Hay House Farm Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hay House Farm Observatory 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	14% 6% 2 6% 4 4 5% 4 6% 8% 42%	100948
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 43%	97800
Transparency	Day	40% 5% 12% 23% 16% 4	100758
	Night	40% 4 11% 23% 18% 4	97660
Seeing	Day	19% 10% 26% 25% 14% 5%	15019
	Night	17% 9% 27% 31% 14% 1	24701

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% 6% 2 4 3 3 3 3 4 6% 50%	2818
	11th to 20th	Day	15% 9% 2 6% 5% 4 5% 4 4 5% 42%	2840
	21st to end	Day	18% 9% 3 6% 4 4 4 4 4 5% 39%	3124
February	1st to 10th	Day	13% 6% 3 6% 5% 5% 5% 3 6% 6% 40%	1710
	11th to 20th	Day	19% 7% 2 5% 4 3 3 3 5% 6% 43%	1680
	21st to end	Day	19% 8% 3 6% 5% 4 4 4 5% 7% 37%	1614
March	1st to 10th	Day	20% 7% 3 6% 4 5% 4 3 4 7% 38%	3435
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 5% 7% 51%	3480
	21st to end	Day	20% 6% 2 6% 5% 4 4 3 5% 6% 37%	3815
April	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 6% 7% 49%	2263
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 48%	2254
	21st to end	Day	16% 6% 3 6% 4 4 4 3 5% 6% 42%	2280
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 7% 7% 32%	4075
	11th to 20th	Day	21% 8% 3 6% 4 4 5% 4 6% 8% 32%	4081
	21st to end	Day	10% 4 2 6% 4 4 5% 5% 7% 10% 44%	4779
June	1st to 10th	Day	10% 5% 2 4 5% 5% 5% 4 7% 9% 43%	2660
	11th to 20th	Day	11% 5% 2 5% 5% 4 7% 4 6% 10% 41%	2660
	21st to end	Day	8% 4 2 6% 5% 5% 6% 5% 7% 9% 43%	2660
July	1st to 10th	Day	7% 4 2 5% 5% 4 7% 5% 8% 11% 42%	4313
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 5% 8% 12% 36%	4120
	21st to end	Day	12% 7% 2 7% 6% 5% 6% 5% 8% 9% 32%	4466
August	1st to 10th	Day	16% 6% 2 6% 5% 6% 5% 5% 8% 10% 32%	4104
	11th to 20th	Day	9% 5% 2 7% 5% 6% 5% 5% 8% 9% 39%	3923
	21st to end	Day	9% 4 1 5% 4 4 5% 4 6% 10% 48%	4180
September	1st to 10th	Day	12% 6% 2 6% 4 4 4 4 5% 7% 45%	2280
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 6% 8% 45%	2236
	21st to end	Day	22% 7% 2 5% 4 3 5% 4 4 6% 37%	2005
October	1st to 10th	Day	15% 5% 2 6% 3 3 3 2 5% 6% 49%	1900
	11th to 20th	Day	16% 4 2 4 4 4 4 3 4 5% 53%	1900
	21st to end	Day	13% 5% 2 5% 4 3 3 3 4 6% 52%	2027
November	1st to 10th	Day	13% 4 1 4 4 4 3 3 4 6% 55%	1857
	11th to 20th	Day	14% 5% 2 4 3 3 3 4 5% 6% 50%	1687
	21st to end	Day	15% 5% 1 5% 3 4 3 4 5% 5% 50%	1520
December	1st to 10th	Day	16% 7% 2 6% 3 5% 4 4 4 7% 41%	1520
	11th to 20th	Day	16% 7% 2 4 3 4 3 3 4 5% 50%	1910
	21st to end	Day	19% 7% 2 6% 4 3 4 3 5% 7% 38%	2772
January	1st to 10th	Night	13% 8% 2 5% 4 3 4 3 4 5% 49%	4109
	11th to 20th	Night	18% 7% 2 5% 3 4 3 3 4 5% 47%	4120
	21st to end	Night	19% 9% 3 6% 3 3 3 2 4 5% 43%	4532
February	1st to 10th	Night	14% 7% 2 5% 4 5% 5% 4 5% 7% 42%	2470
	11th to 20th	Night	19% 9% 2 5% 3 3 3 3 4 6% 43%	2384
