Chipman
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chipman 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	20% 9% 3 6% 5% 3 4 4 5% 6% 33%	74740
	Night	20% 10% 3 6% 5% 3 4 4 4 6% 34%	75202
Transparency	Day	52% 4 11% 21% 11% 1	74439
	Night	53% 3 11% 21% 11% 1	75038
Seeing	Day	29% 14% 30% 19% 7% 1	15347
	Night	27% 13% 30% 23% 6%	23285

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	16% 17% 5% 8% 5% 3 5% 3 3 6% 29%	1327
	11th to 20th	Day	20% 15% 4 8% 6% 3 4 4 3 4 28%	1434
	21st to end	Day	13% 10% 4 6% 5% 2 4 5% 5% 6% 40%	1748
February	1st to 10th	Day	16% 12% 4 5% 6% 4 5% 5% 5% 6% 31%	1620
	11th to 20th	Day	17% 13% 4 6% 5% 3 5% 5% 5% 7% 30%	1573
	21st to end	Day	11% 11% 5% 7% 7% 4 5% 4 4 6% 36%	1403
March	1st to 10th	Day	17% 16% 5% 8% 7% 3 4 3 5% 5% 28%	1909
	11th to 20th	Day	17% 11% 5% 8% 7% 3 4 3 4 5% 32%	1980
	21st to end	Day	19% 12% 4 6% 6% 3 4 3 4 5% 33%	2178
April	1st to 10th	Day	23% 13% 4 7% 5% 4 4 5% 4 6% 25%	2106
	11th to 20th	Day	20% 10% 3 6% 5% 3 4 4 4 6% 34%	2312
	21st to end	Day	27% 11% 4 6% 4 2 4 3 4 6% 30%	2340
May	1st to 10th	Day	26% 8% 3 7% 5% 3 5% 4 4 5% 29%	2340
	11th to 20th	Day	26% 8% 2 6% 5% 3 4 3 4 6% 32%	2475
	21st to end	Day	20% 8% 3 6% 5% 3 4 5% 5% 8% 33%	2782
June	1st to 10th	Day	27% 8% 4 6% 6% 3 5% 4 5% 6% 26%	2700
	11th to 20th	Day	23% 6% 3 5% 5% 3 5% 5% 5% 7% 33%	2700
	21st to end	Day	28% 8% 3 6% 5% 3 5% 3 4 6% 29%	2700
July	1st to 10th	Day	17% 6% 3 6% 5% 3 6% 5% 6% 10% 34%	2700
	11th to 20th	Day	17% 6% 3 5% 5% 4 6% 5% 7% 9% 34%	2700
	21st to end	Day	18% 7% 3 6% 6% 3 7% 7% 6% 9% 29%	2656
August	1st to 10th	Day	18% 5% 3 6% 5% 3 5% 6% 6% 7% 34%	2327
	11th to 20th	Day	17% 7% 3 7% 6% 4 6% 7% 6% 7% 31%	2304
	21st to end	Day	16% 5% 2 5% 5% 3 5% 5% 5% 8% 41%	2570
September	1st to 10th	Day	14% 5% 2 5% 5% 4 5% 5% 6% 7% 43%	2160
	11th to 20th	Day	18% 7% 2 5% 4 3 4 3 4 6% 45%	1990
	21st to end	Day	21% 6% 2 5% 4 3 3 3 4 5% 44%	1980
October	1st to 10th	Day	16% 8% 3 7% 5% 3 4 4 6% 5% 41%	1810
	11th to 20th	Day	21% 6% 3 5% 5% 3 5% 5% 3 6% 38%	1800
	21st to end	Day	23% 8% 3 6% 6% 3 5% 5% 4 7% 31%	1888
November	1st to 10th	Day	22% 8% 3 6% 6% 3 4 4 4 6% 34%	1562
	11th to 20th	Day	19% 7% 3 8% 7% 3 4 3 4 6% 35%	1520
	21st to end	Day	21% 11% 5% 7% 6% 3 4 3 5% 6% 31%	1520
December	1st to 10th	Day	24% 11% 4 8% 6% 2 3 4 4 5% 29%	1520
	11th to 20th	Day	21% 13% 5% 9% 8% 3 4 3 4 5% 28%	1675
	21st to end	Day	21% 12% 5% 6% 5% 3 3 3 3 4 36%	2431
January	1st to 10th	Night	17% 12% 5% 9% 6% 3 4 4 5% 6% 28%	2838
	11th to 20th	Night	19% 11% 4 8% 6% 3 4 4 5% 6% 29%	2741
	21st to end	Night	12% 11% 4 6% 6% 3 5% 4 6% 8% 36%	2640
February	1st to 10th	Night	16% 12% 4 6% 6% 3 5% 5% 5% 7% 32%	2340
	11th to 20th	Night	18% 13% 4 8% 7% 4 4 4 4 5% 30%	2273
	21st to end	Night	14% 13% 5% 6% 6% 4 5% 4 4 5% 33%	1852
