Echo Hill Outdoor School
Clear Sky Chart
History

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

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	14% 6% 2 6% 4 4 4 4 6% 8% 43%	89542
	Night	15% 7% 2 6% 4 4 4 4 5% 7% 43%	89540
Transparency	Day	19% 54% 6% 12% 7% 1	89298
	Night	21% 53% 5% 12% 8% 1	89388
Seeing	Day	16% 7% 23% 27% 19% 8%	14508
	Night	17% 7% 27% 32% 14% 2	23939

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	16% 5% 2 5% 3 3 3 3 5% 7% 48%	2517
	11th to 20th	Day	14% 10% 3 8% 6% 4 4 3 4 5% 39%	2744
	21st to end	Day	19% 7% 2 6% 4 5% 4 3 5% 6% 38%	3124
February	1st to 10th	Day	16% 7% 2 6% 4 4 5% 4 5% 7% 40%	1710
	11th to 20th	Day	17% 8% 2 5% 4 4 4 3 6% 7% 42%	1769
	21st to end	Day	18% 9% 3 7% 3 4 3 3 5% 5% 40%	1570
March	1st to 10th	Day	23% 5% 2 5% 3 3 3 3 5% 7% 41%	3238
	11th to 20th	Day	10% 5% 2 4 4 4 5% 3 6% 7% 50%	3480
	21st to end	Day	21% 6% 2 6% 4 3 3 3 4 5% 43%	3969
April	1st to 10th	Day	14% 6% 2 5% 4 4 5% 4 6% 7% 42%	2280
	11th to 20th	Day	13% 5% 2 5% 4 4 4 3 6% 7% 47%	2254
	21st to end	Day	17% 5% 3 5% 3 3 4 4 6% 7% 43%	2280
May	1st to 10th	Day	25% 8% 2 5% 4 3 4 4 5% 7% 32%	3948
	11th to 20th	Day	21% 7% 2 7% 4 4 4 4 6% 8% 31%	4398
	21st to end	Day	10% 4 2 6% 3 4 4 4 7% 9% 47%	4823
June	1st to 10th	Day	10% 5% 2 5% 5% 5% 5% 5% 7% 11% 42%	2660
	11th to 20th	Day	10% 5% 2 5% 5% 4 5% 5% 6% 9% 44%	2660
	21st to end	Day	10% 3 2 5% 3 4 4 4 7% 10% 48%	2646
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 4 4 8% 10% 45%	2520
	11th to 20th	Day	5% 3 1 4 4 4 5% 5% 8% 12% 48%	2520
	21st to end	Day	8% 5% 2 5% 5% 5% 7% 5% 9% 10% 40%	2593
August	1st to 10th	Day	9% 5% 2 6% 3 5% 6% 5% 8% 10% 41%	2327
	11th to 20th	Day	9% 4 2 6% 4 4 5% 3 7% 10% 44%	2158
	21st to end	Day	10% 5% 2 7% 3 5% 5% 5% 7% 9% 44%	2376
September	1st to 10th	Day	13% 4 2 6% 5% 3 4 4 5% 8% 46%	2160
	11th to 20th	Day	12% 4 1 4 3 4 4 4 6% 8% 50%	2160
	21st to end	Day	17% 7% 3 6% 4 4 4 4 5% 7% 39%	1932
October	1st to 10th	Day	16% 7% 2 5% 3 3 3 3 6% 7% 46%	1800
	11th to 20th	Day	15% 6% 2 5% 3 3 3 3 6% 6% 49%	1800
	21st to end	Day	15% 6% 2 6% 3 3 4 3 5% 5% 47%	1980
November	1st to 10th	Day	13% 5% 2 4 3 3 3 3 5% 6% 52%	1676
	11th to 20th	Day	14% 5% 2 4 3 5% 4 3 5% 7% 49%	1710
	21st to end	Day	14% 6% 3 5% 4 4 4 4 5% 5% 47%	1558
December	1st to 10th	Day	18% 6% 2 6% 4 3 4 4 5% 7% 42%	1520
	11th to 20th	Day	17% 8% 2 5% 4 3 3 2 5% 7% 42%	1910
	21st to end	Day	15% 6% 3 6% 5% 6% 4 4 5% 7% 39%	2772
January	1st to 10th	Night	16% 8% 3 6% 4 4 4 3 4 6% 43%	4429
	11th to 20th	Night	18% 8% 2 5% 4 4 3 3 4 6% 43%	4212
	21st to end	Night	21% 8% 2 6% 4 3 3 3 4 5% 40%	4532
February	1st to 10th	Night	16% 8% 2 5% 5% 4 4 3 5% 6% 41%	2470
	11th to 20th	Night	19% 7% 2 6% 4 3 3 3 4 5% 44%	2295
	21st to end	Night	18% 8% 2 5% 4 3 4 4 4 5% 42%	1884
