Sandy McNabb Campground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sandy McNabb Campground clear sky chart from 2005-11-06 to 2026-02-16.

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	7% 8% 3 8% 5% 5% 5% 4 6% 8% 41%	134701
	Night	4 8% 3 8% 5% 5% 5% 4 6% 8% 44%	134841
Transparency	Day	38% 8% 15% 24% 13% 2	134410
	Night	35% 9% 16% 24% 14% 3	134711
Seeing	Day	13% 16% 32% 26% 11% 3	16851
	Night	10% 13% 36% 28% 11% 2	26113

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	5% 3 10% 6% 6% 7% 5% 7% 9% 42%	4125
	11th to 20th	Day	1 5% 3 9% 5% 6% 5% 4 6% 8% 47%	4358
	21st to end	Day	1 7% 3 8% 5% 4 4 4 6% 11% 49%	5186
February	1st to 10th	Day	1 8% 3 9% 8% 5% 5% 6% 8% 10% 36%	1680
	11th to 20th	Day	1 8% 5% 9% 6% 6% 7% 5% 8% 10% 35%	1777
	21st to end	Day	1 8% 4 14% 6% 6% 6% 5% 8% 8% 34%	1640
March	1st to 10th	Day	1 8% 4 9% 6% 4 4 4 6% 10% 44%	4518
	11th to 20th	Day	2 8% 4 10% 5% 4 5% 4 7% 7% 45%	4906
	21st to end	Day	3 17% 8% 16% 6% 5% 4 4 6% 6% 24%	5615
April	1st to 10th	Day	6% 15% 5% 10% 6% 5% 5% 4 6% 8% 31%	2430
	11th to 20th	Day	7% 17% 5% 11% 4 4 5% 4 6% 7% 31%	2570
	21st to end	Day	10% 14% 5% 8% 5% 4 4 4 5% 8% 32%	2600
May	1st to 10th	Day	12% 15% 4 7% 4 4 3 3 5% 6% 39%	6117
	11th to 20th	Day	10% 12% 4 10% 7% 6% 6% 5% 7% 7% 25%	6729
	21st to end	Day	12% 8% 3 7% 5% 5% 5% 4 6% 7% 38%	7405
June	1st to 10th	Day	16% 10% 3 7% 5% 5% 5% 5% 6% 8% 30%	3000
	11th to 20th	Day	21% 11% 3 8% 5% 4 6% 4 5% 7% 27%	3000
	21st to end	Day	11% 5% 2 7% 6% 6% 6% 5% 7% 8% 38%	3000
July	1st to 10th	Day	7% 5% 2 5% 4 4 5% 4 8% 9% 46%	6780
	11th to 20th	Day	10% 4 2 5% 4 4 5% 4 8% 9% 44%	6780
	21st to end	Day	9% 6% 2 5% 4 3 4 4 6% 8% 50%	7067
August	1st to 10th	Day	10% 6% 2 6% 4 5% 6% 5% 7% 10% 39%	4541
	11th to 20th	Day	9% 5% 2 6% 4 5% 6% 5% 7% 9% 43%	4219
	21st to end	Day	9% 4 2 5% 3 4 4 3 5% 8% 53%	4664
September	1st to 10th	Day	11% 6% 2 5% 4 4 4 3 6% 6% 49%	2460
	11th to 20th	Day	11% 8% 2 6% 3 4 5% 4 4 6% 46%	2200
	21st to end	Day	8% 7% 2 5% 4 4 5% 3 6% 7% 49%	2200
October	1st to 10th	Day	5% 6% 2 6% 4 4 4 3 6% 10% 49%	3487
	11th to 20th	Day	3 7% 2 6% 3 4 5% 4 8% 11% 47%	2974
	21st to end	Day	3 8% 3 6% 4 5% 5% 3 5% 8% 49%	3200
November	1st to 10th	Day	4 12% 4 9% 5% 5% 4 4 7% 7% 38%	1764
	11th to 20th	Day	3 9% 3 8% 4 4 5% 3 6% 9% 47%	1592
	21st to end	Day	2 9% 4 10% 6% 5% 6% 3 7% 7% 41%	1470
December	1st to 10th	Day	1 5% 3 8% 5% 4 4 4 9% 13% 43%	2360
	11th to 20th	Day	1 6% 4 8% 6% 6% 6% 4 7% 10% 41%	2712
	21st to end	Day	2 8% 3 11% 6% 5% 4 4 5% 7% 44%	3575
January	1st to 10th	Night	1 8% 4 10% 5% 6% 7% 5% 7% 10% 37%	8768
	11th to 20th	Night	1 5% 2 9% 5% 6% 6% 5% 9% 9% 43%	8584
	21st to end	Night	1 7% 3 11% 6% 5% 5% 4 6% 9% 43%	8994
February	1st to 10th	Night	1 7% 3 10% 7% 6% 6% 5% 7% 8% 38%	2940
	11th to 20th	Night	1 10% 5% 11% 6% 5% 6% 4 6% 8% 38%	2619
	21st to end	Night	2 7% 4 9% 7% 7% 6% 4 6% 7% 41%	1988
