Caroline
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Caroline clear sky chart from 2005-11-06 to 2025-04-11.

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	9% 9% 3 9% 6% 5% 5% 5% 7% 8% 34%	116913
	Night	6% 10% 4 10% 6% 5% 5% 4 6% 8% 35%	120069
Transparency	Day	43% 8% 16% 22% 10% 1	116660
	Night	44% 8% 15% 21% 10% 2	119969
Seeing	Day	13% 8% 26% 31% 17% 5%	15785
	Night	12% 6% 29% 36% 15% 2	25015

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	3 12% 6% 13% 7% 5% 5% 4 6% 8% 31%	3179
	11th to 20th	Day	2 9% 4 11% 6% 5% 7% 5% 6% 8% 35%	3187
	21st to end	Day	3 9% 3 8% 5% 5% 6% 4 7% 9% 40%	4004
February	1st to 10th	Day	4 13% 5% 11% 9% 6% 7% 5% 6% 7% 28%	1600
	11th to 20th	Day	4 13% 4 14% 7% 6% 6% 4 7% 8% 28%	1687
	21st to end	Day	3 9% 5% 13% 9% 7% 6% 5% 8% 7% 29%	1620
March	1st to 10th	Day	2 8% 4 11% 6% 5% 6% 4 6% 8% 39%	4518
	11th to 20th	Day	5% 10% 5% 10% 5% 4 5% 5% 7% 9% 36%	4867
	21st to end	Day	8% 20% 7% 11% 6% 5% 5% 4 5% 6% 22%	5660
April	1st to 10th	Day	7% 15% 4 9% 7% 6% 6% 5% 7% 8% 26%	2440
	11th to 20th	Day	11% 16% 4 10% 5% 5% 5% 5% 6% 7% 26%	2442
	21st to end	Day	11% 12% 4 9% 6% 5% 5% 5% 6% 9% 28%	2470
May	1st to 10th	Day	16% 14% 3 9% 5% 5% 5% 4 5% 6% 27%	4466
	11th to 20th	Day	11% 11% 4 10% 6% 6% 6% 5% 6% 9% 27%	4694
	21st to end	Day	17% 11% 4 10% 7% 6% 5% 5% 7% 7% 21%	5161
June	1st to 10th	Day	18% 8% 3 7% 7% 6% 5% 5% 8% 7% 26%	2850
	11th to 20th	Day	20% 10% 3 8% 6% 6% 6% 5% 6% 7% 23%	2850
	21st to end	Day	11% 7% 2 6% 6% 6% 6% 6% 7% 9% 33%	2850
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 8% 44%	4740
	11th to 20th	Day	8% 4 2 4 4 4 6% 6% 8% 10% 44%	4740
	21st to end	Day	7% 5% 2 5% 5% 4 5% 5% 8% 9% 45%	5045
August	1st to 10th	Day	11% 5% 2 6% 4 4 5% 5% 7% 9% 41%	4401
	11th to 20th	Day	8% 5% 2 6% 4 5% 6% 5% 8% 11% 39%	4159
	21st to end	Day	10% 5% 2 6% 4 5% 5% 5% 7% 9% 43%	4521
September	1st to 10th	Day	13% 6% 2 6% 3 4 5% 4 6% 8% 44%	2349
	11th to 20th	Day	15% 9% 3 6% 4 4 3 3 5% 6% 43%	2109
	21st to end	Day	10% 8% 3 7% 4 5% 4 4 6% 8% 41%	2090
October	1st to 10th	Day	7% 7% 3 7% 5% 4 6% 5% 6% 9% 41%	3360
	11th to 20th	Day	8% 7% 3 8% 6% 5% 6% 5% 8% 9% 35%	2842
	21st to end	Day	7% 8% 3 9% 5% 5% 5% 4 5% 7% 41%	3101
November	1st to 10th	Day	6% 16% 6% 8% 7% 6% 4 5% 6% 7% 30%	1636
	11th to 20th	Day	5% 12% 4 10% 5% 6% 4 3 7% 7% 36%	1445
