North Branch School
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Branch School clear sky chart from 2005-11-06 to 2024-07-31.

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	18% 12% 4 8% 5% 4 4 4 5% 6% 29%	89877
	Night	19% 14% 4 9% 5% 4 4 3 4 5% 28%	89969
Transparency	Day	55% 7% 11% 18% 9% 1	89596
	Night	57% 6% 11% 16% 8% 1	89804
Seeing	Day	27% 20% 29% 16% 6% 2	14385
	Night	26% 18% 26% 22% 8% 1	23346

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	14% 18% 6% 12% 7% 5% 5% 4 4 4 21%	2517
	11th to 20th	Day	13% 14% 5% 18% 9% 6% 4 2 3 4 21%	2520
	21st to end	Day	16% 19% 7% 12% 6% 5% 4 3 4 4 18%	2772
February	1st to 10th	Day	14% 15% 5% 11% 8% 5% 4 4 5% 5% 23%	1681
	11th to 20th	Day	12% 16% 5% 13% 9% 5% 4 3 4 4 24%	1830
	21st to end	Day	16% 15% 5% 12% 6% 4 4 3 4 5% 26%	1570
March	1st to 10th	Day	23% 17% 5% 10% 5% 5% 4 3 4 4 20%	3116
	11th to 20th	Day	14% 22% 7% 10% 5% 3 3 3 4 4 23%	3265
	21st to end	Day	18% 13% 5% 11% 4 4 4 3 4 4 31%	4166
April	1st to 10th	Day	23% 16% 3 7% 4 3 3 4 4 5% 29%	2280
	11th to 20th	Day	18% 13% 3 7% 5% 3 4 3 5% 5% 33%	2254
	21st to end	Day	23% 13% 4 8% 4 3 3 3 5% 5% 29%	2432
May	1st to 10th	Day	26% 12% 3 8% 5% 4 4 3 5% 5% 26%	4192
	11th to 20th	Day	17% 10% 3 7% 6% 5% 5% 4 6% 7% 29%	4398
	21st to end	Day	14% 7% 2 7% 5% 5% 4 4 7% 8% 36%	4837
June	1st to 10th	Day	23% 8% 3 7% 5% 5% 5% 4 5% 8% 28%	2660
	11th to 20th	Day	19% 7% 3 7% 5% 4 5% 4 6% 8% 32%	2660
	21st to end	Day	22% 9% 3 7% 6% 5% 5% 4 6% 6% 28%	2660
July	1st to 10th	Day	15% 7% 2 6% 5% 4 4 4 7% 7% 38%	2660
	11th to 20th	Day	14% 7% 2 7% 5% 6% 6% 4 8% 9% 33%	2660
	21st to end	Day	17% 5% 3 6% 5% 5% 5% 6% 6% 8% 34%	2887
August	1st to 10th	Day	14% 6% 2 7% 5% 5% 6% 5% 6% 9% 35%	2500
	11th to 20th	Day	16% 8% 3 7% 4 5% 5% 4 6% 9% 34%	2213
	21st to end	Day	14% 6% 3 7% 5% 5% 4 5% 6% 8% 38%	2376
September	1st to 10th	Day	16% 6% 2 4 4 4 4 4 6% 7% 43%	2160
	11th to 20th	Day	17% 6% 2 5% 3 3 3 3 4 7% 46%	2052
	21st to end	Day	18% 8% 2 5% 3 4 4 4 6% 7% 39%	1980
October	1st to 10th	Day	25% 11% 3 7% 4 4 3 3 4 5% 31%	1913
	11th to 20th	Day	18% 12% 4 7% 4 4 4 4 5% 7% 33%	1755
	21st to end	Day	28% 13% 3 8% 4 3 4 3 4 5% 24%	1782
November	1st to 10th	Day	17% 14% 4 8% 5% 4 3 3 5% 5% 34%	1671
	11th to 20th	Day	19% 17% 4 8% 5% 5% 3 3 5% 4 27%	1710
	21st to end	Day	19% 13% 4 10% 5% 5% 5% 3 5% 6% 25%	1550
December	1st to 10th	Day	21% 19% 5% 10% 6% 4 3 3 5% 5% 19%	1520
	11th to 20th	Day	21% 18% 4 10% 5% 4 4 2 5% 6% 22%	1906
	21st to end	Day	21% 22% 5% 11% 5% 5% 4 3 3 4 18%	2772
January	1st to 10th	Night	15% 17% 6% 13% 7% 5% 4 3 4 4 22%	4429
	11th to 20th	Night	12% 17% 7% 19% 11% 6% 4 3 4 4 15%	4440
	21st to end	Night	20% 18% 6% 14% 6% 5% 4 3 4 3 17%	4884
February	1st to 10th	Night	16% 16% 6% 12% 8% 6% 5% 3 4 5% 21%	2496
	11th to 20th	Night	13% 16% 6% 14% 8% 5% 5% 3 4 4 22%	2234
