Engle Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Engle Ridge Observatory clear sky chart from 2005-11-06 to 2024-11-30.

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% 11% 4 9% 5% 4 4 3 5% 6% 33%	101365
	Night	15% 14% 5% 10% 6% 5% 4 3 4 5% 29%	98319
Transparency	Day	50% 7% 11% 21% 11% 1	104862
	Night	56% 7% 10% 17% 9% 1	102897
Seeing	Day	19% 11% 26% 27% 14% 4	15802
	Night	20% 9% 28% 30% 11% 1	25636

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	11% 26% 15% 20% 7% 5% 3 2 2 3 6%	2527
	11th to 20th	Day	12% 18% 7% 21% 14% 10% 5% 3 2 2 4	2530
	21st to end	Day	18% 23% 9% 15% 6% 5% 6% 3 3 3 8%	2783
February	1st to 10th	Day	9% 19% 8% 15% 14% 7% 4 3 4 4 13%	1625
	11th to 20th	Day	12% 16% 8% 16% 11% 7% 5% 3 3 4 15%	1847
	21st to end	Day	12% 18% 7% 14% 8% 5% 5% 3 5% 4 19%	1570
March	1st to 10th	Day	12% 14% 4 10% 6% 4 4 4 5% 5% 32%	3118
	11th to 20th	Day	9% 13% 7% 15% 5% 4 4 3 5% 7% 27%	3384
	21st to end	Day	16% 13% 8% 14% 6% 5% 4 3 4 5% 23%	3959
April	1st to 10th	Day	17% 16% 4 8% 5% 5% 4 3 4 6% 29%	2280
	11th to 20th	Day	20% 13% 4 6% 3 4 4 3 4 6% 34%	2351
	21st to end	Day	15% 11% 4 8% 4 3 4 3 6% 6% 34%	2470
May	1st to 10th	Day	14% 9% 3 7% 4 3 4 3 5% 6% 42%	4108
	11th to 20th	Day	11% 7% 2 6% 3 4 4 3 5% 6% 48%	4226
	21st to end	Day	13% 6% 2 6% 4 4 4 3 6% 7% 44%	4837
June	1st to 10th	Day	14% 6% 2 5% 4 4 5% 4 6% 8% 43%	2703
	11th to 20th	Day	11% 6% 2 6% 4 5% 4 4 6% 9% 42%	2850
	21st to end	Day	14% 6% 3 6% 4 4 4 4 6% 8% 41%	2687
July	1st to 10th	Day	18% 6% 2 6% 3 4 4 3 6% 8% 41%	4440
	11th to 20th	Day	10% 4 1 4 3 4 5% 4 5% 9% 51%	4440
	21st to end	Day	10% 5% 2 5% 4 4 4 4 6% 9% 49%	4814
August	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 5% 8% 8% 40%	4241
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 6% 47%	4044
	21st to end	Day	13% 6% 3 7% 4 4 4 3 5% 6% 44%	4343
September	1st to 10th	Day	15% 5% 1 7% 5% 3 5% 4 5% 8% 43%	2254
	11th to 20th	Day	15% 5% 2 4 4 3 4 4 5% 8% 46%	2090
	21st to end	Day	17% 6% 3 7% 3 4 4 5% 5% 8% 37%	2090
October	1st to 10th	Day	19% 9% 3 7% 4 3 3 4 5% 6% 36%	2090
	11th to 20th	Day	24% 15% 3 8% 6% 5% 4 3 4 5% 22%	1799
	21st to end	Day	25% 16% 4 10% 5% 5% 5% 4 5% 5% 17%	1881
November	1st to 10th	Day	17% 18% 5% 7% 5% 3 4 3 4 6% 27%	1762
	11th to 20th	Day	13% 24% 6% 11% 6% 5% 4 4 5% 5% 17%	1800
	21st to end	Day	17% 26% 9% 12% 4 4 3 3 4 3 14%	1689
December	1st to 10th	Day	15% 25% 11% 17% 7% 5% 3 3 3 2 10%	1330
	11th to 20th	Day	14% 22% 8% 15% 9% 6% 5% 2 4 4 10%	1671
	21st to end	Day	20% 21% 11% 15% 7% 5% 4 4 3 4 8%	2732
January	1st to 10th	Night	13% 24% 9% 20% 8% 4 3 2 2 3 11%	4428
	11th to 20th	Night	11% 19% 7% 22% 13% 9% 4 3 4 3 7%	4440
	21st to end	Night	15% 24% 10% 15% 8% 6% 4 3 3 3 8%	4884
February	1st to 10th	Night	10% 20% 6% 16% 13% 8% 4 3 3 3 14%	2553
	11th to 20th	Night	11% 16% 7% 17% 11% 6% 4 3 4 4 17%	2218
