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 2024-11-10.

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	12% 8% 3 7% 5% 5% 5% 4 6% 8% 38%	101437
	Night	13% 10% 3 8% 5% 4 4 4 5% 7% 37%	97781
Transparency	Day	41% 8% 13% 24% 12% 1	104969
	Night	45% 6% 13% 22% 13% 2	102390
Seeing	Day	14% 8% 27% 31% 16% 4	15945
	Night	17% 8% 29% 29% 14% 2	25802

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% 13% 4 9% 5% 5% 5% 4 6% 7% 29%	2527
	11th to 20th	Day	12% 12% 5% 11% 5% 5% 8% 7% 9% 8% 19%	2530
	21st to end	Day	16% 17% 7% 11% 4 5% 5% 4 5% 5% 21%	2783
February	1st to 10th	Day	10% 11% 6% 11% 5% 5% 5% 5% 6% 8% 27%	1677
	11th to 20th	Day	11% 12% 4 7% 6% 5% 4 4 6% 6% 36%	1848
	21st to end	Day	12% 11% 4 8% 6% 4 5% 5% 6% 7% 32%	1570
March	1st to 10th	Day	12% 8% 2 8% 5% 5% 4 4 5% 7% 42%	3120
	11th to 20th	Day	11% 7% 4 7% 5% 4 4 4 6% 7% 41%	3247
	21st to end	Day	19% 11% 4 10% 5% 5% 4 3 4 5% 30%	4165
April	1st to 10th	Day	15% 11% 4 8% 6% 4 5% 5% 5% 6% 32%	2280
	11th to 20th	Day	16% 9% 3 7% 5% 5% 4 3 6% 6% 34%	2254
	21st to end	Day	17% 9% 3 7% 5% 4 5% 3 5% 6% 35%	2441
May	1st to 10th	Day	14% 8% 3 7% 5% 4 4 4 5% 6% 39%	4082
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 5% 6% 9% 40%	4399
	21st to end	Day	11% 7% 3 7% 5% 4 4 4 6% 7% 42%	4824
June	1st to 10th	Day	10% 6% 2 6% 4 5% 4 5% 7% 9% 42%	2660
	11th to 20th	Day	12% 5% 2 7% 4 4 4 4 7% 9% 42%	2660
	21st to end	Day	9% 5% 2 6% 5% 4 4 4 7% 9% 45%	2660
July	1st to 10th	Day	12% 6% 2 7% 4 5% 5% 5% 7% 9% 38%	4440
	11th to 20th	Day	4 3 1 4 3 4 5% 5% 7% 11% 52%	4440
	21st to end	Day	6% 5% 2 6% 4 4 5% 5% 6% 9% 49%	4813
August	1st to 10th	Day	9% 5% 2 5% 4 5% 5% 5% 6% 9% 44%	4401
	11th to 20th	Day	10% 4 2 6% 4 4 5% 4 6% 8% 49%	3894
	21st to end	Day	8% 6% 2 7% 4 5% 5% 4 7% 7% 45%	4180
September	1st to 10th	Day	10% 5% 2 7% 4 3 5% 4 5% 8% 45%	2280
	11th to 20th	Day	11% 5% 2 5% 4 5% 5% 3 6% 8% 46%	2152
	21st to end	Day	11% 7% 3 6% 4 5% 4 3 7% 9% 42%	2090
October	1st to 10th	Day	14% 6% 3 6% 4 4 4 3 5% 8% 44%	2038
	11th to 20th	Day	20% 7% 3 8% 5% 5% 4 4 6% 8% 28%	1840
	21st to end	Day	16% 9% 3 8% 5% 5% 4 4 5% 6% 35%	1881
November	1st to 10th	Day	13% 8% 3 6% 4 4 4 4 6% 7% 41%	1753
	11th to 20th	Day	10% 12% 4 10% 6% 5% 5% 5% 7% 6% 30%	1710
	21st to end	Day	18% 10% 3 8% 4 4 5% 4 5% 6% 33%	1577
December	1st to 10th	Day	16% 11% 3 9% 8% 7% 4 5% 6% 8% 24%	1520
	11th to 20th	Day	13% 13% 4 9% 6% 5% 5% 4 7% 7% 26%	1918
	21st to end	Day	18% 19% 7% 12% 6% 4 4 3 4 5% 17%	2783
January	1st to 10th	Night	15% 15% 7% 8% 5% 4 3 3 4 6% 31%	4428
	11th to 20th	Night	13% 14% 5% 12% 7% 6% 7% 6% 8% 6% 17%	4440
