Country Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Country Hill Observatory clear sky chart from 2005-11-06 to 2024-11-30.

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	18% 8% 2 6% 4 4 4 4 5% 7% 38%	101411
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 39%	98172
Transparency	Day	45% 4 10% 23% 15% 2	104962
	Night	45% 4 11% 23% 15% 2	102697
Seeing	Day	26% 16% 32% 18% 7% 2	15172
	Night	23% 14% 32% 23% 6% 1	24097

By Month

Percentage Cloud Cover NE (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	14% 8% 3 6% 4 4 3 3 4 5% 46%	2517
	11th to 20th	Day	17% 9% 3 6% 4 4 4 4 4 5% 40%	2520
	21st to end	Day	21% 13% 3 7% 4 3 3 3 4 5% 34%	2772
February	1st to 10th	Day	19% 8% 2 5% 5% 4 4 4 6% 6% 36%	1801
	11th to 20th	Day	15% 7% 3 6% 5% 4 4 3 5% 6% 42%	1848
	21st to end	Day	19% 10% 3 6% 4 3 4 3 4 6% 37%	1570
March	1st to 10th	Day	25% 14% 3 7% 4 3 3 3 4 4 31%	3116
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 5% 6% 8% 43%	3338
	21st to end	Day	23% 10% 2 6% 4 4 4 4 4 6% 35%	4031
April	1st to 10th	Day	19% 9% 3 7% 5% 3 3 4 5% 7% 37%	2280
	11th to 20th	Day	18% 7% 2 5% 4 4 4 3 6% 7% 40%	2255
	21st to end	Day	21% 6% 2 7% 4 4 4 3 5% 5% 38%	2470
May	1st to 10th	Day	26% 11% 3 7% 3 4 3 3 4 7% 28%	4106
	11th to 20th	Day	24% 9% 3 7% 4 4 3 3 4 6% 32%	4112
	21st to end	Day	16% 5% 2 5% 4 4 4 3 5% 8% 45%	4837
June	1st to 10th	Day	18% 7% 2 5% 4 4 5% 4 7% 9% 34%	2660
	11th to 20th	Day	16% 7% 2 6% 4 5% 5% 4 6% 9% 36%	2660
	21st to end	Day	16% 7% 2 6% 5% 5% 4 4 6% 9% 36%	2660
July	1st to 10th	Day	14% 6% 2 7% 5% 6% 6% 5% 7% 9% 33%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 7% 10% 37%	4440
	21st to end	Day	19% 8% 3 7% 5% 5% 5% 4 6% 7% 32%	4814
August	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 8% 31%	4121
	11th to 20th	Day	13% 7% 3 7% 5% 6% 6% 4 5% 7% 39%	3959
	21st to end	Day	8% 4 2 6% 4 5% 6% 5% 7% 9% 45%	4180
September	1st to 10th	Day	15% 6% 2 6% 4 3 5% 4 5% 6% 45%	2275
	11th to 20th	Day	15% 5% 2 5% 3 4 3 3 4 6% 51%	2090
	21st to end	Day	19% 6% 2 5% 4 4 3 3 5% 5% 43%	2090
October	1st to 10th	Day	23% 7% 2 5% 3 4 3 2 4 5% 42%	2090
	11th to 20th	Day	15% 5% 2 6% 3 3 3 3 5% 7% 48%	1868
	21st to end	Day	18% 6% 2 6% 4 3 4 4 4 5% 43%	1881
November	1st to 10th	Day	16% 6% 2 5% 4 3 4 3 3 5% 49%	1761
	11th to 20th	Day	18% 6% 2 4 3 3 3 3 4 6% 47%	1800