	21st to end	Night	15% 17% 6% 12% 7% 5% 4 3 4 5% 21%	1884
March	1st to 10th	Night	14% 12% 4 6% 5% 3 4 3 4 6% 39%	3722
	11th to 20th	Night	9% 16% 5% 9% 4 4 4 3 5% 6% 35%	3575
	21st to end	Night	15% 13% 6% 11% 5% 5% 4 4 5% 5% 26%	3700
April	1st to 10th	Night	19% 13% 4 9% 4 3 4 3 5% 6% 30%	1900
	11th to 20th	Night	20% 12% 3 7% 4 3 4 3 4 6% 34%	1777
	21st to end	Night	17% 11% 3 7% 4 3 4 3 5% 6% 37%	1710
May	1st to 10th	Night	16% 8% 3 6% 5% 4 4 4 6% 6% 40%	2833
	11th to 20th	Night	13% 8% 3 6% 4 5% 4 3 5% 7% 42%	2670
	21st to end	Night	18% 6% 2 5% 4 3 3 3 5% 8% 42%	2750
June	1st to 10th	Night	14% 6% 2 6% 5% 4 5% 3 5% 6% 43%	1468
	11th to 20th	Night	11% 5% 3 5% 4 3 5% 4 7% 9% 43%	1330
	21st to end	Night	12% 6% 3 5% 4 4 4 3 5% 8% 45%	1482
July	1st to 10th	Night	14% 7% 2 6% 3 4 4 3 7% 8% 42%	2530
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 6% 6% 52%	2530
	21st to end	Night	10% 5% 3 6% 4 4 4 3 5% 6% 49%	2750
August	1st to 10th	Night	12% 6% 2 7% 5% 5% 5% 4 5% 8% 41%	2691
	11th to 20th	Night	15% 6% 2 5% 3 3 4 3 5% 7% 48%	2785
	21st to end	Night	14% 5% 2 6% 4 4 4 3 5% 7% 47%	3310
September	1st to 10th	Night	12% 7% 2 6% 4 4 3 3 5% 6% 49%	1906
	11th to 20th	Night	16% 5% 2 4 3 3 4 3 5% 7% 47%	2090
	21st to end	Night	19% 6% 3 6% 4 4 4 2 4 7% 40%	2090
October	1st to 10th	Night	19% 10% 3 7% 4 3 4 3 4 5% 40%	2090
	11th to 20th	Night	23% 12% 3 9% 5% 4 5% 4 5% 6% 25%	2379
	21st to end	Night	25% 16% 4 9% 5% 4 4 3 4 5% 22%	2717
November	1st to 10th	Night	15% 16% 4 9% 5% 4 4 3 5% 6% 28%	2536
	11th to 20th	Night	15% 24% 6% 10% 6% 5% 4 3 4 5% 18%	2600
	21st to end	Night	17% 24% 7% 12% 5% 4 4 3 4 4 14%	2699
December	1st to 10th	Night	14% 25% 10% 16% 7% 5% 3 3 4 3 10%	2850
	11th to 20th	Night	13% 22% 8% 19% 8% 4 4 3 4 4 10%	3526
	21st to end	Night	22% 22% 9% 13% 5% 5% 4 3 3 4 10%	4916

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	86% 5% 4 3 1	2528
	11th to 20th	Day	88% 5% 3 3 1	2530
	21st to end	Day	81% 6% 8% 4 1	2783
February	1st to 10th	Day	75% 7% 8% 8% 2	1625
	11th to 20th	Day	73% 6% 9% 9% 3	1857
	21st to end	Day	66% 7% 10% 14% 3 1	1570
March	1st to 10th	Day	52% 6% 13% 20% 8%	3120
	11th to 20th	Day	55% 6% 14% 18% 5% 1	3384
	21st to end	Day	62% 7% 10% 15% 5% 1	3959
April	1st to 10th	Day	57% 5% 10% 18% 10%	2280
	11th to 20th	Day	51% 5% 9% 20% 13% 1	2351
	21st to end	Day	49% 7% 12% 15% 15% 3	2470
May	1st to 10th	Day	41% 6% 10% 22% 18% 2	4120
	11th to 20th	Day	35% 7% 11% 29% 16% 2	4230
	21st to end	Day	37% 8% 11% 22% 20% 2	4837
June	1st to 10th	Day	37% 8% 11% 26% 15% 2	2703
	11th to 20th	Day	37% 7% 13% 23% 18% 2	2850
	21st to end	Day	39% 7% 14% 24% 14% 1	2687
July	1st to 10th	Day	42% 5% 15% 23% 13% 1	4371
	11th to 20th	Day	29% 6% 13% 35% 15% 1	4365
	21st to end	Day	31% 7% 12% 30% 19% 1	4662
August	1st to 10th	Day	37% 9% 13% 27% 13% 1	4226
