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 2025-01-22.

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	17% 13% 4 9% 5% 4 4 3 5% 6% 29%	104929
	Night	17% 14% 5% 9% 5% 4 4 3 4 6% 28%	104362
Transparency	Day	53% 5% 11% 19% 10% 1	108589
	Night	56% 5% 11% 18% 10% 1	108842
Seeing	Day	25% 15% 29% 19% 9% 3	14761
	Night	25% 14% 27% 24% 10% 1	24523

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	18% 25% 10% 16% 5% 3 3 2 4 4 10%	2865
	11th to 20th	Day	12% 25% 9% 17% 7% 4 3 2 3 4 14%	2930
	21st to end	Day	25% 22% 10% 17% 6% 3 3 2 2 3 8%	3133
February	1st to 10th	Day	17% 22% 6% 15% 9% 3 3 2 2 4 17%	1710
	11th to 20th	Day	15% 17% 9% 15% 9% 3 5% 3 4 3 17%	1663
	21st to end	Day	19% 17% 4 14% 6% 3 4 3 4 4 22%	1556
March	1st to 10th	Day	21% 13% 7% 9% 4 4 3 3 5% 6% 25%	3421
	11th to 20th	Day	12% 19% 7% 9% 4 4 3 2 4 5% 30%	3480
	21st to end	Day	22% 14% 5% 9% 4 3 3 3 4 4 29%	3815
April	1st to 10th	Day	18% 15% 3 6% 4 5% 3 3 6% 6% 31%	2174
	11th to 20th	Day	21% 12% 3 6% 4 3 3 4 4 5% 33%	2356
	21st to end	Day	21% 12% 3 7% 4 3 3 3 4 5% 34%	2470
May	1st to 10th	Day	20% 9% 4 8% 5% 4 4 4 5% 6% 31%	4082
	11th to 20th	Day	20% 10% 3 7% 5% 5% 4 3 6% 7% 31%	4081
	21st to end	Day	12% 5% 2 7% 5% 5% 5% 3 6% 7% 42%	4779
June	1st to 10th	Day	15% 7% 2 7% 4 4 5% 5% 6% 8% 35%	2660
	11th to 20th	Day	13% 7% 3 7% 5% 5% 5% 4 6% 8% 38%	2660
	21st to end	Day	14% 5% 2 6% 4 5% 4 4 7% 10% 38%	2660
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 4 7% 10% 41%	4362
	11th to 20th	Day	11% 5% 2 6% 4 5% 4 4 6% 10% 42%	4120
	21st to end	Day	11% 6% 2 7% 5% 6% 5% 4 6% 8% 41%	4466
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 9% 35%	4104
	11th to 20th	Day	14% 7% 3 8% 5% 6% 5% 4 8% 9% 32%	4044
	21st to end	Day	11% 6% 2 7% 4 5% 5% 4 6% 9% 41%	4387
September	1st to 10th	Day	16% 7% 2 6% 5% 4 5% 3 6% 8% 38%	2255
	11th to 20th	Day	12% 6% 3 6% 4 5% 5% 3 6% 8% 43%	2090
	21st to end	Day	20% 8% 3 8% 5% 3 5% 3 4 7% 34%	2090
October	1st to 10th	Day	17% 6% 2 7% 5% 4 5% 5% 6% 7% 36%	1919
	11th to 20th	Day	23% 9% 3 8% 5% 4 4 4 5% 6% 30%	1900
	21st to end	Day	26% 13% 4 8% 4 4 5% 3 4 6% 24%	2090
November	1st to 10th	Day	14% 13% 4 8% 5% 5% 4 4 5% 6% 33%	1801
	11th to 20th	Day	17% 21% 4 9% 5% 4 4 3 4 7% 23%	1656
	21st to end	Day	19% 24% 5% 9% 5% 5% 4 3 5% 5% 16%	1600
December	1st to 10th	Day	17% 27% 13% 12% 5% 4 3 3 3 3 10%	2600
	11th to 20th	Day	21% 26% 7% 12% 6% 3 3 3 3 5% 11%	2990
	21st to end	Day	24% 25% 7% 15% 5% 5% 3 2 3 3 9%	3960
January	1st to 10th	Night	17% 26% 11% 17% 5% 4 3 2 3 3 10%	4295
	11th to 20th	Night	15% 22% 10% 19% 5% 3 4 3 3 4 12%	4250
	21st to end	Night	26% 22% 8% 14% 5% 3 3 2 2 3 11%	4546
February	1st to 10th	Night	19% 19% 5% 13% 7% 5% 4 3 4 4 18%	2470
	11th to 20th	Night	16% 18% 6% 13% 7% 5% 4 4 4 4 19%	2403
	21st to end	Night	20% 15% 6% 14% 5% 4 4 4 4 5% 21%	1894
