Deep Woods Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deep Woods Observatory clear sky chart from 2005-11-06 to 2024-03-06.

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	14% 10% 4 8% 6% 4 5% 5% 5% 7% 32%	78387
	Night	14% 11% 5% 8% 6% 3 5% 4 5% 7% 34%	81175
Transparency	Day	49% 8% 13% 20% 10% 1	78093
	Night	49% 8% 13% 20% 9% 1	81003
Seeing	Day	20% 17% 33% 19% 8% 3	15014
	Night	19% 14% 33% 25% 8% 1	25119

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	12% 13% 7% 13% 7% 5% 5% 5% 6% 6% 21%	2527
	11th to 20th	Day	11% 15% 5% 12% 9% 4 7% 6% 6% 6% 20%	2530
	21st to end	Day	13% 17% 9% 14% 7% 3 3 4 4 5% 20%	2783
February	1st to 10th	Day	9% 13% 5% 9% 7% 4 5% 5% 6% 7% 30%	1647
	11th to 20th	Day	11% 11% 4 10% 7% 4 5% 5% 5% 6% 31%	1771
	21st to end	Day	13% 13% 4 9% 7% 4 4 4 5% 8% 28%	1570
March	1st to 10th	Day	12% 12% 4 8% 7% 3 4 4 6% 5% 33%	1848
	11th to 20th	Day	11% 12% 5% 8% 5% 3 3 4 5% 7% 36%	1856
	21st to end	Day	16% 13% 5% 8% 7% 4 5% 4 4 6% 27%	2376
April	1st to 10th	Day	16% 14% 5% 8% 6% 3 4 4 5% 8% 27%	2160
	11th to 20th	Day	20% 12% 5% 7% 6% 3 4 4 4 5% 30%	2134
	21st to end	Day	18% 12% 4 7% 6% 3 5% 5% 4 6% 31%	2322
May	1st to 10th	Day	17% 10% 4 7% 7% 3 5% 4 5% 7% 30%	2456
	11th to 20th	Day	16% 7% 4 8% 7% 4 4 5% 5% 6% 35%	2479
	21st to end	Day	13% 6% 3 7% 7% 3 6% 4 7% 9% 35%	2725
June	1st to 10th	Day	12% 6% 3 5% 6% 3 5% 5% 5% 8% 41%	2520
	11th to 20th	Day	15% 6% 3 6% 6% 3 5% 5% 7% 8% 36%	2520
	21st to end	Day	13% 6% 3 7% 6% 3 5% 6% 7% 9% 35%	2520
July	1st to 10th	Day	8% 4 2 4 6% 5% 5% 5% 8% 11% 43%	2520
	11th to 20th	Day	9% 5% 2 5% 6% 5% 6% 5% 6% 8% 42%	2520
	21st to end	Day	9% 5% 2 5% 6% 3 6% 6% 7% 8% 42%	2743
August	1st to 10th	Day	10% 5% 3 5% 7% 4 6% 6% 6% 9% 39%	2507
	11th to 20th	Day	13% 5% 3 6% 6% 4 5% 5% 6% 7% 40%	2314
	21st to end	Day	15% 6% 2 5% 6% 3 5% 4 4 8% 43%	2376
September	1st to 10th	Day	14% 6% 3 6% 6% 3 5% 4 5% 6% 43%	2160
	11th to 20th	Day	14% 6% 3 6% 5% 3 5% 6% 6% 7% 39%	2073
	21st to end	Day	15% 9% 4 7% 6% 4 6% 4 5% 8% 32%	1980
October	1st to 10th	Day	19% 9% 3 6% 6% 3 4 5% 5% 7% 35%	1872
	11th to 20th	Day	21% 11% 4 7% 7% 4 6% 4 6% 6% 24%	1745
	21st to end	Day	21% 15% 4 8% 6% 3 3 4 4 5% 27%	1782
November	1st to 10th	Day	14% 10% 4 7% 6% 3 4 6% 5% 7% 32%	1672
	11th to 20th	Day	16% 13% 7% 10% 7% 4 5% 5% 5% 6% 24%	1642
	21st to end	Day	15% 12% 5% 9% 7% 4 5% 5% 6% 7% 23%	1520
December	1st to 10th	Day	12% 13% 6% 12% 7% 3 5% 6% 6% 5% 25%	1520
	11th to 20th	Day	16% 15% 5% 9% 9% 4 6% 4 5% 6% 22%	1914
	21st to end	Day	21% 22% 8% 10% 5% 3 4 4 3 5% 16%	2783
January	1st to 10th	Night	13% 14% 6% 11% 6% 3 4 4 4 6% 27%	4428
	11th to 20th	Night	10% 14% 6% 11% 10% 5% 6% 5% 6% 7% 20%	4440
	21st to end	Night	10% 16% 9% 14% 8% 4 4 4 5% 6% 21%	4884
February	1st to 10th	Night	10% 11% 6% 9% 7% 3 5% 5% 6% 7% 31%	2532
	11th to 20th	Night	9% 11% 4 9% 9% 4 6% 4 5% 8% 31%	2294
