Dreamstead Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dreamstead Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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	11% 6% 2 6% 4 4 5% 4 6% 8% 42%	138120
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	134898
Transparency	Day	38% 5% 12% 20% 18% 7%	141895
	Night	38% 5% 11% 19% 20% 8%	139195
Seeing	Day	14% 9% 22% 25% 20% 10%	17329
	Night	14% 8% 22% 31% 21% 4	27325

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	13% 6% 3 6% 4 4 4 3 5% 6% 47%	5258
	11th to 20th	Day	13% 5% 2 4 3 2 2 2 4 7% 57%	5280
	21st to end	Day	16% 7% 3 6% 5% 4 4 3 5% 6% 40%	6034
February	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 4 6% 41%	2100
	11th to 20th	Day	19% 6% 2 5% 3 3 3 3 5% 7% 43%	2048
	21st to end	Day	15% 6% 2 6% 4 4 4 3 6% 7% 43%	1730
March	1st to 10th	Day	18% 7% 2 7% 4 4 4 3 5% 7% 38%	4851
	11th to 20th	Day	8% 4 2 5% 4 4 4 3 5% 8% 54%	5090
	21st to end	Day	15% 7% 2 6% 4 4 3 3 4 5% 47%	5586
April	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 5% 6% 49%	2310
	11th to 20th	Day	11% 5% 2 5% 3 3 4 3 5% 7% 53%	2444
	21st to end	Day	6% 4 2 6% 4 4 4 4 5% 8% 53%	2701
May	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 5% 8% 39%	7616
	11th to 20th	Day	13% 5% 2 7% 4 4 5% 5% 7% 9% 39%	7626
	21st to end	Day	10% 6% 2 8% 5% 5% 6% 5% 7% 9% 36%	8391
June	1st to 10th	Day	10% 6% 3 6% 5% 6% 6% 5% 8% 10% 34%	2730
	11th to 20th	Day	6% 5% 2 4 6% 5% 7% 6% 8% 11% 40%	2730
	21st to end	Day	5% 5% 2 7% 6% 6% 7% 5% 8% 11% 37%	2730
July	1st to 10th	Day	9% 6% 3 8% 6% 7% 8% 7% 9% 11% 25%	6030
	11th to 20th	Day	3 4 2 6% 6% 6% 7% 6% 9% 13% 38%	6030
	21st to end	Day	6% 6% 3 8% 6% 7% 8% 6% 10% 13% 26%	6554
August	1st to 10th	Day	12% 6% 2 7% 5% 6% 6% 6% 8% 12% 29%	4234
	11th to 20th	Day	5% 5% 2 6% 4 4 5% 5% 7% 10% 48%	3924
	21st to end	Day	8% 5% 2 5% 4 5% 5% 5% 7% 10% 44%	4220
September	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 5% 8% 9% 39%	2200
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 7% 8% 41%	2200
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 6% 6% 42%	2200
October	1st to 10th	Day	12% 5% 3 4 4 3 4 4 5% 6% 50%	2200
	11th to 20th	Day	9% 4 2 4 2 3 3 4 5% 6% 59%	2067
	21st to end	Day	10% 4 1 5% 4 3 3 3 5% 6% 56%	2200
November	1st to 10th	Day	12% 6% 2 5% 3 4 3 3 4 6% 52%	1978
	11th to 20th	Day	12% 5% 1 5% 3 2 3 3 4 6% 55%	1890
	21st to end	Day	13% 6% 2 5% 4 4 4 4 6% 6% 47%	1890
December	1st to 10th	Day	14% 7% 2 6% 4 3 4 2 4 5% 50%	3020
	11th to 20th	Day	16% 6% 3 5% 3 4 3 3 4 6% 48%	3463
	21st to end	Day	20% 7% 2 5% 4 3 3 3 4 6% 43%	4565
January	1st to 10th	Night	12% 6% 2 5% 4 5% 4 3 6% 6% 48%	7635
	11th to 20th	Night	12% 6% 3 5% 4 4 4 3 5% 6% 48%	7680
	21st to end	Night	18% 9% 3 6% 3 4 3 3 4 6% 40%	8143
February	1st to 10th	Night	14% 6% 3 6% 4 3 4 4 5% 6% 46%	2520
	11th to 20th	Night	18% 7% 2 6% 4 3 3 3 4 5% 46%	2458
