Taylor Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Taylor Dark Sky Site clear sky chart from 2005-11-06 to 2024-01-31.

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	14% 7% 3 6% 5% 3 5% 5% 5% 7% 40%	74971
	Night	15% 7% 3 6% 5% 3 4 4 5% 7% 42%	75175
Transparency	Day	42% 7% 12% 22% 14% 2	74672
	Night	42% 6% 11% 22% 16% 3	74995
Seeing	Day	15% 9% 25% 25% 18% 8%	14491
	Night	17% 8% 27% 31% 15% 2	24461

By Month

Percentage Cloud Cover SE (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	17% 11% 6% 9% 4 3 4 5% 5% 5% 32%	1517
	11th to 20th	Day	20% 12% 4 8% 7% 4 4 3 4 5% 30%	1520
	21st to end	Day	16% 14% 5% 7% 5% 3 5% 4 4 6% 31%	1805
February	1st to 10th	Day	17% 11% 6% 8% 5% 3 4 4 5% 6% 31%	1757
	11th to 20th	Day	16% 10% 4 7% 7% 4 4 5% 5% 7% 31%	1748
	21st to end	Day	17% 11% 5% 7% 5% 4 5% 4 5% 5% 32%	1480
March	1st to 10th	Day	18% 9% 4 6% 5% 4 4 3 4 6% 38%	1800
	11th to 20th	Day	17% 10% 4 7% 5% 3 4 4 4 6% 35%	1852
	21st to end	Day	21% 10% 5% 7% 6% 3 4 4 5% 6% 29%	2376
April	1st to 10th	Day	15% 6% 3 5% 5% 3 5% 4 5% 8% 41%	2160
	11th to 20th	Day	16% 7% 3 6% 6% 3 4 5% 4 6% 40%	2134
	21st to end	Day	19% 7% 2 6% 5% 3 5% 4 5% 6% 37%	2200
May	1st to 10th	Day	18% 7% 2 6% 5% 3 5% 5% 5% 7% 35%	2340
	11th to 20th	Day	18% 7% 3 5% 5% 3 4 5% 5% 7% 38%	2301
	21st to end	Day	8% 5% 2 6% 7% 5% 6% 6% 6% 9% 38%	2697
June	1st to 10th	Day	11% 5% 2 4 5% 3 4 5% 6% 9% 47%	2520
	11th to 20th	Day	7% 4 2 5% 6% 4 5% 5% 6% 7% 48%	2520
	21st to end	Day	8% 5% 2 6% 5% 3 5% 6% 7% 9% 44%	2520
July	1st to 10th	Day	9% 4 2 5% 5% 3 6% 6% 7% 10% 42%	2520
	11th to 20th	Day	7% 4 2 5% 4 3 5% 6% 7% 11% 48%	2520
	21st to end	Day	8% 4 2 4 6% 3 6% 5% 7% 9% 46%	2743
August	1st to 10th	Day	9% 4 2 4 6% 3 5% 5% 6% 11% 45%	2272
	11th to 20th	Day	9% 4 2 5% 6% 3 5% 6% 8% 11% 42%	2125
	21st to end	Day	6% 4 2 4 4 4 4 5% 6% 10% 51%	2376
September	1st to 10th	Day	12% 5% 3 5% 5% 3 4 5% 6% 7% 44%	2160
	11th to 20th	Day	9% 4 2 5% 5% 3 5% 4 6% 7% 49%	2026
	21st to end	Day	10% 4 2 4 4 3 4 4 5% 7% 54%	1980
October	1st to 10th	Day	12% 4 1 4 4 2 4 3 4 7% 53%	1979
	11th to 20th	Day	16% 5% 3 5% 4 3 4 4 5% 6% 46%	1800
	21st to end	Day	20% 6% 3 5% 4 2 4 4 5% 5% 43%	1810
November	1st to 10th	Day	10% 5% 2 4 4 3 3 3 4 7% 53%	1672
	11th to 20th	Day	16% 9% 3 5% 5% 2 3 4 4 7% 43%	1710
	21st to end	Day	17% 9% 4 7% 5% 2 4 4 4 5% 40%	1710
December	1st to 10th	Day	17% 11% 6% 6% 5% 2 4 4 4 5% 35%	1620
	11th to 20th	Day	17% 12% 6% 8% 5% 3 5% 4 5% 6% 30%	1918
	21st to end	Day	24% 16% 5% 9% 6% 3 4 4 4 5% 20%	2783
January	1st to 10th	Night	15% 9% 5% 8% 5% 2 5% 4 4 6% 35%	2648
	11th to 20th	Night	18% 11% 5% 9% 6% 3 4 3 3 4 32%	2660
	21st to end	Night	17% 10% 5% 8% 5% 4 4 4 5% 5% 33%	2776
February	1st to 10th	Night	20% 9% 4 8% 6% 3 4 5% 4 6% 31%	2200
	11th to 20th	Night	16% 9% 4 7% 7% 4 4 4 4 6% 36%	2098