	21st to end	Night	15% 18% 6% 11% 5% 4 3 3 4 6% 24%	4884
February	1st to 10th	Night	12% 13% 4 9% 6% 4 6% 4 5% 6% 31%	2499
	11th to 20th	Night	10% 11% 4 8% 6% 5% 4 4 5% 6% 38%	2218
	21st to end	Night	16% 13% 3 8% 4 3 4 3 4 6% 36%	1884
March	1st to 10th	Night	16% 8% 3 6% 4 4 4 3 5% 6% 41%	3733
	11th to 20th	Night	9% 8% 3 7% 4 5% 5% 4 6% 8% 41%	3736
	21st to end	Night	18% 10% 4 10% 6% 4 4 4 5% 5% 30%	3471
April	1st to 10th	Night	17% 11% 3 6% 5% 5% 4 3 5% 6% 35%	1900
	11th to 20th	Night	19% 9% 2 7% 4 3 4 3 5% 5% 39%	1875
	21st to end	Night	17% 8% 3 6% 4 4 4 3 5% 7% 39%	1738
May	1st to 10th	Night	14% 7% 3 8% 5% 5% 4 4 6% 7% 37%	2796
	11th to 20th	Night	13% 5% 2 8% 5% 5% 6% 5% 7% 8% 36%	2506
	21st to end	Night	15% 8% 3 7% 4 4 5% 3 5% 7% 40%	2743
June	1st to 10th	Night	10% 7% 2 5% 4 4 4 4 7% 8% 45%	1520
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 6% 9% 45%	1520
	21st to end	Night	8% 6% 3 6% 4 4 5% 3 7% 8% 46%	1520
July	1st to 10th	Night	11% 7% 2 7% 4 4 4 5% 6% 9% 40%	2530
	11th to 20th	Night	4 3 1 4 3 4 5% 4 6% 10% 56%	2530
	21st to end	Night	5% 5% 2 7% 4 4 4 3 6% 9% 50%	2750
August	1st to 10th	Night	10% 5% 2 5% 4 4 3 4 6% 10% 46%	2538
	11th to 20th	Night	10% 5% 2 6% 4 4 4 3 6% 8% 48%	2932
	21st to end	Night	9% 6% 2 5% 4 4 5% 4 6% 8% 47%	3476
September	1st to 10th	Night	9% 5% 2 6% 4 4 4 3 6% 7% 51%	1900
	11th to 20th	Night	11% 4 2 5% 3 4 4 4 5% 7% 52%	2007
	21st to end	Night	12% 7% 3 6% 4 4 4 4 5% 7% 45%	2090
October	1st to 10th	Night	12% 6% 2 6% 3 4 4 3 5% 6% 48%	2137
	11th to 20th	Night	17% 8% 2 6% 5% 5% 4 4 4 6% 39%	2338
	21st to end	Night	18% 9% 3 7% 4 3 4 4 6% 7% 36%	2717
November	1st to 10th	Night	12% 7% 2 6% 5% 4 4 3 5% 7% 44%	2530
	11th to 20th	Night	14% 11% 3 9% 5% 6% 5% 4 5% 6% 32%	2470
	21st to end	Night	17% 10% 3 7% 4 4 4 4 5% 5% 38%	2602
December	1st to 10th	Night	15% 12% 4 9% 6% 6% 5% 4 6% 7% 25%	2660
	11th to 20th	Night	15% 14% 4 8% 6% 5% 6% 4 5% 6% 27%	3279
	21st to end	Night	21% 19% 5% 9% 5% 4 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	53% 9% 18% 15% 5%	2528
	11th to 20th	Day	59% 10% 17% 13% 2	2530
	21st to end	Day	63% 6% 11% 15% 4	2783
February	1st to 10th	Day	51% 9% 15% 17% 7% 1	1677
	11th to 20th	Day	47% 8% 12% 21% 10% 2	1858
	21st to end	Day	49% 8% 12% 19% 10% 2	1570
March	1st to 10th	Day	41% 7% 14% 22% 14% 3	3120
	11th to 20th	Day	40% 6% 14% 24% 16% 2	3247
	21st to end	Day	56% 7% 10% 19% 7% 1	4165
April	1st to 10th	Day	50% 9% 12% 18% 11%	2280
	11th to 20th	Day	49% 6% 11% 19% 13% 2	2254
	21st to end	Day	48% 8% 12% 18% 12% 2	2441
May	1st to 10th	Day	42% 8% 11% 23% 16% 1	4120
	11th to 20th	Day	35% 8% 16% 26% 13% 1	4403
	21st to end	Day	38% 9% 11% 22% 17% 4	4837