March	1st to 10th	Night	22% 8% 2 5% 4 3 3 3 4 6% 40%	3611
	11th to 20th	Night	12% 5% 2 5% 4 4 3 4 5% 7% 49%	3480
	21st to end	Night	16% 8% 3 6% 3 4 3 3 3 5% 46%	3663
April	1st to 10th	Night	15% 7% 3 6% 3 4 4 4 5% 7% 41%	1900
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 5% 6% 45%	1875
	21st to end	Night	18% 6% 2 4 3 4 3 3 5% 8% 45%	1900
May	1st to 10th	Night	22% 9% 3 6% 5% 4 5% 3 5% 6% 32%	2959
	11th to 20th	Night	22% 9% 3 7% 4 5% 4 4 6% 7% 29%	2495
	21st to end	Night	11% 5% 2 7% 4 4 4 4 6% 9% 43%	2732
June	1st to 10th	Night	11% 5% 2 6% 4 4 4 3 5% 9% 46%	1520
	11th to 20th	Night	10% 6% 2 7% 5% 5% 5% 4 6% 10% 41%	1520
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 7% 11% 43%	1512
July	1st to 10th	Night	9% 5% 3 7% 5% 6% 6% 4 8% 9% 38%	1440
	11th to 20th	Night	6% 4 2 5% 6% 5% 6% 5% 7% 11% 43%	1440
	21st to end	Night	8% 5% 3 5% 6% 5% 5% 5% 8% 10% 41%	1721
August	1st to 10th	Night	8% 4 2 6% 5% 5% 7% 5% 8% 10% 39%	1611
	11th to 20th	Night	9% 7% 3 7% 5% 5% 6% 4 5% 9% 39%	1723
	21st to end	Night	11% 5% 2 6% 4 4 6% 4 6% 9% 42%	1980
September	1st to 10th	Night	12% 6% 3 7% 3 4 4 3 6% 7% 45%	1800
	11th to 20th	Night	10% 6% 2 5% 4 3 3 3 5% 6% 52%	1800
	21st to end	Night	17% 6% 2 7% 5% 5% 4 3 5% 6% 40%	2025
October	1st to 10th	Night	18% 8% 2 6% 4 4 3 3 4 5% 43%	2160
	11th to 20th	Night	15% 5% 2 4 4 3 3 3 5% 6% 49%	2160
	21st to end	Night	17% 5% 1 5% 4 4 3 3 4 6% 48%	2376
November	1st to 10th	Night	12% 5% 2 5% 3 3 4 3 5% 5% 52%	2399
	11th to 20th	Night	16% 7% 2 5% 3 3 3 3 5% 6% 48%	2470
	21st to end	Night	13% 5% 1 6% 4 4 4 3 6% 7% 47%	2617
December	1st to 10th	Night	18% 6% 3 6% 4 3 4 4 5% 6% 40%	2660
	11th to 20th	Night	18% 5% 2 6% 4 4 4 3 5% 7% 42%	3285
	21st to end	Night	15% 8% 3 6% 4 5% 5% 5% 6% 8% 36%	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	23% 37% 5% 22% 10% 3	2518
	11th to 20th	Day	33% 37% 4 14% 9% 2	2744
	21st to end	Day	30% 40% 10% 13% 6% 1	3124
February	1st to 10th	Day	17% 66% 7% 7% 3 1	1710
	11th to 20th	Day	15% 64% 3 10% 7% 2	1778
	21st to end	Day	17% 65% 4 7% 5% 1	1570
March	1st to 10th	Day	31% 41% 5% 14% 5% 3	3238
	11th to 20th	Day	16% 42% 3 23% 14% 2	3480
	21st to end	Day	27% 40% 6% 12% 12% 3	3969
April	1st to 10th	Day	16% 66% 4 7% 6% 1	2280
	11th to 20th	Day	13% 66% 5% 9% 5% 1	2254
	21st to end	Day	15% 65% 5% 8% 7% 1	2280
May	1st to 10th	Day	37% 41% 6% 12% 4 1	3983
	11th to 20th	Day	34% 41% 11% 13% 2	4402
	21st to end	Day	19% 41% 9% 17% 12% 2	4837
June	1st to 10th	Day	14% 66% 4 9% 6% 1	2660
	11th to 20th	Day	12% 66% 3 10% 7% 1	2660
	21st to end	Day	10% 65% 7% 10% 8%	2646
July	1st to 10th	Day	14% 64% 8% 7% 6% 1	2450
	11th to 20th	Day	11% 63% 7% 12% 6% 1	2445
	21st to end	Day	13% 62% 6% 10% 7% 1	2448
August	1st to 10th	Day	12% 65% 6% 12% 5%	2314
	11th to 20th	Day	12% 65% 8% 10% 5%	2158
	21st to end	Day	11% 63% 6% 11% 8% 1	2376
