North Point Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Point Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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	6% 5% 2 5% 3 3 3 3 4 7% 59%	105331
	Night	8% 5% 2 5% 3 3 3 3 5% 7% 55%	103137
Transparency	Day	26% 3 7% 20% 24% 19%	105091
	Night	29% 3 9% 20% 22% 18%	102967
Seeing	Day	8% 10% 24% 31% 20% 6%	15478
	Night	10% 6% 16% 34% 29% 5%	24797

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	14% 10% 3 8% 5% 4 5% 3 5% 7% 37%	2708
	11th to 20th	Day	17% 12% 4 9% 5% 4 4 3 3 6% 32%	2860
	21st to end	Day	19% 8% 4 10% 5% 5% 4 3 5% 7% 30%	3146
February	1st to 10th	Day	14% 7% 2 6% 4 5% 4 4 5% 5% 45%	1710
	11th to 20th	Day	12% 8% 3 6% 4 5% 3 4 5% 8% 41%	1719
	21st to end	Day	14% 5% 2 5% 5% 4 4 4 5% 5% 47%	1570
March	1st to 10th	Day	12% 9% 4 11% 6% 5% 6% 4 6% 6% 30%	3413
	11th to 20th	Day	9% 5% 2 5% 4 3 5% 3 5% 6% 54%	3490
	21st to end	Day	13% 6% 3 7% 4 5% 5% 4 7% 8% 37%	3854
April	1st to 10th	Day	10% 8% 3 6% 4 4 4 4 6% 8% 43%	2280
	11th to 20th	Day	7% 5% 2 5% 4 4 4 4 5% 8% 53%	2249
	21st to end	Day	3 4 2 4 3 4 3 3 6% 9% 59%	2280
May	1st to 10th	Day	4 3 1 3 2 1 2 2 3 5% 74%	4003
	11th to 20th	Day	2 2 1 4 2 3 2 2 3 7% 70%	4150
	21st to end	Day	2 3 1 3 2 2 2 2 3 6% 73%	4813
June	1st to 10th	Day	5% 4 2 4 3 3 3 3 4 8% 60%	2660
	11th to 20th	Day	1 3 1 3 2 1 2 3 5% 7% 73%	2660
	21st to end	Day	2 3 1 3 3 2 3 2 3 5% 74%	2660
July	1st to 10th	Day	2 1 2 2 1 1 1 2 5% 82%	4420
	11th to 20th	Day	1 3 1 3 2 2 3 2 4 6% 74%	4120
	21st to end	Day	1 3 1 3 2 2 2 2 4 5% 75%	4455
August	1st to 10th	Day	1 3 1 4 3 4 4 4 6% 8% 63%	4091
	11th to 20th	Day	1 2 1 2 1 1 1 2 3 6% 79%	3882
	21st to end	Day	1 3 1 3 3 3 3 3 4 6% 70%	4180
September	1st to 10th	Day	1 3 1 3 2 2 2 2 3 6% 75%	2280
	11th to 20th	Day	2 6% 1 5% 3 3 3 2 4 7% 64%	2280
	21st to end	Day	2 3 1 3 2 3 2 2 3 6% 74%	2000
October	1st to 10th	Day	2 2 1 3 3 2 2 2 4 7% 72%	3180
	11th to 20th	Day	4 4 2 6% 3 3 3 2 4 6% 63%	3161
	21st to end	Day	5% 4 2 5% 4 3 4 4 5% 8% 58%	3448
November	1st to 10th	Day	8% 4 1 4 4 3 4 3 5% 8% 55%	1934
	11th to 20th	Day	9% 8% 3 7% 5% 3 3 3 5% 7% 46%	1793
	21st to end	Day	11% 7% 2 4 4 3 4 4 5% 7% 50%	1600
December	1st to 10th	Day	15% 7% 4 6% 3 3 3 4 6% 6% 44%	1560
	11th to 20th	Day	24% 11% 3 8% 5% 4 4 2 5% 4 29%	1928
	21st to end	Day	22% 8% 3 6% 5% 5% 4 3 6% 8% 31%	2794
January	1st to 10th	Night	13% 7% 3 7% 4 4 4 4 5% 7% 41%	4237
	11th to 20th	Night	17% 9% 4 9% 5% 5% 4 3 5% 6% 33%	4110
	21st to end	Night	20% 8% 2 7% 4 5% 5% 4 5% 7% 32%	4521
February	1st to 10th	Night	14% 6% 2 6% 4 3 4 3 5% 7% 48%	2470
	11th to 20th	Night	11% 6% 3 5% 4 4 5% 4 5% 8% 46%	2346
	21st to end	Night	11% 5% 2 4 3 3 3 3 5% 6% 53%	1884
March	1st to 10th	Night	13% 9% 3 7% 5% 5% 5% 4 5% 7% 38%	3447
