Hale Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hale Hill Observatory clear sky chart from 2005-11-06 to 2024-08-30.

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	15% 9% 3 7% 4 4 4 4 6% 7% 37%	95535
	Night	15% 10% 3 7% 4 4 4 3 5% 6% 38%	93526
Transparency	Day	45% 6% 11% 22% 14% 2	95291
	Night	46% 6% 11% 21% 14% 2	93376
Seeing	Day	18% 12% 28% 23% 14% 5%	15330
	Night	19% 11% 28% 28% 13% 2	25121

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	14% 17% 7% 9% 4 4 4 4 5% 5% 27%	2527
	11th to 20th	Day	16% 12% 4 11% 8% 5% 6% 5% 5% 5% 22%	2530
	21st to end	Day	26% 20% 6% 8% 4 2 2 2 3 5% 22%	2940
February	1st to 10th	Day	17% 13% 6% 8% 5% 4 4 3 4 6% 30%	1900
	11th to 20th	Day	15% 11% 4 10% 5% 5% 4 4 5% 6% 32%	1848
	21st to end	Day	17% 15% 4 9% 4 3 4 3 4 6% 32%	1570
March	1st to 10th	Day	22% 17% 3 7% 3 3 3 2 3 3 33%	3120
	11th to 20th	Day	15% 7% 3 5% 4 4 4 3 5% 7% 44%	3310
	21st to end	Day	15% 10% 5% 8% 6% 5% 5% 4 6% 6% 31%	4064
April	1st to 10th	Day	15% 11% 3 7% 4 4 5% 3 6% 7% 36%	2280
	11th to 20th	Day	18% 8% 3 6% 5% 5% 3 3 5% 6% 39%	2254
	21st to end	Day	19% 8% 2 7% 5% 5% 5% 3 4 6% 36%	2394
May	1st to 10th	Day	19% 9% 3 8% 4 4 6% 4 7% 8% 28%	4082
	11th to 20th	Day	20% 7% 2 6% 5% 4 4 3 5% 6% 37%	4081
	21st to end	Day	11% 6% 3 7% 5% 5% 5% 4 7% 8% 39%	4632
June	1st to 10th	Day	11% 6% 2 5% 5% 5% 5% 3 6% 8% 43%	2660
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 7% 8% 46%	2660
	21st to end	Day	11% 6% 2 6% 5% 4 6% 3 7% 9% 42%	2660
July	1st to 10th	Day	14% 6% 2 6% 5% 4 4 3 7% 10% 38%	4440
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 5% 7% 11% 45%	4440
	21st to end	Day	11% 6% 3 7% 5% 6% 6% 5% 8% 10% 33%	4730
August	1st to 10th	Day	9% 4 1 5% 4 4 6% 4 7% 11% 45%	2457
	11th to 20th	Day	10% 5% 2 6% 4 5% 6% 5% 7% 10% 39%	2259
	21st to end	Day	6% 5% 1 6% 4 4 5% 4 6% 9% 50%	2485
September	1st to 10th	Day	12% 6% 2 5% 4 4 4 5% 5% 8% 44%	2159
	11th to 20th	Day	10% 4 2 6% 4 5% 5% 3 5% 7% 48%	1980
	21st to end	Day	11% 4 1 5% 4 4 4 3 5% 6% 52%	1980
October	1st to 10th	Day	11% 5% 2 6% 4 4 4 3 4 8% 49%	1980
	11th to 20th	Day	15% 7% 3 5% 4 3 5% 3 5% 6% 43%	1837
	21st to end	Day	19% 10% 3 7% 4 4 3 4 4 6% 36%	1782
November	1st to 10th	Day	9% 6% 2 5% 3 4 4 3 5% 7% 52%	1672
	11th to 20th	Day	17% 10% 3 7% 4 3 3 4 4 6% 40%	1710
	21st to end	Day	19% 10% 3 6% 4 3 4 3 5% 5% 37%	1710
December	1st to 10th	Day	19% 14% 4 9% 4 4 3 3 4 6% 31%	1701
	11th to 20th	Day	16% 16% 7% 8% 4 3 4 3 3 6% 30%	1918
	21st to end	Day	22% 20% 7% 9% 4 4 4 2 4 5% 18%	2783
January	1st to 10th	Night	18% 16% 7% 10% 4 4 4 3 4 5% 25%	4428
	11th to 20th	Night	15% 18% 7% 13% 6% 5% 4 3 4 4 22%	4440
	21st to end	Night	26% 18% 6% 7% 4 3 3 2 4 4 23%	4720
February	1st to 10th	Night	19% 12% 5% 10% 5% 4 3 3 5% 5% 28%	2280
	11th to 20th	Night	15% 12% 4 10% 4 5% 4 3 4 6% 33%	2218
