Norton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norton clear sky chart from 2005-11-06 to 2024-02-15.

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	8% 6% 2 4 4 2 4 4 5% 7% 53%	78566
	Night	8% 6% 2 5% 4 2 4 4 5% 7% 54%	80559
Transparency	Day	31% 4 13% 28% 20% 4	78282
	Night	31% 4 13% 27% 21% 5%	80366
Seeing	Day	11% 8% 30% 32% 16% 3	14619
	Night	10% 8% 34% 37% 10%	24727

By Month

Percentage Cloud Cover SW (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	6% 9% 3 5% 4 2 3 4 5% 7% 51%	2538
	11th to 20th	Day	7% 12% 4 6% 4 3 4 4 6% 6% 44%	2544
	21st to end	Day	5% 8% 4 5% 4 2 3 3 4 6% 56%	3135
February	1st to 10th	Day	8% 8% 4 7% 6% 3 4 4 6% 7% 43%	1819
	11th to 20th	Day	5% 7% 3 5% 5% 4 4 5% 6% 8% 48%	1789
	21st to end	Day	7% 6% 3 5% 4 2 3 3 4 6% 55%	1480
March	1st to 10th	Day	6% 6% 2 4 3 2 3 4 5% 8% 56%	1800
	11th to 20th	Day	11% 7% 3 5% 4 2 3 3 4 7% 50%	1968
	21st to end	Day	13% 8% 4 4 4 2 5% 5% 5% 7% 44%	2178
April	1st to 10th	Day	10% 6% 2 3 4 2 4 3 5% 8% 54%	2145
	11th to 20th	Day	10% 6% 2 5% 5% 3 4 4 6% 8% 48%	2169
	21st to end	Day	15% 6% 2 4 4 3 3 4 6% 7% 47%	2340
May	1st to 10th	Day	13% 6% 3 5% 4 2 4 4 6% 8% 46%	2340
	11th to 20th	Day	13% 6% 2 4 4 2 4 4 5% 7% 48%	2302
	21st to end	Day	12% 4 2 5% 6% 3 5% 5% 6% 9% 42%	2531
June	1st to 10th	Day	5% 2 1 2 3 2 4 4 5% 10% 60%	2448
	11th to 20th	Day	7% 3 1 3 4 2 4 4 5% 7% 57%	2520
	21st to end	Day	5% 3 1 3 4 2 4 4 7% 8% 59%	2520
July	1st to 10th	Day	5% 4 2 4 4 2 4 5% 5% 8% 56%	2520
	11th to 20th	Day	4 2 1 3 4 2 4 5% 7% 10% 59%	2520
	21st to end	Day	7% 4 1 4 3 2 5% 5% 8% 10% 51%	2556
August	1st to 10th	Day	8% 5% 2 4 4 3 5% 5% 6% 9% 48%	2328
	11th to 20th	Day	6% 3 2 4 4 2 4 5% 6% 8% 57%	2301
	21st to end	Day	6% 5% 2 4 3 2 3 3 5% 7% 60%	2376
September	1st to 10th	Day	10% 5% 1 3 3 2 3 3 5% 5% 59%	2093
	11th to 20th	Day	9% 4 2 3 3 2 4 3 4 6% 60%	1980
	21st to end	Day	8% 3 1 3 3 2 3 4 4 6% 63%	1980
October	1st to 10th	Day	17% 4 2 2 2 1 2 3 3 6% 58%	1980
	11th to 20th	Day	8% 5% 1 4 3 2 4 2 3 5% 63%	1843
	21st to end	Day	10% 7% 2 4 3 2 3 3 4 5% 59%	1800
November	1st to 10th	Day	5% 3 2 4 3 3 4 4 4 7% 62%	1673
	11th to 20th	Day	7% 4 1 3 3 1 4 4 4 5% 63%	1710