	21st to end	Day	18% 7% 2 5% 4 3 4 3 6% 6% 44%	1798
December	1st to 10th	Day	19% 8% 2 5% 5% 3 4 4 5% 6% 39%	1573
	11th to 20th	Day	21% 6% 2 4 4 3 3 2 4 5% 46%	1906
	21st to end	Day	21% 10% 3 8% 4 4 4 3 5% 6% 34%	2772
January	1st to 10th	Night	17% 8% 2 4 3 3 3 3 4 6% 48%	4429
	11th to 20th	Night	16% 10% 4 8% 4 5% 3 3 3 4 40%	4440
	21st to end	Night	22% 12% 4 7% 4 4 4 3 4 5% 31%	4884
February	1st to 10th	Night	17% 9% 3 6% 4 4 3 4 5% 6% 39%	2373
	11th to 20th	Night	16% 8% 3 7% 4 4 5% 4 5% 5% 40%	2218
	21st to end	Night	18% 10% 2 6% 4 3 4 3 4 5% 42%	1884
March	1st to 10th	Night	29% 11% 2 4 3 3 4 3 4 5% 33%	3724
	11th to 20th	Night	11% 10% 2 6% 5% 4 4 4 6% 6% 42%	3621
	21st to end	Night	25% 8% 2 6% 4 4 4 3 5% 5% 34%	3598
April	1st to 10th	Night	18% 9% 3 7% 4 5% 4 4 4 6% 37%	1900
	11th to 20th	Night	19% 8% 2 6% 5% 4 4 3 5% 6% 38%	1872
	21st to end	Night	20% 9% 2 6% 4 3 3 3 4 6% 40%	1710
May	1st to 10th	Night	24% 10% 3 8% 5% 4 4 4 5% 7% 27%	2834
	11th to 20th	Night	23% 10% 3 8% 5% 5% 5% 4 6% 7% 25%	2795
	21st to end	Night	16% 6% 2 6% 5% 5% 4 3 6% 7% 40%	2738
June	1st to 10th	Night	15% 7% 3 6% 5% 4 4 4 5% 7% 37%	1520
	11th to 20th	Night	19% 7% 3 6% 4 3 5% 4 5% 8% 37%	1520
	21st to end	Night	16% 6% 3 5% 4 4 5% 4 6% 8% 40%	1520
July	1st to 10th	Night	14% 7% 2 6% 5% 5% 5% 4 7% 10% 34%	2520
	11th to 20th	Night	15% 7% 3 7% 4 4 4 4 6% 9% 38%	2520
	21st to end	Night	17% 10% 3 7% 5% 5% 5% 4 6% 7% 31%	2739
August	1st to 10th	Night	21% 7% 3 8% 5% 5% 6% 4 7% 7% 29%	2762
	11th to 20th	Night	10% 8% 3 8% 5% 7% 7% 5% 6% 7% 35%	2865
	21st to end	Night	8% 4 1 5% 3 3 4 3 5% 7% 56%	3476
September	1st to 10th	Night	12% 7% 2 7% 4 5% 5% 5% 5% 6% 44%	1905
	11th to 20th	Night	15% 5% 2 4 3 3 3 2 4 6% 51%	2090
	21st to end	Night	19% 8% 2 6% 4 3 4 3 5% 5% 42%	2090
October	1st to 10th	Night	20% 8% 2 5% 4 3 3 3 5% 6% 41%	2090
	11th to 20th	Night	15% 5% 2 4 4 3 4 3 5% 7% 48%	2308
	21st to end	Night	20% 7% 2 7% 4 4 4 2 4 5% 40%	2717
November	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 4 6% 49%	2537
	11th to 20th	Night	18% 7% 2 5% 3 3 3 2 4 6% 47%	2600
	21st to end	Night	17% 6% 2 4 3 4 4 4 5% 6% 46%	2598
December	1st to 10th	Night	19% 9% 2 6% 4 3 4 3 4 5% 40%	2603
	11th to 20th	Night	19% 7% 2 5% 4 3 3 3 5% 6% 41%	3288
	21st to end	Night	20% 12% 3 6% 4 3 3 3 5% 6% 35%	4884

