Doran Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Doran Planetarium 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	16% 10% 3 8% 5% 4 4 4 5% 7% 33%	101676
	Night	15% 12% 4 9% 5% 4 4 3 5% 6% 32%	97507
Transparency	Day	50% 6% 12% 22% 10% 1	105188
	Night	51% 6% 12% 20% 10% 1	102084
Seeing	Day	21% 13% 31% 23% 10% 3	15280
	Night	22% 10% 30% 28% 9% 1	24395

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	16% 19% 7% 11% 5% 5% 5% 2 4 5% 23%	2208
	11th to 20th	Day	10% 13% 7% 17% 9% 5% 6% 5% 6% 5% 18%	2370
	21st to end	Day	16% 19% 9% 13% 6% 6% 4 3 4 4 16%	3005
February	1st to 10th	Day	10% 18% 4 11% 7% 5% 5% 4 5% 7% 24%	1710
	11th to 20th	Day	11% 16% 5% 11% 7% 5% 4 3 4 5% 29%	1663
	21st to end	Day	12% 17% 5% 12% 5% 4 4 5% 4 6% 25%	1489
March	1st to 10th	Day	18% 14% 4 8% 4 4 4 3 5% 7% 29%	3309
	11th to 20th	Day	10% 14% 5% 12% 6% 4 5% 3 4 7% 28%	3480
	21st to end	Day	12% 13% 5% 10% 5% 5% 3 3 4 5% 34%	3815
April	1st to 10th	Day	19% 12% 4 7% 4 4 5% 4 6% 6% 30%	2232
	11th to 20th	Day	20% 10% 3 6% 5% 3 5% 4 5% 6% 34%	2442
	21st to end	Day	22% 10% 3 7% 4 4 3 3 4 5% 36%	2470
May	1st to 10th	Day	18% 8% 2 6% 5% 4 4 4 5% 7% 36%	4126
	11th to 20th	Day	13% 8% 3 7% 5% 4 5% 4 5% 7% 40%	4398
	21st to end	Day	18% 6% 2 6% 4 3 4 3 5% 7% 43%	4960
June	1st to 10th	Day	16% 8% 3 7% 5% 5% 4 5% 6% 7% 33%	2850
	11th to 20th	Day	12% 7% 2 7% 6% 4 5% 4 6% 8% 40%	2850
	21st to end	Day	18% 8% 3 7% 5% 5% 4 4 7% 7% 33%	2850
July	1st to 10th	Day	16% 7% 3 8% 5% 5% 5% 4 6% 8% 33%	4760
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 4 6% 8% 43%	4760
	21st to end	Day	11% 6% 2 6% 4 3 5% 3 6% 7% 46%	4721
August	1st to 10th	Day	11% 7% 3 7% 4 5% 6% 4 7% 9% 38%	4104
	11th to 20th	Day	19% 6% 2 5% 4 4 4 4 6% 8% 40%	4044
	21st to end	Day	12% 6% 2 7% 4 5% 5% 4 5% 7% 42%	4532
September	1st to 10th	Day	14% 8% 3 8% 5% 4 4 3 5% 7% 40%	2280
	11th to 20th	Day	13% 5% 1 7% 4 5% 3 3 6% 8% 44%	2096
	21st to end	Day	22% 8% 2 7% 4 4 4 4 5% 6% 36%	2090
October	1st to 10th	Day	18% 10% 2 7% 5% 4 5% 4 4 6% 36%	1910
	11th to 20th	Day	24% 11% 3 8% 6% 5% 4 4 5% 6% 24%	1900
	21st to end	Day	26% 14% 4 8% 5% 5% 4 3 5% 6% 22%	1980
November	1st to 10th	Day	18% 13% 3 9% 4 5% 4 3 6% 7% 28%	1633
	11th to 20th	Day	16% 15% 5% 10% 7% 5% 5% 3 4 6% 24%	1520
	21st to end	Day	23% 19% 5% 12% 5% 5% 4 3 3 3 19%	1520
December	1st to 10th	Day	13% 21% 5% 10% 7% 4 5% 4 5% 6% 19%	1497
	11th to 20th	Day	16% 20% 5% 12% 4 5% 4 3 5% 4 23%	1671
	21st to end	Day	24% 21% 6% 14% 5% 4 4 2 3 4 14%	2431
January	1st to 10th	Night	14% 16% 6% 13% 7% 5% 4 3 5% 6% 21%	4748
	11th to 20th	Night	12% 14% 6% 10% 8% 6% 6% 4 6% 7% 21%	4596
	21st to end	Night	14% 19% 8% 12% 6% 5% 4 3 5% 4 18%	4652
February	1st to 10th	Night	11% 16% 5% 11% 8% 5% 5% 4 5% 6% 24%	2470
	11th to 20th	Night	12% 14% 5% 11% 7% 5% 5% 3 5% 5% 28%	2403
