Northhills Observatory
Clear Sky Chart
History

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

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	14% 11% 4 10% 5% 4 4 3 5% 6% 33%	101302
	Night	14% 13% 5% 11% 6% 5% 4 3 4 5% 29%	97924
Transparency	Day	51% 6% 11% 20% 11% 1	104847
	Night	55% 6% 11% 18% 9% 1	102520
Seeing	Day	20% 17% 32% 21% 8% 2	15894
	Night	20% 15% 31% 25% 9% 1	25831

By Month

Percentage Cloud Cover SE (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	11% 25% 15% 23% 7% 5% 2 2 2 2 6%	2527
	11th to 20th	Day	12% 19% 8% 23% 14% 11% 4 1 2 2 4	2530
	21st to end	Day	17% 23% 13% 15% 8% 5% 4 3 3 3 7%	2783
February	1st to 10th	Day	9% 19% 7% 16% 16% 6% 4 2 4 4 13%	1638
	11th to 20th	Day	10% 16% 7% 19% 11% 7% 5% 4 4 3 15%	1848
	21st to end	Day	12% 18% 6% 16% 8% 6% 5% 3 4 4 18%	1570
March	1st to 10th	Day	11% 16% 5% 10% 6% 5% 4 4 5% 5% 30%	3120
	11th to 20th	Day	10% 10% 7% 17% 6% 5% 4 3 5% 6% 28%	3350
	21st to end	Day	18% 14% 6% 16% 5% 4 4 3 3 4 22%	4001
April	1st to 10th	Day	18% 16% 4 8% 6% 4 3 3 5% 6% 28%	2280
	11th to 20th	Day	20% 14% 3 6% 4 4 3 3 4 5% 33%	2323
	21st to end	Day	15% 12% 3 7% 4 5% 4 4 5% 8% 32%	2470
May	1st to 10th	Day	15% 8% 2 6% 4 4 4 4 5% 6% 41%	4082
	11th to 20th	Day	11% 7% 2 6% 4 4 4 3 5% 6% 47%	4261
	21st to end	Day	13% 6% 2 6% 4 4 4 4 6% 8% 42%	4824
June	1st to 10th	Day	13% 6% 2 5% 4 4 4 4 7% 7% 44%	2660
	11th to 20th	Day	11% 6% 2 7% 5% 4 5% 4 6% 9% 41%	2660
	21st to end	Day	15% 6% 2 6% 3 4 4 4 7% 8% 41%	2660
July	1st to 10th	Day	17% 6% 2 6% 4 3 4 4 7% 8% 39%	4440
	11th to 20th	Day	9% 4 2 4 3 3 4 4 6% 9% 52%	4440
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 6% 9% 47%	4813
August	1st to 10th	Day	9% 6% 3 7% 5% 5% 5% 4 7% 9% 41%	4273
	11th to 20th	Day	14% 6% 2 6% 4 3 3 3 5% 6% 48%	4044
	21st to end	Day	13% 6% 3 6% 5% 4 4 4 5% 6% 44%	4276
September	1st to 10th	Day	14% 5% 3 6% 4 4 5% 4 6% 7% 42%	2273
	11th to 20th	Day	13% 6% 2 5% 3 3 4 4 7% 7% 46%	2090
	21st to end	Day	16% 6% 2 7% 5% 4 4 4 7% 6% 39%	2090
October	1st to 10th	Day	16% 7% 3 7% 5% 4 4 3 5% 6% 39%	2090
	11th to 20th	Day	22% 15% 4 10% 6% 5% 5% 3 4 6% 21%	1798
	21st to end	Day	23% 16% 4 10% 6% 5% 4 3 4 5% 19%	1881
November	1st to 10th	Day	18% 17% 3 7% 4 4 5% 3 5% 6% 27%	1762
	11th to 20th	Day	13% 23% 7% 12% 6% 4 4 3 5% 6% 16%	1719
	21st to end	Day	17% 24% 10% 12% 5% 4 3 2 4 4 15%	1652
December	1st to 10th	Day	13% 27% 12% 18% 7% 4 3 2 3 3 9%	1426
	11th to 20th	Day	14% 25% 9% 17% 8% 5% 4 3 4 4 9%	1865
	21st to end	Day	19% 23% 10% 15% 7% 5% 4 2 3 3 8%	2783
January	1st to 10th	Night	12% 25% 11% 18% 7% 6% 4 2 3 3 10%	4428
	11th to 20th	Night	10% 18% 8% 20% 13% 12% 4 2 3 3 7%	4440
	21st to end	Night	15% 23% 11% 17% 9% 6% 5% 2 3 3 7%	4884
February	1st to 10th	Night	10% 16% 7% 17% 14% 7% 5% 2 3 4 14%	2539
