North Ram
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Ram clear sky chart from 2005-11-06 to 2025-05-26.

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	8% 10% 4 9% 6% 5% 5% 5% 6% 8% 35%	118197
	Night	5% 9% 4 10% 6% 5% 5% 4 6% 8% 36%	119784
Transparency	Day	44% 8% 15% 20% 11% 2	117942
	Night	41% 8% 16% 22% 11% 2	119685
Seeing	Day	21% 16% 29% 23% 10% 2	16405
	Night	14% 14% 31% 27% 12% 1	25005

By Month

Percentage Cloud Cover NW (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	1 6% 4 14% 8% 7% 6% 5% 7% 9% 35%	3179
	11th to 20th	Day	1 7% 2 11% 6% 8% 6% 6% 7% 9% 37%	3315
	21st to end	Day	1 6% 3 10% 5% 5% 7% 6% 7% 11% 39%	4004
February	1st to 10th	Day	2 9% 5% 10% 9% 8% 6% 5% 8% 8% 30%	1600
	11th to 20th	Day	1 11% 5% 14% 7% 6% 6% 5% 7% 8% 31%	1654
	21st to end	Day	2 8% 4 16% 8% 5% 8% 4 6% 7% 32%	1650
March	1st to 10th	Day	1 6% 4 10% 7% 5% 5% 5% 7% 11% 39%	4518
	11th to 20th	Day	3 9% 4 8% 5% 5% 6% 5% 7% 10% 39%	4775
	21st to end	Day	4 15% 8% 18% 5% 4 5% 4 7% 7% 24%	5791
April	1st to 10th	Day	4 18% 5% 11% 7% 7% 6% 4 7% 8% 24%	2400
	11th to 20th	Day	7% 17% 6% 12% 6% 5% 5% 4 6% 8% 23%	2568
	21st to end	Day	9% 16% 6% 11% 7% 6% 5% 3 5% 7% 26%	2640
May	1st to 10th	Day	13% 19% 4 9% 6% 5% 4 4 5% 7% 25%	4560
	11th to 20th	Day	12% 13% 4 9% 7% 6% 5% 5% 6% 7% 25%	4841
	21st to end	Day	16% 15% 4 11% 6% 6% 5% 4 5% 6% 20%	5239
June	1st to 10th	Day	19% 10% 3 8% 6% 5% 6% 4 6% 7% 25%	2850
	11th to 20th	Day	23% 11% 4 8% 5% 5% 6% 4 6% 8% 20%	3011
	21st to end	Day	13% 8% 3 8% 6% 6% 6% 5% 7% 8% 31%	3040
July	1st to 10th	Day	9% 6% 3 7% 5% 5% 6% 4 5% 6% 44%	4998
	11th to 20th	Day	9% 4 1 5% 4 5% 5% 5% 7% 8% 49%	4740
	21st to end	Day	8% 5% 2 5% 5% 5% 5% 5% 7% 8% 45%	4953
August	1st to 10th	Day	14% 7% 2 5% 4 4 5% 4 7% 8% 40%	4401
	11th to 20th	Day	12% 6% 2 6% 5% 5% 6% 6% 8% 9% 36%	4246
	21st to end	Day	12% 6% 3 6% 4 4 5% 4 6% 7% 42%	4521
September	1st to 10th	Day	14% 9% 2 6% 5% 5% 5% 4 5% 6% 40%	2294
	11th to 20th	Day	13% 11% 2 6% 4 4 5% 3 6% 8% 40%	2151
	21st to end	Day	10% 9% 3 8% 5% 4 5% 3 6% 7% 39%	2090
October	1st to 10th	Day	6% 9% 3 8% 4 4 5% 5% 6% 9% 42%	3330
	11th to 20th	Day	6% 9% 3 8% 5% 6% 5% 4 6% 9% 39%	2842
	21st to end	Day	4 9% 4 8% 5% 5% 6% 5% 7% 7% 40%	3101
November	1st to 10th	Day	4 11% 6% 12% 6% 5% 5% 5% 7% 7% 32%	1665
