Raven Hill Discovery Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Raven Hill Discovery Center clear sky chart from 2005-11-06 to 2024-11-01.

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% 12% 4 9% 5% 4 4 3 5% 6% 32%	101160
	Night	15% 14% 5% 11% 6% 4 4 3 4 5% 28%	97884
Transparency	Day	52% 6% 10% 20% 11% 1	100916
	Night	58% 6% 10% 16% 8% 1	97747
Seeing	Day	20% 14% 30% 23% 11% 3	15648
	Night	21% 12% 29% 27% 10% 1	25269

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% 24% 14% 24% 7% 5% 2 2 2 2 6%	2527
	11th to 20th	Day	12% 20% 7% 21% 13% 9% 4 2 3 2 5%	2530
	21st to end	Day	17% 24% 10% 16% 6% 6% 4 3 4 3 8%	2783
February	1st to 10th	Day	8% 20% 7% 15% 15% 7% 4 2 3 5% 13%	1638
	11th to 20th	Day	12% 18% 7% 15% 10% 6% 4 3 3 4 18%	1817
	21st to end	Day	11% 19% 7% 14% 7% 4 4 3 5% 5% 20%	1570
March	1st to 10th	Day	12% 14% 4 9% 6% 4 4 4 5% 5% 33%	3118
	11th to 20th	Day	8% 15% 8% 15% 5% 4 4 3 4 6% 27%	3411
	21st to end	Day	16% 13% 7% 15% 6% 4 4 3 4 5% 21%	3927
April	1st to 10th	Day	19% 16% 4 9% 5% 4 4 3 5% 5% 27%	2280
	11th to 20th	Day	21% 15% 4 5% 4 3 3 3 5% 6% 33%	2371
	21st to end	Day	16% 11% 4 8% 4 4 5% 4 5% 7% 31%	2470
May	1st to 10th	Day	15% 8% 2 7% 4 4 4 4 5% 6% 41%	4108
	11th to 20th	Day	11% 8% 2 6% 4 4 4 4 4 6% 47%	4204
	21st to end	Day	13% 6% 2 5% 4 4 5% 3 6% 8% 43%	4837
June	1st to 10th	Day	14% 6% 2 6% 4 5% 4 4 6% 8% 41%	2836
	11th to 20th	Day	14% 6% 2 5% 4 5% 4 5% 6% 9% 40%	2850
	21st to end	Day	16% 6% 2 6% 4 5% 4 4 6% 8% 40%	2826
July	1st to 10th	Day	19% 6% 2 5% 3 4 4 3 6% 8% 39%	4440
	11th to 20th	Day	11% 4 2 4 3 4 4 3 6% 9% 49%	4440
	21st to end	Day	10% 5% 2 5% 4 4 4 4 6% 9% 47%	4814
August	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 4 7% 8% 40%	4231
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 6% 46%	4044
	21st to end	Day	15% 7% 2 7% 4 4 4 3 5% 5% 44%	4387
September	1st to 10th	Day	16% 6% 2 5% 4 4 4 4 5% 8% 42%	2241
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 7% 45%	2090
	21st to end	Day	17% 8% 2 7% 4 3 4 4 5% 9% 37%	2090
October	1st to 10th	Day	19% 10% 3 9% 4 3 3 3 5% 6% 35%	2085
	11th to 20th	Day	26% 16% 3 10% 6% 4 4 3 4 5% 19%	1800
	21st to end	Day	23% 18% 5% 10% 5% 4 5% 3 5% 6% 15%	1881
November	1st to 10th	Day	17% 21% 5% 8% 4 4 3 3 5% 5% 25%	1672
	11th to 20th	Day	12% 27% 8% 13% 5% 4 5% 2 5% 5% 14%	1710
	21st to end	Day	16% 27% 10% 12% 5% 4 2 2 4 4 13%	1536
December	1st to 10th	Day	15% 24% 13% 17% 7% 4 3 2 3 3 9%	1330
	11th to 20th	Day	14% 22% 10% 18% 8% 5% 5% 3 3 3 10%	1671
	21st to end	Day	20% 22% 9% 18% 7% 4 3 1 3 4 8%	2595
January	1st to 10th	Night	13% 23% 10% 22% 7% 4 3 2 2 3 10%	4428
	11th to 20th	Night	12% 17% 7% 20% 16% 9% 4 2 3 2 8%	4440
	21st to end	Night	15% 23% 10% 18% 9% 6% 4 2 3 3 8%	4884
February	1st to 10th	Night	9% 19% 7% 17% 12% 7% 4 3 4 3 14%	2542