	21st to end	Night	20% 12% 4 9% 4 3 3 3 4 5% 32%	1884
March	1st to 10th	Night	22% 17% 3 5% 4 3 3 3 3 5% 32%	3733
	11th to 20th	Night	14% 6% 2 6% 4 4 4 3 4 6% 48%	3650
	21st to end	Night	18% 8% 3 7% 5% 4 4 3 4 6% 38%	3594
April	1st to 10th	Night	14% 10% 2 7% 4 4 4 3 5% 7% 41%	1900
	11th to 20th	Night	17% 9% 3 6% 4 3 3 3 4 7% 41%	1875
	21st to end	Night	16% 9% 3 7% 4 4 4 4 6% 6% 37%	1785
May	1st to 10th	Night	18% 10% 4 8% 5% 3 5% 4 5% 8% 29%	2813
	11th to 20th	Night	19% 7% 2 6% 3 3 3 3 5% 7% 42%	2812
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 6% 9% 44%	2911
June	1st to 10th	Night	9% 6% 2 6% 4 4 4 4 5% 8% 48%	1520
	11th to 20th	Night	9% 4 2 6% 4 3 4 4 5% 9% 49%	1520
	21st to end	Night	6% 5% 1 5% 4 4 5% 5% 7% 10% 47%	1520
July	1st to 10th	Night	10% 6% 2 5% 3 4 4 4 6% 8% 47%	2530
	11th to 20th	Night	6% 4 1 4 4 4 5% 4 6% 8% 55%	2530
	21st to end	Night	10% 7% 2 7% 6% 4 5% 4 7% 9% 38%	2828
August	1st to 10th	Night	7% 4 2 6% 4 5% 4 4 6% 9% 50%	1701
	11th to 20th	Night	6% 5% 2 5% 4 4 5% 4 6% 9% 51%	1858
	21st to end	Night	6% 4 1 4 4 4 4 3 6% 9% 56%	2080
September	1st to 10th	Night	11% 6% 2 6% 4 4 3 4 5% 6% 49%	1800
	11th to 20th	Night	8% 4 2 5% 3 3 3 4 6% 7% 55%	1962
	21st to end	Night	11% 5% 2 5% 4 4 3 3 6% 7% 50%	1980
October	1st to 10th	Night	9% 4 2 5% 3 4 4 3 5% 6% 55%	1980
	11th to 20th	Night	17% 8% 2 4 3 4 3 3 4 6% 46%	2117
	21st to end	Night	19% 9% 2 6% 3 3 4 3 4 6% 40%	2574
November	1st to 10th	Night	12% 8% 2 4 3 3 4 3 5% 6% 50%	2406
	11th to 20th	Night	14% 9% 3 7% 4 4 3 2 5% 7% 42%	2470
	21st to end	Night	20% 12% 4 6% 4 3 3 3 4 6% 35%	2470
December	1st to 10th	Night	17% 13% 5% 9% 5% 3 4 3 5% 6% 30%	2474
	11th to 20th	Night	18% 14% 4 9% 4 3 3 3 5% 5% 33%	3279
	21st to end	Night	25% 19% 6% 9% 4 4 4 3 3 4 19%	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	58% 5% 8% 21% 8% 1	2528
	11th to 20th	Day	61% 7% 13% 13% 7%	2530
	21st to end	Day	67% 3 8% 18% 3 1	2940
February	1st to 10th	Day	55% 5% 9% 19% 10% 2	1900
	11th to 20th	Day	52% 5% 10% 21% 10% 1	1858
	21st to end	Day	54% 4 8% 22% 10% 2	1570
March	1st to 10th	Day	56% 4 6% 18% 11% 3	3120
	11th to 20th	Day	40% 5% 11% 29% 14% 1	3310
	21st to end	Day	50% 8% 13% 21% 7% 1	4064
April	1st to 10th	Day	46% 7% 11% 21% 14% 1	2280
	11th to 20th	Day	45% 5% 10% 25% 12% 4	2254
	21st to end	Day	49% 6% 9% 23% 11% 3	2394
May	1st to 10th	Day	50% 8% 14% 21% 7%	4120
	11th to 20th	Day	47% 7% 10% 26% 10%	4085
	21st to end	Day	39% 8% 13% 18% 19% 3	4645
June	1st to 10th	Day	37% 7% 11% 25% 16% 3	2660
	11th to 20th	Day	33% 8% 12% 24% 20% 3	2660
	21st to end	Day	37% 8% 15% 19% 17% 4	2660
July	1st to 10th	Day	40% 6% 12% 24% 16% 2	4371
	11th to 20th	Day	30% 7% 14% 30% 19% 1	4365
	21st to end	Day	43% 8% 15% 19% 14% 2	4580
August	1st to 10th	Day	32% 9% 14% 27% 16% 2	2444
	11th to 20th	Day	37% 9% 13% 25% 15% 2	2259