	21st to end	Day	5% 13% 3 10% 6% 5% 5% 4 7% 8% 34%	1400
December	1st to 10th	Day	5% 10% 4 13% 7% 7% 7% 5% 6% 9% 26%	2290
	11th to 20th	Day	3 11% 4 12% 6% 6% 6% 6% 7% 8% 31%	2642
	21st to end	Day	3 10% 5% 10% 6% 5% 5% 4 6% 7% 38%	3498
January	1st to 10th	Night	2 12% 7% 14% 8% 7% 6% 4 6% 7% 25%	6766
	11th to 20th	Night	2 8% 5% 13% 8% 6% 6% 6% 6% 7% 34%	6739
	21st to end	Night	3 9% 3 9% 6% 6% 5% 5% 7% 10% 38%	6953
February	1st to 10th	Night	5% 11% 5% 14% 8% 6% 7% 5% 5% 8% 27%	2800
	11th to 20th	Night	4 11% 4 13% 8% 8% 6% 4 7% 7% 28%	2600
	21st to end	Night	2 10% 5% 13% 7% 6% 5% 4 5% 7% 36%	2010
March	1st to 10th	Night	2 9% 4 11% 7% 5% 5% 5% 6% 8% 37%	5376
	11th to 20th	Night	5% 11% 4 10% 6% 5% 5% 5% 8% 10% 32%	5132
	21st to end	Night	8% 17% 5% 11% 6% 5% 5% 4 5% 7% 25%	5314
April	1st to 10th	Night	8% 11% 3 9% 7% 6% 5% 4 7% 9% 31%	1960
	11th to 20th	Night	9% 15% 5% 11% 7% 4 4 3 6% 7% 29%	1695
	21st to end	Night	11% 11% 4 9% 6% 5% 5% 4 6% 8% 31%	1710
May	1st to 10th	Night	21% 14% 4 8% 5% 4 4 3 3 5% 28%	2491
	11th to 20th	Night	11% 8% 3 8% 5% 4 5% 5% 9% 10% 31%	2199
	21st to end	Night	16% 10% 4 9% 7% 5% 6% 6% 7% 7% 23%	2414
June	1st to 10th	Night	17% 9% 3 7% 5% 4 6% 5% 6% 8% 30%	1330
	11th to 20th	Night	16% 10% 3 9% 6% 6% 6% 5% 7% 6% 26%	1330
	21st to end	Night	9% 6% 2 7% 5% 5% 6% 5% 8% 9% 38%	1330
July	1st to 10th	Night	9% 6% 2 8% 5% 6% 6% 4 6% 8% 40%	2220
	11th to 20th	Night	7% 4 1 5% 3 3 4 5% 8% 10% 50%	2220
	21st to end	Night	6% 7% 2 6% 4 4 4 4 6% 9% 48%	2504
August	1st to 10th	Night	13% 5% 2 6% 4 4 4 4 6% 7% 44%	2529
	11th to 20th	Night	10% 6% 3 6% 4 3 5% 5% 8% 11% 39%	2675
	21st to end	Night	11% 6% 3 6% 4 3 5% 4 5% 7% 47%	3146
September	1st to 10th	Night	11% 7% 2 6% 4 3 4 3 5% 7% 47%	1829
	11th to 20th	Night	14% 8% 3 7% 4 3 4 4 6% 7% 40%	2071
	21st to end	Night	10% 7% 2 6% 3 5% 5% 4 7% 8% 44%	2090
October	1st to 10th	Night	6% 7% 2 7% 5% 5% 5% 4 7% 8% 44%	3600
	11th to 20th	Night	6% 8% 3 7% 4 5% 5% 4 6% 10% 41%	4086
	21st to end	Night	6% 9% 3 8% 5% 5% 5% 4 6% 8% 41%	4457
November	1st to 10th	Night	8% 15% 4 10% 5% 5% 5% 5% 6% 7% 32%	2641
	11th to 20th	Night	5% 11% 4 10% 6% 6% 6% 4 7% 8% 32%	2954
	21st to end	Night	4 12% 4 11% 7% 6% 6% 5% 7% 9% 32%	3000
December	1st to 10th	Night	6% 12% 4 11% 7% 6% 7% 5% 6% 8% 29%	4890