June	1st to 10th	Day	35% 8% 12% 27% 16% 2	2660
	11th to 20th	Day	36% 9% 14% 24% 16% 1	2660
	21st to end	Day	33% 9% 15% 26% 15% 2	2660
July	1st to 10th	Day	40% 7% 15% 26% 10% 2	4371
	11th to 20th	Day	24% 8% 18% 33% 15% 2	4365
	21st to end	Day	30% 8% 15% 24% 20% 3	4662
August	1st to 10th	Day	34% 8% 15% 30% 11% 1	4386
	11th to 20th	Day	32% 8% 13% 36% 11% 1	3933
	21st to end	Day	35% 8% 16% 24% 16% 1	4179
September	1st to 10th	Day	36% 9% 13% 27% 14% 1	2280
	11th to 20th	Day	34% 8% 14% 31% 13% 1	2152
	21st to end	Day	38% 7% 14% 30% 11%	2090
October	1st to 10th	Day	24% 5% 8% 38% 23% 2	3389
	11th to 20th	Day	42% 6% 11% 24% 16%	3030
	21st to end	Day	42% 5% 12% 27% 12% 1	3081
November	1st to 10th	Day	41% 7% 15% 22% 13% 1	1753
	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	56% 5% 13% 17% 8% 1	4428
	11th to 20th	Night	65% 7% 15% 10% 4	4440
	21st to end	Night	62% 6% 13% 15% 4	4884
February	1st to 10th	Night	51% 7% 12% 18% 10% 2	2499
	11th to 20th	Night	46% 7% 12% 22% 11% 2	2219
	21st to end	Night	50% 4 14% 18% 12% 2	1884
March	1st to 10th	Night	43% 6% 14% 27% 9% 2	3733
	11th to 20th	Night	38% 7% 12% 23% 18% 2	3736
	21st to end	Night	56% 5% 9% 18% 10% 2	3471
April	1st to 10th	Night	48% 7% 9% 19% 16% 1	1900
	11th to 20th	Night	46% 5% 9% 20% 17% 4	1875
	21st to end	Night	45% 5% 11% 22% 14% 2	1738
May	1st to 10th	Night	44% 6% 13% 18% 17% 2	2823
	11th to 20th	Night	38% 9% 15% 24% 13% 1	2507
	21st to end	Night	44% 7% 9% 19% 14% 8%	2751
June	1st to 10th	Night	35% 7% 13% 27% 17% 1	1520
	11th to 20th	Night	35% 7% 12% 25% 20% 2	1520
	21st to end	Night	33% 8% 16% 24% 16% 3	1520
July	1st to 10th	Night	39% 6% 15% 22% 13% 5%	2490
	11th to 20th	Night	23% 6% 17% 34% 18% 2	2482
	21st to end	Night	30% 7% 14% 24% 22% 3	2662
August	1st to 10th	Night	34% 7% 13% 27% 18% 2	2529
	11th to 20th	Night	34% 7% 12% 30% 17% 1	2959
	21st to end	Night	34% 7% 13% 23% 21% 3	3476
September	1st to 10th	Night	31% 7% 13% 26% 21% 2	1900
	11th to 20th	Night	30% 8% 9% 35% 16% 2	2007
	21st to end	Night	38% 5% 12% 28% 15% 1	2090
October	1st to 10th	Night	27% 5% 7% 40% 21% 1	3566
	11th to 20th	Night	35% 6% 15% 26% 17% 2	3887
	21st to end	Night	41% 5% 12% 24% 17%	4467
November	1st to 10th	Night	40% 6% 12% 23% 16% 2	2530
	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% 27% 8% 1	270
	11th to 20th	Day	18% 13% 37% 25% 6% 1	270
	21st to end	Day	18% 11% 33% 31% 7% 1	297
February	1st to 10th	Day	13% 15% 45% 19% 7% 1	270
	11th to 20th	Day	15% 21% 37% 20% 7%	270
	21st to end	Day	17% 17% 42% 21% 2	225
March	1st to 10th	Day	14% 18% 46% 18% 4	270
	11th to 20th	Day	18% 14% 30% 28% 8% 2	308
