Hebron Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hebron Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	16% 12% 4 9% 5% 4 4 4 5% 6% 29%	101406
	Night	16% 14% 5% 10% 5% 4 4 3 5% 6% 28%	97589
Transparency	Day	55% 3 10% 21% 10% 1	105010
	Night	57% 3 10% 19% 10% 1	102073
Seeing	Day	27% 18% 28% 17% 8% 3	14668
	Night	26% 17% 28% 20% 8% 1	24049

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	13% 23% 12% 14% 5% 3 3 2 3 4 18%	2517
	11th to 20th	Day	10% 20% 10% 20% 8% 4 3 2 3 4 17%	2758
	21st to end	Day	22% 17% 9% 15% 8% 4 3 3 3 4 13%	3124
February	1st to 10th	Day	15% 19% 7% 13% 9% 5% 4 3 4 4 18%	1710
	11th to 20th	Day	12% 15% 8% 16% 6% 5% 4 4 4 5% 20%	1663
	21st to end	Day	18% 15% 4 12% 6% 4 4 2 4 4 26%	1525
March	1st to 10th	Day	18% 15% 7% 9% 5% 3 3 3 4 6% 27%	3402
	11th to 20th	Day	10% 19% 8% 12% 4 4 3 2 4 5% 29%	3480
	21st to end	Day	16% 13% 4 12% 6% 4 4 3 5% 5% 28%	3838
April	1st to 10th	Day	16% 18% 4 8% 5% 4 4 4 4 6% 28%	2280
	11th to 20th	Day	18% 14% 3 8% 4 4 5% 4 5% 5% 31%	2254
	21st to end	Day	20% 12% 3 7% 5% 5% 4 4 4 5% 32%	2399
May	1st to 10th	Day	25% 10% 3 7% 5% 4 4 3 5% 6% 29%	4108
	11th to 20th	Day	20% 12% 4 8% 5% 5% 6% 4 5% 6% 25%	4393
	21st to end	Day	13% 7% 3 7% 5% 4 5% 4 5% 8% 39%	4837
June	1st to 10th	Day	17% 8% 3 7% 6% 5% 5% 4 7% 7% 32%	2660
	11th to 20th	Day	16% 7% 2 7% 6% 5% 6% 4 6% 8% 32%	2660
	21st to end	Day	15% 7% 3 7% 5% 6% 5% 5% 6% 7% 35%	2660
July	1st to 10th	Day	10% 7% 2 7% 5% 6% 6% 5% 7% 10% 35%	4440
	11th to 20th	Day	11% 7% 3 7% 5% 6% 6% 5% 8% 9% 34%	4440
	21st to end	Day	10% 7% 3 8% 6% 6% 5% 5% 8% 8% 35%	4505
August	1st to 10th	Day	18% 9% 3 8% 5% 4 5% 5% 6% 9% 28%	4104
	11th to 20th	Day	16% 7% 3 8% 6% 6% 7% 5% 7% 9% 26%	4044
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 7% 8% 37%	4189
September	1st to 10th	Day	18% 8% 2 6% 4 3 4 4 5% 7% 38%	2280
	11th to 20th	Day	14% 7% 3 7% 4 4 4 3 5% 6% 42%	2256
	21st to end	Day	22% 9% 4 6% 5% 4 5% 4 5% 6% 31%	1995
October	1st to 10th	Day	18% 10% 3 7% 5% 4 5% 3 6% 6% 33%	1900
	11th to 20th	Day	21% 11% 3 9% 4 4 4 3 5% 6% 31%	1900
	21st to end	Day	23% 16% 3 8% 5% 4 4 3 4 6% 25%	2090
November	1st to 10th	Day	14% 13% 4 8% 4 5% 4 3 5% 6% 35%	1753
	11th to 20th	Day	16% 20% 6% 9% 4 3 4 4 6% 6% 22%	1524
	21st to end	Day	18% 22% 5% 9% 6% 3 4 3 4 6% 19%	1520
December	1st to 10th	Day	17% 24% 8% 14% 6% 4 3 3 4 5% 13%	1520
	11th to 20th	Day	16% 20% 7% 15% 4 4 4 4 5% 5% 17%	1906
	21st to end	Day	20% 26% 9% 10% 5% 4 3 2 3 4 14%	2772
January	1st to 10th	Night	15% 19% 12% 15% 6% 4 4 3 4 4 15%	4429
	11th to 20th	Night	12% 19% 11% 18% 8% 5% 4 2 4 4 13%	4184
	21st to end	Night	20% 20% 7% 17% 9% 4 3 2 3 3 12%	4532
February	1st to 10th	Night	14% 18% 6% 11% 10% 5% 4 3 4 5% 19%	2470
	11th to 20th	Night	12% 16% 7% 15% 8% 6% 5% 4 4 5% 19%	2403
