Taylor Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Taylor Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	7% 5% 1 4 3 3 3 3 4 6% 63%	105158
	Night	9% 6% 2 4 3 3 3 3 4 5% 58%	102610
Transparency	Day	23% 4 7% 19% 24% 23%	104916
	Night	27% 5% 8% 17% 22% 21%	102442
Seeing	Day	12% 11% 23% 28% 19% 6%	15316
	Night	12% 7% 17% 30% 28% 7%	24522

By Month

Percentage Cloud Cover SW (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	15% 11% 3 7% 5% 4 3 3 5% 7% 37%	2671
	11th to 20th	Day	23% 11% 4 7% 4 4 3 3 5% 5% 31%	2860
	21st to end	Day	23% 9% 4 7% 4 4 4 3 5% 7% 31%	3146
February	1st to 10th	Day	14% 9% 2 6% 4 3 4 4 5% 5% 44%	1710
	11th to 20th	Day	12% 8% 2 6% 4 3 4 4 6% 6% 43%	1684
	21st to end	Day	17% 7% 2 5% 4 4 3 4 5% 7% 43%	1570
March	1st to 10th	Day	18% 16% 4 9% 5% 5% 4 3 4 4 29%	3432
	11th to 20th	Day	10% 7% 2 5% 3 3 3 3 5% 6% 54%	3490
	21st to end	Day	15% 10% 3 7% 5% 5% 4 3 5% 7% 34%	3843
April	1st to 10th	Day	11% 9% 2 6% 5% 5% 3 3 5% 8% 41%	2280
	11th to 20th	Day	8% 6% 2 4 5% 4 4 4 5% 7% 52%	2249
	21st to end	Day	4 4 2 5% 3 3 3 4 6% 8% 57%	2280
May	1st to 10th	Day	4 3 1 3 2 2 2 2 4 6% 71%	4098
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 5% 77%	4183
	21st to end	Day	3 2 1 2 2 2 3 3 4 7% 73%	4813
June	1st to 10th	Day	4 4 1 4 3 3 3 3 5% 8% 61%	2660
	11th to 20th	Day	2 1 2 2 2 2 2 5% 6% 77%	2660
	21st to end	Day	2 1 1 2 1 1 2 3 4 83%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 91%	4420
	11th to 20th	Day	1 1 1 1 2 1 2 4 86%	4177
	21st to end	Day	1 1 1 1 1 2 3 90%	4455
August	1st to 10th	Day	1 1 1 1 2 2 3 5% 6% 78%	4091
	11th to 20th	Day	1 1 1 1 1 2 4 89%	3943
	21st to end	Day	1 1 2 1 1 1 1 2 4 86%	4180
September	1st to 10th	Day	1 1 1 1 2 1 3 4 85%	2280
	11th to 20th	Day	2 2 1 2 3 2 2 2 4 6% 73%	2264
	21st to end	Day	2 1 2 2 1 2 2 4 5% 79%	2005
October	1st to 10th	Day	3 2 1 2 1 2 2 2 3 6% 76%	3180
	11th to 20th	Day	6% 2 1 3 2 2 2 2 4 7% 69%	3161
	21st to end	Day	6% 2 1 3 4 4 5% 4 6% 7% 58%	3448
November	1st to 10th	Day	9% 4 2 4 4 3 4 3 5% 8% 53%	1857
	11th to 20th	Day	10% 7% 2 5% 5% 4 4 4 6% 6% 48%	1646
	21st to end	Day	9% 6% 2 4 4 3 4 3 6% 6% 51%	1520
December	1st to 10th	Day	14% 8% 3 6% 4 3 4 4 4 6% 45%	1520
	11th to 20th	Day	26% 15% 3 6% 3 3 3 3 4 4 30%	1928
	21st to end	Day	21% 10% 3 6% 4 4 4 4 6% 6% 32%	2794
January	1st to 10th	Night	14% 11% 2 7% 4 4 4 4 6% 8% 37%	4276
	11th to 20th	Night	20% 12% 3 9% 6% 4 4 3 3 5% 30%	4110
	21st to end	Night	23% 13% 3 8% 4 4 4 3 4 6% 29%	4521
February	1st to 10th	Night	13% 7% 2 5% 5% 4 3 4 5% 6% 46%	2470
	11th to 20th	Night	12% 7% 2 7% 4 4 5% 4 5% 7% 42%	2382
	21st to end	Night	12% 7% 1 5% 5% 3 4 3 5% 6% 49%	1884
March	1st to 10th	Night	16% 18% 5% 8% 4 4 3 3 4 5% 29%	3439
	11th to 20th	Night	11% 7% 2 4 2 3 3 3 4 6% 56%	3490
