Halliday Parkwood Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Halliday Parkwood Observatory clear sky chart from 2005-11-06 to 2024-11-12.

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	8% 6% 2 7% 5% 5% 6% 5% 7% 10% 39%	100992
	Night	9% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	98128
Transparency	Day	37% 10% 16% 19% 13% 5%	104773
	Night	36% 10% 16% 19% 14% 5%	102486
Seeing	Day	9% 4 16% 24% 25% 22%	15506
	Night	10% 4 18% 33% 27% 8%	25551

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	12% 7% 3 7% 4 4 4 4 5% 6% 43%	2836
	11th to 20th	Day	20% 9% 3 7% 4 4 4 3 5% 6% 36%	2840
	21st to end	Day	10% 6% 2 6% 4 4 5% 4 6% 7% 46%	3256
February	1st to 10th	Day	14% 5% 2 6% 5% 4 4 4 6% 7% 42%	1900
	11th to 20th	Day	11% 5% 2 5% 3 4 4 3 5% 6% 52%	1848
	21st to end	Day	9% 6% 3 5% 4 5% 4 3 5% 7% 49%	1636
March	1st to 10th	Day	9% 7% 2 8% 5% 6% 5% 4 7% 10% 38%	3435
	11th to 20th	Day	6% 5% 2 5% 4 4 4 4 8% 9% 49%	3480
	21st to end	Day	11% 5% 2 6% 4 4 4 4 5% 7% 50%	3815
April	1st to 10th	Day	7% 4 2 4 4 4 4 4 7% 9% 50%	2090
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 6% 8% 45%	2080
	21st to end	Day	5% 3 1 4 4 5% 5% 4 6% 10% 54%	2301
May	1st to 10th	Day	3 2 1 3 3 3 5% 4 6% 10% 60%	4082
	11th to 20th	Day	9% 5% 2 7% 6% 6% 6% 5% 7% 9% 38%	4081
	21st to end	Day	4 3 1 4 4 4 4 4 6% 10% 53%	4476
June	1st to 10th	Day	9% 7% 3 8% 7% 7% 8% 7% 8% 10% 26%	2470
	11th to 20th	Day	6% 6% 2 9% 8% 8% 9% 6% 9% 11% 28%	2470
	21st to end	Day	8% 7% 2 8% 8% 6% 7% 7% 7% 10% 28%	2470
July	1st to 10th	Day	7% 6% 3 8% 8% 8% 8% 7% 10% 14% 22%	4120
	11th to 20th	Day	4 5% 2 8% 7% 7% 8% 7% 10% 16% 25%	4120
	21st to end	Day	5% 6% 3 7% 7% 7% 8% 7% 11% 15% 24%	4466
August	1st to 10th	Day	7% 6% 3 8% 6% 7% 7% 5% 8% 14% 29%	4104
	11th to 20th	Day	5% 4 2 6% 6% 7% 7% 6% 9% 13% 35%	3843
	21st to end	Day	8% 6% 3 9% 7% 7% 8% 6% 9% 11% 26%	3828
September	1st to 10th	Day	7% 7% 3 11% 9% 7% 8% 7% 8% 10% 22%	2090
	11th to 20th	Day	10% 7% 4 10% 8% 8% 7% 5% 7% 10% 26%	2090
	21st to end	Day	9% 7% 3 8% 6% 7% 6% 5% 7% 9% 33%	2090
October	1st to 10th	Day	12% 6% 3 8% 7% 6% 5% 4 6% 8% 35%	2090
	11th to 20th	Day	6% 5% 2 5% 5% 5% 4 4 5% 8% 51%	1900
	21st to end	Day	8% 5% 2 5% 5% 4 5% 4 6% 7% 50%	2090
November	1st to 10th	Day	8% 5% 2 7% 4 4 4 4 6% 8% 48%	1957
	11th to 20th	Day	10% 6% 3 6% 4 5% 5% 4 5% 7% 45%	1910
	21st to end	Day	11% 6% 3 6% 4 4 4 3 5% 10% 45%	1741
December	1st to 10th	Day	8% 6% 2 6% 4 3 5% 4 7% 8% 47%	1710
	11th to 20th	Day	12% 7% 2 6% 5% 4 4 4 6% 7% 44%	2153
	21st to end	Day	13% 7% 3 8% 5% 5% 4 4 5% 6% 40%	3124
January	1st to 10th	Night	13% 7% 2 6% 4 5% 4 3 5% 8% 42%	4109
	11th to 20th	Night	17% 9% 3 7% 4 4 4 4 6% 8% 34%	4120
	21st to end	Night	14% 7% 2 5% 4 5% 5% 4 6% 7% 41%	4396
February	1st to 10th	Night	12% 7% 2 6% 5% 4 3 4 6% 6% 46%	2280
	11th to 20th	Night	9% 6% 2 6% 4 4 4 4 5% 7% 49%	2218