March	1st to 10th	Night	1 8% 4 10% 7% 5% 6% 5% 6% 9% 40%	5376
	11th to 20th	Night	1 8% 3 8% 5% 5% 5% 4 7% 8% 45%	5093
	21st to end	Night	3 17% 7% 11% 5% 4 3 4 6% 8% 31%	5358
April	1st to 10th	Night	5% 14% 5% 10% 6% 3 4 3 6% 8% 38%	1970
	11th to 20th	Night	6% 13% 5% 10% 5% 4 4 3 6% 7% 36%	1781
	21st to end	Night	6% 13% 4 8% 5% 5% 4 3 6% 8% 37%	1800
May	1st to 10th	Night	10% 14% 3 6% 3 3 3 3 5% 7% 42%	3837
	11th to 20th	Night	12% 12% 4 9% 5% 4 5% 4 6% 8% 33%	3163
	21st to end	Night	10% 7% 2 6% 4 5% 5% 4 6% 6% 44%	3470
June	1st to 10th	Night	12% 9% 4 6% 4 5% 5% 4 6% 7% 39%	1400
	11th to 20th	Night	19% 8% 2 7% 5% 5% 4 4 6% 7% 34%	1400
	21st to end	Night	9% 4 1 4 3 5% 6% 4 6% 8% 50%	1400
July	1st to 10th	Night	6% 5% 2 5% 4 4 5% 3 6% 8% 50%	3180
	11th to 20th	Night	9% 5% 1 5% 3 4 4 4 5% 8% 52%	3180
	21st to end	Night	12% 4 2 5% 3 3 3 3 5% 7% 54%	3773
August	1st to 10th	Night	11% 6% 2 5% 3 4 5% 5% 6% 9% 45%	2609
	11th to 20th	Night	7% 3 2 5% 4 4 5% 5% 8% 9% 49%	2837
	21st to end	Night	7% 4 2 4 3 3 3 4 6% 9% 54%	3245
September	1st to 10th	Night	10% 6% 1 4 3 3 3 3 6% 7% 54%	1937
	11th to 20th	Night	11% 8% 2 4 3 3 3 4 5% 7% 50%	2200
	21st to end	Night	8% 8% 2 5% 3 3 3 3 6% 7% 53%	2200
October	1st to 10th	Night	5% 6% 2 5% 3 3 4 3 6% 8% 54%	3696
	11th to 20th	Night	4 6% 2 5% 3 3 3 4 7% 9% 54%	4173
	21st to end	Night	3 8% 3 7% 4 3 4 4 6% 8% 51%	4600
November	1st to 10th	Night	3 11% 5% 8% 5% 5% 4 4 6% 8% 40%	2733
	11th to 20th	Night	2 7% 3 7% 5% 5% 5% 4 6% 9% 46%	3024
	21st to end	Night	2 8% 4 8% 5% 5% 5% 3 7% 9% 44%	3150
December	1st to 10th	Night	1 5% 3 8% 5% 5% 5% 4 8% 11% 45%	5040
	11th to 20th	Night	1 7% 4 10% 7% 6% 6% 5% 8% 9% 38%	5700
	21st to end	Night	2 10% 4 9% 5% 5% 5% 4 6% 7% 42%	7623

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	36% 8% 13% 24% 14% 6%	4125
	11th to 20th	Day	34% 6% 15% 26% 15% 4	4380
	21st to end	Day	28% 9% 16% 30% 16% 2	5187
February	1st to 10th	Day	39% 12% 13% 21% 11% 4	1680
	11th to 20th	Day	39% 12% 15% 22% 10% 3	1786
	21st to end	Day	43% 10% 15% 17% 13% 2	1640
March	1st to 10th	Day	33% 9% 15% 23% 19% 1	4518
	11th to 20th	Day	34% 8% 16% 23% 17% 2	4907
	21st to end	Day	54% 10% 14% 14% 6% 1	5615
April	1st to 10th	Day	49% 10% 16% 16% 8% 1	2430
	11th to 20th	Day	49% 8% 14% 19% 8% 1	2570
	21st to end	Day	48% 9% 16% 19% 8% 1	2600
May	1st to 10th	Day	46% 5% 10% 23% 14% 3	6117
	11th to 20th	Day	48% 11% 13% 21% 6%	6733
	21st to end	Day	41% 10% 16% 20% 13%	7406
June	1st to 10th	Day	49% 10% 13% 17% 10% 1	3000
	11th to 20th	Day	55% 8% 12% 15% 8% 1	3000
	21st to end	Day	40% 10% 17% 21% 11% 2	3000
July	1st to 10th	Day	30% 8% 16% 24% 19% 4	6706
	11th to 20th	Day	33% 7% 19% 26% 13% 2	6699
	21st to end	Day	31% 6% 13% 25% 18% 7%	6869
August	1st to 10th	Day	37% 9% 15% 30% 8% 1	4524
	11th to 20th	Day	35% 9% 22% 25% 8% 1	4259
	21st to end	Day	28% 6% 16% 33% 14% 2	4663