	21st to end	Day	24% 12% 30% 26% 8% 1	506
April	1st to 10th	Day	23% 10% 33% 25% 9%	460
	11th to 20th	Day	18% 16% 31% 22% 10% 4	452
	21st to end	Day	20% 7% 32% 27% 13% 2	460
May	1st to 10th	Day	17% 6% 36% 28% 11% 2	463
	11th to 20th	Day	16% 5% 27% 35% 15% 3	675
	21st to end	Day	13% 4 26% 30% 23% 5%	734
June	1st to 10th	Day	11% 3 24% 38% 20% 3	680
	11th to 20th	Day	12% 4 26% 34% 19% 4	680
	21st to end	Day	11% 4 22% 40% 19% 4	680
July	1st to 10th	Day	7% 2 17% 36% 30% 8%	671
	11th to 20th	Day	8% 2 20% 38% 25% 7%	668
	21st to end	Day	5% 2 17% 43% 26% 7%	739
August	1st to 10th	Day	6% 3 18% 39% 25% 8%	667
	11th to 20th	Day	10% 4 16% 29% 32% 9%	479
	21st to end	Day	11% 4 19% 33% 26% 7%	539
September	1st to 10th	Day	11% 6% 20% 34% 21% 8%	490
	11th to 20th	Day	10% 3 18% 37% 24% 9%	490
	21st to end	Day	15% 8% 23% 28% 21% 5%	490
October	1st to 10th	Day	17% 8% 26% 30% 16% 4	438
	11th to 20th	Day	20% 17% 28% 27% 8%	300
	21st to end	Day	21% 11% 38% 22% 7% 1	330
November	1st to 10th	Day	14% 13% 30% 30% 11% 1	297
	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% 15% 39% 23% 6%	950
	11th to 20th	Night	21% 15% 35% 23% 5% 1	950
	21st to end	Night	19% 10% 38% 26% 7%	1045
February	1st to 10th	Night	20% 13% 37% 25% 5% 1	945
	11th to 20th	Night	16% 13% 38% 24% 8%	743
	21st to end	Night	22% 12% 39% 22% 4	628
March	1st to 10th	Night	20% 9% 33% 28% 10% 1	760
	11th to 20th	Night	14% 9% 39% 28% 9% 1	760
	21st to end	Night	21% 6% 28% 34% 11% 1	632
April	1st to 10th	Night	19% 9% 37% 27% 7% 1	570
	11th to 20th	Night	24% 7% 28% 30% 10% 2	563
	21st to end	Night	19% 6% 26% 34% 13% 1	570
May	1st to 10th	Night	17% 4 25% 41% 12% 1	570
	11th to 20th	Night	18% 3 25% 36% 16% 1	561
	21st to end	Night	14% 3 18% 38% 23% 4	617
June	1st to 10th	Night	11% 3 21% 40% 22% 2	570
	11th to 20th	Night	14% 3 21% 37% 23% 3	570
	21st to end	Night	9% 3 20% 41% 25% 3	570
July	1st to 10th	Night	9% 2 11% 39% 34% 6%	555
	11th to 20th	Night	7% 1 14% 41% 32% 5%	552
	21st to end	Night	5% 2 17% 41% 34% 1	624
August	1st to 10th	Night	9% 2 10% 43% 33% 4	567
	11th to 20th	Night	9% 2 14% 36% 31% 8%	564
	21st to end	Night	11% 2 18% 34% 32% 4	627
September	1st to 10th	Night	9% 4 21% 32% 27% 7%	570
	11th to 20th	Night	12% 5% 17% 32% 27% 7%	677
	21st to end	Night	15% 6% 25% 27% 22% 5%	760
October	1st to 10th	Night	16% 6% 27% 28% 22% 2	760
	11th to 20th	Night	23% 11% 28% 27% 11% 1	760
	21st to end	Night	22% 10% 30% 27% 10%	836
November	1st to 10th	Night	16% 10% 35% 29% 9% 1	779
	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 2024-11-07 05:55:43. Version ac07

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