	21st to end	Night	13% 15% 4 8% 7% 3 4 4 5% 7% 30%	1884
March	1st to 10th	Night	12% 10% 4 7% 6% 3 5% 4 5% 6% 39%	2216
	11th to 20th	Night	13% 8% 3 6% 6% 3 5% 4 4 8% 39%	2118
	21st to end	Night	15% 10% 4 8% 6% 3 4 3 5% 6% 36%	1980
April	1st to 10th	Night	19% 10% 5% 8% 5% 3 4 4 4 7% 31%	1800
	11th to 20th	Night	21% 10% 4 5% 4 3 4 5% 4 5% 36%	1775
	21st to end	Night	17% 7% 4 7% 7% 3 5% 4 5% 6% 35%	1637
May	1st to 10th	Night	19% 8% 3 7% 7% 3 5% 5% 6% 6% 31%	1502
	11th to 20th	Night	18% 9% 3 7% 4 3 4 4 6% 6% 37%	1416
	21st to end	Night	12% 5% 3 6% 5% 3 5% 6% 6% 9% 41%	1551
June	1st to 10th	Night	11% 6% 2 5% 5% 3 5% 4 5% 8% 46%	1440
	11th to 20th	Night	13% 7% 3 5% 5% 3 5% 5% 5% 7% 40%	1440
	21st to end	Night	12% 5% 2 5% 4 3 5% 5% 7% 9% 42%	1440
July	1st to 10th	Night	7% 4 2 3 3 2 5% 4 6% 11% 53%	1440
	11th to 20th	Night	9% 5% 2 5% 3 3 4 5% 6% 7% 51%	1440
	21st to end	Night	6% 4 2 4 5% 3 4 5% 5% 9% 54%	1575
August	1st to 10th	Night	9% 5% 3 5% 4 3 4 6% 6% 9% 46%	1432
	11th to 20th	Night	10% 5% 2 4 5% 3 4 6% 6% 6% 50%	1582
	21st to end	Night	12% 6% 2 4 4 3 3 4 4 7% 50%	1980
September	1st to 10th	Night	10% 6% 3 5% 4 2 3 4 5% 6% 52%	1800
	11th to 20th	Night	12% 5% 3 4 4 3 4 4 5% 7% 49%	1868
	21st to end	Night	15% 7% 3 5% 5% 3 4 4 4 7% 41%	1980
October	1st to 10th	Night	15% 9% 3 5% 5% 3 4 4 4 7% 42%	2084
	11th to 20th	Night	18% 11% 4 6% 5% 3 4 4 6% 6% 31%	2214
	21st to end	Night	19% 14% 3 7% 6% 4 4 4 5% 7% 27%	2574
November	1st to 10th	Night	15% 10% 4 7% 5% 3 4 5% 5% 7% 35%	2406
	11th to 20th	Night	16% 11% 5% 8% 7% 4 5% 5% 5% 6% 29%	2536
	21st to end	Night	15% 12% 5% 9% 7% 4 5% 6% 5% 7% 26%	2660
December	1st to 10th	Night	13% 13% 6% 8% 7% 3 5% 5% 5% 7% 28%	2660
	11th to 20th	Night	13% 12% 7% 10% 8% 4 5% 5% 5% 5% 27%	3283
	21st to end	Night	23% 20% 9% 9% 5% 2 3 3 3 4 19%	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	59% 9% 11% 16% 5%	2528
	11th to 20th	Day	60% 9% 13% 13% 5%	2530
	21st to end	Day	64% 8% 12% 12% 4 1	2783
February	1st to 10th	Day	50% 7% 13% 19% 12% 1	1647
	11th to 20th	Day	49% 8% 12% 21% 8% 1	1780
	21st to end	Day	53% 6% 11% 17% 11% 1	1570
March	1st to 10th	Day	50% 7% 12% 16% 13% 2	1850
	11th to 20th	Day	49% 6% 11% 20% 11% 2	1856
	21st to end	Day	58% 6% 11% 15% 9% 1	2376
April	1st to 10th	Day	55% 7% 12% 17% 9% 1	2160
	11th to 20th	Day	55% 6% 8% 19% 10% 1	2134
	21st to end	Day	53% 7% 9% 17% 12% 2	2322
May	1st to 10th	Day	51% 8% 11% 18% 11% 2	2456
	11th to 20th	Day	48% 6% 12% 20% 13% 1	2483
	21st to end	Day	44% 8% 12% 22% 11% 2	2725
June	1st to 10th	Day	39% 8% 14% 25% 13% 1	2520
	11th to 20th	Day	43% 9% 14% 19% 14% 1	2520
	21st to end	Day	43% 9% 15% 22% 10% 1	2520
July	1st to 10th	Day	32% 10% 15% 27% 15% 1	2451
	11th to 20th	Day	36% 9% 14% 25% 15% 3	2445
	21st to end	Day	35% 8% 15% 24% 16% 1	2591
August	1st to 10th	Day	38% 10% 15% 24% 11% 2	2492
