Deerwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deerwood clear sky chart from 2005-11-06 to 2025-02-25.

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	10% 8% 3 8% 6% 5% 5% 4 6% 8% 35%	112119
	Night	8% 9% 3 9% 6% 5% 5% 4 6% 7% 35%	115290
Transparency	Day	44% 8% 16% 23% 8%	111868
	Night	45% 7% 15% 23% 9% 1	115188
Seeing	Day	13% 11% 32% 28% 12% 3	16563
	Night	13% 10% 34% 31% 11% 1	26695

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	4 13% 6% 13% 7% 8% 8% 6% 7% 8% 21%	3179
	11th to 20th	Day	4 7% 3 13% 8% 8% 8% 10% 12% 11% 16%	3360
	21st to end	Day	5% 10% 4 12% 7% 6% 9% 4 7% 8% 28%	4004
February	1st to 10th	Day	8% 11% 4 11% 8% 6% 5% 5% 8% 10% 24%	1668
	11th to 20th	Day	5% 9% 3 10% 9% 8% 7% 6% 9% 8% 26%	1754
	21st to end	Day	7% 10% 5% 11% 6% 6% 6% 6% 7% 8% 27%	1591
March	1st to 10th	Day	10% 12% 3 9% 7% 6% 5% 4 6% 9% 29%	3145
	11th to 20th	Day	7% 11% 5% 11% 12% 6% 5% 4 6% 8% 25%	3478
	21st to end	Day	8% 12% 5% 14% 8% 4 5% 4 6% 5% 28%	3814
April	1st to 10th	Day	9% 12% 5% 7% 6% 4 5% 4 5% 7% 36%	2321
	11th to 20th	Day	13% 12% 4 9% 6% 5% 5% 4 5% 6% 30%	2442
	21st to end	Day	17% 10% 4 8% 5% 4 4 4 5% 6% 33%	2470
May	1st to 10th	Day	19% 11% 3 7% 4 4 4 3 6% 8% 32%	4120
	11th to 20th	Day	18% 9% 2 7% 5% 4 5% 4 6% 7% 32%	4690
	21st to end	Day	18% 9% 3 6% 5% 5% 4 4 5% 7% 35%	5173
June	1st to 10th	Day	12% 7% 2 6% 6% 5% 6% 4 7% 9% 36%	2850
	11th to 20th	Day	14% 5% 2 7% 5% 5% 5% 5% 7% 8% 36%	2850
	21st to end	Day	12% 6% 2 6% 5% 5% 6% 5% 7% 10% 36%	2850
July	1st to 10th	Day	8% 4 1 5% 5% 6% 6% 5% 8% 10% 41%	4750
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 6% 10% 50%	4750
	21st to end	Day	5% 4 1 5% 4 4 5% 4 7% 9% 51%	4937
August	1st to 10th	Day	10% 5% 2 6% 4 4 5% 5% 6% 8% 45%	4330
	11th to 20th	Day	11% 5% 2 6% 3 4 4 3 6% 9% 47%	4041
	21st to end	Day	10% 5% 2 5% 4 4 4 4 6% 8% 48%	4532
September	1st to 10th	Day	11% 6% 2 5% 4 3 4 3 5% 7% 51%	2329
	11th to 20th	Day	15% 7% 3 6% 5% 3 4 4 4 6% 44%	2090
	21st to end	Day	14% 7% 2 5% 4 4 4 4 6% 8% 42%	2090
October	1st to 10th	Day	10% 6% 2 6% 4 4 4 3 5% 6% 50%	3295
	11th to 20th	Day	9% 9% 3 7% 5% 5% 5% 4 6% 8% 40%	2996
	21st to end	Day	12% 12% 3 8% 4 5% 4 4 6% 8% 33%	3091
November	1st to 10th	Day	15% 13% 4 10% 5% 5% 4 4 5% 7% 29%	1667
	11th to 20th	Day	9% 13% 6% 14% 7% 5% 5% 4 5% 6% 27%	1600
	21st to end	Day	10% 13% 5% 11% 8% 7% 5% 3 6% 7% 26%	1435
December	1st to 10th	Day	9% 11% 6% 14% 10% 10% 7% 5% 6% 6% 17%	2290
	11th to 20th	Day	8% 12% 4 12% 7% 7% 6% 6% 7% 6% 26%	2639
	21st to end	Day	6% 9% 4 13% 8% 7% 6% 5% 6% 6% 32%	3498
January	1st to 10th	Night	4 10% 5% 14% 9% 7% 8% 6% 7% 8% 22%	6787
	11th to 20th	Night	4 10% 5% 12% 8% 7% 8% 8% 9% 9% 20%	6555
