Dalton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dalton clear sky chart from 2005-11-06 to 2024-02-10.

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% 6% 3 5% 5% 3 5% 5% 6% 7% 40%	78692
	Night	14% 6% 2 5% 5% 3 4 5% 5% 7% 44%	80288
Transparency	Day	41% 8% 12% 19% 17% 4	78415
	Night	39% 7% 11% 20% 18% 4	80084
Seeing	Day	17% 11% 23% 23% 17% 8%	13717
	Night	16% 10% 23% 28% 19% 3	23836

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	17% 12% 3 5% 4 3 4 4 5% 5% 37%	2836
	11th to 20th	Day	19% 8% 5% 5% 5% 3 4 3 4 5% 41%	2840
	21st to end	Day	22% 10% 2 5% 4 3 3 3 4 5% 37%	3288
February	1st to 10th	Day	18% 10% 3 6% 5% 3 4 4 4 7% 37%	1890
	11th to 20th	Day	21% 7% 4 7% 6% 2 5% 4 3 6% 36%	1748
	21st to end	Day	24% 7% 4 5% 5% 3 3 4 3 6% 37%	1480
March	1st to 10th	Day	17% 5% 3 4 4 3 5% 5% 6% 7% 42%	1808
	11th to 20th	Day	19% 6% 4 6% 6% 3 4 5% 5% 6% 37%	1980
	21st to end	Day	15% 6% 3 7% 6% 3 6% 4 5% 8% 37%	2178
April	1st to 10th	Day	12% 5% 2 4 5% 3 6% 6% 5% 8% 44%	2108
	11th to 20th	Day	13% 5% 3 5% 7% 3 5% 4 4 6% 46%	2134
	21st to end	Day	11% 5% 3 5% 5% 4 6% 5% 6% 7% 45%	2276
May	1st to 10th	Day	11% 5% 2 5% 5% 3 4 5% 5% 8% 47%	2340
	11th to 20th	Day	11% 6% 3 7% 6% 5% 6% 6% 6% 7% 39%	2301
	21st to end	Day	10% 5% 2 5% 5% 4 7% 6% 6% 10% 40%	2531
June	1st to 10th	Day	10% 5% 3 6% 7% 4 6% 6% 8% 9% 37%	2340
	11th to 20th	Day	6% 4 2 5% 5% 4 7% 7% 8% 10% 43%	2340
	21st to end	Day	7% 5% 3 5% 6% 5% 6% 6% 8% 11% 38%	2340
July	1st to 10th	Day	9% 5% 4 7% 7% 4 7% 7% 9% 11% 30%	2340
	11th to 20th	Day	10% 4 3 6% 6% 5% 8% 8% 9% 11% 31%	2340
	21st to end	Day	8% 5% 3 6% 7% 5% 8% 8% 9% 11% 30%	2547
August	1st to 10th	Day	8% 4 2 6% 7% 4 8% 8% 9% 11% 32%	2327
	11th to 20th	Day	10% 5% 2 6% 7% 6% 6% 6% 7% 9% 35%	2125
	21st to end	Day	13% 6% 3 6% 7% 4 7% 6% 7% 8% 33%	2376
September	1st to 10th	Day	10% 5% 3 6% 6% 4 6% 6% 7% 9% 39%	2031
	11th to 20th	Day	15% 5% 3 5% 5% 3 4 5% 4 7% 43%	1980
	21st to end	Day	13% 4 2 5% 5% 3 4 4 4 7% 49%	1980
October	1st to 10th	Day	11% 4 3 3 4 3 4 3 5% 5% 54%	1980
	11th to 20th	Day	11% 4 2 5% 4 3 4 5% 4 5% 54%	1910
	21st to end	Day	13% 4 2 4 4 2 3 3 5% 6% 53%	1919
November	1st to 10th	Day	12% 5% 2 4 3 3 3 3 4 5% 56%	1672
	11th to 20th	Day	14% 5% 2 5% 4 3 4 3 5% 5% 51%	1710
	21st to end	Day	16% 6% 2 5% 5% 3 4 4 4 6% 45%	1710
December	1st to 10th	Day	22% 9% 3 5% 5% 3 5% 4 4 5% 36%	1710
	11th to 20th	Day	16% 7% 3 6% 5% 3 4 4 4 6% 41%	2153
	21st to end	Day	20% 10% 3 5% 5% 3 5% 4 5% 7% 35%	3124
January	1st to 10th	Night	19% 10% 2 4 5% 3 5% 3 4 6% 40%	4109
	11th to 20th	Night	18% 8% 3 5% 4 2 3 3 4 5% 44%	4120
	21st to end	Night	23% 11% 2 5% 4 3 4 4 3 4 37%	4367
February	1st to 10th	Night	16% 6% 2 5% 5% 2 4 4 5% 6% 43%	2275
	11th to 20th	Night	21% 5% 4 6% 6% 3 5% 4 4 4 39%	2098
	21st to end	Night	23% 7% 3 5% 5% 3 4 4 5% 5% 36%	1776
