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 2025-01-07.

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%	105032
	Night	19% 14% 4 9% 5% 4 4 3 4 5% 28%	104004
Transparency	Day	53% 7% 11% 19% 9% 1	108531
	Night	57% 6% 11% 16% 9% 1	108594
Seeing	Day	28% 20% 29% 16% 6% 2	14897
	Night	26% 18% 26% 22% 8% 1	23958

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%	2565
	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	14% 7% 2 7% 4 5% 5% 5% 7% 10% 35%	4440
	11th to 20th	Day	14% 7% 2 7% 5% 5% 6% 4 8% 10% 32%	4440
	21st to end	Day	16% 6% 3 7% 5% 5% 5% 5% 6% 8% 35%	4814
August	1st to 10th	Day	18% 8% 2 7% 5% 4 5% 4 6% 8% 31%	4404
	11th to 20th	Day	16% 9% 3 8% 5% 4 5% 4 6% 8% 31%	3870
	21st to end	Day	15% 7% 3 5% 4 4 4 4 6% 8% 40%	4180
September	1st to 10th	Day	16% 6% 2 4 4 4 4 4 6% 7% 44%	2280
	11th to 20th	Day	16% 6% 2 5% 3 3 4 3 4 7% 46%	2166
	21st to end	Day	18% 8% 2 6% 4 4 4 4 6% 7% 38%	2090
October	1st to 10th	Day	24% 11% 3 7% 4 4 3 3 4 5% 31%	2019
	11th to 20th	Day	18% 12% 4 7% 4 4 4 4 4 6% 34%	1852
	21st to end	Day	27% 13% 3 8% 4 3 4 3 4 5% 26%	1881
November	1st to 10th	Day	17% 14% 4 8% 5% 4 3 3 5% 6% 33%	1761
	11th to 20th	Day	18% 17% 4 8% 5% 5% 3 3 5% 5% 28%	1800
	21st to end	Day	19% 14% 4 10% 5% 5% 5% 4 5% 6% 24%	1631
December	1st to 10th	Day	16% 21% 6% 14% 7% 5% 4 4 5% 4 14%	2600
	11th to 20th	Day	21% 19% 4 11% 4 4 4 2 5% 4 22%	2986
	21st to end	Day	19% 20% 5% 10% 4 4 5% 3 3 4 21%	3960
January	1st to 10th	Night	15% 17% 6% 13% 6% 5% 4 3 4 4 22%	4514
	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% 7% 3 7% 5% 5% 6% 5% 7% 7% 33%	2520
	11th to 20th	Night	18% 8% 3 5% 4 4 5% 4 6% 6% 37%	2520
	21st to end	Night	16% 8% 3 7% 5% 4 5% 4 5% 6% 37%	2739
August	1st to 10th	Night	23% 9% 2 6% 4 4 4 3 4 6% 35%	2506
	11th to 20th	Night	17% 8% 3 7% 5% 4 4 3 6% 6% 36%	2928
	21st to end	Night	14% 7% 2 5% 4 4 4 4 6% 8% 42%	3476
September	1st to 10th	Night	17% 7% 3 6% 3 4 3 3 5% 7% 44%	1900
	11th to 20th	Night	15% 6% 2 5% 3 3 4 2 5% 5% 50%	2014
	21st to end	Night	17% 7% 2 5% 4 5% 4 4 5% 5% 42%	2090
October	1st to 10th	Night	23% 11% 3 8% 4 3 4 3 5% 6% 32%	2156
	11th to 20th	Night	20% 13% 3 8% 4 4 5% 3 4 5% 31%	2327
	21st to end	Night	25% 14% 4 7% 5% 4 4 3 4 5% 25%	2717
November	1st to 10th	Night	19% 14% 4 7% 5% 4 5% 3 4 4 31%	2537
	11th to 20th	Night	19% 15% 4 8% 5% 4 4 3 4 6% 29%	2600
	21st to end	Night	18% 17% 5% 11% 5% 4 4 3 5% 5% 24%	2765
December	1st to 10th	Night	17% 22% 9% 18% 7% 4 4 3 3 3 11%	4580
	11th to 20th	Night	23% 20% 4 9% 5% 4 3 3 4 4 22%	5208
	21st to end	Night	20% 19% 6% 11% 5% 5% 4 3 3 4 20%	6996

