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 2024-01-22.

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% 12% 4 8% 6% 3 4 4 5% 7% 30%	74682
	Night	17% 13% 5% 8% 6% 3 4 4 4 6% 29%	75249
Transparency	Day	54% 5% 11% 19% 10% 1	74400
	Night	56% 5% 10% 17% 10% 1	75051
Seeing	Day	25% 15% 29% 19% 9% 3	13466
	Night	25% 13% 27% 24% 10% 1	23244

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% 20% 8% 14% 9% 3 4 4 3 4 13%	1672
	11th to 20th	Day	18% 20% 10% 14% 8% 3 4 3 3 4 13%	1710
	21st to end	Day	15% 21% 9% 17% 10% 3 4 3 3 4 11%	1791
February	1st to 10th	Day	18% 20% 8% 14% 10% 3 3 3 2 4 15%	1620
	11th to 20th	Day	16% 15% 10% 13% 10% 3 4 4 4 3 16%	1573
	21st to end	Day	19% 17% 4 14% 6% 2 4 4 3 4 22%	1467
March	1st to 10th	Day	18% 14% 8% 10% 6% 3 3 3 5% 7% 24%	1966
	11th to 20th	Day	17% 15% 7% 8% 4 3 3 3 4 6% 28%	1980
	21st to end	Day	22% 14% 5% 7% 5% 3 3 4 4 4 28%	2178
April	1st to 10th	Day	18% 13% 4 5% 5% 4 3 4 6% 7% 32%	2059
	11th to 20th	Day	21% 12% 3 6% 5% 3 3 5% 4 6% 33%	2230
	21st to end	Day	22% 11% 4 6% 5% 3 3 3 4 5% 34%	2340
May	1st to 10th	Day	17% 11% 3 7% 6% 4 5% 5% 5% 6% 31%	2340
	11th to 20th	Day	19% 8% 3 6% 6% 4 4 5% 6% 7% 32%	2301
	21st to end	Day	12% 6% 3 5% 6% 4 6% 5% 6% 8% 40%	2695
June	1st to 10th	Day	16% 7% 3 6% 5% 3 6% 5% 6% 8% 36%	2520
	11th to 20th	Day	14% 7% 3 6% 6% 4 5% 5% 5% 8% 38%	2520
	21st to end	Day	14% 5% 2 5% 5% 3 4 5% 6% 10% 39%	2520
July	1st to 10th	Day	11% 5% 2 5% 5% 3 5% 5% 6% 9% 44%	2484
	11th to 20th	Day	13% 5% 2 5% 6% 3 5% 5% 6% 10% 40%	2340
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 5% 6% 8% 40%	2547
August	1st to 10th	Day	10% 6% 3 6% 6% 3 6% 5% 7% 9% 40%	2327
	11th to 20th	Day	11% 6% 3 6% 7% 5% 6% 6% 7% 8% 34%	2303
	21st to end	Day	13% 6% 2 6% 5% 4 5% 5% 6% 9% 39%	2499
September	1st to 10th	Day	16% 7% 2 6% 6% 3 5% 4 6% 8% 37%	2137
	11th to 20th	Day	13% 6% 3 5% 5% 3 5% 4 5% 8% 41%	1980
	21st to end	Day	19% 7% 3 7% 6% 2 4 5% 5% 7% 36%	1980
October	1st to 10th	Day	17% 6% 2 6% 6% 3 4 6% 5% 7% 35%	1818
	11th to 20th	Day	24% 9% 3 7% 6% 3 4 4 5% 6% 29%	1800
	21st to end	Day	28% 12% 4 7% 6% 3 4 5% 4 5% 22%	1980
November	1st to 10th	Day	14% 13% 4 7% 5% 4 4 5% 5% 6% 33%	1709
	11th to 20th	Day	18% 20% 4 8% 6% 2 4 3 4 6% 23%	1574
	21st to end	Day	20% 23% 6% 8% 5% 3 5% 3 5% 6% 16%	1520
December	1st to 10th	Day	18% 25% 10% 10% 6% 3 4 4 3 3 13%	1520
	11th to 20th	Day	17% 22% 9% 14% 5% 2 4 4 3 6% 13%	1910
	21st to end	Day	25% 25% 8% 11% 6% 3 3 2 3 3 10%	2772
January	1st to 10th	Night	20% 19% 9% 14% 8% 3 4 3 3 3 14%	2488
	11th to 20th	Night	20% 19% 9% 14% 8% 3 3 3 3 3 15%	2470
	21st to end	Night	15% 22% 9% 12% 10% 4 4 4 3 4 14%	2599
February	1st to 10th	Night	20% 18% 6% 12% 9% 3 4 4 4 4 16%	2340
	11th to 20th	Night	17% 16% 7% 13% 7% 3 5% 4 4 4 19%	2273