March	1st to 10th	Night	15% 6% 2 5% 5% 3 4 4 5% 7% 45%	2151
	11th to 20th	Night	17% 6% 3 6% 5% 4 3 4 6% 6% 40%	1980
	21st to end	Night	14% 6% 3 7% 6% 3 4 4 4 6% 42%	2178
April	1st to 10th	Night	13% 3 2 3 4 3 4 4 5% 9% 50%	1867
	11th to 20th	Night	11% 6% 2 4 4 2 4 4 5% 7% 50%	1775
	21st to end	Night	10% 4 2 6% 4 2 5% 4 4 8% 50%	1684
May	1st to 10th	Night	10% 4 3 4 4 2 4 5% 5% 8% 50%	1620
	11th to 20th	Night	11% 5% 2 5% 5% 3 5% 5% 6% 9% 43%	1592
	21st to end	Night	9% 5% 2 4 5% 3 6% 5% 7% 9% 44%	1744
June	1st to 10th	Night	8% 4 2 6% 7% 4 6% 6% 7% 11% 40%	1620
	11th to 20th	Night	5% 3 1 4 5% 3 4 5% 9% 11% 50%	1620
	21st to end	Night	6% 4 2 5% 5% 3 5% 6% 7% 13% 45%	1620
July	1st to 10th	Night	10% 4 2 5% 5% 4 7% 7% 8% 11% 37%	1620
	11th to 20th	Night	9% 4 2 5% 5% 2 6% 7% 8% 12% 40%	1620
	21st to end	Night	7% 4 2 5% 7% 4 6% 7% 8% 11% 39%	1771
August	1st to 10th	Night	7% 4 1 5% 5% 4 7% 7% 8% 11% 40%	1611
	11th to 20th	Night	9% 5% 3 5% 5% 3 4 6% 9% 9% 40%	1771
	21st to end	Night	12% 5% 2 5% 6% 3 5% 6% 7% 9% 39%	1980
September	1st to 10th	Night	10% 5% 2 6% 6% 4 5% 6% 6% 8% 41%	1908
	11th to 20th	Night	12% 5% 2 5% 5% 3 5% 6% 6% 8% 43%	1980
	21st to end	Night	11% 4 2 5% 5% 2 4 4 4 8% 50%	1980
October	1st to 10th	Night	9% 4 2 4 4 2 3 3 4 5% 58%	1980
	11th to 20th	Night	12% 5% 2 5% 5% 3 3 3 3 5% 54%	2047
	21st to end	Night	13% 5% 3 4 5% 2 3 4 4 4 54%	2434
November	1st to 10th	Night	12% 4 2 4 4 2 3 4 3 6% 55%	2406
	11th to 20th	Night	13% 5% 3 5% 5% 2 3 4 4 6% 52%	2470
	21st to end	Night	17% 4 2 5% 4 3 4 4 4 6% 46%	2470
December	1st to 10th	Night	20% 7% 3 6% 5% 3 4 5% 5% 6% 36%	2470
	11th to 20th	Night	17% 7% 2 4 5% 2 4 3 4 5% 46%	3042
	21st to end	Night	20% 8% 3 5% 5% 4 5% 5% 5% 7% 33%	4532

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	47% 6% 7% 17% 21% 2	2837
	11th to 20th	Day	45% 5% 8% 17% 23% 2	2840
	21st to end	Day	50% 4 8% 19% 18% 2	3288
February	1st to 10th	Day	48% 5% 8% 18% 18% 3	1890
	11th to 20th	Day	51% 4 6% 19% 16% 4	1758
	21st to end	Day	51% 4 8% 13% 19% 6%	1480
March	1st to 10th	Day	40% 7% 9% 15% 21% 7%	1808
	11th to 20th	Day	47% 8% 9% 16% 16% 4	1980
	21st to end	Day	45% 6% 11% 23% 13% 2	2178
April	1st to 10th	Day	38% 8% 11% 22% 17% 4	2108
	11th to 20th	Day	41% 4 7% 18% 23% 7%	2134
	21st to end	Day	37% 7% 11% 25% 17% 3	2276
May	1st to 10th	Day	36% 7% 13% 24% 16% 4	2340
	11th to 20th	Day	42% 9% 14% 20% 13% 1	2305
	21st to end	Day	37% 11% 14% 22% 14% 3	2531
June	1st to 10th	Day	41% 10% 15% 21% 12% 1	2340
	11th to 20th	Day	32% 12% 18% 24% 12% 2	2340
	21st to end	Day	37% 11% 17% 19% 12% 3	2340
July	1st to 10th	Day	44% 12% 16% 17% 8% 2	2275
	11th to 20th	Day	40% 13% 20% 16% 8% 3	2271
	21st to end	Day	42% 15% 19% 16% 8%	2405
August	1st to 10th	Day	39% 16% 20% 19% 6% 1	2314
	11th to 20th	Day	43% 11% 16% 17% 11% 1	2125
	21st to end	Day	46% 12% 13% 15% 10% 3	2376
