Ellwood H. May Environmental Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ellwood H. May Environmental Park clear sky chart from 2005-11-06 to 2024-01-13.

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	12% 8% 3 6% 6% 3 5% 5% 6% 8% 37%	74802
	Night	14% 9% 3 6% 5% 3 5% 5% 5% 7% 37%	74948
Transparency	Day	43% 8% 14% 22% 11% 1	74503
	Night	45% 7% 13% 21% 12% 2	74768
Seeing	Day	14% 8% 27% 31% 17% 4	14745
	Night	17% 8% 29% 29% 14% 2	24741

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	12% 10% 5% 7% 6% 3 5% 5% 7% 10% 30%	1517
	11th to 20th	Day	14% 14% 6% 10% 7% 4 7% 6% 6% 7% 20%	1456
	21st to end	Day	12% 12% 6% 11% 6% 4 6% 6% 6% 6% 24%	1584
February	1st to 10th	Day	11% 10% 6% 10% 6% 3 5% 6% 6% 8% 28%	1589
	11th to 20th	Day	13% 11% 4 6% 6% 4 5% 4 6% 6% 36%	1748
	21st to end	Day	13% 10% 5% 9% 6% 3 5% 6% 7% 7% 31%	1480
March	1st to 10th	Day	14% 8% 3 8% 6% 4 5% 6% 6% 8% 33%	1800
	11th to 20th	Day	11% 9% 4 7% 6% 3 4 5% 5% 8% 37%	1845
	21st to end	Day	16% 10% 4 6% 7% 4 4 4 6% 8% 31%	2376
April	1st to 10th	Day	15% 10% 5% 7% 6% 3 4 6% 5% 7% 31%	2160
	11th to 20th	Day	16% 8% 3 7% 6% 3 5% 4 6% 7% 34%	2134
	21st to end	Day	18% 9% 3 6% 5% 3 5% 4 5% 6% 35%	2312
May	1st to 10th	Day	15% 7% 3 6% 6% 4 5% 6% 7% 8% 34%	2340
	11th to 20th	Day	14% 7% 3 6% 5% 3 4 5% 5% 7% 39%	2479
	21st to end	Day	11% 5% 3 6% 6% 3 5% 6% 7% 8% 41%	2725
June	1st to 10th	Day	10% 5% 3 6% 4 4 5% 5% 6% 9% 43%	2520
	11th to 20th	Day	12% 4 2 6% 5% 3 4 5% 7% 8% 43%	2520
	21st to end	Day	8% 5% 2 5% 5% 3 5% 5% 7% 10% 46%	2520
July	1st to 10th	Day	5% 3 2 4 4 3 5% 7% 8% 10% 49%	2520
	11th to 20th	Day	7% 3 2 4 4 3 5% 6% 6% 9% 51%	2520
	21st to end	Day	6% 3 2 4 5% 3 5% 6% 6% 9% 51%	2743
August	1st to 10th	Day	6% 4 2 4 5% 4 6% 7% 6% 11% 47%	2499
	11th to 20th	Day	9% 4 2 5% 5% 3 5% 5% 7% 9% 48%	2223
	21st to end	Day	9% 6% 2 5% 5% 3 4 5% 6% 7% 48%	2376
September	1st to 10th	Day	10% 5% 2 6% 6% 2 5% 5% 5% 8% 44%	2160
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 6% 8% 45%	2039
	21st to end	Day	11% 7% 3 5% 5% 4 5% 4 7% 9% 41%	1980
October	1st to 10th	Day	14% 6% 3 6% 5% 3 5% 4 5% 8% 42%	1931
	11th to 20th	Day	21% 8% 3 7% 6% 3 5% 5% 6% 8% 27%	1744
	21st to end	Day	17% 9% 3 7% 6% 4 5% 4 5% 6% 34%	1782
November	1st to 10th	Day	13% 7% 3 6% 5% 3 5% 5% 6% 8% 41%	1672
	11th to 20th	Day	10% 11% 4 8% 8% 4 5% 6% 7% 7% 30%	1710
	21st to end	Day	18% 9% 4 7% 5% 3 6% 5% 4 6% 33%	1577
December	1st to 10th	Day	16% 10% 4 8% 8% 5% 5% 6% 6% 8% 24%	1520
	11th to 20th	Day	13% 12% 4 8% 7% 4 7% 5% 7% 7% 26%	1918
	21st to end	Day	19% 19% 7% 10% 8% 3 4 4 4 5% 17%	2783
January	1st to 10th	Night	13% 12% 6% 8% 7% 3 5% 3 5% 7% 31%	2648
	11th to 20th	Night	16% 13% 7% 8% 6% 3 5% 5% 6% 6% 24%	2549
	21st to end	Night	13% 12% 5% 9% 8% 4 5% 6% 6% 8% 25%	2772
February	1st to 10th	Night	13% 12% 5% 8% 6% 4 5% 5% 5% 7% 31%	2367