	21st to end	Night	8% 6% 2 8% 4 4 4 4 7% 6% 48%	1815
March	1st to 10th	Night	18% 9% 3 7% 4 3 4 3 4 5% 39%	3418
	11th to 20th	Night	6% 5% 2 5% 4 4 4 5% 7% 11% 47%	3480
	21st to end	Night	11% 6% 2 6% 4 4 3 3 5% 8% 49%	3817
April	1st to 10th	Night	8% 4 1 5% 4 3 4 4 6% 9% 52%	2090
	11th to 20th	Night	7% 5% 2 6% 3 4 3 4 5% 8% 52%	2047
	21st to end	Night	6% 4 2 4 4 3 4 4 5% 7% 56%	1893
May	1st to 10th	Night	5% 3 1 4 4 4 4 4 5% 9% 56%	2813
	11th to 20th	Night	7% 5% 2 5% 4 4 5% 5% 6% 10% 47%	2812
	21st to end	Night	3 3 1 4 3 3 3 3 5% 8% 64%	3079
June	1st to 10th	Night	9% 6% 2 7% 6% 5% 6% 5% 8% 10% 36%	1710
	11th to 20th	Night	6% 5% 2 6% 5% 6% 6% 6% 9% 13% 35%	1710
	21st to end	Night	7% 7% 3 8% 6% 5% 6% 5% 8% 11% 34%	1710
July	1st to 10th	Night	7% 8% 4 9% 7% 7% 7% 7% 8% 12% 24%	2840
	11th to 20th	Night	4 5% 3 8% 7% 8% 8% 8% 11% 13% 27%	2840
	21st to end	Night	6% 9% 4 11% 7% 7% 9% 7% 8% 11% 21%	3087
August	1st to 10th	Night	6% 5% 3 8% 6% 7% 6% 5% 9% 12% 34%	2825
	11th to 20th	Night	4 4 2 5% 4 5% 6% 5% 9% 17% 40%	2940
	21st to end	Night	7% 6% 3 7% 6% 7% 7% 5% 9% 12% 31%	3819
September	1st to 10th	Night	7% 6% 4 8% 6% 5% 7% 6% 7% 11% 31%	2090
	11th to 20th	Night	12% 7% 3 8% 5% 6% 5% 5% 8% 11% 30%	2090
	21st to end	Night	8% 8% 3 7% 5% 6% 7% 4 7% 8% 38%	2090
October	1st to 10th	Night	10% 8% 3 6% 5% 5% 5% 5% 6% 8% 40%	2090
	11th to 20th	Night	6% 4 1 5% 4 4 4 3 6% 8% 56%	2278
	21st to end	Night	8% 5% 2 6% 4 4 4 3 5% 7% 52%	2508
November	1st to 10th	Night	10% 5% 2 5% 3 4 4 4 6% 8% 50%	2341
	11th to 20th	Night	8% 7% 3 7% 4 4 4 3 5% 7% 47%	2293
	21st to end	Night	8% 6% 3 7% 5% 5% 3 3 6% 8% 45%	2436
December	1st to 10th	Night	9% 5% 2 6% 5% 4 4 5% 6% 8% 48%	2470
	11th to 20th	Night	12% 7% 2 6% 4 4 3 3 4 6% 49%	3042
	21st to end	Night	16% 7% 3 7% 4 4 4 4 6% 7% 38%	4532

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	40% 6% 7% 18% 19% 10%	2837
	11th to 20th	Day	50% 4 6% 14% 16% 10%	2840
	21st to end	Day	35% 7% 8% 20% 20% 10%	3256
February	1st to 10th	Day	39% 7% 9% 15% 20% 11%	1900
	11th to 20th	Day	32% 5% 9% 18% 25% 12%	1858
	21st to end	Day	34% 6% 10% 17% 22% 11%	1636
March	1st to 10th	Day	38% 10% 13% 19% 14% 6%	3435
	11th to 20th	Day	28% 7% 13% 25% 21% 6%	3480
	21st to end	Day	33% 6% 10% 28% 15% 8%	3815
April	1st to 10th	Day	28% 8% 13% 21% 20% 10%	2090
	11th to 20th	Day	35% 8% 11% 18% 22% 7%	2080
	21st to end	Day	24% 8% 13% 23% 24% 8%	2301
May	1st to 10th	Day	17% 9% 18% 32% 18% 6%	4120
	11th to 20th	Day	36% 12% 16% 24% 10% 2	4085
	21st to end	Day	24% 8% 15% 34% 18% 1	4489
June	1st to 10th	Day	47% 13% 18% 16% 6%	2470
	11th to 20th	Day	45% 13% 20% 20% 3	2470
	21st to end	Day	47% 14% 19% 15% 4	2470
July	1st to 10th	Day	45% 17% 28% 9% 1	4055
	11th to 20th	Day	40% 19% 34% 6%	4051
	21st to end	Day	40% 21% 29% 9% 1	4324
August	1st to 10th	Day	41% 14% 28% 14% 3	4091