	21st to end	Night	14% 16% 5% 9% 5% 6% 4 3 6% 5% 27%	1964
March	1st to 10th	Night	16% 13% 3 8% 4 4 4 3 5% 6% 34%	3517
	11th to 20th	Night	11% 13% 6% 11% 5% 4 4 3 5% 5% 33%	3479
	21st to end	Night	13% 8% 5% 9% 6% 5% 4 3 6% 6% 35%	3817
April	1st to 10th	Night	18% 12% 4 8% 5% 4 4 3 4 6% 31%	1962
	11th to 20th	Night	20% 9% 3 6% 5% 4 4 3 5% 6% 36%	1687
	21st to end	Night	19% 10% 3 7% 5% 5% 4 5% 4 5% 33%	1710
May	1st to 10th	Night	16% 8% 3 7% 5% 5% 4 4 5% 6% 36%	2814
	11th to 20th	Night	12% 8% 2 7% 5% 4 5% 3 5% 9% 39%	2495
	21st to end	Night	12% 8% 3 7% 5% 3 3 4 6% 8% 42%	2614
June	1st to 10th	Night	13% 6% 3 7% 6% 5% 5% 5% 6% 8% 36%	1330
	11th to 20th	Night	13% 6% 2 5% 5% 4 5% 4 6% 8% 42%	1330
	21st to end	Night	13% 5% 3 7% 3 5% 3 4 6% 8% 43%	1330
July	1st to 10th	Night	15% 6% 3 6% 4 3 4 3 6% 8% 42%	2210
	11th to 20th	Night	13% 6% 2 5% 4 4 4 4 5% 8% 45%	2210
	21st to end	Night	9% 6% 2 5% 4 3 4 4 6% 7% 51%	2806
August	1st to 10th	Night	11% 6% 2 6% 4 4 5% 4 6% 7% 43%	2825
	11th to 20th	Night	15% 5% 2 6% 4 4 4 3 5% 7% 45%	2785
	21st to end	Night	12% 5% 2 6% 4 3 5% 4 5% 7% 48%	3124
September	1st to 10th	Night	13% 7% 2 5% 4 4 4 3 6% 6% 47%	1880
	11th to 20th	Night	12% 6% 2 5% 3 5% 3 3 5% 7% 49%	2080
	21st to end	Night	18% 6% 3 6% 4 4 5% 2 4 7% 40%	2090
October	1st to 10th	Night	20% 8% 3 6% 4 4 4 4 5% 5% 38%	2269
	11th to 20th	Night	23% 11% 3 7% 5% 4 4 3 5% 6% 30%	2280
	21st to end	Night	25% 13% 4 8% 4 5% 4 3 4 6% 24%	2617
November	1st to 10th	Night	18% 12% 3 7% 5% 4 4 4 5% 7% 31%	2649
	11th to 20th	Night	18% 14% 3 9% 7% 6% 4 3 6% 5% 26%	2660
	21st to end	Night	21% 17% 4 8% 6% 5% 5% 4 5% 5% 22%	2660
December	1st to 10th	Night	17% 19% 5% 10% 6% 4 3 3 4 6% 21%	2682
	11th to 20th	Night	18% 16% 4 10% 6% 4 4 3 4 5% 25%	3526
	21st to end	Night	22% 22% 5% 14% 5% 3 4 2 3 4 15%	5236

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	66% 5% 13% 13% 3	2209
	11th to 20th	Day	67% 4 12% 11% 4 1	2370
	21st to end	Day	72% 5% 8% 10% 5%	3005
February	1st to 10th	Day	59% 5% 12% 17% 6% 1	1710
	11th to 20th	Day	57% 5% 10% 15% 11% 1	1672
	21st to end	Day	59% 5% 8% 17% 9% 1	1489
March	1st to 10th	Day	55% 4 14% 16% 10% 1	3312
	11th to 20th	Day	55% 5% 11% 20% 7% 1	3480
	21st to end	Day	52% 4 11% 19% 11% 2	3815
April	1st to 10th	Day	53% 5% 13% 19% 9% 1	2232
	11th to 20th	Day	51% 4 8% 24% 12% 1	2442
	21st to end	Day	52% 5% 8% 19% 14% 3	2470
May	1st to 10th	Day	45% 6% 9% 25% 12% 2	4138
	11th to 20th	Day	41% 7% 12% 27% 11% 1	4402
	21st to end	Day	42% 5% 13% 18% 19% 3	4960
June	1st to 10th	Day	47% 7% 12% 22% 12% 1	2850
	11th to 20th	Day	42% 6% 11% 23% 17% 1	2850
	21st to end	Day	49% 7% 11% 21% 11% 2	2850
July	1st to 10th	Day	47% 8% 13% 21% 10% 1	4686
	11th to 20th	Day	36% 7% 14% 33% 9% 1	4679
	21st to end	Day	35% 6% 12% 33% 14%	4571
August	1st to 10th	Day	40% 8% 13% 29% 9% 1	4091
	11th to 20th	Day	41% 7% 15% 27% 9%	4083