	21st to end	Night	12% 16% 5% 9% 5% 4 4 3 4 5% 34%	3808
April	1st to 10th	Night	8% 7% 2 7% 4 4 4 3 5% 7% 48%	1900
	11th to 20th	Night	8% 4 1 5% 4 4 4 4 5% 8% 53%	1879
	21st to end	Night	4 4 2 3 4 3 3 3 5% 8% 62%	1900
May	1st to 10th	Night	4 5% 1 3 2 2 2 2 3 4 71%	2870
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 4 79%	2715
	21st to end	Night	2 1 1 2 2 2 2 2 4 4 79%	2762
June	1st to 10th	Night	4 4 1 4 3 4 2 3 5% 8% 62%	1520
	11th to 20th	Night	2 1 1 1 2 2 2 3 4 81%	1520
	21st to end	Night	2 1 1 3 2 2 2 2 3 4 80%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 92%	2540
	11th to 20th	Night	1 1 1 2 1 1 1 2 4 85%	2786
	21st to end	Night	1 1 1 1 2 3 89%	3109
August	1st to 10th	Night	2 1 1 2 2 2 2 3 5% 79%	2848
	11th to 20th	Night	1 1 1 1 2 2 3 88%	2898
	21st to end	Night	1 1 2 1 1 1 1 2 3 85%	3498
September	1st to 10th	Night	1 1 1 1 1 1 2 4 86%	1900
	11th to 20th	Night	2 2 1 4 2 2 2 2 5% 6% 72%	1912
	21st to end	Night	2 1 2 1 2 3 3 5% 5% 77%	2174
October	1st to 10th	Night	2 2 1 3 2 2 2 2 3 4 78%	3800
	11th to 20th	Night	3 2 2 4 3 3 4 2 5% 5% 67%	3777
	21st to end	Night	6% 3 1 4 3 3 5% 4 6% 7% 59%	4121
November	1st to 10th	Night	8% 7% 2 5% 3 4 4 4 6% 7% 50%	2292
	11th to 20th	Night	10% 5% 2 5% 5% 4 5% 4 7% 7% 48%	2531
	21st to end	Night	8% 6% 2 6% 5% 4 4 3 5% 6% 53%	2660
December	1st to 10th	Night	16% 7% 3 6% 4 3 4 3 5% 7% 43%	2660
	11th to 20th	Night	27% 10% 2 5% 5% 3 4 4 5% 6% 30%	3276
	21st to end	Night	21% 10% 3 8% 4 5% 4 3 4 5% 32%	4862

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	47% 6% 10% 24% 9% 4	2671
	11th to 20th	Day	55% 5% 9% 13% 10% 9%	2860
	21st to end	Day	53% 4 8% 16% 13% 5%	3146
February	1st to 10th	Day	41% 5% 7% 18% 19% 9%	1710
	11th to 20th	Day	40% 5% 8% 20% 20% 8%	1693
	21st to end	Day	39% 7% 9% 22% 16% 6%	1570
March	1st to 10th	Day	58% 6% 7% 15% 11% 3	3432
	11th to 20th	Day	31% 5% 9% 28% 17% 11%	3490
	21st to end	Day	48% 7% 12% 20% 11% 2	3843
April	1st to 10th	Day	41% 6% 11% 23% 15% 4	2280
	11th to 20th	Day	31% 6% 13% 23% 21% 7%	2252
	21st to end	Day	22% 7% 14% 29% 22% 6%	2280
May	1st to 10th	Day	16% 5% 12% 30% 22% 16%	4098
	11th to 20th	Day	12% 3 5% 23% 42% 15%	4186
	21st to end	Day	12% 4 10% 43% 27% 5%	4814
June	1st to 10th	Day	21% 4 12% 29% 26% 8%	2660
	11th to 20th	Day	9% 3 9% 23% 36% 20%	2660
	21st to end	Day	8% 2 3 16% 37% 34%	2660
July	1st to 10th	Day	3 1 2 7% 18% 69%	4351
	11th to 20th	Day	5% 2 3 7% 20% 64%	4105
	21st to end	Day	4 1 1 7% 25% 62%	4315
August	1st to 10th	Day	8% 2 3 11% 25% 51%	4076
	11th to 20th	Day	3 1 2 12% 43% 39%	3982
	21st to end	Day	5% 2 4 12% 39% 38%	4179
September	1st to 10th	Day	5% 2 2 9% 30% 51%	2280
	11th to 20th	Day	12% 4 5% 25% 37% 16%	2264
	21st to end	Day	10% 3 5% 20% 33% 28%	2005
