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 2025-09-04.

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% 3 8% 5% 4 5% 4 5% 7% 35%	126434
	Night	16% 9% 3 8% 5% 4 4 4 5% 7% 34%	122258
Transparency	Day	46% 8% 13% 21% 11% 1	130019
	Night	47% 8% 12% 20% 11% 1	126760
Seeing	Day	18% 11% 27% 27% 13% 4	15488
	Night	19% 10% 29% 28% 12% 2	24764

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	13% 12% 5% 11% 5% 5% 4 3 6% 6% 31%	3597
	11th to 20th	Day	10% 19% 7% 17% 8% 5% 4 3 4 4 17%	3751
	21st to end	Day	16% 17% 7% 13% 6% 5% 4 3 4 5% 20%	4466
February	1st to 10th	Day	15% 14% 5% 13% 7% 5% 6% 3 5% 5% 23%	1800
	11th to 20th	Day	13% 14% 6% 13% 7% 5% 4 3 4 6% 26%	1753
	21st to end	Day	18% 14% 6% 10% 6% 4 4 3 5% 5% 26%	1545
March	1st to 10th	Day	19% 10% 4 9% 5% 4 4 3 4 5% 32%	4888
	11th to 20th	Day	12% 12% 4 9% 5% 5% 5% 4 5% 8% 31%	4980
	21st to end	Day	20% 10% 3 7% 4 3 3 3 4 5% 37%	5482
April	1st to 10th	Day	18% 12% 3 9% 5% 4 5% 4 5% 6% 31%	2400
	11th to 20th	Day	20% 9% 3 6% 5% 3 4 3 5% 5% 37%	2397
	21st to end	Day	19% 9% 3 8% 4 5% 5% 4 4 6% 34%	2600
May	1st to 10th	Day	21% 9% 3 7% 5% 4 5% 3 5% 6% 32%	6017
	11th to 20th	Day	17% 10% 3 8% 4 4 4 3 5% 7% 35%	6318
	21st to end	Day	18% 7% 2 6% 4 4 4 3 5% 8% 38%	6949
June	1st to 10th	Day	16% 6% 3 6% 5% 5% 4 4 6% 8% 37%	2800
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 5% 7% 9% 40%	2800
	21st to end	Day	15% 6% 2 6% 4 5% 5% 4 6% 8% 40%	2800
July	1st to 10th	Day	9% 6% 2 6% 4 4 5% 4 7% 10% 43%	6360
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 6% 9% 48%	6360
	21st to end	Day	7% 4 2 5% 4 5% 5% 5% 7% 9% 47%	6667
August	1st to 10th	Day	16% 7% 3 5% 4 4 5% 4 5% 7% 40%	4234
	11th to 20th	Day	12% 5% 2 6% 5% 4 5% 5% 7% 10% 39%	4174
	21st to end	Day	10% 6% 2 5% 4 4 6% 4 7% 10% 44%	4425
September	1st to 10th	Day	13% 5% 2 6% 4 5% 5% 4 5% 7% 45%	2316
	11th to 20th	Day	11% 5% 1 5% 4 3 5% 3 6% 8% 48%	2232
	21st to end	Day	14% 6% 2 7% 4 5% 5% 4 6% 7% 40%	2012
October	1st to 10th	Day	17% 9% 2 6% 5% 5% 6% 3 6% 6% 36%	1900
	11th to 20th	Day	19% 10% 2 8% 5% 5% 4 3 5% 6% 33%	1900
	21st to end	Day	22% 10% 4 9% 6% 4 4 3 5% 6% 27%	2090
November	1st to 10th	Day	15% 10% 3 7% 5% 5% 5% 4 5% 7% 33%	1675
	11th to 20th	Day	14% 12% 4 8% 5% 5% 5% 4 8% 7% 28%	1600
	21st to end	Day	19% 15% 4 8% 6% 4 4 4 6% 6% 25%	1600
December	1st to 10th	Day	18% 16% 5% 13% 6% 6% 5% 4 4 6% 17%	2600
	11th to 20th	Day	19% 14% 5% 10% 5% 4 4 4 4 5% 26%	2986
	21st to end	Day	26% 16% 6% 12% 5% 5% 3 2 4 4 17%	3960
January	1st to 10th	Night	15% 13% 5% 11% 5% 5% 4 3 5% 6% 27%	6349
	11th to 20th	Night	13% 14% 5% 13% 8% 6% 5% 4 6% 6% 21%	6132
	21st to end	Night	15% 13% 5% 12% 5% 4 5% 3 5% 6% 26%	6490
February	1st to 10th	Night	14% 15% 5% 9% 6% 6% 6% 4 5% 6% 25%	2600
	11th to 20th	Night	15% 12% 5% 11% 6% 5% 4 3 5% 6% 28%	2533
	21st to end	Night	15% 11% 3 9% 5% 5% 5% 5% 5% 6% 30%	2085