	11th to 20th	Night	11% 10% 5% 8% 6% 4 4 5% 5% 6% 37%	2098
	21st to end	Night	17% 13% 4 7% 4 2 4 4 4 5% 35%	1776
March	1st to 10th	Night	14% 8% 4 6% 5% 4 6% 4 6% 7% 36%	2160
	11th to 20th	Night	12% 7% 3 6% 5% 4 5% 5% 6% 7% 41%	2124
	21st to end	Night	18% 9% 4 7% 5% 3 4 5% 6% 6% 34%	1985
April	1st to 10th	Night	17% 10% 4 5% 6% 3 5% 4 5% 7% 35%	1800
	11th to 20th	Night	19% 8% 3 6% 5% 2 4 4 5% 6% 38%	1775
	21st to end	Night	18% 7% 3 5% 5% 3 4 4 5% 7% 39%	1647
May	1st to 10th	Night	16% 7% 3 6% 7% 3 5% 5% 6% 8% 33%	1616
	11th to 20th	Night	18% 5% 2 7% 5% 3 4 5% 6% 6% 38%	1416
	21st to end	Night	13% 6% 3 5% 4 3 5% 5% 7% 9% 41%	1551
June	1st to 10th	Night	11% 6% 2 5% 4 3 5% 5% 7% 8% 45%	1440
	11th to 20th	Night	11% 6% 2 5% 5% 3 4 5% 6% 9% 45%	1440
	21st to end	Night	8% 5% 3 5% 5% 3 5% 5% 6% 9% 47%	1440
July	1st to 10th	Night	6% 4 2 4 4 2 4 5% 7% 10% 52%	1440
	11th to 20th	Night	6% 4 2 5% 5% 3 5% 5% 6% 9% 51%	1440
	21st to end	Night	5% 4 3 6% 5% 2 4 4 5% 9% 52%	1575
August	1st to 10th	Night	7% 5% 2 4 5% 3 3 6% 7% 12% 48%	1440
	11th to 20th	Night	8% 3 2 5% 4 3 4 5% 6% 8% 52%	1675
	21st to end	Night	9% 5% 2 4 5% 2 5% 5% 6% 8% 49%	1980
September	1st to 10th	Night	9% 5% 2 5% 6% 3 4 4 6% 7% 49%	1800
	11th to 20th	Night	12% 4 2 4 3 2 4 5% 4 7% 53%	1901
	21st to end	Night	12% 6% 3 5% 5% 3 4 5% 5% 7% 44%	1980
October	1st to 10th	Night	13% 6% 2 6% 4 3 4 4 5% 6% 47%	2024
	11th to 20th	Night	18% 8% 2 5% 5% 3 4 5% 4 6% 38%	2214
	21st to end	Night	18% 8% 4 6% 5% 3 4 5% 6% 6% 35%	2574
November	1st to 10th	Night	12% 7% 2 5% 6% 3 5% 4 5% 7% 44%	2406
	11th to 20th	Night	14% 10% 4 8% 6% 4 5% 5% 5% 7% 32%	2470
	21st to end	Night	17% 9% 3 6% 5% 3 4 5% 4 5% 38%	2602
December	1st to 10th	Night	16% 11% 4 8% 7% 4 6% 5% 6% 8% 25%	2660
	11th to 20th	Night	15% 13% 4 7% 6% 4 7% 5% 5% 6% 27%	3279
	21st to end	Night	21% 18% 5% 8% 6% 3 5% 4 4 5% 20%	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	49% 11% 16% 16% 7% 1	1518
	11th to 20th	Day	61% 7% 15% 13% 3	1456
	21st to end	Day	57% 8% 13% 14% 7%	1584
February	1st to 10th	Day	52% 8% 14% 18% 7% 1	1589
	11th to 20th	Day	48% 8% 12% 20% 10% 2	1758
	21st to end	Day	51% 9% 11% 18% 10% 2	1480
March	1st to 10th	Day	48% 8% 15% 19% 8% 2	1800
	11th to 20th	Day	44% 8% 12% 20% 13% 2	1845
	21st to end	Day	51% 8% 13% 19% 8% 1	2376
April	1st to 10th	Day	50% 9% 12% 17% 11%	2160
	11th to 20th	Day	49% 6% 11% 19% 13% 3	2134
	21st to end	Day	49% 8% 12% 18% 12% 2	2312
May	1st to 10th	Day	45% 8% 14% 22% 10% 1	2340
	11th to 20th	Day	43% 8% 12% 23% 12% 2	2483
	21st to end	Day	39% 9% 12% 24% 14% 2	2725
June	1st to 10th	Day	35% 8% 11% 28% 15% 2	2520
	11th to 20th	Day	36% 9% 14% 24% 16% 1	2520
	21st to end	Day	32% 9% 16% 26% 15% 2	2520
July	1st to 10th	Day	27% 9% 16% 32% 14% 3	2451
	11th to 20th	Day	29% 10% 15% 27% 17% 3	2445
	21st to end	Day	28% 8% 15% 28% 17% 4	2591
August	1st to 10th	Day	29% 10% 18% 29% 11% 2	2484