	21st to end	Night	21% 9% 4 7% 5% 3 3 4 4 5% 36%	1776
March	1st to 10th	Night	17% 9% 4 6% 4 3 4 4 5% 5% 40%	2160
	11th to 20th	Night	18% 8% 4 6% 5% 3 4 4 4 7% 37%	2121
	21st to end	Night	21% 8% 3 6% 5% 3 4 4 5% 6% 34%	1980
April	1st to 10th	Night	12% 6% 3 7% 6% 3 4 4 5% 6% 45%	1800
	11th to 20th	Night	16% 6% 2 5% 4 3 4 4 4 7% 45%	1775
	21st to end	Night	18% 8% 3 6% 5% 3 5% 4 5% 7% 36%	1760
May	1st to 10th	Night	15% 6% 2 7% 6% 3 5% 5% 5% 7% 38%	1620
	11th to 20th	Night	15% 5% 3 6% 4 3 5% 5% 6% 7% 40%	1592
	21st to end	Night	10% 4 2 6% 5% 3 7% 4 8% 11% 40%	1575
June	1st to 10th	Night	9% 6% 3 5% 5% 3 4 3 6% 7% 50%	1440
	11th to 20th	Night	7% 4 2 4 3 3 6% 5% 6% 7% 53%	1440
	21st to end	Night	7% 3 3 5% 5% 3 5% 5% 7% 10% 48%	1440
July	1st to 10th	Night	8% 4 2 4 4 3 4 5% 6% 11% 48%	1440
	11th to 20th	Night	5% 4 2 5% 5% 3 4 5% 6% 7% 54%	1440
	21st to end	Night	6% 4 2 5% 4 3 5% 4 7% 8% 53%	1575
August	1st to 10th	Night	7% 4 2 4 4 4 4 6% 6% 10% 49%	1662
	11th to 20th	Night	6% 3 2 5% 5% 3 5% 6% 6% 9% 51%	1776
	21st to end	Night	6% 4 2 3 4 3 4 4 6% 10% 55%	1980
September	1st to 10th	Night	12% 5% 2 4 3 3 4 3 5% 7% 53%	1800
	11th to 20th	Night	7% 3 2 4 4 2 3 4 5% 7% 56%	1914
	21st to end	Night	11% 5% 2 4 3 3 4 4 4 7% 53%	1980
October	1st to 10th	Night	8% 4 2 3 4 3 4 4 5% 5% 57%	1980
	11th to 20th	Night	16% 5% 2 3 4 2 3 3 3 6% 51%	2158
	21st to end	Night	18% 8% 3 5% 5% 3 3 4 5% 5% 43%	2545
November	1st to 10th	Night	10% 6% 2 5% 4 2 4 4 4 6% 53%	2406
	11th to 20th	Night	13% 8% 2 4 5% 3 4 4 4 6% 47%	2470
	21st to end	Night	20% 8% 3 5% 4 3 3 3 4 6% 40%	2470
December	1st to 10th	Night	17% 10% 4 6% 6% 2 4 5% 5% 7% 34%	2555
	11th to 20th	Night	18% 9% 4 7% 5% 3 4 3 4 5% 37%	3279
	21st to end	Night	27% 16% 4 7% 6% 3 4 4 4 4 22%	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	53% 5% 10% 18% 13% 1	1518
	11th to 20th	Day	57% 5% 10% 20% 8%	1520
	21st to end	Day	54% 5% 12% 21% 7% 1	1805
February	1st to 10th	Day	54% 5% 11% 20% 9% 1	1757
	11th to 20th	Day	52% 5% 12% 20% 9% 2	1758
	21st to end	Day	52% 6% 9% 20% 10% 2	1480
March	1st to 10th	Day	47% 6% 11% 23% 13% 1	1800
	11th to 20th	Day	50% 5% 13% 20% 10% 1	1852
	21st to end	Day	55% 6% 11% 20% 7% 1	2376
April	1st to 10th	Day	41% 7% 14% 24% 15% 1	2160
	11th to 20th	Day	44% 6% 10% 23% 14% 3	2134
	21st to end	Day	46% 6% 11% 23% 11% 3	2200
May	1st to 10th	Day	48% 9% 14% 20% 9% 1	2340
	11th to 20th	Day	45% 8% 13% 18% 15% 1	2305
	21st to end	Day	39% 10% 15% 20% 13% 2	2697
June	1st to 10th	Day	33% 8% 15% 24% 17% 3	2520
	11th to 20th	Day	33% 8% 13% 22% 20% 4	2520
	21st to end	Day	34% 10% 16% 21% 15% 4	2520
July	1st to 10th	Day	34% 9% 16% 22% 14% 4	2451
	11th to 20th	Day	29% 9% 16% 29% 16% 2	2445
	21st to end	Day	32% 10% 15% 26% 15% 2	2591
August	1st to 10th	Day	32% 9% 15% 29% 15% 1	2257
	11th to 20th	Day	33% 10% 15% 27% 13% 2	2125
