Timerson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Timerson Observatory clear sky chart from 2005-11-06 to 2024-08-30.

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% 11% 4 9% 6% 5% 5% 4 6% 7% 30%	95901
	Night	16% 12% 4 9% 6% 5% 4 4 5% 6% 29%	93151
Transparency	Day	51% 9% 13% 18% 9% 1	95621
	Night	53% 9% 12% 17% 8% 1	92984
Seeing	Day	22% 17% 30% 19% 9% 3	14354
	Night	22% 16% 29% 23% 9% 1	23594

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	14% 22% 9% 15% 6% 5% 5% 3 3 3 16%	2517
	11th to 20th	Day	13% 21% 8% 17% 9% 5% 4 3 4 4 12%	2565
	21st to end	Day	18% 21% 8% 14% 9% 6% 4 3 4 4 10%	3124
February	1st to 10th	Day	15% 17% 7% 15% 9% 5% 5% 4 4 4 15%	1710
	11th to 20th	Day	13% 17% 9% 17% 7% 5% 5% 3 4 4 15%	1663
	21st to end	Day	19% 15% 4 14% 8% 5% 4 3 5% 6% 18%	1553
March	1st to 10th	Day	19% 14% 5% 11% 5% 4 3 2 4 5% 28%	3290
	11th to 20th	Day	9% 20% 5% 8% 6% 5% 4 4 5% 5% 29%	3480
	21st to end	Day	16% 12% 4 11% 5% 5% 4 3 5% 6% 28%	3926
April	1st to 10th	Day	18% 15% 4 8% 5% 3 4 3 4 5% 30%	2280
	11th to 20th	Day	19% 11% 3 6% 5% 4 4 3 5% 6% 35%	2254
	21st to end	Day	20% 12% 4 7% 4 4 3 3 4 6% 32%	2370
May	1st to 10th	Day	20% 10% 3 7% 4 4 4 4 5% 6% 33%	4286
	11th to 20th	Day	16% 9% 3 8% 6% 5% 5% 4 5% 8% 31%	4398
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	4837
June	1st to 10th	Day	17% 7% 2 7% 5% 4 5% 3 7% 8% 35%	2660
	11th to 20th	Day	13% 6% 3 6% 4 4 5% 5% 7% 9% 37%	2660
	21st to end	Day	13% 6% 3 7% 6% 5% 5% 5% 7% 9% 36%	2660
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 6% 5% 7% 10% 39%	4440
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 9% 11% 38%	4440
	21st to end	Day	8% 5% 3 7% 7% 6% 6% 5% 7% 9% 37%	4734
August	1st to 10th	Day	12% 5% 3 6% 5% 6% 6% 5% 7% 8% 38%	2457
	11th to 20th	Day	12% 5% 2 8% 7% 7% 6% 5% 8% 8% 32%	2419
	21st to end	Day	14% 6% 2 7% 4 6% 5% 4 7% 9% 37%	2486
September	1st to 10th	Day	14% 7% 2 6% 4 4 6% 4 6% 8% 39%	2160
	11th to 20th	Day	14% 6% 2 6% 4 5% 4 4 5% 8% 42%	2160
	21st to end	Day	15% 8% 2 7% 7% 5% 5% 4 5% 7% 35%	1895
October	1st to 10th	Day	18% 8% 3 7% 6% 5% 5% 4 5% 6% 34%	1800
	11th to 20th	Day	19% 10% 4 8% 6% 5% 4 3 6% 6% 29%	1800
	21st to end	Day	26% 12% 4 8% 6% 5% 4 3 5% 5% 23%	1949
November	1st to 10th	Day	14% 13% 4 8% 6% 5% 4 4 4 5% 32%	1671
	11th to 20th	Day	13% 15% 6% 9% 6% 5% 4 3 6% 7% 25%	1539
	21st to end	Day	20% 16% 5% 9% 6% 4 5% 4 5% 6% 21%	1520
December	1st to 10th	Day	19% 17% 7% 13% 7% 4 5% 3 4 5% 16%	1520
	11th to 20th	Day	18% 17% 7% 15% 6% 4 4 3 5% 4 17%	1906
	21st to end	Day	26% 21% 6% 13% 5% 4 4 3 3 4 11%	2772
January	1st to 10th	Night	17% 19% 7% 15% 7% 5% 4 3 4 4 14%	4429
	11th to 20th	Night	13% 21% 8% 15% 9% 5% 4 3 4 5% 14%	4394
	21st to end	Night	21% 20% 7% 13% 9% 5% 4 3 3 3 11%	4532
February	1st to 10th	Night	16% 16% 6% 13% 7% 4 5% 3 4 6% 20%	2470