March	1st to 10th	Night	16% 15% 5% 7% 5% 3 4 4 4 4 33%	2037
	11th to 20th	Night	18% 10% 4 6% 7% 3 5% 6% 5% 6% 31%	1979
	21st to end	Night	18% 11% 5% 7% 7% 4 4 3 4 4 33%	2178
April	1st to 10th	Night	26% 11% 3 7% 6% 3 5% 4 4 5% 27%	1852
	11th to 20th	Night	22% 10% 3 5% 4 3 4 5% 5% 5% 34%	1598
	21st to end	Night	24% 11% 4 6% 5% 3 4 4 5% 6% 29%	1620
May	1st to 10th	Night	24% 8% 3 5% 5% 3 6% 4 4 6% 32%	1620
	11th to 20th	Night	27% 9% 2 5% 4 2 5% 3 4 6% 33%	1416
	21st to end	Night	16% 9% 4 7% 5% 3 5% 5% 6% 7% 33%	1507
June	1st to 10th	Night	26% 8% 3 6% 6% 3 4 5% 5% 6% 28%	1260
	11th to 20th	Night	21% 7% 3 6% 6% 3 5% 5% 4 5% 36%	1260
	21st to end	Night	27% 8% 3 5% 5% 3 5% 2 4 5% 32%	1260
July	1st to 10th	Night	17% 7% 3 7% 5% 3 5% 5% 5% 9% 36%	1260
	11th to 20th	Night	18% 5% 3 6% 5% 3 6% 4 6% 8% 37%	1260
	21st to end	Night	21% 6% 3 6% 6% 4 6% 5% 5% 8% 31%	1641
August	1st to 10th	Night	15% 7% 3 5% 4 3 5% 6% 6% 8% 39%	1612
	11th to 20th	Night	16% 9% 3 8% 4 3 4 5% 6% 7% 35%	1596
	21st to end	Night	15% 6% 2 5% 5% 2 3 4 5% 8% 44%	1786
September	1st to 10th	Night	17% 5% 2 5% 5% 3 4 5% 5% 7% 43%	1800
	11th to 20th	Night	18% 6% 2 5% 4 2 4 4 4 7% 46%	1967
	21st to end	Night	20% 5% 2 4 3 2 3 4 4 6% 45%	1980
October	1st to 10th	Night	20% 6% 2 6% 4 2 4 4 5% 7% 40%	2150
	11th to 20th	Night	18% 7% 3 6% 5% 3 4 5% 4 8% 37%	2160
	21st to end	Night	24% 8% 3 6% 5% 3 4 3 3 5% 34%	2466
November	1st to 10th	Night	23% 8% 3 6% 6% 2 4 4 4 6% 36%	2516
	11th to 20th	Night	22% 8% 3 5% 5% 3 4 5% 4 7% 33%	2660
	21st to end	Night	22% 9% 4 7% 5% 3 5% 4 5% 6% 31%	2660
December	1st to 10th	Night	26% 11% 4 6% 5% 3 4 4 4 4 29%	2660
	11th to 20th	Night	26% 11% 4 7% 5% 3 4 4 4 4 29%	3521
	21st to end	Night	21% 14% 5% 7% 5% 3 3 3 4 4 32%	5236

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% 3 11% 16% 10%	1328
	11th to 20th	Day	62% 3 7% 17% 10% 1	1434
	21st to end	Day	46% 3 11% 22% 16% 2	1748
February	1st to 10th	Day	54% 4 11% 19% 10% 2	1620
	11th to 20th	Day	55% 3 10% 19% 11% 1	1581
	21st to end	Day	50% 3 9% 23% 13% 3	1403
March	1st to 10th	Day	60% 3 9% 18% 10% 1	1913
	11th to 20th	Day	56% 2 9% 18% 12% 3	1980
	21st to end	Day	56% 2 7% 19% 11% 4	2178
April	1st to 10th	Day	62% 3 7% 15% 11% 3	2106
	11th to 20th	Day	52% 3 8% 23% 13% 2	2312
	21st to end	Day	57% 3 9% 16% 12% 4	2340
May	1st to 10th	Day	58% 3 7% 19% 12% 1	2340
	11th to 20th	Day	55% 3 8% 21% 12% 1	2479
	21st to end	Day	50% 5% 13% 23% 10% 1	2782
June	1st to 10th	Day	59% 4 10% 18% 9%	2700
	11th to 20th	Day	51% 4 11% 20% 12% 1	2700
	21st to end	Day	57% 4 11% 17% 10% 1	2700
July	1st to 10th	Day	46% 4 17% 22% 10%	2625
	11th to 20th	Day	45% 5% 17% 24% 10% 1	2619
	21st to end	Day	50% 6% 15% 21% 8%	2507
August	1st to 10th	Day	48% 4 15% 25% 7%	2314
	11th to 20th	Day	50% 5% 14% 24% 7%	2304