	21st to end	Night	16% 8% 3 5% 5% 4 3 3 4 6% 44%	1837
March	1st to 10th	Night	20% 7% 2 7% 3 4 4 4 4 7% 38%	3418
	11th to 20th	Night	12% 5% 2 4 3 3 4 4 6% 8% 51%	3480
	21st to end	Night	15% 6% 3 6% 4 3 4 3 4 6% 48%	3817
April	1st to 10th	Night	13% 7% 2 6% 4 3 3 3 5% 8% 45%	1915
	11th to 20th	Night	11% 5% 2 6% 3 3 5% 3 6% 8% 48%	1875
	21st to end	Night	14% 5% 2 5% 4 4 3 4 6% 7% 45%	1900
May	1st to 10th	Night	19% 10% 3 7% 4 4 4 3 5% 8% 33%	2848
	11th to 20th	Night	23% 7% 2 6% 4 4 5% 4 6% 6% 32%	2812
	21st to end	Night	10% 5% 2 6% 4 5% 5% 5% 6% 10% 43%	2772
June	1st to 10th	Night	10% 5% 2 5% 5% 4 4 5% 8% 9% 43%	1520
	11th to 20th	Night	10% 6% 2 6% 5% 5% 4 4 7% 9% 42%	1520
	21st to end	Night	8% 4 2 6% 4 5% 6% 4 8% 10% 43%	1520
July	1st to 10th	Night	7% 5% 2 7% 5% 5% 5% 6% 8% 10% 41%	2641
	11th to 20th	Night	9% 6% 3 8% 5% 5% 5% 5% 8% 10% 36%	2840
	21st to end	Night	11% 8% 2 9% 7% 6% 7% 5% 7% 8% 31%	3087
August	1st to 10th	Night	17% 5% 2 8% 5% 5% 6% 4 6% 8% 33%	2825
	11th to 20th	Night	11% 7% 3 9% 6% 5% 5% 4 6% 8% 36%	2872
	21st to end	Night	10% 6% 2 7% 5% 5% 4 4 5% 9% 43%	3476
September	1st to 10th	Night	14% 5% 2 6% 3 5% 4 4 5% 7% 44%	1900
	11th to 20th	Night	12% 6% 2 6% 4 3 4 4 5% 8% 46%	1941
	21st to end	Night	23% 6% 3 6% 4 3 4 3 4 6% 39%	2174
October	1st to 10th	Night	18% 5% 2 5% 4 3 3 3 5% 6% 46%	2280
	11th to 20th	Night	15% 5% 2 6% 3 4 3 3 5% 5% 50%	2280
	21st to end	Night	14% 5% 2 4 4 3 4 2 4 6% 52%	2435
November	1st to 10th	Night	12% 5% 2 6% 4 3 3 3 4 5% 52%	2221
	11th to 20th	Night	13% 5% 2 6% 4 3 4 3 5% 6% 50%	2490
	21st to end	Night	13% 4 1 5% 4 4 4 4 5% 6% 50%	2660
December	1st to 10th	Night	16% 8% 3 6% 4 4 4 3 5% 5% 42%	2660
	11th to 20th	Night	17% 7% 2 5% 4 3 3 3 4 6% 47%	3285
	21st to end	Night	16% 6% 2 6% 4 4 4 4 6% 7% 40%	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	37% 3 5% 31% 17% 5%	2819
	11th to 20th	Day	43% 3 7% 20% 20% 7%	2840
	21st to end	Day	48% 3 9% 22% 16% 3	3124
February	1st to 10th	Day	42% 4 9% 27% 15% 3	1710
	11th to 20th	Day	43% 3 7% 21% 21% 5%	1689
	21st to end	Day	48% 3 11% 16% 18% 5%	1614
March	1st to 10th	Day	47% 3 9% 19% 14% 7%	3435
	11th to 20th	Day	31% 5% 7% 25% 25% 8%	3480
	21st to end	Day	48% 3 9% 20% 16% 4	3815
April	1st to 10th	Day	34% 4 10% 23% 19% 9%	2263
	11th to 20th	Day	36% 3 11% 21% 23% 6%	2254
	21st to end	Day	42% 4 10% 23% 15% 5%	2280
May	1st to 10th	Day	49% 4 13% 19% 12% 2	4113
	11th to 20th	Day	48% 7% 12% 22% 11% 1	4085
	21st to end	Day	34% 5% 16% 22% 21% 2	4793
June	1st to 10th	Day	35% 6% 16% 27% 14% 2	2660
	11th to 20th	Day	38% 6% 15% 23% 16% 2	2660
	21st to end	Day	34% 7% 16% 26% 16% 2	2660
July	1st to 10th	Day	34% 6% 23% 20% 11% 6%	4246
	11th to 20th	Day	38% 5% 20% 28% 8% 1	4051
	21st to end	Day	45% 6% 13% 21% 14% 1	4324
August	1st to 10th	Day	45% 5% 18% 25% 6% 1	4091
	11th to 20th	Day	39% 5% 15% 25% 15% 1	3962
