DRAACO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DRAACO 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	15% 9% 4 7% 6% 3 5% 5% 5% 7% 34%	78772
	Night	16% 9% 4 7% 6% 3 5% 5% 5% 7% 34%	81353
Transparency	Day	47% 9% 14% 19% 10% 1	78483
	Night	49% 9% 13% 18% 10% 1	81176
Seeing	Day	18% 10% 27% 28% 14% 4	13601
	Night	19% 9% 29% 28% 13% 2	23102

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	17% 14% 5% 8% 6% 3 3 3 4 6% 30%	2517
	11th to 20th	Day	12% 19% 7% 13% 9% 3 5% 5% 4 4 19%	2646
	21st to end	Day	21% 19% 7% 9% 7% 3 5% 3 3 5% 19%	3124
February	1st to 10th	Day	15% 13% 5% 12% 9% 4 6% 5% 5% 5% 22%	1710
	11th to 20th	Day	13% 13% 7% 11% 8% 3 4 4 4 6% 27%	1663
	21st to end	Day	18% 13% 6% 8% 6% 3 4 4 5% 5% 27%	1470
March	1st to 10th	Day	15% 10% 4 8% 8% 4 4 5% 5% 6% 30%	2068
	11th to 20th	Day	14% 12% 5% 8% 6% 3 4 4 4 6% 34%	2090
	21st to end	Day	20% 10% 4 6% 5% 3 4 3 4 6% 37%	2304
April	1st to 10th	Day	17% 11% 4 8% 6% 3 5% 4 5% 6% 31%	2184
	11th to 20th	Day	20% 7% 3 6% 6% 2 4 4 5% 6% 38%	2154
	21st to end	Day	20% 8% 3 6% 5% 4 5% 5% 4 6% 35%	2340
May	1st to 10th	Day	16% 8% 3 7% 6% 3 6% 5% 5% 6% 34%	2385
	11th to 20th	Day	15% 6% 3 5% 5% 3 5% 5% 5% 7% 42%	2478
	21st to end	Day	12% 5% 2 5% 5% 3 5% 5% 6% 9% 43%	2725
June	1st to 10th	Day	17% 5% 3 5% 5% 4 5% 5% 6% 8% 38%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 5% 6% 10% 41%	2520
	21st to end	Day	14% 5% 2 5% 5% 3 6% 5% 6% 8% 41%	2520
July	1st to 10th	Day	8% 5% 1 4 4 2 6% 5% 7% 10% 46%	2520
	11th to 20th	Day	11% 4 2 4 6% 3 6% 5% 6% 9% 43%	2520
	21st to end	Day	8% 5% 2 5% 5% 5% 6% 7% 7% 10% 40%	2650
August	1st to 10th	Day	8% 6% 3 4 6% 4 6% 6% 7% 8% 42%	2327
	11th to 20th	Day	9% 4 2 5% 6% 3 6% 7% 7% 9% 43%	2303
	21st to end	Day	11% 6% 3 5% 4 3 6% 5% 6% 9% 42%	2444
September	1st to 10th	Day	13% 5% 2 5% 5% 4 5% 5% 5% 7% 44%	2160
	11th to 20th	Day	12% 5% 1 4 4 2 5% 5% 6% 9% 47%	2115
	21st to end	Day	13% 5% 3 6% 5% 4 5% 5% 5% 8% 41%	1907
October	1st to 10th	Day	18% 9% 2 6% 6% 4 6% 5% 6% 6% 34%	1800
	11th to 20th	Day	20% 10% 3 7% 6% 4 4 5% 6% 6% 31%	1800
	21st to end	Day	23% 10% 4 8% 7% 3 5% 4 5% 5% 26%	1980
November	1st to 10th	Day	15% 9% 3 6% 5% 3 6% 5% 5% 8% 33%	1590
	11th to 20th	Day	15% 11% 5% 8% 6% 4 5% 5% 8% 7% 28%	1520
	21st to end	Day	20% 14% 4 6% 6% 3 5% 4 5% 6% 26%	1520
December	1st to 10th	Day	18% 13% 6% 9% 7% 4 6% 5% 4 6% 21%	1520
	11th to 20th	Day	18% 13% 5% 8% 6% 2 5% 5% 4 7% 27%	1906
	21st to end	Day	28% 16% 6% 8% 7% 4 4 3 4 4 16%	2772
January	1st to 10th	Night	18% 13% 5% 8% 7% 3 5% 4 5% 5% 25%	4429
	11th to 20th	Night	15% 12% 5% 10% 11% 4 5% 6% 5% 6% 21%	4312
	21st to end	Night	20% 13% 5% 9% 6% 3 5% 4 4 5% 25%	4532
February	1st to 10th	Night	14% 14% 5% 8% 7% 4 6% 5% 5% 6% 25%	2470
	11th to 20th	Night	15% 11% 5% 9% 7% 4 5% 4 5% 6% 29%	2403
	21st to end	Night	16% 11% 3 8% 6% 4 5% 5% 5% 6% 31%	1984
