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 2024-11-30.

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% 9% 3 8% 5% 5% 5% 4 7% 8% 40%	105780
	Night	5% 8% 3 8% 5% 5% 5% 4 6% 8% 44%	102398
Transparency	Day	38% 9% 15% 23% 12% 2	105530
	Night	35% 10% 16% 23% 13% 3	102294
Seeing	Day	13% 16% 31% 26% 11% 3	15380
	Night	10% 14% 36% 28% 11% 2	24475

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 10% 6% 6% 5% 4 9% 9% 40%	2219
	11th to 20th	Day	1 7% 3 9% 4 6% 6% 5% 7% 9% 41%	2326
	21st to end	Day	1 8% 3 7% 5% 5% 5% 5% 7% 10% 44%	2794
February	1st to 10th	Day	1 8% 3 9% 8% 5% 5% 6% 8% 10% 36%	1520
	11th to 20th	Day	1 8% 5% 9% 7% 6% 7% 6% 8% 10% 34%	1644
	21st to end	Day	1 9% 4 14% 6% 6% 6% 5% 8% 8% 34%	1560
March	1st to 10th	Day	1 6% 4 11% 8% 6% 5% 5% 7% 9% 38%	3138
	11th to 20th	Day	2 10% 4 6% 4 3 4 4 6% 8% 49%	3422
	21st to end	Day	4 18% 7% 19% 5% 5% 4 4 5% 5% 24%	3915
April	1st to 10th	Day	6% 15% 5% 10% 6% 5% 4 4 6% 8% 30%	2308
	11th to 20th	Day	7% 17% 5% 11% 4 4 4 4 6% 7% 30%	2440
	21st to end	Day	10% 14% 5% 8% 5% 4 4 4 6% 8% 31%	2470
May	1st to 10th	Day	16% 19% 4 8% 5% 5% 4 3 5% 5% 26%	4282
	11th to 20th	Day	8% 11% 3 9% 6% 5% 6% 5% 8% 8% 31%	4689
	21st to end	Day	17% 10% 3 8% 6% 6% 5% 4 6% 7% 28%	5161
June	1st to 10th	Day	17% 10% 3 7% 5% 5% 5% 5% 6% 7% 29%	2850
	11th to 20th	Day	21% 11% 3 8% 5% 4 5% 4 5% 7% 26%	2850
	21st to end	Day	11% 5% 2 7% 5% 6% 5% 5% 7% 8% 38%	2850
July	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 7% 9% 47%	4740
	11th to 20th	Day	7% 4 1 4 3 4 5% 5% 9% 10% 49%	4740
	21st to end	Day	3 4 1 4 4 4 5% 4 6% 8% 57%	4927
August	1st to 10th	Day	10% 6% 2 6% 4 5% 6% 5% 7% 10% 39%	4401
	11th to 20th	Day	9% 5% 1 6% 4 5% 6% 5% 7% 9% 42%	4087
	21st to end	Day	9% 4 2 5% 3 4 4 3 5% 8% 52%	4521
September	1st to 10th	Day	11% 7% 2 5% 4 4 4 3 5% 6% 49%	2337
	11th to 20th	Day	11% 9% 2 6% 3 4 5% 4 4 6% 45%	2090
	21st to end	Day	8% 7% 2 5% 4 4 5% 3 6% 7% 48%	2090
October	1st to 10th	Day	5% 7% 2 6% 4 4 4 3 6% 10% 49%	3380
	11th to 20th	Day	4 7% 2 6% 4 4 5% 4 8% 11% 46%	2883
	21st to end	Day	3 8% 3 6% 4 5% 5% 3 5% 8% 49%	3101
November	1st to 10th	Day	4 12% 4 9% 6% 5% 4 4 7% 8% 37%	1679
	11th to 20th	Day	3 8% 3 7% 4 4 5% 3 6% 9% 47%	1516
	21st to end	Day	2 9% 4 10% 6% 5% 6% 3 7% 7% 41%	1396
December	1st to 10th	Day	2 6% 3 9% 7% 5% 5% 4 8% 10% 40%	1330
	11th to 20th	Day	2 8% 5% 9% 6% 6% 5% 4 8% 9% 38%	1682
	21st to end	Day	2 9% 3 8% 5% 4 3 4 6% 8% 47%	2442
January	1st to 10th	Night	1 8% 4 11% 7% 7% 6% 5% 7% 10% 34%	4726
	11th to 20th	Night	1 6% 3 10% 6% 6% 6% 5% 10% 8% 38%	4602
	21st to end	Night	1 10% 4 10% 6% 5% 5% 4 6% 9% 40%	4862
February	1st to 10th	Night	2 8% 3 10% 7% 5% 5% 5% 7% 8% 39%	2660
	11th to 20th	Night	1 10% 5% 11% 6% 5% 6% 4 6% 8% 38%	2422
	21st to end	Night	2 7% 4 9% 7% 7% 7% 4 5% 7% 41%	1892