	11th to 20th	Night	13% 14% 6% 14% 8% 6% 6% 3 5% 5% 20%	2403
	21st to end	Night	17% 12% 5% 15% 7% 5% 4 4 5% 5% 22%	1900
March	1st to 10th	Night	19% 12% 4 9% 6% 4 4 4 4 6% 29%	3546
	11th to 20th	Night	15% 17% 6% 9% 5% 4 4 4 6% 7% 24%	3479
	21st to end	Night	17% 10% 5% 10% 5% 4 3 3 4 6% 32%	3704
April	1st to 10th	Night	19% 11% 4 7% 7% 5% 4 3 5% 6% 29%	1900
	11th to 20th	Night	19% 10% 3 7% 5% 5% 4 3 4 6% 34%	1875
	21st to end	Night	18% 8% 3 8% 5% 4 4 3 6% 8% 34%	1825
May	1st to 10th	Night	23% 9% 3 9% 5% 4 5% 3 4 7% 29%	2654
	11th to 20th	Night	17% 8% 3 6% 5% 4 4 3 6% 9% 35%	2495
	21st to end	Night	11% 5% 3 6% 5% 4 5% 4 7% 8% 43%	2738
June	1st to 10th	Night	15% 7% 2 6% 4 4 5% 4 7% 8% 38%	1520
	11th to 20th	Night	11% 7% 3 6% 4 5% 4 5% 6% 8% 41%	1520
	21st to end	Night	10% 6% 2 7% 5% 5% 5% 4 7% 9% 41%	1520
July	1st to 10th	Night	10% 7% 3 7% 5% 5% 4 4 6% 9% 41%	2520
	11th to 20th	Night	9% 5% 2 6% 5% 5% 4 4 6% 9% 46%	2520
	21st to end	Night	11% 5% 3 7% 4 4 5% 5% 6% 8% 42%	2816
August	1st to 10th	Night	8% 6% 2 7% 5% 4 4 4 6% 9% 46%	1701
	11th to 20th	Night	11% 6% 2 7% 5% 4 6% 4 6% 7% 42%	1688
	21st to end	Night	9% 5% 2 7% 4 4 4 5% 6% 9% 46%	2075
September	1st to 10th	Night	14% 6% 2 6% 3 4 4 4 6% 7% 45%	1800
	11th to 20th	Night	13% 6% 2 7% 4 4 3 4 5% 8% 45%	1800
	21st to end	Night	14% 7% 2 7% 4 4 4 4 6% 8% 39%	2061
October	1st to 10th	Night	19% 8% 3 8% 5% 4 5% 4 5% 5% 35%	2160
	11th to 20th	Night	20% 9% 3 7% 5% 5% 4 4 5% 7% 32%	2160
	21st to end	Night	25% 12% 4 8% 5% 4 4 2 5% 5% 25%	2407
November	1st to 10th	Night	16% 12% 4 8% 5% 4 4 4 5% 7% 33%	2407
	11th to 20th	Night	16% 12% 3 8% 6% 5% 5% 4 6% 7% 28%	2640
	21st to end	Night	17% 17% 4 8% 6% 4 4 4 6% 6% 24%	2660
December	1st to 10th	Night	19% 16% 7% 9% 6% 6% 5% 4 5% 5% 18%	2660
	11th to 20th	Night	19% 17% 6% 12% 6% 5% 4 3 4 5% 20%	3288
	21st to end	Night	29% 17% 5% 10% 5% 4 4 3 5% 5% 12%	4884

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	70% 8% 11% 10% 2	2518
	11th to 20th	Day	72% 8% 10% 8% 2	2565
	21st to end	Day	76% 8% 10% 5% 1	3124
February	1st to 10th	Day	70% 8% 9% 10% 3	1710
	11th to 20th	Day	70% 8% 8% 11% 3	1672
	21st to end	Day	66% 6% 10% 12% 5% 1	1553
March	1st to 10th	Day	58% 7% 10% 20% 5%	3293
	11th to 20th	Day	52% 10% 15% 14% 9% 1	3480
	21st to end	Day	51% 9% 11% 21% 7% 1	3926
April	1st to 10th	Day	55% 6% 11% 17% 9% 1	2280
	11th to 20th	Day	50% 6% 11% 18% 13% 1	2254
	21st to end	Day	52% 7% 9% 17% 14% 2	2370
May	1st to 10th	Day	49% 8% 11% 18% 12% 1	4298
	11th to 20th	Day	48% 10% 13% 20% 7% 1	4402
	21st to end	Day	37% 10% 12% 25% 14% 2	4837
June	1st to 10th	Day	44% 8% 12% 18% 16% 1	2660
	11th to 20th	Day	40% 9% 15% 23% 13% 1	2660
	21st to end	Day	41% 9% 15% 20% 14% 1	2660
July	1st to 10th	Day	38% 7% 15% 27% 13% 1	4370
	11th to 20th	Day	35% 10% 16% 23% 15%	4365
	21st to end	Day	40% 10% 15% 23% 12% 1	4583