March	1st to 10th	Night	14% 8% 4 8% 7% 3 5% 4 5% 6% 35%	2097
	11th to 20th	Night	18% 9% 5% 6% 5% 3 4 4 5% 5% 36%	2089
	21st to end	Night	16% 7% 3 5% 6% 3 4 4 4 5% 41%	2294
April	1st to 10th	Night	19% 8% 3 6% 5% 3 5% 5% 5% 6% 34%	1821
	11th to 20th	Night	15% 8% 3 6% 6% 3 5% 5% 5% 6% 38%	1771
	21st to end	Night	17% 8% 4 6% 6% 3 5% 5% 5% 7% 35%	1620
May	1st to 10th	Night	18% 5% 2 4 5% 3 5% 5% 6% 7% 38%	1572
	11th to 20th	Night	13% 5% 2 5% 5% 3 5% 5% 5% 8% 45%	1415
	21st to end	Night	11% 4 3 3 4 3 4 4 5% 8% 50%	1550
June	1st to 10th	Night	12% 5% 2 5% 5% 4 6% 7% 6% 8% 40%	1440
	11th to 20th	Night	10% 4 2 6% 5% 3 4 5% 7% 8% 45%	1440
	21st to end	Night	12% 6% 2 6% 5% 3 4 4 6% 8% 44%	1440
July	1st to 10th	Night	5% 4 2 5% 4 3 4 5% 5% 8% 53%	1440
	11th to 20th	Night	11% 5% 2 4 5% 3 4 5% 5% 8% 49%	1440
	21st to end	Night	9% 4 2 4 4 3 5% 5% 6% 9% 48%	1665
August	1st to 10th	Night	9% 4 2 5% 4 3 4 5% 7% 9% 49%	1611
	11th to 20th	Night	8% 4 2 5% 5% 3 5% 5% 5% 8% 50%	1598
	21st to end	Night	10% 5% 2 5% 4 3 4 5% 5% 8% 48%	1894
September	1st to 10th	Night	12% 6% 2 5% 4 3 6% 5% 5% 6% 47%	1800
	11th to 20th	Night	12% 4 2 3 4 3 3 4 5% 7% 53%	1843
	21st to end	Night	16% 6% 2 4 5% 3 4 4 4 7% 45%	2052
October	1st to 10th	Night	16% 6% 2 7% 5% 4 4 4 5% 6% 40%	2160
	11th to 20th	Night	20% 8% 3 6% 6% 3 5% 5% 5% 7% 33%	2160
	21st to end	Night	22% 8% 3 6% 7% 3 4 5% 5% 6% 30%	2376
November	1st to 10th	Night	17% 7% 3 5% 5% 3 4 4 5% 7% 38%	2483
	11th to 20th	Night	17% 9% 3 7% 5% 4 5% 5% 6% 8% 31%	2660
	21st to end	Night	20% 11% 4 6% 5% 3 5% 6% 5% 8% 26%	2660
December	1st to 10th	Night	19% 14% 5% 9% 7% 3 5% 5% 4 6% 23%	2660
	11th to 20th	Night	17% 15% 5% 7% 6% 4 5% 5% 6% 6% 25%	3288
	21st to end	Night	30% 14% 4 7% 5% 3 5% 5% 5% 6% 17%	4884

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	53% 12% 17% 11% 6% 1	2518
	11th to 20th	Day	68% 11% 11% 5% 4	2646
	21st to end	Day	69% 8% 11% 9% 3 1	3124
February	1st to 10th	Day	63% 9% 12% 13% 3 1	1710
	11th to 20th	Day	57% 9% 10% 15% 8% 1	1672
	21st to end	Day	58% 6% 13% 17% 6%	1470
March	1st to 10th	Day	52% 7% 15% 16% 10% 1	2071
	11th to 20th	Day	51% 7% 11% 18% 12% 2	2090
	21st to end	Day	48% 6% 9% 18% 16% 3	2304
April	1st to 10th	Day	52% 6% 12% 18% 10% 2	2184
	11th to 20th	Day	47% 6% 10% 21% 15% 1	2154
	21st to end	Day	48% 7% 11% 19% 12% 2	2340
May	1st to 10th	Day	46% 8% 12% 18% 14% 3	2385
	11th to 20th	Day	40% 8% 11% 25% 14% 2	2482
	21st to end	Day	36% 8% 17% 24% 13% 2	2725
June	1st to 10th	Day	41% 9% 14% 21% 14% 1	2520
	11th to 20th	Day	36% 8% 15% 25% 15% 2	2520
	21st to end	Day	37% 9% 17% 23% 13% 1	2520
July	1st to 10th	Day	29% 9% 15% 27% 18% 2	2450
	11th to 20th	Day	34% 9% 17% 29% 10% 1	2445
	21st to end	Day	34% 11% 18% 24% 12% 1	2502
August	1st to 10th	Day	34% 10% 17% 25% 12% 1	2314
	11th to 20th	Day	32% 10% 17% 27% 12%	2303
