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 2024-04-03.

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	9% 5% 2 4 4 2 3 3 4 6% 59%	78987
	Night	10% 6% 2 4 4 2 3 4 4 6% 54%	81182
Transparency	Day	27% 4 8% 20% 24% 18%	78705
	Night	31% 5% 9% 18% 21% 17%	80986
Seeing	Day	12% 11% 23% 28% 19% 6%	14456
	Night	12% 7% 17% 29% 28% 7%	23826

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 6% 6% 3 3 4 4 7% 37%	2671
	11th to 20th	Day	23% 10% 4 6% 5% 3 3 4 5% 5% 31%	2860
	21st to end	Day	23% 9% 4 6% 5% 3 4 4 5% 7% 31%	3146
February	1st to 10th	Day	14% 9% 2 5% 5% 2 4 4 5% 5% 45%	1710
	11th to 20th	Day	13% 8% 2 6% 5% 3 4 5% 5% 7% 43%	1684
	21st to end	Day	17% 6% 2 4 5% 3 3 4 5% 7% 43%	1570
March	1st to 10th	Day	16% 11% 4 7% 5% 3 5% 4 5% 6% 34%	2080
	11th to 20th	Day	14% 8% 3 7% 6% 3 4 5% 5% 7% 39%	2090
	21st to end	Day	14% 7% 2 5% 5% 4 5% 4 5% 7% 41%	2306
April	1st to 10th	Day	12% 8% 3 5% 6% 3 4 4 5% 9% 41%	2185
	11th to 20th	Day	8% 5% 2 4 5% 3 4 4 5% 7% 53%	2129
	21st to end	Day	4 4 2 5% 4 2 3 4 6% 8% 57%	2160
May	1st to 10th	Day	5% 4 1 4 4 1 4 3 5% 7% 62%	2328
	11th to 20th	Day	5% 3 1 3 4 2 4 4 5% 8% 61%	2361
	21st to end	Day	5% 3 1 3 3 2 4 4 6% 7% 61%	2723
June	1st to 10th	Day	4 4 2 3 4 2 3 4 4 9% 61%	2520
	11th to 20th	Day	2 1 2 2 1 2 2 4 7% 77%	2520
	21st to end	Day	2 1 1 2 1 2 2 3 4 83%	2520
July	1st to 10th	Day	1 1 1 1 2 2 2 3 85%	2520
	11th to 20th	Day	1 1 1 1 2 2 2 5% 83%	2381
	21st to end	Day	1 1 1 2 1 1 2 2 4 85%	2546
August	1st to 10th	Day	1 1 1 2 1 2 3 4 4 81%	2328
	11th to 20th	Day	1 1 1 1 1 1 2 2 4 86%	2254
	21st to end	Day	1 1 1 1 1 2 2 4 87%	2376
September	1st to 10th	Day	1 1 1 1 1 2 2 2 4 85%	2160
	11th to 20th	Day	2 2 1 2 3 2 2 3 4 6% 74%	2145
	21st to end	Day	2 1 2 2 1 2 2 4 5% 78%	1900
October	1st to 10th	Day	5% 3 2 3 2 2 2 3 3 5% 71%	1800
	11th to 20th	Day	6% 3 2 3 3 2 3 3 4 6% 67%	1800
	21st to end	Day	9% 3 1 3 3 2 3 3 5% 6% 62%	1980
November	1st to 10th	Day	9% 4 1 4 4 2 4 5% 5% 8% 53%	1826
	11th to 20th	Day	10% 6% 2 4 5% 3 4 4 6% 6% 49%	1646
	21st to end	Day	10% 5% 2 4 5% 3 4 4 6% 6% 52%	1520
December	1st to 10th	Day	14% 7% 3 5% 5% 2 4 4 4 6% 45%	1520
	11th to 20th	Day	26% 13% 4 6% 4 2 3 4 4 4 30%	1928
	21st to end	Day	21% 10% 3 5% 5% 3 4 4 6% 6% 32%	2794
January	1st to 10th	Night	14% 11% 3 6% 5% 3 4 5% 5% 8% 37%	4276
	11th to 20th	Night	20% 12% 3 8% 7% 3 4 4 4 5% 30%	4110
	21st to end	Night	23% 12% 3 7% 5% 3 4 4 4 6% 29%	4521
February	1st to 10th	Night	13% 6% 2 5% 5% 3 4 5% 5% 6% 47%	2470
	11th to 20th	Night	12% 7% 2 6% 5% 3 5% 5% 5% 7% 43%	2382
	21st to end	Night	12% 6% 2 4 5% 2 4 4 5% 6% 49%	1884
March	1st to 10th	Night	15% 9% 4 7% 6% 3 5% 5% 5% 6% 36%	2097
	11th to 20th	Night	13% 9% 3 5% 5% 3 4 4 5% 8% 41%	2090
	21st to end	Night	12% 8% 3 6% 5% 3 5% 4 4 5% 45%	2290
April	1st to 10th	Night	9% 6% 3 7% 5% 3 5% 4 5% 7% 47%	1820
	11th to 20th	Night	8% 4 2 5% 4 2 5% 4 5% 8% 53%	1779
	21st to end	Night	4 3 2 3 4 2 4 4 5% 8% 62%	1800
