21st to end	Day	14% 17% 6% 14% 7% 4 3 4 5% 5% 21%	1715
December	1st to 10th	Day	9% 18% 7% 24% 11% 5% 4 3 3 3 13%	2600
	11th to 20th	Day	8% 18% 9% 16% 8% 4 4 3 4 4 22%	2986
	21st to end	Day	13% 17% 6% 12% 8% 5% 5% 4 5% 4 21%	3960
January	1st to 10th	Night	8% 17% 9% 25% 11% 7% 5% 3 3 3 10%	6349
	11th to 20th	Night	7% 16% 10% 23% 15% 6% 5% 3 3 3 10%	6315
	21st to end	Night	10% 13% 6% 16% 11% 8% 6% 4 5% 5% 18%	6996
February	1st to 10th	Night	11% 15% 6% 17% 10% 7% 5% 3 4 5% 17%	2657
	11th to 20th	Night	9% 14% 7% 18% 11% 8% 6% 3 4 3 17%	2338
	21st to end	Night	8% 18% 6% 13% 9% 6% 5% 3 5% 5% 23%	1980
March	1st to 10th	Night	13% 15% 6% 17% 7% 7% 6% 3 3 5% 17%	5364
	11th to 20th	Night	12% 18% 7% 11% 6% 5% 5% 3 5% 6% 24%	5217
	21st to end	Night	17% 17% 6% 13% 7% 4 4 3 3 4 23%	5103
April	1st to 10th	Night	18% 18% 5% 9% 5% 5% 3 3 4 5% 24%	2000
	11th to 20th	Night	16% 16% 4 8% 6% 5% 4 4 4 5% 28%	1936
	21st to end	Night	19% 14% 4 9% 4 3 4 3 5% 6% 29%	1762
May	1st to 10th	Night	25% 14% 4 7% 4 4 4 3 5% 6% 24%	2834
	11th to 20th	Night	18% 12% 3 9% 5% 5% 5% 4 5% 6% 28%	2591
	21st to end	Night	15% 7% 3 7% 4 4 5% 4 6% 9% 36%	2738
June	1st to 10th	Night	28% 10% 3 6% 4 4 4 3 4 8% 26%	1520
	11th to 20th	Night	19% 7% 2 7% 5% 6% 4 4 5% 7% 33%	1520
	21st to end	Night	21% 9% 2 7% 5% 5% 4 6% 6% 6% 29%	1520
July	1st to 10th	Night	16% 8% 3 8% 5% 6% 5% 5% 6% 8% 31%	2520
	11th to 20th	Night	18% 10% 3 8% 4 4 5% 3 6% 6% 32%	2520
	21st to end	Night	15% 8% 3 8% 6% 5% 5% 4 6% 7% 33%	2739
August	1st to 10th	Night	23% 11% 4 7% 4 4 4 4 4 6% 29%	2616
	11th to 20th	Night	18% 9% 3 8% 5% 4 6% 4 6% 7% 29%	2782
	21st to end	Night	16% 11% 2 5% 4 4 4 3 5% 7% 38%	3462
September	1st to 10th	Night	18% 7% 2 5% 4 2 3 3 5% 6% 44%	1900
	11th to 20th	Night	17% 8% 2 5% 3 3 3 2 5% 6% 46%	2072
	21st to end	Night	18% 8% 2 5% 4 4 5% 4 6% 7% 39%	2090
October	1st to 10th	Night	20% 12% 3 6% 5% 4 4 4 5% 6% 30%	2090
	11th to 20th	Night	17% 16% 3 7% 5% 4 4 3 5% 5% 30%	2379
	21st to end	Night	20% 18% 4 7% 5% 5% 5% 4 5% 5% 23%	2717
November	1st to 10th	Night	16% 17% 5% 9% 4 4 4 2 4 5% 28%	2537
	11th to 20th	Night	13% 17% 6% 13% 6% 4 3 4 4 6% 25%	2600
	21st to end	Night	14% 18% 8% 14% 8% 5% 3 3 4 5% 19%	2683
December	1st to 10th	Night	11% 17% 10% 24% 10% 5% 4 3 3 3 9%	4580
	11th to 20th	Night	13% 19% 8% 16% 9% 5% 4 4 4 3 15%	5208
	21st to end	Night	13% 16% 6% 16% 7% 5% 6% 3 4 4 20%	6996

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	67% 12% 9% 10% 2	3598
	11th to 20th	Day	59% 15% 10% 10% 5% 2	3600
	21st to end	Day	60% 10% 9% 12% 8% 1	3960
February	1st to 10th	Day	67% 7% 7% 12% 5% 2	1738
	11th to 20th	Day	63% 10% 10% 10% 6% 2	1957
	21st to end	Day	61% 8% 9% 12% 8% 2	1650
March	1st to 10th	Day	64% 8% 9% 7% 8% 4	4479
	11th to 20th	Day	48% 13% 13% 13% 10% 3	4740
	21st to end	Day	57% 9% 8% 13% 13% 1	5827
April	1st to 10th	Day	61% 5% 8% 14% 9% 2	2400
	11th to 20th	Day	54% 8% 9% 17% 11% 1	2413
	21st to end	Day	59% 6% 8% 16% 9% 2	2535
May	1st to 10th	Day	62% 8% 8% 16% 5% 1	4120