August	1st to 10th	Day	39% 10% 15% 22% 12% 1	2444
	11th to 20th	Day	44% 10% 16% 21% 9%	2419
	21st to end	Day	42% 9% 13% 24% 10% 1	2486
September	1st to 10th	Day	40% 9% 14% 26% 10% 1	2160
	11th to 20th	Day	39% 8% 13% 24% 16% 1	2160
	21st to end	Day	46% 8% 11% 22% 12% 1	1895
October	1st to 10th	Day	47% 9% 14% 17% 12% 1	1800
	11th to 20th	Day	53% 8% 14% 17% 7%	1800
	21st to end	Day	62% 8% 11% 13% 6% 1	1949
November	1st to 10th	Day	52% 9% 12% 16% 10% 2	1671
	11th to 20th	Day	56% 8% 14% 15% 6% 1	1539
	21st to end	Day	61% 9% 14% 14% 2	1520
December	1st to 10th	Day	69% 9% 11% 10% 2	1520
	11th to 20th	Day	68% 8% 13% 7% 3	1906
	21st to end	Day	76% 7% 9% 7% 1	2772
January	1st to 10th	Night	70% 10% 11% 6% 2	4429
	11th to 20th	Night	69% 10% 9% 9% 3	4394
	21st to end	Night	76% 7% 8% 7% 2	4532
February	1st to 10th	Night	64% 8% 10% 13% 5%	2470
	11th to 20th	Night	63% 8% 11% 13% 4 1	2405
	21st to end	Night	59% 9% 12% 12% 6%	1900
March	1st to 10th	Night	54% 8% 13% 19% 6%	3556
	11th to 20th	Night	57% 9% 13% 15% 6%	3480
	21st to end	Night	48% 10% 10% 21% 10% 1	3704
April	1st to 10th	Night	54% 7% 11% 18% 8% 1	1900
	11th to 20th	Night	51% 7% 10% 16% 14% 1	1875
	21st to end	Night	46% 7% 11% 20% 13% 3	1825
May	1st to 10th	Night	52% 10% 11% 15% 9% 3	2661
	11th to 20th	Night	44% 11% 16% 20% 8% 1	2496
	21st to end	Night	33% 11% 15% 20% 19% 2	2739
June	1st to 10th	Night	41% 9% 12% 21% 15% 1	1520
	11th to 20th	Night	37% 8% 15% 22% 16% 2	1520
	21st to end	Night	37% 11% 11% 25% 15% 1	1520
July	1st to 10th	Night	38% 7% 15% 22% 15% 2	2480
	11th to 20th	Night	33% 8% 14% 30% 14% 1	2472
	21st to end	Night	37% 8% 14% 24% 16% 1	2726
August	1st to 10th	Night	34% 8% 15% 29% 12% 1	1690
	11th to 20th	Night	38% 9% 15% 28% 9%	1688
	21st to end	Night	32% 9% 15% 29% 13% 2	2075
September	1st to 10th	Night	38% 8% 14% 25% 12% 2	1800
	11th to 20th	Night	36% 8% 13% 26% 16% 1	1800
	21st to end	Night	40% 9% 14% 24% 12% 1	2061
October	1st to 10th	Night	49% 8% 12% 18% 12% 1	2160
	11th to 20th	Night	49% 8% 15% 18% 9% 1	2160
	21st to end	Night	60% 7% 13% 12% 7% 1	2407
November	1st to 10th	Night	49% 8% 12% 19% 8% 2	2407
	11th to 20th	Night	52% 10% 14% 15% 7% 2	2640
	21st to end	Night	57% 10% 15% 14% 3	2660
December	1st to 10th	Night	65% 10% 14% 10% 2	2660
	11th to 20th	Night	65% 8% 11% 11% 3	3288
	21st to end	Night	72% 10% 9% 8% 1	4884

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	28% 26% 32% 9% 6%	180
	11th to 20th	Day	33% 29% 27% 10% 1 1	195
	21st to end	Day	24% 29% 33% 11% 3	297
February	1st to 10th	Day	31% 30% 31% 7%	270
	11th to 20th	Day	34% 28% 34% 4	270
	21st to end	Day	36% 22% 28% 12% 1	365
March	1st to 10th	Day	26% 23% 33% 14% 3 1	460
	11th to 20th	Day	29% 24% 31% 12% 3	460
	21st to end	Day	34% 21% 27% 14% 4 1	506
April	1st to 10th	Day	30% 21% 33% 12% 4 1	460
	11th to 20th	Day	31% 22% 24% 14% 6% 3	452
