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 2024-01-13.

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% 4 7% 6% 3 5% 5% 5% 7% 32%	74664
	Night	16% 11% 4 8% 6% 3 5% 4 5% 6% 32%	75078
Transparency	Day	51% 6% 12% 20% 10% 1	74363
	Night	53% 6% 11% 19% 10% 1	74915
Seeing	Day	21% 12% 30% 23% 10% 3	14090
	Night	22% 10% 30% 28% 9% 1	23398

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	15% 18% 6% 10% 6% 4 6% 4 4 5% 21%	1328
	11th to 20th	Day	15% 15% 8% 10% 7% 3 4 5% 5% 5% 23%	1364
	21st to end	Day	15% 15% 6% 10% 7% 5% 4 4 5% 5% 23%	1715
February	1st to 10th	Day	10% 17% 5% 9% 9% 4 6% 5% 5% 7% 23%	1620
	11th to 20th	Day	12% 15% 5% 10% 7% 4 4 4 4 6% 29%	1573
	21st to end	Day	13% 16% 5% 11% 7% 3 5% 6% 4 6% 24%	1404
March	1st to 10th	Day	15% 11% 4 7% 6% 3 5% 4 5% 7% 34%	1905
	11th to 20th	Day	12% 11% 4 9% 7% 3 4 4 4 6% 36%	1980
	21st to end	Day	16% 10% 4 7% 6% 3 4 4 4 5% 38%	2178
April	1st to 10th	Day	19% 11% 5% 6% 6% 3 4 5% 6% 6% 29%	2114
	11th to 20th	Day	20% 9% 3 5% 6% 2 5% 5% 4 7% 35%	2312
	21st to end	Day	22% 10% 3 6% 5% 3 3 4 4 6% 35%	2340
May	1st to 10th	Day	17% 8% 3 6% 6% 3 4 4 6% 7% 34%	2344
	11th to 20th	Day	17% 8% 3 6% 5% 3 5% 4 5% 7% 36%	2478
	21st to end	Day	16% 5% 2 5% 5% 3 4 5% 6% 8% 40%	2792
June	1st to 10th	Day	16% 8% 4 7% 5% 3 5% 6% 6% 7% 34%	2700
	11th to 20th	Day	12% 6% 3 6% 7% 3 5% 5% 5% 8% 39%	2700
	21st to end	Day	17% 7% 3 6% 6% 3 5% 5% 6% 7% 33%	2700
July	1st to 10th	Day	11% 5% 3 5% 5% 4 5% 5% 6% 9% 42%	2700
	11th to 20th	Day	12% 6% 3 6% 6% 5% 6% 6% 5% 8% 38%	2700
	21st to end	Day	12% 6% 3 6% 6% 3 6% 6% 6% 8% 37%	2704
August	1st to 10th	Day	14% 7% 3 6% 5% 4 6% 6% 6% 9% 34%	2327
	11th to 20th	Day	15% 5% 2 5% 6% 3 5% 5% 5% 8% 40%	2303
	21st to end	Day	14% 6% 3 6% 6% 4 5% 6% 5% 9% 36%	2574
September	1st to 10th	Day	14% 8% 3 6% 6% 3 4 4 5% 7% 39%	2160
	11th to 20th	Day	14% 5% 2 6% 5% 4 4 4 6% 8% 43%	1986
	21st to end	Day	22% 7% 2 6% 5% 3 4 5% 5% 6% 35%	1980
October	1st to 10th	Day	18% 10% 2 6% 6% 3 5% 4 4 7% 34%	1810
	11th to 20th	Day	25% 10% 4 8% 7% 3 5% 5% 5% 6% 23%	1800
	21st to end	Day	26% 13% 4 7% 6% 4 4 5% 5% 5% 21%	1876
November	1st to 10th	Day	18% 12% 3 7% 6% 4 4 4 6% 7% 28%	1558
	11th to 20th	Day	17% 13% 6% 9% 8% 4 5% 4 4 6% 24%	1520
	21st to end	Day	23% 18% 5% 10% 7% 4 5% 3 3 3 19%	1520
December	1st to 10th	Day	14% 20% 6% 9% 8% 3 5% 5% 6% 5% 19%	1497
	11th to 20th	Day	16% 20% 5% 10% 6% 4 4 3 5% 4 23%	1671
	21st to end	Day	24% 20% 6% 13% 6% 3 4 3 3 4 14%	2431
January	1st to 10th	Night	15% 16% 6% 11% 7% 4 5% 4 4 6% 22%	2838
	11th to 20th	Night	17% 17% 7% 9% 7% 3 5% 4 4 5% 22%	2649