September	1st to 10th	Day	34% 6% 15% 25% 16% 4	2460
	11th to 20th	Day	36% 8% 15% 26% 13% 2	2200
	21st to end	Day	32% 9% 15% 28% 14% 3	2200
October	1st to 10th	Day	30% 7% 18% 35% 9% 1	3487
	11th to 20th	Day	29% 7% 23% 24% 14% 4	2974
	21st to end	Day	33% 6% 13% 30% 16% 3	3200
November	1st to 10th	Day	43% 10% 14% 19% 12% 2	1764
	11th to 20th	Day	33% 9% 19% 24% 12% 2	1592
	21st to end	Day	39% 10% 17% 21% 9% 4	1470
December	1st to 10th	Day	30% 9% 22% 25% 11% 2	2360
	11th to 20th	Day	35% 10% 20% 24% 9% 1	2714
	21st to end	Day	35% 8% 10% 24% 18% 5%	3575
January	1st to 10th	Night	39% 11% 13% 22% 13% 3	8769
	11th to 20th	Night	33% 8% 15% 23% 14% 7%	8624
	21st to end	Night	33% 10% 16% 24% 15% 2	8994
February	1st to 10th	Night	40% 11% 13% 19% 14% 4	2940
	11th to 20th	Night	42% 9% 15% 18% 13% 3	2620
	21st to end	Night	41% 9% 12% 21% 14% 3	1988
March	1st to 10th	Night	36% 11% 14% 22% 15% 3	5376
	11th to 20th	Night	33% 10% 16% 24% 17% 1	5093
	21st to end	Night	49% 9% 14% 18% 9% 1	5358
April	1st to 10th	Night	44% 9% 14% 20% 12% 1	1970
	11th to 20th	Night	46% 9% 13% 22% 8% 1	1781
	21st to end	Night	43% 9% 14% 23% 9% 2	1800
May	1st to 10th	Night	41% 6% 11% 25% 14% 3	3834
	11th to 20th	Night	44% 9% 13% 27% 6%	3163
	21st to end	Night	36% 10% 17% 26% 11% 1	3470
June	1st to 10th	Night	43% 8% 16% 23% 10% 1	1400
	11th to 20th	Night	47% 8% 14% 20% 10% 2	1400
	21st to end	Night	30% 10% 20% 26% 13% 2	1400
July	1st to 10th	Night	30% 6% 16% 24% 19% 5%	3145
	11th to 20th	Night	30% 5% 21% 30% 11% 3	3138
	21st to end	Night	29% 5% 17% 25% 16% 8%	3666
August	1st to 10th	Night	33% 7% 17% 28% 13% 2	2601
	11th to 20th	Night	28% 8% 25% 29% 9% 1	2863
	21st to end	Night	25% 6% 21% 32% 15% 2	3245
September	1st to 10th	Night	29% 7% 16% 28% 16% 4	1937
	11th to 20th	Night	33% 6% 16% 28% 14% 4	2200
	21st to end	Night	30% 8% 16% 28% 15% 3	2200
October	1st to 10th	Night	27% 7% 14% 27% 22% 3	3696
	11th to 20th	Night	25% 6% 21% 26% 20% 2	4173
	21st to end	Night	30% 8% 13% 31% 17% 1	4600
November	1st to 10th	Night	40% 10% 15% 21% 13% 2	2733
	11th to 20th	Night	33% 11% 17% 22% 16% 2	3024
	21st to end	Night	34% 9% 18% 23% 12% 4	3150
December	1st to 10th	Night	30% 9% 24% 24% 10% 3	5040
	11th to 20th	Night	38% 11% 20% 19% 11% 1	5697
	21st to end	Night	37% 9% 11% 22% 16% 5%	7623

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	5% 13% 39% 26% 12% 5%	220
	11th to 20th	Day	7% 13% 40% 27% 11% 1	220
	21st to end	Day	4 14% 52% 20% 8% 2	242
February	1st to 10th	Day	4 26% 41% 20% 6% 3	220
	11th to 20th	Day	5% 17% 41% 30% 7% 1	304
	21st to end	Day	6% 22% 31% 31% 8% 1	404
March	1st to 10th	Day	8% 22% 36% 23% 9% 1	500
	11th to 20th	Day	7% 20% 34% 27% 9% 3	500
	21st to end	Day	11% 22% 34% 23% 7% 3	550
April	1st to 10th	Day	12% 22% 35% 23% 8% 1	500
	11th to 20th	Day	17% 14% 31% 25% 10% 3	492
	21st to end	Day	16% 20% 28% 23% 9% 4	500