	21st to end	Day	34% 9% 17% 27% 11% 1	2444
September	1st to 10th	Day	36% 9% 15% 28% 11% 1	2160
	11th to 20th	Day	32% 7% 16% 29% 15% 1	2115
	21st to end	Day	39% 10% 15% 26% 10% 1	1907
October	1st to 10th	Day	48% 9% 13% 19% 10% 1	1800
	11th to 20th	Day	51% 9% 15% 18% 6% 1	1800
	21st to end	Day	58% 7% 14% 14% 6% 1	1980
November	1st to 10th	Day	46% 10% 14% 19% 9% 1	1590
	11th to 20th	Day	52% 10% 16% 14% 7% 1	1520
	21st to end	Day	57% 9% 14% 16% 5%	1520
December	1st to 10th	Day	64% 9% 13% 11% 2	1520
	11th to 20th	Day	57% 11% 14% 11% 6%	1906
	21st to end	Day	70% 11% 8% 9% 2	2772
January	1st to 10th	Night	59% 13% 14% 11% 4	4429
	11th to 20th	Night	62% 16% 12% 6% 3 1	4312
	21st to end	Night	63% 12% 10% 10% 4 1	4532
February	1st to 10th	Night	60% 9% 12% 15% 4 1	2470
	11th to 20th	Night	57% 7% 11% 16% 8%	2405
	21st to end	Night	52% 8% 14% 18% 7% 1	1984
March	1st to 10th	Night	50% 7% 13% 19% 9% 2	2107
	11th to 20th	Night	49% 7% 11% 21% 11% 1	2090
	21st to end	Night	44% 6% 9% 22% 16% 3	2294
April	1st to 10th	Night	50% 6% 10% 19% 13% 2	1821
	11th to 20th	Night	46% 7% 10% 18% 18% 2	1771
	21st to end	Night	47% 6% 12% 18% 14% 2	1620
May	1st to 10th	Night	44% 8% 11% 19% 16% 3	1572
	11th to 20th	Night	37% 7% 11% 25% 16% 4	1416
	21st to end	Night	32% 7% 14% 24% 19% 4	1551
June	1st to 10th	Night	40% 9% 10% 22% 16% 3	1440
	11th to 20th	Night	34% 8% 13% 21% 22% 3	1440
	21st to end	Night	38% 8% 13% 24% 15% 1	1440
July	1st to 10th	Night	27% 8% 14% 24% 24% 3	1400
	11th to 20th	Night	33% 5% 13% 29% 18% 1	1392
	21st to end	Night	31% 8% 15% 29% 16% 2	1572
August	1st to 10th	Night	31% 8% 19% 27% 14% 1	1600
	11th to 20th	Night	32% 7% 16% 30% 14% 1	1598
	21st to end	Night	34% 8% 14% 29% 15% 1	1894
September	1st to 10th	Night	36% 7% 16% 25% 14% 2	1800
	11th to 20th	Night	31% 7% 14% 30% 17% 1	1843
	21st to end	Night	40% 8% 11% 28% 13% 1	2052
October	1st to 10th	Night	45% 8% 12% 20% 14% 1	2160
	11th to 20th	Night	51% 10% 12% 20% 7%	2160
	21st to end	Night	53% 9% 14% 14% 10% 1	2376
November	1st to 10th	Night	43% 9% 14% 21% 12% 1	2483
	11th to 20th	Night	50% 10% 14% 16% 10% 1	2660
	21st to end	Night	56% 10% 17% 13% 4	2660
December	1st to 10th	Night	63% 9% 12% 12% 4	2660
	11th to 20th	Night	59% 10% 13% 14% 4	3288
	21st to end	Night	68% 10% 11% 8% 3	4884

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	24% 17% 32% 18% 8% 1	180
	11th to 20th	Day	25% 24% 33% 13% 5% 1	216
	21st to end	Day	22% 20% 33% 22% 4	297
February	1st to 10th	Day	22% 24% 35% 15% 4	270
	11th to 20th	Day	21% 21% 40% 17% 1	270
	21st to end	Day	28% 21% 32% 18% 1	282
March	1st to 10th	Day	22% 13% 38% 21% 5%	460
	11th to 20th	Day	19% 19% 33% 23% 5% 1	460
	21st to end	Day	26% 11% 34% 20% 8% 1	506
April	1st to 10th	Day	19% 14% 33% 25% 7% 1	428
	11th to 20th	Day	24% 10% 31% 22% 9% 4	412
	21st to end	Day	23% 9% 33% 25% 8% 2	420