	11th to 20th	Day	32% 9% 16% 30% 12% 2	2223
	21st to end	Day	34% 8% 14% 26% 17% 1	2376
September	1st to 10th	Day	37% 9% 13% 25% 14% 1	2160
	11th to 20th	Day	35% 8% 14% 30% 12% 1	2039
	21st to end	Day	38% 8% 15% 30% 10%	1980
October	1st to 10th	Day	40% 8% 12% 27% 12% 1	1931
	11th to 20th	Day	54% 8% 11% 18% 8% 1	1744
	21st to end	Day	51% 7% 13% 19% 10%	1782
November	1st to 10th	Day	40% 7% 14% 22% 14% 1	1672
	11th to 20th	Day	51% 7% 15% 19% 7% 1	1710
	21st to end	Day	51% 7% 15% 20% 6% 1	1577
December	1st to 10th	Day	54% 12% 14% 14% 6%	1520
	11th to 20th	Day	53% 7% 17% 16% 5% 2	1915
	21st to end	Day	70% 6% 10% 11% 4	2783
January	1st to 10th	Night	54% 6% 14% 15% 10% 1	2648
	11th to 20th	Night	58% 8% 16% 13% 5%	2549
	21st to end	Night	56% 7% 14% 15% 7%	2772
February	1st to 10th	Night	53% 7% 11% 18% 9% 1	2367
	11th to 20th	Night	48% 7% 11% 21% 11% 2	2099
	21st to end	Night	51% 5% 13% 16% 13% 2	1776
March	1st to 10th	Night	47% 6% 16% 20% 9% 2	2160
	11th to 20th	Night	40% 8% 13% 22% 15% 2	2124
	21st to end	Night	51% 5% 11% 22% 10% 1	1985
April	1st to 10th	Night	48% 7% 9% 19% 16% 1	1800
	11th to 20th	Night	47% 5% 9% 19% 17% 4	1775
	21st to end	Night	45% 6% 11% 21% 14% 2	1647
May	1st to 10th	Night	47% 7% 13% 20% 12% 1	1616
	11th to 20th	Night	44% 7% 11% 23% 13% 2	1417
	21st to end	Night	38% 8% 11% 25% 15% 2	1552
June	1st to 10th	Night	35% 7% 13% 28% 17% 2	1440
	11th to 20th	Night	35% 7% 12% 25% 19% 2	1440
	21st to end	Night	32% 8% 16% 25% 16% 3	1440
July	1st to 10th	Night	25% 8% 15% 29% 20% 3	1400
	11th to 20th	Night	28% 7% 15% 28% 18% 4	1392
	21st to end	Night	28% 7% 15% 28% 18% 4	1487
August	1st to 10th	Night	29% 8% 16% 30% 14% 3	1431
	11th to 20th	Night	29% 8% 16% 29% 17% 1	1675
	21st to end	Night	32% 7% 13% 27% 20% 2	1980
September	1st to 10th	Night	33% 7% 12% 24% 21% 2	1800
	11th to 20th	Night	30% 8% 10% 36% 15% 2	1901
	21st to end	Night	39% 6% 13% 29% 13% 1	1980
October	1st to 10th	Night	38% 7% 10% 29% 16% 1	2024
	11th to 20th	Night	46% 7% 14% 20% 12% 1	2214
	21st to end	Night	47% 8% 16% 19% 11%	2574
November	1st to 10th	Night	40% 6% 12% 23% 17% 2	2406
	11th to 20th	Night	50% 6% 14% 18% 11% 1	2470
	21st to end	Night	48% 6% 17% 22% 6% 1	2602
December	1st to 10th	Night	56% 8% 14% 17% 5%	2660
	11th to 20th	Night	55% 8% 12% 15% 8% 1	3281
	21st to end	Night	65% 7% 11% 13% 5%	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	17% 10% 36% 28% 8% 1	270
	11th to 20th	Day	19% 11% 36% 26% 7% 1	246
	21st to end	Day	17% 11% 33% 30% 8% 1	264
February	1st to 10th	Day	14% 14% 47% 19% 6%	240
	11th to 20th	Day	16% 22% 36% 20% 6%	240
	21st to end	Day	19% 18% 42% 19% 2	198
March	1st to 10th	Day	14% 17% 48% 17% 4	240
	11th to 20th	Day	18% 12% 30% 29% 8% 3	276
	21st to end	Day	24% 11% 30% 26% 8% 1	462
April	1st to 10th	Day	22% 9% 34% 25% 10%	420
	11th to 20th	Day	19% 14% 31% 22% 11% 4	412