	21st to end	Day	9% 6% 2 4 4 2 3 4 4 7% 56%	1710
December	1st to 10th	Day	6% 5% 3 5% 4 3 3 4 5% 7% 55%	1710
	11th to 20th	Day	7% 7% 3 5% 4 2 3 3 5% 7% 55%	2126
	21st to end	Day	11% 13% 5% 9% 5% 3 4 4 4 4 39%	2794
January	1st to 10th	Night	6% 10% 4 10% 5% 2 3 3 4 5% 47%	4417
	11th to 20th	Night	5% 7% 3 5% 5% 2 4 4 5% 7% 53%	4422
	21st to end	Night	7% 9% 3 6% 5% 2 4 4 5% 5% 51%	4532
February	1st to 10th	Night	9% 7% 3 6% 4 2 5% 5% 4 6% 47%	2375
	11th to 20th	Night	5% 7% 3 5% 5% 4 4 5% 6% 7% 49%	2152
	21st to end	Night	6% 6% 2 5% 5% 3 4 4 4 6% 55%	1776
March	1st to 10th	Night	8% 6% 2 4 3 2 3 4 5% 7% 55%	2160
	11th to 20th	Night	11% 6% 3 3 4 2 4 4 5% 5% 53%	1991
	21st to end	Night	11% 7% 3 5% 4 3 4 4 6% 8% 44%	2178
April	1st to 10th	Night	9% 6% 2 5% 3 2 4 4 5% 7% 52%	1813
	11th to 20th	Night	13% 6% 2 5% 4 3 4 5% 5% 8% 45%	1738
	21st to end	Night	13% 5% 2 3 5% 3 3 4 5% 8% 49%	1620
May	1st to 10th	Night	11% 6% 2 4 5% 4 4 5% 5% 8% 46%	1620
	11th to 20th	Night	13% 6% 3 4 4 3 4 3 4 8% 49%	1593
	21st to end	Night	12% 5% 2 5% 4 3 6% 5% 6% 9% 43%	1745
June	1st to 10th	Night	5% 2 2 3 5% 2 4 5% 6% 10% 56%	1508
	11th to 20th	Night	7% 3 2 4 4 3 4 6% 6% 9% 53%	1440
	21st to end	Night	4 3 2 4 5% 3 4 5% 8% 10% 52%	1440
July	1st to 10th	Night	7% 3 2 5% 4 3 5% 6% 6% 8% 50%	1440
	11th to 20th	Night	3 2 1 4 3 3 4 5% 8% 10% 57%	1440
	21st to end	Night	6% 3 1 4 4 3 5% 5% 7% 10% 52%	1760
August	1st to 10th	Night	6% 3 2 4 5% 3 5% 6% 8% 9% 50%	1611
	11th to 20th	Night	6% 4 2 4 5% 3 4 4 6% 8% 55%	1600
	21st to end	Night	4 3 2 2 4 2 4 4 5% 8% 62%	1975
September	1st to 10th	Night	7% 4 1 3 3 2 4 4 5% 7% 60%	1867
	11th to 20th	Night	8% 4 1 3 3 2 3 4 5% 6% 61%	1980
	21st to end	Night	7% 4 2 3 3 1 3 4 4 6% 63%	1980
October	1st to 10th	Night	12% 3 2 3 4 3 3 3 4 7% 56%	1980
	11th to 20th	Night	8% 4 1 3 3 2 2 3 4 6% 65%	2098
	21st to end	Night	9% 5% 1 3 3 2 2 3 4 6% 63%	2553
November	1st to 10th	Night	4 3 1 3 3 2 3 4 4 7% 67%	2405
	11th to 20th	Night	6% 4 2 4 3 2 3 4 5% 7% 61%	2470
	21st to end	Night	7% 6% 2 4 3 2 3 3 4 6% 60%	2470
December	1st to 10th	Night	5% 5% 3 5% 5% 2 4 3 4 7% 57%	2470
	11th to 20th	Night	7% 4 2 4 4 2 3 3 4 7% 59%	3067
	21st to end	Night	10% 13% 3 5% 5% 2 3 3 4 5% 46%	4873