	21st to end	Day	28% 8% 15% 25% 17% 7%	2376
September	1st to 10th	Day	37% 7% 11% 22% 18% 4	2160
	11th to 20th	Day	32% 6% 12% 25% 22% 3	2026
	21st to end	Day	30% 4 11% 25% 26% 4	1980
October	1st to 10th	Day	31% 6% 11% 26% 22% 4	1979
	11th to 20th	Day	38% 5% 8% 24% 22% 3	1800
	21st to end	Day	44% 4 10% 25% 16% 1	1810
November	1st to 10th	Day	32% 5% 11% 30% 17% 6%	1672
	11th to 20th	Day	43% 4 10% 22% 17% 4	1710
	21st to end	Day	47% 6% 9% 22% 15% 1	1710
December	1st to 10th	Day	51% 6% 12% 19% 11% 1	1620
	11th to 20th	Day	55% 6% 8% 24% 7% 1	1915
	21st to end	Day	65% 7% 10% 12% 5% 1	2783
January	1st to 10th	Night	50% 6% 9% 22% 13% 1	2648
	11th to 20th	Night	57% 5% 10% 20% 9%	2660
	21st to end	Night	52% 5% 12% 20% 10% 1	2776
February	1st to 10th	Night	55% 7% 12% 17% 8% 1	2200
	11th to 20th	Night	49% 4 11% 20% 13% 2	2099
	21st to end	Night	50% 5% 11% 21% 10% 2	1776
March	1st to 10th	Night	46% 6% 8% 22% 15% 2	2160
	11th to 20th	Night	47% 5% 12% 21% 12% 2	2121
	21st to end	Night	51% 5% 13% 21% 8% 2	1980
April	1st to 10th	Night	39% 6% 11% 27% 14% 3	1800
	11th to 20th	Night	38% 6% 10% 22% 20% 4	1775
	21st to end	Night	46% 7% 10% 21% 13% 3	1760
May	1st to 10th	Night	44% 8% 13% 24% 11% 1	1620
	11th to 20th	Night	42% 8% 13% 21% 16% 1	1593
	21st to end	Night	36% 10% 16% 18% 16% 5%	1576
June	1st to 10th	Night	33% 5% 10% 25% 23% 3	1440
	11th to 20th	Night	28% 9% 11% 24% 23% 5%	1440
	21st to end	Night	28% 9% 15% 22% 19% 7%	1440
July	1st to 10th	Night	30% 10% 16% 22% 17% 5%	1400
	11th to 20th	Night	27% 7% 14% 28% 20% 4	1392
	21st to end	Night	27% 7% 14% 28% 21% 3	1487
August	1st to 10th	Night	28% 9% 16% 25% 19% 2	1653
	11th to 20th	Night	28% 9% 14% 27% 19% 2	1776
	21st to end	Night	24% 8% 14% 25% 22% 7%	1980
September	1st to 10th	Night	31% 5% 11% 27% 19% 6%	1800
	11th to 20th	Night	26% 5% 9% 28% 27% 5%	1914
	21st to end	Night	31% 5% 10% 22% 26% 6%	1980
October	1st to 10th	Night	28% 6% 11% 25% 26% 5%	1980
	11th to 20th	Night	35% 5% 8% 25% 23% 5%	2158
	21st to end	Night	43% 6% 9% 21% 17% 3	2545
November	1st to 10th	Night	33% 5% 11% 24% 22% 6%	2406
	11th to 20th	Night	37% 4 10% 24% 22% 3	2470
	21st to end	Night	46% 4 11% 23% 15% 1	2470
December	1st to 10th	Night	48% 6% 13% 20% 13% 1	2555
	11th to 20th	Night	48% 6% 11% 21% 14% 1	3281
	21st to end	Night	66% 6% 8% 13% 6% 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	23% 16% 34% 20% 7% 1	270
	11th to 20th	Day	29% 17% 32% 20% 3	270
	21st to end	Day	23% 17% 37% 17% 5%	294
February	1st to 10th	Day	27% 18% 38% 13% 5%	240
	11th to 20th	Day	23% 23% 31% 19% 4 1	240
	21st to end	Day	29% 13% 34% 19% 4 1	198
March	1st to 10th	Day	23% 18% 37% 19% 3	240
	11th to 20th	Day	26% 17% 36% 15% 6%	270
	21st to end	Day	27% 15% 34% 17% 6% 1	462
April	1st to 10th	Day	16% 13% 35% 25% 8% 2	420
	11th to 20th	Day	18% 16% 28% 22% 15% 2	412