	11th to 20th	Night	10% 16% 7% 17% 10% 6% 4 4 5% 5% 17%	2218
	21st to end	Night	15% 16% 6% 15% 8% 5% 4 3 4 5% 20%	1884
March	1st to 10th	Night	15% 11% 4 8% 4 4 3 3 5% 7% 37%	3733
	11th to 20th	Night	8% 12% 5% 11% 5% 4 4 3 5% 6% 36%	3608
	21st to end	Night	15% 12% 6% 13% 6% 4 4 3 4 5% 26%	3658
April	1st to 10th	Night	17% 13% 3 9% 4 4 4 4 5% 6% 30%	1900
	11th to 20th	Night	21% 11% 4 6% 4 3 3 2 5% 6% 34%	1806
	21st to end	Night	15% 11% 4 7% 4 4 4 4 4 5% 37%	1710
May	1st to 10th	Night	15% 8% 2 7% 5% 4 4 4 6% 6% 40%	2813
	11th to 20th	Night	13% 8% 2 6% 4 4 4 4 5% 7% 41%	2638
	21st to end	Night	18% 6% 2 5% 3 3 3 3 5% 7% 43%	2743
June	1st to 10th	Night	14% 7% 2 6% 5% 5% 4 3 5% 7% 43%	1520
	11th to 20th	Night	11% 5% 2 6% 5% 4 5% 3 7% 8% 43%	1520
	21st to end	Night	10% 6% 3 6% 5% 4 4 4 6% 7% 45%	1520
July	1st to 10th	Night	14% 9% 2 6% 4 4 4 4 6% 7% 41%	2530
	11th to 20th	Night	7% 4 2 5% 3 4 4 4 5% 6% 56%	2530
	21st to end	Night	7% 6% 2 7% 4 4 5% 3 6% 7% 48%	2750
August	1st to 10th	Night	12% 6% 3 7% 4 4 5% 4 6% 7% 42%	2660
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 7% 51%	2785
	21st to end	Night	9% 7% 2 7% 4 4 4 3 5% 7% 48%	3375
September	1st to 10th	Night	11% 6% 3 6% 4 3 4 3 5% 7% 49%	1900
	11th to 20th	Night	12% 5% 1 5% 4 3 4 3 5% 7% 50%	2077
	21st to end	Night	16% 7% 3 7% 4 4 4 4 5% 7% 40%	2090
October	1st to 10th	Night	17% 8% 2 7% 4 4 4 3 5% 5% 41%	2090
	11th to 20th	Night	21% 14% 3 9% 5% 4 4 3 4 6% 27%	2378
	21st to end	Night	23% 14% 4 10% 4 4 4 3 4 6% 25%	2717
November	1st to 10th	Night	14% 15% 4 10% 6% 4 4 3 5% 6% 29%	2536
	11th to 20th	Night	13% 21% 6% 13% 6% 5% 4 3 4 5% 19%	2484
	21st to end	Night	16% 21% 9% 12% 6% 5% 4 3 4 5% 16%	2527
December	1st to 10th	Night	14% 23% 10% 18% 7% 5% 4 2 3 3 11%	2736
	11th to 20th	Night	13% 22% 9% 20% 8% 5% 3 2 4 4 10%	3313
	21st to end	Night	20% 24% 9% 15% 5% 4 3 3 3 4 10%	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	88% 3 5% 4 1	2528
	11th to 20th	Day	90% 4 3 3 1	2530
	21st to end	Day	83% 6% 6% 3 1	2783
February	1st to 10th	Day	75% 5% 8% 10% 2	1638
	11th to 20th	Day	74% 6% 8% 9% 3	1858
	21st to end	Day	68% 5% 11% 13% 3 1	1570
March	1st to 10th	Day	55% 6% 11% 19% 9%	3120
	11th to 20th	Day	55% 6% 14% 17% 7% 2	3350
	21st to end	Day	64% 6% 8% 15% 5% 1	4001
April	1st to 10th	Day	56% 7% 9% 18% 11%	2280
	11th to 20th	Day	53% 5% 8% 18% 14% 2	2323
	21st to end	Day	49% 7% 10% 16% 15% 2	2470
May	1st to 10th	Day	42% 7% 9% 23% 18% 2	4120
	11th to 20th	Day	36% 7% 9% 27% 18% 2	4265
	21st to end	Day	38% 7% 11% 22% 19% 3	4837
June	1st to 10th	Day	37% 7% 11% 27% 16% 2	2660
	11th to 20th	Day	38% 7% 12% 22% 19% 1	2660
	21st to end	Day	38% 7% 14% 25% 15% 1	2660
July	1st to 10th	Day	41% 7% 14% 23% 14% 2	4371
	11th to 20th	Day	26% 7% 14% 34% 16% 2	4365
	21st to end	Day	31% 9% 13% 26% 20% 2	4662
August	1st to 10th	Day	37% 7% 13% 27% 14% 1	4258