	11th to 20th	Day	35% 16% 23% 22% 4	3882
	21st to end	Day	46% 16% 21% 16% 2	3828
September	1st to 10th	Day	50% 18% 17% 10% 5%	2090
	11th to 20th	Day	50% 13% 20% 12% 5%	2090
	21st to end	Day	44% 10% 14% 17% 11% 4	2090
October	1st to 10th	Day	56% 9% 12% 11% 7% 5%	3480
	11th to 20th	Day	25% 5% 8% 21% 32% 9%	3140
	21st to end	Day	26% 6% 8% 22% 31% 7%	3428
November	1st to 10th	Day	32% 7% 11% 19% 18% 11%	1957
	11th to 20th	Day	38% 7% 9% 16% 21% 9%	1910
	21st to end	Day	36% 6% 9% 21% 21% 6%	1741
December	1st to 10th	Day	32% 7% 14% 23% 17% 6%	1710
	11th to 20th	Day	37% 7% 9% 17% 17% 11%	2150
	21st to end	Day	43% 6% 9% 21% 15% 6%	3124
January	1st to 10th	Night	41% 5% 9% 16% 20% 9%	4109
	11th to 20th	Night	47% 5% 8% 18% 16% 6%	4120
	21st to end	Night	39% 9% 11% 14% 17% 10%	4396
February	1st to 10th	Night	37% 6% 10% 16% 17% 13%	2280
	11th to 20th	Night	33% 7% 11% 18% 21% 11%	2219
	21st to end	Night	33% 7% 11% 18% 22% 9%	1815
March	1st to 10th	Night	45% 8% 11% 16% 15% 5%	3418
	11th to 20th	Night	27% 9% 20% 23% 15% 5%	3480
	21st to end	Night	34% 6% 9% 24% 21% 7%	3817
April	1st to 10th	Night	27% 8% 16% 23% 16% 9%	2090
	11th to 20th	Night	29% 7% 12% 26% 19% 7%	2047
	21st to end	Night	25% 7% 14% 25% 22% 7%	1893
May	1st to 10th	Night	20% 12% 21% 29% 14% 5%	2840
	11th to 20th	Night	28% 13% 22% 26% 10% 2	2813
	21st to end	Night	19% 7% 15% 38% 20% 1	3087
June	1st to 10th	Night	38% 13% 21% 21% 6%	1710
	11th to 20th	Night	37% 15% 25% 21% 2	1710
	21st to end	Night	41% 14% 23% 17% 5% 1	1710
July	1st to 10th	Night	47% 18% 25% 9% 1	2795
	11th to 20th	Night	42% 20% 31% 7% 1	2786
	21st to end	Night	52% 17% 22% 8% 1	2988
August	1st to 10th	Night	38% 15% 32% 12% 3	2814
	11th to 20th	Night	27% 16% 31% 22% 5%	2967
	21st to end	Night	42% 16% 25% 15% 2	3819
September	1st to 10th	Night	43% 17% 21% 14% 5%	2090
	11th to 20th	Night	45% 16% 20% 16% 3 1	2090
	21st to end	Night	41% 11% 17% 18% 10% 2	2090
October	1st to 10th	Night	53% 11% 12% 12% 7% 5%	3480
	11th to 20th	Night	24% 5% 9% 23% 34% 5%	3777
	21st to end	Night	28% 6% 9% 18% 32% 7%	4120
November	1st to 10th	Night	30% 7% 13% 21% 18% 11%	2341
	11th to 20th	Night	37% 6% 9% 20% 19% 10%	2293
	21st to end	Night	36% 6% 10% 21% 20% 8%	2436
December	1st to 10th	Night	32% 7% 13% 27% 15% 6%	2470
	11th to 20th	Night	35% 7% 9% 19% 20% 11%	3044
	21st to end	Night	43% 8% 11% 19% 14% 4	4532

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	11% 8% 37% 29% 12% 3	270
	11th to 20th	Day	9% 12% 29% 29% 17% 4	270
	21st to end	Day	12% 15% 37% 28% 7%	297
February	1st to 10th	Day	12% 10% 28% 27% 18% 5%	270
	11th to 20th	Day	12% 8% 27% 31% 17% 6%	270
	21st to end	Day	9% 7% 27% 32% 20% 5%	291
March	1st to 10th	Day	5% 7% 33% 34% 19% 2	460
	11th to 20th	Day	10% 7% 26% 31% 21% 5%	460
	21st to end	Day	9% 6% 26% 31% 23% 5%	506
April	1st to 10th	Day	10% 6% 25% 33% 22% 3	460
