Highland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Highland clear sky chart from 2005-11-06 to 2024-10-25.

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	6% 8% 2 6% 4 4 4 4 5% 7% 50%	100745
	Night	7% 8% 3 6% 4 4 4 4 5% 6% 48%	98252
Transparency	Day	32% 5% 11% 19% 19% 13%	100510
	Night	34% 6% 12% 20% 18% 11%	98076
Seeing	Day	11% 8% 24% 33% 20% 4	14767
	Night	12% 5% 20% 38% 23% 3	25321

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	9% 13% 6% 11% 6% 5% 5% 5% 6% 5% 28%	2858
	11th to 20th	Day	10% 18% 6% 14% 5% 4 3 3 5% 5% 27%	2860
	21st to end	Day	9% 16% 5% 9% 5% 4 4 4 4 6% 34%	3146
February	1st to 10th	Day	10% 14% 4 9% 5% 6% 5% 4 5% 6% 33%	1710
	11th to 20th	Day	9% 14% 4 9% 5% 5% 5% 5% 6% 6% 33%	1735
	21st to end	Day	9% 15% 4 8% 6% 4 4 4 6% 7% 32%	1570
March	1st to 10th	Day	6% 14% 5% 8% 5% 5% 6% 6% 6% 7% 32%	3369
	11th to 20th	Day	6% 11% 3 6% 4 5% 6% 5% 6% 7% 41%	3490
	21st to end	Day	9% 19% 5% 11% 6% 5% 5% 4 5% 7% 23%	3825
April	1st to 10th	Day	9% 9% 3 9% 4 4 5% 3 7% 7% 40%	2107
	11th to 20th	Day	8% 10% 2 7% 5% 4 5% 4 6% 7% 40%	2390
	21st to end	Day	8% 8% 3 6% 5% 4 4 3 5% 8% 45%	2470
May	1st to 10th	Day	8% 10% 4 7% 5% 5% 5% 4 6% 7% 39%	4110
	11th to 20th	Day	5% 4 1 4 3 4 4 4 6% 9% 55%	4071
	21st to end	Day	8% 6% 2 5% 4 4 5% 4 6% 8% 49%	4477
June	1st to 10th	Day	4 4 2 5% 3 4 3 4 6% 9% 55%	2470
	11th to 20th	Day	5% 4 2 4 4 3 3 3 4 6% 62%	2530
	21st to end	Day	3 2 1 3 2 3 4 3 4 6% 70%	2470
July	1st to 10th	Day	1 2 2 2 2 3 2 4 5% 78%	4110
	11th to 20th	Day	2 3 1 4 4 4 5% 4 7% 8% 57%	4110
	21st to end	Day	3 2 1 3 3 3 4 4 6% 7% 65%	4454
August	1st to 10th	Day	2 3 1 4 3 4 4 4 6% 7% 62%	4092
	11th to 20th	Day	2 2 1 4 4 4 4 3 5% 6% 64%	4028
	21st to end	Day	3 3 1 3 3 3 3 3 4 6% 69%	4473
September	1st to 10th	Day	3 3 1 3 2 3 3 3 5% 6% 69%	2143
	11th to 20th	Day	4 3 1 4 3 3 4 3 6% 6% 64%	2090
	21st to end	Day	6% 3 1 3 2 3 2 3 4 5% 68%	2090
October	1st to 10th	Day	9% 5% 2 4 4 3 3 4 5% 5% 56%	1998
	11th to 20th	Day	6% 6% 1 5% 3 3 3 3 4 7% 60%	1900
	21st to end	Day	6% 5% 2 5% 3 4 4 4 5% 6% 56%	2025
November	1st to 10th	Day	11% 6% 2 5% 5% 4 4 4 5% 6% 48%	1676
	11th to 20th	Day	11% 7% 2 5% 4 5% 4 3 6% 7% 45%	1710
	21st to end	Day	8% 9% 4 8% 5% 6% 4 3 6% 6% 41%	1596
December	1st to 10th	Day	12% 11% 3 8% 4 3 4 4 6% 8% 38%	1520
	11th to 20th	Day	12% 11% 3 10% 5% 5% 5% 5% 6% 7% 30%	1926
	21st to end	Day	8% 11% 4 9% 6% 5% 5% 5% 6% 8% 32%	3146
January	1st to 10th	Night	7% 12% 5% 8% 5% 5% 6% 7% 7% 7% 32%	4097
	11th to 20th	Night	13% 17% 4 12% 5% 5% 4 3 4 5% 28%	4110
	21st to end	Night	7% 15% 4 8% 5% 5% 4 4 6% 7% 35%	4521
February	1st to 10th	Night	9% 12% 3 7% 5% 4 5% 5% 6% 7% 37%	2470
	11th to 20th	Night	8% 11% 3 8% 5% 4 4 3 5% 6% 42%	2329
	21st to end	Night	7% 12% 3 8% 5% 5% 4 4 7% 6% 37%	1884
March	1st to 10th	Night	7% 11% 5% 10% 5% 5% 6% 5% 6% 7% 32%	3504