March	1st to 10th	Night	6% 4 11% 8% 6% 8% 6% 7% 8% 36%	3736
	11th to 20th	Night	2 9% 3 5% 4 4 3 3 6% 8% 52%	3557
	21st to end	Night	4 19% 7% 12% 5% 4 4 4 6% 6% 28%	3736
April	1st to 10th	Night	5% 14% 5% 10% 6% 3 4 3 6% 7% 37%	1872
	11th to 20th	Night	6% 14% 5% 10% 4 4 4 3 6% 7% 35%	1691
	21st to end	Night	6% 13% 4 8% 5% 5% 4 3 6% 8% 37%	1710
May	1st to 10th	Night	14% 18% 4 7% 4 3 4 3 5% 6% 32%	2681
	11th to 20th	Night	9% 10% 3 7% 5% 4 5% 4 6% 9% 37%	2203
	21st to end	Night	14% 9% 2 7% 5% 6% 5% 5% 7% 7% 33%	2414
June	1st to 10th	Night	13% 9% 4 7% 4 5% 5% 4 6% 7% 38%	1330
	11th to 20th	Night	19% 9% 2 7% 5% 5% 4 4 7% 7% 33%	1330
	21st to end	Night	9% 3 1 4 3 5% 6% 4 6% 8% 50%	1330
July	1st to 10th	Night	6% 4 2 5% 4 4 5% 4 6% 7% 53%	2220
	11th to 20th	Night	5% 3 1 3 3 4 5% 4 6% 8% 58%	2220
	21st to end	Night	6% 3 1 3 2 3 3 3 5% 7% 64%	2622
August	1st to 10th	Night	11% 6% 2 5% 3 4 5% 5% 6% 8% 46%	2529
	11th to 20th	Night	6% 3 2 5% 4 4 5% 5% 8% 9% 49%	2749
	21st to end	Night	8% 4 2 4 3 3 3 4 6% 9% 53%	3146
September	1st to 10th	Night	11% 6% 1 4 3 3 3 3 6% 7% 54%	1840
	11th to 20th	Night	11% 9% 2 5% 3 3 3 4 5% 7% 50%	2090
	21st to end	Night	8% 8% 2 5% 3 3 3 3 6% 7% 52%	2090
October	1st to 10th	Night	5% 6% 2 5% 3 3 4 3 6% 8% 54%	3583
	11th to 20th	Night	4 5% 2 4 3 3 3 4 7% 9% 54%	4044
	21st to end	Night	3 8% 3 7% 4 4 4 4 6% 8% 50%	4457
November	1st to 10th	Night	3 11% 5% 8% 5% 5% 4 5% 6% 8% 40%	2600
	11th to 20th	Night	2 7% 3 7% 5% 5% 5% 4 6% 9% 47%	2880
	21st to end	Night	2 8% 4 8% 6% 5% 5% 4 7% 9% 43%	3000
December	1st to 10th	Night	2 8% 4 9% 6% 5% 4 5% 7% 9% 42%	2850
	11th to 20th	Night	1 7% 4 10% 7% 6% 6% 5% 7% 9% 39%	3510
	21st to end	Night	2 9% 3 8% 5% 5% 6% 4 6% 7% 46%	5214

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% 12% 13% 25% 11% 3	2219
	11th to 20th	Day	37% 10% 12% 19% 18% 4	2348
	21st to end	Day	29% 15% 17% 28% 9% 1	2794
February	1st to 10th	Day	39% 13% 13% 22% 10% 4	1520
	11th to 20th	Day	39% 12% 16% 20% 10% 3	1653
	21st to end	Day	45% 10% 15% 16% 12% 2	1560
March	1st to 10th	Day	37% 12% 16% 19% 15% 1	3138
	11th to 20th	Day	31% 8% 21% 26% 13% 1	3423
	21st to end	Day	56% 11% 13% 15% 5%	3915
April	1st to 10th	Day	49% 10% 16% 16% 8% 1	2308
	11th to 20th	Day	50% 8% 14% 19% 8% 1	2440
	21st to end	Day	48% 9% 16% 19% 7% 1	2470
May	1st to 10th	Day	58% 6% 11% 21% 4	4282
	11th to 20th	Day	41% 12% 13% 24% 9%	4693
	21st to end	Day	50% 12% 14% 12% 11% 1	5162
June	1st to 10th	Day	51% 10% 13% 15% 10% 1	2850
	11th to 20th	Day	56% 9% 12% 14% 8% 1	2850
	21st to end	Day	39% 10% 17% 20% 11% 2	2850
July	1st to 10th	Day	30% 8% 14% 24% 18% 5%	4666
	11th to 20th	Day	27% 8% 17% 30% 16% 3	4659
	21st to end	Day	22% 7% 10% 25% 25% 10%	4771
August	1st to 10th	Day	36% 9% 15% 30% 9% 1	4384
	11th to 20th	Day	35% 9% 23% 25% 8% 1	4127
	21st to end	Day	29% 7% 17% 33% 13% 2	4520