	11th to 20th	Day	55% 11% 14% 12% 7% 1	4335
	21st to end	Day	42% 11% 14% 23% 9% 1	4837
June	1st to 10th	Day	60% 6% 11% 17% 6%	2660
	11th to 20th	Day	49% 8% 11% 19% 12% 1	2660
	21st to end	Day	58% 8% 10% 15% 7% 1	2660
July	1st to 10th	Day	47% 9% 15% 20% 8%	4370
	11th to 20th	Day	45% 10% 17% 24% 4	4365
	21st to end	Day	49% 7% 12% 24% 7%	4661
August	1st to 10th	Day	55% 8% 14% 17% 6%	4266
	11th to 20th	Day	54% 9% 17% 15% 4	4084
	21st to end	Day	42% 10% 16% 17% 11% 3	4190
September	1st to 10th	Day	40% 8% 13% 27% 12% 1	2280
	11th to 20th	Day	39% 6% 10% 29% 14% 2	2106
	21st to end	Day	44% 9% 13% 22% 11% 1	2090
October	1st to 10th	Day	51% 6% 11% 20% 12% 1	3480
	11th to 20th	Day	49% 7% 10% 22% 11% 1	2949
	21st to end	Day	47% 7% 13% 22% 10% 1	3081
November	1st to 10th	Day	53% 8% 11% 16% 11% 1	1761
	11th to 20th	Day	58% 9% 9% 10% 11% 2	1800
	21st to end	Day	63% 8% 12% 13% 3	1715
December	1st to 10th	Day	75% 6% 8% 8% 2	2600
	11th to 20th	Day	63% 8% 6% 11% 10% 1	2986
	21st to end	Day	58% 11% 9% 9% 9% 4	3960
January	1st to 10th	Night	71% 11% 9% 7% 2	6349
	11th to 20th	Night	71% 11% 8% 6% 3 1	6360
	21st to end	Night	62% 11% 9% 9% 8% 2	6996
February	1st to 10th	Night	66% 9% 8% 9% 6% 1	2657
	11th to 20th	Night	65% 9% 8% 10% 7% 1	2340
	21st to end	Night	57% 9% 10% 14% 7% 2	1980
March	1st to 10th	Night	65% 8% 10% 9% 6% 1	5374
	11th to 20th	Night	53% 12% 14% 12% 8% 1	5218
	21st to end	Night	60% 8% 7% 11% 14% 1	5103
April	1st to 10th	Night	60% 8% 7% 14% 9% 1	2000
	11th to 20th	Night	56% 8% 8% 18% 10%	1936
	21st to end	Night	55% 7% 9% 15% 12% 2	1762
May	1st to 10th	Night	59% 8% 10% 16% 6% 1	2840
	11th to 20th	Night	53% 12% 11% 15% 7% 1	2592
	21st to end	Night	40% 13% 16% 18% 12% 1	2739
June	1st to 10th	Night	56% 8% 11% 17% 8%	1520
	11th to 20th	Night	48% 10% 12% 19% 9% 2	1520
	21st to end	Night	52% 10% 13% 17% 7%	1520
July	1st to 10th	Night	49% 8% 15% 18% 10%	2480
	11th to 20th	Night	49% 8% 14% 24% 6%	2472
	21st to end	Night	47% 9% 12% 23% 9%	2651
August	1st to 10th	Night	56% 7% 13% 18% 6%	2606
	11th to 20th	Night	48% 13% 16% 15% 7%	2809
	21st to end	Night	42% 8% 17% 19% 12% 2	3462
September	1st to 10th	Night	39% 8% 15% 27% 11%	1900
	11th to 20th	Night	39% 6% 11% 29% 13% 1	2072
	21st to end	Night	43% 9% 13% 22% 12% 2	2090
October	1st to 10th	Night	50% 8% 16% 17% 9% 1	3480
	11th to 20th	Night	53% 7% 10% 16% 12% 2	3954
	21st to end	Night	53% 6% 14% 18% 9% 1	4467
November	1st to 10th	Night	57% 7% 11% 16% 8% 1	2537
	11th to 20th	Night	57% 9% 10% 13% 9% 3	2600
	21st to end	Night	64% 9% 11% 11% 5%	2683
December	1st to 10th	Night	79% 7% 6% 6% 2	4580
	11th to 20th	Night	67% 12% 5% 8% 8%	5208
	21st to end	Night	61% 11% 8% 10% 6% 4	6996

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% 3	200
	11th to 20th	Day	33% 26% 25% 14% 2 1	200
	21st to end	Day	24% 28% 30% 14% 4	220
February	1st to 10th	Day	37% 28% 21% 12% 1	300
	11th to 20th	Day	32% 27% 28% 11% 2	496
	21st to end	Day	29% 24% 30% 14% 2	414
March	1st to 10th	Day	30% 24% 27% 15% 3	500
	11th to 20th	Day	30% 27% 27% 12% 3 1	500
