Dorset Wilderness Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dorset Wilderness Area clear sky chart from 2005-11-06 to 2026-05-17.

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% 12% 5% 10% 5% 4 4 3 5% 6% 29%	131921
	Night	16% 14% 5% 11% 5% 4 4 3 4 6% 28%	130856
Transparency	Day	55% 5% 11% 19% 10% 1	135537
	Night	57% 5% 10% 17% 10% 1	135311
Seeing	Day	26% 16% 29% 18% 9% 3	16474
	Night	25% 14% 27% 23% 10% 1	26228

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	16% 22% 8% 28% 5% 3 3 2 3 3 7%	5158
	11th to 20th	Day	10% 23% 10% 22% 8% 7% 3 2 2 3 9%	5280
	21st to end	Day	17% 17% 7% 17% 10% 7% 4 3 3 3 12%	5780
February	1st to 10th	Day	16% 21% 6% 15% 8% 4 3 2 2 4 17%	1890
	11th to 20th	Day	15% 17% 8% 16% 9% 3 4 2 4 3 17%	1843
	21st to end	Day	18% 18% 4 14% 6% 3 4 4 4 5% 21%	1716
March	1st to 10th	Day	17% 13% 7% 12% 5% 4 3 2 4 5% 27%	5030
	11th to 20th	Day	12% 15% 7% 10% 4 4 3 2 4 6% 32%	5090
	21st to end	Day	21% 15% 7% 10% 4 4 3 3 3 4 26%	5586
April	1st to 10th	Day	19% 14% 3 7% 4 5% 3 3 6% 6% 30%	2403
	11th to 20th	Day	20% 13% 3 6% 4 3 4 4 4 5% 33%	2607
	21st to end	Day	20% 12% 3 7% 4 3 3 3 4 6% 34%	2730
May	1st to 10th	Day	21% 9% 4 8% 5% 5% 4 4 5% 6% 30%	5992
	11th to 20th	Day	19% 9% 3 7% 5% 5% 5% 3 6% 7% 31%	5939
	21st to end	Day	19% 8% 3 7% 5% 4 5% 3 5% 7% 35%	6862
June	1st to 10th	Day	16% 7% 2 7% 4 4 5% 4 6% 8% 36%	2800
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 4 5% 8% 37%	2800
	21st to end	Day	14% 5% 2 6% 5% 5% 4 4 7% 10% 39%	2800
July	1st to 10th	Day	9% 6% 2 6% 4 5% 5% 4 6% 9% 43%	6254
	11th to 20th	Day	12% 5% 2 7% 5% 5% 5% 4 7% 10% 38%	5900
	21st to end	Day	12% 5% 2 6% 4 5% 5% 3 5% 8% 44%	6424
August	1st to 10th	Day	14% 6% 3 7% 5% 5% 5% 4 6% 9% 35%	4234
	11th to 20th	Day	14% 7% 3 8% 5% 6% 5% 4 7% 9% 33%	4174
	21st to end	Day	11% 6% 2 7% 4 5% 5% 4 7% 9% 41%	4526
September	1st to 10th	Day	15% 7% 2 6% 5% 4 5% 3 6% 8% 39%	2373
	11th to 20th	Day	12% 6% 3 6% 4 4 4 3 5% 8% 44%	2200
	21st to end	Day	20% 8% 3 8% 5% 3 5% 4 4 7% 34%	2200
October	1st to 10th	Day	16% 6% 2 7% 5% 4 4 5% 6% 7% 39%	2020
	11th to 20th	Day	22% 9% 3 8% 5% 4 4 4 5% 6% 31%	2000
	21st to end	Day	25% 12% 4 8% 4 4 5% 4 4 6% 24%	2200
November	1st to 10th	Day	15% 13% 4 8% 4 5% 4 4 5% 6% 32%	1893
	11th to 20th	Day	17% 22% 4 9% 5% 4 4 3 4 6% 23%	1739
	21st to end	Day	19% 25% 6% 9% 4 4 4 3 5% 5% 15%	1680
December	1st to 10th	Day	17% 27% 13% 12% 5% 4 3 3 3 3 10%	2680
	11th to 20th	Day	21% 26% 7% 12% 6% 3 3 3 3 5% 11%	3070
	21st to end	Day	24% 25% 7% 15% 5% 4 3 2 3 3 9%	4048
January	1st to 10th	Night	15% 22% 10% 26% 5% 4 3 2 2 3 8%	7717
	11th to 20th	Night	11% 20% 11% 22% 8% 5% 4 2 3 3 10%	7680
	21st to end	Night	17% 18% 7% 14% 7% 5% 5% 3 3 4 17%	8401
February	1st to 10th	Night	18% 19% 5% 13% 7% 5% 4 3 4 4 19%	2730
	11th to 20th	Night	16% 17% 6% 14% 7% 6% 4 3 4 4 18%	2663