	11th to 20th	Day	37% 6% 11% 33% 12% 1	4083
	21st to end	Day	40% 6% 12% 29% 11% 1	4342
September	1st to 10th	Day	39% 6% 14% 25% 15% 1	2254
	11th to 20th	Day	35% 8% 14% 28% 13% 1	2090
	21st to end	Day	43% 8% 15% 23% 10%	2090
October	1st to 10th	Day	35% 5% 8% 33% 18% 1	3480
	11th to 20th	Day	56% 5% 9% 19% 11%	2950
	21st to end	Day	64% 6% 13% 15% 3	3081
November	1st to 10th	Day	58% 6% 10% 18% 7%	1762
	11th to 20th	Day	69% 7% 11% 10% 4	1800
	21st to end	Day	74% 5% 11% 7% 2	1689
December	1st to 10th	Day	82% 6% 6% 5% 1	1330
	11th to 20th	Day	78% 7% 7% 6% 1	1671
	21st to end	Day	80% 9% 6% 4 2	2732
January	1st to 10th	Night	80% 6% 6% 7% 1	4428
	11th to 20th	Night	84% 7% 4 4 1	4440
	21st to end	Night	81% 8% 6% 4 1	4884
February	1st to 10th	Night	75% 6% 6% 9% 3	2553
	11th to 20th	Night	69% 7% 9% 12% 3	2219
	21st to end	Night	65% 6% 12% 14% 4	1884
March	1st to 10th	Night	46% 7% 16% 22% 8%	3733
	11th to 20th	Night	49% 7% 12% 23% 8% 1	3576
	21st to end	Night	56% 9% 10% 18% 6% 1	3700
April	1st to 10th	Night	55% 6% 9% 20% 10% 1	1900
	11th to 20th	Night	51% 4 9% 20% 13% 2	1777
	21st to end	Night	47% 6% 10% 20% 14% 2	1710
May	1st to 10th	Night	42% 8% 12% 19% 16% 3	2840
	11th to 20th	Night	40% 7% 9% 25% 17% 2	2671
	21st to end	Night	39% 7% 14% 20% 16% 4	2751
June	1st to 10th	Night	40% 6% 10% 28% 15% 1	1468
	11th to 20th	Night	34% 9% 14% 24% 17% 2	1330
	21st to end	Night	38% 6% 12% 26% 16% 2	1482
July	1st to 10th	Night	39% 5% 13% 24% 14% 4	2490
	11th to 20th	Night	30% 7% 14% 30% 18% 1	2482
	21st to end	Night	34% 7% 14% 25% 19% 1	2662
August	1st to 10th	Night	41% 7% 15% 25% 12% 1	2682
	11th to 20th	Night	35% 5% 15% 28% 15% 1	2812
	21st to end	Night	36% 6% 14% 25% 19% 1	3310
September	1st to 10th	Night	36% 6% 13% 24% 19% 1	1906
	11th to 20th	Night	35% 7% 15% 29% 13%	2090
	21st to end	Night	45% 6% 14% 24% 9% 1	2090
October	1st to 10th	Night	43% 6% 9% 29% 13%	3480
	11th to 20th	Night	51% 5% 9% 22% 12%	3954
	21st to end	Night	57% 5% 12% 21% 5%	4467
November	1st to 10th	Night	56% 8% 11% 18% 7% 1	2536
	11th to 20th	Night	68% 7% 10% 9% 5% 1	2600
	21st to end	Night	73% 6% 11% 8% 1	2699
December	1st to 10th	Night	79% 8% 6% 7% 1	2850
	11th to 20th	Night	78% 8% 8% 4 2	3525
	21st to end	Night	78% 10% 7% 3 1	4916

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% 16% 37% 20% 8% 2	270
	11th to 20th	Day	20% 14% 35% 26% 3 1	270
	21st to end	Day	24% 10% 31% 28% 6%	297
February	1st to 10th	Day	20% 20% 33% 19% 6% 1	270
	11th to 20th	Day	17% 20% 36% 21% 5%	270
	21st to end	Day	20% 24% 36% 16% 3	225
March	1st to 10th	Day	20% 17% 37% 21% 5%	270
	11th to 20th	Day	20% 13% 29% 28% 10% 1	403
	21st to end	Day	26% 11% 27% 25% 10% 1	506
April	1st to 10th	Day	23% 13% 30% 26% 7% 1	460
	11th to 20th	Day	26% 17% 24% 19% 10% 3	452
	21st to end	Day	21% 11% 28% 25% 13% 2	460
May	1st to 10th	Day	22% 14% 24% 25% 12% 3	463