	21st to end	Night	14% 15% 6% 12% 6% 5% 4 3 4 5% 27%	1884
March	1st to 10th	Night	22% 15% 4 8% 6% 4 3 3 4 5% 25%	3724
	11th to 20th	Night	14% 20% 6% 10% 5% 4 3 3 3 5% 28%	3690
	21st to end	Night	17% 17% 5% 10% 5% 3 3 2 3 4 31%	3466
April	1st to 10th	Night	21% 17% 3 9% 4 3 4 2 4 5% 28%	1900
	11th to 20th	Night	22% 14% 3 7% 5% 3 4 3 4 5% 30%	1875
	21st to end	Night	23% 11% 4 8% 4 3 3 4 4 5% 31%	1747
May	1st to 10th	Night	28% 11% 3 6% 4 4 4 4 5% 6% 25%	2778
	11th to 20th	Night	21% 12% 3 10% 5% 4 4 3 4 5% 30%	2495
	21st to end	Night	17% 7% 3 5% 4 4 4 5% 7% 8% 36%	2738
June	1st to 10th	Night	23% 8% 2 7% 5% 4 5% 3 6% 6% 31%	1520
	11th to 20th	Night	21% 6% 3 5% 4 5% 3 4 5% 8% 37%	1520
	21st to end	Night	21% 7% 3 7% 5% 5% 4 4 5% 7% 32%	1520
July	1st to 10th	Night	15% 6% 2 6% 4 5% 4 4 7% 8% 38%	1520
	11th to 20th	Night	14% 8% 2 5% 4 4 5% 5% 7% 7% 38%	1520
	21st to end	Night	14% 6% 3 6% 4 4 5% 5% 6% 7% 41%	1662
August	1st to 10th	Night	15% 5% 2 5% 3 4 6% 4 6% 9% 42%	1432
	11th to 20th	Night	15% 7% 3 6% 4 5% 4 3 7% 7% 38%	1672
	21st to end	Night	14% 8% 2 6% 4 4 4 4 6% 7% 41%	1980
September	1st to 10th	Night	17% 7% 3 6% 3 4 3 3 5% 7% 43%	1800
	11th to 20th	Night	15% 6% 2 5% 3 3 4 2 5% 5% 49%	1908
	21st to end	Night	18% 7% 2 5% 4 5% 4 4 5% 5% 42%	1980
October	1st to 10th	Night	24% 10% 3 8% 4 3 3 3 5% 5% 32%	2042
	11th to 20th	Night	20% 12% 3 8% 4 4 5% 4 4 5% 29%	2204
	21st to end	Night	26% 15% 4 7% 5% 4 4 3 4 4 24%	2574
November	1st to 10th	Night	19% 14% 4 8% 5% 4 5% 3 4 4 30%	2407
	11th to 20th	Night	20% 15% 4 8% 5% 4 4 3 4 6% 29%	2470
	21st to end	Night	18% 17% 5% 11% 4 4 4 3 5% 5% 24%	2626
December	1st to 10th	Night	20% 21% 7% 11% 6% 4 4 3 4 4 15%	2660
	11th to 20th	Night	21% 17% 4 10% 5% 4 4 4 5% 4 22%	3288
	21st to end	Night	23% 18% 7% 13% 5% 4 3 2 3 4 17%	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	62% 5% 13% 16% 4	2518
	11th to 20th	Day	69% 5% 8% 11% 5% 1	2520
	21st to end	Day	67% 7% 11% 10% 5% 1	2772
February	1st to 10th	Day	62% 6% 9% 15% 6% 2	1681
	11th to 20th	Day	64% 5% 8% 15% 7% 1	1839
	21st to end	Day	61% 6% 9% 12% 10% 1	1570
March	1st to 10th	Day	67% 5% 9% 11% 7% 1	3119
	11th to 20th	Day	62% 6% 12% 11% 8% 1	3265
	21st to end	Day	57% 3 7% 14% 16% 2	4166
April	1st to 10th	Day	57% 4 8% 18% 10% 2	2280
	11th to 20th	Day	53% 6% 9% 18% 14% 1	2254
	21st to end	Day	58% 5% 9% 15% 11% 2	2432
May	1st to 10th	Day	60% 6% 9% 18% 7% 1	4206
	11th to 20th	Day	51% 8% 14% 17% 9% 1	4402
	21st to end	Day	42% 9% 12% 25% 11% 1	4837
June	1st to 10th	Day	54% 7% 13% 16% 8% 1	2660
	11th to 20th	Day	49% 7% 11% 20% 12% 1	2660
	21st to end	Day	55% 7% 10% 18% 9% 1	2660
July	1st to 10th	Day	42% 8% 12% 24% 14%	2590
	11th to 20th	Day	44% 9% 14% 26% 7%	2585
	21st to end	Day	45% 9% 13% 23% 9%	2734
August	1st to 10th	Day	44% 10% 14% 23% 8%	2486