	11th to 20th	Night	3 13% 5% 13% 9% 7% 7% 5% 6% 7% 25%	5550
	21st to end	Night	3 10% 4 10% 6% 5% 5% 4 6% 8% 40%	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	50% 5% 10% 21% 11% 3	3179
	11th to 20th	Day	44% 7% 11% 16% 19% 3	3208
	21st to end	Day	34% 9% 14% 31% 12%	4004
February	1st to 10th	Day	52% 7% 14% 15% 10% 3	1600
	11th to 20th	Day	50% 10% 14% 16% 8% 2	1695
	21st to end	Day	49% 8% 12% 18% 11% 1	1620
March	1st to 10th	Day	40% 7% 15% 22% 15%	4518
	11th to 20th	Day	40% 7% 15% 23% 13% 1	4868
	21st to end	Day	60% 8% 11% 14% 6% 1	5660
April	1st to 10th	Day	52% 10% 17% 15% 7%	2440
	11th to 20th	Day	54% 7% 12% 18% 8%	2442
	21st to end	Day	49% 10% 15% 18% 6% 1	2470
May	1st to 10th	Day	54% 8% 12% 20% 5%	4466
	11th to 20th	Day	46% 12% 16% 18% 8%	4698
	21st to end	Day	54% 12% 15% 13% 5% 1	5162
June	1st to 10th	Day	53% 10% 15% 15% 5% 2	2850
	11th to 20th	Day	57% 10% 15% 13% 5% 1	2850
	21st to end	Day	42% 12% 19% 20% 6% 1	2850
July	1st to 10th	Day	33% 9% 17% 24% 14% 4	4666
	11th to 20th	Day	30% 9% 19% 32% 8% 1	4659
	21st to end	Day	31% 8% 17% 26% 16% 3	4886
August	1st to 10th	Day	37% 9% 18% 28% 8%	4384
	11th to 20th	Day	33% 10% 23% 25% 8% 1	4201
	21st to end	Day	34% 8% 22% 29% 7% 1	4520
September	1st to 10th	Day	36% 8% 22% 21% 11% 3	2349
	11th to 20th	Day	41% 8% 14% 27% 9% 1	2109
	21st to end	Day	38% 9% 16% 23% 11% 3	2090
October	1st to 10th	Day	37% 6% 21% 29% 6% 1	3360
	11th to 20th	Day	41% 7% 17% 20% 12% 2	2842
	21st to end	Day	41% 7% 10% 32% 10% 1	3101
November	1st to 10th	Day	51% 8% 13% 17% 9% 2	1636
	11th to 20th	Day	45% 8% 13% 22% 11% 1	1445
	21st to end	Day	45% 9% 17% 18% 8% 3	1400
December	1st to 10th	Day	54% 6% 14% 19% 7% 1	2290
	11th to 20th	Day	47% 8% 20% 18% 6% 1	2644
	21st to end	Day	41% 7% 10% 21% 18% 3	3498
January	1st to 10th	Night	54% 7% 11% 18% 6% 2	6766
	11th to 20th	Night	47% 7% 11% 17% 14% 4	6780
	21st to end	Night	37% 9% 16% 25% 12% 1	6953
February	1st to 10th	Night	53% 8% 10% 17% 10% 2	2800
	11th to 20th	Night	51% 7% 13% 16% 11% 1	2602
	21st to end	Night	45% 5% 13% 22% 13% 2	2010
March	1st to 10th	Night	41% 9% 16% 21% 12% 1	5376
	11th to 20th	Night	41% 10% 15% 19% 14% 1	5132
	21st to end	Night	57% 8% 10% 15% 10% 1	5314
April	1st to 10th	Night	47% 8% 15% 19% 11% 1	1960
	11th to 20th	Night	52% 7% 14% 17% 8% 1	1695
