Highland Road Park Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Highland Road Park Observatory 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	12% 6% 3 7% 5% 5% 5% 5% 6% 8% 38%	100746
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	98290
Transparency	Day	41% 6% 12% 18% 17% 6%	104399
	Night	36% 6% 13% 18% 18% 9%	102778
Seeing	Day	13% 6% 18% 24% 24% 15%	14815
	Night	13% 5% 19% 32% 25% 6%	24506

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	16% 8% 4 7% 4 4 4 3 5% 6% 38%	2847
	11th to 20th	Day	13% 7% 1 5% 4 3 2 2 3 5% 55%	2850
	21st to end	Day	23% 9% 3 6% 4 4 4 3 4 5% 35%	3228
February	1st to 10th	Day	17% 8% 3 8% 5% 4 4 3 4 6% 37%	1900
	11th to 20th	Day	19% 6% 2 6% 3 4 4 3 4 7% 41%	1848
	21st to end	Day	19% 8% 3 6% 5% 4 5% 4 4 6% 38%	1570
March	1st to 10th	Day	24% 9% 4 8% 5% 4 4 4 5% 7% 26%	3436
	11th to 20th	Day	14% 8% 3 8% 5% 6% 6% 5% 6% 8% 32%	3480
	21st to end	Day	12% 7% 3 7% 5% 5% 4 4 4 7% 43%	3904
April	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 4 7% 7% 41%	2280
	11th to 20th	Day	14% 7% 3 6% 4 5% 5% 4 6% 9% 37%	2254
	21st to end	Day	10% 5% 2 5% 6% 5% 5% 4 6% 8% 44%	2280
May	1st to 10th	Day	11% 7% 3 7% 6% 6% 6% 5% 6% 8% 34%	3765
	11th to 20th	Day	12% 6% 3 7% 5% 5% 5% 4 5% 7% 42%	3764
	21st to end	Day	6% 5% 2 6% 6% 7% 6% 5% 8% 10% 41%	4129
June	1st to 10th	Day	9% 5% 3 7% 6% 7% 8% 6% 8% 9% 33%	2385
	11th to 20th	Day	6% 5% 2 8% 7% 8% 8% 5% 9% 10% 31%	2470
	21st to end	Day	8% 7% 3 8% 7% 7% 9% 8% 9% 9% 26%	2470
July	1st to 10th	Day	6% 8% 3 9% 7% 8% 8% 8% 8% 11% 23%	4120
	11th to 20th	Day	7% 5% 3 10% 7% 9% 9% 7% 10% 12% 23%	4120
	21st to end	Day	10% 9% 4 11% 7% 8% 8% 6% 8% 9% 21%	4276
August	1st to 10th	Day	3 4 2 5% 4 4 5% 4 6% 10% 54%	3785
	11th to 20th	Day	6% 4 2 6% 5% 6% 7% 6% 9% 12% 37%	3729
	21st to end	Day	11% 6% 3 8% 7% 7% 6% 5% 7% 7% 33%	4180
September	1st to 10th	Day	13% 6% 2 8% 5% 6% 6% 5% 8% 8% 32%	2280
	11th to 20th	Day	11% 7% 2 8% 5% 6% 6% 4 6% 8% 38%	2276
	21st to end	Day	10% 5% 3 6% 4 4 5% 4 6% 7% 48%	2084
October	1st to 10th	Day	7% 3 1 6% 4 4 3 4 5% 6% 55%	1900
	11th to 20th	Day	8% 4 2 5% 4 4 4 3 6% 7% 54%	1900
	21st to end	Day	11% 5% 1 5% 3 3 4 3 4 6% 54%	2090
November	1st to 10th	Day	9% 5% 2 6% 4 4 5% 3 6% 7% 51%	1888
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 3 3 6% 52%	1900
	21st to end	Day	14% 6% 2 6% 5% 4 4 4 5% 6% 45%	1900
December	1st to 10th	Day	17% 7% 2 6% 4 4 4 4 5% 6% 42%	1900
	11th to 20th	Day	16% 9% 4 7% 5% 5% 4 4 5% 6% 37%	2396
	21st to end	Day	16% 8% 2 6% 4 5% 5% 4 5% 7% 38%	3162
January	1st to 10th	Night	17% 8% 3 5% 3 4 4 3 5% 5% 45%	4108
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 4 5% 53%	4120
	21st to end	Night	26% 8% 2 5% 3 3 3 2 4 6% 39%	4432
February	1st to 10th	Night	16% 8% 3 5% 5% 4 4 3 5% 6% 41%	2280
	11th to 20th	Night	19% 7% 3 6% 4 3 3 3 5% 6% 42%	2218