	11th to 20th	Day	46% 8% 15% 22% 8%	2213
	21st to end	Day	43% 8% 12% 24% 12% 1	2376
September	1st to 10th	Day	40% 7% 12% 28% 12% 1	2160
	11th to 20th	Day	38% 5% 10% 29% 16% 1	2052
	21st to end	Day	43% 6% 15% 23% 11% 2	1980
October	1st to 10th	Day	57% 5% 8% 19% 10% 1	1913
	11th to 20th	Day	51% 7% 14% 20% 7%	1755
	21st to end	Day	64% 6% 8% 13% 8% 1	1782
November	1st to 10th	Day	51% 6% 13% 19% 10%	1671
	11th to 20th	Day	59% 5% 11% 13% 10% 2	1710
	21st to end	Day	60% 6% 13% 15% 5% 1	1550
December	1st to 10th	Day	66% 8% 11% 11% 4	1520
	11th to 20th	Day	64% 5% 12% 14% 5% 1	1906
	21st to end	Day	70% 6% 9% 11% 4	2772
January	1st to 10th	Night	62% 7% 16% 11% 4	4429
	11th to 20th	Night	73% 5% 11% 8% 3	4440
	21st to end	Night	72% 4 8% 9% 5% 1	4884
February	1st to 10th	Night	66% 5% 10% 11% 7% 1	2496
	11th to 20th	Night	64% 5% 8% 14% 9% 1	2236
	21st to end	Night	59% 5% 11% 16% 7% 2	1884
March	1st to 10th	Night	62% 5% 10% 15% 8% 1	3734
	11th to 20th	Night	58% 7% 11% 14% 9% 1	3691
	21st to end	Night	58% 3 7% 13% 16% 3	3466
April	1st to 10th	Night	58% 5% 7% 16% 11% 2	1900
	11th to 20th	Night	56% 5% 9% 17% 12% 1	1875
	21st to end	Night	55% 5% 8% 17% 11% 3	1747
May	1st to 10th	Night	57% 8% 9% 16% 9% 1	2784
	11th to 20th	Night	56% 7% 10% 17% 9% 1	2496
	21st to end	Night	42% 10% 13% 20% 14% 2	2739
June	1st to 10th	Night	50% 9% 12% 17% 11% 1	1520
	11th to 20th	Night	46% 7% 15% 20% 11% 2	1520
	21st to end	Night	50% 7% 12% 22% 8% 1	1520
July	1st to 10th	Night	41% 8% 16% 21% 13% 1	1480
	11th to 20th	Night	40% 11% 14% 25% 10%	1472
	21st to end	Night	40% 8% 14% 25% 11% 1	1574
August	1st to 10th	Night	38% 9% 15% 28% 10%	1422
	11th to 20th	Night	43% 7% 15% 24% 10%	1672
	21st to end	Night	41% 8% 14% 25% 12%	1980
September	1st to 10th	Night	40% 8% 14% 27% 11% 1	1800
	11th to 20th	Night	38% 5% 12% 29% 15%	1908
	21st to end	Night	42% 6% 13% 24% 13% 2	1980
October	1st to 10th	Night	54% 6% 9% 20% 10% 1	2042
	11th to 20th	Night	54% 7% 12% 18% 7%	2204
	21st to end	Night	64% 6% 9% 13% 7% 1	2574
November	1st to 10th	Night	56% 6% 11% 16% 9% 2	2407
	11th to 20th	Night	56% 6% 11% 16% 9% 3	2470
	21st to end	Night	60% 6% 13% 15% 6%	2626
December	1st to 10th	Night	72% 6% 9% 10% 2	2660
	11th to 20th	Night	63% 7% 11% 11% 7%	3288
	21st to end	Night	71% 6% 8% 13% 3	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	28% 27% 29% 14% 2	180
	11th to 20th	Day	32% 25% 32% 9% 1 1	180
	21st to end	Day	22% 34% 32% 9% 3	198
February	1st to 10th	Day	36% 38% 20% 5% 1	256
	11th to 20th	Day	31% 31% 28% 8% 2	438
	21st to end	Day	34% 25% 28% 11% 2	382
March	1st to 10th	Day	31% 21% 32% 13% 2	460
	11th to 20th	Day	31% 28% 26% 12% 2 1	460
	21st to end	Day	34% 26% 23% 11% 5% 2	506
April	1st to 10th	Day	39% 21% 24% 12% 4 1	460
	11th to 20th	Day	37% 25% 21% 11% 5% 1	452
	21st to end	Day	35% 20% 28% 10% 5% 2	460