	21st to end	Night	14% 12% 6% 9% 8% 4 5% 5% 6% 6% 24%	2638
February	1st to 10th	Night	11% 15% 5% 10% 9% 4 5% 5% 6% 6% 23%	2340
	11th to 20th	Night	13% 13% 6% 10% 8% 4 5% 4 5% 5% 28%	2273
	21st to end	Night	14% 15% 6% 8% 6% 5% 5% 4 5% 6% 27%	1852
March	1st to 10th	Night	12% 10% 5% 8% 6% 3 4 4 6% 7% 34%	2042
	11th to 20th	Night	15% 10% 5% 8% 6% 3 4 4 5% 5% 34%	1979
	21st to end	Night	15% 8% 4 7% 5% 3 4 4 5% 6% 38%	2178
April	1st to 10th	Night	19% 11% 5% 8% 5% 3 4 4 4 7% 31%	1859
	11th to 20th	Night	19% 8% 4 5% 6% 3 4 4 4 6% 37%	1597
	21st to end	Night	18% 10% 3 6% 6% 4 5% 6% 4 5% 33%	1620
May	1st to 10th	Night	14% 7% 4 6% 6% 3 6% 5% 6% 6% 36%	1615
	11th to 20th	Night	14% 7% 4 6% 6% 3 5% 5% 6% 8% 38%	1415
	21st to end	Night	12% 5% 3 6% 5% 3 4 5% 5% 8% 44%	1478
June	1st to 10th	Night	12% 5% 4 6% 6% 4 6% 6% 6% 8% 37%	1260
	11th to 20th	Night	14% 6% 2 4 5% 3 5% 5% 7% 9% 42%	1260
	21st to end	Night	13% 5% 3 6% 3 3 4 4 7% 8% 43%	1260
July	1st to 10th	Night	8% 4 3 4 5% 2 5% 5% 7% 10% 48%	1260
	11th to 20th	Night	10% 6% 2 4 5% 4 4 5% 5% 9% 47%	1260
	21st to end	Night	9% 6% 3 5% 5% 3 5% 6% 6% 9% 45%	1611
August	1st to 10th	Night	10% 6% 3 6% 5% 3 5% 5% 6% 6% 45%	1611
	11th to 20th	Night	12% 6% 3 5% 4 2 4 4 6% 7% 47%	1598
	21st to end	Night	14% 6% 2 6% 4 3 6% 5% 4 7% 42%	1782
September	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 6% 7% 47%	1781
	11th to 20th	Night	13% 5% 3 5% 4 4 4 4 5% 7% 47%	1970
	21st to end	Night	18% 6% 3 5% 5% 3 5% 3 4 8% 40%	1980
October	1st to 10th	Night	20% 8% 3 5% 5% 3 4 4 5% 5% 37%	2149
	11th to 20th	Night	25% 9% 3 6% 5% 3 4 3 5% 6% 29%	2160
	21st to end	Night	25% 13% 4 7% 5% 3 5% 5% 4 5% 24%	2479
November	1st to 10th	Night	17% 11% 4 7% 5% 3 4 5% 5% 8% 31%	2520
	11th to 20th	Night	18% 12% 4 8% 8% 4 4 4 5% 5% 26%	2660
	21st to end	Night	21% 16% 4 7% 7% 3 5% 5% 5% 5% 22%	2660
December	1st to 10th	Night	18% 18% 6% 9% 7% 3 4 4 5% 6% 21%	2682
	11th to 20th	Night	18% 15% 4 9% 7% 3 4 4 4 6% 25%	3526
	21st to end	Night	22% 21% 5% 13% 6% 3 4 3 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% 4 10% 15% 4	1329
	11th to 20th	Day	63% 4 8% 15% 8% 2	1364
	21st to end	Day	63% 5% 7% 16% 9% 1	1715
February	1st to 10th	Day	60% 5% 12% 16% 6% 1	1620
	11th to 20th	Day	58% 4 10% 15% 11% 1	1582
	21st to end	Day	60% 5% 8% 17% 9%	1404
March	1st to 10th	Day	51% 4 14% 16% 14% 1	1908
	11th to 20th	Day	51% 4 9% 24% 10% 2	1980
	21st to end	Day	49% 3 10% 20% 14% 3	2178
April	1st to 10th	Day	54% 5% 13% 17% 9% 1	2114
	11th to 20th	Day	50% 4 8% 25% 12% 1	2312
	21st to end	Day	52% 4 8% 18% 14% 3	2340
May	1st to 10th	Day	48% 5% 11% 20% 13% 3	2344
	11th to 20th	Day	47% 6% 9% 21% 16% 2	2482