	11th to 20th	Night	5% 7% 2 6% 4 4 5% 4 6% 8% 48%	3490
	21st to end	Night	8% 16% 5% 10% 5% 4 4 4 5% 6% 33%	3828
April	1st to 10th	Night	11% 10% 2 6% 3 3 3 3 5% 7% 45%	2071
	11th to 20th	Night	7% 8% 2 6% 5% 4 6% 4 4 7% 46%	1734
	21st to end	Night	9% 6% 3 6% 5% 4 4 3 6% 5% 48%	1710
May	1st to 10th	Night	9% 10% 3 6% 5% 5% 5% 4 6% 7% 41%	2860
	11th to 20th	Night	5% 4 1 4 4 3 3 3 5% 7% 60%	2834
	21st to end	Night	9% 5% 2 5% 3 3 4 3 5% 8% 54%	3110
June	1st to 10th	Night	6% 5% 1 4 3 3 5% 4 6% 8% 55%	1708
	11th to 20th	Night	5% 4 1 4 2 3 2 3 4 6% 66%	1581
	21st to end	Night	3 3 1 4 2 2 3 3 5% 7% 67%	1710
July	1st to 10th	Night	4 2 1 3 3 3 2 3 4 4 71%	2860
	11th to 20th	Night	3 3 2 5% 4 5% 6% 5% 8% 8% 52%	2860
	21st to end	Night	3 5% 1 6% 3 4 4 4 5% 6% 59%	3109
August	1st to 10th	Night	3 2 1 4 4 4 5% 5% 6% 8% 59%	2847
	11th to 20th	Night	2 3 1 5% 4 4 4 4 6% 6% 60%	2811
	21st to end	Night	5% 3 1 3 2 3 3 3 4 5% 69%	3194
September	1st to 10th	Night	3 3 1 4 3 3 4 3 3 6% 66%	2033
	11th to 20th	Night	6% 3 1 3 3 3 4 3 5% 7% 63%	2090
	21st to end	Night	6% 3 2 4 2 2 2 2 3 5% 70%	2090
October	1st to 10th	Night	8% 4 1 4 3 3 4 3 4 6% 60%	2181
	11th to 20th	Night	7% 5% 2 5% 3 3 3 2 4 5% 62%	2280
	21st to end	Night	6% 5% 2 4 2 3 4 4 4 6% 60%	2436
November	1st to 10th	Night	10% 7% 2 4 3 3 3 4 6% 6% 51%	2400
	11th to 20th	Night	10% 5% 1 5% 4 3 3 4 6% 7% 52%	2470
	21st to end	Night	8% 8% 3 6% 4 3 4 4 5% 7% 47%	2560
December	1st to 10th	Night	10% 9% 3 6% 4 3 4 3 6% 6% 45%	2660
	11th to 20th	Night	14% 12% 3 6% 4 4 6% 4 5% 7% 35%	3271
	21st to end	Night	9% 11% 4 10% 6% 6% 5% 5% 5% 7% 32%	4549

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	51% 12% 17% 15% 4	2859
	11th to 20th	Day	60% 7% 16% 11% 5% 1	2860
	21st to end	Day	48% 13% 18% 13% 7% 1	3146
February	1st to 10th	Day	50% 10% 15% 15% 9% 1	1710
	11th to 20th	Day	49% 5% 16% 19% 11% 1	1744
	21st to end	Day	49% 5% 15% 20% 10% 1	1570
March	1st to 10th	Day	43% 8% 17% 21% 9% 2	3369
	11th to 20th	Day	34% 7% 14% 33% 11% 2	3490
	21st to end	Day	56% 5% 18% 14% 6% 2	3825
April	1st to 10th	Day	43% 5% 13% 19% 16% 5%	2107
	11th to 20th	Day	41% 4 14% 22% 17% 3	2393
	21st to end	Day	36% 4 12% 25% 20% 2	2470
May	1st to 10th	Day	38% 6% 11% 23% 18% 5%	4110
	11th to 20th	Day	22% 5% 8% 31% 29% 5%	4074
	21st to end	Day	29% 6% 10% 25% 26% 4	4477
June	1st to 10th	Day	24% 4 9% 21% 30% 12%	2470
	11th to 20th	Day	23% 3 7% 17% 29% 22%	2530
	21st to end	Day	16% 2 3 12% 27% 40%	2470
July	1st to 10th	Day	11% 2 4 7% 16% 60%	4046
	11th to 20th	Day	20% 5% 7% 12% 25% 31%	4041
	21st to end	Day	17% 4 8% 11% 25% 35%	4314
August	1st to 10th	Day	19% 4 7% 21% 25% 24%	4078
	11th to 20th	Day	20% 4 6% 17% 28% 25%	4067
	21st to end	Day	16% 3 5% 15% 31% 29%	4472
September	1st to 10th	Day	16% 3 6% 17% 28% 30%	2143
