Addison Oaks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Addison Oaks Observatory clear sky chart from 2005-11-06 to 2024-04-03.

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% 10% 4 7% 6% 4 5% 5% 6% 7% 32%	78646
	Night	15% 10% 4 7% 6% 3 5% 5% 5% 7% 34%	81465
Transparency	Day	49% 7% 12% 19% 11% 1	78355
	Night	50% 6% 12% 20% 11% 1	81277
Seeing	Day	17% 11% 29% 23% 14% 6%	14488
	Night	18% 10% 29% 30% 12% 1	24343

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	14% 17% 7% 11% 7% 4 4 4 5% 6% 21%	2527
	11th to 20th	Day	15% 17% 7% 11% 11% 5% 6% 5% 5% 5% 13%	2530
	21st to end	Day	26% 18% 6% 9% 7% 3 4 3 3 4 15%	3074
February	1st to 10th	Day	13% 12% 5% 11% 11% 5% 6% 4 5% 6% 21%	1710
	11th to 20th	Day	13% 12% 6% 10% 9% 4 5% 5% 5% 7% 24%	1775
	21st to end	Day	13% 14% 5% 11% 8% 4 5% 5% 5% 5% 26%	1570
March	1st to 10th	Day	15% 11% 5% 8% 7% 4 5% 5% 5% 6% 29%	1950
	11th to 20th	Day	12% 12% 5% 8% 7% 3 4 4 5% 6% 32%	2090
	21st to end	Day	18% 12% 4 8% 7% 4 5% 4 5% 5% 28%	2299
April	1st to 10th	Day	16% 11% 5% 7% 6% 3 5% 5% 5% 7% 30%	2103
	11th to 20th	Day	16% 10% 3 7% 5% 3 5% 5% 6% 7% 33%	2294
	21st to end	Day	17% 8% 3 8% 6% 3 5% 4 5% 7% 34%	2340
May	1st to 10th	Day	16% 8% 4 7% 6% 3 6% 5% 5% 7% 34%	2340
	11th to 20th	Day	18% 8% 3 6% 5% 3 5% 4 5% 7% 36%	2301
	21st to end	Day	12% 6% 3 6% 5% 3 5% 5% 6% 9% 40%	2531
June	1st to 10th	Day	10% 6% 2 6% 6% 4 5% 6% 6% 9% 41%	2651
	11th to 20th	Day	10% 5% 3 5% 6% 3 5% 5% 5% 9% 42%	2700
	21st to end	Day	10% 5% 3 5% 5% 4 6% 7% 7% 9% 38%	2636
July	1st to 10th	Day	7% 4 2 5% 6% 3 5% 6% 7% 10% 45%	2520
	11th to 20th	Day	8% 5% 2 5% 5% 4 5% 6% 7% 11% 42%	2520
	21st to end	Day	6% 5% 2 6% 5% 4 6% 7% 7% 10% 40%	2587
August	1st to 10th	Day	8% 5% 2 5% 6% 4 7% 6% 8% 10% 39%	2327
	11th to 20th	Day	9% 5% 2 6% 6% 4 6% 6% 7% 9% 40%	2303
	21st to end	Day	10% 6% 2 6% 6% 4 5% 5% 6% 7% 42%	2572
September	1st to 10th	Day	11% 6% 3 6% 6% 3 7% 6% 6% 9% 38%	2028
	11th to 20th	Day	11% 4 2 4 5% 3 5% 6% 6% 10% 44%	1980
	21st to end	Day	14% 6% 3 5% 6% 4 5% 5% 7% 9% 36%	1980
October	1st to 10th	Day	12% 8% 3 6% 5% 4 5% 5% 5% 6% 41%	1918
	11th to 20th	Day	17% 9% 4 7% 5% 4 6% 4 5% 7% 32%	1800
	21st to end	Day	19% 12% 4 6% 6% 4 4 4 5% 6% 29%	1841
November	1st to 10th	Day	12% 8% 4 7% 6% 3 5% 5% 6% 8% 37%	1672
	11th to 20th	Day	13% 11% 4 7% 8% 3 6% 5% 5% 6% 31%	1710
	21st to end	Day	17% 12% 5% 7% 6% 3 5% 4 5% 7% 29%	1558
December	1st to 10th	Day	13% 13% 7% 11% 9% 4 5% 5% 4 6% 23%	1520
	11th to 20th	Day	16% 14% 5% 9% 7% 3 5% 5% 7% 7% 24%	1756
	21st to end	Day	24% 20% 7% 9% 7% 3 4 4 5% 5% 12%	2633
January	1st to 10th	Night	16% 13% 7% 9% 7% 3 5% 4 4 6% 26%	4428
	11th to 20th	Night	13% 16% 7% 12% 9% 5% 6% 5% 5% 5% 17%	4440
	21st to end	Night	22% 14% 9% 10% 7% 3 4 4 3 5% 19%	4568
February	1st to 10th	Night	13% 15% 6% 9% 8% 4 6% 5% 5% 5% 24%	2470
	11th to 20th	Night	12% 11% 5% 10% 7% 4 6% 5% 6% 6% 28%	2288