September	1st to 10th	Day	14% 64% 7% 10% 4 1	2160
	11th to 20th	Day	13% 63% 4 10% 8% 2	2160
	21st to end	Day	19% 63% 3 10% 5%	1932
October	1st to 10th	Day	15% 63% 5% 10% 7% 1	1800
	11th to 20th	Day	12% 62% 5% 9% 10% 1	1800
	21st to end	Day	13% 61% 4 13% 8% 1	1980
November	1st to 10th	Day	16% 59% 6% 9% 7% 3	1676
	11th to 20th	Day	12% 60% 3 10% 12% 2	1710
	21st to end	Day	14% 60% 4 15% 5% 2	1558
December	1st to 10th	Day	21% 60% 6% 8% 5% 1	1520
	11th to 20th	Day	22% 48% 5% 16% 8% 1	1906
	21st to end	Day	30% 38% 10% 14% 7%	2772
January	1st to 10th	Night	29% 37% 5% 17% 9% 3	4429
	11th to 20th	Night	27% 37% 5% 18% 11% 2	4212
	21st to end	Night	31% 39% 4 17% 7% 1	4532
February	1st to 10th	Night	16% 65% 6% 9% 3 1	2470
	11th to 20th	Night	16% 63% 2 7% 9% 1	2297
	21st to end	Night	16% 64% 5% 8% 5% 3	1884
March	1st to 10th	Night	34% 40% 5% 15% 5% 1	3611
	11th to 20th	Night	17% 41% 6% 23% 11% 3	3480
	21st to end	Night	25% 40% 4 11% 16% 3	3663
April	1st to 10th	Night	16% 65% 2 8% 7% 1	1900
	11th to 20th	Night	14% 66% 5% 9% 5% 2	1875
	21st to end	Night	15% 65% 4 8% 7% 1	1900
May	1st to 10th	Night	36% 41% 6% 12% 5% 1	2989
	11th to 20th	Night	36% 42% 9% 10% 3	2496
	21st to end	Night	23% 41% 10% 13% 10% 3	2739
June	1st to 10th	Night	14% 66% 4 9% 7%	1520
	11th to 20th	Night	13% 67% 4 10% 6%	1520
	21st to end	Night	11% 65% 5% 12% 7% 1	1512
July	1st to 10th	Night	15% 65% 8% 5% 5% 2	1400
	11th to 20th	Night	12% 64% 7% 11% 6% 1	1392
	21st to end	Night	13% 63% 6% 11% 7%	1625
August	1st to 10th	Night	14% 66% 6% 7% 6%	1600
	11th to 20th	Night	13% 67% 6% 9% 5% 1	1723
	21st to end	Night	12% 64% 5% 10% 8% 1	1980
September	1st to 10th	Night	14% 64% 6% 11% 4 1	1800
	11th to 20th	Night	12% 64% 4 9% 10% 2	1800
	21st to end	Night	19% 64% 4 8% 6%	2025
October	1st to 10th	Night	18% 63% 5% 7% 6% 1	2160
	11th to 20th	Night	12% 63% 3 12% 8% 1	2160
	21st to end	Night	14% 62% 3 11% 8% 2	2376
November	1st to 10th	Night	15% 60% 6% 11% 6% 3	2399
	11th to 20th	Night	14% 60% 3 8% 11% 3	2470
	21st to end	Night	13% 60% 5% 13% 8% 1	2617
December	1st to 10th	Night	20% 60% 6% 9% 5%	2660
	11th to 20th	Night	21% 49% 5% 10% 11% 3	3288
	21st to end	Night	30% 39% 9% 15% 6%	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	19% 18% 35% 20% 6% 2	180
	11th to 20th	Day	18% 22% 31% 20% 8%	243
	21st to end	Day	18% 14% 40% 20% 7% 1	297
February	1st to 10th	Day	21% 9% 39% 21% 9% 1	270
	11th to 20th	Day	24% 16% 35% 21% 3 1	377
	21st to end	Day	26% 13% 33% 23% 5% 1	382
March	1st to 10th	Day	16% 13% 34% 30% 6% 1	460
	11th to 20th	Day	19% 12% 35% 23% 8% 2	460
	21st to end	Day	21% 10% 29% 29% 8% 2	506
April	1st to 10th	Day	20% 8% 36% 25% 8% 3	460
	11th to 20th	Day	14% 13% 27% 26% 16% 5%	452
	21st to end	Day	20% 9% 24% 32% 13% 2	460
May	1st to 10th	Day	24% 9% 23% 25% 15% 3	463