March	1st to 10th	Night	17% 10% 4 9% 5% 5% 5% 3 5% 5% 32%	4939
	11th to 20th	Night	12% 8% 3 7% 5% 5% 5% 4 6% 8% 37%	4979
	21st to end	Night	21% 7% 3 5% 4 4 3 3 4 5% 41%	5450
April	1st to 10th	Night	20% 9% 3 7% 4 5% 5% 3 6% 6% 33%	2000
	11th to 20th	Night	16% 9% 2 7% 4 5% 5% 4 5% 6% 38%	1969
	21st to end	Night	16% 8% 3 7% 5% 4 5% 4 5% 7% 35%	1800
May	1st to 10th	Night	26% 7% 3 6% 4 4 4 4 5% 6% 33%	3921
	11th to 20th	Night	15% 7% 2 6% 4 5% 4 4 6% 9% 37%	3575
	21st to end	Night	18% 6% 2 6% 4 4 4 3 5% 8% 39%	3926
June	1st to 10th	Night	12% 6% 2 6% 5% 5% 6% 5% 5% 8% 40%	1600
	11th to 20th	Night	10% 5% 2 7% 4 3 5% 5% 7% 9% 44%	1600
	21st to end	Night	12% 7% 2 6% 4 4 3 4 6% 8% 43%	1600
July	1st to 10th	Night	8% 6% 2 6% 4 5% 5% 4 6% 10% 44%	3600
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 6% 8% 49%	3600
	21st to end	Night	10% 4 2 4 3 4 4 4 5% 8% 52%	4168
August	1st to 10th	Night	11% 5% 2 6% 3 4 5% 3 6% 8% 49%	2915
	11th to 20th	Night	13% 5% 2 5% 3 4 4 3 5% 7% 50%	2875
	21st to end	Night	10% 5% 2 5% 3 4 4 4 5% 9% 49%	3439
September	1st to 10th	Night	12% 6% 1 5% 3 4 4 4 5% 7% 48%	1931
	11th to 20th	Night	11% 5% 1 4 3 3 4 3 5% 7% 54%	1946
	21st to end	Night	16% 7% 2 5% 4 4 4 3 3 7% 44%	2167
October	1st to 10th	Night	16% 6% 2 8% 4 5% 4 3 5% 6% 41%	2280
	11th to 20th	Night	19% 8% 3 7% 5% 4 6% 4 5% 7% 34%	2280
	21st to end	Night	21% 9% 3 7% 6% 4 5% 4 6% 6% 31%	2508
November	1st to 10th	Night	17% 8% 3 6% 4 4 4 3 6% 7% 38%	2617
	11th to 20th	Night	17% 10% 3 7% 5% 5% 5% 4 6% 8% 31%	2800
	21st to end	Night	20% 12% 3 7% 4 5% 5% 6% 6% 8% 26%	2800
December	1st to 10th	Night	16% 15% 4 10% 6% 4 5% 4 6% 7% 22%	4580
	11th to 20th	Night	17% 16% 4 9% 5% 5% 5% 4 6% 6% 24%	5208
	21st to end	Night	26% 14% 5% 11% 5% 4 5% 3 5% 5% 17%	6996

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	51% 10% 14% 15% 9% 1	3598
	11th to 20th	Day	70% 9% 10% 6% 4	3782
	21st to end	Day	67% 7% 10% 9% 7% 1	4466
February	1st to 10th	Day	63% 9% 11% 13% 4 1	1800
	11th to 20th	Day	58% 9% 9% 14% 8% 1	1762
	21st to end	Day	59% 6% 12% 17% 6%	1545
March	1st to 10th	Day	51% 7% 13% 15% 14%	4891
	11th to 20th	Day	48% 7% 19% 16% 8% 2	4980
	21st to end	Day	47% 6% 9% 21% 16% 1	5482
April	1st to 10th	Day	52% 7% 12% 18% 11% 2	2400
	11th to 20th	Day	48% 6% 9% 20% 15% 1	2397
	21st to end	Day	48% 7% 11% 18% 12% 3	2600
May	1st to 10th	Day	50% 8% 12% 15% 11% 4	6026
	11th to 20th	Day	48% 10% 11% 15% 15% 1	6322
	21st to end	Day	43% 7% 13% 23% 12% 2	6949
June	1st to 10th	Day	42% 9% 14% 20% 14% 1	2800
	11th to 20th	Day	36% 8% 16% 25% 14% 1	2800
	21st to end	Day	38% 9% 16% 23% 13% 1	2800
July	1st to 10th	Day	34% 7% 15% 27% 15% 1	6290
	11th to 20th	Day	30% 7% 14% 33% 15% 1	6285
	21st to end	Day	29% 9% 16% 32% 14%	6476
August	1st to 10th	Day	41% 8% 14% 23% 13% 1	4221
	11th to 20th	Day	37% 8% 16% 29% 10%	4213