	11th to 20th	Day	36% 6% 13% 28% 16% 1	4083
	21st to end	Day	38% 8% 12% 28% 12% 1	4275
September	1st to 10th	Day	40% 7% 13% 25% 14% 1	2273
	11th to 20th	Day	35% 7% 14% 29% 14% 1	2090
	21st to end	Day	43% 8% 14% 24% 11%	2090
October	1st to 10th	Day	31% 5% 9% 33% 21% 1	3480
	11th to 20th	Day	54% 6% 10% 19% 10%	2962
	21st to end	Day	62% 6% 13% 15% 4	3081
November	1st to 10th	Day	57% 7% 9% 19% 8%	1762
	11th to 20th	Day	70% 5% 11% 10% 4	1719
	21st to end	Day	74% 6% 11% 8% 2	1652
December	1st to 10th	Day	83% 4 5% 7% 1	1426
	11th to 20th	Day	79% 6% 9% 5% 1	1862
	21st to end	Day	82% 4 7% 6% 1	2783
January	1st to 10th	Night	79% 5% 8% 7% 1	4428
	11th to 20th	Night	85% 4 6% 4 1	4440
	21st to end	Night	83% 6% 7% 4 1	4884
February	1st to 10th	Night	75% 4 6% 11% 4	2539
	11th to 20th	Night	70% 6% 9% 12% 3	2219
	21st to end	Night	67% 5% 11% 13% 4	1884
March	1st to 10th	Night	48% 6% 16% 21% 8%	3733
	11th to 20th	Night	48% 6% 12% 24% 9% 1	3608
	21st to end	Night	59% 5% 9% 19% 6% 1	3658
April	1st to 10th	Night	54% 5% 9% 20% 11% 1	1900
	11th to 20th	Night	52% 5% 8% 20% 13% 3	1806
	21st to end	Night	48% 5% 10% 20% 14% 3	1710
May	1st to 10th	Night	43% 7% 13% 18% 16% 3	2840
	11th to 20th	Night	41% 8% 9% 26% 15% 2	2639
	21st to end	Night	41% 6% 13% 20% 16% 5%	2751
June	1st to 10th	Night	40% 6% 11% 26% 15% 1	1520
	11th to 20th	Night	37% 7% 12% 24% 18% 2	1520
	21st to end	Night	38% 7% 12% 26% 15% 2	1520
July	1st to 10th	Night	42% 5% 12% 24% 13% 5%	2490
	11th to 20th	Night	26% 6% 16% 32% 19% 1	2482
	21st to end	Night	33% 7% 13% 25% 21% 1	2662
August	1st to 10th	Night	39% 8% 14% 25% 13% 1	2651
	11th to 20th	Night	33% 5% 14% 31% 16% 1	2812
	21st to end	Night	35% 7% 14% 22% 20% 2	3375
September	1st to 10th	Night	35% 5% 13% 26% 20% 2	1900
	11th to 20th	Night	33% 7% 14% 30% 15% 1	2077
	21st to end	Night	43% 6% 14% 25% 11% 1	2090
October	1st to 10th	Night	38% 6% 9% 34% 12%	3480
	11th to 20th	Night	50% 4 10% 24% 12%	3953
	21st to end	Night	52% 5% 14% 23% 6%	4467
November	1st to 10th	Night	56% 6% 12% 18% 7% 1	2536
	11th to 20th	Night	69% 6% 11% 10% 4 1	2484
	21st to end	Night	70% 6% 13% 9% 1	2527
December	1st to 10th	Night	79% 5% 7% 7% 1	2736
	11th to 20th	Night	79% 6% 9% 5% 2	3315
	21st to end	Night	79% 6% 10% 5% 1	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	21% 26% 36% 12% 6% 1	270
	11th to 20th	Day	29% 23% 35% 11% 2	270
	21st to end	Day	26% 19% 38% 15% 1	297
February	1st to 10th	Day	22% 30% 31% 11% 4 1	270
	11th to 20th	Day	22% 31% 36% 9% 1	270
	21st to end	Day	29% 31% 36% 3	225
March	1st to 10th	Day	26% 30% 34% 10% 1	270
	11th to 20th	Day	27% 19% 32% 14% 7%	382
	21st to end	Day	30% 19% 27% 18% 5% 1	506
April	1st to 10th	Day	28% 21% 35% 13% 3 1	460
	11th to 20th	Day	30% 22% 27% 13% 6% 2	452
	21st to end	Day	25% 21% 26% 21% 6% 2	460
