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 2024-03-01.

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	15% 12% 5% 8% 7% 3 4 4 5% 6% 30%	78125
	Night	15% 14% 6% 10% 8% 4 4 4 4 5% 26%	81308
Transparency	Day	55% 6% 10% 18% 9% 1	77831
	Night	61% 6% 10% 15% 7% 1	81137
Seeing	Day	20% 14% 30% 23% 11% 3	14617
	Night	21% 12% 29% 27% 10% 1	24483

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	12% 23% 15% 22% 9% 4 3 2 2 2 6%	2527
	11th to 20th	Day	12% 19% 8% 17% 17% 7% 6% 3 3 2 6%	2530
	21st to end	Day	17% 22% 11% 14% 8% 5% 4 4 4 3 8%	2783
February	1st to 10th	Day	9% 19% 8% 13% 17% 5% 5% 3 3 5% 13%	1638
	11th to 20th	Day	12% 16% 9% 13% 11% 5% 5% 5% 3 4 18%	1817
	21st to end	Day	12% 18% 8% 12% 9% 3 5% 4 5% 5% 20%	1570
March	1st to 10th	Day	13% 12% 6% 10% 9% 4 4 5% 5% 5% 28%	1798
	11th to 20th	Day	11% 12% 5% 10% 7% 3 4 4 4 6% 34%	1939
	21st to end	Day	18% 13% 4 6% 7% 3 4 4 5% 8% 29%	2236
April	1st to 10th	Day	20% 14% 5% 8% 5% 3 4 4 5% 6% 27%	2160
	11th to 20th	Day	21% 14% 4 4 4 2 4 3 5% 6% 33%	2244
	21st to end	Day	17% 11% 4 7% 5% 3 5% 5% 5% 8% 31%	2340
May	1st to 10th	Day	17% 9% 3 6% 4 3 4 5% 5% 6% 37%	2340
	11th to 20th	Day	15% 9% 3 6% 5% 3 5% 4 4 6% 40%	2368
	21st to end	Day	12% 6% 2 5% 5% 3 5% 5% 6% 8% 43%	2725
June	1st to 10th	Day	14% 5% 2 5% 5% 3 5% 5% 5% 8% 42%	2686
	11th to 20th	Day	14% 6% 2 5% 5% 3 5% 5% 6% 9% 40%	2700
	21st to end	Day	15% 6% 2 5% 4 3 5% 5% 6% 8% 41%	2678
July	1st to 10th	Day	10% 3 1 3 4 3 5% 5% 6% 10% 50%	2520
	11th to 20th	Day	13% 5% 2 4 5% 3 4 4 6% 9% 44%	2520
	21st to end	Day	11% 5% 2 4 5% 3 4 6% 6% 9% 45%	2743
August	1st to 10th	Day	10% 5% 3 6% 6% 3 6% 6% 7% 8% 41%	2399
	11th to 20th	Day	12% 6% 2 5% 5% 4 5% 5% 6% 8% 44%	2303
	21st to end	Day	16% 6% 2 5% 4 3 4 4 5% 7% 44%	2499
September	1st to 10th	Day	16% 6% 2 5% 4 3 4 4 5% 8% 42%	2124
	11th to 20th	Day	15% 5% 3 5% 5% 2 5% 4 5% 7% 44%	1980
	21st to end	Day	18% 8% 2 6% 5% 3 4 5% 5% 9% 35%	1980
October	1st to 10th	Day	20% 10% 4 8% 5% 2 4 4 5% 6% 33%	1976
	11th to 20th	Day	27% 16% 4 8% 7% 3 4 3 5% 5% 18%	1706
	21st to end	Day	24% 18% 5% 9% 6% 3 5% 4 5% 6% 15%	1782
November	1st to 10th	Day	17% 20% 6% 8% 5% 3 4 4 5% 5% 25%	1672
	11th to 20th	Day	12% 25% 9% 11% 7% 4 4 3 4 5% 14%	1710
	21st to end	Day	16% 25% 11% 10% 6% 3 3 3 4 4 13%	1536
December	1st to 10th	Day	15% 22% 14% 17% 7% 4 3 3 3 3 10%	1330