	11th to 20th	Day	19% 3 9% 19% 27% 22%	2090
	21st to end	Day	18% 4 5% 20% 33% 20%	2090
October	1st to 10th	Day	30% 5% 8% 21% 27% 10%	1998
	11th to 20th	Day	25% 4 9% 29% 27% 6%	1900
	21st to end	Day	27% 6% 16% 28% 21% 3	2025
November	1st to 10th	Day	37% 5% 14% 22% 18% 4	1676
	11th to 20th	Day	38% 5% 14% 26% 15% 1	1710
	21st to end	Day	42% 8% 15% 21% 13% 2	1596
December	1st to 10th	Day	45% 8% 19% 19% 8% 2	1520
	11th to 20th	Day	52% 8% 14% 20% 6%	1924
	21st to end	Day	45% 10% 19% 15% 10%	3146
January	1st to 10th	Night	45% 11% 20% 18% 5% 1	4097
	11th to 20th	Night	58% 10% 15% 12% 5% 1	4110
	21st to end	Night	45% 12% 22% 14% 7% 1	4521
February	1st to 10th	Night	45% 9% 18% 19% 8% 1	2470
	11th to 20th	Night	43% 5% 14% 22% 14% 1	2330
	21st to end	Night	43% 5% 15% 24% 11% 2	1884
March	1st to 10th	Night	45% 7% 14% 23% 10%	3504
	11th to 20th	Night	30% 6% 13% 34% 15% 2	3490
	21st to end	Night	49% 6% 12% 18% 13% 2	3828
April	1st to 10th	Night	38% 4 13% 22% 16% 7%	2071
	11th to 20th	Night	35% 4 13% 22% 22% 4	1734
	21st to end	Night	35% 5% 13% 22% 22% 2	1710
May	1st to 10th	Night	36% 5% 11% 23% 22% 3	2860
	11th to 20th	Night	23% 4 8% 29% 28% 8%	2835
	21st to end	Night	27% 5% 9% 28% 27% 4	3110
June	1st to 10th	Night	25% 5% 9% 21% 28% 12%	1708
	11th to 20th	Night	20% 3 7% 17% 30% 23%	1581
	21st to end	Night	17% 2 5% 9% 27% 39%	1710
July	1st to 10th	Night	16% 3 4 8% 11% 59%	2815
	11th to 20th	Night	25% 5% 7% 11% 23% 29%	2806
	21st to end	Night	25% 4 7% 13% 21% 31%	3011
August	1st to 10th	Night	21% 5% 9% 19% 23% 24%	2838
	11th to 20th	Night	24% 5% 7% 13% 26% 25%	2838
	21st to end	Night	18% 3 6% 12% 29% 32%	3194
September	1st to 10th	Night	20% 4 6% 14% 26% 32%	2033
	11th to 20th	Night	21% 3 7% 19% 26% 24%	2090
	21st to end	Night	20% 3 5% 16% 33% 24%	2090
October	1st to 10th	Night	26% 3 8% 22% 30% 11%	2181
	11th to 20th	Night	26% 3 8% 26% 28% 8%	2280
	21st to end	Night	25% 4 12% 30% 25% 4	2436
November	1st to 10th	Night	31% 5% 11% 26% 21% 5%	2400
	11th to 20th	Night	32% 5% 16% 28% 16% 3	2470
	21st to end	Night	36% 6% 16% 27% 13% 3	2560
December	1st to 10th	Night	39% 7% 19% 24% 10% 2	2660
	11th to 20th	Night	47% 8% 17% 21% 8%	3272
	21st to end	Night	48% 8% 20% 15% 8%	4549

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	27% 7% 21% 24% 15% 5%	270
	11th to 20th	Day	15% 9% 27% 30% 17% 2	270
	21st to end	Day	16% 3 27% 35% 16% 3	297
February	1st to 10th	Day	21% 9% 30% 27% 10% 2	270
	11th to 20th	Day	18% 8% 31% 30% 12% 2	340
	21st to end	Day	15% 12% 33% 28% 11% 2	382
March	1st to 10th	Day	17% 13% 28% 28% 13% 2	460
	11th to 20th	Day	15% 8% 27% 32% 17% 1	460
	21st to end	Day	20% 13% 31% 26% 11%	506
April	1st to 10th	Day	17% 13% 23% 30% 15% 2	460
	11th to 20th	Day	15% 16% 30% 26% 11% 2	452
	21st to end	Day	15% 14% 26% 26% 16% 3	460
May	1st to 10th	Day	11% 14% 29% 29% 13% 3	463