May	1st to 10th	Day	20% 14% 28% 21% 13% 4	503
	11th to 20th	Day	19% 10% 23% 25% 17% 4	720
	21st to end	Day	22% 10% 20% 28% 16% 4	789
June	1st to 10th	Day	15% 16% 32% 24% 10% 2	730
	11th to 20th	Day	23% 17% 27% 24% 8% 2	730
	21st to end	Day	14% 12% 26% 28% 16% 3	730
July	1st to 10th	Day	12% 9% 28% 30% 17% 3	721
	11th to 20th	Day	12% 11% 30% 29% 17% 2	718
	21st to end	Day	8% 9% 34% 31% 14% 4	664
August	1st to 10th	Day	13% 11% 27% 34% 11% 4	527
	11th to 20th	Day	11% 12% 35% 28% 11% 4	517
	21st to end	Day	12% 15% 31% 27% 12% 4	583
September	1st to 10th	Day	14% 16% 29% 25% 11% 4	530
	11th to 20th	Day	14% 15% 30% 28% 12% 2	530
	21st to end	Day	15% 24% 32% 20% 6% 2	530
October	1st to 10th	Day	12% 18% 31% 26% 11% 3	469
	11th to 20th	Day	13% 18% 31% 26% 9% 2	330
	21st to end	Day	15% 23% 34% 20% 6% 2	363
November	1st to 10th	Day	15% 21% 40% 17% 6% 2	330
	11th to 20th	Day	14% 21% 38% 20% 5% 2	283
	21st to end	Day	10% 18% 35% 21% 10% 7%	220
December	1st to 10th	Day	7% 14% 48% 23% 7% 2	220
	11th to 20th	Day	8% 22% 35% 27% 6% 2	220
	21st to end	Day	8% 12% 38% 29% 9% 3	242
January	1st to 10th	Night	8% 20% 45% 20% 6% 1	1050
	11th to 20th	Night	7% 16% 51% 20% 5% 1	984
	21st to end	Night	7% 20% 44% 23% 6% 1	924
February	1st to 10th	Night	5% 17% 40% 24% 10% 3	840
	11th to 20th	Night	6% 15% 40% 30% 9%	804
	21st to end	Night	6% 12% 40% 27% 14% 2	660
March	1st to 10th	Night	5% 15% 42% 25% 10% 3	800
	11th to 20th	Night	6% 16% 41% 27% 9% 1	800
	21st to end	Night	7% 13% 36% 31% 11% 3	880
April	1st to 10th	Night	10% 15% 31% 31% 11% 1	770
	11th to 20th	Night	12% 11% 35% 31% 10% 1	593
	21st to end	Night	13% 11% 33% 31% 11% 1	600
May	1st to 10th	Night	15% 10% 26% 32% 15% 2	493
	11th to 20th	Night	16% 7% 25% 31% 18% 3	394
	21st to end	Night	22% 5% 20% 32% 19% 2	433
June	1st to 10th	Night	17% 9% 27% 32% 13% 2	400
	11th to 20th	Night	22% 7% 26% 32% 14%	400
	21st to end	Night	11% 6% 25% 34% 23% 1	400
July	1st to 10th	Night	11% 5% 18% 43% 22% 1	390
	11th to 20th	Night	10% 3 26% 40% 18% 3	388
	21st to end	Night	8% 6% 19% 43% 23% 2	438
August	1st to 10th	Night	13% 3 18% 38% 26% 2	398
	11th to 20th	Night	10% 3 22% 41% 20% 3	554
	21st to end	Night	11% 6% 25% 39% 17% 2	660
September	1st to 10th	Night	13% 6% 24% 33% 19% 5%	737
	11th to 20th	Night	16% 8% 22% 31% 19% 5%	800
	21st to end	Night	13% 11% 36% 28% 9% 4	800
October	1st to 10th	Night	13% 8% 35% 30% 12% 3	800
	11th to 20th	Night	10% 14% 36% 29% 9% 2	800
	21st to end	Night	10% 16% 39% 27% 6% 2	880
November	1st to 10th	Night	11% 17% 45% 19% 7% 1	888
	11th to 20th	Night	9% 22% 44% 20% 4 1	1050
	21st to end	Night	6% 20% 44% 22% 6% 2	1050
December	1st to 10th	Night	6% 18% 44% 23% 8% 2	1050
	11th to 20th	Night	6% 16% 46% 25% 6% 1	1050
	21st to end	Night	7% 17% 45% 23% 7% 2	1155

Page generated at 2026-02-12 23:42:10. Version ac07

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