	11th to 20th	Day	14% 20% 12% 16% 9% 4 5% 4 3 3 10%	1671
	21st to end	Day	20% 21% 10% 17% 8% 3 3 2 3 4 8%	2595
January	1st to 10th	Night	13% 22% 11% 20% 9% 3 3 2 2 3 11%	4428
	11th to 20th	Night	12% 16% 8% 17% 19% 7% 5% 3 3 2 8%	4440
	21st to end	Night	15% 22% 10% 16% 12% 4 4 3 3 3 8%	4884
February	1st to 10th	Night	10% 17% 8% 15% 14% 6% 6% 3 4 3 14%	2542
	11th to 20th	Night	11% 13% 8% 16% 12% 5% 5% 4 3 5% 19%	2247
	21st to end	Night	14% 18% 6% 11% 8% 4 5% 4 4 5% 22%	1884
March	1st to 10th	Night	12% 11% 5% 9% 7% 4 4 4 4 5% 35%	2156
	11th to 20th	Night	12% 13% 4 9% 7% 3 4 4 4 4 34%	2020
	21st to end	Night	16% 10% 4 7% 5% 3 5% 5% 5% 6% 34%	2136
April	1st to 10th	Night	20% 12% 5% 8% 6% 3 5% 4 4 6% 27%	1800
	11th to 20th	Night	20% 11% 4 5% 5% 2 5% 4 3 7% 33%	1664
	21st to end	Night	17% 10% 4 7% 5% 3 5% 4 5% 6% 35%	1620
May	1st to 10th	Night	15% 9% 3 6% 7% 4 6% 5% 6% 6% 33%	1620
	11th to 20th	Night	15% 10% 4 7% 6% 3 5% 5% 5% 6% 34%	1523
	21st to end	Night	13% 6% 1 5% 5% 3 4 4 5% 9% 44%	1551
June	1st to 10th	Night	14% 5% 3 5% 5% 4 5% 4 5% 8% 42%	1270
	11th to 20th	Night	11% 5% 3 5% 6% 3 4 5% 5% 10% 43%	1260
	21st to end	Night	12% 7% 2 4 5% 3 4 5% 5% 7% 46%	1276
July	1st to 10th	Night	10% 4 1 4 4 2 4 5% 6% 8% 52%	1440
	11th to 20th	Night	9% 5% 3 5% 5% 3 5% 4 6% 6% 49%	1440
	21st to end	Night	8% 5% 3 5% 5% 4 5% 5% 5% 8% 49%	1575
August	1st to 10th	Night	8% 5% 3 4 6% 3 4 4 6% 9% 48%	1538
	11th to 20th	Night	11% 4 2 4 5% 3 4 4 6% 8% 49%	1598
	21st to end	Night	15% 6% 2 5% 5% 3 3 5% 5% 6% 44%	1854
September	1st to 10th	Night	13% 5% 3 5% 4 3 3 4 5% 7% 49%	1818
	11th to 20th	Night	17% 6% 2 4 4 2 4 4 4 7% 46%	1980
	21st to end	Night	20% 8% 3 4 5% 3 4 4 6% 7% 36%	1980
October	1st to 10th	Night	19% 9% 3 6% 5% 3 4 3 5% 6% 37%	1984
	11th to 20th	Night	24% 15% 4 7% 6% 3 4 4 5% 6% 23%	2250
	21st to end	Night	27% 16% 4 6% 6% 3 5% 3 3 5% 21%	2574
November	1st to 10th	Night	17% 19% 6% 7% 5% 3 4 3 4 6% 26%	2406
	11th to 20th	Night	15% 22% 8% 11% 8% 3 4 4 4 5% 17%	2470
	21st to end	Night	17% 22% 11% 10% 8% 3 4 4 4 4 14%	2637
December	1st to 10th	Night	13% 24% 14% 17% 8% 4 4 2 3 3 10%	2850
	11th to 20th	Night	14% 20% 10% 18% 10% 3 4 3 3 4 11%	3526
	21st to end	Night	21% 22% 9% 14% 7% 3 4 4 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	58% 7% 11% 16% 8% 1	1800