	11th to 20th	Night	10% 4 1 5% 3 3 3 3 4 6% 57%	3490
	21st to end	Night	12% 7% 3 7% 4 4 5% 3 5% 7% 43%	3798
April	1st to 10th	Night	7% 5% 2 6% 4 4 3 3 5% 8% 51%	1900
	11th to 20th	Night	7% 4 2 5% 3 3 3 3 5% 6% 59%	1879
	21st to end	Night	4 3 1 3 3 3 3 3 6% 8% 63%	1900
May	1st to 10th	Night	2 2 2 3 2 2 2 2 3 4 74%	2966
	11th to 20th	Night	1 2 2 5% 5% 3 3 2 4 7% 65%	2748
	21st to end	Night	2 2 1 2 2 2 2 2 3 5% 76%	2762
June	1st to 10th	Night	3 3 1 4 3 4 3 3 6% 9% 60%	1520
	11th to 20th	Night	1 1 1 3 2 2 2 2 5% 7% 74%	1520
	21st to end	Night	1 2 1 4 2 3 2 2 4 7% 71%	1520
July	1st to 10th	Night	1 1 1 3 2 2 2 1 2 5% 80%	2540
	11th to 20th	Night	1 1 1 4 3 3 4 4 7% 8% 65%	2846
	21st to end	Night	4 2 7% 3 3 4 4 7% 9% 57%	3109
August	1st to 10th	Night	3 4 2 8% 5% 4 5% 3 7% 8% 52%	2848
	11th to 20th	Night	2 1 3 2 2 3 3 4 8% 72%	2962
	21st to end	Night	1 3 1 4 3 2 3 3 4 7% 69%	3498
September	1st to 10th	Night	1 2 1 3 2 3 2 3 4 9% 71%	1900
	11th to 20th	Night	2 5% 2 6% 3 3 3 3 6% 7% 61%	1900
	21st to end	Night	1 3 2 4 3 3 3 3 4 7% 67%	2175
October	1st to 10th	Night	3 2 1 3 2 2 3 2 4 6% 72%	3800
	11th to 20th	Night	2 4 2 5% 3 3 4 3 5% 7% 62%	3777
	21st to end	Night	5% 3 1 5% 3 3 3 3 5% 7% 62%	4121
November	1st to 10th	Night	7% 4 2 4 4 3 3 3 4 9% 56%	2364
	11th to 20th	Night	9% 5% 2 6% 4 3 4 3 5% 8% 51%	2605
	21st to end	Night	9% 4 2 5% 4 4 3 3 5% 8% 54%	2800
December	1st to 10th	Night	14% 6% 3 7% 3 3 4 4 5% 8% 44%	2736
	11th to 20th	Night	27% 8% 3 6% 4 3 3 3 6% 7% 31%	3276
	21st to end	Night	18% 8% 3 7% 5% 4 5% 4 6% 7% 34%	4862

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% 4 12% 25% 8% 3	2708
	11th to 20th	Day	56% 3 11% 13% 11% 6%	2860
	21st to end	Day	55% 3 9% 18% 11% 4	3146
February	1st to 10th	Day	41% 3 7% 21% 20% 8%	1710
	11th to 20th	Day	41% 5% 8% 20% 19% 7%	1728
	21st to end	Day	38% 4 9% 25% 17% 7%	1570
March	1st to 10th	Day	54% 3 11% 17% 12% 2	3413
	11th to 20th	Day	30% 4 11% 32% 12% 11%	3490
	21st to end	Day	43% 5% 15% 24% 11% 2	3854
April	1st to 10th	Day	37% 6% 14% 22% 18% 4	2280
	11th to 20th	Day	30% 4 15% 25% 21% 5%	2252
	21st to end	Day	22% 4 14% 31% 25% 4	2280
May	1st to 10th	Day	16% 3 10% 32% 24% 15%	4003
	11th to 20th	Day	14% 4 5% 28% 34% 15%	4153
	21st to end	Day	15% 3 9% 37% 33% 3	4814
June	1st to 10th	Day	23% 3 11% 28% 28% 7%	2660
	11th to 20th	Day	13% 2 9% 22% 37% 17%	2660
	21st to end	Day	14% 3 3 15% 36% 30%	2660
July	1st to 10th	Day	8% 2 2 6% 15% 67%	4351
	11th to 20th	Day	11% 3 2 7% 20% 57%	4050
	21st to end	Day	11% 3 2 9% 30% 46%	4315
August	1st to 10th	Day	15% 4 3 12% 30% 35%	4076
	11th to 20th	Day	9% 2 2 11% 44% 32%	3921
	21st to end	Day	13% 3 3 16% 36% 28%	4179
September	1st to 10th	Day	12% 2 2 11% 32% 41%	2280
	11th to 20th	Day	21% 3 4 24% 34% 13%	2280