	21st to end	Day	33% 8% 14% 35% 10% 1	4425
September	1st to 10th	Day	35% 9% 15% 29% 11% 1	2316
	11th to 20th	Day	32% 7% 16% 30% 15% 1	2232
	21st to end	Day	40% 9% 15% 25% 10%	2012
October	1st to 10th	Day	37% 7% 13% 29% 13% 1	3160
	11th to 20th	Day	38% 7% 18% 22% 15%	3140
	21st to end	Day	48% 8% 16% 20% 7%	3428
November	1st to 10th	Day	46% 9% 14% 20% 9% 1	1675
	11th to 20th	Day	52% 9% 15% 14% 8% 1	1600
	21st to end	Day	57% 9% 13% 16% 5%	1600
December	1st to 10th	Day	66% 10% 13% 9% 2	2600
	11th to 20th	Day	59% 10% 11% 13% 8%	2986
	21st to end	Day	69% 10% 7% 9% 6%	3960
January	1st to 10th	Night	56% 11% 11% 15% 8%	6349
	11th to 20th	Night	62% 13% 10% 10% 5% 1	6176
	21st to end	Night	59% 9% 11% 12% 8% 1	6490
February	1st to 10th	Night	59% 9% 12% 15% 4 1	2600
	11th to 20th	Night	58% 7% 11% 16% 8%	2535
	21st to end	Night	52% 8% 14% 18% 7% 1	2085
March	1st to 10th	Night	52% 6% 10% 17% 12% 3	4949
	11th to 20th	Night	42% 7% 18% 21% 10% 1	4980
	21st to end	Night	44% 5% 10% 21% 17% 2	5450
April	1st to 10th	Night	51% 6% 10% 19% 13% 2	2000
	11th to 20th	Night	47% 6% 10% 19% 17% 2	1969
	21st to end	Night	46% 7% 11% 18% 15% 2	1800
May	1st to 10th	Night	52% 6% 11% 13% 13% 5%	3928
	11th to 20th	Night	43% 11% 12% 19% 13% 2	3576
	21st to end	Night	43% 8% 12% 21% 15% 2	3927
June	1st to 10th	Night	41% 9% 10% 23% 16% 3	1600
	11th to 20th	Night	35% 8% 13% 22% 20% 3	1600
	21st to end	Night	39% 7% 13% 24% 15% 1	1600
July	1st to 10th	Night	34% 7% 16% 22% 20% 1	3560
	11th to 20th	Night	33% 5% 13% 31% 17% 1	3552
	21st to end	Night	30% 7% 12% 31% 20% 1	4045
August	1st to 10th	Night	34% 7% 14% 28% 16% 2	2904
	11th to 20th	Night	34% 5% 15% 31% 13% 1	2902
	21st to end	Night	31% 7% 13% 33% 15% 1	3439
September	1st to 10th	Night	34% 7% 15% 28% 14% 2	1931
	11th to 20th	Night	30% 7% 14% 31% 18% 1	1946
	21st to end	Night	42% 7% 11% 27% 13% 1	2167
October	1st to 10th	Night	34% 6% 10% 27% 22% 1	3800
	11th to 20th	Night	41% 7% 13% 30% 8%	3779
	21st to end	Night	40% 8% 15% 27% 10% 1	4120
November	1st to 10th	Night	44% 8% 14% 21% 12% 1	2617
	11th to 20th	Night	50% 10% 14% 16% 10% 1	2800
	21st to end	Night	55% 10% 17% 14% 4	2800
December	1st to 10th	Night	60% 8% 14% 14% 3	4580
	11th to 20th	Night	59% 10% 11% 12% 8%	5208
	21st to end	Night	68% 10% 9% 8% 5%	6996

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	23% 19% 33% 17% 8% 1	200
	11th to 20th	Day	26% 23% 33% 13% 4 1	240
	21st to end	Day	22% 23% 32% 20% 3	330
February	1st to 10th	Day	25% 24% 34% 14% 3	300
	11th to 20th	Day	24% 23% 36% 16% 1	300
	21st to end	Day	27% 21% 34% 17% 1	309
March	1st to 10th	Day	22% 15% 37% 21% 5%	500
	11th to 20th	Day	20% 19% 34% 22% 5% 1	500
	21st to end	Day	28% 13% 32% 19% 7% 1	550
April	1st to 10th	Day	22% 14% 32% 24% 6% 1	500
	11th to 20th	Day	25% 14% 29% 20% 8% 3	492
	21st to end	Day	22% 12% 34% 22% 8% 1	500