	21st to end	Day	33% 24% 24% 13% 5% 2	550
April	1st to 10th	Day	37% 22% 23% 13% 4 1	500
	11th to 20th	Day	31% 28% 21% 13% 5% 2	492
	21st to end	Day	33% 22% 27% 12% 4 2	480
May	1st to 10th	Day	35% 21% 25% 14% 3 3	463
	11th to 20th	Day	28% 16% 31% 18% 6% 2	487
	21st to end	Day	20% 20% 32% 21% 6%	529
June	1st to 10th	Day	32% 17% 31% 12% 7% 1	490
	11th to 20th	Day	21% 16% 34% 20% 8% 1	490
	21st to end	Day	27% 20% 28% 17% 6% 2	490
July	1st to 10th	Day	20% 15% 29% 23% 11% 2	485
	11th to 20th	Day	14% 14% 38% 24% 9% 2	484
	21st to end	Day	20% 13% 35% 24% 6% 2	532
August	1st to 10th	Day	17% 14% 30% 25% 13% 2	486
	11th to 20th	Day	20% 14% 29% 19% 14% 5%	479
	21st to end	Day	17% 15% 29% 23% 11% 6%	539
September	1st to 10th	Day	19% 16% 26% 21% 14% 4	490
	11th to 20th	Day	20% 13% 23% 21% 16% 7%	490
	21st to end	Day	19% 15% 29% 20% 13% 5%	490
October	1st to 10th	Day	27% 17% 22% 19% 12% 4	490
	11th to 20th	Day	27% 17% 25% 18% 12% 1	427
	21st to end	Day	31% 20% 25% 18% 5%	429
November	1st to 10th	Day	31% 20% 19% 23% 6% 1	395
	11th to 20th	Day	31% 18% 28% 16% 5% 2	400
	21st to end	Day	31% 23% 26% 15% 4 1	315
December	1st to 10th	Day	27% 29% 23% 15% 8%	200
	11th to 20th	Day	35% 25% 28% 9% 4 1	200
	21st to end	Day	33% 22% 26% 16% 2	220
January	1st to 10th	Night	26% 24% 26% 19% 4	800
	11th to 20th	Night	23% 25% 29% 20% 4	800
	21st to end	Night	18% 23% 36% 19% 4	880
February	1st to 10th	Night	24% 23% 33% 18% 3	800
	11th to 20th	Night	24% 26% 31% 16% 3	783
	21st to end	Night	24% 21% 32% 20% 3	660
March	1st to 10th	Night	28% 20% 29% 20% 3	800
	11th to 20th	Night	25% 22% 28% 20% 6%	800
	21st to end	Night	28% 21% 24% 20% 6% 1	880
April	1st to 10th	Night	31% 21% 24% 19% 4	800
	11th to 20th	Night	25% 21% 24% 24% 5% 1	752
	21st to end	Night	29% 17% 29% 19% 6%	588
May	1st to 10th	Night	29% 13% 25% 23% 8% 1	570
	11th to 20th	Night	20% 13% 31% 27% 9% 1	431
	21st to end	Night	20% 11% 20% 38% 11%	411
June	1st to 10th	Night	30% 10% 22% 29% 9%	380
	11th to 20th	Night	18% 12% 19% 37% 14%	380
	21st to end	Night	23% 9% 21% 37% 10%	380
July	1st to 10th	Night	17% 5% 21% 42% 14% 1	370
	11th to 20th	Night	18% 4 20% 40% 16% 2	368
	21st to end	Night	18% 4 20% 41% 15% 1	416
August	1st to 10th	Night	18% 4 17% 42% 17% 2	436
	11th to 20th	Night	18% 8% 23% 32% 17% 2	562
	21st to end	Night	19% 6% 20% 33% 19% 3	822
September	1st to 10th	Night	19% 9% 20% 32% 17% 2	760
	11th to 20th	Night	21% 8% 17% 30% 21% 4	760
	21st to end	Night	21% 11% 20% 29% 16% 3	760
October	1st to 10th	Night	26% 11% 22% 26% 13% 2	760
	11th to 20th	Night	26% 14% 24% 24% 10% 2	760
	21st to end	Night	31% 16% 26% 21% 5%	836
November	1st to 10th	Night	28% 17% 21% 25% 7% 1	780
	11th to 20th	Night	25% 19% 27% 21% 7% 2	800
	21st to end	Night	27% 22% 25% 20% 5% 2	800
December	1st to 10th	Night	28% 24% 25% 19% 4	800
	11th to 20th	Night	28% 21% 27% 20% 4	800
	21st to end	Night	29% 21% 29% 19% 3	880

Page generated at 2025-04-23 09:25:02. Version ac07

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