May	1st to 10th	Day	20% 9% 26% 28% 13% 4	423
	11th to 20th	Day	17% 5% 24% 34% 16% 4	447
	21st to end	Day	12% 3 22% 36% 22% 6%	485
June	1st to 10th	Day	16% 4 27% 36% 16% 2	450
	11th to 20th	Day	14% 6% 21% 34% 21% 4	450
	21st to end	Day	16% 5% 20% 37% 18% 5%	450
July	1st to 10th	Day	8% 2 18% 36% 28% 7%	445
	11th to 20th	Day	13% 3 18% 35% 24% 8%	444
	21st to end	Day	8% 3 23% 43% 18% 5%	488
August	1st to 10th	Day	9% 2 17% 37% 26% 9%	446
	11th to 20th	Day	10% 3 18% 33% 28% 8%	439
	21st to end	Day	11% 4 22% 35% 21% 7%	495
September	1st to 10th	Day	11% 5% 23% 29% 23% 9%	450
	11th to 20th	Day	11% 4 20% 32% 21% 13%	450
	21st to end	Day	14% 7% 27% 28% 17% 6%	450
October	1st to 10th	Day	22% 8% 24% 24% 16% 6%	450
	11th to 20th	Day	19% 16% 31% 25% 8% 1	450
	21st to end	Day	27% 15% 28% 22% 8%	495
November	1st to 10th	Day	21% 16% 27% 26% 9% 1	275
	11th to 20th	Day	19% 19% 36% 20% 4 2	180
	21st to end	Day	27% 12% 36% 19% 5%	180
December	1st to 10th	Day	22% 18% 34% 20% 6% 1	180
	11th to 20th	Day	23% 24% 32% 17% 3 1	180
	21st to end	Day	29% 17% 36% 17% 1	198
January	1st to 10th	Night	23% 17% 37% 16% 6%	760
	11th to 20th	Night	27% 15% 33% 21% 4	760
	21st to end	Night	21% 13% 36% 25% 5% 1	836
February	1st to 10th	Night	22% 17% 40% 19% 3	760
	11th to 20th	Night	21% 16% 37% 23% 4	743
	21st to end	Night	21% 15% 38% 22% 4	628
March	1st to 10th	Night	20% 12% 36% 26% 5%	760
	11th to 20th	Night	21% 14% 34% 25% 5% 1	760
	21st to end	Night	19% 10% 33% 27% 11% 1	836
April	1st to 10th	Night	22% 9% 32% 29% 7%	729
	11th to 20th	Night	18% 9% 33% 27% 12% 1	707
	21st to end	Night	20% 7% 29% 31% 13% 1	540
May	1st to 10th	Night	21% 3 24% 34% 15% 3	492
	11th to 20th	Night	15% 3 28% 38% 15% 1	354
	21st to end	Night	11% 3 19% 40% 25% 2	389
June	1st to 10th	Night	13% 2 23% 42% 18% 2	360
	11th to 20th	Night	10% 3 24% 42% 20% 2	360
	21st to end	Night	12% 2 20% 44% 21% 1	360
July	1st to 10th	Night	5% 3 15% 51% 24% 3	350
	11th to 20th	Night	12% 2 17% 37% 29% 2	348
	21st to end	Night	11% 1 15% 46% 24% 3	485
August	1st to 10th	Night	10% 2 14% 38% 31% 4	537
	11th to 20th	Night	10% 2 13% 37% 33% 5%	534
	21st to end	Night	12% 4 19% 35% 27% 3	706
September	1st to 10th	Night	13% 4 19% 34% 25% 5%	720
	11th to 20th	Night	13% 4 18% 32% 26% 7%	720
	21st to end	Night	17% 6% 20% 27% 24% 5%	720
October	1st to 10th	Night	20% 5% 28% 26% 20% 2	720
	11th to 20th	Night	23% 11% 29% 26% 10% 1	720
	21st to end	Night	23% 11% 31% 27% 6%	792
November	1st to 10th	Night	22% 10% 25% 31% 11% 1	740
	11th to 20th	Night	21% 14% 32% 24% 7% 2	760
	21st to end	Night	25% 11% 34% 23% 7%	760
December	1st to 10th	Night	27% 14% 35% 20% 4	760
	11th to 20th	Night	23% 14% 37% 22% 4 1	760
	21st to end	Night	31% 14% 35% 17% 2	836

Page generated at 2024-03-31 06:08:50. Version ac07

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