	21st to end	Day	21% 6% 31% 27% 13% 2	420
May	1st to 10th	Day	18% 5% 35% 29% 11% 2	423
	11th to 20th	Day	16% 5% 27% 34% 15% 3	625
	21st to end	Day	13% 3 25% 30% 24% 5%	679
June	1st to 10th	Day	11% 2 24% 39% 22% 3	630
	11th to 20th	Day	13% 4 24% 35% 20% 4	630
	21st to end	Day	10% 4 20% 41% 21% 4	630
July	1st to 10th	Day	6% 2 15% 36% 32% 9%	621
	11th to 20th	Day	9% 2 20% 38% 26% 6%	618
	21st to end	Day	5% 1 18% 43% 26% 7%	684
August	1st to 10th	Day	6% 2 17% 40% 25% 9%	618
	11th to 20th	Day	9% 4 15% 28% 33% 10%	439
	21st to end	Day	11% 4 19% 33% 25% 7%	495
September	1st to 10th	Day	12% 6% 18% 35% 21% 8%	450
	11th to 20th	Day	11% 3 19% 36% 23% 8%	450
	21st to end	Day	15% 8% 24% 26% 22% 6%	450
October	1st to 10th	Day	19% 7% 24% 30% 16% 4	401
	11th to 20th	Day	21% 17% 27% 26% 8%	270
	21st to end	Day	22% 10% 38% 21% 7% 1	297
November	1st to 10th	Day	14% 13% 29% 31% 11% 1	270
	11th to 20th	Day	13% 19% 34% 26% 6%	270
	21st to end	Day	24% 10% 35% 25% 5%	270
December	1st to 10th	Day	19% 17% 38% 20% 5%	270
	11th to 20th	Day	23% 17% 37% 16% 7%	270
	21st to end	Day	24% 18% 36% 18% 5%	297
January	1st to 10th	Night	18% 14% 39% 23% 6%	950
	11th to 20th	Night	21% 14% 35% 24% 5% 1	911
	21st to end	Night	19% 10% 38% 26% 7%	990
February	1st to 10th	Night	21% 13% 37% 25% 4	895
	11th to 20th	Night	17% 13% 38% 24% 8%	703
	21st to end	Night	23% 12% 38% 22% 4	592
March	1st to 10th	Night	19% 9% 33% 28% 10% 1	720
	11th to 20th	Night	15% 8% 39% 28% 9% 1	720
	21st to end	Night	21% 6% 27% 34% 11% 1	599
April	1st to 10th	Night	19% 9% 37% 27% 8% 1	540
	11th to 20th	Night	24% 6% 26% 31% 11% 2	533
	21st to end	Night	20% 6% 26% 34% 14% 1	540
May	1st to 10th	Night	18% 4 25% 40% 12% 1	540
	11th to 20th	Night	19% 3 26% 35% 16% 1	531
	21st to end	Night	14% 3 18% 38% 24% 4	584
June	1st to 10th	Night	11% 3 21% 40% 24% 2	540
	11th to 20th	Night	14% 3 20% 36% 24% 3	540
	21st to end	Night	9% 2 19% 41% 26% 3	540
July	1st to 10th	Night	8% 2 10% 38% 36% 6%	525
	11th to 20th	Night	7% 1 15% 41% 31% 5%	522
	21st to end	Night	6% 2 17% 42% 33% 1	591
August	1st to 10th	Night	9% 1 9% 44% 33% 4	537
	11th to 20th	Night	9% 2 14% 34% 32% 8%	534
	21st to end	Night	11% 2 18% 34% 31% 4	594
September	1st to 10th	Night	9% 4 20% 33% 26% 7%	540
	11th to 20th	Night	13% 5% 18% 32% 26% 7%	641
	21st to end	Night	15% 6% 25% 26% 23% 5%	720
October	1st to 10th	Night	17% 6% 26% 28% 22% 2	720
	11th to 20th	Night	23% 11% 29% 26% 11% 1	720
	21st to end	Night	23% 11% 30% 26% 10% 1	792
November	1st to 10th	Night	16% 10% 34% 30% 10% 1	740
	11th to 20th	Night	19% 16% 35% 23% 8%	760
	21st to end	Night	23% 13% 35% 22% 7%	892
December	1st to 10th	Night	21% 16% 35% 23% 5%	950
	11th to 20th	Night	24% 12% 38% 20% 6% 1	950
	21st to end	Night	27% 13% 37% 20% 4	1045

Page generated at 2024-01-10 00:25:04. Version ac07

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