	21st to end	Day	14% 2 4 22% 35% 24%	2000
October	1st to 10th	Day	15% 3 3 12% 29% 38%	3180
	11th to 20th	Day	22% 3 7% 24% 25% 19%	3161
	21st to end	Day	23% 4 8% 27% 26% 12%	3448
November	1st to 10th	Day	28% 5% 9% 28% 19% 11%	1934
	11th to 20th	Day	39% 5% 9% 22% 18% 6%	1793
	21st to end	Day	33% 4 10% 21% 21% 11%	1600
December	1st to 10th	Day	40% 4 9% 21% 18% 8%	1560
	11th to 20th	Day	59% 3 7% 12% 15% 3	1928
	21st to end	Day	51% 4 14% 19% 9% 3	2794
January	1st to 10th	Night	42% 3 19% 25% 7% 3	4237
	11th to 20th	Night	54% 3 13% 13% 10% 7%	4110
	21st to end	Night	53% 3 11% 15% 12% 6%	4521
February	1st to 10th	Night	37% 4 8% 21% 19% 11%	2470
	11th to 20th	Night	37% 4 10% 21% 20% 8%	2348
	21st to end	Night	33% 4 10% 29% 19% 5%	1884
March	1st to 10th	Night	46% 3 16% 18% 14% 3	3447
	11th to 20th	Night	30% 2 9% 25% 23% 11%	3490
	21st to end	Night	41% 3 15% 26% 12% 3	3798
April	1st to 10th	Night	32% 4 14% 23% 21% 6%	1900
	11th to 20th	Night	27% 4 12% 28% 20% 9%	1879
	21st to end	Night	20% 3 11% 32% 27% 7%	1900
May	1st to 10th	Night	16% 2 8% 27% 31% 16%	2966
	11th to 20th	Night	18% 8% 7% 19% 28% 20%	2749
	21st to end	Night	13% 2 9% 36% 36% 4	2762
June	1st to 10th	Night	21% 5% 11% 22% 32% 9%	1520
	11th to 20th	Night	12% 2 8% 23% 36% 20%	1520
	21st to end	Night	15% 2 3 13% 35% 33%	1520
July	1st to 10th	Night	8% 2 1 6% 16% 67%	2500
	11th to 20th	Night	13% 3 4 7% 19% 55%	2793
	21st to end	Night	16% 3 2 10% 24% 45%	3011
August	1st to 10th	Night	21% 4 3 14% 28% 30%	2839
	11th to 20th	Night	12% 3 2 9% 41% 34%	2989
	21st to end	Night	14% 3 4 14% 34% 31%	3498
September	1st to 10th	Night	12% 2 2 9% 33% 41%	1900
	11th to 20th	Night	20% 4 5% 22% 32% 18%	1900
	21st to end	Night	16% 3 4 20% 30% 27%	2175
October	1st to 10th	Night	15% 3 4 11% 25% 43%	3800
	11th to 20th	Night	20% 3 6% 26% 22% 23%	3777
	21st to end	Night	23% 2 6% 23% 28% 18%	4121
November	1st to 10th	Night	27% 4 10% 28% 19% 12%	2364
	11th to 20th	Night	32% 4 13% 26% 18% 8%	2605
	21st to end	Night	30% 5% 9% 22% 23% 12%	2800
December	1st to 10th	Night	40% 4 8% 19% 18% 10%	2736
	11th to 20th	Night	54% 4 9% 15% 15% 4	3276
	21st to end	Night	51% 3 14% 18% 11% 3	4862

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% 10% 31% 18% 11% 2	284
	11th to 20th	Day	19% 13% 22% 26% 17% 3	370
	21st to end	Day	14% 10% 27% 30% 17% 3	407
February	1st to 10th	Day	18% 13% 20% 26% 19% 4	370
	11th to 20th	Day	19% 15% 26% 23% 14% 3	391
	21st to end	Day	13% 18% 25% 25% 16% 2	382
March	1st to 10th	Day	19% 18% 30% 21% 10% 2	460
	11th to 20th	Day	19% 14% 28% 20% 14% 6%	460
	21st to end	Day	13% 21% 31% 22% 11% 1	506
April	1st to 10th	Day	12% 17% 30% 25% 11% 4	460
	11th to 20th	Day	12% 19% 29% 21% 14% 5%	452
	21st to end	Day	5% 20% 29% 27% 13% 6%	460
May	1st to 10th	Day	6% 19% 29% 29% 17% 1	463
