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 2025-02-06.

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 10% 6% 5% 5% 4 5% 7% 29%	108636
	Night	16% 12% 5% 10% 6% 5% 4 4 5% 6% 28%	109610
Transparency	Day	51% 8% 12% 19% 9% 1	112239
	Night	53% 8% 11% 17% 9% 1	114170
Seeing	Day	22% 17% 30% 19% 9% 3	14826
	Night	22% 16% 29% 23% 9% 1	24231

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	12% 19% 8% 22% 8% 4 4 3 3 4 13%	3597
	11th to 20th	Day	12% 20% 8% 19% 9% 5% 4 3 4 5% 11%	3643
	21st to end	Day	15% 17% 7% 15% 8% 7% 5% 3 4 5% 13%	4466
February	1st to 10th	Day	15% 17% 7% 15% 9% 5% 5% 4 4 4 15%	1755
	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	18% 5% 3 6% 5% 5% 5% 4 6% 7% 37%	4104
	11th to 20th	Day	14% 5% 3 8% 6% 6% 6% 5% 7% 8% 32%	4017
	21st to end	Day	13% 7% 3 7% 4 5% 5% 3 6% 8% 40%	4180
September	1st to 10th	Day	13% 7% 2 6% 4 4 6% 4 6% 8% 40%	2280
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 8% 43%	2280
	21st to end	Day	16% 9% 2 7% 7% 5% 5% 4 5% 7% 34%	1999
October	1st to 10th	Day	17% 8% 3 7% 6% 5% 5% 4 5% 7% 35%	1900
	11th to 20th	Day	19% 10% 3 8% 6% 5% 4 3 6% 6% 30%	1900
	21st to end	Day	25% 12% 4 8% 5% 4 4 3 5% 6% 24%	2057
November	1st to 10th	Day	13% 13% 4 8% 6% 5% 4 4 5% 6% 32%	1761
	11th to 20th	Day	13% 15% 6% 9% 5% 5% 4 3 6% 7% 25%	1620
	21st to end	Day	20% 16% 5% 9% 6% 4 5% 4 6% 6% 21%	1600
December	1st to 10th	Day	17% 17% 7% 14% 8% 5% 5% 4 5% 5% 12%	2600
	11th to 20th	Day	18% 17% 6% 14% 5% 4 4 3 4 4 19%	2986
	21st to end	Day	20% 18% 6% 15% 8% 5% 4 3 4 5% 12%	3960
January	1st to 10th	Night	15% 17% 8% 23% 7% 5% 4 3 4 4 12%	6349
	11th to 20th	Night	10% 20% 8% 18% 8% 6% 5% 4 5% 5% 12%	6241
	21st to end	Night	15% 18% 7% 13% 8% 5% 5% 3 4 4 16%	6490
February	1st to 10th	Night	16% 16% 6% 13% 7% 4 5% 3 4 6% 20%	2536
	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	13% 8% 2 7% 4 4 4 4 6% 9% 40%	2825
	11th to 20th	Night	14% 6% 2 7% 5% 4 5% 4 6% 7% 39%	2785
	21st to end	Night	7% 5% 2 7% 5% 4 4 4 6% 9% 47%	3471
September	1st to 10th	Night	14% 6% 2 6% 3 4 4 4 5% 7% 46%	1900
	11th to 20th	Night	13% 6% 2 6% 4 4 3 4 5% 8% 46%	1900
	21st to end	Night	15% 8% 2 7% 4 4 4 4 6% 7% 37%	2177
October	1st to 10th	Night	19% 8% 3 7% 5% 4 5% 4 5% 5% 35%	2280
	11th to 20th	Night	20% 8% 3 7% 5% 5% 4 4 5% 7% 33%	2280
	21st to end	Night	24% 11% 4 8% 5% 4 4 3 5% 6% 26%	2541
November	1st to 10th	Night	16% 11% 4 8% 5% 4 4 4 4 7% 34%	2537
	11th to 20th	Night	16% 12% 3 8% 6% 4 4 4 6% 7% 28%	2779
	21st to end	Night	18% 17% 4 8% 6% 4 4 4 6% 6% 24%	2800
December	1st to 10th	Night	16% 17% 7% 14% 6% 6% 5% 4 5% 5% 14%	4580
	11th to 20th	Night	20% 17% 6% 11% 6% 4 4 3 4 4 21%	5208
	21st to end	Night	24% 17% 5% 12% 6% 4 4 3 5% 5% 14%	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	72% 8% 9% 9% 2	3598
	11th to 20th	Day	72% 7% 8% 7% 4 1	3673
	21st to end	Day	71% 7% 10% 9% 3	4466
February	1st to 10th	Day	71% 8% 9% 10% 3	1755
	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	44% 8% 13% 20% 14% 1	4091
	11th to 20th	Day	45% 9% 15% 24% 6%	4056
	21st to end	Day	41% 7% 11% 32% 8% 1	4180
September	1st to 10th	Day	39% 9% 13% 27% 11% 1	2280