	21st to end	Day	29% 7% 14% 25% 17% 7%	2485
September	1st to 10th	Day	37% 7% 11% 25% 16% 4	2159
	11th to 20th	Day	34% 5% 12% 26% 21% 3	1980
	21st to end	Day	32% 5% 10% 25% 25% 2	1980
October	1st to 10th	Day	34% 6% 11% 24% 22% 3	1980
	11th to 20th	Day	40% 5% 9% 23% 21% 2	1837
	21st to end	Day	49% 4 9% 23% 14% 1	1782
November	1st to 10th	Day	32% 5% 12% 29% 17% 5%	1672
	11th to 20th	Day	45% 4 9% 21% 16% 4	1710
	21st to end	Day	48% 5% 8% 22% 15% 1	1710
December	1st to 10th	Day	56% 4 10% 19% 11% 1	1701
	11th to 20th	Day	57% 4 7% 23% 8% 1	1915
	21st to end	Day	68% 5% 9% 11% 6%	2783
January	1st to 10th	Night	61% 5% 11% 16% 7%	4428
	11th to 20th	Night	67% 4 9% 13% 7%	4440
	21st to end	Night	66% 3 8% 15% 8% 1	4720
February	1st to 10th	Night	58% 5% 11% 18% 7% 1	2280
	11th to 20th	Night	52% 4 10% 20% 12% 1	2219
	21st to end	Night	54% 6% 9% 19% 10% 2	1884
March	1st to 10th	Night	56% 4 7% 21% 11% 1	3733
	11th to 20th	Night	37% 6% 11% 23% 22% 1	3650
	21st to end	Night	46% 6% 11% 28% 8% 1	3594
April	1st to 10th	Night	44% 5% 10% 25% 14% 2	1900
	11th to 20th	Night	44% 4 10% 20% 18% 5%	1875
	21st to end	Night	45% 7% 9% 23% 13% 3	1785
May	1st to 10th	Night	51% 10% 13% 19% 7% 1	2840
	11th to 20th	Night	42% 6% 14% 27% 11% 1	2813
	21st to end	Night	35% 9% 13% 22% 17% 4	2919
June	1st to 10th	Night	34% 6% 11% 25% 21% 4	1520
	11th to 20th	Night	32% 6% 11% 24% 21% 6%	1520
	21st to end	Night	29% 8% 16% 21% 20% 5%	1520
July	1st to 10th	Night	35% 7% 10% 26% 20% 3	2490
	11th to 20th	Night	25% 7% 13% 31% 21% 2	2482
	21st to end	Night	40% 6% 15% 23% 14% 3	2738
August	1st to 10th	Night	30% 8% 14% 28% 17% 3	1690
	11th to 20th	Night	28% 8% 15% 26% 20% 2	1858
	21st to end	Night	25% 7% 13% 28% 21% 6%	2080
September	1st to 10th	Night	35% 6% 11% 23% 18% 6%	1800
	11th to 20th	Night	27% 5% 10% 27% 25% 5%	1962
	21st to end	Night	32% 7% 10% 22% 24% 5%	1980
October	1st to 10th	Night	29% 7% 11% 24% 25% 5%	1980
	11th to 20th	Night	39% 4 7% 25% 21% 4	2117
	21st to end	Night	45% 4 9% 22% 17% 3	2574
November	1st to 10th	Night	36% 5% 9% 24% 21% 5%	2406
	11th to 20th	Night	43% 4 9% 22% 18% 3	2470
	21st to end	Night	51% 4 9% 22% 13% 1	2470
December	1st to 10th	Night	54% 4 10% 19% 11% 1	2474
	11th to 20th	Night	53% 4 11% 19% 13% 1	3281
	21st to end	Night	70% 5% 7% 11% 7%	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	26% 21% 33% 17% 3	270
	11th to 20th	Day	32% 20% 35% 11% 1	270
	21st to end	Day	29% 24% 34% 11% 3	297
February	1st to 10th	Day	27% 26% 31% 14% 1	270
	11th to 20th	Day	25% 30% 30% 12% 3	270
	21st to end	Day	32% 19% 39% 8% 1	225
March	1st to 10th	Day	24% 29% 34% 11% 1	270
	11th to 20th	Day	28% 21% 35% 11% 5% 1	355
	21st to end	Day	29% 20% 31% 16% 4	506
April	1st to 10th	Day	23% 19% 32% 19% 7% 1	460
	11th to 20th	Day	24% 19% 26% 22% 8% 1	452
	21st to end	Day	25% 19% 33% 14% 7% 1	460