May	1st to 10th	Night	4 4 1 3 4 2 3 4 4 5% 66%	1630
	11th to 20th	Night	3 3 1 3 4 2 4 4 5% 7% 64%	1531
	21st to end	Night	3 2 2 2 3 2 3 4 5% 7% 66%	1552
June	1st to 10th	Night	4 4 2 3 3 2 4 3 5% 8% 62%	1440
	11th to 20th	Night	2 1 1 1 2 2 3 3 5% 80%	1440
	21st to end	Night	2 1 1 3 2 2 2 2 3 4 80%	1440
July	1st to 10th	Night	1 1 1 1 1 1 1 3 4 86%	1440
	11th to 20th	Night	1 1 1 1 2 1 2 2 2 4 84%	1574
	21st to end	Night	1 1 1 1 2 2 2 5% 86%	1773
August	1st to 10th	Night	1 1 2 2 2 2 3 4 82%	1611
	11th to 20th	Night	1 2 1 2 3 3 5% 83%	1646
	21st to end	Night	1 2 2 1 2 1 2 4 85%	1980
September	1st to 10th	Night	1 1 1 1 1 2 2 4 86%	1800
	11th to 20th	Night	2 2 1 3 3 1 3 3 4 6% 72%	1811
	21st to end	Night	2 1 2 2 1 3 3 5% 5% 76%	2059
October	1st to 10th	Night	4 3 1 4 3 2 2 2 4 5% 71%	2160
	11th to 20th	Night	4 2 2 3 3 3 4 4 5% 5% 66%	2160
	21st to end	Night	8% 2 1 3 3 2 3 4 4 6% 61%	2376
November	1st to 10th	Night	8% 7% 2 5% 4 3 4 5% 6% 7% 50%	2251
	11th to 20th	Night	10% 4 2 4 5% 3 4 5% 7% 7% 48%	2531
	21st to end	Night	8% 6% 2 5% 5% 3 4 4 5% 6% 53%	2660
December	1st to 10th	Night	16% 7% 3 5% 5% 2 4 4 5% 7% 44%	2660
	11th to 20th	Night	27% 9% 3 5% 5% 3 3 5% 5% 6% 30%	3276
	21st to end	Night	21% 10% 3 7% 5% 4 5% 4 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	50% 7% 9% 15% 14% 4	2080
	11th to 20th	Day	44% 6% 8% 20% 15% 7%	2090
	21st to end	Day	42% 7% 12% 18% 17% 4	2306
April	1st to 10th	Day	42% 5% 11% 21% 16% 5%	2185
	11th to 20th	Day	31% 5% 13% 23% 22% 7%	2132
	21st to end	Day	23% 7% 14% 29% 21% 7%	2160
May	1st to 10th	Day	21% 6% 10% 29% 26% 8%	2328
	11th to 20th	Day	21% 5% 9% 30% 27% 8%	2364
	21st to end	Day	21% 6% 13% 36% 19% 4	2724
June	1st to 10th	Day	21% 5% 12% 29% 26% 8%	2520
	11th to 20th	Day	9% 3 10% 23% 35% 19%	2520
	21st to end	Day	8% 2 4 16% 38% 32%	2520
July	1st to 10th	Day	6% 2 3 12% 31% 45%	2451
	11th to 20th	Day	6% 3 5% 11% 32% 44%	2309
	21st to end	Day	6% 2 2 10% 27% 53%	2405
August	1st to 10th	Day	8% 3 4 18% 33% 35%	2312
	11th to 20th	Day	5% 2 2 13% 38% 39%	2254
	21st to end	Day	5% 2 3 14% 37% 39%	2376
September	1st to 10th	Day	5% 2 3 10% 31% 49%	2160
	11th to 20th	Day	12% 4 5% 25% 37% 17%	2145
	21st to end	Day	10% 4 5% 21% 33% 27%	1900
October	1st to 10th	Day	18% 3 5% 17% 31% 25%	1800
	11th to 20th	Day	20% 4 8% 18% 24% 26%	1800
	21st to end	Day	24% 4 7% 18% 27% 20%	1980
November	1st to 10th	Day	29% 7% 7% 26% 19% 13%	1826
	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	47% 9% 10% 13% 17% 4	2097
	11th to 20th	Night	40% 6% 8% 21% 18% 8%	2090
	21st to end	Night	39% 7% 13% 21% 16% 5%	2290
April	1st to 10th	Night	35% 7% 14% 21% 17% 5%	1820
	11th to 20th	Night	27% 7% 13% 24% 20% 9%	1779
	21st to end	Night	21% 6% 12% 31% 25% 6%	1800
May	1st to 10th	Night	21% 5% 5% 26% 32% 10%	1630
	11th to 20th	Night	19% 5% 9% 27% 30% 10%	1532
	21st to end	Night	15% 6% 17% 33% 24% 5%	1552
June	1st to 10th	Night	20% 5% 10% 24% 31% 9%	1440