March	1st to 10th	Night	21% 15% 3 8% 5% 3 3 3 3 5% 29%	3430
	11th to 20th	Night	17% 15% 7% 8% 4 3 3 2 4 6% 31%	3480
	21st to end	Night	18% 14% 5% 8% 4 4 3 3 3 4 34%	3817
April	1st to 10th	Night	18% 15% 4 7% 6% 4 4 3 4 5% 30%	2005
	11th to 20th	Night	19% 11% 3 6% 4 4 5% 4 6% 7% 32%	1788
	21st to end	Night	15% 10% 4 6% 6% 5% 4 5% 5% 7% 34%	1710
May	1st to 10th	Night	24% 10% 3 6% 4 4 4 3 4 7% 30%	2813
	11th to 20th	Night	15% 10% 3 7% 4 3 4 3 5% 9% 36%	2812
	21st to end	Night	13% 4 1 5% 4 3 3 3 6% 11% 46%	2772
June	1st to 10th	Night	10% 6% 2 8% 6% 4 5% 5% 6% 7% 41%	1520
	11th to 20th	Night	10% 5% 3 8% 5% 5% 5% 4 6% 9% 43%	1520
	21st to end	Night	12% 6% 2 5% 5% 5% 5% 4 5% 9% 42%	1520
July	1st to 10th	Night	11% 7% 2 6% 5% 4 4 3 6% 9% 43%	2579
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 6% 9% 46%	2840
	21st to end	Night	8% 6% 2 6% 5% 5% 5% 5% 6% 8% 45%	3087
August	1st to 10th	Night	10% 8% 3 8% 5% 4 5% 4 6% 7% 40%	2825
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 3 4 6% 39%	2785
	21st to end	Night	9% 5% 3 6% 4 5% 5% 5% 7% 8% 43%	3235
September	1st to 10th	Night	14% 6% 2 5% 3 4 4 4 6% 7% 46%	1923
	11th to 20th	Night	12% 5% 2 5% 4 3 4 4 5% 6% 50%	2090
	21st to end	Night	18% 7% 2 7% 6% 4 5% 3 4 6% 37%	2090
October	1st to 10th	Night	18% 6% 2 6% 3 4 3 3 5% 7% 42%	2260
	11th to 20th	Night	19% 10% 4 7% 5% 4 5% 3 5% 5% 31%	2280
	21st to end	Night	27% 10% 3 7% 4 4 3 4 4 5% 28%	2508
November	1st to 10th	Night	16% 12% 3 7% 4 4 4 3 5% 6% 35%	2493
	11th to 20th	Night	18% 19% 4 9% 5% 5% 4 3 4 6% 23%	2741
	21st to end	Night	20% 22% 5% 8% 5% 4 4 3 4 5% 19%	2800
December	1st to 10th	Night	16% 24% 12% 11% 5% 5% 4 3 4 4 14%	4580
	11th to 20th	Night	19% 25% 9% 12% 5% 3 3 2 3 4 14%	5205
	21st to end	Night	21% 24% 7% 12% 6% 5% 4 3 4 5% 12%	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	77% 5% 8% 7% 2	2866
	11th to 20th	Day	77% 3 8% 10% 2	2930
	21st to end	Day	85% 3 5% 5% 2	3133
February	1st to 10th	Day	74% 3 7% 11% 5%	1710
	11th to 20th	Day	71% 5% 6% 11% 6%	1672
	21st to end	Day	65% 4 10% 14% 5% 2	1556
March	1st to 10th	Day	60% 5% 10% 22% 4	3421
	11th to 20th	Day	57% 5% 16% 17% 5% 1	3480
	21st to end	Day	58% 5% 8% 18% 10% 1	3815
April	1st to 10th	Day	53% 4 13% 17% 12% 1	2174
	11th to 20th	Day	52% 4 10% 19% 12% 2	2356
	21st to end	Day	53% 4 10% 20% 10% 3	2470
May	1st to 10th	Day	53% 5% 8% 24% 9% 1	4120
	11th to 20th	Day	50% 6% 12% 22% 8% 1	4085
	21st to end	Day	40% 6% 13% 22% 14% 4	4793
June	1st to 10th	Day	45% 6% 12% 25% 12% 1	2660
	11th to 20th	Day	43% 6% 14% 22% 14% 1	2660
	21st to end	Day	40% 7% 12% 25% 15% 1	2660
July	1st to 10th	Day	37% 6% 14% 25% 15% 3	4294
	11th to 20th	Day	36% 6% 12% 28% 17% 1	4051
	21st to end	Day	40% 6% 14% 22% 17% 1	4324
August	1st to 10th	Day	44% 6% 15% 23% 12%	4091
