HiRes 1
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the HiRes 1 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	4 6% 2 5% 4 4 4 3 5% 7% 56%	105585
	Night	5% 7% 2 6% 4 4 4 3 5% 7% 52%	102171
Transparency	Day	26% 6% 10% 18% 22% 18%	105350
	Night	30% 6% 10% 20% 20% 14%	101996
Seeing	Day	8% 9% 22% 32% 22% 8%	14851
	Night	8% 5% 19% 40% 23% 4	24670

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	5% 16% 6% 10% 6% 5% 5% 4 5% 6% 32%	2858
	11th to 20th	Day	7% 15% 5% 12% 7% 5% 4 4 4 6% 31%	2860
	21st to end	Day	7% 10% 3 8% 5% 5% 5% 5% 6% 11% 35%	3146
February	1st to 10th	Day	7% 10% 4 8% 5% 5% 4 4 6% 8% 39%	1710
	11th to 20th	Day	7% 9% 3 7% 4 4 5% 4 6% 8% 42%	1802
	21st to end	Day	5% 9% 4 8% 5% 4 4 4 6% 7% 44%	1570
March	1st to 10th	Day	4 9% 3 8% 5% 5% 4 4 6% 8% 45%	3283
	11th to 20th	Day	4 7% 2 6% 5% 5% 5% 4 6% 8% 48%	3490
	21st to end	Day	7% 14% 3 8% 6% 5% 6% 5% 6% 7% 32%	3825
April	1st to 10th	Day	6% 9% 2 6% 5% 5% 4 4 5% 7% 47%	2115
	11th to 20th	Day	7% 7% 3 7% 4 4 3 3 4 6% 51%	2399
	21st to end	Day	8% 6% 2 4 4 4 3 3 6% 7% 54%	2470
May	1st to 10th	Day	5% 7% 2 6% 4 4 5% 4 6% 7% 50%	4110
	11th to 20th	Day	4 3 1 4 3 3 4 4 4 7% 62%	4071
	21st to end	Day	5% 5% 1 4 4 3 4 3 5% 7% 58%	4477
June	1st to 10th	Day	3 3 1 4 3 4 3 4 6% 9% 59%	2470
	11th to 20th	Day	4 4 1 3 3 3 3 2 4 6% 68%	2490
	21st to end	Day	2 2 1 2 2 3 3 3 4 5% 74%	2660
July	1st to 10th	Day	1 1 2 2 2 2 2 4 5% 78%	4301
	11th to 20th	Day	2 2 1 3 3 3 4 4 6% 9% 63%	4110
	21st to end	Day	2 2 1 3 3 3 3 3 6% 8% 67%	4454
August	1st to 10th	Day	2 1 1 3 3 3 4 4 6% 7% 68%	4092
	11th to 20th	Day	1 1 1 3 3 3 4 4 5% 6% 68%	4028
	21st to end	Day	2 2 1 2 2 2 3 3 4 5% 75%	4464
September	1st to 10th	Day	2 2 1 2 2 2 2 3 4 6% 74%	2114
	11th to 20th	Day	2 2 1 4 3 3 3 3 4 6% 70%	2090
	21st to end	Day	3 2 1 2 2 2 3 2 3 5% 74%	2090
October	1st to 10th	Day	3 2 1 2 2 3 3 2 4 5% 72%	3408
	11th to 20th	Day	5% 5% 1 4 2 2 3 3 4 6% 65%	3150
	21st to end	Day	3 5% 2 4 3 3 2 3 4 6% 65%	3332
November	1st to 10th	Day	6% 5% 2 5% 3 4 5% 4 7% 7% 53%	1701
	11th to 20th	Day	7% 7% 1 6% 3 4 3 4 5% 7% 52%	1710
	21st to end	Day	6% 9% 3 5% 5% 3 5% 4 5% 6% 49%	1710
December	1st to 10th	Day	7% 9% 3 7% 4 4 3 4 5% 7% 45%	1710
	11th to 20th	Day	7% 11% 4 8% 5% 5% 5% 5% 7% 9% 33%	2169
	21st to end	Day	6% 10% 4 10% 6% 5% 5% 5% 7% 9% 35%	3146
January	1st to 10th	Night	7% 15% 4 7% 5% 4 4 3 5% 8% 37%	4097
	11th to 20th	Night	10% 13% 5% 10% 6% 5% 4 3 4 7% 31%	4110
	21st to end	Night	7% 12% 3 9% 5% 5% 4 4 7% 13% 33%	4521
February	1st to 10th	Night	6% 10% 3 6% 6% 5% 5% 4 6% 8% 42%	2470
	11th to 20th	Night	7% 11% 3 8% 4 4 4 3 5% 7% 45%	2263
	21st to end	Night	4 9% 3 7% 5% 4 4 5% 6% 7% 45%	1884
March	1st to 10th	Night	4 11% 4 9% 6% 5% 5% 4 5% 7% 40%	3589
	11th to 20th	Night	3 7% 2 6% 4 5% 5% 4 6% 8% 50%	3490