	21st to end	Day	32% 4 17% 29% 17% 2	4180
September	1st to 10th	Day	38% 5% 12% 19% 21% 5%	2280
	11th to 20th	Day	37% 5% 7% 28% 20% 4	2236
	21st to end	Day	47% 5% 9% 18% 17% 3	2005
October	1st to 10th	Day	38% 3 9% 25% 22% 4	1900
	11th to 20th	Day	35% 3 8% 25% 24% 4	1900
	21st to end	Day	35% 3 6% 26% 23% 7%	2027
November	1st to 10th	Day	33% 3 8% 24% 28% 5%	1857
	11th to 20th	Day	34% 4 9% 23% 22% 8%	1687
	21st to end	Day	35% 4 9% 24% 24% 4	1520
December	1st to 10th	Day	43% 4 11% 24% 14% 4	1520
	11th to 20th	Day	37% 3 7% 30% 16% 6%	1906
	21st to end	Day	46% 3 11% 26% 13% 1	2772
January	1st to 10th	Night	38% 3 7% 24% 22% 5%	4109
	11th to 20th	Night	41% 2 7% 21% 23% 5%	4120
	21st to end	Night	46% 2 6% 24% 18% 4	4532
February	1st to 10th	Night	41% 4 10% 25% 17% 3	2470
	11th to 20th	Night	44% 3 7% 20% 19% 7%	2386
	21st to end	Night	43% 3 9% 21% 17% 6%	1837
March	1st to 10th	Night	46% 5% 7% 23% 16% 3	3418
	11th to 20th	Night	31% 4 8% 22% 28% 7%	3480
	21st to end	Night	39% 3 9% 22% 21% 5%	3817
April	1st to 10th	Night	39% 4 9% 19% 23% 7%	1915
	11th to 20th	Night	33% 5% 13% 22% 22% 6%	1875
	21st to end	Night	37% 4 12% 25% 16% 6%	1900
May	1st to 10th	Night	50% 4 14% 19% 11% 2	2875
	11th to 20th	Night	49% 7% 12% 21% 9% 2	2813
	21st to end	Night	36% 6% 16% 25% 15% 2	2779
June	1st to 10th	Night	34% 7% 14% 28% 16% 1	1520
	11th to 20th	Night	37% 7% 18% 23% 14% 2	1520
	21st to end	Night	33% 8% 16% 23% 18% 3	1520
July	1st to 10th	Night	37% 7% 25% 16% 12% 3	2598
	11th to 20th	Night	41% 7% 21% 23% 7% 1	2786
	21st to end	Night	48% 7% 15% 19% 10%	2988
August	1st to 10th	Night	48% 5% 18% 23% 7% 1	2814
	11th to 20th	Night	44% 5% 14% 24% 13%	2899
	21st to end	Night	39% 4 13% 29% 13% 1	3476
September	1st to 10th	Night	39% 6% 12% 20% 15% 7%	1900
	11th to 20th	Night	37% 5% 10% 25% 21% 3	1941
	21st to end	Night	47% 5% 8% 21% 16% 3	2174
October	1st to 10th	Night	40% 4 9% 25% 19% 4	2280
	11th to 20th	Night	37% 4 6% 25% 23% 6%	2280
	21st to end	Night	34% 3 8% 24% 24% 6%	2435
November	1st to 10th	Night	35% 4 7% 23% 24% 6%	2221
	11th to 20th	Night	37% 3 8% 20% 25% 8%	2490
	21st to end	Night	35% 3 8% 25% 22% 6%	2660
December	1st to 10th	Night	43% 4 9% 24% 16% 4	2660
	11th to 20th	Night	40% 3 9% 22% 21% 6%	3288
	21st to end	Night	43% 4 11% 25% 16% 2	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	24% 21% 30% 20% 5%	267
	11th to 20th	Day	27% 25% 32% 13% 3	270
	21st to end	Day	27% 19% 38% 13% 3	297
February	1st to 10th	Day	23% 19% 41% 11% 5%	270
	11th to 20th	Day	39% 22% 27% 10% 2	287
	21st to end	Day	31% 18% 27% 21% 3	382
March	1st to 10th	Day	23% 16% 35% 19% 6%	460
	11th to 20th	Day	22% 19% 35% 17% 6%	460
	21st to end	Day	24% 16% 35% 19% 5% 1	506
April	1st to 10th	Day	22% 18% 32% 18% 8% 1	460
	11th to 20th	Day	19% 14% 30% 22% 10% 4	452
	21st to end	Day	23% 11% 34% 23% 8% 2	460
