McCurdy Road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McCurdy Road clear sky chart from 2005-11-06 to 2025-06-10.

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	4 4 2 4 3 3 4 4 6% 8% 57%	123367
	Night	4 5% 2 5% 4 4 4 3 5% 7% 57%	123751
Transparency	Day	23% 5% 10% 24% 26% 13%	123110
	Night	26% 6% 10% 23% 24% 11%	123597
Seeing	Day	7% 7% 26% 31% 22% 7%	16323
	Night	7% 6% 28% 39% 18% 2	26386

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	1 6% 3 5% 2 3 3 3 6% 8% 59%	3638
	11th to 20th	Day	1 3 2 6% 5% 4 4 3 6% 7% 60%	3703
	21st to end	Day	2 6% 3 5% 4 3 3 2 4 6% 62%	4510
February	1st to 10th	Day	2 7% 3 5% 3 3 4 3 5% 8% 57%	1874
	11th to 20th	Day	1 5% 2 7% 4 4 3 3 5% 6% 59%	1949
	21st to end	Day	2 6% 2 6% 4 4 3 3 4 5% 59%	1650
March	1st to 10th	Day	2 3 1 4 3 3 4 4 5% 7% 65%	4500
	11th to 20th	Day	3 8% 3 5% 3 4 3 3 5% 7% 55%	4770
	21st to end	Day	2 5% 2 5% 4 4 4 4 6% 9% 54%	5920
April	1st to 10th	Day	5% 6% 2 4 4 4 3 3 6% 6% 57%	2400
	11th to 20th	Day	7% 8% 2 5% 4 3 5% 3 6% 8% 50%	2371
	21st to end	Day	8% 5% 2 5% 4 4 4 3 7% 8% 50%	2400
May	1st to 10th	Day	12% 6% 2 5% 3 3 4 3 5% 6% 51%	5808
	11th to 20th	Day	6% 4 2 4 3 4 4 4 6% 9% 54%	5990
	21st to end	Day	8% 5% 1 4 3 4 4 4 7% 10% 51%	6925
June	1st to 10th	Day	6% 3 1 4 3 4 4 5% 9% 10% 51%	2788
	11th to 20th	Day	5% 3 1 3 4 3 4 4 6% 9% 57%	2660
	21st to end	Day	3 3 2 5% 4 5% 5% 5% 8% 9% 52%	2660
July	1st to 10th	Day	4 3 2 5% 4 4 6% 5% 8% 10% 50%	4430
	11th to 20th	Day	3 2 1 5% 5% 5% 6% 5% 8% 9% 50%	4430
	21st to end	Day	4 3 2 4 4 4 5% 4 7% 8% 54%	4778
August	1st to 10th	Day	9% 4 2 4 4 4 5% 5% 9% 12% 42%	3939
	11th to 20th	Day	4 3 1 4 4 4 5% 5% 7% 10% 52%	3726
	21st to end	Day	3 3 2 4 4 4 5% 5% 8% 10% 52%	4180
September	1st to 10th	Day	4 3 1 4 3 3 4 3 7% 8% 58%	2280
	11th to 20th	Day	6% 3 1 3 2 3 3 4 6% 6% 64%	2210
	21st to end	Day	6% 3 1 3 2 3 3 2 4 7% 68%	2090
October	1st to 10th	Day	5% 3 1 2 2 2 2 2 3 4 76%	3332
	11th to 20th	Day	4 4 2 5% 3 3 3 3 4 7% 62%	3150
	21st to end	Day	4 4 2 3 1 2 2 2 3 5% 73%	3256
November	1st to 10th	Day	3 4 1 3 3 3 3 2 6% 6% 65%	1763
	11th to 20th	Day	2 4 2 4 3 2 3 3 5% 5% 67%	1800
	21st to end	Day	2 5% 2 5% 3 2 3 2 5% 7% 65%	1800
December	1st to 10th	Day	1 6% 2 3 2 3 2 2 3 5% 71%	2657
	11th to 20th	Day	1 4 1 4 3 2 3 3 5% 7% 66%	3026
	21st to end	Day	2 5% 2 6% 4 3 3 3 5% 7% 60%	4004
January	1st to 10th	Night	1 7% 3 7% 4 4 4 3 5% 7% 55%	6327
	11th to 20th	Night	1 4 2 6% 4 4 4 3 5% 6% 61%	6322
	21st to end	Night	2 4 4 5% 3 3 3 3 4 6% 63%	6468
February	1st to 10th	Night	3 6% 2 5% 4 3 4 3 5% 7% 58%	2525
	11th to 20th	Night	3 8% 3 7% 3 4 4 3 6% 6% 52%	2338
	21st to end	Night	3 6% 2 5% 2 3 4 3 5% 6% 63%	1980
March	1st to 10th	Night	2 5% 2 5% 3 4 4 4 5% 6% 62%	5374
	11th to 20th	Night	5% 7% 2 7% 4 4 3 3 4 5% 55%	5205