	21st to end	Night	7% 13% 4 9% 5% 4 5% 3 5% 6% 39%	3828
April	1st to 10th	Night	9% 9% 2 5% 4 3 4 2 4 7% 51%	2062
	11th to 20th	Night	6% 8% 2 6% 4 5% 4 4 5% 7% 50%	1727
	21st to end	Night	9% 6% 3 5% 4 3 4 3 5% 7% 51%	1710
May	1st to 10th	Night	9% 8% 2 6% 4 4 5% 4 7% 7% 45%	2860
	11th to 20th	Night	4 4 1 4 3 4 4 3 5% 7% 61%	2834
	21st to end	Night	6% 5% 2 5% 4 4 4 4 6% 7% 53%	3110
June	1st to 10th	Night	4 4 2 4 4 4 5% 4 6% 9% 54%	1710
	11th to 20th	Night	5% 3 1 4 3 3 3 3 4 6% 66%	1680
	21st to end	Night	2 2 1 3 4 3 4 3 6% 8% 64%	1520
July	1st to 10th	Night	1 2 1 2 2 2 3 3 4 5% 74%	2654
	11th to 20th	Night	3 5% 2 6% 5% 5% 6% 6% 7% 9% 46%	2860
	21st to end	Night	2 4 2 6% 4 4 4 4 7% 7% 56%	3109
August	1st to 10th	Night	2 3 2 6% 5% 4 6% 4 7% 8% 54%	2847
	11th to 20th	Night	1 2 1 4 3 3 4 3 5% 6% 67%	2811
	21st to end	Night	3 2 1 3 2 2 2 2 3 5% 75%	3202
September	1st to 10th	Night	3 2 1 3 3 3 2 3 4 6% 69%	2066
	11th to 20th	Night	3 3 1 4 2 2 3 2 3 6% 70%	2090
	21st to end	Night	5% 3 1 3 2 2 2 2 3 5% 73%	2090
October	1st to 10th	Night	3 2 1 3 2 3 3 3 4 5% 71%	3567
	11th to 20th	Night	6% 5% 1 3 2 2 3 3 5% 5% 65%	3778
	21st to end	Night	5% 3 1 4 3 3 4 4 6% 8% 60%	4210
November	1st to 10th	Night	6% 7% 2 4 3 3 3 3 6% 8% 54%	2450
	11th to 20th	Night	6% 5% 2 6% 4 3 4 3 5% 6% 56%	2470
	21st to end	Night	6% 8% 3 5% 4 4 3 2 5% 7% 52%	2470
December	1st to 10th	Night	8% 9% 2 6% 4 3 4 3 6% 7% 47%	2470
	11th to 20th	Night	8% 10% 3 7% 5% 5% 5% 4 6% 8% 41%	3041
	21st to end	Night	7% 11% 4 10% 7% 4 4 4 5% 8% 35%	4521

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	49% 10% 19% 17% 5%	2859
	11th to 20th	Day	51% 9% 19% 17% 4	2860
	21st to end	Day	41% 12% 23% 15% 7% 1	3146
February	1st to 10th	Day	42% 7% 17% 21% 10% 1	1710
	11th to 20th	Day	38% 7% 18% 23% 13% 1	1812
	21st to end	Day	36% 6% 16% 27% 13% 1	1570
March	1st to 10th	Day	34% 8% 14% 26% 18% 1	3283
	11th to 20th	Day	30% 9% 11% 33% 15% 2	3490
	21st to end	Day	44% 9% 15% 19% 10% 2	3825
April	1st to 10th	Day	36% 6% 11% 22% 17% 8%	2115
	11th to 20th	Day	34% 4 9% 22% 23% 6%	2402
	21st to end	Day	29% 5% 10% 26% 25% 6%	2470
May	1st to 10th	Day	27% 7% 12% 22% 24% 9%	4110
	11th to 20th	Day	20% 4 9% 21% 35% 11%	4074
	21st to end	Day	23% 7% 8% 23% 29% 11%	4477
June	1st to 10th	Day	20% 4 9% 18% 32% 16%	2470
	11th to 20th	Day	19% 3 6% 15% 30% 28%	2490
	21st to end	Day	12% 2 4 9% 27% 45%	2660
July	1st to 10th	Day	10% 2 4 6% 12% 66%	4235
	11th to 20th	Day	16% 4 4 10% 23% 44%	4041
	21st to end	Day	14% 4 6% 10% 26% 40%	4314
August	1st to 10th	Day	15% 4 5% 13% 28% 35%	4078
	11th to 20th	Day	15% 4 5% 9% 31% 35%	4067
	21st to end	Day	12% 3 4 13% 26% 43%	4463
September	1st to 10th	Day	12% 3 5% 13% 30% 36%	2114
	11th to 20th	Day	16% 4 7% 19% 26% 28%	2090
	21st to end	Day	14% 4 6% 17% 31% 27%	2090