	21st to end	Night	16% 15% 5% 16% 7% 4 4 3 5% 4 22%	1928
March	1st to 10th	Night	18% 17% 4 10% 5% 4 3 3 4 5% 26%	3424
	11th to 20th	Night	15% 19% 8% 11% 5% 3 3 3 4 6% 23%	3479
	21st to end	Night	13% 13% 4 10% 5% 4 3 3 5% 6% 35%	3793
April	1st to 10th	Night	18% 15% 4 9% 5% 4 4 4 4 5% 27%	1900
	11th to 20th	Night	18% 14% 3 6% 4 3 3 3 5% 6% 35%	1875
	21st to end	Night	17% 12% 3 7% 4 4 4 4 5% 7% 34%	1797
May	1st to 10th	Night	26% 11% 3 6% 4 4 3 3 3 6% 30%	2833
	11th to 20th	Night	21% 14% 2 7% 4 4 4 3 5% 6% 29%	2500
	21st to end	Night	14% 9% 3 7% 5% 4 4 3 5% 7% 39%	2738
June	1st to 10th	Night	13% 9% 3 6% 5% 5% 4 4 6% 9% 36%	1520
	11th to 20th	Night	12% 7% 2 7% 5% 4 4 5% 7% 9% 37%	1520
	21st to end	Night	14% 7% 3 6% 4 4 5% 3 6% 6% 42%	1520
July	1st to 10th	Night	13% 9% 3 7% 5% 4 5% 4 5% 7% 38%	2520
	11th to 20th	Night	11% 7% 3 6% 5% 4 4 3 6% 10% 41%	2520
	21st to end	Night	13% 7% 2 6% 5% 5% 5% 3 5% 7% 41%	3045
August	1st to 10th	Night	18% 10% 2 7% 4 5% 5% 3 5% 6% 35%	2825
	11th to 20th	Night	18% 9% 4 6% 4 4 4 3 6% 6% 37%	2785
	21st to end	Night	11% 7% 2 6% 5% 4 5% 4 6% 8% 42%	3434
September	1st to 10th	Night	15% 8% 2 6% 5% 3 3 2 4 6% 44%	1900
	11th to 20th	Night	13% 8% 2 6% 3 4 4 3 5% 6% 46%	1920
	21st to end	Night	20% 10% 3 7% 4 4 4 3 5% 6% 35%	2184
October	1st to 10th	Night	18% 9% 3 6% 4 4 3 3 4 6% 39%	2280
	11th to 20th	Night	19% 13% 3 7% 4 5% 3 3 5% 7% 32%	2280
	21st to end	Night	24% 16% 3 7% 4 3 4 3 5% 6% 27%	2508
November	1st to 10th	Night	12% 14% 4 8% 4 4 4 3 5% 5% 37%	2396
	11th to 20th	Night	16% 19% 4 9% 5% 5% 4 3 5% 5% 25%	2655
	21st to end	Night	15% 19% 7% 11% 5% 4 4 4 4 6% 20%	2660
December	1st to 10th	Night	18% 21% 9% 12% 6% 5% 4 2 4 5% 14%	2660
	11th to 20th	Night	17% 18% 8% 16% 6% 5% 4 3 4 4 17%	3288
	21st to end	Night	20% 20% 10% 11% 6% 5% 4 3 4 5% 12%	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	72% 2 7% 14% 4 2	2518
	11th to 20th	Day	74% 2 6% 13% 5% 1	2758
	21st to end	Day	76% 1 7% 11% 4 1	3124
February	1st to 10th	Day	71% 2 10% 11% 6% 1	1710
	11th to 20th	Day	66% 3 6% 17% 8%	1672
	21st to end	Day	63% 2 7% 19% 8% 2	1525
March	1st to 10th	Day	60% 2 7% 23% 7% 1	3405
	11th to 20th	Day	59% 2 12% 18% 8% 2	3480
	21st to end	Day	58% 3 5% 22% 11% 2	3838
April	1st to 10th	Day	57% 3 9% 18% 12% 1	2280
	11th to 20th	Day	55% 3 9% 18% 13% 1	2254
	21st to end	Day	55% 2 7% 20% 13% 2	2399
May	1st to 10th	Day	58% 2 7% 23% 8% 2	4120
	11th to 20th	Day	60% 3 10% 18% 7% 1	4397
	21st to end	Day	43% 4 12% 26% 14% 1	4837
June	1st to 10th	Day	49% 4 11% 21% 13% 1	2660
	11th to 20th	Day	49% 4 13% 21% 12% 1	2660
	21st to end	Day	46% 5% 11% 26% 12%	2660
July	1st to 10th	Day	43% 5% 13% 25% 12% 1	4370
	11th to 20th	Day	42% 6% 13% 25% 14%	4365
	21st to end	Day	43% 6% 13% 26% 11% 1	4361
August	1st to 10th	Day	52% 5% 12% 22% 9%	4091