	21st to end	Night	48% 9% 16% 20% 6% 1	1710
May	1st to 10th	Night	56% 7% 12% 20% 5%	2491
	11th to 20th	Night	40% 12% 16% 23% 10%	2199
	21st to end	Night	50% 16% 14% 15% 5% 1	2414
June	1st to 10th	Night	49% 10% 13% 18% 9% 1	1330
	11th to 20th	Night	53% 9% 14% 17% 5% 2	1330
	21st to end	Night	39% 12% 19% 23% 6% 1	1330
July	1st to 10th	Night	38% 9% 15% 22% 11% 4	2185
	11th to 20th	Night	26% 8% 23% 31% 8% 4	2178
	21st to end	Night	31% 7% 14% 32% 15% 1	2425
August	1st to 10th	Night	37% 9% 17% 30% 7%	2521
	11th to 20th	Night	34% 11% 24% 24% 6% 1	2699
	21st to end	Night	36% 6% 19% 30% 8% 1	3146
September	1st to 10th	Night	35% 7% 19% 23% 14% 3	1829
	11th to 20th	Night	40% 8% 15% 24% 10% 4	2071
	21st to end	Night	36% 7% 17% 24% 13% 3	2090
October	1st to 10th	Night	35% 6% 18% 28% 12% 1	3600
	11th to 20th	Night	38% 6% 17% 28% 10% 1	4086
	21st to end	Night	39% 6% 13% 30% 12%	4457
November	1st to 10th	Night	49% 8% 12% 19% 11% 2	2641
	11th to 20th	Night	46% 8% 15% 18% 11% 1	2954
	21st to end	Night	45% 9% 16% 19% 8% 3	3000
December	1st to 10th	Night	52% 6% 15% 18% 7% 2	4890
	11th to 20th	Night	55% 9% 14% 16% 6% 1	5547
	21st to end	Night	40% 6% 11% 23% 17% 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	6% 5% 30% 31% 18% 11%	200
	11th to 20th	Day	5% 4 35% 36% 16% 5%	200
	21st to end	Day	8% 8% 28% 33% 17% 6%	220
February	1st to 10th	Day	9% 11% 27% 36% 12% 6%	200
	11th to 20th	Day	10% 5% 32% 33% 17% 3	265
	21st to end	Day	4 8% 29% 38% 18% 3	384
March	1st to 10th	Day	8% 10% 33% 31% 14% 4	500
	11th to 20th	Day	8% 8% 32% 33% 15% 5%	500
	21st to end	Day	16% 9% 31% 26% 14% 4	550
April	1st to 10th	Day	12% 12% 32% 27% 13% 3	500
	11th to 20th	Day	16% 10% 27% 28% 14% 5%	453
	21st to end	Day	16% 13% 24% 29% 14% 4	460
May	1st to 10th	Day	19% 12% 22% 27% 15% 4	509
	11th to 20th	Day	14% 7% 24% 33% 19% 4	675
	21st to end	Day	19% 6% 19% 30% 20% 6%	734
June	1st to 10th	Day	18% 8% 24% 35% 13% 3	680
	11th to 20th	Day	22% 7% 24% 28% 14% 4	680
	21st to end	Day	11% 5% 23% 32% 20% 8%	680
July	1st to 10th	Day	13% 4 20% 33% 23% 8%	671
	11th to 20th	Day	15% 5% 19% 32% 24% 5%	668
	21st to end	Day	8% 5% 23% 32% 24% 7%	682
August	1st to 10th	Day	10% 5% 24% 34% 18% 8%	487
	11th to 20th	Day	8% 5% 24% 33% 25% 5%	477
	21st to end	Day	11% 7% 24% 31% 20% 7%	539
September	1st to 10th	Day	15% 7% 27% 29% 15% 7%	490