October	1st to 10th	Day	16% 3 5% 11% 37% 28%	3408
	11th to 20th	Day	21% 3 5% 25% 33% 12%	3150
	21st to end	Day	22% 3 7% 26% 35% 7%	3332
November	1st to 10th	Day	29% 7% 13% 25% 22% 4	1701
	11th to 20th	Day	31% 6% 11% 33% 18% 1	1710
	21st to end	Day	35% 5% 15% 28% 15% 2	1710
December	1st to 10th	Day	36% 8% 18% 25% 11% 2	1710
	11th to 20th	Day	44% 10% 17% 20% 9%	2168
	21st to end	Day	43% 9% 17% 17% 14% 1	3146
January	1st to 10th	Night	41% 10% 16% 25% 8%	4097
	11th to 20th	Night	49% 10% 18% 16% 7% 1	4110
	21st to end	Night	40% 10% 22% 18% 8% 1	4521
February	1st to 10th	Night	39% 7% 16% 27% 9% 1	2470
	11th to 20th	Night	38% 6% 13% 24% 17% 2	2264
	21st to end	Night	35% 6% 12% 27% 17% 3	1884
March	1st to 10th	Night	40% 7% 13% 21% 17% 1	3589
	11th to 20th	Night	28% 8% 11% 34% 17% 3	3490
	21st to end	Night	41% 8% 11% 20% 17% 3	3828
April	1st to 10th	Night	33% 5% 9% 25% 19% 8%	2062
	11th to 20th	Night	31% 6% 10% 24% 23% 5%	1727
	21st to end	Night	31% 5% 11% 25% 24% 4	1710
May	1st to 10th	Night	32% 7% 10% 19% 24% 8%	2860
	11th to 20th	Night	20% 6% 8% 24% 32% 10%	2835
	21st to end	Night	25% 7% 10% 20% 33% 6%	3110
June	1st to 10th	Night	25% 7% 7% 19% 26% 16%	1710
	11th to 20th	Night	20% 3 6% 15% 29% 26%	1680
	21st to end	Night	16% 3 6% 11% 25% 39%	1520
July	1st to 10th	Night	12% 3 4 6% 9% 65%	2611
	11th to 20th	Night	29% 5% 5% 8% 20% 33%	2806
	21st to end	Night	24% 5% 7% 9% 19% 36%	3011
August	1st to 10th	Night	23% 5% 6% 13% 22% 31%	2838
	11th to 20th	Night	17% 4 6% 12% 26% 36%	2838
	21st to end	Night	14% 2 4 11% 20% 48%	3202
September	1st to 10th	Night	16% 3 6% 13% 25% 37%	2066
	11th to 20th	Night	17% 4 7% 16% 26% 31%	2090
	21st to end	Night	16% 3 4 13% 31% 32%	2090
October	1st to 10th	Night	17% 3 5% 11% 32% 32%	3567
	11th to 20th	Night	23% 3 4 21% 33% 16%	3778
	21st to end	Night	22% 4 5% 27% 35% 7%	4210
November	1st to 10th	Night	28% 4 10% 27% 23% 7%	2450
	11th to 20th	Night	28% 5% 11% 32% 21% 4	2470
	21st to end	Night	32% 4 11% 30% 20% 2	2470
December	1st to 10th	Night	35% 7% 14% 28% 14% 3	2470
	11th to 20th	Night	40% 7% 15% 27% 11%	3041
	21st to end	Night	45% 8% 14% 19% 13%	4521

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	14% 7% 27% 25% 22% 5%	270
	11th to 20th	Day	8% 6% 27% 36% 17% 7%	270
	21st to end	Day	9% 6% 16% 38% 23% 8%	297
February	1st to 10th	Day	14% 9% 28% 29% 14% 6%	270
	11th to 20th	Day	11% 8% 29% 33% 14% 5%	407
	21st to end	Day	6% 11% 32% 36% 12% 2	382
March	1st to 10th	Day	12% 12% 24% 32% 17% 2	460
	11th to 20th	Day	8% 14% 30% 27% 17% 5%	460
	21st to end	Day	15% 16% 31% 27% 11% 1	506
April	1st to 10th	Day	13% 15% 26% 26% 16% 4	460
	11th to 20th	Day	13% 20% 26% 26% 14% 1	452
	21st to end	Day	12% 17% 27% 24% 15% 5%	460
May	1st to 10th	Day	7% 16% 32% 30% 12% 4	463