	11th to 20th	Day	18% 6% 22% 30% 18% 6%	487
	21st to end	Day	17% 2 15% 24% 29% 13%	529
June	1st to 10th	Day	11% 4 18% 29% 26% 13%	490
	11th to 20th	Day	12% 3 17% 29% 27% 11%	490
	21st to end	Day	10% 3 16% 33% 26% 12%	486
July	1st to 10th	Day	11% 10% 29% 31% 19%	445
	11th to 20th	Day	4 1 6% 33% 37% 19%	444
	21st to end	Day	9% 2 11% 31% 36% 11%	488
August	1st to 10th	Day	11% 2 8% 28% 35% 15%	446
	11th to 20th	Day	11% 2 7% 29% 35% 16%	439
	21st to end	Day	9% 2 13% 31% 28% 17%	495
September	1st to 10th	Day	17% 2 14% 24% 24% 19%	450
	11th to 20th	Day	12% 3 14% 28% 28% 15%	450
	21st to end	Day	22% 5% 17% 30% 20% 6%	450
October	1st to 10th	Day	20% 4 19% 26% 20% 11%	450
	11th to 20th	Day	16% 6% 26% 26% 21% 5%	450
	21st to end	Day	18% 6% 29% 28% 15% 4	495
November	1st to 10th	Day	16% 7% 28% 25% 18% 5%	368
	11th to 20th	Day	12% 14% 32% 27% 13% 2	370
	21st to end	Day	13% 11% 32% 27% 13% 4	218
December	1st to 10th	Day	20% 9% 35% 27% 8% 1	180
	11th to 20th	Day	21% 16% 29% 24% 10%	180
	21st to end	Day	21% 9% 31% 27% 10% 2	198
January	1st to 10th	Night	19% 11% 42% 24% 4	760
	11th to 20th	Night	22% 13% 32% 27% 5%	760
	21st to end	Night	19% 12% 38% 30% 2	836
February	1st to 10th	Night	20% 9% 36% 32% 3	760
	11th to 20th	Night	23% 14% 40% 22% 1	743
	21st to end	Night	22% 14% 35% 25% 4	628
March	1st to 10th	Night	18% 12% 37% 27% 6%	760
	11th to 20th	Night	18% 12% 37% 26% 7% 1	760
	21st to end	Night	19% 7% 36% 30% 7% 1	836
April	1st to 10th	Night	19% 10% 38% 26% 7%	760
	11th to 20th	Night	16% 8% 31% 34% 12%	751
	21st to end	Night	19% 8% 29% 33% 11%	760
May	1st to 10th	Night	21% 7% 24% 36% 12% 1	667
	11th to 20th	Night	19% 8% 23% 37% 14%	374
	21st to end	Night	13% 3 14% 42% 25% 2	411
June	1st to 10th	Night	12% 3 19% 43% 22% 2	380
	11th to 20th	Night	11% 2 18% 43% 25% 2	380
	21st to end	Night	11% 4 17% 45% 22% 1	378
July	1st to 10th	Night	8% 3 15% 41% 30% 4	350
	11th to 20th	Night	6% 1 9% 42% 39% 3	348
	21st to end	Night	7% 2 11% 46% 31% 4	541
August	1st to 10th	Night	9% 3 10% 40% 34% 4	537
	11th to 20th	Night	11% 3 11% 34% 34% 6%	659
	21st to end	Night	12% 3 11% 35% 33% 6%	792
September	1st to 10th	Night	15% 1 13% 34% 30% 6%	720
	11th to 20th	Night	12% 3 12% 36% 32% 6%	720
	21st to end	Night	19% 4 18% 33% 24% 2	720
October	1st to 10th	Night	21% 5% 19% 30% 21% 5%	720
	11th to 20th	Night	18% 6% 25% 34% 16% 1	720
	21st to end	Night	19% 7% 30% 30% 13% 1	792
November	1st to 10th	Night	16% 5% 31% 33% 14% 2	740
	11th to 20th	Night	19% 12% 28% 31% 10% 1	760
	21st to end	Night	16% 13% 31% 30% 10% 1	760
December	1st to 10th	Night	23% 10% 34% 24% 9% 1	760
	11th to 20th	Night	17% 9% 37% 30% 6%	760
	21st to end	Night	19% 8% 35% 34% 4	836

Page generated at 2024-06-26 22:18:41. Version ac07

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