	11th to 20th	Day	53% 5% 12% 21% 6% 3	1939
	21st to end	Day	55% 6% 11% 18% 9% 1	2236
April	1st to 10th	Day	59% 5% 10% 17% 9%	2160
	11th to 20th	Day	52% 4 11% 18% 14% 1	2244
	21st to end	Day	52% 7% 10% 14% 14% 3	2340
May	1st to 10th	Day	46% 7% 9% 23% 12% 3	2340
	11th to 20th	Day	45% 6% 8% 22% 15% 3	2372
	21st to end	Day	38% 7% 12% 26% 15% 1	2725
June	1st to 10th	Day	39% 8% 10% 27% 15% 2	2686
	11th to 20th	Day	39% 8% 12% 23% 17% 1	2700
	21st to end	Day	41% 7% 13% 25% 14% 1	2678
July	1st to 10th	Day	30% 7% 13% 30% 18% 2	2451
	11th to 20th	Day	35% 8% 11% 30% 16% 1	2445
	21st to end	Day	35% 8% 13% 27% 17% 1	2591
August	1st to 10th	Day	37% 11% 14% 26% 11% 1	2384
	11th to 20th	Day	37% 9% 13% 27% 13% 1	2303
	21st to end	Day	40% 7% 13% 26% 13% 2	2499
September	1st to 10th	Day	41% 7% 11% 23% 16% 1	2124
	11th to 20th	Day	39% 8% 14% 29% 10% 1	1980
	21st to end	Day	46% 7% 15% 24% 9%	1980
October	1st to 10th	Day	53% 6% 10% 24% 8% 1	1976
	11th to 20th	Day	70% 5% 8% 13% 3	1706
	21st to end	Day	71% 6% 11% 9% 3	1782
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	52% 5% 13% 21% 10% 1	2167
	11th to 20th	Night	52% 6% 9% 19% 11% 2	2021
	21st to end	Night	51% 5% 10% 20% 13% 1	2136
April	1st to 10th	Night	58% 5% 9% 17% 11% 1	1800
	11th to 20th	Night	52% 5% 8% 20% 13% 3	1664
	21st to end	Night	50% 6% 9% 19% 14% 3	1620
May	1st to 10th	Night	50% 6% 10% 19% 12% 4	1620
	11th to 20th	Night	50% 6% 8% 20% 14% 2	1524
	21st to end	Night	39% 6% 12% 25% 15% 3	1552
June	1st to 10th	Night	40% 6% 11% 25% 16% 1	1270
	11th to 20th	Night	38% 7% 13% 25% 14% 3	1260
	21st to end	Night	39% 7% 12% 25% 15% 2	1276
July	1st to 10th	Night	28% 7% 15% 29% 17% 3	1400
	11th to 20th	Night	34% 7% 13% 26% 19% 1	1392
	21st to end	Night	34% 8% 16% 25% 16% 1	1487
August	1st to 10th	Night	32% 8% 17% 30% 11% 1	1529
	11th to 20th	Night	33% 7% 16% 29% 14% 1	1598
	21st to end	Night	40% 7% 15% 22% 15% 1	1854
September	1st to 10th	Night	36% 7% 14% 23% 18% 2	1818
	11th to 20th	Night	39% 7% 14% 29% 10% 1	1980
	21st to end	Night	47% 7% 15% 23% 8%	1980
October	1st to 10th	Night	48% 6% 11% 23% 11% 1	1984
	11th to 20th	Night	62% 6% 11% 15% 5%	2250
	21st to end	Night	67% 5% 9% 13% 5%	2574
November	1st to 10th	Night	60% 7% 10% 17% 6% 1	2406
	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% 38% 10% 1	225
March	1st to 10th	Day	21% 26% 34% 16% 3	240