	11th to 20th	Night	11% 15% 7% 17% 11% 6% 5% 2 3 5% 19%	2247
	21st to end	Night	13% 20% 4 13% 6% 5% 4 3 4 5% 22%	1884
March	1st to 10th	Night	15% 10% 4 8% 4 3 3 2 4 6% 40%	3722
	11th to 20th	Night	8% 18% 5% 9% 5% 4 4 3 4 5% 34%	3548
	21st to end	Night	15% 13% 7% 11% 5% 4 4 4 5% 6% 27%	3734
April	1st to 10th	Night	20% 13% 4 9% 5% 4 4 3 4 6% 27%	1900
	11th to 20th	Night	21% 11% 4 6% 4 3 4 4 3 6% 33%	1757
	21st to end	Night	17% 11% 3 8% 5% 4 4 3 6% 6% 35%	1710
May	1st to 10th	Night	16% 9% 2 6% 5% 5% 4 3 5% 6% 40%	2833
	11th to 20th	Night	12% 8% 3 7% 4 4 5% 4 6% 6% 41%	2691
	21st to end	Night	18% 7% 2 6% 4 4 3 3 5% 7% 42%	2750
June	1st to 10th	Night	15% 5% 3 6% 4 4 5% 3 5% 8% 42%	1340
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 4 6% 9% 43%	1330
	21st to end	Night	13% 8% 1 4 5% 4 4 4 4 7% 44%	1347
July	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 5% 7% 43%	2530
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 3 5% 5% 51%	2530
	21st to end	Night	9% 6% 2 6% 4 4 4 4 6% 7% 48%	2750
August	1st to 10th	Night	13% 6% 3 6% 4 5% 4 4 6% 7% 43%	2701
	11th to 20th	Night	16% 5% 2 4 3 3 3 3 5% 7% 49%	2785
	21st to end	Night	12% 6% 2 6% 4 4 4 4 5% 6% 47%	3252
September	1st to 10th	Night	13% 6% 2 6% 3 3 4 3 5% 7% 49%	1919
	11th to 20th	Night	15% 6% 2 5% 3 3 4 3 4 8% 47%	2090
	21st to end	Night	19% 8% 3 4 5% 4 4 4 6% 7% 38%	2090
October	1st to 10th	Night	19% 9% 3 7% 4 4 3 2 5% 6% 38%	2095
	11th to 20th	Night	22% 16% 4 8% 4 4 4 3 5% 5% 24%	2375
	21st to end	Night	26% 16% 3 8% 5% 4 5% 2 3 5% 22%	2717
November	1st to 10th	Night	17% 20% 5% 8% 5% 4 4 3 4 6% 25%	2413
	11th to 20th	Night	14% 24% 7% 13% 6% 4 4 3 4 5% 17%	2470
	21st to end	Night	17% 23% 10% 12% 6% 4 4 3 4 4 14%	2637
December	1st to 10th	Night	13% 27% 10% 18% 7% 4 3 1 3 3 10%	2850
	11th to 20th	Night	13% 22% 8% 21% 8% 5% 3 3 3 4 11%	3526
	21st to end	Night	20% 22% 9% 15% 6% 4 4 3 3 4 9%	5067

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	88% 3 4 4 1	2528
	11th to 20th	Day	87% 4 4 3 1	2530
	21st to end	Day	81% 7% 6% 4 2	2783
February	1st to 10th	Day	76% 6% 7% 9% 2	1638
	11th to 20th	Day	69% 6% 9% 9% 6%	1827
	21st to end	Day	66% 6% 10% 15% 4 1	1570
March	1st to 10th	Day	52% 6% 12% 19% 10% 1	3120
	11th to 20th	Day	56% 5% 13% 19% 5% 2	3411
	21st to end	Day	64% 6% 9% 13% 8% 1	3927
April	1st to 10th	Day	58% 5% 9% 17% 9% 1	2280
	11th to 20th	Day	52% 4 10% 19% 13% 1	2371
	21st to end	Day	51% 7% 10% 15% 15% 3	2470
May	1st to 10th	Day	41% 7% 10% 21% 19% 2	4120
	11th to 20th	Day	37% 7% 9% 28% 18% 2	4208
	21st to end	Day	37% 7% 12% 22% 20% 2	4837
June	1st to 10th	Day	40% 7% 10% 27% 15% 2	2836
	11th to 20th	Day	39% 8% 12% 23% 17% 1	2850
	21st to end	Day	42% 7% 12% 25% 13% 1	2826
July	1st to 10th	Day	43% 6% 14% 24% 12% 1	4371
	11th to 20th	Day	29% 7% 13% 36% 14% 1	4365
	21st to end	Day	32% 8% 12% 30% 18%	4662