May	1st to 10th	Day	22% 14% 31% 21% 10% 3	463
	11th to 20th	Day	21% 10% 29% 24% 12% 4	487
	21st to end	Day	17% 4 27% 29% 19% 4	529
June	1st to 10th	Day	14% 5% 25% 31% 21% 5%	490
	11th to 20th	Day	13% 5% 26% 30% 18% 8%	490
	21st to end	Day	10% 5% 25% 35% 20% 6%	490
July	1st to 10th	Day	12% 2 16% 35% 26% 10%	485
	11th to 20th	Day	8% 3 14% 36% 28% 11%	484
	21st to end	Day	11% 4 19% 33% 23% 10%	532
August	1st to 10th	Day	13% 3 18% 29% 25% 11%	486
	11th to 20th	Day	12% 2 19% 31% 25% 11%	479
	21st to end	Day	11% 3 16% 31% 24% 15%	539
September	1st to 10th	Day	15% 6% 16% 26% 23% 16%	490
	11th to 20th	Day	16% 3 15% 34% 22% 10%	490
	21st to end	Day	30% 5% 23% 28% 9% 5%	490
October	1st to 10th	Day	19% 5% 22% 29% 17% 7%	490
	11th to 20th	Day	15% 12% 24% 27% 19% 3	490
	21st to end	Day	17% 11% 33% 26% 10% 3	514
November	1st to 10th	Day	18% 8% 27% 29% 14% 4	455
	11th to 20th	Day	18% 13% 32% 25% 9% 3	337
	21st to end	Day	18% 13% 37% 22% 9% 1	180
December	1st to 10th	Day	22% 16% 41% 13% 8% 1	180
	11th to 20th	Day	24% 14% 31% 21% 8% 2	180
	21st to end	Day	28% 16% 32% 15% 9% 1	198
January	1st to 10th	Night	20% 14% 39% 24% 3	760
	11th to 20th	Night	21% 14% 34% 28% 4	760
	21st to end	Night	19% 15% 40% 24% 2	836
February	1st to 10th	Night	18% 12% 39% 28% 3	760
	11th to 20th	Night	25% 17% 37% 19% 2	743
	21st to end	Night	23% 16% 37% 22% 2	628
March	1st to 10th	Night	18% 16% 37% 26% 4	760
	11th to 20th	Night	22% 15% 36% 21% 6% 1	760
	21st to end	Night	19% 14% 35% 26% 6%	836
April	1st to 10th	Night	17% 16% 37% 23% 5%	760
	11th to 20th	Night	13% 12% 37% 28% 9%	751
	21st to end	Night	16% 10% 34% 32% 8%	760
May	1st to 10th	Night	20% 7% 30% 30% 12%	592
	11th to 20th	Night	21% 3 24% 35% 16% 1	561
	21st to end	Night	14% 2 19% 39% 24% 3	439
June	1st to 10th	Night	11% 1 19% 44% 24% 1	380
	11th to 20th	Night	10% 4 14% 45% 25% 2	380
	21st to end	Night	8% 2 20% 46% 22% 1	380
July	1st to 10th	Night	12% 2 15% 39% 28% 4	436
	11th to 20th	Night	7% 1 11% 41% 36% 4	552
	21st to end	Night	9% 2 13% 42% 29% 4	624
August	1st to 10th	Night	13% 2 9% 41% 31% 4	567
	11th to 20th	Night	16% 3 8% 40% 29% 3	612
	21st to end	Night	12% 3 11% 38% 31% 5%	836
September	1st to 10th	Night	16% 2 13% 34% 30% 6%	760
	11th to 20th	Night	14% 4 15% 34% 30% 4	760
	21st to end	Night	25% 3 18% 32% 21% 1	760
October	1st to 10th	Night	21% 4 19% 30% 23% 4	760
	11th to 20th	Night	17% 8% 24% 33% 16% 1	760
	21st to end	Night	16% 8% 29% 33% 12% 1	812
November	1st to 10th	Night	15% 7% 29% 33% 14% 2	740
	11th to 20th	Night	16% 11% 33% 31% 8%	760
	21st to end	Night	15% 9% 33% 33% 9% 1	760
December	1st to 10th	Night	21% 11% 34% 27% 7%	760
	11th to 20th	Night	18% 9% 35% 32% 6%	760
	21st to end	Night	21% 10% 30% 34% 4	836

Page generated at 2024-10-22 20:21:06. Version ac07

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