	11th to 20th	Day	51% 6% 15% 22% 6%	4083
	21st to end	Day	43% 5% 10% 31% 10% 1	4189
September	1st to 10th	Day	47% 3 9% 25% 15% 2	2280
	11th to 20th	Day	43% 3 10% 26% 17% 1	2256
	21st to end	Day	53% 3 9% 21% 13% 1	1995
October	1st to 10th	Day	45% 4 11% 22% 17% 1	3160
	11th to 20th	Day	48% 3 11% 19% 15% 4	3140
	21st to end	Day	45% 4 14% 25% 11% 1	3428
November	1st to 10th	Day	49% 3 10% 21% 13% 3	1753
	11th to 20th	Day	62% 3 9% 17% 7% 2	1524
	21st to end	Day	67% 2 9% 16% 5% 1	1520
December	1st to 10th	Day	74% 2 8% 9% 6%	1520
	11th to 20th	Day	69% 3 10% 13% 5%	1906
	21st to end	Day	76% 2 9% 11% 2	2772
January	1st to 10th	Night	73% 2 6% 13% 5%	4429
	11th to 20th	Night	75% 3 8% 11% 3 1	4184
	21st to end	Night	79% 2 4 10% 5% 1	4532
February	1st to 10th	Night	68% 2 9% 14% 7%	2470
	11th to 20th	Night	67% 3 8% 15% 6% 1	2405
	21st to end	Night	65% 2 9% 13% 9% 2	1928
March	1st to 10th	Night	63% 3 9% 17% 7% 1	3434
	11th to 20th	Night	63% 3 10% 18% 6% 1	3480
	21st to end	Night	51% 3 6% 22% 16% 2	3793
April	1st to 10th	Night	59% 4 8% 17% 12%	1900
	11th to 20th	Night	52% 3 11% 20% 12% 2	1875
	21st to end	Night	51% 3 9% 22% 13% 2	1797
May	1st to 10th	Night	57% 2 8% 22% 9% 1	2840
	11th to 20th	Night	57% 3 14% 18% 8% 1	2501
	21st to end	Night	46% 3 11% 21% 15% 4	2739
June	1st to 10th	Night	45% 3 12% 25% 14% 1	1520
	11th to 20th	Night	42% 4 15% 25% 12% 2	1520
	21st to end	Night	42% 5% 12% 26% 13% 1	1520
July	1st to 10th	Night	46% 4 12% 21% 16% 1	2480
	11th to 20th	Night	38% 5% 17% 26% 14% 1	2472
	21st to end	Night	42% 4 12% 24% 17% 1	2948
August	1st to 10th	Night	49% 6% 14% 24% 7% 1	2814
	11th to 20th	Night	47% 4 13% 28% 8%	2812
	21st to end	Night	38% 5% 13% 33% 10% 1	3434
September	1st to 10th	Night	42% 2 11% 27% 14% 3	1900
	11th to 20th	Night	39% 3 12% 27% 18% 2	1920
	21st to end	Night	50% 3 12% 21% 13% 1	2184
October	1st to 10th	Night	48% 4 9% 21% 17% 1	3800
	11th to 20th	Night	45% 4 11% 20% 13% 8%	3779
	21st to end	Night	45% 3 15% 24% 12% 1	4120
November	1st to 10th	Night	48% 4 11% 20% 14% 3	2396
	11th to 20th	Night	60% 3 9% 17% 9% 3	2655
	21st to end	Night	64% 3 10% 17% 5% 1	2660
December	1st to 10th	Night	74% 3 8% 11% 4	2660
	11th to 20th	Night	71% 2 7% 15% 4	3288
	21st to end	Night	76% 2 8% 11% 3	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	38% 23% 26% 9% 3 1	180
	11th to 20th	Day	37% 29% 28% 5% 2	249
	21st to end	Day	34% 28% 30% 7% 2	297
February	1st to 10th	Day	40% 27% 27% 5%	270
	11th to 20th	Day	39% 29% 29% 2	270
	21st to end	Day	43% 25% 25% 6%	337
March	1st to 10th	Day	37% 24% 27% 9% 2 1	460
	11th to 20th	Day	33% 26% 26% 11% 2 1	460
	21st to end	Day	37% 21% 27% 11% 3 1	506
April	1st to 10th	Day	34% 24% 27% 11% 3 1	460
	11th to 20th	Day	32% 23% 25% 13% 5% 2	452
	21st to end	Day	31% 20% 32% 13% 3	460