August	1st to 10th	Day	38% 9% 12% 27% 13% 1	4216
	11th to 20th	Day	38% 6% 11% 31% 13% 1	4083
	21st to end	Day	41% 7% 12% 29% 10% 1	4386
September	1st to 10th	Day	40% 7% 11% 24% 16% 1	2241
	11th to 20th	Day	38% 8% 13% 28% 12% 1	2090
	21st to end	Day	44% 7% 14% 24% 10%	2090
October	1st to 10th	Day	51% 5% 9% 25% 9% 1	2085
	11th to 20th	Day	69% 5% 9% 13% 4	1800
	21st to end	Day	70% 7% 11% 9% 3	1881
November	1st to 10th	Day	61% 6% 9% 18% 6%	1672
	11th to 20th	Day	73% 6% 10% 8% 3	1710
	21st to end	Day	77% 5% 10% 7% 1	1536
December	1st to 10th	Day	83% 4 6% 6% 1	1330
	11th to 20th	Day	81% 6% 7% 5% 1	1671
	21st to end	Day	84% 4 7% 3 2	2595
January	1st to 10th	Night	80% 5% 6% 8% 1	4428
	11th to 20th	Night	83% 4 7% 4 1	4440
	21st to end	Night	82% 6% 6% 4 1	4884
February	1st to 10th	Night	77% 5% 6% 8% 3 1	2542
	11th to 20th	Night	70% 5% 8% 14% 3	2248
	21st to end	Night	65% 5% 10% 13% 6%	1884
March	1st to 10th	Night	47% 5% 16% 22% 10%	3733
	11th to 20th	Night	52% 5% 10% 23% 8% 1	3549
	21st to end	Night	57% 7% 10% 18% 8% 1	3734
April	1st to 10th	Night	58% 5% 9% 17% 10% 1	1900
	11th to 20th	Night	53% 4 8% 20% 12% 2	1757
	21st to end	Night	50% 6% 9% 18% 15% 3	1710
May	1st to 10th	Night	44% 6% 11% 20% 15% 3	2840
	11th to 20th	Night	42% 5% 9% 25% 17% 1	2692
	21st to end	Night	42% 6% 13% 20% 15% 5%	2751
June	1st to 10th	Night	40% 6% 11% 25% 16% 1	1340
	11th to 20th	Night	38% 7% 13% 25% 15% 3	1330
	21st to end	Night	40% 7% 11% 25% 15% 2	1347
July	1st to 10th	Night	40% 6% 14% 23% 13% 3	2490
	11th to 20th	Night	32% 8% 13% 29% 17% 1	2482
	21st to end	Night	33% 8% 15% 24% 19% 1	2662
August	1st to 10th	Night	39% 8% 15% 25% 13% 1	2692
	11th to 20th	Night	36% 5% 15% 30% 14% 1	2812
	21st to end	Night	35% 7% 14% 27% 16% 1	3252
September	1st to 10th	Night	35% 7% 14% 25% 18% 2	1919
	11th to 20th	Night	38% 7% 13% 29% 12% 1	2090
	21st to end	Night	46% 7% 15% 23% 9%	2090
October	1st to 10th	Night	47% 6% 11% 24% 12% 1	2095
	11th to 20th	Night	61% 6% 11% 15% 6%	2375
	21st to end	Night	66% 5% 10% 14% 5%	2717
November	1st to 10th	Night	60% 7% 10% 16% 6% 1	2413
	11th to 20th	Night	71% 5% 10% 9% 5%	2470
	21st to end	Night	75% 7% 11% 7% 1	2637
December	1st to 10th	Night	82% 4 7% 6% 1	2850
	11th to 20th	Night	79% 6% 9% 4 2	3525
	21st to end	Night	80% 8% 8% 3 1	5067

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	20% 17% 41% 15% 6%	270
	11th to 20th	Day	26% 18% 36% 16% 3 1	270
	21st to end	Day	23% 15% 37% 19% 6%	297
February	1st to 10th	Day	17% 32% 35% 10% 5% 1	270
	11th to 20th	Day	21% 27% 35% 14% 3	270
	21st to end	Day	22% 30% 37% 10% 1	225
March	1st to 10th	Day	20% 26% 36% 16% 3	270
	11th to 20th	Day	21% 17% 35% 20% 6%	417
	21st to end	Day	27% 15% 27% 22% 8% 1	506
April	1st to 10th	Day	26% 17% 33% 17% 7% 1	460
	11th to 20th	Day	33% 15% 29% 13% 8% 2	452
	21st to end	Day	20% 17% 31% 21% 9% 2	460