	11th to 20th	Day	3 9% 4 11% 5% 6% 5% 5% 7% 8% 37%	1400
	21st to end	Day	2 10% 3 10% 6% 6% 5% 5% 8% 11% 35%	1400
December	1st to 10th	Day	2 10% 4 13% 8% 6% 7% 5% 6% 7% 30%	2290
	11th to 20th	Day	1 7% 3 12% 7% 7% 6% 5% 6% 8% 39%	2642
	21st to end	Day	1 9% 4 10% 7% 6% 6% 4 5% 7% 42%	3498
January	1st to 10th	Night	1 7% 5% 16% 9% 7% 7% 5% 7% 8% 30%	6766
	11th to 20th	Night	1 6% 3 11% 9% 7% 7% 5% 8% 8% 35%	6628
	21st to end	Night	1 7% 4 11% 7% 6% 6% 5% 7% 9% 36%	6952
February	1st to 10th	Night	2 9% 4 11% 10% 8% 7% 4 6% 9% 31%	2800
	11th to 20th	Night	2 10% 5% 12% 7% 7% 6% 6% 7% 8% 31%	2631
	21st to end	Night	7% 5% 13% 8% 6% 6% 5% 7% 7% 35%	1980
March	1st to 10th	Night	1 8% 4 12% 6% 6% 6% 5% 6% 10% 37%	5376
	11th to 20th	Night	3 7% 5% 11% 6% 5% 5% 5% 8% 10% 36%	5223
	21st to end	Night	4 15% 7% 15% 5% 4 4 3 5% 7% 28%	5182
April	1st to 10th	Night	4 12% 5% 10% 7% 6% 6% 5% 6% 9% 32%	2000
	11th to 20th	Night	6% 14% 5% 12% 6% 5% 4 4 6% 7% 29%	1782
	21st to end	Night	6% 16% 4 9% 5% 5% 5% 4 6% 6% 34%	1758
May	1st to 10th	Night	13% 21% 4 9% 5% 4 4 3 4 6% 27%	2620
	11th to 20th	Night	9% 12% 3 9% 6% 6% 6% 5% 7% 8% 30%	2270
	21st to end	Night	14% 11% 3 7% 4 4 6% 5% 8% 8% 30%	2452
June	1st to 10th	Night	19% 8% 3 7% 4 4 4 4 6% 7% 34%	1330
	11th to 20th	Night	19% 9% 3 8% 5% 5% 6% 4 6% 8% 28%	1164
	21st to end	Night	11% 7% 2 6% 5% 4 4 4 6% 9% 42%	1140
July	1st to 10th	Night	10% 6% 3 8% 5% 4 4 3 5% 8% 44%	1959
	11th to 20th	Night	7% 4 1 4 3 3 3 3 7% 9% 57%	2220
	21st to end	Night	6% 4 2 5% 4 4 4 4 6% 7% 52%	2597
August	1st to 10th	Night	14% 7% 2 5% 3 3 4 3 5% 9% 45%	2529
	11th to 20th	Night	13% 7% 2 5% 3 4 5% 4 7% 11% 40%	2583
	21st to end	Night	13% 7% 2 6% 4 4 3 3 5% 8% 45%	3146
September	1st to 10th	Night	11% 7% 3 5% 4 3 4 4 5% 8% 46%	1884
	11th to 20th	Night	14% 10% 3 6% 3 3 3 4 5% 8% 41%	2028
	21st to end	Night	8% 9% 3 6% 3 3 4 4 7% 7% 44%	2090
October	1st to 10th	Night	6% 8% 3 6% 5% 5% 5% 5% 7% 8% 41%	3644
	11th to 20th	Night	6% 8% 3 8% 5% 4 5% 4 7% 8% 42%	4086
	21st to end	Night	4 9% 4 9% 5% 4 4 4 6% 6% 45%	4457
November	1st to 10th	Night	3 13% 5% 11% 5% 5% 4 4 6% 7% 35%	2609
	11th to 20th	Night	2 9% 4 9% 6% 6% 6% 5% 6% 10% 36%	3000
	21st to end	Night	2 9% 4 12% 8% 5% 6% 5% 6% 9% 34%	3000
December	1st to 10th	Night	2 8% 4 12% 8% 7% 7% 5% 7% 8% 32%	4890