	21st to end	Night	18% 9% 2 6% 4 3 4 4 5% 6% 39%	1884
March	1st to 10th	Night	24% 13% 3 7% 4 4 4 3 4 5% 29%	3433
	11th to 20th	Night	16% 8% 3 7% 4 4 4 4 6% 8% 35%	3480
	21st to end	Night	14% 7% 2 6% 4 4 4 4 6% 7% 43%	3726
April	1st to 10th	Night	13% 5% 2 6% 4 4 4 3 6% 8% 44%	1900
	11th to 20th	Night	13% 7% 2 6% 4 3 3 3 6% 6% 47%	1875
	21st to end	Night	7% 4 1 5% 3 4 4 5% 6% 7% 54%	1900
May	1st to 10th	Night	13% 7% 3 7% 5% 4 4 4 6% 8% 40%	3130
	11th to 20th	Night	15% 6% 2 6% 4 4 4 4 5% 8% 42%	3129
	21st to end	Night	7% 5% 2 5% 5% 4 5% 4 8% 11% 44%	3426
June	1st to 10th	Night	6% 5% 2 6% 5% 5% 6% 5% 9% 9% 44%	1788
	11th to 20th	Night	4 4 2 5% 5% 4 6% 5% 7% 12% 47%	1710
	21st to end	Night	6% 4 3 7% 6% 6% 6% 6% 8% 12% 37%	1710
July	1st to 10th	Night	4 6% 2 7% 6% 6% 7% 6% 8% 14% 34%	2850
	11th to 20th	Night	3 4 1 6% 5% 6% 6% 6% 10% 14% 39%	2850
	21st to end	Night	6% 6% 3 7% 7% 6% 6% 6% 10% 14% 31%	3277
August	1st to 10th	Night	2 2 1 3 3 3 4 4 6% 11% 60%	3144
	11th to 20th	Night	3 3 2 5% 4 6% 6% 5% 9% 13% 43%	3100
	21st to end	Night	6% 6% 3 8% 6% 6% 5% 6% 7% 9% 39%	3476
September	1st to 10th	Night	8% 5% 2 7% 6% 5% 4 5% 7% 11% 40%	1900
	11th to 20th	Night	9% 7% 3 6% 6% 5% 5% 4 8% 9% 39%	1900
	21st to end	Night	7% 5% 2 6% 4 5% 4 3 5% 7% 51%	2074
October	1st to 10th	Night	6% 4 1 3 4 3 3 3 5% 7% 60%	2280
	11th to 20th	Night	7% 4 1 4 4 3 3 3 5% 6% 59%	2280
	21st to end	Night	11% 5% 2 5% 3 2 3 3 4 6% 58%	2508
November	1st to 10th	Night	10% 5% 2 5% 4 3 4 3 4 5% 57%	2263
	11th to 20th	Night	12% 5% 2 5% 3 3 4 3 4 6% 55%	2280
	21st to end	Night	12% 7% 3 6% 4 3 4 3 5% 6% 47%	2280
December	1st to 10th	Night	15% 8% 2 7% 4 3 3 3 4 6% 45%	2280
	11th to 20th	Night	14% 9% 3 7% 4 4 4 3 5% 7% 42%	2799
	21st to end	Night	18% 10% 3 6% 4 4 3 3 4 6% 40%	4500

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	46% 3 6% 14% 22% 8%	2848
	11th to 20th	Day	34% 3 5% 17% 32% 9%	2850
	21st to end	Day	51% 4 4 14% 19% 7%	3228
February	1st to 10th	Day	49% 4 8% 12% 16% 10%	1900
	11th to 20th	Day	44% 6% 6% 15% 20% 9%	1858
	21st to end	Day	47% 4 8% 16% 17% 8%	1570
March	1st to 10th	Day	56% 5% 10% 15% 10% 4	3436
	11th to 20th	Day	48% 6% 9% 17% 15% 5%	3480
	21st to end	Day	41% 5% 10% 16% 22% 7%	3904
April	1st to 10th	Day	40% 6% 10% 16% 18% 10%	2280
	11th to 20th	Day	43% 4 8% 19% 17% 8%	2254
	21st to end	Day	35% 5% 11% 21% 23% 5%	2280
May	1st to 10th	Day	44% 7% 13% 22% 11% 4	3800
	11th to 20th	Day	40% 6% 9% 18% 24% 3	3768
	21st to end	Day	35% 7% 14% 31% 12% 1	4141
June	1st to 10th	Day	44% 9% 13% 21% 11% 1	2385
	11th to 20th	Day	44% 9% 14% 19% 13% 1	2470
	21st to end	Day	48% 10% 17% 18% 6%	2470
July	1st to 10th	Day	50% 11% 21% 16% 2	4056
	11th to 20th	Day	46% 15% 27% 9% 2	4051
	21st to end	Day	56% 10% 16% 14% 3	4141
August	1st to 10th	Day	26% 7% 15% 29% 23%	3773
	11th to 20th	Day	35% 10% 22% 26% 6% 1	3765