May	1st to 10th	Day	24% 16% 31% 18% 9% 3	463
	11th to 20th	Day	16% 15% 33% 25% 8% 4	558
	21st to end	Day	15% 12% 30% 28% 12% 2	734
June	1st to 10th	Day	15% 14% 32% 27% 10% 2	680
	11th to 20th	Day	17% 11% 29% 30% 11% 3	680
	21st to end	Day	20% 8% 31% 28% 11% 2	680
July	1st to 10th	Day	12% 7% 30% 30% 16% 5%	671
	11th to 20th	Day	12% 10% 27% 32% 15% 5%	668
	21st to end	Day	11% 6% 29% 34% 16% 4	739
August	1st to 10th	Day	9% 7% 26% 29% 22% 8%	562
	11th to 20th	Day	14% 4 20% 33% 18% 10%	479
	21st to end	Day	19% 8% 23% 27% 18% 5%	539
September	1st to 10th	Day	18% 10% 25% 23% 17% 6%	490
	11th to 20th	Day	14% 8% 21% 30% 19% 7%	490
	21st to end	Day	18% 12% 20% 30% 16% 4	490
October	1st to 10th	Day	22% 17% 27% 20% 12% 2	490
	11th to 20th	Day	31% 17% 31% 18% 3 1	390
	21st to end	Day	32% 20% 30% 12% 3 1	330
November	1st to 10th	Day	29% 14% 33% 16% 7%	270
	11th to 20th	Day	21% 25% 37% 14% 3	270
	21st to end	Day	27% 29% 28% 14% 3	203
December	1st to 10th	Day	31% 15% 38% 11% 3 2	180
	11th to 20th	Day	23% 28% 34% 12% 1 1	180
	21st to end	Day	30% 30% 31% 7% 2 1	245
January	1st to 10th	Night	21% 19% 32% 21% 6% 1	950
	11th to 20th	Night	23% 19% 30% 21% 5%	950
	21st to end	Night	20% 15% 34% 25% 6%	1045
February	1st to 10th	Night	18% 19% 35% 23% 4 1	832
	11th to 20th	Night	20% 20% 31% 24% 5%	743
	21st to end	Night	25% 15% 33% 23% 3	628
March	1st to 10th	Night	18% 13% 34% 25% 9% 1	760
	11th to 20th	Night	19% 16% 34% 25% 6%	760
	21st to end	Night	21% 12% 28% 31% 7% 1	791
April	1st to 10th	Night	26% 12% 31% 25% 5% 1	570
	11th to 20th	Night	26% 10% 30% 25% 8%	563
	21st to end	Night	21% 9% 32% 30% 8% 1	570
May	1st to 10th	Night	18% 8% 30% 35% 8% 1	570
	11th to 20th	Night	20% 7% 30% 33% 10% 1	561
	21st to end	Night	16% 6% 25% 37% 14% 1	617
June	1st to 10th	Night	17% 6% 28% 37% 10% 1	390
	11th to 20th	Night	11% 7% 24% 44% 14%	380
	21st to end	Night	15% 6% 28% 36% 15% 1	397
July	1st to 10th	Night	14% 3 17% 46% 18% 2	555
	11th to 20th	Night	10% 5% 22% 36% 24% 3	552
	21st to end	Night	9% 3 25% 38% 23% 1	624
August	1st to 10th	Night	10% 3 20% 41% 24% 1	567
	11th to 20th	Night	13% 6% 15% 34% 30% 3	564
	21st to end	Night	18% 5% 21% 37% 19% 1	627
September	1st to 10th	Night	15% 4 23% 36% 20% 3	589
	11th to 20th	Night	18% 6% 20% 34% 21% 3	760
	21st to end	Night	22% 8% 20% 33% 14% 3	760
October	1st to 10th	Night	23% 11% 25% 29% 12% 1	760
	11th to 20th	Night	31% 13% 28% 22% 6% 1	760
	21st to end	Night	36% 11% 28% 19% 5%	836
November	1st to 10th	Night	27% 14% 32% 21% 6%	743
	11th to 20th	Night	27% 19% 31% 20% 3	760
	21st to end	Night	30% 17% 32% 18% 3	790
December	1st to 10th	Night	25% 21% 33% 18% 3	950
	11th to 20th	Night	23% 21% 34% 17% 3 1	950
	21st to end	Night	28% 16% 36% 17% 3	1045

Page generated at 2024-10-29 11:20:44. Version ac07

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