	21st to end	Night	5% 6% 2 6% 4 4 4 4 5% 8% 52%	5033
April	1st to 10th	Night	5% 7% 2 5% 4 3 3 4 5% 7% 56%	2000
	11th to 20th	Night	9% 6% 2 5% 4 3 3 4 6% 8% 50%	1977
	21st to end	Night	11% 7% 2 4 4 4 4 4 5% 7% 47%	2000
May	1st to 10th	Night	12% 6% 2 5% 3 3 3 4 5% 7% 50%	4172
	11th to 20th	Night	7% 7% 2 5% 4 4 4 4 6% 8% 49%	3910
	21st to end	Night	11% 7% 2 4 4 4 5% 3 5% 6% 47%	3972
June	1st to 10th	Night	6% 3 1 5% 4 5% 3 5% 8% 8% 52%	1596
	11th to 20th	Night	4 3 2 3 3 3 5% 4 6% 9% 58%	1520
	21st to end	Night	5% 6% 1 5% 5% 4 5% 5% 7% 10% 48%	1520
July	1st to 10th	Night	6% 4 2 6% 4 5% 5% 5% 8% 9% 46%	2540
	11th to 20th	Night	3 3 1 4 5% 5% 7% 6% 9% 11% 46%	2540
	21st to end	Night	5% 4 2 4 4 4 4 4 7% 8% 53%	2782
August	1st to 10th	Night	11% 6% 2 9% 6% 6% 6% 5% 7% 7% 34%	2997
	11th to 20th	Night	6% 5% 2 8% 5% 5% 6% 5% 8% 9% 42%	3113
	21st to end	Night	3 3 2 5% 5% 5% 6% 6% 10% 12% 44%	3487
September	1st to 10th	Night	6% 4 2 6% 4 4 3 4 5% 9% 54%	1900
	11th to 20th	Night	6% 3 1 3 4 3 4 4 6% 8% 60%	1969
	21st to end	Night	6% 4 1 4 3 2 3 2 4 6% 64%	2090
October	1st to 10th	Night	5% 2 1 3 2 2 3 2 3 5% 70%	3630
	11th to 20th	Night	5% 5% 2 4 3 3 4 3 6% 7% 59%	3778
	21st to end	Night	3 4 2 3 2 3 2 3 4 5% 69%	4268
November	1st to 10th	Night	3 5% 2 3 3 2 3 3 4 7% 67%	2535
	11th to 20th	Night	2 4 2 3 2 2 3 2 4 5% 70%	2600
	21st to end	Night	3 5% 2 5% 3 3 2 3 4 6% 63%	2600
December	1st to 10th	Night	1 4 1 5% 2 2 2 2 4 6% 71%	4528
	11th to 20th	Night	1 4 2 5% 4 3 3 3 6% 7% 62%	5181
	21st to end	Night	2 6% 2 6% 4 4 5% 3 5% 7% 56%	6974

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	23% 3 7% 32% 24% 10%	3639
	11th to 20th	Day	23% 5% 9% 22% 28% 12%	3703
	21st to end	Day	25% 3 7% 24% 28% 13%	4510
February	1st to 10th	Day	26% 5% 11% 24% 23% 12%	1874
	11th to 20th	Day	27% 4 7% 26% 27% 9%	1959
	21st to end	Day	27% 3 7% 19% 24% 20%	1650
March	1st to 10th	Day	18% 4 6% 18% 31% 23%	4500
	11th to 20th	Day	27% 4 7% 22% 31% 9%	4770
	21st to end	Day	23% 6% 10% 37% 20% 4	5920
April	1st to 10th	Day	25% 5% 11% 25% 22% 12%	2400
	11th to 20th	Day	29% 6% 10% 24% 19% 12%	2374
	21st to end	Day	28% 6% 13% 25% 22% 6%	2400
May	1st to 10th	Day	30% 5% 11% 24% 20% 10%	5808
	11th to 20th	Day	23% 7% 12% 20% 24% 15%	5994
	21st to end	Day	25% 7% 14% 24% 21% 9%	6926
June	1st to 10th	Day	23% 8% 15% 27% 18% 10%	2788
	11th to 20th	Day	21% 5% 11% 18% 25% 19%	2660
	21st to end	Day	23% 8% 10% 22% 24% 13%	2660
July	1st to 10th	Day	23% 7% 12% 16% 27% 14%	4361
	11th to 20th	Day	21% 9% 14% 23% 24% 9%	4355
	21st to end	Day	23% 7% 12% 20% 20% 18%	4627
August	1st to 10th	Day	29% 10% 17% 27% 12% 5%	3925
	11th to 20th	Day	22% 8% 15% 21% 24% 11%	3762
	21st to end	Day	22% 7% 12% 25% 25% 11%	4179
September	1st to 10th	Day	21% 5% 9% 24% 25% 16%	2280
	11th to 20th	Day	19% 4 8% 17% 30% 21%	2210