	11th to 20th	Night	9% 3 9% 22% 35% 22%	1440
	21st to end	Night	10% 3 3 13% 34% 37%	1440
July	1st to 10th	Night	5% 2 2 10% 31% 50%	1400
	11th to 20th	Night	5% 1 4 11% 26% 52%	1523
	21st to end	Night	5% 1 2 9% 22% 61%	1674
August	1st to 10th	Night	8% 2 2 12% 32% 44%	1602
	11th to 20th	Night	6% 2 3 10% 30% 48%	1646
	21st to end	Night	6% 2 3 12% 33% 44%	1980
September	1st to 10th	Night	4 1 3 11% 29% 53%	1800
	11th to 20th	Night	12% 3 5% 17% 37% 25%	1811
	21st to end	Night	8% 4 5% 22% 27% 33%	2059
October	1st to 10th	Night	17% 3 6% 18% 28% 28%	2160
	11th to 20th	Night	18% 6% 6% 18% 24% 28%	2160
	21st to end	Night	23% 5% 6% 19% 22% 25%	2376
November	1st to 10th	Night	30% 7% 10% 20% 18% 14%	2251
	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% 30% 19% 10% 3	429
	11th to 20th	Day	18% 21% 28% 20% 10% 3	412
	21st to end	Day	10% 18% 32% 21% 13% 5%	420
May	1st to 10th	Day	12% 17% 29% 26% 14% 3	423
	11th to 20th	Day	12% 15% 32% 22% 14% 6%	448
	21st to end	Day	9% 14% 23% 29% 20% 6%	485
June	1st to 10th	Day	8% 14% 25% 29% 17% 7%	450
	11th to 20th	Day	6% 11% 31% 30% 18% 3	450
	21st to end	Day	2 5% 26% 35% 24% 8%	450
July	1st to 10th	Day	3 3 21% 43% 25% 6%	446
	11th to 20th	Day	1 1 17% 41% 30% 10%	444
	21st to end	Day	2 11% 45% 28% 14%	487
August	1st to 10th	Day	1 2 20% 39% 28% 9%	447
	11th to 20th	Day	2 1 21% 37% 27% 12%	437
	21st to end	Day	1 3 16% 40% 29% 11%	495
September	1st to 10th	Day	1 3 18% 40% 29% 8%	450
	11th to 20th	Day	5% 5% 22% 35% 26% 7%	450
	21st to end	Day	3 9% 22% 35% 23% 8%	450
October	1st to 10th	Day	8% 9% 24% 27% 24% 8%	450
	11th to 20th	Day	9% 8% 18% 26% 29% 11%	450
	21st to end	Day	13% 9% 21% 26% 24% 7%	495
November	1st to 10th	Day	14% 11% 18% 25% 25% 8%	422
	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	728
	11th to 20th	Night	12% 15% 23% 27% 18% 5%	711
	21st to end	Night	8% 15% 26% 25% 21% 5%	720
May	1st to 10th	Night	8% 9% 26% 28% 24% 5%	550
	11th to 20th	Night	6% 6% 25% 30% 30% 4	469
	21st to end	Night	7% 10% 19% 29% 32% 4	389
June	1st to 10th	Night	7% 10% 21% 33% 26% 3	360
	11th to 20th	Night	3 8% 21% 36% 31% 2	360
	21st to end	Night	3 3 14% 40% 37% 4	360
July	1st to 10th	Night	1 3 14% 31% 44% 7%	350
	11th to 20th	Night	1 1 9% 29% 46% 14%	479
	21st to end	Night	1 8% 25% 51% 15%	591
August	1st to 10th	Night	1 1 9% 30% 42% 17%	537
	11th to 20th	Night	11% 31% 44% 14%	578
	21st to end	Night	1 1 8% 30% 50% 10%	792
September	1st to 10th	Night	1 3 8% 33% 46% 10%	720
	11th to 20th	Night	4 3 12% 34% 36% 11%	720
	21st to end	Night	3 5% 16% 28% 36% 12%	720
October	1st to 10th	Night	6% 4 15% 31% 34% 9%	720
	11th to 20th	Night	8% 5% 12% 28% 40% 8%	720
	21st to end	Night	10% 5% 12% 28% 31% 13%	792
November	1st to 10th	Night	14% 6% 14% 27% 31% 8%	740
	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

Page generated at 2024-03-31 03:08:55. Version ac07

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