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 2024-03-23.

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 6% 6% 4 6% 6% 6% 8% 39%	79441
	Night	12% 6% 2 5% 5% 3 4 5% 6% 8% 46%	80481
Transparency	Day	43% 6% 11% 17% 17% 6%	79174
	Night	36% 6% 13% 19% 18% 8%	80270
Seeing	Day	13% 6% 18% 23% 24% 16%	13901
	Night	13% 5% 19% 32% 24% 6%	23781

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% 8% 4 6% 5% 3 4 4 5% 6% 38%	2847
	11th to 20th	Day	13% 6% 2 5% 4 2 3 3 3 5% 55%	2850
	21st to end	Day	23% 9% 3 6% 5% 3 4 4 4 5% 35%	3228
February	1st to 10th	Day	17% 8% 3 7% 6% 4 4 4 4 6% 37%	1900
	11th to 20th	Day	19% 6% 2 5% 4 3 4 4 4 7% 41%	1848
	21st to end	Day	19% 8% 3 5% 5% 3 5% 5% 4 6% 38%	1570
March	1st to 10th	Day	17% 6% 3 7% 6% 3 4 4 4 7% 38%	2090
	11th to 20th	Day	13% 7% 3 7% 6% 5% 4 5% 6% 8% 37%	2090
	21st to end	Day	11% 6% 3 6% 5% 3 5% 5% 4 8% 44%	2249
April	1st to 10th	Day	12% 6% 3 6% 5% 3 6% 5% 7% 7% 41%	2160
	11th to 20th	Day	15% 6% 3 5% 5% 4 5% 5% 5% 9% 37%	2134
	21st to end	Day	10% 5% 2 4 6% 4 5% 5% 6% 9% 44%	2160
May	1st to 10th	Day	10% 6% 2 5% 5% 3 6% 5% 6% 9% 42%	2160
	11th to 20th	Day	10% 5% 2 6% 6% 4 6% 6% 6% 7% 42%	2124
	21st to end	Day	7% 5% 2 6% 7% 6% 7% 6% 7% 9% 36%	2337
June	1st to 10th	Day	9% 5% 3 6% 7% 5% 9% 7% 8% 10% 32%	2259
	11th to 20th	Day	6% 4 3 8% 8% 6% 8% 7% 9% 10% 31%	2340
	21st to end	Day	8% 6% 3 7% 8% 6% 8% 10% 8% 9% 26%	2340
July	1st to 10th	Day	9% 8% 4 7% 8% 5% 9% 9% 7% 9% 26%	2340
	11th to 20th	Day	8% 5% 4 9% 8% 6% 9% 7% 7% 12% 24%	2340
	21st to end	Day	7% 6% 4 9% 8% 5% 8% 8% 8% 10% 27%	2438
August	1st to 10th	Day	6% 6% 3 7% 8% 5% 8% 7% 9% 12% 30%	2148
	11th to 20th	Day	11% 5% 4 7% 8% 5% 7% 8% 9% 9% 27%	2125
	21st to end	Day	11% 6% 3 6% 9% 5% 7% 6% 8% 8% 31%	2376
September	1st to 10th	Day	11% 6% 3 7% 6% 5% 5% 7% 8% 9% 33%	2160
	11th to 20th	Day	10% 6% 3 7% 6% 4 6% 5% 6% 8% 38%	2157
	21st to end	Day	10% 5% 3 5% 4 4 5% 5% 6% 7% 46%	1975
October	1st to 10th	Day	7% 3 1 5% 5% 3 4 4 6% 7% 54%	1800
	11th to 20th	Day	8% 4 2 5% 5% 3 4 4 6% 7% 53%	1800
	21st to end	Day	11% 4 2 4 3 3 4 5% 4 6% 53%	1980
November	1st to 10th	Day	8% 4 2 5% 4 3 5% 5% 5% 7% 52%	1858
	11th to 20th	Day	11% 4 3 4 5% 3 5% 4 3 6% 52%	1900
	21st to end	Day	14% 6% 3 5% 6% 3 5% 4 5% 6% 45%	1900
December	1st to 10th	Day	17% 6% 2 5% 5% 3 5% 4 5% 6% 42%	1900