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	34% 3 13% 32% 17% 1	2539
	11th to 20th	Day	40% 7% 9% 26% 13% 5%	2544
	21st to end	Day	32% 3 16% 32% 15% 2	3135
February	1st to 10th	Day	41% 5% 14% 22% 14% 4	1819
	11th to 20th	Day	34% 4 16% 26% 16% 4	1799
	21st to end	Day	31% 3 13% 25% 21% 7%	1480
March	1st to 10th	Day	27% 4 13% 27% 24% 5%	1800
	11th to 20th	Day	35% 4 11% 25% 19% 6%	1968
	21st to end	Day	40% 5% 14% 27% 13% 2	2178
April	1st to 10th	Day	30% 4 14% 27% 21% 4	2145
	11th to 20th	Day	35% 5% 14% 25% 17% 4	2172
	21st to end	Day	36% 4 12% 28% 17% 2	2340
May	1st to 10th	Day	37% 5% 14% 26% 15% 3	2340
	11th to 20th	Day	36% 5% 18% 29% 12% 1	2306
	21st to end	Day	37% 7% 19% 22% 12% 3	2531
June	1st to 10th	Day	20% 5% 20% 35% 16% 3	2448
	11th to 20th	Day	26% 4 15% 27% 21% 7%	2520
	21st to end	Day	22% 5% 11% 31% 25% 6%	2520
July	1st to 10th	Day	27% 5% 12% 29% 23% 4	2451
	11th to 20th	Day	20% 7% 12% 30% 26% 5%	2445
	21st to end	Day	25% 6% 17% 32% 18% 2	2414
August	1st to 10th	Day	31% 7% 17% 28% 14% 3	2314
	11th to 20th	Day	24% 5% 14% 33% 20% 3	2301
	21st to end	Day	24% 4 10% 26% 27% 8%	2376
September	1st to 10th	Day	28% 4 9% 24% 26% 9%	2093
	11th to 20th	Day	26% 4 9% 28% 26% 6%	1980
	21st to end	Day	23% 3 9% 30% 31% 4	1980
October	1st to 10th	Day	30% 3 8% 29% 26% 4	1980
	11th to 20th	Day	26% 2 7% 30% 24% 11%	1843
	21st to end	Day	29% 3 9% 25% 27% 7%	1800
November	1st to 10th	Day	24% 3 11% 31% 26% 6%	1673
	11th to 20th	Day	25% 2 10% 30% 28% 5%	1710
	21st to end	Day	30% 3 8% 27% 27% 5%	1710
December	1st to 10th	Day	30% 3 14% 30% 20% 3	1710
	11th to 20th	Day	31% 3 12% 37% 17% 1	2124
	21st to end	Day	50% 2 9% 22% 15% 2	2794
January	1st to 10th	Night	41% 3 13% 27% 16% 1	4417
	11th to 20th	Night	31% 3 15% 27% 21% 3	4422
	21st to end	Night	36% 3 14% 28% 18% 2	4532
February	1st to 10th	Night	38% 5% 13% 24% 15% 6%	2375
	11th to 20th	Night	34% 4 10% 31% 18% 3	2152
	21st to end	Night	31% 4 11% 23% 23% 8%	1776
March	1st to 10th	Night	30% 3 11% 24% 24% 8%	2160
	11th to 20th	Night	33% 3 10% 24% 23% 7%	1991
	21st to end	Night	38% 4 15% 24% 16% 2	2178
April	1st to 10th	Night	31% 5% 13% 23% 22% 5%	1813
	11th to 20th	Night	38% 4 12% 24% 18% 3	1738
	21st to end	Night	34% 5% 13% 27% 19% 2	1620
May	1st to 10th	Night	36% 6% 16% 21% 18% 3	1620
	11th to 20th	Night	35% 5% 17% 27% 16% 1	1594
	21st to end	Night	37% 8% 19% 22% 12% 3	1746
June	1st to 10th	Night	23% 7% 21% 31% 15% 3	1508
	11th to 20th	Night	29% 6% 15% 25% 19% 7%	1440
	21st to end	Night	25% 5% 15% 28% 22% 5%	1440
July	1st to 10th	Night	30% 6% 14% 27% 18% 5%	1400
	11th to 20th	Night	19% 6% 16% 29% 23% 7%	1392
	21st to end	Night	25% 7% 16% 31% 18% 3	1662
August	1st to 10th	Night	29% 7% 18% 28% 15% 3	1601
	11th to 20th	Night	27% 5% 14% 31% 19% 4	1600
	21st to end	Night	21% 5% 11% 28% 25% 10%	1975
September	1st to 10th	Night	23% 4 11% 25% 25% 12%	1867
	11th to 20th	Night	24% 5% 8% 26% 29% 8%	1980
	21st to end	Night	23% 3 9% 27% 32% 6%	1980
October	1st to 10th	Night	30% 4 9% 25% 26% 6%	1980
	11th to 20th	Night	22% 3 8% 28% 28% 11%	2098
	21st to end	Night	25% 3 12% 25% 23% 12%	2553
November	1st to 10th	Night	18% 3 10% 29% 30% 10%	2405
	11th to 20th	Night	24% 3 9% 28% 29% 8%	2470
	21st to end	Night	27% 3 10% 26% 26% 7%	2470
December	1st to 10th	Night	28% 3 13% 30% 21% 4	2470
	11th to 20th	Night	27% 2 10% 38% 22% 2	3068
	21st to end	Night	42% 2 11% 29% 14% 2	4873