	21st to end	Night	14% 6% 2 6% 3 4 4 4 5% 6% 45%	2076
March	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 5% 7% 40%	5220
	11th to 20th	Night	9% 4 1 4 3 4 4 4 6% 8% 52%	5090
	21st to end	Night	13% 5% 2 5% 4 4 4 4 5% 6% 47%	5588
April	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 6% 6% 48%	2310
	11th to 20th	Night	10% 4 1 5% 3 4 3 4 5% 7% 53%	2141
	21st to end	Night	6% 4 2 5% 5% 4 4 3 5% 7% 54%	1916
May	1st to 10th	Night	12% 7% 2 6% 5% 5% 4 4 6% 10% 39%	5237
	11th to 20th	Night	12% 5% 2 6% 4 4 5% 5% 7% 9% 40%	5234
	21st to end	Night	10% 7% 3 7% 5% 4 5% 4 7% 11% 36%	5761
June	1st to 10th	Night	9% 7% 3 8% 5% 5% 5% 6% 7% 11% 34%	1890
	11th to 20th	Night	5% 5% 2 6% 5% 4 5% 5% 9% 12% 43%	1890
	21st to end	Night	5% 5% 2 7% 6% 6% 6% 6% 9% 10% 39%	1890
July	1st to 10th	Night	11% 7% 3 9% 6% 7% 7% 7% 8% 11% 25%	4148
	11th to 20th	Night	4 4 2 7% 6% 7% 8% 7% 10% 14% 33%	4147
	21st to end	Night	8% 6% 3 9% 7% 7% 7% 6% 10% 12% 25%	4517
August	1st to 10th	Night	13% 7% 3 7% 5% 5% 7% 5% 8% 11% 28%	2915
	11th to 20th	Night	7% 4 2 5% 4 5% 4 5% 7% 12% 44%	3120
	21st to end	Night	6% 4 2 5% 4 4 4 4 8% 11% 47%	3642
September	1st to 10th	Night	9% 7% 2 7% 6% 5% 6% 4 7% 11% 37%	2200
	11th to 20th	Night	11% 6% 3 7% 5% 4 5% 4 6% 6% 43%	2200
	21st to end	Night	10% 6% 2 7% 5% 4 6% 3 6% 8% 43%	2200
October	1st to 10th	Night	11% 4 2 5% 3 4 4 3 5% 7% 51%	2200
	11th to 20th	Night	11% 4 1 4 3 3 3 3 3 5% 60%	2330
	21st to end	Night	10% 5% 2 4 3 3 4 3 4 6% 56%	2640
November	1st to 10th	Night	11% 6% 2 5% 3 3 3 3 5% 5% 55%	2535
	11th to 20th	Night	13% 5% 2 4 3 2 2 3 4 6% 55%	2730
	21st to end	Night	13% 5% 2 6% 5% 4 3 3 4 8% 48%	2730
December	1st to 10th	Night	13% 6% 2 4 3 3 3 3 4 5% 55%	4380
	11th to 20th	Night	15% 6% 2 5% 4 3 3 3 4 6% 50%	4952
	21st to end	Night	19% 7% 3 6% 4 3 4 3 4 5% 43%	6633

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	38% 3 6% 19% 26% 7%	5259
	11th to 20th	Day	30% 2 4 16% 33% 16%	5280
	21st to end	Day	45% 3 6% 15% 21% 10%	6034
February	1st to 10th	Day	44% 3 7% 16% 21% 8%	2100
	11th to 20th	Day	42% 4 5% 18% 24% 7%	2058
	21st to end	Day	42% 2 7% 17% 21% 11%	1730
March	1st to 10th	Day	48% 2 7% 13% 22% 8%	4851
	11th to 20th	Day	30% 3 9% 15% 21% 21%	5090
	21st to end	Day	41% 3 7% 19% 18% 11%	5586
April	1st to 10th	Day	36% 4 10% 21% 18% 9%	2310
	11th to 20th	Day	32% 3 7% 21% 25% 12%	2444
	21st to end	Day	30% 4 11% 25% 25% 6%	2701
May	1st to 10th	Day	43% 4 14% 20% 17% 3	7651
	11th to 20th	Day	40% 6% 17% 23% 11% 3	7630
	21st to end	Day	43% 8% 15% 17% 16% 1	8405
June	1st to 10th	Day	42% 6% 16% 20% 13% 2	2730
	11th to 20th	Day	34% 7% 17% 25% 15% 2	2730
	21st to end	Day	38% 8% 18% 21% 12% 3	2730
July	1st to 10th	Day	45% 13% 21% 17% 3 1	5965
	11th to 20th	Day	33% 13% 29% 22% 3 1	5961
	21st to end	Day	43% 14% 21% 19% 3	6370
August	1st to 10th	Day	43% 9% 20% 24% 3	4221
	11th to 20th	Day	30% 7% 16% 34% 13% 1	3962