	21st to end	Day	41% 5% 15% 23% 13% 2	2792
June	1st to 10th	Day	47% 7% 11% 22% 12% 1	2700
	11th to 20th	Day	43% 6% 11% 22% 17% 1	2700
	21st to end	Day	48% 7% 11% 22% 10% 2	2700
July	1st to 10th	Day	36% 8% 13% 26% 16% 1	2626
	11th to 20th	Day	41% 7% 11% 27% 11% 1	2619
	21st to end	Day	42% 8% 13% 26% 11%	2554
August	1st to 10th	Day	44% 8% 16% 22% 9% 1	2314
	11th to 20th	Day	40% 8% 17% 26% 8% 1	2303
	21st to end	Day	43% 7% 15% 27% 8% 1	2574
September	1st to 10th	Day	44% 6% 15% 25% 10% 1	2160
	11th to 20th	Day	40% 7% 16% 27% 9%	1986
	21st to end	Day	50% 6% 15% 23% 6%	1980
October	1st to 10th	Day	50% 6% 12% 20% 11%	1810
	11th to 20th	Day	61% 7% 10% 15% 7%	1800
	21st to end	Day	64% 6% 12% 11% 7%	1876
November	1st to 10th	Day	55% 6% 14% 18% 7%	1558
	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	64% 5% 9% 15% 6%	2838
	11th to 20th	Night	64% 5% 9% 12% 8% 1	2649
	21st to end	Night	59% 5% 8% 17% 10% 1	2638
February	1st to 10th	Night	61% 5% 10% 17% 7% 1	2340
	11th to 20th	Night	58% 5% 11% 17% 7% 1	2275
	21st to end	Night	60% 4 11% 15% 9% 1	1852
March	1st to 10th	Night	48% 5% 12% 18% 15% 2	2052
	11th to 20th	Night	51% 5% 11% 17% 14% 2	1980
	21st to end	Night	46% 5% 12% 17% 15% 5%	2178
April	1st to 10th	Night	54% 4 9% 19% 13% 1	1859
	11th to 20th	Night	48% 5% 6% 23% 16% 2	1597
	21st to end	Night	52% 5% 10% 15% 15% 2	1620
May	1st to 10th	Night	47% 6% 11% 21% 12% 3	1615
	11th to 20th	Night	43% 6% 8% 24% 16% 2	1416
	21st to end	Night	38% 6% 13% 23% 17% 3	1479
June	1st to 10th	Night	41% 8% 12% 23% 13% 2	1260
	11th to 20th	Night	38% 6% 13% 21% 19% 2	1260
	21st to end	Night	38% 8% 15% 22% 14% 2	1260
July	1st to 10th	Night	28% 8% 15% 30% 16% 3	1225
	11th to 20th	Night	33% 6% 15% 30% 14% 1	1218
	21st to end	Night	35% 7% 18% 27% 12%	1522
August	1st to 10th	Night	38% 7% 19% 23% 12% 1	1600
	11th to 20th	Night	36% 8% 17% 27% 11% 2	1598
	21st to end	Night	41% 7% 15% 25% 11% 1	1782
September	1st to 10th	Night	37% 7% 14% 30% 11% 3	1781
	11th to 20th	Night	36% 7% 15% 33% 9%	1970
	21st to end	Night	44% 6% 15% 27% 7%	1980
October	1st to 10th	Night	49% 5% 13% 21% 12%	2149
	11th to 20th	Night	56% 6% 11% 22% 6%	2160
	21st to end	Night	62% 5% 10% 15% 7% 1	2479
November	1st to 10th	Night	50% 7% 14% 21% 8%	2520
	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	25% 20% 27% 21% 6% 1	180
	11th to 20th	Day	18% 10% 34% 28% 7% 2	204
	21st to end	Day	26% 8% 29% 23% 11% 3	264
February	1st to 10th	Day	23% 23% 32% 18% 4	240
	11th to 20th	Day	23% 16% 37% 21% 4	240
	21st to end	Day	22% 25% 38% 14% 1	198
March	1st to 10th	Day	21% 15% 37% 21% 6%	348