	21st to end	Day	39% 7% 13% 32% 9% 1	4531
September	1st to 10th	Day	44% 6% 14% 25% 10% 1	2280
	11th to 20th	Day	39% 6% 16% 28% 11% 1	2096
	21st to end	Day	49% 6% 15% 22% 8%	2090
October	1st to 10th	Day	41% 6% 10% 30% 13%	3170
	11th to 20th	Day	48% 7% 12% 23% 10%	3140
	21st to end	Day	63% 5% 13% 12% 6%	3243
November	1st to 10th	Day	55% 6% 13% 18% 7%	1633
	11th to 20th	Day	61% 5% 12% 16% 6%	1520
	21st to end	Day	71% 5% 9% 10% 5%	1520
December	1st to 10th	Day	66% 6% 9% 14% 5%	1497
	11th to 20th	Day	63% 7% 7% 18% 4 1	1671
	21st to end	Day	76% 4 6% 12% 3	2431
January	1st to 10th	Night	62% 7% 13% 12% 6%	4748
	11th to 20th	Night	60% 7% 14% 13% 5%	4596
	21st to end	Night	69% 5% 8% 13% 5%	4652
February	1st to 10th	Night	60% 5% 10% 18% 6% 1	2470
	11th to 20th	Night	58% 6% 11% 18% 7% 1	2405
	21st to end	Night	59% 5% 11% 15% 10% 1	1964
March	1st to 10th	Night	50% 6% 11% 19% 13% 1	3527
	11th to 20th	Night	51% 6% 13% 18% 10% 2	3480
	21st to end	Night	48% 7% 10% 19% 13% 3	3817
April	1st to 10th	Night	54% 4 9% 19% 13% 1	1962
	11th to 20th	Night	48% 5% 6% 23% 16% 2	1687
	21st to end	Night	52% 5% 10% 16% 16% 2	1710
May	1st to 10th	Night	46% 7% 9% 23% 12% 2	2821
	11th to 20th	Night	40% 7% 10% 27% 14% 1	2496
	21st to end	Night	39% 7% 11% 24% 14% 5%	2615
June	1st to 10th	Night	42% 8% 12% 23% 13% 2	1330
	11th to 20th	Night	38% 6% 13% 21% 19% 2	1330
	21st to end	Night	39% 8% 15% 23% 14% 2	1330
July	1st to 10th	Night	39% 6% 14% 26% 13% 1	2175
	11th to 20th	Night	35% 6% 17% 32% 9% 1	2168
	21st to end	Night	32% 6% 13% 30% 19%	2717
August	1st to 10th	Night	39% 6% 15% 26% 13% 1	2814
	11th to 20th	Night	37% 8% 18% 27% 9% 1	2812
	21st to end	Night	35% 7% 15% 30% 12% 1	3124
September	1st to 10th	Night	37% 7% 14% 30% 10% 2	1880
	11th to 20th	Night	35% 7% 15% 33% 11%	2080
	21st to end	Night	44% 6% 15% 26% 9%	2090
October	1st to 10th	Night	41% 5% 11% 30% 12%	3789
	11th to 20th	Night	45% 6% 13% 30% 7%	3779
	21st to end	Night	55% 7% 18% 15% 5% 1	4304
November	1st to 10th	Night	50% 7% 14% 21% 8%	2649
	11th to 20th	Night	59% 6% 12% 16% 7% 1	2660
	21st to end	Night	63% 7% 12% 13% 6%	2660
December	1st to 10th	Night	65% 6% 10% 16% 4	2682
	11th to 20th	Night	61% 6% 10% 15% 8% 1	3525
	21st to end	Night	74% 4 8% 10% 4	5236

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	26% 19% 27% 21% 6% 1	180
	11th to 20th	Day	17% 10% 36% 28% 7% 2	225
	21st to end	Day	26% 7% 31% 23% 10% 3	297
February	1st to 10th	Day	23% 20% 33% 18% 5%	270
	11th to 20th	Day	21% 15% 38% 21% 4	270
	21st to end	Day	23% 25% 37% 14% 1	225
March	1st to 10th	Day	21% 15% 37% 21% 6%	384
	11th to 20th	Day	19% 15% 32% 25% 8% 1	460
	21st to end	Day	23% 13% 34% 23% 6% 1	506
April	1st to 10th	Day	24% 11% 30% 24% 10% 1	460
	11th to 20th	Day	31% 16% 23% 16% 10% 4	452
	21st to end	Day	32% 14% 24% 19% 9% 3	460