May	1st to 10th	Day	31% 21% 26% 12% 8% 2	463
	11th to 20th	Day	29% 17% 29% 17% 7% 3	487
	21st to end	Day	20% 14% 30% 21% 12% 4	529
June	1st to 10th	Day	23% 16% 30% 21% 9% 2	490
	11th to 20th	Day	21% 13% 28% 26% 10% 2	490
	21st to end	Day	21% 14% 33% 22% 7% 2	490
July	1st to 10th	Day	14% 11% 31% 25% 13% 5%	485
	11th to 20th	Day	13% 12% 27% 30% 14% 5%	484
	21st to end	Day	14% 11% 34% 27% 10% 4	532
August	1st to 10th	Day	15% 10% 24% 28% 16% 6%	486
	11th to 20th	Day	19% 8% 29% 25% 13% 7%	479
	21st to end	Day	16% 12% 28% 25% 13% 6%	539
September	1st to 10th	Day	22% 12% 23% 23% 14% 7%	490
	11th to 20th	Day	14% 9% 24% 25% 19% 8%	490
	21st to end	Day	28% 15% 24% 18% 11% 3	490
October	1st to 10th	Day	24% 16% 24% 19% 13% 4	490
	11th to 20th	Day	31% 18% 29% 14% 7% 1	490
	21st to end	Day	37% 18% 27% 16% 3	539
November	1st to 10th	Day	28% 19% 28% 16% 7% 2	402
	11th to 20th	Day	41% 21% 27% 10% 1 1	184
	21st to end	Day	38% 25% 30% 6% 1 1	180
December	1st to 10th	Day	44% 24% 22% 5% 3 1	180
	11th to 20th	Day	42% 25% 26% 6% 2	180
	21st to end	Day	39% 28% 29% 3 1	198
January	1st to 10th	Night	31% 27% 30% 10% 2	760
	11th to 20th	Night	31% 25% 29% 12% 2	760
	21st to end	Night	29% 28% 29% 12% 1	836
February	1st to 10th	Night	30% 26% 32% 12%	760
	11th to 20th	Night	31% 29% 30% 9% 1	743
	21st to end	Night	35% 26% 27% 10% 2	628
March	1st to 10th	Night	29% 27% 31% 11% 2	760
	11th to 20th	Night	33% 23% 26% 14% 4	760
	21st to end	Night	26% 24% 32% 14% 4 1	836
April	1st to 10th	Night	28% 21% 31% 17% 3	760
	11th to 20th	Night	30% 18% 29% 17% 6% 1	751
	21st to end	Night	25% 15% 33% 23% 4	657
May	1st to 10th	Night	27% 13% 24% 27% 9%	570
	11th to 20th	Night	18% 13% 32% 28% 9%	379
	21st to end	Night	16% 9% 28% 32% 15% 1	411
June	1st to 10th	Night	18% 9% 29% 31% 12% 1	380
	11th to 20th	Night	15% 11% 26% 38% 10%	380
	21st to end	Night	14% 8% 32% 34% 12%	380
July	1st to 10th	Night	14% 4 24% 39% 17% 3	370
	11th to 20th	Night	11% 4 26% 38% 20% 1	368
	21st to end	Night	14% 5% 22% 40% 18% 1	595
August	1st to 10th	Night	14% 4 20% 37% 23% 2	567
	11th to 20th	Night	18% 5% 19% 31% 24% 2	564
	21st to end	Night	15% 8% 20% 32% 23% 2	807
September	1st to 10th	Night	20% 8% 24% 30% 16% 3	760
	11th to 20th	Night	17% 6% 21% 27% 25% 4	760
	21st to end	Night	23% 12% 23% 23% 15% 3	760
October	1st to 10th	Night	23% 12% 27% 19% 16% 2	760
	11th to 20th	Night	28% 15% 30% 19% 6% 1	760
	21st to end	Night	35% 15% 29% 17% 3	836
November	1st to 10th	Night	21% 19% 32% 21% 6%	755
	11th to 20th	Night	31% 20% 29% 14% 5% 1	760
	21st to end	Night	31% 22% 30% 14% 3 1	760
December	1st to 10th	Night	34% 26% 27% 9% 3	760
	11th to 20th	Night	32% 26% 28% 13% 2	760
	21st to end	Night	33% 24% 31% 10% 1	836

Page generated at 2024-11-01 22:47:44. Version ac07

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