	11th to 20th	Day	16% 9% 4 6% 6% 3 4 5% 5% 6% 37%	2396
	21st to end	Day	16% 8% 3 6% 5% 3 5% 5% 5% 7% 38%	3162
January	1st to 10th	Night	17% 7% 3 4 4 3 4 4 4 5% 45%	4108
	11th to 20th	Night	14% 5% 2 4 3 2 3 3 4 5% 53%	4120
	21st to end	Night	26% 7% 3 4 4 2 3 3 4 6% 39%	4432
February	1st to 10th	Night	16% 8% 3 5% 6% 3 4 4 5% 6% 41%	2280
	11th to 20th	Night	20% 6% 3 5% 4 2 3 4 4 6% 42%	2218
	21st to end	Night	19% 8% 2 5% 5% 2 3 5% 5% 6% 40%	1884
March	1st to 10th	Night	15% 7% 3 5% 4 3 4 4 5% 7% 43%	2104
	11th to 20th	Night	14% 6% 3 6% 5% 3 4 5% 6% 8% 40%	2090
	21st to end	Night	11% 5% 2 4 4 2 4 4 5% 7% 52%	2150
April	1st to 10th	Night	13% 5% 2 5% 6% 3 4 4 6% 9% 45%	1800
	11th to 20th	Night	14% 6% 2 5% 4 2 3 3 6% 6% 47%	1775
	21st to end	Night	7% 4 2 4 4 2 4 6% 5% 8% 54%	1800
May	1st to 10th	Night	9% 4 2 4 5% 2 4 4 6% 8% 52%	1800
	11th to 20th	Night	8% 4 2 5% 4 3 4 5% 6% 9% 49%	1769
	21st to end	Night	6% 3 2 5% 5% 3 5% 6% 7% 10% 50%	1938
June	1st to 10th	Night	5% 4 2 5% 5% 4 6% 6% 8% 9% 44%	1694
	11th to 20th	Night	3 3 2 5% 6% 3 6% 6% 7% 13% 47%	1620
	21st to end	Night	6% 4 3 6% 7% 5% 7% 6% 7% 12% 38%	1620
July	1st to 10th	Night	4 5% 3 5% 6% 4 6% 7% 7% 14% 40%	1620
	11th to 20th	Night	4 5% 2 4 5% 3 7% 7% 10% 14% 39%	1620
	21st to end	Night	5% 4 2 5% 6% 4 5% 7% 10% 13% 38%	1875
August	1st to 10th	Night	4 3 1 4 4 3 4 6% 7% 13% 52%	1790
	11th to 20th	Night	5% 4 2 5% 7% 4 7% 7% 10% 12% 37%	1776
	21st to end	Night	7% 5% 3 6% 6% 4 5% 7% 7% 12% 37%	1980
September	1st to 10th	Night	7% 5% 2 6% 6% 4 5% 6% 8% 11% 42%	1800
	11th to 20th	Night	8% 6% 3 5% 7% 3 5% 5% 8% 9% 40%	1800
	21st to end	Night	7% 5% 3 5% 5% 3 5% 4 5% 8% 50%	1963
October	1st to 10th	Night	6% 4 2 3 4 2 4 4 4 7% 60%	2160
	11th to 20th	Night	7% 4 2 4 4 2 3 4 5% 6% 58%	2160
	21st to end	Night	11% 5% 2 4 4 2 3 3 4 6% 57%	2376
November	1st to 10th	Night	9% 5% 2 4 4 2 3 4 4 5% 58%	2220
	11th to 20th	Night	12% 4 2 4 4 2 4 4 4 6% 55%	2280
	21st to end	Night	12% 6% 3 5% 5% 2 4 4 4 7% 48%	2280
December	1st to 10th	Night	15% 7% 3 6% 5% 2 3 3 4 6% 45%	2280
	11th to 20th	Night	14% 8% 3 5% 6% 3 3 4 5% 7% 43%	2799
	21st to end	Night	18% 10% 3 6% 5% 3 4 3 4 5% 41%	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	46% 5% 8% 19% 16% 7%	2090
	11th to 20th	Day	45% 6% 10% 12% 20% 6%	2090