	21st to end	Night	20% 13% 7% 13% 6% 3 4 4 4 5% 20%	1785
March	1st to 10th	Night	16% 13% 6% 10% 8% 3 4 5% 4 5% 26%	1992
	11th to 20th	Night	18% 12% 6% 8% 5% 2 4 3 4 7% 32%	1980
	21st to end	Night	19% 14% 6% 7% 6% 3 4 4 4 4 29%	2178
April	1st to 10th	Night	18% 14% 4 6% 6% 3 4 4 4 6% 31%	1900
	11th to 20th	Night	18% 11% 3 5% 5% 3 5% 5% 5% 7% 33%	1693
	21st to end	Night	15% 9% 4 6% 6% 4 4 6% 5% 7% 34%	1620
May	1st to 10th	Night	19% 8% 4 6% 6% 4 5% 4 4 7% 33%	1620
	11th to 20th	Night	15% 10% 4 7% 5% 3 4 4 4 9% 36%	1592
	21st to end	Night	12% 4 2 5% 5% 3 3 4 6% 11% 45%	1576
June	1st to 10th	Night	9% 6% 2 7% 6% 3 5% 6% 6% 8% 42%	1440
	11th to 20th	Night	10% 5% 3 7% 5% 3 6% 5% 5% 9% 43%	1440
	21st to end	Night	13% 5% 2 5% 5% 3 5% 5% 5% 9% 43%	1440
July	1st to 10th	Night	8% 4 2 4 6% 4 5% 4 6% 9% 49%	1471
	11th to 20th	Night	9% 5% 2 5% 5% 3 5% 5% 5% 10% 46%	1620
	21st to end	Night	9% 5% 2 5% 5% 3 6% 6% 6% 9% 44%	1771
August	1st to 10th	Night	9% 4 1 6% 5% 2 5% 5% 6% 8% 48%	1611
	11th to 20th	Night	10% 5% 2 5% 6% 4 4 5% 6% 8% 43%	1598
	21st to end	Night	11% 5% 2 5% 4 3 5% 5% 6% 8% 45%	1837
September	1st to 10th	Night	14% 6% 2 4 4 3 5% 5% 5% 8% 45%	1821
	11th to 20th	Night	13% 5% 2 5% 4 2 4 5% 5% 7% 49%	1980
	21st to end	Night	17% 6% 2 6% 6% 3 5% 4 4 7% 39%	1980
October	1st to 10th	Night	18% 6% 2 5% 4 3 4 3 5% 7% 41%	2141
	11th to 20th	Night	20% 9% 4 7% 6% 4 5% 5% 5% 6% 31%	2160
	21st to end	Night	28% 10% 3 7% 5% 3 4 4 4 5% 27%	2376
November	1st to 10th	Night	17% 11% 4 7% 5% 3 4 4 5% 6% 35%	2365
	11th to 20th	Night	17% 17% 5% 8% 6% 4 4 4 4 6% 24%	2603
	21st to end	Night	21% 20% 6% 8% 5% 3 4 4 4 5% 20%	2660
December	1st to 10th	Night	22% 23% 10% 8% 5% 3 4 3 3 4 15%	2660
	11th to 20th	Night	18% 22% 9% 12% 6% 3 4 3 3 4 16%	3285
	21st to end	Night	24% 24% 8% 9% 7% 4 4 4 3 4 9%	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	76% 4 8% 9% 3	1673
	11th to 20th	Day	77% 4 9% 9% 2	1710
	21st to end	Day	79% 4 6% 9% 3	1791
February	1st to 10th	Day	76% 2 7% 10% 4	1620
	11th to 20th	Day	73% 4 7% 11% 5%	1582
	21st to end	Day	66% 4 9% 13% 5% 2	1467
March	1st to 10th	Day	59% 6% 11% 19% 5%	1966
	11th to 20th	Day	59% 4 10% 17% 9% 2	1980
	21st to end	Day	60% 4 6% 19% 9% 2	2178
April	1st to 10th	Day	53% 4 13% 18% 12% 1	2059
	11th to 20th	Day	52% 4 10% 19% 12% 2	2230
	21st to end	Day	53% 4 10% 20% 10% 3	2340
May	1st to 10th	Day	52% 6% 10% 21% 10% 2	2340
	11th to 20th	Day	50% 5% 11% 19% 13% 3	2305
	21st to end	Day	42% 6% 14% 24% 12% 1	2695
June	1st to 10th	Day	44% 6% 12% 25% 12% 1	2520
	11th to 20th	Day	44% 5% 14% 22% 13% 1	2520
	21st to end	Day	39% 7% 12% 25% 15% 1	2520
July	1st to 10th	Day	37% 6% 13% 25% 17% 2	2416
	11th to 20th	Day	40% 5% 13% 26% 15% 1	2271
	21st to end	Day	40% 7% 13% 24% 15% 2	2405
August	1st to 10th	Day	39% 5% 16% 27% 12%	2314
