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 2024-04-10.

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% 5% 8% 6% 3 5% 4 5% 6% 28%	83152
	Night	16% 14% 6% 9% 7% 3 4 4 4 6% 27%	85597
Transparency	Day	57% 3 10% 19% 10% 1	82867
	Night	59% 3 10% 18% 9% 1	85416
Seeing	Day	28% 18% 28% 17% 8% 3	13838
	Night	26% 18% 28% 20% 8% 1	23409

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% 23% 12% 13% 6% 2 3 3 3 4 18%	2517
	11th to 20th	Day	10% 19% 10% 19% 10% 3 3 3 3 4 17%	2758
	21st to end	Day	22% 16% 10% 13% 9% 3 3 4 3 4 13%	3124
February	1st to 10th	Day	15% 17% 8% 12% 10% 4 5% 4 4 4 18%	1710
	11th to 20th	Day	12% 14% 9% 15% 8% 4 5% 4 4 6% 21%	1663
	21st to end	Day	18% 14% 4 10% 8% 2 4 3 4 4 26%	1525
March	1st to 10th	Day	19% 14% 7% 8% 5% 3 3 3 4 6% 27%	3402
	11th to 20th	Day	10% 18% 9% 10% 6% 3 4 3 4 5% 29%	3480
	21st to end	Day	16% 12% 5% 10% 8% 3 4 5% 5% 5% 28%	3838
April	1st to 10th	Day	16% 16% 5% 7% 5% 3 4 5% 4 6% 29%	2270
	11th to 20th	Day	18% 13% 4 7% 4 3 5% 5% 5% 5% 31%	2134
	21st to end	Day	21% 12% 3 6% 5% 3 4 5% 4 4 32%	2272
May	1st to 10th	Day	20% 11% 4 7% 7% 3 5% 4 5% 6% 27%	2340
	11th to 20th	Day	21% 10% 3 6% 6% 4 5% 5% 5% 6% 30%	2473
	21st to end	Day	15% 6% 3 6% 6% 3 6% 6% 5% 8% 37%	2725
June	1st to 10th	Day	17% 7% 3 6% 6% 4 5% 5% 6% 7% 33%	2520
	11th to 20th	Day	17% 7% 3 6% 6% 4 6% 5% 6% 8% 32%	2520
	21st to end	Day	15% 7% 3 6% 6% 4 6% 6% 6% 7% 35%	2520
July	1st to 10th	Day	11% 6% 3 7% 6% 4 7% 6% 6% 8% 37%	2520
	11th to 20th	Day	12% 7% 3 6% 6% 3 7% 6% 8% 10% 33%	2520
	21st to end	Day	12% 7% 3 7% 6% 4 6% 7% 7% 7% 34%	2572
August	1st to 10th	Day	11% 7% 3 7% 7% 4 5% 7% 7% 10% 33%	2327
	11th to 20th	Day	14% 7% 3 7% 8% 4 7% 6% 6% 8% 29%	2303
	21st to end	Day	15% 7% 3 6% 7% 4 6% 6% 7% 8% 31%	2385
September	1st to 10th	Day	19% 8% 2 5% 5% 2 4 5% 5% 7% 37%	2160
	11th to 20th	Day	15% 7% 3 6% 5% 3 4 4 5% 6% 41%	2138
	21st to end	Day	19% 8% 4 6% 6% 3 5% 5% 5% 6% 33%	1890
October	1st to 10th	Day	19% 10% 3 6% 6% 2 5% 5% 5% 7% 32%	1800
	11th to 20th	Day	22% 11% 3 8% 5% 3 4 4 5% 6% 29%	1800
	21st to end	Day	24% 16% 4 6% 6% 3 4 4 4 5% 24%	1980
November	1st to 10th	Day	14% 13% 4 7% 5% 4 4 4 4 6% 35%	1724
	11th to 20th	Day	16% 18% 7% 8% 5% 3 4 5% 6% 6% 23%	1524
	21st to end	Day	18% 21% 6% 8% 6% 3 4 4 4 6% 20%	1520
December	1st to 10th	Day	17% 21% 10% 14% 6% 3 3 4 4 5% 13%	1520
	11th to 20th	Day	16% 19% 7% 14% 6% 3 3 5% 4 5% 17%	1906
	21st to end	Day	20% 25% 9% 9% 6% 3 3 3 3 4 14%	2772
January	1st to 10th	Night	15% 18% 12% 14% 7% 3 4 3 4 4 15%	4429
	11th to 20th	Night	12% 18% 11% 16% 9% 4 5% 3 4 4 14%	4184
	21st to end	Night	21% 19% 8% 15% 10% 3 4 3 3 3 12%	4532
February	1st to 10th	Night	14% 16% 9% 10% 11% 4 5% 4 4 5% 20%	2470
	11th to 20th	Night	13% 14% 8% 13% 9% 5% 6% 5% 4 5% 19%	2403
	21st to end	Night	16% 14% 6% 14% 9% 3 5% 3 5% 4 22%	1928
March	1st to 10th	Night	18% 16% 5% 10% 6% 3 4 4 3 5% 26%	3424
	11th to 20th	Night	15% 18% 9% 10% 5% 2 3 3 4 6% 23%	3479