	11th to 20th	Day	11% 7% 25% 34% 18% 5%	488
	21st to end	Day	9% 10% 23% 30% 23% 5%	529
June	1st to 10th	Day	6% 8% 21% 37% 24% 4	490
	11th to 20th	Day	9% 9% 27% 31% 22% 2	550
	21st to end	Day	4 8% 26% 39% 19% 4	490
July	1st to 10th	Day	3 5% 20% 42% 25% 5%	486
	11th to 20th	Day	5% 2 19% 46% 24% 3	484
	21st to end	Day	3 3 13% 46% 28% 7%	531
August	1st to 10th	Day	7% 2 19% 42% 26% 3	487
	11th to 20th	Day	5% 4 21% 35% 28% 6%	477
	21st to end	Day	5% 5% 17% 39% 28% 5%	539
September	1st to 10th	Day	4 4 18% 37% 30% 7%	490
	11th to 20th	Day	9% 7% 22% 31% 26% 5%	490
	21st to end	Day	8% 8% 19% 33% 27% 6%	490
October	1st to 10th	Day	11% 8% 23% 29% 24% 5%	398
	11th to 20th	Day	10% 10% 21% 28% 24% 8%	300
	21st to end	Day	10% 7% 30% 34% 17% 2	311
November	1st to 10th	Day	20% 7% 21% 27% 20% 4	270
	11th to 20th	Day	12% 8% 20% 39% 14% 7%	270
	21st to end	Day	15% 5% 18% 31% 26% 5%	270
December	1st to 10th	Day	16% 7% 20% 32% 20% 5%	270
	11th to 20th	Day	15% 7% 23% 38% 14% 3	270
	21st to end	Day	23% 7% 20% 36% 12% 1	297
January	1st to 10th	Night	18% 4 20% 34% 20% 4	760
	11th to 20th	Night	16% 4 20% 35% 20% 4	760
	21st to end	Night	15% 5% 19% 39% 19% 3	836
February	1st to 10th	Night	18% 4 22% 40% 13% 3	760
	11th to 20th	Night	14% 6% 26% 37% 16% 1	744
	21st to end	Night	13% 7% 26% 39% 13% 1	628
March	1st to 10th	Night	18% 6% 24% 37% 13% 3	760
	11th to 20th	Night	11% 4 22% 40% 19% 2	760
	21st to end	Night	15% 9% 25% 36% 13% 2	836
April	1st to 10th	Night	18% 8% 21% 37% 15% 1	741
	11th to 20th	Night	10% 7% 28% 40% 13% 1	563
	21st to end	Night	13% 6% 23% 36% 20% 2	570
May	1st to 10th	Night	10% 8% 23% 41% 17% 1	570
	11th to 20th	Night	10% 4 18% 36% 29% 2	561
	21st to end	Night	12% 6% 18% 36% 25% 3	617
June	1st to 10th	Night	8% 6% 17% 38% 29% 2	570
	11th to 20th	Night	7% 5% 23% 42% 21% 2	570
	21st to end	Night	5% 2 18% 41% 31% 3	570
July	1st to 10th	Night	6% 3 17% 31% 39% 5%	555
	11th to 20th	Night	5% 1 11% 47% 31% 4	552
	21st to end	Night	6% 1 9% 33% 49% 2	624
August	1st to 10th	Night	5% 1 13% 44% 35% 2	567
	11th to 20th	Night	4 2 12% 42% 36% 3	564
	21st to end	Night	6% 3 9% 43% 37% 2	627
September	1st to 10th	Night	5% 3 13% 41% 35% 4	703
	11th to 20th	Night	8% 3 17% 34% 34% 5%	760
	21st to end	Night	8% 3 16% 32% 33% 7%	760
October	1st to 10th	Night	11% 4 20% 36% 25% 4	760
	11th to 20th	Night	10% 4 18% 37% 27% 4	760
	21st to end	Night	10% 4 20% 39% 24% 3	812
November	1st to 10th	Night	13% 5% 19% 36% 23% 4	740
	11th to 20th	Night	14% 4 20% 41% 18% 4	760
	21st to end	Night	13% 5% 20% 36% 21% 4	850
December	1st to 10th	Night	17% 4 23% 36% 17% 2	950
	11th to 20th	Night	20% 6% 19% 40% 13% 2	950
	21st to end	Night	20% 6% 23% 39% 12% 1	851

Page generated at 2024-10-22 18:20:59. Version ac07

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