	11th to 20th	Night	1 9% 4 12% 9% 8% 6% 5% 8% 8% 29%	5550
	21st to end	Night	1 9% 5% 13% 6% 5% 5% 4 6% 8% 36%	7458

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	41% 7% 13% 23% 11% 5%	3179
	11th to 20th	Day	39% 7% 15% 17% 16% 5%	3336
	21st to end	Day	30% 11% 20% 27% 12% 1	4004
February	1st to 10th	Day	46% 9% 13% 16% 13% 4	1600
	11th to 20th	Day	46% 10% 12% 18% 12% 2	1662
	21st to end	Day	48% 7% 14% 14% 14% 2	1650
March	1st to 10th	Day	34% 5% 21% 19% 19% 2	4518
	11th to 20th	Day	35% 8% 16% 20% 20% 1	4776
	21st to end	Day	55% 8% 12% 15% 8% 2	5791
April	1st to 10th	Day	55% 8% 16% 14% 6%	2400
	11th to 20th	Day	58% 8% 12% 16% 6% 1	2568
	21st to end	Day	58% 8% 12% 15% 6% 1	2640
May	1st to 10th	Day	58% 8% 11% 18% 5%	4560
	11th to 20th	Day	52% 8% 15% 17% 8%	4845
	21st to end	Day	58% 8% 16% 10% 7%	5240
June	1st to 10th	Day	56% 9% 12% 14% 7% 1	2850
	11th to 20th	Day	60% 9% 11% 12% 7% 1	3011
	21st to end	Day	47% 10% 15% 16% 9% 2	3040
July	1st to 10th	Day	38% 7% 10% 18% 20% 7%	4920
	11th to 20th	Day	30% 9% 12% 26% 18% 4	4659
	21st to end	Day	34% 8% 14% 24% 18% 2	4796
August	1st to 10th	Day	40% 9% 13% 29% 9%	4384
	11th to 20th	Day	40% 10% 18% 22% 9% 1	4288
	21st to end	Day	38% 8% 19% 27% 7% 1	4520
September	1st to 10th	Day	43% 8% 14% 21% 11% 2	2294
	11th to 20th	Day	42% 7% 15% 24% 11% 2	2151
	21st to end	Day	42% 7% 18% 18% 12% 3	2090
October	1st to 10th	Day	36% 7% 20% 28% 8% 1	3330
	11th to 20th	Day	39% 7% 18% 22% 13% 1	2842
	21st to end	Day	38% 7% 13% 33% 8% 1	3101
November	1st to 10th	Day	47% 9% 15% 17% 9% 2	1665
	11th to 20th	Day	39% 10% 19% 20% 12% 1	1400
	21st to end	Day	39% 10% 20% 20% 9% 4	1400
December	1st to 10th	Day	48% 9% 18% 16% 8% 1	2290
	11th to 20th	Day	40% 7% 19% 23% 10% 2	2644
	21st to end	Day	38% 5% 11% 23% 17% 5%	3498
January	1st to 10th	Night	46% 7% 12% 22% 10% 3	6766
	11th to 20th	Night	40% 8% 15% 14% 15% 7%	6669
	21st to end	Night	36% 10% 22% 20% 11% 1	6952
February	1st to 10th	Night	46% 9% 13% 16% 13% 3	2800
	11th to 20th	Night	44% 9% 17% 15% 12% 2	2633
	21st to end	Night	44% 6% 13% 22% 14% 2	1980
March	1st to 10th	Night	38% 6% 21% 17% 16% 2	5376
	11th to 20th	Night	37% 7% 16% 21% 18%	5223
	21st to end	Night	52% 6% 11% 17% 13% 1	5182
April	1st to 10th	Night	46% 8% 16% 18% 11% 1	2000
	11th to 20th	Night	52% 6% 14% 17% 10% 1	1782