	21st to end	Day	33% 6% 18% 29% 13% 1	4220
September	1st to 10th	Day	38% 8% 16% 19% 16% 4	2200
	11th to 20th	Day	40% 6% 10% 21% 19% 5%	2200
	21st to end	Day	41% 5% 8% 21% 18% 6%	2200
October	1st to 10th	Day	33% 3 7% 14% 29% 14%	3590
	11th to 20th	Day	16% 2 4 17% 27% 33%	3346
	21st to end	Day	21% 2 5% 18% 38% 16%	3538
November	1st to 10th	Day	34% 3 7% 14% 26% 15%	1978
	11th to 20th	Day	31% 3 5% 19% 26% 15%	1890
	21st to end	Day	36% 4 9% 17% 24% 10%	1890
December	1st to 10th	Day	37% 2 7% 18% 26% 10%	3020
	11th to 20th	Day	39% 3 7% 22% 22% 8%	3460
	21st to end	Day	44% 2 6% 21% 24% 3	4565
January	1st to 10th	Night	37% 3 7% 20% 26% 7%	7636
	11th to 20th	Night	38% 3 4 17% 27% 12%	7680
	21st to end	Night	47% 2 5% 15% 23% 8%	8143
February	1st to 10th	Night	39% 3 7% 18% 22% 11%	2520
	11th to 20th	Night	42% 4 5% 17% 21% 10%	2459
	21st to end	Night	40% 4 7% 17% 18% 15%	2076
March	1st to 10th	Night	45% 3 9% 15% 16% 12%	5220
	11th to 20th	Night	30% 4 9% 13% 25% 19%	5090
	21st to end	Night	38% 3 7% 18% 21% 13%	5588
April	1st to 10th	Night	35% 4 10% 19% 19% 12%	2310
	11th to 20th	Night	31% 3 6% 22% 25% 13%	2141
	21st to end	Night	30% 4 10% 24% 24% 9%	1916
May	1st to 10th	Night	41% 5% 15% 19% 16% 4	5264
	11th to 20th	Night	38% 6% 16% 26% 12% 2	5235
	21st to end	Night	41% 8% 14% 20% 15% 2	5771
June	1st to 10th	Night	42% 8% 17% 19% 13% 1	1890
	11th to 20th	Night	31% 7% 19% 27% 13% 2	1890
	21st to end	Night	36% 9% 22% 17% 12% 4	1890
July	1st to 10th	Night	48% 14% 20% 14% 3 1	4105
	11th to 20th	Night	35% 14% 30% 17% 3	4096
	21st to end	Night	47% 14% 21% 15% 2	4387
August	1st to 10th	Night	46% 10% 20% 21% 3	2904
	11th to 20th	Night	30% 8% 20% 28% 12% 1	3148
	21st to end	Night	29% 7% 20% 32% 12% 1	3642
September	1st to 10th	Night	39% 8% 18% 17% 14% 4	2200
	11th to 20th	Night	40% 7% 12% 18% 20% 4	2200
	21st to end	Night	39% 5% 12% 17% 21% 6%	2200
October	1st to 10th	Night	34% 3 8% 14% 26% 15%	3590
	11th to 20th	Night	17% 2 4 12% 31% 34%	3790
	21st to end	Night	20% 3 4 19% 34% 20%	4252
November	1st to 10th	Night	32% 3 7% 15% 28% 15%	2535
	11th to 20th	Night	32% 2 5% 17% 28% 15%	2730
	21st to end	Night	38% 3 6% 19% 23% 11%	2730
December	1st to 10th	Night	34% 3 6% 20% 29% 8%	4380
	11th to 20th	Night	37% 3 10% 19% 23% 8%	4954
	21st to end	Night	46% 2 4 21% 24% 3	6633

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	18% 21% 43% 15% 2	330
	11th to 20th	Day	21% 22% 32% 16% 7% 1	330
	21st to end	Day	24% 21% 37% 14% 4	363
February	1st to 10th	Day	18% 19% 41% 16% 6%	330
	11th to 20th	Day	29% 19% 32% 19% 1	330
	21st to end	Day	23% 19% 41% 12% 5%	273
March	1st to 10th	Day	17% 20% 29% 24% 9% 1	445
	11th to 20th	Day	17% 15% 36% 21% 9% 2	540
	21st to end	Day	19% 13% 35% 23% 9% 1	594
April	1st to 10th	Day	18% 13% 29% 25% 12% 3	540
	11th to 20th	Day	12% 15% 28% 25% 17% 4	532
	21st to end	Day	12% 9% 26% 29% 19% 5%	540