September	1st to 10th	Day	34% 6% 15% 25% 16% 4	2337
	11th to 20th	Day	37% 8% 15% 25% 13% 2	2090
	21st to end	Day	32% 9% 15% 27% 14% 3	2090
October	1st to 10th	Day	31% 7% 18% 35% 9% 1	3380
	11th to 20th	Day	29% 7% 23% 24% 13% 4	2883
	21st to end	Day	34% 6% 13% 30% 15% 3	3101
November	1st to 10th	Day	44% 10% 14% 19% 12% 1	1679
	11th to 20th	Day	32% 10% 20% 24% 12% 2	1516
	21st to end	Day	38% 10% 18% 21% 9% 4	1396
December	1st to 10th	Day	36% 11% 17% 19% 13% 4	1330
	11th to 20th	Day	37% 14% 16% 22% 10% 1	1684
	21st to end	Day	31% 9% 11% 24% 18% 7%	2442
January	1st to 10th	Night	39% 15% 15% 20% 9% 2	4726
	11th to 20th	Night	37% 11% 14% 16% 15% 7%	4642
	21st to end	Night	34% 15% 15% 22% 13% 2	4862
February	1st to 10th	Night	39% 12% 13% 19% 13% 4	2660
	11th to 20th	Night	42% 9% 16% 18% 13% 2	2423
	21st to end	Night	41% 9% 11% 21% 14% 3	1892
March	1st to 10th	Night	37% 14% 14% 19% 15% 1	3736
	11th to 20th	Night	28% 10% 21% 25% 16% 1	3557
	21st to end	Night	53% 11% 10% 19% 6% 1	3736
April	1st to 10th	Night	44% 9% 14% 19% 11% 1	1872
	11th to 20th	Night	46% 9% 13% 22% 8% 1	1691
	21st to end	Night	43% 9% 15% 22% 8% 2	1710
May	1st to 10th	Night	52% 8% 11% 23% 6%	2681
	11th to 20th	Night	38% 11% 13% 28% 9% 1	2203
	21st to end	Night	44% 12% 16% 18% 10% 1	2414
June	1st to 10th	Night	44% 8% 16% 22% 9% 1	1330
	11th to 20th	Night	48% 8% 15% 19% 9% 2	1330
	21st to end	Night	29% 10% 20% 25% 13% 2	1330
July	1st to 10th	Night	27% 7% 16% 23% 19% 7%	2185
	11th to 20th	Night	23% 6% 22% 32% 13% 4	2178
	21st to end	Night	20% 5% 10% 30% 23% 11%	2539
August	1st to 10th	Night	33% 7% 16% 28% 14% 2	2521
	11th to 20th	Night	28% 8% 25% 28% 9% 2	2775
	21st to end	Night	25% 6% 22% 31% 14% 2	3146
September	1st to 10th	Night	30% 7% 16% 27% 17% 4	1840
	11th to 20th	Night	34% 6% 16% 27% 13% 4	2090
	21st to end	Night	31% 8% 16% 27% 14% 3	2090
October	1st to 10th	Night	27% 7% 14% 27% 22% 3	3583
	11th to 20th	Night	25% 6% 21% 26% 19% 2	4044
	21st to end	Night	31% 8% 13% 31% 17% 1	4457
November	1st to 10th	Night	40% 10% 15% 21% 12% 2	2600
	11th to 20th	Night	32% 11% 17% 22% 16% 2	2880
	21st to end	Night	35% 10% 18% 21% 12% 4	3000
December	1st to 10th	Night	37% 11% 15% 22% 12% 5%	2850
	11th to 20th	Night	36% 16% 18% 22% 8% 1	3507
	21st to end	Night	33% 11% 13% 22% 14% 7%	5214

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	2 14% 38% 26% 14% 6%	180
	11th to 20th	Day	6% 12% 39% 28% 13% 2	180
	21st to end	Day	4 14% 51% 21% 9% 3	198
February	1st to 10th	Day	3 27% 39% 22% 6% 3	180
	11th to 20th	Day	5% 17% 40% 28% 8% 2	261
	21st to end	Day	5% 21% 31% 33% 9% 1	372
March	1st to 10th	Day	7% 23% 38% 23% 9% 1	460
	11th to 20th	Day	7% 20% 33% 27% 10% 3	460
	21st to end	Day	11% 22% 34% 23% 8% 3	506
April	1st to 10th	Day	13% 21% 35% 24% 7%	460
	11th to 20th	Day	16% 14% 32% 26% 10% 3	452
	21st to end	Day	16% 20% 29% 22% 9% 3	460