	21st to end	Night	47% 11% 13% 22% 7% 1	1758
May	1st to 10th	Night	58% 6% 13% 18% 5%	2620
	11th to 20th	Night	44% 7% 15% 25% 9%	2270
	21st to end	Night	44% 8% 18% 21% 10%	2452
June	1st to 10th	Night	47% 9% 14% 20% 9% 1	1330
	11th to 20th	Night	53% 10% 15% 15% 7% 1	1164
	21st to end	Night	36% 9% 19% 25% 9% 2	1140
July	1st to 10th	Night	36% 7% 12% 24% 14% 7%	1928
	11th to 20th	Night	22% 7% 20% 32% 12% 7%	2178
	21st to end	Night	29% 6% 16% 32% 16% 1	2515
August	1st to 10th	Night	36% 8% 14% 37% 5%	2521
	11th to 20th	Night	35% 9% 22% 26% 7%	2607
	21st to end	Night	37% 6% 18% 31% 7% 1	3146
September	1st to 10th	Night	35% 8% 17% 26% 10% 3	1884
	11th to 20th	Night	41% 6% 16% 25% 10% 3	2028
	21st to end	Night	36% 7% 18% 25% 13% 1	2090
October	1st to 10th	Night	35% 8% 16% 27% 13% 1	3644
	11th to 20th	Night	36% 7% 16% 30% 10%	4086
	21st to end	Night	37% 7% 15% 31% 10%	4457
November	1st to 10th	Night	45% 9% 14% 20% 11% 3	2609
	11th to 20th	Night	40% 10% 17% 21% 12% 2	3000
	21st to end	Night	43% 10% 14% 20% 9% 3	3000
December	1st to 10th	Night	46% 7% 19% 18% 9% 2	4890
	11th to 20th	Night	48% 9% 15% 15% 11% 1	5547
	21st to end	Night	42% 6% 12% 22% 13% 4	7458

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	10% 18% 27% 29% 14% 5%	200
	11th to 20th	Day	14% 14% 35% 27% 9% 3	200
	21st to end	Day	16% 17% 40% 19% 6% 2	220
February	1st to 10th	Day	20% 14% 38% 19% 8% 2	200
	11th to 20th	Day	11% 20% 37% 23% 10%	256
	21st to end	Day	17% 22% 30% 22% 8% 2	414
March	1st to 10th	Day	17% 23% 33% 17% 7% 2	500
	11th to 20th	Day	17% 20% 35% 20% 6% 2	500
	21st to end	Day	23% 23% 27% 19% 7% 2	550
April	1st to 10th	Day	24% 21% 29% 19% 6% 1	500
	11th to 20th	Day	20% 22% 28% 20% 8% 2	492
	21st to end	Day	23% 19% 27% 20% 9% 2	500
May	1st to 10th	Day	27% 18% 25% 20% 9% 1	503
	11th to 20th	Day	19% 10% 30% 25% 13% 2	722
	21st to end	Day	27% 8% 24% 24% 12% 3	760
June	1st to 10th	Day	25% 14% 30% 22% 8% 2	680
	11th to 20th	Day	29% 14% 24% 21% 11% 2	841
	21st to end	Day	18% 12% 24% 27% 16% 3	870
July	1st to 10th	Day	17% 11% 26% 30% 14% 2	821
	11th to 20th	Day	18% 10% 27% 25% 18% 2	668
	21st to end	Day	15% 12% 28% 27% 15% 3	629
August	1st to 10th	Day	16% 14% 28% 27% 11% 4	487
	11th to 20th	Day	16% 16% 30% 25% 10% 3	477
	21st to end	Day	19% 15% 29% 24% 10% 3	539
September	1st to 10th	Day	25% 18% 26% 20% 9% 1	490