September	1st to 10th	Day	39% 11% 15% 15% 14% 5%	2031
	11th to 20th	Day	40% 8% 13% 19% 18% 2	1980
	21st to end	Day	34% 7% 12% 17% 22% 7%	1980
October	1st to 10th	Day	32% 7% 9% 18% 26% 8%	1980
	11th to 20th	Day	31% 6% 9% 22% 23% 8%	1910
	21st to end	Day	33% 4 8% 21% 27% 7%	1919
November	1st to 10th	Day	32% 4 7% 18% 31% 8%	1672
	11th to 20th	Day	36% 4 7% 20% 25% 8%	1710
	21st to end	Day	41% 5% 8% 17% 25% 5%	1710
December	1st to 10th	Day	51% 4 7% 19% 16% 3	1710
	11th to 20th	Day	45% 4 8% 18% 21% 4	2150
	21st to end	Day	48% 6% 10% 22% 13% 2	3124
January	1st to 10th	Night	45% 5% 7% 19% 21% 2	4109
	11th to 20th	Night	43% 5% 9% 20% 18% 6%	4120
	21st to end	Night	52% 4 6% 16% 20% 2	4367
February	1st to 10th	Night	42% 5% 9% 19% 20% 5%	2275
	11th to 20th	Night	49% 5% 7% 16% 18% 5%	2099
	21st to end	Night	50% 5% 9% 15% 16% 5%	1776
March	1st to 10th	Night	40% 5% 8% 17% 21% 9%	2151
	11th to 20th	Night	44% 6% 10% 18% 17% 4	1980
	21st to end	Night	42% 6% 10% 23% 16% 2	2178
April	1st to 10th	Night	32% 6% 13% 21% 23% 5%	1867
	11th to 20th	Night	35% 4 7% 24% 21% 9%	1775
	21st to end	Night	33% 6% 13% 26% 19% 3	1684
May	1st to 10th	Night	31% 8% 15% 20% 23% 3	1620
	11th to 20th	Night	36% 10% 19% 22% 13% 1	1593
	21st to end	Night	34% 9% 15% 23% 16% 2	1745
June	1st to 10th	Night	36% 11% 17% 20% 13% 2	1620
	11th to 20th	Night	25% 9% 24% 27% 13% 2	1620
	21st to end	Night	30% 11% 22% 19% 13% 5%	1620
July	1st to 10th	Night	38% 12% 16% 20% 12% 2	1575
	11th to 20th	Night	33% 13% 22% 18% 10% 4	1566
	21st to end	Night	34% 12% 20% 22% 10% 2	1672
August	1st to 10th	Night	33% 14% 21% 23% 9% 1	1600
	11th to 20th	Night	36% 13% 20% 16% 14% 2	1771
	21st to end	Night	38% 12% 17% 18% 12% 3	1980
September	1st to 10th	Night	37% 10% 17% 17% 14% 5%	1908
	11th to 20th	Night	37% 11% 12% 19% 18% 2	1980
	21st to end	Night	33% 7% 12% 21% 21% 8%	1980
October	1st to 10th	Night	28% 5% 10% 20% 28% 8%	1980
	11th to 20th	Night	33% 5% 9% 20% 24% 9%	2047
	21st to end	Night	33% 5% 5% 21% 26% 10%	2434
November	1st to 10th	Night	31% 5% 8% 21% 25% 10%	2406
	11th to 20th	Night	34% 4 7% 19% 27% 10%	2470
	21st to end	Night	39% 6% 7% 20% 24% 5%	2470
December	1st to 10th	Night	48% 6% 9% 17% 17% 3	2470
	11th to 20th	Night	40% 6% 8% 18% 26% 3	3044
	21st to end	Night	48% 7% 9% 22% 13% 1	4532

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	30% 24% 31% 14% 1	270
	11th to 20th	Day	33% 23% 30% 11% 4	270
	21st to end	Day	26% 27% 34% 10% 2	297
February	1st to 10th	Day	33% 21% 33% 12% 2	267
	11th to 20th	Day	40% 25% 26% 8%	240
	21st to end	Day	41% 22% 30% 7%	198
March	1st to 10th	Day	28% 22% 31% 16% 3	248
	11th to 20th	Day	26% 21% 31% 14% 7%	420
	21st to end	Day	21% 22% 34% 16% 7%	462
April	1st to 10th	Day	20% 18% 29% 18% 13% 2	420
	11th to 20th	Day	16% 18% 29% 25% 11% 1	412
	21st to end	Day	18% 12% 30% 25% 11% 3	420