	21st to end	Day	38% 5% 10% 20% 20% 7%	2249
April	1st to 10th	Day	39% 6% 11% 17% 18% 9%	2160
	11th to 20th	Day	44% 5% 8% 19% 17% 8%	2134
	21st to end	Day	35% 5% 11% 21% 23% 5%	2160
May	1st to 10th	Day	36% 6% 11% 22% 18% 7%	2160
	11th to 20th	Day	39% 7% 10% 23% 18% 2	2128
	21st to end	Day	42% 8% 14% 22% 13% 1	2337
June	1st to 10th	Day	45% 10% 13% 21% 11% 1	2259
	11th to 20th	Day	44% 9% 15% 20% 12% 1	2340
	21st to end	Day	49% 10% 17% 17% 6%	2340
July	1st to 10th	Day	51% 11% 18% 16% 4	2276
	11th to 20th	Day	49% 12% 18% 15% 4 1	2271
	21st to end	Day	48% 11% 20% 16% 5% 1	2303
August	1st to 10th	Day	44% 11% 21% 17% 7%	2136
	11th to 20th	Day	49% 13% 18% 15% 4 1	2125
	21st to end	Day	49% 9% 17% 14% 9% 2	2376
September	1st to 10th	Day	44% 9% 17% 15% 12% 4	2160
	11th to 20th	Day	43% 7% 14% 16% 14% 6%	2157
	21st to end	Day	37% 6% 10% 22% 18% 8%	1975
October	1st to 10th	Day	29% 4 10% 22% 22% 13%	1800
	11th to 20th	Day	30% 5% 7% 17% 28% 13%	1800
	21st to end	Day	33% 4 6% 16% 26% 16%	1980
November	1st to 10th	Day	31% 4 8% 20% 26% 11%	1858
	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	39% 4 10% 18% 18% 10%	2104
	11th to 20th	Night	41% 5% 13% 16% 17% 8%	2090
	21st to end	Night	32% 5% 11% 22% 22% 7%	2150
April	1st to 10th	Night	37% 5% 13% 18% 17% 11%	1800
	11th to 20th	Night	38% 4 11% 19% 17% 11%	1775
	21st to end	Night	28% 6% 11% 22% 26% 8%	1800
May	1st to 10th	Night	29% 5% 12% 27% 20% 7%	1800
	11th to 20th	Night	31% 7% 15% 24% 21% 3	1770
	21st to end	Night	28% 8% 18% 29% 16% 2	1939
June	1st to 10th	Night	32% 10% 18% 26% 14% 1	1694
	11th to 20th	Night	27% 10% 21% 27% 13% 2	1620
	21st to end	Night	36% 9% 22% 25% 8%	1620
July	1st to 10th	Night	33% 11% 30% 20% 5%	1575
	11th to 20th	Night	30% 14% 32% 18% 4 1	1566
	21st to end	Night	31% 13% 29% 22% 5%	1771
August	1st to 10th	Night	21% 13% 34% 24% 7% 1	1778
	11th to 20th	Night	34% 14% 27% 20% 4 1	1776
	21st to end	Night	37% 13% 23% 16% 8% 3	1980
September	1st to 10th	Night	34% 9% 21% 20% 11% 5%	1800
	11th to 20th	Night	37% 9% 17% 18% 13% 6%	1800
	21st to end	Night	32% 6% 13% 24% 16% 10%	1963
October	1st to 10th	Night	24% 5% 10% 23% 23% 14%	2160
	11th to 20th	Night	26% 5% 8% 20% 26% 15%	2160
	21st to end	Night	30% 4 5% 17% 26% 18%	2376
November	1st to 10th	Night	29% 4 8% 20% 25% 13%	2220