	21st to end	Day	41% 4 15% 29% 11%	2570
September	1st to 10th	Day	40% 4 15% 27% 13%	2160
	11th to 20th	Day	42% 3 11% 28% 14% 2	1990
	21st to end	Day	43% 3 9% 28% 15% 1	1980
October	1st to 10th	Day	45% 3 12% 26% 13%	1810
	11th to 20th	Day	48% 4 13% 26% 8%	1800
	21st to end	Day	55% 4 11% 19% 11%	1888
November	1st to 10th	Day	53% 3 10% 23% 11% 1	1562
	11th to 20th	Day	53% 3 13% 18% 13% 1	1520
	21st to end	Day	56% 4 14% 18% 7%	1520
December	1st to 10th	Day	59% 3 11% 19% 6%	1520
	11th to 20th	Day	62% 2 8% 18% 9% 1	1675
	21st to end	Day	55% 2 12% 20% 9% 2	2431
January	1st to 10th	Night	59% 3 10% 19% 9% 1	2838
	11th to 20th	Night	57% 4 11% 17% 9% 1	2741
	21st to end	Night	48% 3 11% 24% 12% 2	2640
February	1st to 10th	Night	53% 3 11% 19% 13% 2	2340
	11th to 20th	Night	58% 3 8% 17% 12% 2	2276
	21st to end	Night	54% 3 8% 20% 13% 2	1852
March	1st to 10th	Night	56% 3 7% 20% 12% 2	2046
	11th to 20th	Night	55% 3 9% 17% 13% 2	1980
	21st to end	Night	56% 3 5% 19% 14% 3	2178
April	1st to 10th	Night	61% 3 6% 15% 11% 4	1852
	11th to 20th	Night	52% 3 8% 21% 14% 1	1598
	21st to end	Night	57% 3 10% 16% 13% 2	1620
May	1st to 10th	Night	54% 4 9% 20% 11% 3	1620
	11th to 20th	Night	55% 2 8% 22% 12% 1	1417
	21st to end	Night	49% 5% 14% 19% 11% 1	1508
June	1st to 10th	Night	56% 5% 10% 20% 9% 1	1260
	11th to 20th	Night	52% 4 10% 23% 9% 2	1260
	21st to end	Night	56% 4 12% 18% 9% 1	1260
July	1st to 10th	Night	45% 5% 17% 25% 8%	1225
	11th to 20th	Night	46% 4 16% 24% 10%	1218
	21st to end	Night	52% 5% 13% 21% 9% 1	1550
August	1st to 10th	Night	43% 5% 17% 27% 8%	1600
	11th to 20th	Night	47% 4 19% 24% 5%	1596
	21st to end	Night	40% 3 17% 29% 12% 1	1786
September	1st to 10th	Night	42% 4 11% 30% 13% 1	1800
	11th to 20th	Night	41% 3 12% 28% 16% 1	1967
	21st to end	Night	42% 3 11% 28% 15% 1	1980
October	1st to 10th	Night	46% 3 11% 26% 14%	2150
	11th to 20th	Night	47% 3 12% 28% 9% 1	2160
	21st to end	Night	55% 3 10% 20% 11% 1	2466
November	1st to 10th	Night	52% 4 12% 21% 11% 1	2516
	11th to 20th	Night	54% 3 12% 20% 10% 1	2660
	21st to end	Night	56% 4 13% 16% 10%	2660
December	1st to 10th	Night	61% 2 10% 20% 7%	2660
	11th to 20th	Night	61% 2 7% 19% 9% 1	3522
	21st to end	Night	58% 2 10% 19% 9% 2	5236

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	33% 12% 33% 20% 2	180
	11th to 20th	Day	42% 17% 27% 11% 3 1	180
	21st to end	Day	22% 18% 36% 18% 6% 1	334
February	1st to 10th	Day	31% 16% 33% 15% 4	340
	11th to 20th	Day	32% 22% 28% 14% 3 1	336
	21st to end	Day	27% 22% 29% 16% 5%	312
March	1st to 10th	Day	31% 20% 32% 13% 3 1	420
	11th to 20th	Day	30% 19% 30% 16% 3 1	420
	21st to end	Day	34% 16% 30% 13% 4 2	462
April	1st to 10th	Day	40% 19% 26% 11% 3	420
	11th to 20th	Day	33% 19% 28% 15% 5% 1	412
	21st to end	Day	38% 17% 25% 12% 5% 2	420