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	2566
	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	41% 9% 14% 25% 11%	4370
	11th to 20th	Day	44% 9% 14% 27% 5%	4365
	21st to end	Day	46% 8% 11% 25% 8%	4661
August	1st to 10th	Day	49% 9% 14% 20% 9%	4390
	11th to 20th	Day	50% 8% 15% 22% 5%	3909
	21st to end	Day	40% 8% 17% 22% 12% 1	4180
September	1st to 10th	Day	39% 7% 12% 29% 12% 1	2280
	11th to 20th	Day	38% 5% 10% 30% 16% 1	2166
	21st to end	Day	44% 7% 15% 23% 11% 2	2090
October	1st to 10th	Day	50% 6% 8% 23% 12% 1	3357
	11th to 20th	Day	47% 4 13% 21% 10% 3	3055
	21st to end	Day	48% 5% 12% 26% 9% 1	3081
November	1st to 10th	Day	51% 7% 13% 20% 10%	1761
	11th to 20th	Day	58% 5% 11% 13% 12% 2	1800
	21st to end	Day	61% 6% 13% 15% 4 1	1631
December	1st to 10th	Day	71% 10% 8% 9% 2	2600
	11th to 20th	Day	66% 4 10% 13% 7%	2986
	21st to end	Day	65% 4 8% 11% 8% 3	3960
January	1st to 10th	Night	62% 7% 15% 11% 4	4514
	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	46% 8% 15% 19% 12%	2480
	11th to 20th	Night	45% 9% 11% 26% 9%	2472
	21st to end	Night	46% 7% 11% 27% 9% 1	2651
August	1st to 10th	Night	51% 6% 12% 22% 9%	2496
	11th to 20th	Night	47% 7% 16% 22% 9%	2955
	21st to end	Night	37% 8% 17% 25% 11% 1	3476
September	1st to 10th	Night	40% 8% 13% 27% 12% 1	1900
	11th to 20th	Night	37% 5% 13% 30% 15% 1	2014
	21st to end	Night	42% 6% 13% 23% 13% 2	2090
October	1st to 10th	Night	56% 6% 9% 21% 8% 1	3598
	11th to 20th	Night	49% 6% 10% 19% 12% 4	3863
	21st to end	Night	52% 6% 13% 22% 7% 1	4467
November	1st to 10th	Night	55% 6% 11% 17% 9% 2	2537
	11th to 20th	Night	55% 6% 11% 16% 10% 3	2600
	21st to end	Night	60% 6% 13% 15% 5%	2765
December	1st to 10th	Night	76% 7% 7% 8% 1	4580
	11th to 20th	Night	66% 5% 9% 9% 11%	5208
	21st to end	Night	68% 5% 7% 11% 6% 4	6996

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	29% 27% 29% 13% 2	192
	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% 38% 21% 7% 1	532
August	1st to 10th	Day	18% 12% 31% 26% 11% 2	486
	11th to 20th	Day	21% 13% 26% 23% 12% 4	479
	21st to end	Day	16% 16% 30% 24% 9% 4	539
September	1st to 10th	Day	19% 15% 29% 22% 10% 6%	490
	11th to 20th	Day	19% 13% 24% 21% 15% 8%	490
	21st to end	Day	20% 17% 29% 18% 11% 4	490
October	1st to 10th	Day	31% 15% 25% 14% 11% 4	490
	11th to 20th	Day	28% 18% 28% 17% 8% 1	464
	21st to end	Day	35% 21% 26% 15% 3	429
November	1st to 10th	Day	31% 22% 24% 17% 6%	395
	11th to 20th	Day	31% 26% 23% 14% 4 1	400
	21st to end	Day	39% 19% 29% 11% 2	231
December	1st to 10th	Day	33% 27% 27% 12% 3	200
	11th to 20th	Day	41% 25% 26% 7% 1	200
	21st to end	Day	35% 23% 32% 9% 2	220
January	1st to 10th	Night	26% 26% 32% 15% 2	785
	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% 22% 43% 14%	416
August	1st to 10th	Night	19% 5% 19% 40% 17% 1	378
	11th to 20th	Night	19% 7% 22% 32% 17% 3	643
	21st to end	Night	18% 9% 21% 32% 19% 2	836
September	1st to 10th	Night	21% 9% 25% 29% 14% 2	760
	11th to 20th	Night	19% 9% 21% 27% 20% 4	760
	21st to end	Night	20% 12% 25% 23% 18% 2	760
October	1st to 10th	Night	31% 11% 21% 22% 14% 2	760
	11th to 20th	Night	28% 16% 21% 23% 10% 1	760
	21st to end	Night	35% 17% 25% 17% 6%	836
November	1st to 10th	Night	27% 21% 27% 18% 7%	780
	11th to 20th	Night	28% 22% 26% 16% 6% 1	800
	21st to end	Night	27% 27% 25% 16% 5% 1	800
December	1st to 10th	Night	31% 26% 26% 15% 3	800
	11th to 20th	Night	31% 23% 25% 19% 3	800
	21st to end	Night	32% 23% 29% 14% 2	880

Page generated at 2025-01-04 03:24:03. Version ac07

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