	21st to end	Day	18% 4 6% 19% 36% 17%	2090
October	1st to 10th	Day	14% 2 5% 16% 36% 27%	3332
	11th to 20th	Day	21% 4 9% 22% 33% 10%	3150
	21st to end	Day	17% 2 5% 20% 39% 17%	3256
November	1st to 10th	Day	18% 2 9% 25% 28% 19%	1763
	11th to 20th	Day	19% 3 6% 28% 34% 12%	1800
	21st to end	Day	20% 3 7% 21% 30% 19%	1800
December	1st to 10th	Day	19% 2 7% 29% 34% 10%	2657
	11th to 20th	Day	18% 3 6% 28% 35% 9%	3024
	21st to end	Day	23% 5% 8% 28% 26% 11%	4004
January	1st to 10th	Night	28% 5% 7% 32% 22% 7%	6327
	11th to 20th	Night	23% 5% 9% 24% 26% 14%	6322
	21st to end	Night	22% 5% 9% 25% 27% 12%	6468
February	1st to 10th	Night	27% 5% 9% 25% 24% 11%	2525
	11th to 20th	Night	31% 5% 10% 25% 21% 7%	2338
	21st to end	Night	22% 4 6% 23% 28% 17%	1980
March	1st to 10th	Night	21% 5% 6% 15% 36% 17%	5374
	11th to 20th	Night	29% 4 11% 15% 26% 14%	5205
	21st to end	Night	29% 7% 12% 30% 19% 3	5033
April	1st to 10th	Night	27% 6% 9% 24% 23% 12%	2000
	11th to 20th	Night	31% 5% 11% 23% 19% 10%	1977
	21st to end	Night	35% 6% 12% 23% 18% 6%	2000
May	1st to 10th	Night	32% 8% 13% 26% 13% 7%	4170
	11th to 20th	Night	30% 7% 12% 23% 17% 11%	3911
	21st to end	Night	34% 9% 13% 22% 17% 5%	3972
June	1st to 10th	Night	25% 10% 19% 23% 15% 8%	1596
	11th to 20th	Night	21% 7% 16% 21% 19% 16%	1520
	21st to end	Night	30% 8% 10% 22% 20% 11%	1520
July	1st to 10th	Night	33% 7% 10% 21% 23% 5%	2500
	11th to 20th	Night	25% 9% 18% 24% 19% 5%	2492
	21st to end	Night	26% 8% 13% 19% 22% 12%	2695
August	1st to 10th	Night	46% 8% 15% 18% 8% 6%	2988
	11th to 20th	Night	36% 10% 13% 19% 18% 4	3143
	21st to end	Night	27% 10% 15% 26% 17% 5%	3487
September	1st to 10th	Night	26% 6% 11% 21% 23% 12%	1900
	11th to 20th	Night	19% 5% 11% 22% 26% 16%	1969
	21st to end	Night	22% 4 8% 19% 32% 14%	2090
October	1st to 10th	Night	18% 4 6% 20% 33% 19%	3630
	11th to 20th	Night	22% 5% 8% 27% 27% 11%	3778
	21st to end	Night	19% 3 7% 24% 29% 17%	4268
November	1st to 10th	Night	18% 3 9% 25% 27% 17%	2535
	11th to 20th	Night	18% 3 8% 24% 34% 14%	2600
	21st to end	Night	23% 3 8% 21% 31% 14%	2600
December	1st to 10th	Night	17% 3 7% 32% 32% 10%	4528
	11th to 20th	Night	22% 4 5% 24% 35% 10%	5182
	21st to end	Night	26% 5% 10% 22% 26% 11%	6974

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	7% 6% 28% 38% 18% 4	300
	11th to 20th	Day	7% 10% 30% 35% 15% 2	300
	21st to end	Day	4 10% 29% 34% 18% 4	330
February	1st to 10th	Day	5% 8% 44% 31% 9% 3	300
	11th to 20th	Day	2 8% 44% 33% 12% 1	300
	21st to end	Day	4 10% 45% 29% 9% 2	249
March	1st to 10th	Day	3 8% 35% 33% 18% 3	300
	11th to 20th	Day	9% 13% 31% 31% 13% 4	400
	21st to end	Day	9% 17% 39% 24% 9% 2	550
April	1st to 10th	Day	9% 15% 36% 27% 10% 3	500
	11th to 20th	Day	9% 18% 40% 21% 8% 3	492
	21st to end	Day	13% 13% 33% 28% 11% 2	500