	21st to end	Night	19% 15% 6% 14% 5% 4 4 4 4 5% 20%	2086
March	1st to 10th	Night	19% 16% 4 8% 6% 3 3 3 4 5% 28%	5041
	11th to 20th	Night	13% 13% 6% 7% 4 3 4 3 5% 7% 36%	5090
	21st to end	Night	18% 15% 6% 9% 4 4 4 3 4 4 30%	5588
April	1st to 10th	Night	19% 15% 4 7% 6% 5% 4 3 4 5% 28%	2216
	11th to 20th	Night	18% 11% 3 6% 4 4 5% 4 6% 7% 31%	1978
	21st to end	Night	15% 10% 3 6% 6% 5% 4 5% 5% 7% 35%	1890
May	1st to 10th	Night	25% 10% 4 7% 5% 4 4 3 4 6% 29%	4123
	11th to 20th	Night	15% 10% 3 8% 4 4 4 3 5% 8% 36%	4086
	21st to end	Night	21% 7% 2 5% 4 3 3 3 6% 9% 38%	3974
June	1st to 10th	Night	10% 6% 2 8% 5% 4 5% 5% 6% 7% 41%	1600
	11th to 20th	Night	10% 5% 3 8% 5% 5% 5% 4 6% 9% 41%	1600
	21st to end	Night	12% 6% 2 5% 5% 4 5% 4 5% 9% 43%	1600
July	1st to 10th	Night	10% 7% 2 6% 5% 5% 4 3 6% 10% 43%	3685
	11th to 20th	Night	11% 6% 2 6% 5% 4 5% 4 6% 9% 42%	4057
	21st to end	Night	8% 5% 2 6% 5% 4 5% 4 5% 8% 48%	4427
August	1st to 10th	Night	10% 8% 3 8% 5% 4 5% 4 6% 7% 40%	2915
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 3 4 6% 40%	2875
	21st to end	Night	9% 5% 3 6% 4 5% 5% 5% 7% 9% 43%	3337
September	1st to 10th	Night	13% 6% 2 5% 3 4 4 4 6% 8% 46%	2024
	11th to 20th	Night	11% 5% 2 5% 3 3 4 4 5% 7% 51%	2200
	21st to end	Night	18% 7% 2 7% 5% 4 5% 3 5% 6% 37%	2200
October	1st to 10th	Night	17% 6% 2 6% 3 4 3 3 5% 7% 43%	2379
	11th to 20th	Night	19% 10% 4 7% 5% 4 5% 4 5% 5% 33%	2400
	21st to end	Night	27% 10% 3 7% 4 4 3 3 4 5% 29%	2640
November	1st to 10th	Night	16% 12% 3 7% 5% 4 4 3 5% 6% 35%	2621
	11th to 20th	Night	17% 19% 4 9% 5% 5% 4 3 4 6% 23%	2878
	21st to end	Night	21% 22% 5% 8% 5% 4 4 3 4 5% 19%	2940
December	1st to 10th	Night	15% 24% 12% 11% 5% 5% 4 3 4 4 14%	4720
	11th to 20th	Night	19% 25% 9% 12% 5% 3 3 2 3 4 15%	5345
	21st to end	Night	21% 23% 6% 12% 6% 4 4 3 3 5% 12%	7150

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	84% 4 7% 4 2	5159
	11th to 20th	Day	83% 2 6% 6% 3	5280
	21st to end	Day	79% 2 6% 9% 4	5780
February	1st to 10th	Day	73% 3 6% 12% 5%	1890
	11th to 20th	Day	72% 4 7% 11% 5%	1852
	21st to end	Day	65% 4 10% 14% 5% 2	1716
March	1st to 10th	Day	59% 4 12% 20% 5%	5030
	11th to 20th	Day	54% 4 15% 20% 6% 2	5090
	21st to end	Day	61% 4 6% 18% 9% 1	5586
April	1st to 10th	Day	54% 4 13% 16% 12% 1	2403
	11th to 20th	Day	53% 4 10% 19% 12% 2	2607
	21st to end	Day	52% 4 10% 21% 11% 2	2730
May	1st to 10th	Day	54% 5% 8% 20% 9% 4	6027
	11th to 20th	Day	51% 6% 10% 21% 10% 1	5943
	21st to end	Day	48% 6% 12% 20% 11% 3	6877
June	1st to 10th	Day	44% 6% 12% 25% 12% 1	2800
	11th to 20th	Day	44% 6% 14% 21% 14% 1	2800
	21st to end	Day	39% 7% 13% 25% 16% 1	2800
July	1st to 10th	Day	36% 6% 13% 27% 17% 2	6186
	11th to 20th	Day	39% 6% 13% 26% 15% 1	5831
	21st to end	Day	38% 5% 11% 25% 20% 1	6240
August	1st to 10th	Day	43% 6% 16% 23% 12%	4221