	11th to 20th	Day	40% 9% 14% 25% 12% 1	2314
	21st to end	Day	40% 7% 14% 24% 13% 1	2376
September	1st to 10th	Day	41% 7% 12% 27% 13%	2160
	11th to 20th	Day	42% 9% 18% 24% 7%	2073
	21st to end	Day	48% 8% 13% 24% 7%	1980
October	1st to 10th	Day	46% 8% 13% 24% 8%	1872
	11th to 20th	Day	57% 8% 12% 16% 6% 1	1745
	21st to end	Day	58% 7% 12% 17% 5%	1782
November	1st to 10th	Day	48% 7% 13% 21% 10% 1	1672
	11th to 20th	Day	59% 8% 12% 13% 7%	1642
	21st to end	Day	57% 10% 14% 15% 3 1	1520
December	1st to 10th	Day	56% 7% 13% 18% 5%	1520
	11th to 20th	Day	60% 8% 12% 13% 6% 1	1915
	21st to end	Day	69% 7% 7% 11% 5%	2783
January	1st to 10th	Night	55% 7% 13% 18% 6% 1	4428
	11th to 20th	Night	59% 9% 14% 14% 4	4440
	21st to end	Night	62% 8% 10% 15% 4	4884
February	1st to 10th	Night	50% 7% 11% 19% 12% 2	2532
	11th to 20th	Night	48% 7% 13% 20% 9% 2	2295
	21st to end	Night	54% 5% 13% 18% 9% 1	1884
March	1st to 10th	Night	44% 6% 15% 22% 11% 2	2227
	11th to 20th	Night	44% 6% 12% 23% 13% 1	2119
	21st to end	Night	49% 6% 11% 19% 13% 2	1980
April	1st to 10th	Night	52% 7% 11% 15% 14% 1	1800
	11th to 20th	Night	50% 7% 9% 21% 11% 3	1775
	21st to end	Night	49% 7% 11% 18% 13% 1	1637
May	1st to 10th	Night	51% 8% 12% 19% 9% 2	1502
	11th to 20th	Night	47% 7% 9% 22% 12% 2	1417
	21st to end	Night	38% 8% 17% 22% 13% 1	1552
June	1st to 10th	Night	35% 9% 15% 26% 14% 1	1440
	11th to 20th	Night	42% 8% 13% 23% 14% 1	1440
	21st to end	Night	35% 10% 16% 27% 11% 2	1440
July	1st to 10th	Night	25% 8% 17% 31% 19% 1	1400
	11th to 20th	Night	29% 10% 17% 27% 13% 3	1392
	21st to end	Night	25% 9% 19% 30% 15% 2	1487
August	1st to 10th	Night	33% 10% 17% 26% 13% 3	1423
	11th to 20th	Night	32% 10% 13% 28% 15% 2	1582
	21st to end	Night	34% 8% 15% 25% 17% 2	1980
September	1st to 10th	Night	32% 8% 14% 31% 14% 1	1800
	11th to 20th	Night	33% 9% 16% 33% 9%	1868
	21st to end	Night	42% 8% 16% 25% 8%	1980
October	1st to 10th	Night	41% 7% 13% 27% 10% 1	2084
	11th to 20th	Night	51% 8% 13% 21% 7% 1	2214
	21st to end	Night	54% 7% 14% 17% 8%	2574
November	1st to 10th	Night	47% 6% 13% 22% 11% 1	2406
	11th to 20th	Night	53% 8% 13% 16% 9%	2536
	21st to end	Night	54% 9% 15% 18% 4 1	2660
December	1st to 10th	Night	53% 8% 16% 18% 5%	2660
	11th to 20th	Night	56% 9% 11% 17% 6%	3281
	21st to end	Night	68% 5% 7% 14% 5%	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	22% 17% 34% 20% 6% 1	270
	11th to 20th	Day	29% 19% 32% 16% 4	270
	21st to end	Day	24% 16% 42% 15% 2	297
February	1st to 10th	Day	17% 30% 37% 11% 3 1	270
	11th to 20th	Day	23% 31% 30% 13% 3 1	270
	21st to end	Day	26% 27% 39% 7% 1	225
March	1st to 10th	Day	21% 25% 41% 12% 1	255
	11th to 20th	Day	25% 22% 34% 14% 5%	248
	21st to end	Day	26% 21% 29% 16% 7% 1	462
April	1st to 10th	Day	28% 19% 31% 18% 4	420
	11th to 20th	Day	30% 19% 27% 17% 5% 2	412
	21st to end	Day	31% 16% 27% 17% 7% 1	420