	21st to end	Day	29% 20% 28% 16% 6% 1	460
May	1st to 10th	Day	25% 19% 32% 15% 8% 2	463
	11th to 20th	Day	17% 16% 34% 23% 9% 2	487
	21st to end	Day	16% 13% 32% 23% 12% 4	529
June	1st to 10th	Day	20% 15% 30% 26% 7% 2	490
	11th to 20th	Day	14% 12% 33% 26% 12% 2	490
	21st to end	Day	14% 16% 37% 23% 9% 2	490
July	1st to 10th	Day	12% 9% 27% 30% 18% 4	485
	11th to 20th	Day	13% 8% 28% 29% 19% 4	484
	21st to end	Day	9% 9% 36% 30% 12% 3	532
August	1st to 10th	Day	12% 8% 29% 28% 18% 5%	486
	11th to 20th	Day	14% 7% 32% 25% 15% 7%	479
	21st to end	Day	12% 12% 29% 25% 15% 7%	532
September	1st to 10th	Day	16% 12% 24% 26% 14% 8%	450
	11th to 20th	Day	13% 10% 26% 24% 18% 9%	450
	21st to end	Day	17% 14% 29% 22% 14% 4	450
October	1st to 10th	Day	21% 15% 30% 17% 13% 4	450
	11th to 20th	Day	24% 18% 32% 18% 6% 2	450
	21st to end	Day	31% 20% 30% 15% 4	480
November	1st to 10th	Day	25% 19% 29% 19% 7% 1	365
	11th to 20th	Day	28% 25% 29% 15% 4	199
	21st to end	Day	33% 25% 28% 13% 1	180
December	1st to 10th	Day	29% 22% 32% 12% 4 1	180
	11th to 20th	Day	34% 24% 28% 12% 2	180
	21st to end	Day	35% 24% 31% 10% 1	198
January	1st to 10th	Night	26% 28% 30% 13% 3	760
	11th to 20th	Night	27% 24% 30% 16% 2 1	760
	21st to end	Night	22% 23% 35% 17% 3	836
February	1st to 10th	Night	27% 22% 34% 15% 1	760
	11th to 20th	Night	24% 26% 34% 14% 2	743
	21st to end	Night	26% 24% 32% 15% 2	628
March	1st to 10th	Night	26% 21% 33% 18% 3	760
	11th to 20th	Night	27% 21% 29% 19% 4	760
	21st to end	Night	26% 16% 33% 18% 6% 1	836
April	1st to 10th	Night	25% 17% 34% 21% 3	760
	11th to 20th	Night	24% 18% 30% 22% 5% 1	751
	21st to end	Night	22% 14% 29% 25% 9%	685
May	1st to 10th	Night	24% 9% 26% 30% 10% 1	469
	11th to 20th	Night	17% 7% 33% 34% 7% 1	374
	21st to end	Night	9% 8% 35% 30% 17%	411
June	1st to 10th	Night	16% 8% 29% 33% 15% 1	380
	11th to 20th	Night	13% 9% 27% 35% 15%	380
	21st to end	Night	12% 7% 33% 39% 9% 1	380
July	1st to 10th	Night	8% 4 24% 44% 20% 1	370
	11th to 20th	Night	11% 3 22% 42% 21% 1	368
	21st to end	Night	11% 5% 25% 42% 15% 2	457
August	1st to 10th	Night	12% 4 24% 35% 21% 3	567
	11th to 20th	Night	11% 5% 22% 34% 24% 3	564
	21st to end	Night	9% 7% 24% 35% 23% 1	827
September	1st to 10th	Night	15% 8% 23% 30% 21% 3	720
	11th to 20th	Night	14% 9% 21% 29% 23% 5%	720
	21st to end	Night	15% 12% 24% 27% 19% 3	720
October	1st to 10th	Night	23% 11% 27% 20% 17% 2	720
	11th to 20th	Night	24% 16% 30% 23% 6%	720
	21st to end	Night	30% 16% 32% 20% 2	792
November	1st to 10th	Night	24% 16% 31% 22% 7%	740
	11th to 20th	Night	22% 21% 33% 16% 6% 2	760
	21st to end	Night	26% 23% 29% 17% 5%	760
December	1st to 10th	Night	29% 23% 33% 13% 3	760
	11th to 20th	Night	27% 23% 31% 16% 3	760
	21st to end	Night	33% 24% 30% 13% 1	836

Page generated at 2024-08-27 09:49:38. Version ac07

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