	11th to 20th	Day	8% 9% 26% 29% 22% 5%	488
	21st to end	Day	8% 12% 21% 30% 22% 7%	529
June	1st to 10th	Day	5% 9% 23% 31% 23% 9%	490
	11th to 20th	Day	6% 13% 25% 29% 21% 6%	490
	21st to end	Day	2 6% 26% 36% 25% 6%	490
July	1st to 10th	Day	2 3 19% 39% 29% 8%	486
	11th to 20th	Day	4 3 17% 38% 29% 9%	484
	21st to end	Day	3 1 12% 38% 34% 11%	531
August	1st to 10th	Day	4 3 18% 39% 28% 9%	487
	11th to 20th	Day	4 3 17% 33% 29% 14%	477
	21st to end	Day	4 5% 16% 31% 34% 11%	539
September	1st to 10th	Day	4 5% 16% 30% 28% 17%	490
	11th to 20th	Day	5% 7% 18% 31% 28% 10%	490
	21st to end	Day	5% 8% 17% 28% 32% 10%	490
October	1st to 10th	Day	6% 9% 21% 25% 24% 15%	447
	11th to 20th	Day	5% 8% 17% 30% 24% 16%	300
	21st to end	Day	6% 8% 20% 32% 28% 5%	330
November	1st to 10th	Day	13% 8% 19% 31% 19% 10%	279
	11th to 20th	Day	7% 7% 22% 32% 23% 10%	270
	21st to end	Day	13% 8% 15% 28% 25% 11%	270
December	1st to 10th	Day	9% 8% 17% 38% 20% 9%	270
	11th to 20th	Day	11% 6% 20% 36% 22% 6%	270
	21st to end	Day	11% 10% 22% 36% 16% 4	297
January	1st to 10th	Night	13% 4 19% 36% 23% 6%	760
	11th to 20th	Night	9% 6% 17% 39% 24% 5%	760
	21st to end	Night	10% 5% 16% 41% 22% 6%	836
February	1st to 10th	Night	10% 6% 22% 41% 17% 4	760
	11th to 20th	Night	11% 4 21% 42% 20% 2	744
	21st to end	Night	8% 6% 25% 44% 16% 1	628
March	1st to 10th	Night	11% 8% 22% 43% 14% 3	760
	11th to 20th	Night	6% 7% 23% 40% 21% 2	760
	21st to end	Night	9% 9% 30% 37% 13% 2	836
April	1st to 10th	Night	13% 10% 23% 38% 15% 1	760
	11th to 20th	Night	8% 12% 28% 37% 14% 2	599
	21st to end	Night	11% 8% 25% 38% 16% 2	570
May	1st to 10th	Night	7% 8% 26% 42% 14% 2	570
	11th to 20th	Night	7% 5% 21% 39% 23% 4	561
	21st to end	Night	9% 9% 20% 33% 25% 3	617
June	1st to 10th	Night	5% 9% 17% 41% 26% 1	570
	11th to 20th	Night	8% 10% 20% 40% 23% 1	540
	21st to end	Night	2 2 20% 45% 29% 3	380
July	1st to 10th	Night	3 2 16% 43% 33% 3	429
	11th to 20th	Night	5% 4 16% 44% 28% 3	552
	21st to end	Night	5% 1 11% 42% 39% 2	624
August	1st to 10th	Night	4 2 18% 46% 29% 2	567
	11th to 20th	Night	3 2 18% 44% 30% 3	564
	21st to end	Night	4 3 16% 40% 33% 4	657
September	1st to 10th	Night	3 3 12% 40% 35% 7%	760
	11th to 20th	Night	4 3 18% 39% 30% 7%	760
	21st to end	Night	5% 4 16% 36% 31% 9%	760
October	1st to 10th	Night	6% 4 17% 39% 28% 5%	760
	11th to 20th	Night	7% 3 15% 39% 30% 6%	760
	21st to end	Night	6% 3 21% 37% 27% 6%	836
November	1st to 10th	Night	10% 4 17% 38% 25% 6%	754
	11th to 20th	Night	8% 4 17% 46% 21% 5%	760
	21st to end	Night	9% 4 17% 39% 24% 7%	760
December	1st to 10th	Night	10% 5% 16% 44% 21% 4	760
	11th to 20th	Night	15% 4 18% 38% 22% 2	760
	21st to end	Night	16% 6% 22% 38% 15% 3	836

Page generated at 2024-11-01 20:47:50. Version ac07

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