	11th to 20th	Day	44% 6% 13% 28% 7% 1	4213
	21st to end	Day	38% 6% 13% 29% 13% 1	4526
September	1st to 10th	Day	42% 6% 13% 23% 14% 2	2373
	11th to 20th	Day	38% 5% 14% 28% 15% 1	2200
	21st to end	Day	48% 6% 11% 22% 12% 1	2200
October	1st to 10th	Day	35% 5% 15% 26% 19% 1	3293
	11th to 20th	Day	46% 5% 13% 20% 13% 3	3240
	21st to end	Day	46% 5% 14% 25% 9% 1	3538
November	1st to 10th	Day	52% 6% 10% 20% 12% 1	1893
	11th to 20th	Day	63% 4 9% 14% 7% 2	1739
	21st to end	Day	70% 5% 9% 12% 5%	1680
December	1st to 10th	Day	81% 5% 7% 6% 1	2680
	11th to 20th	Day	77% 4 7% 9% 2	3066
	21st to end	Day	83% 3 7% 6% 1	4048
January	1st to 10th	Night	85% 3 5% 6% 2	7718
	11th to 20th	Night	81% 2 8% 6% 2	7680
	21st to end	Night	73% 3 8% 11% 4	8401
February	1st to 10th	Night	69% 5% 9% 13% 4	2730
	11th to 20th	Night	69% 5% 8% 13% 5%	2665
	21st to end	Night	67% 4 8% 13% 7% 1	2086
March	1st to 10th	Night	59% 4 12% 16% 8% 1	5041
	11th to 20th	Night	48% 5% 14% 22% 10% 1	5090
	21st to end	Night	57% 5% 9% 16% 13% 1	5588
April	1st to 10th	Night	58% 4 9% 17% 10% 2	2216
	11th to 20th	Night	50% 6% 11% 18% 12% 2	1978
	21st to end	Night	48% 6% 10% 22% 11% 3	1890
May	1st to 10th	Night	56% 5% 9% 15% 10% 6%	4150
	11th to 20th	Night	47% 6% 10% 24% 12% 1	4087
	21st to end	Night	43% 6% 13% 23% 13% 2	3981
June	1st to 10th	Night	39% 7% 10% 26% 14% 3	1600
	11th to 20th	Night	39% 5% 14% 22% 18% 2	1600
	21st to end	Night	37% 8% 13% 23% 17% 1	1600
July	1st to 10th	Night	37% 6% 11% 25% 19% 2	3646
	11th to 20th	Night	37% 6% 13% 26% 15% 2	4006
	21st to end	Night	34% 6% 12% 21% 26% 1	4297
August	1st to 10th	Night	41% 7% 11% 27% 13% 1	2904
	11th to 20th	Night	45% 5% 11% 28% 10% 1	2902
	21st to end	Night	36% 7% 14% 29% 13% 2	3337
September	1st to 10th	Night	35% 6% 13% 28% 15% 3	2024
	11th to 20th	Night	31% 6% 14% 27% 21% 1	2200
	21st to end	Night	47% 5% 11% 21% 15% 1	2200
October	1st to 10th	Night	36% 5% 9% 26% 22% 1	3886
	11th to 20th	Night	47% 5% 10% 18% 15% 3	3899
	21st to end	Night	44% 4 14% 23% 14% 1	4252
November	1st to 10th	Night	49% 6% 11% 21% 10% 2	2621
	11th to 20th	Night	62% 6% 9% 15% 6% 3	2878
	21st to end	Night	69% 4 10% 14% 3	2940
December	1st to 10th	Night	75% 4 11% 8% 2	4720
	11th to 20th	Night	75% 4 9% 11% 2	5348
	21st to end	Night	76% 5% 9% 9% 1	7150

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	37% 27% 26% 7% 2	311
	11th to 20th	Day	38% 31% 23% 6% 2 1	330
	21st to end	Day	35% 28% 29% 6% 2	363
February	1st to 10th	Day	32% 27% 32% 8% 1	330
	11th to 20th	Day	39% 25% 28% 7% 1	330
	21st to end	Day	41% 26% 27% 5%	273
March	1st to 10th	Day	31% 24% 30% 12% 3	525
	11th to 20th	Day	35% 20% 33% 10% 2 1	540
	21st to end	Day	37% 21% 26% 13% 2	594
April	1st to 10th	Day	32% 24% 27% 13% 4 1	540
	11th to 20th	Day	35% 19% 24% 13% 7% 2	532
	21st to end	Day	29% 19% 31% 14% 6% 1	540