	11th to 20th	Day	44% 7% 16% 23% 9% 2	2303
	21st to end	Day	40% 6% 13% 24% 15% 2	2499
September	1st to 10th	Day	45% 6% 13% 21% 13% 2	2137
	11th to 20th	Day	40% 5% 14% 25% 14% 1	1980
	21st to end	Day	47% 6% 11% 23% 13% 1	1980
October	1st to 10th	Day	46% 6% 14% 21% 13% 1	1818
	11th to 20th	Day	55% 6% 13% 19% 7% 1	1800
	21st to end	Day	63% 4 11% 14% 7% 1	1980
November	1st to 10th	Day	52% 6% 10% 19% 12% 1	1709
	11th to 20th	Day	63% 5% 10% 14% 7% 2	1574
	21st to end	Day	69% 5% 10% 12% 5%	1520
December	1st to 10th	Day	76% 5% 7% 10% 2	1520
	11th to 20th	Day	75% 5% 8% 10% 2	1906
	21st to end	Day	82% 3 7% 7% 1	2772
January	1st to 10th	Night	76% 4 7% 9% 4	2488
	11th to 20th	Night	75% 4 9% 9% 2	2470
	21st to end	Night	75% 4 7% 10% 3 1	2599
February	1st to 10th	Night	72% 4 9% 11% 3	2340
	11th to 20th	Night	69% 5% 8% 13% 5%	2275
	21st to end	Night	67% 4 8% 13% 7% 1	1785
March	1st to 10th	Night	59% 6% 8% 19% 8%	1992
	11th to 20th	Night	54% 4 10% 19% 11% 1	1980
	21st to end	Night	59% 4 5% 17% 13% 2	2178
April	1st to 10th	Night	55% 4 10% 19% 10% 2	1900
	11th to 20th	Night	49% 5% 12% 18% 13% 3	1693
	21st to end	Night	49% 5% 10% 21% 11% 4	1620
May	1st to 10th	Night	51% 4 10% 19% 11% 3	1620
	11th to 20th	Night	47% 5% 10% 20% 15% 3	1593
	21st to end	Night	34% 5% 18% 27% 14% 2	1577
June	1st to 10th	Night	39% 7% 10% 27% 14% 2	1440
	11th to 20th	Night	39% 5% 13% 22% 19% 3	1440
	21st to end	Night	37% 7% 13% 23% 17% 1	1440
July	1st to 10th	Night	34% 7% 9% 27% 19% 4	1430
	11th to 20th	Night	33% 6% 13% 25% 19% 3	1566
	21st to end	Night	36% 7% 14% 24% 17% 2	1672
August	1st to 10th	Night	33% 7% 12% 31% 15% 2	1600
	11th to 20th	Night	38% 6% 15% 28% 12% 1	1598
	21st to end	Night	35% 7% 13% 26% 16% 3	1837
September	1st to 10th	Night	37% 6% 14% 26% 14% 3	1821
	11th to 20th	Night	34% 6% 14% 25% 20% 1	1980
	21st to end	Night	45% 5% 12% 22% 15% 1	1980
October	1st to 10th	Night	43% 5% 11% 22% 17% 1	2141
	11th to 20th	Night	52% 6% 12% 18% 11% 1	2160
	21st to end	Night	59% 6% 9% 16% 8% 2	2376
November	1st to 10th	Night	50% 6% 12% 20% 10% 3	2365
	11th to 20th	Night	61% 6% 8% 16% 6% 3	2603
	21st to end	Night	68% 4 10% 14% 4	2660
December	1st to 10th	Night	75% 3 9% 9% 3	2660
	11th to 20th	Night	73% 5% 10% 10% 2	3288
	21st to end	Night	79% 5% 9% 7% 1	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	37% 25% 26% 9% 3	254
	11th to 20th	Day	34% 30% 25% 7% 3 1	270
	21st to end	Day	32% 29% 30% 6% 3	267
February	1st to 10th	Day	37% 26% 32% 6%	240
	11th to 20th	Day	38% 27% 30% 5%	240
	21st to end	Day	43% 25% 26% 5%	198
March	1st to 10th	Day	32% 23% 29% 13% 3	406
	11th to 20th	Day	31% 20% 35% 11% 3 1	420
	21st to end	Day	36% 21% 24% 15% 3	462
April	1st to 10th	Day	29% 25% 27% 14% 5% 1	420
	11th to 20th	Day	33% 18% 24% 14% 8% 2	412