May	1st to 10th	Day	21% 21% 35% 16% 6% 1	463
	11th to 20th	Day	16% 16% 35% 23% 7% 2	589
	21st to end	Day	13% 15% 35% 25% 10% 2	734
June	1st to 10th	Day	15% 15% 37% 22% 9% 2	680
	11th to 20th	Day	16% 12% 41% 23% 7% 2	680
	21st to end	Day	19% 12% 33% 25% 9% 1	680
July	1st to 10th	Day	10% 11% 32% 31% 13% 4	671
	11th to 20th	Day	12% 12% 30% 30% 13% 4	668
	21st to end	Day	9% 7% 35% 32% 12% 4	739
August	1st to 10th	Day	10% 8% 30% 29% 16% 6%	591
	11th to 20th	Day	15% 7% 25% 29% 15% 8%	479
	21st to end	Day	17% 11% 24% 29% 15% 4	539
September	1st to 10th	Day	20% 9% 27% 26% 13% 6%	490
	11th to 20th	Day	10% 9% 27% 32% 17% 4	490
	21st to end	Day	18% 14% 25% 27% 11% 5%	490
October	1st to 10th	Day	21% 18% 28% 21% 11% 1	490
	11th to 20th	Day	32% 20% 32% 15% 2	349
	21st to end	Day	38% 22% 28% 9% 3	330
November	1st to 10th	Day	30% 21% 30% 16% 3	300
	11th to 20th	Day	26% 29% 36% 8% 2	273
	21st to end	Day	29% 29% 32% 9% 2	270
December	1st to 10th	Day	32% 25% 27% 13% 2	225
	11th to 20th	Day	28% 30% 29% 9% 3	245
	21st to end	Day	32% 28% 31% 8% 1 1	297
January	1st to 10th	Night	22% 21% 33% 19% 4	950
	11th to 20th	Night	24% 21% 33% 17% 5%	950
	21st to end	Night	20% 17% 36% 22% 5%	1045
February	1st to 10th	Night	19% 19% 36% 21% 4 1	864
	11th to 20th	Night	20% 21% 32% 23% 3	743
	21st to end	Night	24% 21% 34% 19% 3	628
March	1st to 10th	Night	16% 19% 36% 23% 6% 1	760
	11th to 20th	Night	19% 18% 36% 23% 4 1	760
	21st to end	Night	22% 14% 33% 25% 5% 1	741
April	1st to 10th	Night	23% 16% 34% 22% 4 1	570
	11th to 20th	Night	25% 15% 31% 22% 7%	563
	21st to end	Night	21% 12% 33% 26% 7% 1	570
May	1st to 10th	Night	19% 11% 32% 31% 6% 1	570
	11th to 20th	Night	17% 11% 34% 29% 9%	561
	21st to end	Night	14% 9% 30% 33% 14%	617
June	1st to 10th	Night	14% 8% 34% 34% 9% 1	570
	11th to 20th	Night	13% 9% 29% 35% 12% 2	570
	21st to end	Night	13% 6% 29% 38% 14% 1	570
July	1st to 10th	Night	12% 3 23% 39% 21% 2	555
	11th to 20th	Night	9% 4 26% 38% 22% 1	552
	21st to end	Night	9% 4 24% 39% 21% 2	624
August	1st to 10th	Night	9% 5% 20% 43% 21% 1	567
	11th to 20th	Night	12% 6% 20% 34% 26% 3	564
	21st to end	Night	15% 7% 23% 38% 15% 1	627
September	1st to 10th	Night	13% 8% 25% 32% 19% 3	570
	11th to 20th	Night	13% 9% 24% 33% 19% 2	747
	21st to end	Night	19% 10% 25% 29% 15% 2	760
October	1st to 10th	Night	21% 12% 26% 27% 12% 1	760
	11th to 20th	Night	28% 17% 27% 23% 5%	760
	21st to end	Night	30% 18% 27% 19% 5% 1	836
November	1st to 10th	Night	27% 15% 34% 19% 5%	780
	11th to 20th	Night	25% 22% 33% 17% 2	765
	21st to end	Night	27% 20% 31% 18% 3	817
December	1st to 10th	Night	27% 22% 34% 15% 3	950
	11th to 20th	Night	25% 23% 33% 15% 3 1	950
	21st to end	Night	29% 19% 36% 14% 2	1045

Page generated at 2024-11-08 22:45:38. Version ac07

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