May	1st to 10th	Day	20% 9% 28% 28% 11% 4	503
	11th to 20th	Day	17% 7% 24% 33% 16% 4	527
	21st to end	Day	13% 6% 23% 33% 20% 5%	573
June	1st to 10th	Day	16% 6% 27% 33% 15% 2	530
	11th to 20th	Day	12% 8% 24% 34% 20% 3	530
	21st to end	Day	16% 8% 22% 34% 16% 4	530
July	1st to 10th	Day	9% 4 22% 35% 24% 6%	525
	11th to 20th	Day	13% 4 21% 34% 22% 7%	524
	21st to end	Day	8% 4 24% 41% 18% 4	576
August	1st to 10th	Day	12% 3 19% 36% 23% 7%	526
	11th to 20th	Day	11% 4 19% 33% 26% 8%	519
	21st to end	Day	11% 4 23% 36% 20% 7%	583
September	1st to 10th	Day	11% 6% 23% 29% 22% 9%	502
	11th to 20th	Day	10% 3 18% 31% 23% 15%	490
	21st to end	Day	16% 7% 26% 29% 16% 6%	490
October	1st to 10th	Day	21% 8% 26% 24% 16% 5%	490
	11th to 20th	Day	18% 16% 31% 24% 9% 2	490
	21st to end	Day	25% 16% 29% 22% 8%	539
November	1st to 10th	Day	21% 16% 28% 25% 9% 1	300
	11th to 20th	Day	19% 21% 36% 19% 5% 2	200
	21st to end	Day	28% 13% 36% 19% 5%	200
December	1st to 10th	Day	23% 19% 34% 19% 6% 1	200
	11th to 20th	Day	26% 24% 32% 16% 3 1	200
	21st to end	Day	29% 17% 36% 16% 2	220
January	1st to 10th	Night	23% 18% 38% 15% 6%	800
	11th to 20th	Night	27% 15% 33% 20% 4	800
	21st to end	Night	21% 14% 35% 24% 5% 1	880
February	1st to 10th	Night	22% 17% 40% 19% 2	800
	11th to 20th	Night	21% 17% 36% 22% 3	783
	21st to end	Night	21% 15% 38% 22% 4	660
March	1st to 10th	Night	20% 13% 37% 26% 5%	800
	11th to 20th	Night	20% 15% 34% 26% 5% 1	800
	21st to end	Night	20% 11% 32% 26% 11% 1	880
April	1st to 10th	Night	23% 10% 33% 28% 7%	800
	11th to 20th	Night	18% 10% 33% 27% 11% 1	785
	21st to end	Night	19% 8% 30% 30% 13% 1	600
May	1st to 10th	Night	22% 5% 24% 33% 14% 3	546
	11th to 20th	Night	15% 4 27% 39% 14% 1	394
	21st to end	Night	12% 3 20% 39% 24% 2	433
June	1st to 10th	Night	12% 3 25% 42% 17% 2	400
	11th to 20th	Night	10% 3 23% 43% 19% 2	400
	21st to end	Night	12% 3 22% 43% 20% 1	400
July	1st to 10th	Night	5% 3 15% 51% 23% 3	390
	11th to 20th	Night	11% 3 16% 38% 29% 2	388
	21st to end	Night	11% 3 15% 45% 24% 3	540
August	1st to 10th	Night	10% 2 14% 38% 31% 4	597
	11th to 20th	Night	10% 3 14% 36% 33% 5%	594
	21st to end	Night	12% 4 20% 36% 26% 3	785
September	1st to 10th	Night	12% 4 19% 34% 26% 5%	773
	11th to 20th	Night	13% 4 17% 32% 28% 8%	760
	21st to end	Night	18% 6% 20% 27% 23% 5%	760
October	1st to 10th	Night	19% 5% 28% 26% 19% 3	760
	11th to 20th	Night	23% 11% 28% 27% 10% 1	760
	21st to end	Night	22% 12% 31% 27% 7%	836
November	1st to 10th	Night	22% 10% 26% 30% 11% 1	780
	11th to 20th	Night	21% 15% 33% 23% 7% 2	800
	21st to end	Night	25% 12% 34% 22% 7%	800
December	1st to 10th	Night	27% 15% 34% 20% 4	800
	11th to 20th	Night	24% 14% 37% 21% 4 1	800
	21st to end	Night	30% 14% 36% 18% 2	880

Page generated at 2025-09-01 01:51:05. Version ac07

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