	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% 21% 7% 1	270
	21st to end	Day	18% 13% 35% 23% 11% 1	319
April	1st to 10th	Day	15% 10% 33% 28% 13% 2	420
	11th to 20th	Day	19% 11% 30% 24% 14% 2	412
	21st to end	Day	10% 7% 24% 36% 19% 3	420
May	1st to 10th	Day	13% 6% 21% 32% 23% 5%	423
	11th to 20th	Day	11% 3 16% 31% 27% 11%	447
	21st to end	Day	5% 1 13% 30% 32% 19%	485
June	1st to 10th	Day	9% 3 8% 28% 32% 21%	549
	11th to 20th	Day	8% 2 9% 26% 37% 18%	630
	21st to end	Day	10% 4 7% 23% 31% 25%	630
July	1st to 10th	Day	9% 2 6% 17% 36% 30%	621
	11th to 20th	Day	8% 3 4 12% 39% 34%	618
	21st to end	Day	9% 2 5% 16% 37% 32%	576
August	1st to 10th	Day	6% 2 2 13% 33% 43%	446
	11th to 20th	Day	10% 2 3 11% 29% 46%	439
	21st to end	Day	12% 4 6% 16% 32% 31%	495
September	1st to 10th	Day	10% 2 4 18% 37% 29%	450
	11th to 20th	Day	10% 2 8% 20% 40% 20%	450
	21st to end	Day	12% 2 8% 24% 36% 18%	445
October	1st to 10th	Day	7% 3 17% 39% 25% 10%	270
	11th to 20th	Day	7% 6% 15% 34% 25% 13%	270
	21st to end	Day	18% 6% 21% 32% 17% 6%	297
November	1st to 10th	Day	13% 3 19% 37% 22% 6%	270
	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% 36% 10% 1	570
	21st to end	Night	12% 8% 32% 35% 12%	600
April	1st to 10th	Night	15% 7% 29% 36% 12% 1	540
	11th to 20th	Night	16% 8% 28% 35% 13% 1	533
	21st to end	Night	9% 4 27% 44% 15% 1	540
May	1st to 10th	Night	10% 3 19% 48% 19% 1	540
	11th to 20th	Night	9% 2 18% 42% 26% 3	531
	21st to end	Night	6% 2 8% 41% 36% 7%	584
June	1st to 10th	Night	6% 2 6% 35% 43% 9%	540
	11th to 20th	Night	3 1 5% 31% 49% 11%	540
	21st to end	Night	6% 1 4 26% 45% 17%	540
July	1st to 10th	Night	5% 1 2 17% 53% 22%	525
	11th to 20th	Night	5% 1 2 12% 49% 29%	522
	21st to end	Night	5% 3 4 15% 53% 20%	591
August	1st to 10th	Night	3 1 2 15% 50% 29%	537
	11th to 20th	Night	6% 1 1 13% 52% 28%	534
	21st to end	Night	9% 2 4 18% 43% 25%	594
September	1st to 10th	Night	7% 1 4 18% 49% 20%	540
	11th to 20th	Night	11% 2 4 24% 48% 10%	540
	21st to end	Night	9% 2 7% 30% 44% 8%	703
October	1st to 10th	Night	8% 1 10% 36% 39% 5%	720
	11th to 20th	Night	9% 3 15% 42% 29% 2	720
	21st to end	Night	14% 5% 18% 38% 23% 2	792
November	1st to 10th	Night	11% 3 16% 43% 25% 2	740
	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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