May	1st to 10th	Day	11% 10% 29% 29% 14% 6%	543
	11th to 20th	Day	11% 5% 22% 31% 21% 10%	567
	21st to end	Day	13% 5% 17% 30% 24% 11%	617
June	1st to 10th	Day	12% 2 16% 30% 26% 14%	570
	11th to 20th	Day	8% 3 14% 27% 25% 23%	570
	21st to end	Day	7% 4 11% 29% 30% 19%	570
July	1st to 10th	Day	8% 3 6% 24% 32% 27%	565
	11th to 20th	Day	7% 2 4 20% 37% 30%	564
	21st to end	Day	4 2 7% 25% 37% 25%	616
August	1st to 10th	Day	14% 3 9% 23% 31% 19%	526
	11th to 20th	Day	8% 1 7% 21% 39% 24%	519
	21st to end	Day	14% 3 8% 26% 32% 17%	583
September	1st to 10th	Day	12% 3 11% 28% 31% 16%	530
	11th to 20th	Day	15% 2 12% 32% 28% 10%	530
	21st to end	Day	15% 4 12% 29% 28% 12%	530
October	1st to 10th	Day	15% 4 24% 28% 19% 8%	530
	11th to 20th	Day	10% 6% 22% 32% 23% 7%	530
	21st to end	Day	13% 7% 28% 29% 20% 4	583
November	1st to 10th	Day	18% 6% 26% 30% 17% 4	456
	11th to 20th	Day	14% 15% 36% 22% 11% 2	330
	21st to end	Day	13% 17% 36% 22% 12% 1	330
December	1st to 10th	Day	26% 16% 34% 16% 7% 1	330
	11th to 20th	Day	21% 17% 36% 16% 8% 2	330
	21st to end	Day	25% 13% 29% 24% 8% 1	363
January	1st to 10th	Night	20% 15% 33% 26% 5%	840
	11th to 20th	Night	17% 15% 30% 27% 10%	840
	21st to end	Night	20% 14% 37% 25% 4	924
February	1st to 10th	Night	17% 12% 32% 31% 7%	840
	11th to 20th	Night	22% 15% 33% 27% 4	823
	21st to end	Night	18% 15% 36% 28% 4	692
March	1st to 10th	Night	15% 13% 31% 33% 8%	840
	11th to 20th	Night	14% 14% 32% 30% 10%	840
	21st to end	Night	13% 13% 33% 30% 10%	924
April	1st to 10th	Night	14% 11% 31% 31% 13%	840
	11th to 20th	Night	12% 9% 29% 32% 16% 1	689
	21st to end	Night	8% 6% 26% 39% 19% 1	630
May	1st to 10th	Night	9% 8% 24% 38% 19% 2	630
	11th to 20th	Night	10% 3 23% 35% 23% 5%	621
	21st to end	Night	10% 2 15% 38% 30% 5%	683
June	1st to 10th	Night	10% 3 13% 36% 33% 4	630
	11th to 20th	Night	5% 2 12% 33% 37% 10%	630
	21st to end	Night	7% 2 9% 31% 42% 8%	630
July	1st to 10th	Night	7% 2 6% 28% 41% 16%	615
	11th to 20th	Night	8% 2 3 22% 47% 19%	612
	21st to end	Night	7% 2 5% 31% 44% 11%	687
August	1st to 10th	Night	10% 2 6% 29% 41% 11%	597
	11th to 20th	Night	13% 2 3 27% 45% 11%	594
	21st to end	Night	12% 2 7% 30% 38% 11%	690
September	1st to 10th	Night	12% 2 8% 30% 39% 9%	800
	11th to 20th	Night	14% 2 10% 33% 35% 6%	800
	21st to end	Night	14% 3 12% 32% 36% 4	800
October	1st to 10th	Night	13% 4 19% 35% 24% 5%	800
	11th to 20th	Night	12% 6% 21% 32% 25% 3	800
	21st to end	Night	12% 7% 23% 33% 24% 1	880
November	1st to 10th	Night	14% 7% 20% 36% 21% 1	820
	11th to 20th	Night	15% 10% 25% 34% 15% 1	840
	21st to end	Night	14% 11% 28% 31% 15% 1	840
December	1st to 10th	Night	16% 12% 30% 28% 12% 2	840
	11th to 20th	Night	18% 9% 28% 32% 12% 1	840
	21st to end	Night	24% 10% 24% 32% 9%	924

Page generated at 2026-07-28 03:25:24. Version ac07

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