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	42% 3 7% 31% 14% 2	2518
	11th to 20th	Day	47% 4 9% 25% 13% 2	2520
	21st to end	Day	54% 3 8% 23% 11% 2	2772
February	1st to 10th	Day	48% 3 11% 19% 14% 3	1801
	11th to 20th	Day	44% 4 10% 23% 16% 3	1857
	21st to end	Day	49% 3 9% 21% 14% 3	1570
March	1st to 10th	Day	58% 3 10% 15% 11% 3	3119
	11th to 20th	Day	39% 5% 11% 28% 14% 3	3338
	21st to end	Day	52% 3 4 17% 16% 7%	4031
April	1st to 10th	Day	49% 3 8% 20% 17% 4	2280
	11th to 20th	Day	44% 4 9% 23% 18% 3	2255
	21st to end	Day	48% 3 8% 20% 17% 4	2470
May	1st to 10th	Day	58% 3 12% 15% 10% 1	4120
	11th to 20th	Day	54% 4 14% 16% 11% 2	4116
	21st to end	Day	38% 5% 11% 26% 19% 2	4837
June	1st to 10th	Day	47% 5% 12% 24% 12% 1	2660
	11th to 20th	Day	45% 4 12% 22% 15% 2	2660
	21st to end	Day	45% 5% 13% 22% 14% 1	2660
July	1st to 10th	Day	45% 7% 11% 20% 14% 2	4370
	11th to 20th	Day	42% 5% 15% 24% 13% 2	4365
	21st to end	Day	50% 5% 11% 20% 13% 2	4661
August	1st to 10th	Day	50% 6% 15% 20% 8%	4107
	11th to 20th	Day	44% 5% 13% 28% 10% 1	3998
	21st to end	Day	32% 6% 13% 28% 19% 2	4180
September	1st to 10th	Day	39% 5% 9% 23% 22% 2	2275
	11th to 20th	Day	35% 4 9% 25% 24% 3	2090
	21st to end	Day	44% 3 7% 20% 24% 2	2090
October	1st to 10th	Day	41% 4 8% 23% 21% 4	3480
	11th to 20th	Day	32% 2 6% 28% 28% 4	3071
	21st to end	Day	32% 2 12% 29% 21% 3	3081
November	1st to 10th	Day	39% 3 12% 24% 19% 2	1761
	11th to 20th	Day	39% 3 9% 23% 23% 4	1800
	21st to end	Day	43% 3 11% 27% 13% 3	1798
December	1st to 10th	Day	47% 3 13% 18% 17% 2	1573
	11th to 20th	Day	44% 3 11% 18% 16% 6%	1906
	21st to end	Day	53% 4 10% 22% 11% 1	2772
January	1st to 10th	Night	40% 2 10% 32% 13% 3	4429
	11th to 20th	Night	49% 3 10% 23% 12% 3	4440
	21st to end	Night	59% 3 8% 17% 12% 2	4884
February	1st to 10th	Night	46% 4 12% 21% 14% 2	2373
	11th to 20th	Night	46% 4 9% 20% 17% 4	2220
	21st to end	Night	46% 2 8% 24% 16% 4	1884
March	1st to 10th	Night	55% 3 8% 20% 12% 3	3734
	11th to 20th	Night	42% 4 14% 21% 17% 3	3622
	21st to end	Night	54% 3 4 15% 17% 7%	3598
April	1st to 10th	Night	49% 4 8% 20% 16% 3	1900
	11th to 20th	Night	48% 2 8% 21% 18% 3	1872
	21st to end	Night	48% 4 9% 20% 15% 4	1710
May	1st to 10th	Night	58% 4 12% 16% 8% 2	2840
	11th to 20th	Night	59% 4 13% 14% 8% 2	2796
	21st to end	Night	43% 6% 13% 23% 13% 1	2739
June	1st to 10th	Night	45% 5% 13% 23% 13% 1	1520
	11th to 20th	Night	46% 4 12% 23% 14% 1	1520
	21st to end	Night	42% 7% 14% 24% 13% 1	1520
July	1st to 10th	Night	44% 7% 13% 21% 14%	2480
	11th to 20th	Night	42% 5% 17% 25% 11% 1	2472
	21st to end	Night	51% 6% 10% 17% 14% 2	2651
August	1st to 10th	Night	53% 7% 13% 18% 8% 1	2752
	11th to 20th	Night	44% 7% 13% 27% 9%	2892
	21st to end	Night	28% 4 15% 29% 22% 1	3476
September	1st to 10th	Night	41% 4 10% 24% 19% 2	1905
	11th to 20th	Night	36% 4 9% 24% 26% 2	2090
	21st to end	Night	46% 4 7% 21% 20% 2	2090
October	1st to 10th	Night	41% 4 12% 25% 16% 3	3480
	11th to 20th	Night	27% 2 8% 28% 31% 3	3831
	21st to end	Night	35% 3 11% 29% 20% 2	4467
November	1st to 10th	Night	38% 4 11% 23% 20% 4	2537
	11th to 20th	Night	42% 2 8% 23% 21% 4	2600
	21st to end	Night	40% 3 13% 28% 14% 2	2598
December	1st to 10th	Night	48% 3 11% 22% 15% 1	2603
	11th to 20th	Night	44% 4 14% 18% 18% 2	3288
	21st to end	Night	52% 4 7% 25% 12% 1	4884