	21st to end	Night	13% 13% 5% 9% 6% 3 3 3 4 6% 35%	3793
April	1st to 10th	Night	19% 13% 6% 8% 6% 3 5% 5% 4 5% 27%	1900
	11th to 20th	Night	18% 13% 4 6% 5% 2 3 4 5% 6% 35%	1775
	21st to end	Night	17% 12% 3 6% 5% 3 5% 4 5% 7% 33%	1703
May	1st to 10th	Night	18% 11% 4 7% 5% 3 5% 4 3 6% 33%	1620
	11th to 20th	Night	15% 10% 3 7% 6% 4 5% 4 5% 6% 35%	1420
	21st to end	Night	13% 7% 2 6% 6% 3 4 5% 5% 8% 42%	1550
June	1st to 10th	Night	14% 8% 4 5% 5% 3 4 5% 5% 10% 36%	1440
	11th to 20th	Night	12% 7% 3 7% 5% 3 4 6% 6% 10% 37%	1440
	21st to end	Night	13% 6% 2 5% 5% 3 4 5% 6% 6% 44%	1440
July	1st to 10th	Night	10% 6% 2 6% 6% 3 5% 5% 5% 8% 43%	1440
	11th to 20th	Night	10% 5% 3 5% 5% 3 4 4 5% 9% 48%	1440
	21st to end	Night	12% 5% 2 5% 5% 3 6% 5% 5% 9% 40%	1743
August	1st to 10th	Night	9% 7% 2 6% 5% 4 5% 5% 7% 8% 43%	1611
	11th to 20th	Night	14% 7% 4 5% 6% 3 4 4 7% 7% 38%	1598
	21st to end	Night	12% 6% 2 6% 5% 3 5% 5% 7% 8% 40%	1952
September	1st to 10th	Night	15% 8% 3 5% 6% 2 4 3 4 7% 44%	1800
	11th to 20th	Night	14% 7% 2 5% 4 2 4 4 5% 7% 46%	1818
	21st to end	Night	18% 9% 3 6% 5% 3 4 4 5% 6% 37%	2069
October	1st to 10th	Night	17% 9% 3 6% 5% 3 3 5% 4 7% 38%	2160
	11th to 20th	Night	19% 13% 3 6% 5% 4 3 4 5% 7% 31%	2160
	21st to end	Night	25% 16% 3 6% 5% 2 4 3 4 6% 26%	2376
November	1st to 10th	Night	12% 13% 4 7% 6% 3 4 4 5% 5% 38%	2353
	11th to 20th	Night	16% 18% 5% 8% 5% 3 5% 4 5% 6% 26%	2655
	21st to end	Night	16% 18% 7% 10% 7% 3 5% 4 4 6% 21%	2660
December	1st to 10th	Night	18% 19% 10% 12% 7% 4 4 3 3 5% 14%	2660
	11th to 20th	Night	18% 17% 8% 15% 8% 3 4 3 4 4 17%	3288
	21st to end	Night	20% 19% 11% 10% 7% 4 4 4 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 10% 18% 12% 1	2270
	11th to 20th	Day	55% 4 9% 18% 14% 1	2134
	21st to end	Day	56% 2 7% 20% 13% 2	2272
May	1st to 10th	Day	59% 2 9% 18% 9% 2	2340
	11th to 20th	Day	56% 3 9% 18% 12% 1	2477
	21st to end	Day	45% 4 16% 22% 12% 1	2725
June	1st to 10th	Day	49% 4 12% 21% 13% 1	2520
	11th to 20th	Day	50% 4 13% 21% 12% 1	2520
	21st to end	Day	47% 5% 11% 26% 11%	2520
July	1st to 10th	Day	46% 5% 9% 25% 13% 1	2450
	11th to 20th	Day	44% 4 14% 24% 13%	2445
	21st to end	Day	46% 5% 12% 25% 12% 1	2428
August	1st to 10th	Day	46% 5% 12% 27% 10% 1	2314
	11th to 20th	Day	50% 5% 14% 21% 9% 1	2303
	21st to end	Day	49% 5% 10% 22% 13% 2	2385
September	1st to 10th	Day	48% 3 9% 24% 14% 2	2160
	11th to 20th	Day	44% 3 10% 25% 16% 2	2138
	21st to end	Day	52% 3 9% 22% 14% 1	1890
October	1st to 10th	Day	52% 3 10% 20% 13% 2	1800
	11th to 20th	Day	56% 3 11% 20% 10% 1	1800
	21st to end	Day	63% 3 8% 15% 8% 2	1980
November	1st to 10th	Day	50% 3 10% 20% 13% 3	1724
	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 10% 20% 13% 2	1775
	21st to end	Night	52% 3 9% 21% 13% 2	1703
May	1st to 10th	Night	54% 2 9% 21% 11% 2	1620
	11th to 20th	Night	51% 4 9% 22% 14% 1	1421
	21st to end	Night	43% 4 13% 24% 13% 3	1551