	11th to 20th	Day	38% 8% 13% 25% 16% 1	2280
	21st to end	Day	47% 8% 12% 21% 11% 1	1999
October	1st to 10th	Day	39% 9% 14% 25% 13%	3160
	11th to 20th	Day	46% 6% 15% 21% 12%	3140
	21st to end	Day	47% 8% 14% 24% 7% 1	3371
November	1st to 10th	Day	52% 9% 12% 17% 9% 2	1761
	11th to 20th	Day	55% 7% 14% 16% 7% 1	1620
	21st to end	Day	61% 9% 14% 14% 2	1600
December	1st to 10th	Day	69% 10% 13% 7% 1	2600
	11th to 20th	Day	67% 6% 12% 8% 6%	2986
	21st to end	Day	73% 6% 12% 7% 2	3960
January	1st to 10th	Night	72% 10% 8% 8% 2	6349
	11th to 20th	Night	68% 10% 8% 9% 4	6286
	21st to end	Night	68% 7% 7% 9% 8% 1	6490
February	1st to 10th	Night	65% 8% 10% 12% 5%	2536
	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	40% 7% 14% 27% 11% 1	2814
	11th to 20th	Night	42% 8% 15% 27% 8%	2812
	21st to end	Night	32% 8% 13% 34% 12% 1	3471
September	1st to 10th	Night	37% 8% 14% 26% 13% 2	1900
	11th to 20th	Night	35% 8% 13% 27% 16% 1	1900
	21st to end	Night	43% 8% 14% 23% 11% 1	2177
October	1st to 10th	Night	46% 7% 9% 26% 12%	3800
	11th to 20th	Night	46% 7% 12% 21% 13% 1	3779
	21st to end	Night	46% 7% 13% 26% 8% 1	4177
November	1st to 10th	Night	49% 8% 12% 20% 8% 2	2537
	11th to 20th	Night	53% 9% 14% 16% 7% 2	2779
	21st to end	Night	57% 10% 15% 14% 3	2800
December	1st to 10th	Night	68% 9% 13% 9% 1	4580
	11th to 20th	Night	65% 8% 8% 11% 8% 1	5208
	21st to end	Night	71% 9% 8% 9% 3	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	29% 27% 31% 9% 5%	200
	11th to 20th	Day	33% 29% 27% 9% 1	217
	21st to end	Day	25% 29% 32% 10% 2	330
February	1st to 10th	Day	32% 30% 31% 7%	285
	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	13% 11% 29% 25% 15% 7%	539
September	1st to 10th	Day	16% 12% 24% 26% 14% 8%	490
	11th to 20th	Day	12% 9% 24% 24% 20% 11%	490
	21st to end	Day	18% 14% 28% 22% 13% 4	490
October	1st to 10th	Day	20% 16% 30% 18% 13% 4	490
	11th to 20th	Day	23% 18% 32% 18% 7% 2	490
	21st to end	Day	30% 20% 31% 16% 4	522
November	1st to 10th	Day	25% 19% 29% 19% 7% 1	395
	11th to 20th	Day	26% 26% 29% 15% 4	220
	21st to end	Day	35% 25% 28% 13% 1	200
December	1st to 10th	Day	30% 23% 33% 12% 4 1	200
	11th to 20th	Day	36% 24% 28% 11% 2	200
	21st to end	Day	33% 23% 30% 12% 2	220
January	1st to 10th	Night	26% 29% 30% 13% 3	800
	11th to 20th	Night	27% 25% 30% 16% 2 1	800
	21st to end	Night	22% 23% 36% 17% 3	880
February	1st to 10th	Night	28% 22% 33% 15% 1	781
	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% 25% 35% 23% 1	831
September	1st to 10th	Night	15% 8% 24% 30% 20% 3	760
	11th to 20th	Night	14% 8% 20% 29% 24% 5%	760
	21st to end	Night	16% 12% 23% 27% 19% 3	760
October	1st to 10th	Night	23% 11% 27% 20% 17% 2	760
	11th to 20th	Night	24% 16% 29% 24% 6% 1	760
	21st to end	Night	29% 16% 32% 20% 2	836
November	1st to 10th	Night	24% 17% 31% 21% 7%	780
	11th to 20th	Night	23% 21% 33% 16% 6% 2	800
	21st to end	Night	27% 23% 29% 16% 5%	800
December	1st to 10th	Night	29% 23% 33% 13% 3	800
	11th to 20th	Night	28% 24% 30% 16% 3	800
	21st to end	Night	32% 23% 29% 14% 1	880

Page generated at 2025-02-03 03:05:49. Version ac07

Copyright © 2025 Attilla Danko.