October	1st to 10th	Day	13% 2 3 12% 25% 44%	3180
	11th to 20th	Day	16% 4 5% 25% 31% 19%	3161
	21st to end	Day	23% 6% 9% 20% 30% 13%	3448
November	1st to 10th	Day	29% 7% 7% 26% 18% 13%	1857
	11th to 20th	Day	34% 5% 11% 21% 19% 9%	1646
	21st to end	Day	32% 6% 10% 18% 19% 15%	1520
December	1st to 10th	Day	40% 5% 7% 16% 20% 12%	1520
	11th to 20th	Day	59% 4 5% 12% 16% 5%	1928
	21st to end	Day	50% 5% 10% 18% 12% 4	2794
January	1st to 10th	Night	43% 5% 18% 19% 10% 4	4276
	11th to 20th	Night	56% 5% 9% 11% 11% 8%	4110
	21st to end	Night	54% 7% 7% 12% 13% 6%	4521
February	1st to 10th	Night	38% 6% 7% 18% 20% 12%	2470
	11th to 20th	Night	38% 6% 8% 19% 20% 8%	2384
	21st to end	Night	32% 6% 12% 24% 20% 5%	1884
March	1st to 10th	Night	53% 9% 11% 11% 14% 2	3439
	11th to 20th	Night	29% 4 7% 27% 22% 11%	3490
	21st to end	Night	46% 9% 11% 20% 10% 3	3808
April	1st to 10th	Night	35% 7% 14% 22% 17% 5%	1900
	11th to 20th	Night	27% 7% 13% 25% 19% 8%	1879
	21st to end	Night	20% 6% 12% 31% 25% 6%	1900
May	1st to 10th	Night	16% 5% 5% 30% 28% 15%	2870
	11th to 20th	Night	10% 3 5% 18% 39% 25%	2716
	21st to end	Night	8% 4 10% 39% 32% 7%	2762
June	1st to 10th	Night	20% 5% 10% 24% 31% 10%	1520
	11th to 20th	Night	8% 3 9% 21% 37% 22%	1520
	21st to end	Night	10% 3 3 12% 33% 38%	1520
July	1st to 10th	Night	3 1 1 6% 17% 72%	2500
	11th to 20th	Night	5% 1 3 6% 16% 68%	2735
	21st to end	Night	3 1 1 6% 23% 64%	3011
August	1st to 10th	Night	9% 2 2 7% 25% 55%	2839
	11th to 20th	Night	4 1 2 7% 42% 44%	2925
	21st to end	Night	7% 2 3 11% 36% 41%	3498
September	1st to 10th	Night	3 1 3 10% 27% 55%	1900
	11th to 20th	Night	13% 3 5% 19% 37% 24%	1912
	21st to end	Night	8% 4 4 22% 28% 34%	2174
October	1st to 10th	Night	13% 2 4 11% 22% 48%	3800
	11th to 20th	Night	15% 5% 8% 24% 28% 20%	3777
	21st to end	Night	21% 6% 7% 22% 25% 20%	4121
November	1st to 10th	Night	30% 7% 10% 21% 18% 14%	2292
	11th to 20th	Night	31% 6% 14% 20% 20% 10%	2531
	21st to end	Night	32% 4 8% 18% 23% 15%	2660
December	1st to 10th	Night	40% 6% 7% 14% 20% 12%	2660
	11th to 20th	Night	55% 4 6% 14% 16% 5%	3276
	21st to end	Night	52% 5% 11% 17% 12% 4	4862

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	36% 16% 19% 15% 12% 2	260
	11th to 20th	Day	26% 14% 24% 20% 14% 2	370
	21st to end	Day	20% 13% 24% 23% 15% 4	407
February	1st to 10th	Day	23% 13% 23% 21% 17% 2	370
	11th to 20th	Day	25% 18% 22% 22% 11% 1	374
	21st to end	Day	21% 17% 21% 28% 12% 1	382
March	1st to 10th	Day	30% 18% 24% 19% 8% 2	460
	11th to 20th	Day	24% 15% 26% 21% 12% 3	460
	21st to end	Day	22% 18% 32% 20% 7% 1	506
April	1st to 10th	Day	20% 18% 29% 20% 10% 3	460
	11th to 20th	Day	17% 20% 27% 20% 12% 3	452
	21st to end	Day	11% 18% 32% 21% 13% 5%	460
May	1st to 10th	Day	12% 17% 30% 26% 13% 3	463