	21st to end	Night	18% 11% 4 7% 7% 3 5% 4 5% 6% 29%	1884
March	1st to 10th	Night	15% 11% 4 8% 6% 3 5% 4 4 6% 34%	2228
	11th to 20th	Night	12% 8% 3 6% 6% 4 5% 6% 5% 7% 38%	2090
	21st to end	Night	18% 8% 3 8% 5% 3 5% 5% 4 5% 34%	2299
April	1st to 10th	Night	16% 9% 3 7% 5% 4 5% 4 6% 6% 35%	1918
	11th to 20th	Night	18% 7% 2 6% 6% 3 3 4 5% 7% 38%	1615
	21st to end	Night	17% 7% 3 5% 4 4 4 4 6% 7% 39%	1620
May	1st to 10th	Night	15% 8% 3 6% 6% 4 5% 5% 5% 9% 33%	1620
	11th to 20th	Night	17% 5% 3 5% 4 3 4 5% 6% 7% 41%	1592
	21st to end	Night	9% 5% 2 6% 5% 3 4 5% 6% 9% 46%	1744
June	1st to 10th	Night	9% 6% 3 5% 5% 3 4 4 6% 9% 47%	1301
	11th to 20th	Night	8% 6% 3 5% 4 3 5% 5% 6% 10% 45%	1260
	21st to end	Night	8% 6% 3 5% 5% 3 4 5% 5% 9% 48%	1317
July	1st to 10th	Night	7% 4 2 4 4 4 4 4 5% 8% 54%	1440
	11th to 20th	Night	9% 4 2 3 4 3 4 5% 6% 10% 51%	1440
	21st to end	Night	5% 4 1 4 5% 3 5% 5% 8% 10% 50%	1726
August	1st to 10th	Night	7% 3 2 4 4 2 5% 5% 7% 11% 49%	1611
	11th to 20th	Night	6% 4 2 5% 5% 3 4 6% 7% 8% 49%	1598
	21st to end	Night	9% 4 2 4 5% 3 4 5% 5% 7% 52%	1782
September	1st to 10th	Night	9% 6% 3 6% 4 4 4 5% 6% 7% 46%	1911
	11th to 20th	Night	9% 4 2 5% 4 2 4 4 6% 7% 52%	1980
	21st to end	Night	14% 4 2 7% 5% 2 4 5% 5% 8% 44%	1980
October	1st to 10th	Night	15% 7% 2 5% 4 3 4 4 5% 7% 44%	2040
	11th to 20th	Night	18% 9% 3 5% 5% 4 5% 5% 5% 6% 35%	2160
	21st to end	Night	20% 9% 3 7% 6% 4 5% 5% 5% 5% 31%	2510
November	1st to 10th	Night	13% 7% 3 5% 5% 3 4 5% 5% 7% 43%	2406
	11th to 20th	Night	15% 9% 3 8% 6% 4 5% 7% 7% 6% 31%	2470
	21st to end	Night	18% 11% 5% 7% 6% 3 6% 5% 5% 7% 28%	2619
December	1st to 10th	Night	17% 13% 5% 10% 8% 4 5% 5% 6% 6% 22%	2660
	11th to 20th	Night	13% 12% 6% 11% 7% 4 5% 5% 5% 6% 25%	3436
	21st to end	Night	25% 23% 7% 8% 5% 3 3 4 4 4 13%	5014

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	63% 7% 11% 13% 6% 1	2528
	11th to 20th	Day	70% 8% 12% 7% 3	2530
	21st to end	Day	74% 5% 10% 6% 3 1	3074
February	1st to 10th	Day	63% 7% 8% 14% 7%	1710
	11th to 20th	Day	60% 4 10% 16% 8% 1	1784
	21st to end	Day	58% 6% 12% 15% 7% 2	1570
March	1st to 10th	Day	55% 7% 13% 17% 8% 1	1950
	11th to 20th	Day	51% 6% 11% 19% 11% 3	2090
	21st to end	Day	59% 5% 10% 17% 8% 1	2299
April	1st to 10th	Day	52% 6% 12% 19% 11% 1	2103
	11th to 20th	Day	49% 6% 12% 19% 13% 2	2294
	21st to end	Day	50% 6% 14% 16% 13% 2	2340
May	1st to 10th	Day	49% 7% 12% 20% 10% 2	2340
	11th to 20th	Day	48% 6% 11% 20% 13% 2	2305
	21st to end	Day	40% 7% 14% 22% 14% 2	2531
June	1st to 10th	Day	38% 7% 13% 25% 14% 2	2651
	11th to 20th	Day	38% 6% 14% 24% 16% 3	2700
	21st to end	Day	39% 9% 12% 22% 16% 2	2636
July	1st to 10th	Day	33% 9% 11% 25% 18% 3	2451
	11th to 20th	Day	34% 8% 14% 25% 17% 2	2445
	21st to end	Day	36% 10% 14% 21% 17% 3	2443
August	1st to 10th	Day	36% 10% 14% 26% 12% 1	2314