June	1st to 10th	Night	45% 4 12% 25% 14% 1	1440
	11th to 20th	Night	43% 4 15% 25% 12% 2	1440
	21st to end	Night	41% 6% 12% 27% 13% 1	1440
July	1st to 10th	Night	40% 5% 12% 26% 17% 1	1400
	11th to 20th	Night	35% 4 16% 26% 18% 1	1392
	21st to end	Night	40% 4 15% 23% 16% 1	1646
August	1st to 10th	Night	38% 5% 15% 31% 10% 1	1600
	11th to 20th	Night	43% 5% 14% 28% 10%	1598
	21st to end	Night	40% 4 13% 27% 13% 2	1952
September	1st to 10th	Night	43% 2 12% 27% 13% 3	1800
	11th to 20th	Night	39% 3 12% 27% 18% 2	1818
	21st to end	Night	48% 3 12% 22% 13% 1	2069
October	1st to 10th	Night	48% 4 12% 21% 15% 1	2160
	11th to 20th	Night	52% 4 13% 19% 10% 1	2160
	21st to end	Night	62% 2 10% 17% 8% 1	2376
November	1st to 10th	Night	48% 4 11% 20% 14% 3	2353
	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	457
	11th to 20th	Day	31% 22% 25% 14% 6% 2	412
	21st to end	Day	32% 20% 31% 13% 4	420
May	1st to 10th	Day	31% 22% 26% 12% 8% 2	423
	11th to 20th	Day	30% 17% 29% 16% 6% 2	447
	21st to end	Day	20% 14% 29% 21% 12% 4	485
June	1st to 10th	Day	22% 15% 31% 22% 8% 2	450
	11th to 20th	Day	22% 13% 27% 25% 10% 2	450
	21st to end	Day	20% 12% 35% 23% 8% 2	450
July	1st to 10th	Day	14% 10% 29% 26% 15% 6%	445
	11th to 20th	Day	13% 11% 27% 30% 14% 5%	444
	21st to end	Day	15% 11% 34% 27% 9% 4	488
August	1st to 10th	Day	13% 10% 24% 29% 17% 7%	446
	11th to 20th	Day	18% 7% 29% 26% 13% 7%	439
	21st to end	Day	17% 12% 28% 24% 13% 7%	495
September	1st to 10th	Day	23% 11% 23% 23% 13% 7%	450
	11th to 20th	Day	15% 10% 26% 23% 18% 8%	450
	21st to end	Day	24% 16% 25% 20% 12% 4	450
October	1st to 10th	Day	25% 15% 24% 18% 14% 4	450
	11th to 20th	Day	32% 19% 30% 14% 6%	450
	21st to end	Day	39% 17% 26% 15% 2	495
November	1st to 10th	Day	29% 18% 28% 16% 7% 2	391
	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	29% 20% 31% 17% 3	760
	11th to 20th	Night	30% 17% 29% 17% 6% 1	711
	21st to end	Night	26% 14% 34% 23% 4	623
May	1st to 10th	Night	27% 12% 24% 27% 9%	540
	11th to 20th	Night	18% 14% 32% 28% 8%	359
	21st to end	Night	16% 9% 29% 31% 15% 1	389
June	1st to 10th	Night	18% 8% 29% 31% 12% 1	360
	11th to 20th	Night	16% 11% 26% 36% 11%	360
	21st to end	Night	12% 8% 33% 34% 12%	360
July	1st to 10th	Night	13% 4 24% 38% 18% 3	350
	11th to 20th	Night	11% 4 26% 37% 21% 1	348
	21st to end	Night	14% 5% 22% 39% 18% 1	563
August	1st to 10th	Night	12% 4 21% 37% 23% 2	537
	11th to 20th	Night	18% 5% 19% 32% 25% 2	534
	21st to end	Night	15% 8% 20% 32% 23% 3	764
September	1st to 10th	Night	20% 8% 24% 30% 16% 3	720
	11th to 20th	Night	18% 7% 22% 27% 23% 4	720
	21st to end	Night	21% 12% 23% 24% 16% 3	720
October	1st to 10th	Night	23% 12% 27% 20% 16% 2	720
	11th to 20th	Night	28% 15% 31% 19% 5% 1	720
	21st to end	Night	37% 15% 29% 16% 3	792
November	1st to 10th	Night	21% 19% 32% 21% 6%	740
	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 2024-04-07 09:28:09. Version ac07

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