	11th to 20th	Day	45% 6% 13% 28% 7% 1	4083
	21st to end	Day	38% 6% 13% 29% 13% 1	4387
September	1st to 10th	Day	43% 6% 13% 22% 14% 2	2255
	11th to 20th	Day	39% 5% 13% 25% 16% 1	2090
	21st to end	Day	49% 5% 11% 22% 12% 1	2090
October	1st to 10th	Day	36% 5% 15% 25% 18% 1	3192
	11th to 20th	Day	47% 5% 13% 19% 13% 3	3140
	21st to end	Day	46% 5% 14% 26% 9%	3428
November	1st to 10th	Day	51% 6% 10% 20% 12% 1	1801
	11th to 20th	Day	62% 5% 9% 14% 8% 2	1656
	21st to end	Day	70% 5% 9% 11% 5%	1600
December	1st to 10th	Day	81% 5% 7% 6% 1	2600
	11th to 20th	Day	78% 4 7% 9% 2	2986
	21st to end	Day	83% 3 7% 7% 1	3960
January	1st to 10th	Night	81% 4 6% 7% 2	4295
	11th to 20th	Night	77% 3 10% 8% 2	4250
	21st to end	Night	81% 3 7% 7% 2	4546
February	1st to 10th	Night	70% 5% 9% 12% 4	2470
	11th to 20th	Night	68% 5% 8% 13% 5%	2405
	21st to end	Night	67% 4 8% 13% 7% 1	1894
March	1st to 10th	Night	58% 4 11% 18% 8%	3430
	11th to 20th	Night	54% 5% 15% 17% 8% 1	3480
	21st to end	Night	53% 6% 9% 18% 13% 1	3817
April	1st to 10th	Night	56% 4 9% 18% 11% 2	2005
	11th to 20th	Night	49% 6% 12% 18% 13% 3	1788
	21st to end	Night	48% 6% 10% 22% 11% 3	1710
May	1st to 10th	Night	54% 4 10% 19% 10% 3	2840
	11th to 20th	Night	46% 6% 12% 24% 12% 2	2813
	21st to end	Night	32% 6% 15% 27% 17% 2	2779
June	1st to 10th	Night	39% 7% 10% 27% 14% 2	1520
	11th to 20th	Night	38% 5% 14% 22% 19% 3	1520
	21st to end	Night	38% 7% 13% 23% 17% 1	1520
July	1st to 10th	Night	38% 6% 11% 24% 18% 3	2538
	11th to 20th	Night	34% 6% 12% 29% 17% 3	2786
	21st to end	Night	36% 7% 13% 21% 22% 1	2988
August	1st to 10th	Night	42% 7% 11% 27% 13% 1	2814
	11th to 20th	Night	46% 5% 11% 28% 9% 1	2812
	21st to end	Night	36% 7% 14% 28% 14% 2	3235
September	1st to 10th	Night	36% 6% 13% 27% 15% 3	1923
	11th to 20th	Night	33% 6% 13% 25% 21% 1	2090
	21st to end	Night	47% 5% 11% 21% 15% 1	2090
October	1st to 10th	Night	37% 5% 9% 26% 22% 1	3767
	11th to 20th	Night	48% 6% 10% 18% 15% 3	3779
	21st to end	Night	44% 5% 14% 23% 14% 1	4120
November	1st to 10th	Night	50% 6% 11% 21% 10% 2	2493
	11th to 20th	Night	62% 6% 8% 15% 6% 3	2741
	21st to end	Night	68% 4 10% 14% 3	2800
December	1st to 10th	Night	76% 4 11% 7% 2	4580
	11th to 20th	Night	75% 4 8% 11% 2	5208
	21st to end	Night	76% 5% 9% 9% 1	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	35% 28% 26% 8% 2	283
	11th to 20th	Day	35% 31% 24% 7% 2 1	300
	21st to end	Day	34% 27% 30% 6% 3	300
February	1st to 10th	Day	34% 26% 32% 8%	270
	11th to 20th	Day	37% 26% 29% 7% 1	270
	21st to end	Day	44% 24% 27% 5%	225
March	1st to 10th	Day	32% 22% 30% 13% 3	446
	11th to 20th	Day	32% 19% 35% 11% 2 1	460
	21st to end	Day	37% 21% 25% 14% 3	506
April	1st to 10th	Day	30% 24% 27% 14% 5% 1	460
	11th to 20th	Day	35% 19% 23% 14% 7% 2	452
	21st to end	Day	29% 19% 31% 13% 6% 1	460