May	1st to 10th	Day	15% 16% 26% 26% 12% 5%	423
	11th to 20th	Day	12% 6% 28% 28% 17% 8%	447
	21st to end	Day	13% 6% 19% 32% 20% 12%	485
June	1st to 10th	Day	12% 6% 19% 28% 22% 13%	450
	11th to 20th	Day	8% 4 14% 29% 27% 19%	450
	21st to end	Day	9% 4 20% 28% 21% 18%	450
July	1st to 10th	Day	10% 4 13% 24% 28% 21%	445
	11th to 20th	Day	9% 2 10% 26% 31% 21%	444
	21st to end	Day	10% 2 9% 24% 32% 22%	488
August	1st to 10th	Day	11% 2 15% 24% 28% 20%	446
	11th to 20th	Day	11% 2 13% 32% 27% 15%	439
	21st to end	Day	17% 3 11% 23% 30% 16%	495
September	1st to 10th	Day	10% 3 14% 27% 32% 14%	450
	11th to 20th	Day	15% 6% 11% 27% 31% 10%	450
	21st to end	Day	12% 6% 17% 30% 29% 6%	450
October	1st to 10th	Day	13% 7% 23% 28% 21% 8%	450
	11th to 20th	Day	13% 11% 30% 26% 18% 2	450
	21st to end	Day	18% 12% 25% 27% 15% 3	434
November	1st to 10th	Day	24% 10% 31% 21% 11% 2	270
	11th to 20th	Day	18% 16% 36% 24% 4	270
	21st to end	Day	15% 23% 36% 19% 6% 1	270
December	1st to 10th	Day	30% 19% 31% 14% 3 1	270
	11th to 20th	Day	22% 22% 32% 19% 4 1	270
	21st to end	Day	29% 21% 31% 16% 3	297
January	1st to 10th	Night	25% 22% 29% 20% 4	760
	11th to 20th	Night	24% 17% 31% 22% 7%	760
	21st to end	Night	21% 20% 31% 25% 3	836
February	1st to 10th	Night	20% 14% 35% 26% 4	759
	11th to 20th	Night	26% 20% 33% 20% 2	703
	21st to end	Night	28% 20% 31% 18% 2	592
March	1st to 10th	Night	19% 16% 35% 26% 4	720
	11th to 20th	Night	20% 17% 30% 23% 9% 1	720
	21st to end	Night	18% 15% 30% 28% 9%	792
April	1st to 10th	Night	13% 14% 31% 31% 11% 1	607
	11th to 20th	Night	16% 11% 33% 27% 12%	533
	21st to end	Night	12% 10% 29% 35% 14% 1	540
May	1st to 10th	Night	11% 7% 29% 33% 20% 1	540
	11th to 20th	Night	11% 6% 23% 31% 24% 5%	531
	21st to end	Night	9% 4 12% 36% 33% 6%	584
June	1st to 10th	Night	6% 3 17% 36% 33% 4	540
	11th to 20th	Night	4 3 12% 34% 36% 10%	540
	21st to end	Night	6% 1 9% 31% 43% 9%	540
July	1st to 10th	Night	12% 2 8% 25% 42% 11%	525
	11th to 20th	Night	9% 2 7% 26% 43% 13%	522
	21st to end	Night	9% 1 8% 26% 46% 10%	591
August	1st to 10th	Night	8% 1 7% 27% 47% 10%	537
	11th to 20th	Night	10% 2 9% 32% 38% 9%	534
	21st to end	Night	14% 2 8% 28% 40% 8%	594
September	1st to 10th	Night	10% 3 11% 28% 40% 8%	648
	11th to 20th	Night	13% 3 12% 31% 37% 4	720
	21st to end	Night	13% 3 16% 33% 33% 2	720
October	1st to 10th	Night	11% 5% 22% 30% 26% 6%	720
	11th to 20th	Night	14% 7% 30% 30% 18% 1	720
	21st to end	Night	16% 9% 22% 36% 15% 2	792
November	1st to 10th	Night	15% 9% 23% 33% 19% 2	740
	11th to 20th	Night	14% 15% 30% 31% 10% 1	760
	21st to end	Night	20% 14% 29% 27% 10% 1	760
December	1st to 10th	Night	25% 18% 26% 24% 7%	760
	11th to 20th	Night	22% 15% 30% 26% 7%	760
	21st to end	Night	26% 14% 29% 25% 6%	836

Page generated at 2024-02-07 06:11:53. Version ac07

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