	11th to 20th	Day	38% 10% 15% 24% 12% 2	2303
	21st to end	Day	39% 7% 11% 25% 16% 1	2572
September	1st to 10th	Day	40% 9% 14% 23% 12% 2	2028
	11th to 20th	Day	34% 7% 12% 33% 13%	1980
	21st to end	Day	43% 7% 14% 24% 12% 1	1980
October	1st to 10th	Day	42% 6% 12% 25% 13% 2	1918
	11th to 20th	Day	51% 7% 13% 19% 10% 1	1800
	21st to end	Day	54% 7% 13% 17% 8%	1841
November	1st to 10th	Day	44% 7% 13% 24% 11% 1	1672
	11th to 20th	Day	52% 6% 13% 18% 9% 1	1710
	21st to end	Day	56% 6% 13% 18% 7% 1	1558
December	1st to 10th	Day	63% 5% 12% 16% 4	1520
	11th to 20th	Day	58% 7% 14% 15% 6%	1752
	21st to end	Day	75% 5% 11% 6% 3	2633
January	1st to 10th	Night	59% 6% 13% 15% 5% 1	4428
	11th to 20th	Night	67% 7% 12% 10% 4	4440
	21st to end	Night	68% 5% 10% 13% 3	4568
February	1st to 10th	Night	62% 6% 10% 14% 7% 1	2470
	11th to 20th	Night	55% 6% 12% 17% 9% 1	2290
	21st to end	Night	54% 5% 13% 18% 9% 1	1884
March	1st to 10th	Night	51% 6% 11% 22% 10% 1	2228
	11th to 20th	Night	44% 6% 11% 21% 15% 2	2090
	21st to end	Night	51% 6% 9% 21% 11% 1	2299
April	1st to 10th	Night	48% 5% 11% 21% 13% 2	1918
	11th to 20th	Night	44% 6% 12% 17% 18% 2	1615
	21st to end	Night	43% 6% 12% 20% 16% 3	1620
May	1st to 10th	Night	47% 7% 11% 21% 12% 2	1620
	11th to 20th	Night	42% 6% 10% 20% 19% 3	1593
	21st to end	Night	33% 8% 15% 24% 17% 3	1745
June	1st to 10th	Night	35% 6% 10% 29% 17% 3	1301
	11th to 20th	Night	34% 8% 14% 24% 18% 2	1260
	21st to end	Night	33% 7% 12% 26% 21% 1	1317
July	1st to 10th	Night	28% 7% 11% 28% 23% 3	1400
	11th to 20th	Night	29% 6% 13% 32% 17% 3	1392
	21st to end	Night	26% 9% 19% 22% 20% 3	1630
August	1st to 10th	Night	28% 8% 16% 32% 14% 2	1600
	11th to 20th	Night	30% 9% 14% 32% 12% 3	1598
	21st to end	Night	30% 8% 13% 30% 18% 1	1782
September	1st to 10th	Night	35% 7% 14% 26% 15% 2	1911
	11th to 20th	Night	30% 6% 13% 31% 19% 1	1980
	21st to end	Night	38% 6% 13% 31% 12% 1	1980
October	1st to 10th	Night	39% 6% 11% 24% 19% 1	2040
	11th to 20th	Night	48% 7% 14% 19% 12% 1	2160
	21st to end	Night	53% 6% 12% 20% 8% 1	2510
November	1st to 10th	Night	39% 7% 13% 25% 15% 1	2406
	11th to 20th	Night	50% 7% 14% 20% 8% 1	2470
	21st to end	Night	56% 5% 14% 18% 6%	2619
December	1st to 10th	Night	62% 6% 12% 15% 5%	2660
	11th to 20th	Night	57% 7% 14% 14% 7% 1	3439
	21st to end	Night	75% 5% 11% 7% 3	5014

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	19% 22% 36% 16% 6%	270
	11th to 20th	Day	23% 17% 43% 13% 4 1	270
	21st to end	Day	29% 11% 37% 18% 4 1	297
February	1st to 10th	Day	23% 20% 39% 14% 3 1	270
	11th to 20th	Day	23% 19% 39% 17% 2	270
	21st to end	Day	22% 22% 43% 12% 2	225
March	1st to 10th	Day	26% 21% 33% 17% 3 1	320
	11th to 20th	Day	22% 14% 33% 24% 6% 1	460
	21st to end	Day	27% 13% 34% 21% 5% 1	506
April	1st to 10th	Day	16% 16% 36% 21% 9% 1	428
	11th to 20th	Day	25% 16% 29% 15% 9% 6%	412