	11th to 20th	Day	11% 14% 31% 22% 15% 7%	488
	21st to end	Day	8% 13% 23% 30% 19% 6%	529
June	1st to 10th	Day	8% 14% 26% 29% 16% 7%	490
	11th to 20th	Day	6% 12% 32% 29% 17% 4	490
	21st to end	Day	2 6% 27% 34% 23% 8%	490
July	1st to 10th	Day	2 3 20% 43% 25% 7%	486
	11th to 20th	Day	1 1 18% 41% 29% 10%	484
	21st to end	Day	2 12% 45% 27% 14%	531
August	1st to 10th	Day	1 2 21% 39% 27% 9%	487
	11th to 20th	Day	2 3 22% 36% 25% 11%	477
	21st to end	Day	2 3 16% 40% 28% 11%	539
September	1st to 10th	Day	1 3 20% 41% 28% 8%	490
	11th to 20th	Day	5% 6% 23% 34% 25% 7%	490
	21st to end	Day	3 8% 22% 35% 24% 8%	490
October	1st to 10th	Day	7% 9% 24% 28% 24% 8%	490
	11th to 20th	Day	10% 7% 19% 26% 28% 10%	490
	21st to end	Day	12% 10% 22% 25% 23% 7%	539
November	1st to 10th	Day	14% 11% 20% 24% 24% 7%	435
	11th to 20th	Day	11% 8% 18% 25% 24% 14%	239
	21st to end	Day	16% 9% 25% 23% 17% 9%	180
December	1st to 10th	Day	24% 13% 18% 21% 14% 10%	180
	11th to 20th	Day	27% 13% 19% 18% 13% 9%	180
	21st to end	Day	25% 11% 22% 24% 15% 4	198
January	1st to 10th	Night	22% 10% 14% 28% 21% 5%	760
	11th to 20th	Night	23% 8% 16% 32% 16% 5%	760
	21st to end	Night	20% 7% 18% 29% 21% 5%	836
February	1st to 10th	Night	21% 8% 15% 32% 21% 3	760
	11th to 20th	Night	18% 9% 21% 28% 20% 4	744
	21st to end	Night	19% 12% 19% 30% 18% 2	628
March	1st to 10th	Night	24% 11% 18% 27% 17% 3	760
	11th to 20th	Night	20% 8% 21% 28% 20% 4	760
	21st to end	Night	20% 11% 26% 27% 13% 3	836
April	1st to 10th	Night	16% 11% 26% 25% 19% 3	760
	11th to 20th	Night	12% 14% 23% 27% 19% 5%	751
	21st to end	Night	8% 15% 27% 25% 21% 5%	760
May	1st to 10th	Night	8% 9% 28% 28% 23% 5%	580
	11th to 20th	Night	5% 6% 24% 30% 32% 3	495
	21st to end	Night	7% 9% 20% 29% 32% 3	411
June	1st to 10th	Night	7% 10% 21% 33% 25% 3	380
	11th to 20th	Night	3 8% 22% 36% 29% 2	380
	21st to end	Night	2 3 14% 40% 37% 4	380
July	1st to 10th	Night	1 3 14% 31% 44% 6%	370
	11th to 20th	Night	1 1 10% 30% 46% 13%	507
	21st to end	Night	1 9% 25% 51% 14%	624
August	1st to 10th	Night	2 1 9% 31% 42% 16%	567
	11th to 20th	Night	1 14% 30% 42% 13%	611
	21st to end	Night	1 2 8% 30% 49% 10%	836
September	1st to 10th	Night	1 3 8% 34% 45% 9%	760
	11th to 20th	Night	4 4 13% 34% 35% 10%	760
	21st to end	Night	3 5% 15% 29% 37% 11%	760
October	1st to 10th	Night	6% 4 15% 31% 35% 9%	760
	11th to 20th	Night	7% 5% 13% 28% 39% 8%	760
	21st to end	Night	10% 6% 12% 30% 30% 12%	836
November	1st to 10th	Night	14% 7% 15% 26% 30% 8%	754
	11th to 20th	Night	13% 5% 16% 36% 25% 5%	760
	21st to end	Night	12% 9% 17% 32% 22% 8%	760
December	1st to 10th	Night	23% 7% 16% 28% 19% 7%	760
	11th to 20th	Night	26% 9% 14% 28% 17% 5%	760
	21st to end	Night	25% 9% 19% 29% 15% 3	836

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