	11th to 20th	Day	24% 14% 27% 25% 7% 3	490
	21st to end	Day	27% 19% 27% 18% 7% 2	490
October	1st to 10th	Day	23% 16% 29% 18% 10% 4	466
	11th to 20th	Day	23% 14% 30% 22% 9% 2	300
	21st to end	Day	22% 17% 32% 21% 7% 1	330
November	1st to 10th	Day	23% 23% 30% 17% 5% 2	290
	11th to 20th	Day	24% 19% 34% 17% 7% 1	200
	21st to end	Day	18% 20% 31% 21% 8% 4	200
December	1st to 10th	Day	15% 18% 35% 18% 10% 5%	200
	11th to 20th	Day	14% 22% 35% 22% 8% 1	200
	21st to end	Day	14% 10% 33% 30% 11% 2	220
January	1st to 10th	Night	13% 18% 38% 25% 6%	1000
	11th to 20th	Night	11% 18% 43% 21% 6% 1	954
	21st to end	Night	15% 18% 41% 18% 7% 1	880
February	1st to 10th	Night	12% 17% 32% 27% 11% 1	800
	11th to 20th	Night	11% 14% 38% 30% 7% 1	784
	21st to end	Night	7% 13% 37% 26% 15% 2	660
March	1st to 10th	Night	9% 17% 35% 28% 10% 2	800
	11th to 20th	Night	10% 15% 37% 28% 9% 1	800
	21st to end	Night	13% 13% 31% 29% 11% 2	880
April	1st to 10th	Night	13% 16% 27% 29% 14% 1	800
	11th to 20th	Night	15% 16% 32% 26% 9%	594
	21st to end	Night	20% 15% 27% 27% 10% 1	558
May	1st to 10th	Night	22% 9% 24% 32% 13% 1	400
	11th to 20th	Night	16% 7% 24% 35% 15% 3	394
	21st to end	Night	25% 5% 19% 28% 22% 1	422
June	1st to 10th	Night	25% 9% 23% 26% 15% 2	380
	11th to 20th	Night	22% 9% 21% 30% 17% 2	380
	21st to end	Night	16% 10% 18% 31% 22% 3	380
July	1st to 10th	Night	17% 4 19% 37% 23% 1	370
	11th to 20th	Night	15% 8% 21% 36% 21%	368
	21st to end	Night	12% 6% 14% 41% 25% 3	416
August	1st to 10th	Night	19% 3 12% 33% 29% 4	378
	11th to 20th	Night	14% 4 17% 38% 25% 2	423
	21st to end	Night	17% 9% 19% 35% 19% 1	627
September	1st to 10th	Night	15% 9% 23% 35% 16% 2	744
	11th to 20th	Night	21% 7% 20% 32% 18% 2	760
	21st to end	Night	17% 15% 29% 26% 12% 1	760
October	1st to 10th	Night	17% 11% 26% 33% 11% 2	760
	11th to 20th	Night	15% 14% 33% 28% 8% 1	760
	21st to end	Night	16% 15% 38% 23% 7% 1	836
November	1st to 10th	Night	16% 19% 35% 23% 8%	837
	11th to 20th	Night	14% 23% 38% 20% 4 1	1000
	21st to end	Night	12% 22% 35% 22% 8% 1	1000
December	1st to 10th	Night	12% 18% 39% 22% 8% 1	1000
	11th to 20th	Night	9% 20% 38% 25% 8% 1	1000
	21st to end	Night	9% 16% 40% 25% 9% 2	1100

Page generated at 2025-05-23 07:21:00. Version ac07

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