May	1st to 10th	Day	31% 16% 30% 17% 4 2	463
	11th to 20th	Day	23% 14% 30% 21% 9% 2	487
	21st to end	Day	16% 9% 30% 27% 12% 5%	529
June	1st to 10th	Day	20% 12% 34% 23% 9% 2	490
	11th to 20th	Day	19% 11% 31% 24% 13% 3	490
	21st to end	Day	16% 10% 37% 25% 10% 2	490
July	1st to 10th	Day	12% 7% 26% 29% 18% 8%	485
	11th to 20th	Day	16% 6% 29% 29% 14% 6%	484
	21st to end	Day	11% 8% 31% 28% 15% 7%	532
August	1st to 10th	Day	14% 7% 26% 29% 16% 7%	486
	11th to 20th	Day	18% 7% 27% 26% 14% 9%	479
	21st to end	Day	14% 8% 25% 28% 18% 6%	539
September	1st to 10th	Day	16% 9% 26% 24% 17% 7%	490
	11th to 20th	Day	13% 5% 25% 28% 19% 10%	490
	21st to end	Day	24% 11% 29% 21% 12% 4	490
October	1st to 10th	Day	18% 10% 29% 24% 15% 3	490
	11th to 20th	Day	29% 15% 34% 14% 6% 2	490
	21st to end	Day	36% 17% 30% 14% 2	539
November	1st to 10th	Day	31% 19% 26% 15% 7% 1	339
	11th to 20th	Day	39% 21% 24% 12% 4	227
	21st to end	Day	34% 21% 37% 9%	200
December	1st to 10th	Day	37% 24% 32% 5% 3 1	200
	11th to 20th	Day	35% 25% 30% 10% 1	200
	21st to end	Day	35% 22% 32% 9% 1	220
January	1st to 10th	Night	30% 25% 31% 10% 3	800
	11th to 20th	Night	35% 22% 28% 13% 2	800
	21st to end	Night	31% 20% 31% 16% 3	841
February	1st to 10th	Night	33% 21% 28% 16% 2	760
	11th to 20th	Night	30% 21% 31% 16% 2	743
	21st to end	Night	33% 20% 30% 15% 1	628
March	1st to 10th	Night	28% 18% 32% 19% 3	760
	11th to 20th	Night	28% 19% 29% 19% 5% 1	760
	21st to end	Night	27% 16% 30% 21% 5%	836
April	1st to 10th	Night	28% 15% 32% 21% 4	760
	11th to 20th	Night	27% 13% 31% 21% 7% 1	664
	21st to end	Night	21% 11% 33% 27% 7% 1	570
May	1st to 10th	Night	24% 9% 26% 29% 11%	570
	11th to 20th	Night	19% 6% 29% 34% 11% 1	561
	21st to end	Night	12% 6% 30% 30% 19% 2	439
June	1st to 10th	Night	12% 6% 32% 36% 13% 1	380
	11th to 20th	Night	13% 6% 25% 44% 12% 1	380
	21st to end	Night	12% 7% 26% 38% 17%	380
July	1st to 10th	Night	8% 5% 18% 42% 23% 3	402
	11th to 20th	Night	11% 3 21% 37% 24% 3	552
	21st to end	Night	10% 4 19% 41% 25% 2	624
August	1st to 10th	Night	10% 3 18% 42% 23% 4	567
	11th to 20th	Night	14% 4 16% 33% 30% 4	564
	21st to end	Night	13% 4 22% 32% 26% 3	686
September	1st to 10th	Night	16% 7% 17% 34% 23% 4	760
	11th to 20th	Night	14% 3 20% 34% 25% 5%	760
	21st to end	Night	22% 9% 23% 26% 15% 4	760
October	1st to 10th	Night	23% 7% 26% 26% 16% 2	760
	11th to 20th	Night	27% 13% 28% 24% 7% 1	760
	21st to end	Night	34% 13% 29% 20% 3	836
November	1st to 10th	Night	24% 16% 28% 23% 8% 1	780
	11th to 20th	Night	32% 18% 28% 16% 6% 1	800
	21st to end	Night	35% 18% 29% 13% 4	800
December	1st to 10th	Night	37% 19% 28% 13% 4	800
	11th to 20th	Night	32% 26% 28% 12% 2	800
	21st to end	Night	34% 21% 30% 13% 2	880

Page generated at 2025-01-19 03:06:43. Version ac07

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