May	1st to 10th	Day	32% 17% 29% 16% 4 2	543
	11th to 20th	Day	24% 15% 30% 21% 8% 2	551
	21st to end	Day	20% 10% 29% 26% 11% 5%	573
June	1st to 10th	Day	20% 13% 34% 22% 9% 2	530
	11th to 20th	Day	20% 11% 30% 24% 12% 3	530
	21st to end	Day	15% 10% 36% 25% 12% 2	530
July	1st to 10th	Day	12% 7% 26% 29% 19% 7%	525
	11th to 20th	Day	15% 7% 29% 29% 14% 6%	524
	21st to end	Day	11% 8% 31% 29% 15% 7%	576
August	1st to 10th	Day	13% 6% 26% 31% 17% 7%	526
	11th to 20th	Day	18% 7% 25% 27% 14% 9%	519
	21st to end	Day	14% 9% 26% 28% 17% 6%	583
September	1st to 10th	Day	16% 10% 25% 23% 18% 7%	530
	11th to 20th	Day	12% 5% 24% 29% 20% 10%	530
	21st to end	Day	23% 11% 29% 21% 12% 5%	530
October	1st to 10th	Day	17% 10% 29% 25% 16% 3	530
	11th to 20th	Day	28% 16% 34% 15% 6% 2	530
	21st to end	Day	35% 18% 30% 14% 2	583
November	1st to 10th	Day	33% 20% 25% 15% 6% 1	371
	11th to 20th	Day	42% 21% 22% 12% 4	250
	21st to end	Day	35% 21% 35% 8%	220
December	1st to 10th	Day	38% 22% 32% 5% 2	220
	11th to 20th	Day	35% 25% 29% 10% 1	220
	21st to end	Day	38% 21% 30% 9% 1	242
January	1st to 10th	Night	31% 25% 31% 11% 3	840
	11th to 20th	Night	35% 23% 28% 13% 2	840
	21st to end	Night	31% 21% 30% 15% 2	924
February	1st to 10th	Night	32% 21% 28% 17% 2	840
	11th to 20th	Night	30% 21% 31% 15% 2	823
	21st to end	Night	33% 20% 31% 14% 1	692
March	1st to 10th	Night	28% 18% 32% 18% 3	840
	11th to 20th	Night	29% 19% 29% 18% 4	840
	21st to end	Night	28% 16% 31% 20% 5%	924
April	1st to 10th	Night	30% 15% 31% 20% 4	840
	11th to 20th	Night	27% 15% 30% 21% 7% 1	734
	21st to end	Night	21% 12% 32% 27% 7%	630
May	1st to 10th	Night	25% 9% 26% 29% 10%	630
	11th to 20th	Night	19% 6% 30% 34% 10% 1	609
	21st to end	Night	14% 7% 29% 29% 18% 2	462
June	1st to 10th	Night	12% 6% 33% 35% 13% 1	400
	11th to 20th	Night	13% 7% 26% 42% 12% 1	400
	21st to end	Night	12% 6% 26% 38% 18%	400
July	1st to 10th	Night	8% 4 18% 43% 23% 3	424
	11th to 20th	Night	11% 4 21% 38% 24% 3	582
	21st to end	Night	11% 4 19% 40% 25% 2	657
August	1st to 10th	Night	9% 3 18% 43% 23% 4	597
	11th to 20th	Night	14% 4 15% 34% 29% 4	594
	21st to end	Night	13% 5% 21% 33% 25% 3	722
September	1st to 10th	Night	15% 7% 17% 35% 23% 4	800
	11th to 20th	Night	13% 3 19% 34% 26% 5%	800
	21st to end	Night	22% 9% 23% 27% 16% 4	800
October	1st to 10th	Night	22% 7% 26% 27% 17% 2	800
	11th to 20th	Night	26% 13% 29% 24% 7% 1	800
	21st to end	Night	34% 13% 30% 20% 3	880
November	1st to 10th	Night	25% 16% 28% 23% 8% 1	820
	11th to 20th	Night	32% 18% 28% 15% 6% 1	840
	21st to end	Night	36% 19% 29% 13% 4	840
December	1st to 10th	Night	36% 20% 28% 13% 3	840
	11th to 20th	Night	32% 26% 28% 12% 2	840
	21st to end	Night	34% 21% 30% 13% 2	924

Page generated at 2026-05-14 01:58:54. Version ac07

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