	11th to 20th	Day	10% 7% 22% 29% 27% 6%	452
	21st to end	Day	6% 3 19% 30% 29% 13%	460
May	1st to 10th	Day	4 3 17% 27% 32% 17%	463
	11th to 20th	Day	7% 3 11% 28% 30% 21%	487
	21st to end	Day	8% 1 7% 17% 33% 34%	529
June	1st to 10th	Day	10% 2 9% 19% 29% 31%	490
	11th to 20th	Day	8% 2 9% 18% 26% 38%	490
	21st to end	Day	6% 1 5% 15% 22% 51%	490
July	1st to 10th	Day	6% 1 4 8% 23% 57%	485
	11th to 20th	Day	6% 5% 7% 26% 55%	484
	21st to end	Day	7% 1 4 14% 27% 47%	532
August	1st to 10th	Day	8% 1 8% 15% 23% 44%	486
	11th to 20th	Day	6% 4 10% 25% 55%	479
	21st to end	Day	11% 1 6% 13% 28% 41%	539
September	1st to 10th	Day	9% 2 8% 12% 28% 41%	490
	11th to 20th	Day	10% 1 7% 20% 33% 28%	490
	21st to end	Day	10% 2 8% 18% 31% 30%	490
October	1st to 10th	Day	13% 4 15% 29% 29% 10%	490
	11th to 20th	Day	6% 4 16% 28% 32% 13%	490
	21st to end	Day	8% 3 19% 35% 29% 7%	539
November	1st to 10th	Day	9% 6% 21% 29% 28% 7%	495
	11th to 20th	Day	16% 5% 20% 32% 22% 5%	464
	21st to end	Day	11% 9% 21% 37% 20% 2	301
December	1st to 10th	Day	5% 8% 31% 29% 21% 6%	270
	11th to 20th	Day	15% 8% 24% 33% 17% 2	270
	21st to end	Day	9% 8% 24% 34% 20% 4	297
January	1st to 10th	Night	12% 8% 31% 36% 13% 1	760
	11th to 20th	Night	12% 7% 27% 39% 15% 1	760
	21st to end	Night	17% 8% 33% 34% 8%	836
February	1st to 10th	Night	15% 6% 28% 37% 14%	760
	11th to 20th	Night	10% 6% 29% 41% 12% 1	743
	21st to end	Night	11% 5% 30% 46% 9%	628
March	1st to 10th	Night	8% 6% 31% 42% 13% 1	760
	11th to 20th	Night	10% 6% 26% 42% 15% 1	760
	21st to end	Night	8% 5% 28% 43% 15% 1	836
April	1st to 10th	Night	8% 5% 28% 42% 17% 1	760
	11th to 20th	Night	8% 6% 27% 42% 16% 1	751
	21st to end	Night	7% 3 22% 44% 23%	753
May	1st to 10th	Night	4 2 12% 51% 28% 2	570
	11th to 20th	Night	6% 2 11% 42% 35% 4	561
	21st to end	Night	6% 1 7% 34% 45% 7%	617
June	1st to 10th	Night	11% 1 8% 30% 41% 9%	570
	11th to 20th	Night	6% 1 5% 22% 42% 24%	570
	21st to end	Night	9% 1 4 15% 45% 25%	570
July	1st to 10th	Night	8% 3 14% 43% 32%	555
	11th to 20th	Night	6% 1 2 9% 49% 34%	552
	21st to end	Night	8% 4 11% 49% 28%	624
August	1st to 10th	Night	7% 1 5% 11% 48% 29%	567
	11th to 20th	Night	5% 1 4 9% 44% 37%	564
	21st to end	Night	11% 2 7% 17% 40% 23%	827
September	1st to 10th	Night	10% 2 7% 19% 41% 20%	760
	11th to 20th	Night	12% 2 8% 24% 40% 13%	760
	21st to end	Night	10% 2 9% 27% 42% 9%	760
October	1st to 10th	Night	13% 2 15% 36% 30% 4	760
	11th to 20th	Night	5% 3 14% 39% 35% 4	760
	21st to end	Night	11% 2 17% 39% 28% 3	836
November	1st to 10th	Night	10% 3 20% 37% 27% 2	780
	11th to 20th	Night	11% 5% 20% 41% 21% 2	765
	21st to end	Night	10% 3 26% 43% 17% 1	760
December	1st to 10th	Night	11% 4 23% 37% 24% 1	760
	11th to 20th	Night	12% 5% 24% 37% 21% 1	760
	21st to end	Night	12% 6% 24% 40% 18% 1	836

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