May	1st to 10th	Day	26% 20% 31% 14% 7% 1	539
	11th to 20th	Day	21% 19% 34% 17% 5% 3	625
	21st to end	Day	19% 14% 34% 20% 8% 4	679
June	1st to 10th	Day	15% 17% 33% 22% 10% 3	630
	11th to 20th	Day	19% 13% 37% 20% 9% 2	630
	21st to end	Day	17% 14% 32% 24% 10% 4	630
July	1st to 10th	Day	7% 11% 36% 27% 14% 5%	621
	11th to 20th	Day	12% 12% 35% 25% 9% 6%	618
	21st to end	Day	9% 12% 36% 26% 12% 6%	684
August	1st to 10th	Day	12% 11% 31% 26% 15% 5%	626
	11th to 20th	Day	17% 7% 24% 27% 18% 7%	512
	21st to end	Day	20% 11% 26% 23% 16% 5%	495
September	1st to 10th	Day	20% 10% 26% 27% 12% 6%	450
	11th to 20th	Day	16% 11% 34% 27% 9% 4	450
	21st to end	Day	22% 14% 29% 23% 10% 3	450
October	1st to 10th	Day	23% 18% 28% 19% 10% 2	342
	11th to 20th	Day	28% 26% 32% 12% 2	270
	21st to end	Day	31% 26% 32% 9% 2	297
November	1st to 10th	Day	21% 21% 37% 15% 4 1	270
	11th to 20th	Day	24% 27% 35% 9% 3 2	270
	21st to end	Day	27% 22% 36% 11% 4	270
December	1st to 10th	Day	22% 18% 40% 15% 4 1	270
	11th to 20th	Day	28% 24% 33% 12% 3	270
	21st to end	Day	32% 22% 33% 11% 2	297
January	1st to 10th	Night	17% 20% 41% 19% 3 1	950
	11th to 20th	Night	20% 17% 39% 17% 6% 1	950
	21st to end	Night	18% 14% 40% 21% 5%	1045
February	1st to 10th	Night	19% 18% 39% 18% 6%	950
	11th to 20th	Night	20% 22% 33% 19% 6%	819
	21st to end	Night	21% 21% 40% 17% 2	628
March	1st to 10th	Night	19% 17% 34% 23% 7%	743
	11th to 20th	Night	18% 19% 36% 20% 5% 1	688
	21st to end	Night	22% 10% 31% 28% 8% 1	594
April	1st to 10th	Night	25% 14% 33% 23% 5%	540
	11th to 20th	Night	28% 13% 28% 26% 5% 1	533
	21st to end	Night	23% 12% 32% 26% 6% 1	540
May	1st to 10th	Night	23% 12% 31% 26% 7% 1	540
	11th to 20th	Night	23% 10% 35% 24% 6% 1	531
	21st to end	Night	15% 9% 30% 34% 11% 1	584
June	1st to 10th	Night	13% 10% 29% 35% 13%	540
	11th to 20th	Night	17% 8% 30% 36% 9% 1	540
	21st to end	Night	13% 6% 31% 35% 14% 1	540
July	1st to 10th	Night	9% 5% 29% 39% 17% 1	525
	11th to 20th	Night	10% 5% 34% 32% 17% 1	522
	21st to end	Night	7% 4 31% 40% 16% 2	591
August	1st to 10th	Night	12% 3 27% 39% 18% 1	537
	11th to 20th	Night	12% 4 23% 34% 23% 3	534
	21st to end	Night	14% 7% 26% 33% 19% 1	594
September	1st to 10th	Night	13% 8% 26% 31% 19% 3	540
	11th to 20th	Night	16% 7% 31% 30% 14% 2	608
	21st to end	Night	20% 11% 30% 28% 9% 1	720
October	1st to 10th	Night	20% 13% 30% 23% 13% 1	720
	11th to 20th	Night	24% 18% 28% 23% 7%	720
	21st to end	Night	28% 12% 31% 22% 6%	792
November	1st to 10th	Night	20% 15% 39% 21% 5%	740
	11th to 20th	Night	24% 20% 34% 17% 5% 1	826
	21st to end	Night	23% 19% 32% 22% 4	950
December	1st to 10th	Night	22% 20% 36% 16% 5% 1	950
	11th to 20th	Night	20% 19% 34% 19% 5% 1	950
	21st to end	Night	29% 17% 35% 16% 4	1045

Page generated at 2024-03-03 05:29:00. Version ac07

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