May	1st to 10th	Day	37% 19% 23% 13% 7% 1	463
	11th to 20th	Day	23% 19% 36% 15% 5% 1	487
	21st to end	Day	22% 17% 33% 21% 7% 1	529
June	1st to 10th	Day	28% 18% 32% 17% 6%	490
	11th to 20th	Day	23% 17% 33% 18% 7% 1	490
	21st to end	Day	29% 17% 30% 18% 6% 1	490
July	1st to 10th	Day	19% 13% 33% 24% 9% 2	485
	11th to 20th	Day	19% 11% 38% 22% 9% 1	484
	21st to end	Day	18% 14% 37% 22% 7% 1	529
August	1st to 10th	Day	16% 12% 32% 26% 12% 2	446
	11th to 20th	Day	21% 12% 26% 24% 13% 5%	439
	21st to end	Day	16% 17% 29% 24% 9% 4	495
September	1st to 10th	Day	19% 13% 28% 24% 10% 6%	450
	11th to 20th	Day	21% 14% 24% 19% 14% 8%	450
	21st to end	Day	20% 17% 29% 18% 11% 5%	450
October	1st to 10th	Day	31% 15% 23% 15% 12% 4	450
	11th to 20th	Day	27% 18% 29% 18% 7%	427
	21st to end	Day	36% 20% 26% 15% 3	396
November	1st to 10th	Day	30% 21% 24% 18% 7%	365
	11th to 20th	Day	31% 26% 23% 14% 5% 1	370
	21st to end	Day	34% 20% 31% 12% 2	210
December	1st to 10th	Day	32% 27% 27% 12% 3	180
	11th to 20th	Day	38% 26% 27% 7% 1	180
	21st to end	Day	36% 25% 30% 7% 2	198
January	1st to 10th	Night	26% 26% 32% 15% 2	760
	11th to 20th	Night	28% 25% 27% 16% 4	760
	21st to end	Night	20% 24% 32% 21% 3	836
February	1st to 10th	Night	22% 27% 33% 16% 1	760
	11th to 20th	Night	24% 26% 31% 16% 2	743
	21st to end	Night	27% 24% 30% 17% 3	628
March	1st to 10th	Night	27% 21% 31% 19% 3	760
	11th to 20th	Night	27% 25% 25% 18% 4	760
	21st to end	Night	30% 21% 24% 19% 6%	836
April	1st to 10th	Night	29% 21% 26% 19% 4	760
	11th to 20th	Night	30% 23% 24% 17% 6% 1	751
	21st to end	Night	29% 19% 25% 21% 6% 1	607
May	1st to 10th	Night	31% 14% 27% 19% 8%	540
	11th to 20th	Night	21% 15% 32% 25% 6% 1	374
	21st to end	Night	21% 9% 30% 30% 9% 1	411
June	1st to 10th	Night	26% 7% 29% 26% 11% 1	380
	11th to 20th	Night	22% 9% 24% 32% 12% 1	380
	21st to end	Night	23% 8% 23% 35% 10% 1	380
July	1st to 10th	Night	18% 4 24% 36% 17% 1	370
	11th to 20th	Night	18% 4 24% 36% 16% 2	368
	21st to end	Night	14% 6% 21% 43% 14%	416
August	1st to 10th	Night	16% 5% 20% 41% 18% 1	358
	11th to 20th	Night	18% 6% 23% 33% 17% 3	608
	21st to end	Night	18% 8% 20% 32% 19% 2	792
September	1st to 10th	Night	20% 8% 25% 30% 14% 3	720
	11th to 20th	Night	20% 9% 21% 27% 18% 4	720
	21st to end	Night	20% 12% 24% 24% 18% 2	720
October	1st to 10th	Night	31% 11% 20% 22% 14% 2	720
	11th to 20th	Night	28% 16% 22% 23% 10% 1	720
	21st to end	Night	35% 17% 25% 17% 6%	792
November	1st to 10th	Night	26% 20% 28% 18% 7%	740
	11th to 20th	Night	27% 22% 27% 16% 6% 1	760
	21st to end	Night	26% 26% 26% 16% 5% 1	760
December	1st to 10th	Night	31% 26% 25% 15% 3	760
	11th to 20th	Night	30% 23% 25% 19% 3	760
	21st to end	Night	33% 23% 29% 13% 1	836

Page generated at 2024-07-28 09:52:10. Version ac07

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