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	11% 7% 39% 34% 9% 1	270
	11th to 20th	Day	13% 16% 35% 27% 7% 1	270
	21st to end	Day	11% 9% 46% 25% 8% 1	297
February	1st to 10th	Day	14% 11% 43% 27% 6%	270
	11th to 20th	Day	11% 10% 40% 29% 8% 1	252
	21st to end	Day	11% 14% 45% 26% 4 1	198
March	1st to 10th	Day	11% 12% 46% 22% 8% 1	240
	11th to 20th	Day	19% 11% 30% 29% 10% 1	240
	21st to end	Day	20% 13% 39% 21% 6% 1	264
April	1st to 10th	Day	12% 19% 38% 24% 6%	405
	11th to 20th	Day	16% 14% 39% 24% 6%	450
	21st to end	Day	18% 12% 36% 24% 10% 1	600
May	1st to 10th	Day	15% 9% 33% 30% 13% 1	603
	11th to 20th	Day	18% 10% 29% 26% 15% 2	625
	21st to end	Day	14% 8% 34% 30% 12% 2	679
June	1st to 10th	Day	5% 5% 29% 32% 23% 7%	630
	11th to 20th	Day	6% 5% 32% 39% 15% 2	630
	21st to end	Day	6% 5% 28% 38% 21% 1	630
July	1st to 10th	Day	7% 2 24% 39% 24% 5%	621
	11th to 20th	Day	5% 3 18% 43% 27% 5%	618
	21st to end	Day	7% 3 18% 40% 27% 5%	684
August	1st to 10th	Day	8% 1 16% 41% 29% 4	626
	11th to 20th	Day	6% 2 21% 42% 26% 3	615
	21st to end	Day	7% 2 17% 48% 20% 5%	495
September	1st to 10th	Day	9% 4 25% 42% 15% 4	383
	11th to 20th	Day	6% 6% 22% 37% 25% 4	270
	21st to end	Day	10% 9% 31% 30% 18% 3	270
October	1st to 10th	Day	22% 6% 24% 30% 13% 4	270
	11th to 20th	Day	7% 13% 37% 29% 11% 4	270
	21st to end	Day	17% 12% 32% 26% 12% 1	297
November	1st to 10th	Day	10% 12% 35% 26% 14% 3	270
	11th to 20th	Day	12% 10% 38% 26% 11% 2	270
	21st to end	Day	17% 10% 37% 21% 13% 3	270
December	1st to 10th	Day	9% 9% 37% 33% 12%	270
	11th to 20th	Day	13% 12% 39% 29% 6% 1	270
	21st to end	Day	19% 13% 35% 24% 8%	297
January	1st to 10th	Night	9% 8% 38% 37% 7% 1	950
	11th to 20th	Night	10% 12% 35% 35% 8% 1	950
	21st to end	Night	9% 8% 44% 32% 6%	1045
February	1st to 10th	Night	13% 9% 41% 32% 6%	855
	11th to 20th	Night	9% 11% 41% 34% 5%	722
	21st to end	Night	9% 13% 39% 33% 5%	592
March	1st to 10th	Night	12% 11% 38% 34% 4	720
	11th to 20th	Night	13% 11% 36% 31% 7% 1	551
	21st to end	Night	16% 14% 38% 26% 6%	594
April	1st to 10th	Night	13% 13% 47% 25% 3	540
	11th to 20th	Night	16% 13% 40% 26% 5%	533
	21st to end	Night	14% 16% 31% 31% 9%	540
May	1st to 10th	Night	14% 8% 36% 32% 8%	540
	11th to 20th	Night	17% 7% 35% 32% 9% 1	531
	21st to end	Night	13% 10% 35% 33% 9%	584
June	1st to 10th	Night	6% 6% 33% 41% 13% 1	540
	11th to 20th	Night	9% 7% 35% 39% 10%	540
	21st to end	Night	5% 6% 34% 43% 13%	540
July	1st to 10th	Night	7% 2 24% 49% 18%	525
	11th to 20th	Night	3 2 24% 52% 18% 1	522
	21st to end	Night	6% 2 19% 49% 23% 1	591
August	1st to 10th	Night	7% 1 17% 52% 22% 1	537
	11th to 20th	Night	7% 3 22% 49% 19%	534
	21st to end	Night	5% 1 24% 51% 18% 2	594
September	1st to 10th	Night	9% 2 27% 50% 11% 1	540
	11th to 20th	Night	10% 4 29% 41% 16% 1	540
	21st to end	Night	10% 7% 34% 36% 14% 1	540
October	1st to 10th	Night	14% 7% 31% 36% 11% 1	540
	11th to 20th	Night	10% 8% 37% 36% 8%	658
	21st to end	Night	13% 9% 31% 34% 12%	969
November	1st to 10th	Night	7% 8% 32% 44% 9%	925
	11th to 20th	Night	8% 10% 36% 39% 8%	950
	21st to end	Night	11% 8% 31% 37% 11% 1	950
December	1st to 10th	Night	8% 9% 38% 39% 6%	950
	11th to 20th	Night	11% 10% 35% 35% 9%	950
	21st to end	Night	13% 11% 34% 36% 5%	1045

Page generated at 2024-02-12 05:35:34. Version ac07

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