May	1st to 10th	Day	21% 13% 27% 22% 13% 4	463
	11th to 20th	Day	20% 10% 23% 25% 17% 4	670
	21st to end	Day	23% 10% 19% 28% 17% 3	734
June	1st to 10th	Day	16% 16% 31% 24% 10% 2	680
	11th to 20th	Day	23% 17% 27% 23% 8% 2	680
	21st to end	Day	13% 13% 27% 28% 16% 4	680
July	1st to 10th	Day	13% 9% 27% 30% 18% 3	671
	11th to 20th	Day	11% 11% 29% 29% 17% 2	668
	21st to end	Day	6% 9% 36% 30% 14% 4	616
August	1st to 10th	Day	13% 11% 28% 33% 10% 4	487
	11th to 20th	Day	11% 11% 34% 28% 12% 4	477
	21st to end	Day	13% 15% 32% 26% 11% 3	539
September	1st to 10th	Day	15% 17% 31% 23% 10% 3	490
	11th to 20th	Day	15% 16% 31% 27% 11% 1	490
	21st to end	Day	16% 24% 32% 19% 6% 2	490
October	1st to 10th	Day	13% 19% 30% 25% 11% 3	432
	11th to 20th	Day	13% 18% 31% 27% 9% 3	300
	21st to end	Day	14% 24% 34% 19% 7% 2	330
November	1st to 10th	Day	12% 22% 41% 16% 7% 2	300
	11th to 20th	Day	14% 21% 39% 20% 5% 2	257
	21st to end	Day	9% 19% 34% 21% 10% 8%	199
December	1st to 10th	Day	5% 14% 48% 23% 8% 2	180
	11th to 20th	Day	6% 21% 37% 28% 8% 1	180
	21st to end	Day	7% 13% 37% 29% 11% 4	198
January	1st to 10th	Night	8% 21% 43% 21% 6% 1	950
	11th to 20th	Night	6% 16% 49% 21% 6% 1	891
	21st to end	Night	7% 21% 42% 23% 6% 1	836
February	1st to 10th	Night	5% 18% 39% 23% 11% 4	760
	11th to 20th	Night	6% 16% 40% 29% 9% 1	744
	21st to end	Night	6% 11% 39% 28% 14% 2	628
March	1st to 10th	Night	4 15% 44% 25% 9% 3	760
	11th to 20th	Night	6% 16% 40% 27% 10% 1	760
	21st to end	Night	6% 13% 34% 32% 11% 3	836
April	1st to 10th	Night	10% 15% 31% 31% 11% 1	732
	11th to 20th	Night	12% 11% 34% 31% 10% 1	563
	21st to end	Night	14% 11% 33% 31% 11% 1	570
May	1st to 10th	Night	16% 11% 25% 31% 15% 2	469
	11th to 20th	Night	16% 6% 25% 32% 19% 3	374
	21st to end	Night	23% 5% 20% 31% 18% 2	411
June	1st to 10th	Night	18% 9% 27% 32% 13% 2	380
	11th to 20th	Night	23% 7% 26% 30% 14%	380
	21st to end	Night	11% 6% 25% 33% 23% 1	380
July	1st to 10th	Night	11% 5% 17% 43% 22% 1	370
	11th to 20th	Night	9% 4 26% 41% 18% 3	368
	21st to end	Night	8% 5% 19% 44% 23% 2	416
August	1st to 10th	Night	13% 2 17% 39% 26% 2	378
	11th to 20th	Night	9% 3 22% 41% 21% 3	526
	21st to end	Night	11% 7% 26% 37% 17% 2	627
September	1st to 10th	Night	14% 6% 25% 32% 18% 5%	700
	11th to 20th	Night	17% 8% 23% 31% 17% 5%	760
	21st to end	Night	13% 11% 35% 27% 9% 4	760
October	1st to 10th	Night	13% 9% 34% 29% 12% 3	760
	11th to 20th	Night	10% 14% 35% 29% 10% 3	760
	21st to end	Night	10% 17% 38% 28% 6% 2	836
November	1st to 10th	Night	11% 17% 45% 19% 7% 1	845
	11th to 20th	Night	9% 23% 44% 19% 3 1	1000
	21st to end	Night	6% 21% 43% 22% 6% 2	1000
December	1st to 10th	Night	5% 19% 42% 23% 9% 2	950
	11th to 20th	Night	6% 17% 45% 25% 6% 1	950
	21st to end	Night	6% 17% 44% 23% 8% 2	1045

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