	11th to 20th	Day	20% 7% 22% 28% 18% 7%	490
	21st to end	Day	14% 10% 30% 28% 12% 4	490
October	1st to 10th	Day	14% 9% 25% 29% 17% 7%	428
	11th to 20th	Day	14% 8% 30% 28% 15% 5%	300
	21st to end	Day	13% 14% 30% 28% 12% 3	330
November	1st to 10th	Day	15% 5% 24% 38% 14% 4	300
	11th to 20th	Day	14% 10% 34% 28% 12% 2	223
	21st to end	Day	5% 8% 29% 38% 14% 7%	200
December	1st to 10th	Day	7% 5% 30% 37% 18% 4	200
	11th to 20th	Day	6% 12% 33% 32% 13% 5%	200
	21st to end	Day	6% 5% 26% 31% 25% 7%	220
January	1st to 10th	Night	10% 8% 34% 34% 13% 1	1000
	11th to 20th	Night	8% 9% 35% 36% 12% 1	1000
	21st to end	Night	10% 10% 34% 33% 11% 2	881
February	1st to 10th	Night	10% 8% 28% 34% 16% 3	800
	11th to 20th	Night	7% 7% 32% 37% 15% 1	784
	21st to end	Night	6% 5% 30% 35% 18% 5%	660
March	1st to 10th	Night	8% 5% 30% 39% 15% 3	800
	11th to 20th	Night	8% 5% 33% 40% 13% 2	800
	21st to end	Night	13% 6% 28% 37% 14% 2	880
April	1st to 10th	Night	11% 7% 31% 36% 14% 1	760
	11th to 20th	Night	15% 6% 35% 33% 10% 1	565
	21st to end	Night	16% 11% 24% 35% 12% 1	570
May	1st to 10th	Night	20% 8% 23% 36% 11% 2	404
	11th to 20th	Night	13% 5% 24% 42% 15% 1	374
	21st to end	Night	22% 5% 20% 34% 18% 1	411
June	1st to 10th	Night	19% 6% 23% 38% 13% 1	380
	11th to 20th	Night	18% 5% 24% 35% 15% 2	380
	21st to end	Night	12% 3 19% 38% 25% 3	380
July	1st to 10th	Night	15% 2 16% 42% 23% 1	370
	11th to 20th	Night	14% 3 18% 44% 19% 1	368
	21st to end	Night	8% 4 17% 44% 25% 2	416
August	1st to 10th	Night	12% 4 16% 36% 29% 4	378
	11th to 20th	Night	12% 5% 14% 40% 27% 2	476
	21st to end	Night	13% 3 20% 42% 22%	627
September	1st to 10th	Night	15% 2 19% 40% 21% 2	689
	11th to 20th	Night	18% 3 21% 33% 22% 3	760
	21st to end	Night	13% 5% 30% 36% 15% 2	760
October	1st to 10th	Night	15% 5% 27% 36% 15% 2	760
	11th to 20th	Night	11% 4 31% 37% 14% 2	760
	21st to end	Night	12% 7% 33% 35% 11% 1	836
November	1st to 10th	Night	15% 7% 33% 31% 12% 2	886
	11th to 20th	Night	11% 8% 40% 32% 8% 1	1000
	21st to end	Night	9% 5% 39% 35% 10% 3	1000
December	1st to 10th	Night	11% 8% 33% 34% 12% 2	1000
	11th to 20th	Night	9% 6% 35% 37% 12% 1	1000
	21st to end	Night	10% 5% 33% 36% 13% 3	1100

Page generated at 2025-04-08 07:17:27. Version ac07

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