	21st to end	Day	49% 8% 14% 15% 14% 2	4179
September	1st to 10th	Day	45% 9% 17% 14% 11% 3	2280
	11th to 20th	Day	43% 7% 14% 16% 14% 6%	2276
	21st to end	Day	35% 5% 10% 22% 18% 9%	2084
October	1st to 10th	Day	26% 3 7% 13% 22% 30%	3160
	11th to 20th	Day	18% 3 4 21% 27% 28%	3140
	21st to end	Day	24% 3 4 11% 40% 17%	3428
November	1st to 10th	Day	32% 4 8% 20% 26% 10%	1888
	11th to 20th	Day	35% 4 6% 17% 26% 12%	1900
	21st to end	Day	40% 4 7% 17% 21% 10%	1900
December	1st to 10th	Day	42% 4 10% 19% 17% 8%	1900
	11th to 20th	Day	49% 3 6% 13% 22% 7%	2394
	21st to end	Day	45% 5% 9% 15% 23% 3	3162
January	1st to 10th	Night	41% 4 7% 14% 26% 9%	4108
	11th to 20th	Night	34% 4 6% 19% 27% 11%	4120
	21st to end	Night	48% 3 5% 16% 19% 9%	4432
February	1st to 10th	Night	44% 3 7% 16% 19% 10%	2280
	11th to 20th	Night	43% 5% 5% 15% 19% 13%	2219
	21st to end	Night	45% 5% 10% 15% 14% 12%	1884
March	1st to 10th	Night	56% 5% 9% 13% 11% 6%	3433
	11th to 20th	Night	46% 5% 12% 16% 16% 5%	3480
	21st to end	Night	40% 5% 10% 20% 20% 6%	3726
April	1st to 10th	Night	38% 5% 12% 17% 16% 11%	1900
	11th to 20th	Night	38% 4 11% 18% 18% 11%	1875
	21st to end	Night	28% 6% 10% 22% 25% 8%	1900
May	1st to 10th	Night	39% 7% 14% 21% 14% 4	3160
	11th to 20th	Night	39% 6% 11% 21% 20% 2	3130
	21st to end	Night	31% 7% 20% 29% 12% 2	3435
June	1st to 10th	Night	32% 10% 18% 25% 14% 1	1788
	11th to 20th	Night	28% 10% 21% 27% 13% 2	1710
	21st to end	Night	35% 9% 22% 24% 8%	1710
July	1st to 10th	Night	37% 14% 32% 14% 3	2805
	11th to 20th	Night	30% 17% 41% 10% 2	2796
	21st to end	Night	40% 17% 21% 18% 3	3173
August	1st to 10th	Night	16% 9% 22% 30% 23% 1	3132
	11th to 20th	Night	28% 11% 28% 29% 4	3130
	21st to end	Night	38% 10% 18% 18% 13% 2	3476
September	1st to 10th	Night	36% 9% 21% 20% 10% 5%	1900
	11th to 20th	Night	38% 9% 17% 17% 13% 6%	1900
	21st to end	Night	31% 6% 12% 24% 16% 10%	2074
October	1st to 10th	Night	26% 4 7% 14% 21% 28%	3800
	11th to 20th	Night	16% 3 5% 19% 30% 26%	3779
	21st to end	Night	19% 3 5% 12% 38% 23%	4120
November	1st to 10th	Night	30% 5% 9% 20% 25% 13%	2263
	11th to 20th	Night	31% 3 8% 16% 27% 15%	2280
	21st to end	Night	37% 4 7% 19% 21% 11%	2280
December	1st to 10th	Night	41% 4 7% 21% 20% 7%	2280
	11th to 20th	Night	42% 4 8% 14% 18% 14%	2800
	21st to end	Night	47% 3 9% 15% 19% 7%	4500

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	19% 15% 37% 19% 8% 2	270
	11th to 20th	Day	16% 14% 35% 26% 8%	270
	21st to end	Day	24% 15% 37% 18% 6%	297
February	1st to 10th	Day	25% 13% 30% 24% 7% 1	270
	11th to 20th	Day	27% 14% 30% 19% 10% 1	270
	21st to end	Day	18% 21% 37% 20% 4	225
March	1st to 10th	Day	21% 14% 37% 21% 6%	270
	11th to 20th	Day	19% 17% 35% 22% 6% 1	270
	21st to end	Day	18% 12% 37% 22% 10% 1	349
April	1st to 10th	Day	16% 12% 33% 27% 12% 2	460