	11th to 20th	Day	16% 8% 27% 31% 14% 4	567
	21st to end	Day	13% 9% 26% 28% 19% 5%	734
June	1st to 10th	Day	15% 8% 27% 30% 16% 4	680
	11th to 20th	Day	16% 7% 26% 33% 14% 4	680
	21st to end	Day	16% 6% 25% 32% 18% 3	680
July	1st to 10th	Day	11% 4 21% 35% 21% 8%	671
	11th to 20th	Day	12% 6% 23% 32% 20% 7%	668
	21st to end	Day	10% 3 23% 37% 20% 6%	739
August	1st to 10th	Day	12% 4 20% 30% 26% 10%	572
	11th to 20th	Day	13% 4 18% 30% 23% 13%	479
	21st to end	Day	16% 8% 17% 29% 22% 8%	539
September	1st to 10th	Day	20% 5% 20% 28% 19% 9%	490
	11th to 20th	Day	13% 5% 16% 31% 24% 10%	490
	21st to end	Day	19% 10% 18% 26% 21% 6%	490
October	1st to 10th	Day	21% 13% 23% 23% 14% 5%	490
	11th to 20th	Day	32% 12% 27% 22% 7% 1	375
	21st to end	Day	33% 13% 31% 16% 5% 2	330
November	1st to 10th	Day	28% 18% 27% 17% 10% 1	300
	11th to 20th	Day	21% 23% 34% 18% 4	300
	21st to end	Day	30% 20% 33% 15% 3	267
December	1st to 10th	Day	31% 17% 28% 17% 6% 1	180
	11th to 20th	Day	23% 24% 32% 17% 3 1	180
	21st to end	Day	24% 21% 34% 18% 2 1	285
January	1st to 10th	Night	20% 14% 34% 24% 7% 1	950
	11th to 20th	Night	23% 15% 31% 25% 6% 1	950
	21st to end	Night	20% 10% 34% 29% 7% 1	1045
February	1st to 10th	Night	16% 10% 39% 28% 6% 1	843
	11th to 20th	Night	19% 13% 37% 26% 6%	743
	21st to end	Night	24% 13% 32% 26% 5%	628
March	1st to 10th	Night	15% 12% 33% 29% 10% 1	760
	11th to 20th	Night	17% 11% 34% 30% 6% 1	760
	21st to end	Night	21% 9% 29% 33% 8% 1	770
April	1st to 10th	Night	24% 10% 29% 30% 6% 1	570
	11th to 20th	Night	24% 11% 27% 28% 9% 1	563
	21st to end	Night	21% 7% 27% 34% 11% 1	570
May	1st to 10th	Night	19% 5% 28% 37% 11% 1	570
	11th to 20th	Night	19% 4 26% 36% 15% 1	561
	21st to end	Night	15% 5% 22% 38% 19% 1	617
June	1st to 10th	Night	16% 3 26% 38% 15% 1	518
	11th to 20th	Night	12% 6% 21% 44% 17%	380
	21st to end	Night	14% 4 23% 36% 22% 1	532
July	1st to 10th	Night	11% 2 14% 44% 25% 3	555
	11th to 20th	Night	10% 3 20% 38% 26% 3	552
	21st to end	Night	10% 3 18% 42% 24% 2	624
August	1st to 10th	Night	10% 4 15% 42% 27% 2	567
	11th to 20th	Night	11% 3 16% 37% 29% 4	564
	21st to end	Night	16% 4 16% 40% 22% 2	627
September	1st to 10th	Night	14% 4 21% 37% 20% 4	576
	11th to 20th	Night	16% 5% 19% 35% 22% 4	760
	21st to end	Night	22% 7% 19% 31% 18% 3	760
October	1st to 10th	Night	22% 8% 24% 29% 16% 1	760
	11th to 20th	Night	30% 10% 26% 27% 6% 1	760
	21st to end	Night	35% 12% 25% 22% 6% 1	836
November	1st to 10th	Night	26% 12% 30% 26% 6%	780
	11th to 20th	Night	26% 17% 33% 20% 4	800
	21st to end	Night	30% 13% 34% 20% 3	840
December	1st to 10th	Night	23% 17% 36% 19% 4	950
	11th to 20th	Night	23% 15% 38% 19% 4 1	950
	21st to end	Night	26% 13% 36% 22% 2	1045

Page generated at 2024-11-27 17:30:51. Version ac07

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