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	36% 20% 27% 14% 3	180
	11th to 20th	Day	33% 22% 35% 9% 2	180
	21st to end	Day	29% 23% 35% 11% 2 1	198
February	1st to 10th	Day	35% 20% 31% 12% 2	391
	11th to 20th	Day	34% 28% 30% 7% 2	456
	21st to end	Day	34% 19% 32% 11% 3	382
March	1st to 10th	Day	34% 18% 32% 12% 3	460
	11th to 20th	Day	35% 21% 29% 10% 4 1	460
	21st to end	Day	32% 21% 32% 8% 5% 2	506
April	1st to 10th	Day	37% 19% 27% 11% 5% 1	460
	11th to 20th	Day	32% 22% 29% 13% 3 1	452
	21st to end	Day	30% 17% 32% 17% 2 2	460
May	1st to 10th	Day	37% 19% 28% 13% 2	463
	11th to 20th	Day	23% 18% 40% 14% 4 1	487
	21st to end	Day	21% 14% 36% 22% 6% 2	529
June	1st to 10th	Day	24% 12% 33% 21% 8% 1	490
	11th to 20th	Day	18% 16% 39% 20% 6% 1	490
	21st to end	Day	19% 12% 40% 20% 7% 1	490
July	1st to 10th	Day	20% 8% 31% 26% 13% 2	485
	11th to 20th	Day	18% 7% 33% 28% 11% 2	484
	21st to end	Day	14% 10% 40% 26% 10% 1	532
August	1st to 10th	Day	15% 9% 34% 30% 9% 3	486
	11th to 20th	Day	15% 10% 32% 28% 12% 3	479
	21st to end	Day	14% 9% 32% 26% 14% 5%	539
September	1st to 10th	Day	20% 11% 28% 24% 13% 5%	490
	11th to 20th	Day	19% 11% 28% 21% 13% 8%	490
	21st to end	Day	23% 11% 35% 18% 8% 4	490
October	1st to 10th	Day	29% 12% 26% 20% 8% 5%	490
	11th to 20th	Day	22% 14% 36% 15% 11% 3	438
	21st to end	Day	28% 14% 30% 18% 8% 1	429
November	1st to 10th	Day	24% 15% 32% 17% 9% 2	395
	11th to 20th	Day	30% 20% 29% 16% 5% 1	400
	21st to end	Day	30% 18% 30% 15% 6% 1	400
December	1st to 10th	Day	28% 28% 29% 10% 4	233
	11th to 20th	Day	38% 22% 33% 6% 2	180
	21st to end	Day	31% 21% 30% 12% 3 2	198
January	1st to 10th	Night	24% 19% 35% 19% 3	760
	11th to 20th	Night	30% 19% 34% 15% 2	760
	21st to end	Night	25% 20% 33% 19% 3	836
February	1st to 10th	Night	25% 19% 34% 20% 1	760
	11th to 20th	Night	27% 23% 34% 14% 2	743
	21st to end	Night	29% 19% 32% 16% 3	628
March	1st to 10th	Night	26% 19% 34% 18% 3	760
	11th to 20th	Night	23% 23% 33% 17% 4	760
	21st to end	Night	28% 20% 33% 15% 4	836
April	1st to 10th	Night	27% 20% 33% 17% 3	760
	11th to 20th	Night	25% 19% 33% 18% 5%	748
	21st to end	Night	26% 15% 38% 17% 3	570
May	1st to 10th	Night	32% 14% 31% 19% 4	570
	11th to 20th	Night	24% 16% 37% 20% 2	557
	21st to end	Night	20% 7% 38% 29% 5%	411
June	1st to 10th	Night	18% 9% 34% 29% 10%	380
	11th to 20th	Night	22% 6% 35% 31% 7%	380
	21st to end	Night	18% 6% 38% 32% 6% 1	380
July	1st to 10th	Night	15% 3 34% 37% 10%	370
	11th to 20th	Night	16% 3 31% 39% 10% 1	368
	21st to end	Night	15% 4 31% 41% 8%	416
August	1st to 10th	Night	14% 5% 35% 36% 9%	530
	11th to 20th	Night	15% 5% 28% 40% 12% 1	606
	21st to end	Night	16% 4 25% 37% 15% 2	836
September	1st to 10th	Night	16% 6% 32% 34% 11% 1	760
	11th to 20th	Night	17% 8% 28% 28% 17% 2	760
	21st to end	Night	22% 8% 29% 26% 12% 2	760
October	1st to 10th	Night	25% 10% 26% 26% 11% 2	760
	11th to 20th	Night	21% 11% 33% 22% 12% 1	760
	21st to end	Night	26% 14% 32% 20% 8%	836
November	1st to 10th	Night	19% 15% 32% 24% 9% 1	780
	11th to 20th	Night	24% 17% 34% 17% 7%	800
	21st to end	Night	25% 19% 32% 19% 5% 1	800
December	1st to 10th	Night	28% 16% 32% 19% 4	760
	11th to 20th	Night	27% 19% 31% 20% 3	760
	21st to end	Night	29% 18% 33% 18% 2	836

Page generated at 2024-11-27 17:30:52. Version ac07

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