	11th to 20th	Day	19% 11% 30% 24% 13% 2	452
	21st to end	Day	10% 7% 25% 35% 19% 3	460
May	1st to 10th	Day	13% 6% 22% 32% 22% 5%	463
	11th to 20th	Day	12% 5% 18% 30% 25% 11%	487
	21st to end	Day	5% 1 16% 32% 29% 17%	529
June	1st to 10th	Day	9% 3 10% 27% 31% 20%	595
	11th to 20th	Day	8% 2 10% 27% 36% 17%	680
	21st to end	Day	10% 4 7% 23% 31% 25%	680
July	1st to 10th	Day	9% 2 6% 18% 36% 29%	671
	11th to 20th	Day	8% 3 4 13% 39% 34%	668
	21st to end	Day	9% 2 5% 16% 38% 30%	625
August	1st to 10th	Day	6% 2 2 14% 36% 40%	486
	11th to 20th	Day	9% 2 3 11% 29% 46%	479
	21st to end	Day	12% 4 6% 18% 31% 29%	539
September	1st to 10th	Day	12% 2 5% 18% 35% 27%	490
	11th to 20th	Day	11% 2 9% 21% 38% 19%	490
	21st to end	Day	11% 3 9% 24% 34% 18%	484
October	1st to 10th	Day	7% 3 18% 39% 24% 9%	300
	11th to 20th	Day	6% 6% 17% 34% 23% 13%	300
	21st to end	Day	16% 6% 21% 32% 18% 6%	330
November	1st to 10th	Day	14% 3 18% 38% 22% 5%	279
	11th to 20th	Day	16% 9% 27% 29% 15% 4	270
	21st to end	Day	18% 10% 33% 24% 12% 3	270
December	1st to 10th	Day	20% 10% 23% 27% 14% 5%	270
	11th to 20th	Day	20% 11% 37% 26% 6% 1	270
	21st to end	Day	23% 11% 34% 19% 11% 1	297
January	1st to 10th	Night	21% 8% 30% 33% 7%	950
	11th to 20th	Night	17% 8% 31% 35% 10%	950
	21st to end	Night	20% 10% 34% 29% 7%	984
February	1st to 10th	Night	19% 10% 31% 35% 6%	760
	11th to 20th	Night	22% 10% 28% 31% 8%	743
	21st to end	Night	22% 10% 38% 27% 3	628
March	1st to 10th	Night	17% 7% 31% 35% 9%	584
	11th to 20th	Night	16% 6% 30% 37% 10% 1	570
	21st to end	Night	12% 9% 32% 34% 12%	627
April	1st to 10th	Night	16% 8% 29% 35% 12% 1	570
	11th to 20th	Night	16% 8% 28% 35% 12% 1	563
	21st to end	Night	9% 4 27% 43% 15% 1	570
May	1st to 10th	Night	11% 3 20% 47% 18% 1	570
	11th to 20th	Night	10% 2 18% 42% 25% 3	561
	21st to end	Night	6% 3 9% 41% 34% 6%	617
June	1st to 10th	Night	7% 2 6% 35% 42% 8%	570
	11th to 20th	Night	4 1 6% 31% 48% 11%	570
	21st to end	Night	6% 1 5% 26% 45% 17%	570
July	1st to 10th	Night	5% 2 3 17% 52% 21%	555
	11th to 20th	Night	5% 1 2 13% 50% 30%	552
	21st to end	Night	6% 3 4 15% 53% 19%	624
August	1st to 10th	Night	3 1 2 16% 51% 28%	567
	11th to 20th	Night	5% 1 1 14% 51% 27%	564
	21st to end	Night	8% 1 4 18% 44% 24%	627
September	1st to 10th	Night	9% 1 5% 18% 47% 19%	570
	11th to 20th	Night	12% 2 5% 24% 48% 10%	570
	21st to end	Night	9% 2 8% 30% 43% 8%	743
October	1st to 10th	Night	9% 2 11% 37% 37% 5%	760
	11th to 20th	Night	8% 3 15% 43% 28% 2	760
	21st to end	Night	13% 5% 18% 39% 23% 2	836
November	1st to 10th	Night	11% 3 16% 43% 25% 2	755
	11th to 20th	Night	14% 6% 22% 41% 17% 1	760
	21st to end	Night	16% 6% 26% 34% 16% 1	760
December	1st to 10th	Night	17% 9% 24% 34% 16% 1	760
	11th to 20th	Night	19% 6% 27% 36% 11%	760
	21st to end	Night	26% 8% 26% 31% 9%	1026

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