	21st to end	Day	22% 12% 34% 22% 7% 3	420
May	1st to 10th	Day	21% 13% 29% 25% 10% 2	423
	11th to 20th	Day	20% 7% 24% 27% 15% 7%	447
	21st to end	Day	9% 4 29% 29% 19% 11%	651
June	1st to 10th	Day	11% 5% 22% 28% 25% 8%	630
	11th to 20th	Day	8% 5% 23% 33% 25% 7%	630
	21st to end	Day	9% 5% 27% 27% 23% 9%	630
July	1st to 10th	Day	9% 2 12% 26% 28% 22%	621
	11th to 20th	Day	7% 2 14% 36% 26% 15%	618
	21st to end	Day	10% 2 13% 31% 32% 12%	684
August	1st to 10th	Day	10% 4 9% 28% 34% 16%	474
	11th to 20th	Day	12% 3 14% 28% 29% 15%	439
	21st to end	Day	5% 1 13% 24% 38% 18%	495
September	1st to 10th	Day	12% 3 15% 25% 33% 12%	450
	11th to 20th	Day	8% 1 12% 30% 32% 17%	450
	21st to end	Day	14% 4 21% 24% 24% 13%	450
October	1st to 10th	Day	10% 3 26% 31% 23% 6%	449
	11th to 20th	Day	14% 13% 38% 23% 11% 1	270
	21st to end	Day	26% 18% 29% 23% 4	297
November	1st to 10th	Day	12% 10% 34% 24% 15% 5%	270
	11th to 20th	Day	16% 21% 29% 22% 10% 2	270
	21st to end	Day	20% 13% 31% 26% 9%	270
December	1st to 10th	Day	13% 20% 37% 20% 6% 4	270
	11th to 20th	Day	23% 13% 35% 21% 7%	270
	21st to end	Day	30% 17% 32% 15% 5% 1	297
January	1st to 10th	Night	19% 14% 36% 26% 4	950
	11th to 20th	Night	24% 13% 37% 21% 4	950
	21st to end	Night	21% 13% 37% 26% 3	1043
February	1st to 10th	Night	25% 11% 37% 24% 2	760
	11th to 20th	Night	21% 15% 35% 25% 3	703
	21st to end	Night	25% 13% 39% 23% 1	592
March	1st to 10th	Night	22% 12% 36% 26% 4	720
	11th to 20th	Night	21% 12% 36% 24% 6%	712
	21st to end	Night	25% 9% 31% 29% 6% 1	594
April	1st to 10th	Night	15% 12% 32% 34% 7%	540
	11th to 20th	Night	19% 10% 27% 31% 13% 1	533
	21st to end	Night	22% 7% 31% 32% 6% 1	540
May	1st to 10th	Night	16% 6% 34% 34% 9% 1	540
	11th to 20th	Night	15% 5% 26% 36% 16% 2	531
	21st to end	Night	12% 3 19% 36% 27% 3	584
June	1st to 10th	Night	11% 5% 19% 42% 22% 1	540
	11th to 20th	Night	7% 3 18% 47% 24% 1	540
	21st to end	Night	7% 2 22% 40% 29% 1	540
July	1st to 10th	Night	9% 2 11% 32% 36% 9%	525
	11th to 20th	Night	6% 3 13% 38% 36% 5%	522
	21st to end	Night	7% 2 12% 41% 34% 4	591
August	1st to 10th	Night	8% 1 8% 42% 35% 5%	537
	11th to 20th	Night	6% 1 10% 42% 37% 4	534
	21st to end	Night	6% 2 11% 33% 42% 6%	594
September	1st to 10th	Night	13% 2 12% 34% 34% 5%	540
	11th to 20th	Night	8% 2 13% 35% 37% 5%	654
	21st to end	Night	12% 4 20% 30% 28% 5%	720
October	1st to 10th	Night	9% 5% 22% 37% 22% 4	720
	11th to 20th	Night	18% 9% 29% 29% 13% 1	720
	21st to end	Night	22% 10% 32% 27% 7%	792
November	1st to 10th	Night	14% 7% 35% 31% 13% 1	740
	11th to 20th	Night	16% 11% 32% 31% 9%	760
	21st to end	Night	23% 11% 30% 28% 8%	760
December	1st to 10th	Night	21% 10% 37% 25% 6%	845
	11th to 20th	Night	24% 8% 32% 29% 7% 1	950
	21st to end	Night	30% 13% 31% 21% 4	1045

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