	11th to 20th	Day	7% 16% 28% 28% 16% 5%	488
	21st to end	Day	6% 12% 26% 31% 20% 5%	529
June	1st to 10th	Day	7% 11% 29% 30% 17% 6%	490
	11th to 20th	Day	3 10% 30% 38% 15% 3	490
	21st to end	Day	1 5% 24% 40% 25% 5%	490
July	1st to 10th	Day	3 3 21% 46% 22% 6%	486
	11th to 20th	Day	1 15% 44% 31% 7%	484
	21st to end	Day	1 1 16% 48% 27% 7%	531
August	1st to 10th	Day	3 3 20% 44% 23% 7%	487
	11th to 20th	Day	2 1 24% 41% 24% 8%	477
	21st to end	Day	2 2 18% 42% 27% 9%	539
September	1st to 10th	Day	1 4 17% 39% 28% 10%	490
	11th to 20th	Day	3 8% 21% 35% 24% 8%	490
	21st to end	Day	3 7% 21% 30% 30% 9%	490
October	1st to 10th	Day	4 8% 22% 28% 24% 14%	490
	11th to 20th	Day	6% 8% 20% 23% 31% 12%	490
	21st to end	Day	10% 7% 21% 27% 25% 10%	539
November	1st to 10th	Day	10% 9% 19% 21% 32% 9%	470
	11th to 20th	Day	8% 11% 17% 32% 25% 7%	295
	21st to end	Day	13% 8% 23% 33% 21% 4	200
December	1st to 10th	Day	19% 13% 17% 26% 15% 9%	190
	11th to 20th	Day	18% 18% 21% 24% 16% 3	180
	21st to end	Day	20% 14% 23% 30% 12% 1	198
January	1st to 10th	Night	19% 9% 13% 30% 24% 5%	760
	11th to 20th	Night	18% 7% 14% 34% 23% 5%	760
	21st to end	Night	17% 7% 15% 33% 25% 4	836
February	1st to 10th	Night	16% 8% 15% 34% 24% 4	760
	11th to 20th	Night	13% 10% 19% 30% 23% 5%	744
	21st to end	Night	14% 11% 20% 31% 20% 3	628
March	1st to 10th	Night	17% 11% 21% 28% 20% 3	760
	11th to 20th	Night	15% 10% 18% 31% 23% 3	760
	21st to end	Night	14% 10% 26% 32% 17% 1	836
April	1st to 10th	Night	11% 9% 27% 31% 19% 3	760
	11th to 20th	Night	11% 14% 23% 26% 22% 4	751
	21st to end	Night	6% 12% 28% 28% 24% 3	760
May	1st to 10th	Night	5% 7% 27% 31% 26% 4	637
	11th to 20th	Night	3 4 23% 33% 34% 3	515
	21st to end	Night	5% 8% 18% 37% 30% 3	411
June	1st to 10th	Night	3 5% 23% 40% 28% 1	380
	11th to 20th	Night	1 5% 18% 50% 24% 2	380
	21st to end	Night	2 1 16% 45% 35% 1	380
July	1st to 10th	Night	2 1 9% 43% 42% 3	370
	11th to 20th	Night	3 1 4 40% 44% 10%	539
	21st to end	Night	2 1 5% 41% 45% 5%	624
August	1st to 10th	Night	5% 2 8% 37% 42% 6%	567
	11th to 20th	Night	2 11% 42% 39% 7%	649
	21st to end	Night	3 1 8% 39% 42% 8%	836
September	1st to 10th	Night	1 1 8% 39% 43% 8%	760
	11th to 20th	Night	4 3 13% 37% 36% 6%	760
	21st to end	Night	2 4 13% 33% 40% 8%	760
October	1st to 10th	Night	5% 4 16% 30% 35% 9%	760
	11th to 20th	Night	5% 4 15% 32% 35% 9%	760
	21st to end	Night	9% 4 11% 31% 33% 11%	836
November	1st to 10th	Night	7% 6% 16% 28% 34% 9%	780
	11th to 20th	Night	11% 4 14% 35% 30% 6%	800
	21st to end	Night	11% 5% 16% 37% 25% 6%	800
December	1st to 10th	Night	16% 6% 16% 31% 24% 6%	782
	11th to 20th	Night	23% 8% 14% 31% 20% 4	760
	21st to end	Night	19% 9% 20% 31% 19% 1	836

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