	21st to end	Day	29% 19% 31% 13% 6% 1	420
May	1st to 10th	Day	31% 16% 29% 17% 5% 2	423
	11th to 20th	Day	24% 15% 29% 22% 9% 2	447
	21st to end	Day	17% 9% 29% 27% 12% 5%	485
June	1st to 10th	Day	18% 11% 36% 22% 10% 3	450
	11th to 20th	Day	20% 11% 30% 23% 13% 3	450
	21st to end	Day	15% 10% 37% 26% 11% 2	450
July	1st to 10th	Day	12% 6% 26% 29% 19% 8%	445
	11th to 20th	Day	17% 5% 28% 30% 15% 6%	444
	21st to end	Day	10% 9% 32% 29% 14% 7%	488
August	1st to 10th	Day	13% 6% 26% 30% 17% 8%	446
	11th to 20th	Day	17% 6% 26% 26% 14% 10%	439
	21st to end	Day	15% 9% 25% 27% 18% 6%	495
September	1st to 10th	Day	17% 8% 26% 25% 16% 8%	450
	11th to 20th	Day	14% 6% 25% 27% 19% 10%	450
	21st to end	Day	21% 11% 30% 21% 13% 5%	450
October	1st to 10th	Day	18% 10% 29% 24% 15% 4	450
	11th to 20th	Day	30% 15% 35% 14% 5% 1	450
	21st to end	Day	38% 17% 30% 13% 2	495
November	1st to 10th	Day	30% 19% 26% 16% 7% 2	307
	11th to 20th	Day	40% 20% 22% 13% 4	205
	21st to end	Day	33% 22% 37% 9%	180
December	1st to 10th	Day	38% 24% 30% 5% 3 1	180
	11th to 20th	Day	33% 26% 31% 9% 1	180
	21st to end	Day	37% 22% 31% 9% 1	198
January	1st to 10th	Night	31% 24% 31% 11% 3	760
	11th to 20th	Night	35% 20% 29% 14% 2	760
	21st to end	Night	29% 21% 32% 16% 3	800
February	1st to 10th	Night	33% 21% 28% 15% 2	720
	11th to 20th	Night	30% 21% 31% 16% 2	703
	21st to end	Night	33% 21% 30% 14% 1	592
March	1st to 10th	Night	27% 18% 33% 19% 3	720
	11th to 20th	Night	28% 18% 30% 19% 5% 1	720
	21st to end	Night	27% 16% 30% 22% 5% 1	792
April	1st to 10th	Night	27% 16% 32% 22% 4	720
	11th to 20th	Night	27% 13% 30% 21% 8% 1	629
	21st to end	Night	20% 11% 34% 27% 7% 1	540
May	1st to 10th	Night	24% 9% 26% 29% 11%	540
	11th to 20th	Night	19% 5% 30% 34% 10% 1	531
	21st to end	Night	12% 6% 31% 29% 20% 2	416
June	1st to 10th	Night	11% 5% 33% 36% 14% 1	360
	11th to 20th	Night	13% 5% 25% 44% 12% 1	360
	21st to end	Night	13% 6% 26% 39% 16%	360
July	1st to 10th	Night	8% 4 18% 42% 24% 3	380
	11th to 20th	Night	11% 3 21% 37% 24% 3	522
	21st to end	Night	11% 4 19% 40% 24% 2	591
August	1st to 10th	Night	9% 3 17% 42% 24% 4	537
	11th to 20th	Night	13% 3 15% 34% 30% 4	534
	21st to end	Night	13% 4 22% 31% 26% 3	649
September	1st to 10th	Night	17% 7% 16% 34% 23% 4	720
	11th to 20th	Night	14% 3 20% 33% 24% 5%	720
	21st to end	Night	21% 9% 24% 26% 16% 4	720
October	1st to 10th	Night	23% 7% 26% 25% 16% 2	720
	11th to 20th	Night	27% 13% 28% 24% 6% 1	720
	21st to end	Night	35% 13% 29% 19% 3	792
November	1st to 10th	Night	24% 15% 27% 23% 9% 1	740
	11th to 20th	Night	31% 18% 28% 16% 6% 1	760
	21st to end	Night	35% 18% 29% 14% 4	760
December	1st to 10th	Night	37% 19% 27% 13% 4	760
	11th to 20th	Night	32% 25% 28% 13% 3	760
	21st to end	Night	34% 21% 30% 13% 2	836

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