May	1st to 10th	Day	14% 10% 32% 27% 13% 4	663
	11th to 20th	Day	12% 7% 28% 27% 20% 6%	725
	21st to end	Day	10% 8% 30% 28% 18% 6%	789
June	1st to 10th	Day	6% 5% 21% 30% 28% 9%	726
	11th to 20th	Day	5% 5% 26% 31% 26% 6%	680
	21st to end	Day	4 4 21% 35% 27% 9%	680
July	1st to 10th	Day	5% 3 15% 28% 38% 11%	671
	11th to 20th	Day	4 1 10% 32% 38% 15%	668
	21st to end	Day	6% 1 11% 27% 39% 17%	727
August	1st to 10th	Day	6% 2 16% 33% 29% 15%	487
	11th to 20th	Day	3 3 16% 34% 31% 12%	477
	21st to end	Day	4 1 16% 36% 30% 13%	539
September	1st to 10th	Day	4 1 19% 36% 27% 12%	490
	11th to 20th	Day	5% 1 25% 33% 24% 11%	420
	21st to end	Day	9% 3 19% 25% 27% 16%	300
October	1st to 10th	Day	9% 4 19% 24% 28% 15%	300
	11th to 20th	Day	4 5% 28% 32% 22% 10%	300
	21st to end	Day	9% 10% 25% 27% 22% 7%	330
November	1st to 10th	Day	5% 6% 33% 31% 18% 6%	300
	11th to 20th	Day	3 6% 30% 35% 22% 4	300
	21st to end	Day	6% 10% 24% 36% 17% 6%	300
December	1st to 10th	Day	4 9% 33% 31% 18% 5%	300
	11th to 20th	Day	6% 7% 30% 33% 21% 3	300
	21st to end	Day	5% 12% 33% 38% 10% 1	330
January	1st to 10th	Night	5% 5% 33% 40% 15% 3	1000
	11th to 20th	Night	5% 7% 37% 36% 12% 2	995
	21st to end	Night	4 4 30% 47% 13% 2	880
February	1st to 10th	Night	6% 5% 42% 39% 8% 1	800
	11th to 20th	Night	6% 6% 40% 38% 8% 1	784
	21st to end	Night	6% 8% 42% 36% 8% 1	660
March	1st to 10th	Night	5% 9% 36% 39% 11% 1	800
	11th to 20th	Night	8% 8% 31% 40% 13% 1	800
	21st to end	Night	9% 9% 40% 33% 9% 1	683
April	1st to 10th	Night	7% 11% 42% 32% 8%	600
	11th to 20th	Night	12% 13% 34% 33% 8%	593
	21st to end	Night	14% 13% 26% 36% 11%	600
May	1st to 10th	Night	13% 9% 33% 33% 12% 1	600
	11th to 20th	Night	13% 7% 26% 36% 17% 1	591
	21st to end	Night	11% 8% 34% 32% 14% 1	650
June	1st to 10th	Night	7% 6% 23% 44% 19% 1	599
	11th to 20th	Night	5% 4 31% 46% 14% 1	570
	21st to end	Night	6% 5% 21% 45% 23% 1	570
July	1st to 10th	Night	7% 3 16% 42% 30% 3	555
	11th to 20th	Night	5% 1 10% 45% 37% 3	552
	21st to end	Night	8% 1 10% 37% 40% 4	624
August	1st to 10th	Night	8% 3 12% 41% 34% 2	567
	11th to 20th	Night	6% 2 14% 47% 29% 2	564
	21st to end	Night	6% 1 11% 44% 34% 3	627
September	1st to 10th	Night	6% 3 14% 44% 29% 3	570
	11th to 20th	Night	6% 3 16% 45% 27% 3	570
	21st to end	Night	9% 3 21% 41% 24% 2	570
October	1st to 10th	Night	10% 6% 24% 36% 21% 3	655
	11th to 20th	Night	5% 6% 26% 38% 21% 4	760
	21st to end	Night	7% 8% 26% 34% 21% 3	922
November	1st to 10th	Night	5% 4 26% 43% 20% 2	975
	11th to 20th	Night	5% 5% 31% 41% 16% 2	1000
	21st to end	Night	7% 7% 28% 38% 17% 3	1000
December	1st to 10th	Night	3 6% 33% 42% 15% 2	1000
	11th to 20th	Night	5% 6% 30% 43% 15% 2	1000
	21st to end	Night	7% 9% 33% 40% 10% 1	1100

Page generated at 2025-06-07 08:28:20. Version ac07

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