May	1st to 10th	Day	21% 10% 31% 23% 12% 3	463
	11th to 20th	Day	21% 14% 30% 21% 11% 4	487
	21st to end	Day	21% 12% 31% 23% 10% 3	600
June	1st to 10th	Day	18% 16% 36% 24% 6% 1	680
	11th to 20th	Day	18% 16% 34% 23% 8% 2	680
	21st to end	Day	21% 12% 33% 24% 9% 2	680
July	1st to 10th	Day	12% 11% 33% 28% 13% 3	671
	11th to 20th	Day	13% 11% 32% 27% 12% 4	668
	21st to end	Day	14% 7% 28% 31% 14% 6%	624
August	1st to 10th	Day	16% 8% 25% 26% 19% 6%	486
	11th to 20th	Day	14% 7% 23% 25% 20% 11%	479
	21st to end	Day	17% 6% 29% 25% 15% 8%	539
September	1st to 10th	Day	18% 11% 26% 27% 13% 6%	490
	11th to 20th	Day	14% 6% 27% 31% 16% 7%	490
	21st to end	Day	26% 11% 23% 23% 13% 4	490
October	1st to 10th	Day	23% 15% 25% 23% 11% 3	490
	11th to 20th	Day	26% 17% 34% 18% 5% 1	490
	21st to end	Day	31% 16% 30% 18% 3 1	429
November	1st to 10th	Day	29% 13% 37% 16% 5%	237
	11th to 20th	Day	20% 19% 34% 19% 6% 1	180
	21st to end	Day	28% 18% 30% 16% 8% 1	180
December	1st to 10th	Day	24% 13% 31% 23% 9%	180
	11th to 20th	Day	34% 13% 34% 13% 6%	180
	21st to end	Day	32% 12% 37% 14% 6%	198
January	1st to 10th	Night	23% 12% 32% 25% 7% 1	950
	11th to 20th	Night	25% 13% 29% 25% 8%	950
	21st to end	Night	21% 8% 29% 30% 10% 1	904
February	1st to 10th	Night	19% 14% 37% 25% 4	760
	11th to 20th	Night	20% 15% 35% 24% 6% 1	743
	21st to end	Night	21% 16% 35% 24% 4	628
March	1st to 10th	Night	20% 14% 36% 24% 6%	760
	11th to 20th	Night	22% 13% 33% 24% 8% 1	760
	21st to end	Night	20% 10% 36% 26% 7% 1	836
April	1st to 10th	Night	24% 12% 31% 28% 5%	746
	11th to 20th	Night	23% 12% 29% 27% 8% 1	563
	21st to end	Night	24% 10% 29% 28% 9%	570
May	1st to 10th	Night	17% 8% 32% 34% 9% 1	564
	11th to 20th	Night	16% 9% 31% 36% 8% 1	374
	21st to end	Night	15% 7% 38% 31% 9%	411
June	1st to 10th	Night	16% 6% 38% 32% 8%	380
	11th to 20th	Night	16% 9% 30% 36% 9%	380
	21st to end	Night	15% 7% 29% 34% 14% 1	380
July	1st to 10th	Night	8% 5% 34% 43% 9% 1	370
	11th to 20th	Night	10% 4 32% 40% 14%	368
	21st to end	Night	11% 4 28% 39% 16% 1	548
August	1st to 10th	Night	11% 5% 26% 37% 19% 1	567
	11th to 20th	Night	14% 4 24% 34% 21% 2	564
	21st to end	Night	17% 4 26% 34% 18% 1	627
September	1st to 10th	Night	17% 5% 28% 30% 19% 1	740
	11th to 20th	Night	15% 8% 25% 30% 19% 3	760
	21st to end	Night	21% 6% 26% 29% 16% 3	760
October	1st to 10th	Night	24% 9% 27% 28% 10% 1	760
	11th to 20th	Night	31% 10% 28% 23% 8% 1	760
	21st to end	Night	31% 13% 28% 23% 4 1	836
November	1st to 10th	Night	26% 11% 30% 25% 6% 1	779
	11th to 20th	Night	26% 13% 29% 25% 7%	760
	21st to end	Night	30% 12% 28% 24% 7%	760
December	1st to 10th	Night	29% 13% 31% 21% 6%	782
	11th to 20th	Night	27% 15% 31% 21% 7% 1	950
	21st to end	Night	30% 13% 28% 22% 7%	1045

Page generated at 2024-11-07 06:55:45. Version ac07

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