	11th to 20th	Day	20% 16% 32% 24% 8% 1	420
	21st to end	Day	24% 13% 33% 23% 6% 2	462
April	1st to 10th	Day	24% 10% 30% 25% 10% 1	420
	11th to 20th	Day	29% 16% 23% 18% 11% 4	412
	21st to end	Day	31% 13% 24% 20% 9% 2	420
May	1st to 10th	Day	22% 10% 30% 23% 12% 3	423
	11th to 20th	Day	22% 13% 29% 20% 12% 4	447
	21st to end	Day	21% 13% 31% 22% 11% 3	552
June	1st to 10th	Day	18% 15% 36% 24% 6% 1	630
	11th to 20th	Day	18% 15% 33% 23% 8% 2	630
	21st to end	Day	20% 11% 33% 25% 9% 2	630
July	1st to 10th	Day	11% 11% 33% 29% 13% 3	621
	11th to 20th	Day	14% 12% 32% 26% 12% 5%	618
	21st to end	Day	13% 7% 29% 31% 13% 6%	576
August	1st to 10th	Day	17% 7% 23% 26% 19% 7%	446
	11th to 20th	Day	13% 7% 22% 27% 20% 11%	439
	21st to end	Day	18% 6% 29% 24% 15% 8%	495
September	1st to 10th	Day	16% 11% 27% 26% 13% 6%	450
	11th to 20th	Day	15% 6% 28% 31% 14% 5%	450
	21st to end	Day	26% 12% 24% 23% 12% 4	450
October	1st to 10th	Day	23% 15% 24% 23% 12% 3	450
	11th to 20th	Day	27% 16% 32% 18% 5% 1	450
	21st to end	Day	30% 16% 31% 18% 3 1	391
November	1st to 10th	Day	29% 12% 38% 18% 4	216
	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	26% 12% 28% 25% 8%	915
	21st to end	Night	21% 8% 29% 31% 10% 1	856
February	1st to 10th	Night	19% 14% 38% 24% 3	720
	11th to 20th	Night	20% 14% 35% 24% 6% 1	703
	21st to end	Night	22% 16% 33% 25% 4	592
March	1st to 10th	Night	20% 15% 34% 25% 6%	720
	11th to 20th	Night	22% 13% 33% 23% 8% 1	720
	21st to end	Night	20% 10% 35% 26% 7% 1	792
April	1st to 10th	Night	24% 12% 30% 28% 5%	707
	11th to 20th	Night	22% 12% 28% 28% 8% 1	533
	21st to end	Night	24% 10% 29% 29% 8%	540
May	1st to 10th	Night	17% 7% 31% 34% 9% 1	535
	11th to 20th	Night	16% 9% 31% 35% 8% 1	354
	21st to end	Night	13% 8% 39% 30% 9% 1	389
June	1st to 10th	Night	15% 5% 39% 32% 9%	360
	11th to 20th	Night	17% 9% 29% 36% 9%	360
	21st to end	Night	15% 6% 29% 35% 15% 1	360
July	1st to 10th	Night	8% 5% 35% 43% 9% 1	350
	11th to 20th	Night	11% 4 32% 40% 14%	348
	21st to end	Night	11% 4 29% 40% 15% 1	519
August	1st to 10th	Night	11% 4 26% 38% 19% 1	537
	11th to 20th	Night	14% 4 23% 34% 22% 3	534
	21st to end	Night	17% 4 26% 32% 19% 1	594
September	1st to 10th	Night	16% 5% 28% 30% 20% 1	701
	11th to 20th	Night	16% 8% 27% 30% 17% 3	720
	21st to end	Night	21% 6% 26% 28% 16% 3	720
October	1st to 10th	Night	25% 9% 27% 28% 11% 1	720
	11th to 20th	Night	32% 10% 28% 22% 7% 1	720
	21st to end	Night	32% 12% 27% 24% 4 1	792
November	1st to 10th	Night	25% 12% 31% 25% 7% 1	740
	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 2024-01-10 10:16:13. Version ac07

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