	21st to end	Day	23% 13% 28% 22% 10% 3	420
May	1st to 10th	Day	23% 10% 29% 24% 11% 3	423
	11th to 20th	Day	20% 10% 28% 21% 13% 7%	447
	21st to end	Day	14% 6% 22% 28% 19% 9%	485
June	1st to 10th	Day	12% 9% 32% 29% 15% 4	617
	11th to 20th	Day	11% 6% 32% 29% 18% 3	630
	21st to end	Day	12% 7% 29% 30% 18% 5%	630
July	1st to 10th	Day	8% 5% 19% 31% 23% 14%	621
	11th to 20th	Day	9% 6% 25% 32% 19% 8%	618
	21st to end	Day	7% 5% 24% 29% 24% 10%	528
August	1st to 10th	Day	9% 4 20% 25% 27% 14%	446
	11th to 20th	Day	12% 3 19% 27% 24% 15%	439
	21st to end	Day	12% 5% 21% 29% 20% 13%	495
September	1st to 10th	Day	13% 4 25% 24% 22% 12%	450
	11th to 20th	Day	10% 4 20% 23% 27% 16%	450
	21st to end	Day	15% 11% 24% 23% 20% 8%	450
October	1st to 10th	Day	18% 10% 26% 21% 16% 10%	450
	11th to 20th	Day	21% 15% 31% 25% 8% 1	450
	21st to end	Day	27% 13% 36% 19% 4 1	356
November	1st to 10th	Day	15% 21% 34% 21% 9% 1	270
	11th to 20th	Day	20% 20% 34% 17% 7% 1	270
	21st to end	Day	23% 17% 37% 19% 4	198
December	1st to 10th	Day	22% 18% 38% 14% 7% 1	180
	11th to 20th	Day	27% 21% 37% 12% 4 1	180
	21st to end	Day	26% 21% 35% 15% 3	257
January	1st to 10th	Night	21% 14% 37% 23% 5% 1	950
	11th to 20th	Night	25% 14% 33% 24% 4 1	950
	21st to end	Night	19% 13% 34% 28% 6%	859
February	1st to 10th	Night	21% 14% 38% 24% 2	760
	11th to 20th	Night	19% 15% 35% 26% 4	743
	21st to end	Night	24% 16% 38% 20% 2	628
March	1st to 10th	Night	20% 12% 36% 26% 6%	760
	11th to 20th	Night	16% 15% 38% 25% 6% 1	760
	21st to end	Night	22% 12% 31% 28% 7%	836
April	1st to 10th	Night	20% 15% 33% 28% 4 1	644
	11th to 20th	Night	22% 9% 32% 27% 8% 2	533
	21st to end	Night	20% 8% 31% 31% 9%	540
May	1st to 10th	Night	18% 8% 29% 35% 9% 1	540
	11th to 20th	Night	21% 5% 26% 32% 15% 1	531
	21st to end	Night	11% 2 23% 41% 20% 2	584
June	1st to 10th	Night	12% 4 26% 44% 15%	392
	11th to 20th	Night	11% 4 24% 50% 11% 1	360
	21st to end	Night	10% 3 22% 47% 18%	417
July	1st to 10th	Night	7% 3 18% 40% 29% 3	525
	11th to 20th	Night	10% 2 18% 41% 25% 4	522
	21st to end	Night	6% 3 19% 47% 23% 2	591
August	1st to 10th	Night	8% 2 17% 38% 31% 3	537
	11th to 20th	Night	9% 1 18% 38% 30% 4	534
	21st to end	Night	11% 3 18% 33% 32% 3	594
September	1st to 10th	Night	12% 5% 18% 34% 25% 5%	652
	11th to 20th	Night	11% 5% 17% 35% 27% 6%	720
	21st to end	Night	16% 6% 22% 30% 21% 5%	720
October	1st to 10th	Night	18% 7% 25% 30% 18% 3	720
	11th to 20th	Night	22% 13% 28% 28% 8% 1	720
	21st to end	Night	24% 12% 32% 26% 4	792
November	1st to 10th	Night	19% 11% 30% 27% 14% 1	740
	11th to 20th	Night	20% 15% 33% 24% 7% 1	760
	21st to end	Night	24% 14% 34% 22% 6%	760
December	1st to 10th	Night	23% 14% 36% 21% 6% 1	760
	11th to 20th	Night	22% 14% 37% 23% 3	864
	21st to end	Night	29% 13% 33% 22% 3	1045

Page generated at 2024-03-31 06:08:54. Version ac07

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