May	1st to 10th	Day	21% 17% 31% 21% 7% 2	463
	11th to 20th	Day	22% 9% 32% 20% 13% 5%	487
	21st to end	Day	12% 8% 29% 27% 16% 8%	620
June	1st to 10th	Day	13% 7% 29% 30% 18% 4	680
	11th to 20th	Day	11% 7% 26% 34% 17% 5%	680
	21st to end	Day	12% 7% 30% 27% 17% 6%	680
July	1st to 10th	Day	13% 4 18% 27% 25% 13%	671
	11th to 20th	Day	7% 4 25% 32% 22% 9%	668
	21st to end	Day	12% 3 19% 34% 24% 8%	692
August	1st to 10th	Day	11% 4 18% 28% 29% 10%	486
	11th to 20th	Day	14% 4 23% 30% 22% 7%	479
	21st to end	Day	8% 3 16% 33% 29% 12%	532
September	1st to 10th	Day	12% 5% 18% 32% 25% 8%	450
	11th to 20th	Day	9% 3 18% 29% 30% 11%	450
	21st to end	Day	12% 10% 23% 25% 23% 7%	450
October	1st to 10th	Day	11% 9% 29% 31% 16% 4	450
	11th to 20th	Day	16% 17% 36% 21% 8% 1	343
	21st to end	Day	30% 17% 35% 16% 1	297
November	1st to 10th	Day	13% 23% 30% 21% 10% 3	270
	11th to 20th	Day	24% 21% 31% 17% 5% 1	270
	21st to end	Day	27% 16% 36% 18% 3 1	270
December	1st to 10th	Day	20% 26% 32% 17% 4 1	270
	11th to 20th	Day	26% 19% 37% 12% 4 1	270
	21st to end	Day	32% 20% 34% 11% 2 1	297
January	1st to 10th	Night	23% 18% 34% 21% 4	950
	11th to 20th	Night	26% 20% 33% 18% 3	950
	21st to end	Night	24% 18% 34% 22% 2	1007
February	1st to 10th	Night	25% 15% 38% 20% 2	760
	11th to 20th	Night	22% 20% 36% 20% 2	743
	21st to end	Night	27% 17% 36% 18% 2	628
March	1st to 10th	Night	26% 17% 32% 22% 2	760
	11th to 20th	Night	23% 15% 35% 20% 6% 1	760
	21st to end	Night	26% 10% 33% 25% 5%	703
April	1st to 10th	Night	20% 14% 32% 28% 6%	570
	11th to 20th	Night	20% 14% 29% 26% 10% 1	563
	21st to end	Night	20% 10% 38% 25% 7% 1	570
May	1st to 10th	Night	19% 9% 32% 29% 11%	570
	11th to 20th	Night	16% 8% 27% 30% 16% 3	561
	21st to end	Night	11% 4 25% 36% 21% 4	617
June	1st to 10th	Night	12% 4 23% 39% 22% 1	570
	11th to 20th	Night	11% 4 22% 43% 19% 1	570
	21st to end	Night	9% 3 23% 38% 26% 2	570
July	1st to 10th	Night	9% 2 15% 36% 31% 7%	555
	11th to 20th	Night	6% 4 16% 37% 33% 4	552
	21st to end	Night	8% 4 13% 42% 29% 4	624
August	1st to 10th	Night	8% 2 11% 41% 33% 5%	567
	11th to 20th	Night	7% 2 15% 37% 34% 4	564
	21st to end	Night	6% 3 15% 32% 39% 6%	624
September	1st to 10th	Night	14% 2 15% 36% 28% 4	540
	11th to 20th	Night	8% 4 16% 34% 33% 5%	702
	21st to end	Night	13% 7% 19% 32% 26% 3	720
October	1st to 10th	Night	12% 5% 24% 32% 23% 3	720
	11th to 20th	Night	20% 12% 28% 27% 13% 1	720
	21st to end	Night	23% 14% 33% 23% 6%	792
November	1st to 10th	Night	16% 10% 34% 29% 11% 1	740
	11th to 20th	Night	18% 18% 28% 28% 7% 1	760
	21st to end	Night	24% 17% 26% 25% 7%	760
December	1st to 10th	Night	25% 14% 37% 19% 5%	764
	11th to 20th	Night	26% 11% 33% 23% 6% 1	950
	21st to end	Night	31% 17% 31% 18% 4	1045

Page generated at 2024-08-27 09:49:43. Version ac07

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