May	1st to 10th	Day	37% 15% 27% 16% 4 1	423
	11th to 20th	Day	33% 12% 29% 18% 5% 2	621
	21st to end	Day	30% 15% 31% 19% 4 1	680
June	1st to 10th	Day	32% 13% 29% 19% 6%	630
	11th to 20th	Day	30% 13% 27% 22% 6% 1	630
	21st to end	Day	31% 9% 29% 22% 8%	630
July	1st to 10th	Day	24% 10% 35% 22% 9% 1	620
	11th to 20th	Day	23% 6% 32% 28% 10% 2	618
	21st to end	Day	21% 6% 37% 25% 10% 1	548
August	1st to 10th	Day	19% 7% 36% 29% 8% 2	446
	11th to 20th	Day	24% 9% 26% 27% 13% 1	439
	21st to end	Day	22% 10% 26% 28% 11% 3	495
September	1st to 10th	Day	14% 13% 35% 28% 8% 2	450
	11th to 20th	Day	27% 9% 30% 21% 11% 3	450
	21st to end	Day	23% 14% 35% 15% 9% 5%	450
October	1st to 10th	Day	23% 12% 27% 20% 15% 2	365
	11th to 20th	Day	28% 14% 26% 20% 10% 3	360
	21st to end	Day	29% 16% 32% 17% 5% 1	396
November	1st to 10th	Day	33% 12% 33% 16% 5% 1	365
	11th to 20th	Day	32% 16% 29% 15% 6% 1	370
	21st to end	Day	33% 18% 28% 18% 3	370
December	1st to 10th	Day	34% 11% 31% 18% 6% 1	370
	11th to 20th	Day	40% 21% 28% 9% 1 1	187
	21st to end	Day	35% 15% 35% 13% 2	198
January	1st to 10th	Night	27% 17% 30% 21% 4	850
	11th to 20th	Night	29% 17% 28% 22% 5%	799
	21st to end	Night	22% 16% 35% 22% 6%	800
February	1st to 10th	Night	27% 17% 32% 20% 3	720
	11th to 20th	Night	27% 21% 31% 16% 3 1	703
	21st to end	Night	24% 16% 33% 22% 5%	592
March	1st to 10th	Night	28% 13% 37% 20% 2	720
	11th to 20th	Night	26% 16% 32% 21% 6% 1	720
	21st to end	Night	26% 16% 32% 20% 5% 1	792
April	1st to 10th	Night	35% 16% 28% 19% 3	612
	11th to 20th	Night	30% 17% 31% 18% 5%	534
	21st to end	Night	32% 15% 30% 19% 5%	540
May	1st to 10th	Night	31% 14% 28% 23% 5%	540
	11th to 20th	Night	32% 12% 30% 21% 5%	532
	21st to end	Night	22% 14% 39% 20% 4	540
June	1st to 10th	Night	29% 7% 32% 28% 4	360
	11th to 20th	Night	25% 9% 28% 31% 6% 1	360
	21st to end	Night	33% 4 25% 33% 6%	360
July	1st to 10th	Night	21% 5% 38% 30% 7%	350
	11th to 20th	Night	21% 3 29% 36% 10%	348
	21st to end	Night	25% 5% 30% 31% 8% 1	524
August	1st to 10th	Night	18% 2 33% 36% 10%	538
	11th to 20th	Night	20% 5% 27% 35% 12%	532
	21st to end	Night	18% 8% 26% 34% 14% 1	594
September	1st to 10th	Night	21% 7% 36% 26% 9%	540
	11th to 20th	Night	23% 7% 26% 30% 13% 1	707
	21st to end	Night	24% 9% 30% 25% 10% 1	720
October	1st to 10th	Night	25% 9% 28% 26% 10% 1	720
	11th to 20th	Night	24% 11% 33% 22% 10% 1	720
	21st to end	Night	31% 15% 29% 20% 5%	792
November	1st to 10th	Night	31% 13% 26% 23% 6% 1	791
	11th to 20th	Night	30% 15% 29% 19% 7% 1	850
	21st to end	Night	29% 18% 27% 21% 4	850
December	1st to 10th	Night	35% 11% 29% 20% 5%	850
	11th to 20th	Night	33% 18% 27% 18% 4	850
	21st to end	Night	33% 16% 27% 20% 4 1	935

Page generated at 2024-01-19 10:28:30. Version ac07

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