	11th to 20th	Day	21% 15% 36% 21% 6% 1	379
	21st to end	Day	28% 14% 26% 23% 8% 1	462
April	1st to 10th	Day	27% 15% 32% 18% 7% 1	420
	11th to 20th	Day	33% 14% 29% 14% 9% 2	412
	21st to end	Day	20% 16% 31% 21% 10% 2	420
May	1st to 10th	Day	24% 16% 30% 18% 9% 3	423
	11th to 20th	Day	18% 15% 33% 24% 7% 4	514
	21st to end	Day	15% 11% 30% 28% 12% 3	679
June	1st to 10th	Day	14% 13% 32% 27% 11% 2	630
	11th to 20th	Day	17% 10% 28% 31% 11% 3	630
	21st to end	Day	17% 7% 32% 30% 12% 2	630
July	1st to 10th	Day	11% 7% 29% 31% 17% 5%	621
	11th to 20th	Day	12% 9% 26% 32% 14% 5%	618
	21st to end	Day	11% 6% 30% 33% 15% 4	684
August	1st to 10th	Day	10% 6% 26% 28% 22% 8%	518
	11th to 20th	Day	14% 4 19% 34% 18% 11%	439
	21st to end	Day	19% 8% 23% 28% 18% 5%	495
September	1st to 10th	Day	18% 10% 26% 23% 17% 6%	450
	11th to 20th	Day	15% 9% 22% 30% 18% 6%	450
	21st to end	Day	19% 13% 20% 30% 14% 5%	450
October	1st to 10th	Day	24% 15% 27% 20% 12% 2	450
	11th to 20th	Day	33% 16% 31% 17% 3 1	356
	21st to end	Day	33% 19% 30% 13% 4 1	297
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	723
	11th to 20th	Night	20% 16% 34% 24% 6%	720
	21st to end	Night	21% 11% 28% 31% 7% 1	750
April	1st to 10th	Night	26% 12% 31% 25% 5% 1	540
	11th to 20th	Night	26% 9% 30% 26% 8%	533
	21st to end	Night	21% 8% 32% 30% 8% 1	540
May	1st to 10th	Night	19% 8% 30% 34% 9% 1	540
	11th to 20th	Night	20% 7% 30% 32% 10% 1	531
	21st to end	Night	16% 5% 26% 38% 14% 1	584
June	1st to 10th	Night	17% 6% 27% 38% 11% 1	370
	11th to 20th	Night	11% 6% 24% 44% 15%	360
	21st to end	Night	14% 6% 27% 36% 16% 1	376
July	1st to 10th	Night	13% 2 18% 46% 19% 2	525
	11th to 20th	Night	10% 4 23% 35% 25% 3	522
	21st to end	Night	9% 3 25% 39% 22% 2	591
August	1st to 10th	Night	9% 3 20% 42% 25% 1	537
	11th to 20th	Night	12% 6% 16% 34% 30% 3	534
	21st to end	Night	18% 5% 21% 36% 19% 2	594
September	1st to 10th	Night	15% 4 23% 36% 20% 3	558
	11th to 20th	Night	19% 6% 21% 32% 19% 3	720
	21st to end	Night	23% 8% 21% 31% 14% 3	720
October	1st to 10th	Night	23% 10% 25% 29% 12% 1	720
	11th to 20th	Night	32% 13% 29% 21% 5% 1	720
	21st to end	Night	37% 10% 28% 19% 5% 1	792
November	1st to 10th	Night	27% 14% 32% 21% 6%	740
	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 2024-02-27 06:30:13. Version ac07

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