	21st to end	Night	6% 13% 6% 14% 7% 6% 6% 4 6% 7% 25%	6974
February	1st to 10th	Night	7% 12% 4 10% 7% 7% 6% 5% 8% 7% 27%	2731
	11th to 20th	Night	5% 8% 3 8% 7% 6% 7% 5% 7% 10% 34%	2533
	21st to end	Night	6% 11% 4 9% 6% 6% 6% 4 7% 8% 33%	1973
March	1st to 10th	Night	8% 11% 4 10% 7% 5% 5% 4 6% 7% 33%	3717
	11th to 20th	Night	5% 10% 4 9% 8% 5% 4 3 6% 8% 39%	3480
	21st to end	Night	7% 10% 5% 14% 7% 6% 4 4 6% 6% 32%	3817
April	1st to 10th	Night	7% 7% 3 7% 6% 5% 5% 4 7% 7% 42%	1857
	11th to 20th	Night	13% 11% 4 9% 5% 4 6% 4 6% 6% 32%	1689
	21st to end	Night	12% 10% 4 6% 6% 4 5% 4 7% 7% 35%	1710
May	1st to 10th	Night	21% 8% 3 5% 4 4 4 4 5% 6% 37%	2850
	11th to 20th	Night	15% 8% 2 7% 4 4 4 4 5% 7% 41%	2211
	21st to end	Night	18% 8% 2 5% 3 3 4 3 4 6% 44%	2414
June	1st to 10th	Night	10% 6% 2 6% 5% 4 5% 3 6% 8% 45%	1330
	11th to 20th	Night	12% 6% 2 7% 4 5% 4 5% 7% 7% 43%	1330
	21st to end	Night	10% 4 2 5% 4 4 5% 4 7% 10% 46%	1330
July	1st to 10th	Night	8% 3 1 4 3 3 4 4 7% 11% 53%	2220
	11th to 20th	Night	6% 3 1 3 3 3 4 3 5% 8% 60%	2220
	21st to end	Night	4 5% 1 4 4 4 5% 4 8% 10% 51%	2625
August	1st to 10th	Night	5% 5% 2 6% 4 4 4 4 6% 8% 51%	2610
	11th to 20th	Night	9% 3 1 6% 4 4 5% 3 6% 10% 50%	2798
	21st to end	Night	9% 4 2 5% 4 4 4 3 5% 7% 53%	3135
September	1st to 10th	Night	9% 5% 2 4 3 3 4 3 5% 8% 55%	1847
	11th to 20th	Night	12% 5% 2 4 3 4 4 4 5% 7% 49%	2090
	21st to end	Night	15% 6% 2 6% 4 4 4 4 5% 6% 44%	2090
October	1st to 10th	Night	10% 6% 2 5% 4 4 4 4 5% 8% 47%	3632
	11th to 20th	Night	9% 9% 2 7% 5% 4 4 4 5% 8% 43%	3927
	21st to end	Night	7% 9% 3 9% 5% 4 5% 4 6% 7% 41%	4467
November	1st to 10th	Night	12% 11% 4 9% 5% 5% 5% 5% 6% 7% 32%	2630
	11th to 20th	Night	10% 15% 5% 11% 6% 5% 6% 4 5% 6% 28%	2800
	21st to end	Night	9% 13% 5% 11% 7% 6% 4 4 6% 6% 29%	2963
December	1st to 10th	Night	7% 11% 4 13% 11% 10% 7% 5% 6% 7% 20%	4900
	11th to 20th	Night	7% 13% 5% 13% 8% 8% 6% 4 6% 7% 23%	5568
	21st to end	Night	7% 9% 3 12% 9% 7% 6% 4 6% 7% 31%	7480

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	56% 7% 13% 18% 5%	3179
	11th to 20th	Day	55% 7% 12% 17% 8%	3382
	21st to end	Day	52% 6% 18% 20% 4	4004
February	1st to 10th	Day	54% 6% 13% 18% 8% 1	1668
	11th to 20th	Day	49% 9% 12% 18% 10%	1763
	21st to end	Day	52% 9% 14% 16% 9%	1591
March	1st to 10th	Day	47% 9% 18% 19% 6%	3145
	11th to 20th	Day	53% 10% 14% 17% 6%	3480
	21st to end	Day	53% 10% 11% 20% 6%	3814
April	1st to 10th	Day	46% 8% 14% 23% 9% 1	2321
	11th to 20th	Day	51% 8% 12% 18% 10% 1	2442
	21st to end	Day	49% 7% 17% 17% 8% 1	2470
May	1st to 10th	Day	47% 8% 15% 21% 9% 1	4120
	11th to 20th	Day	46% 9% 13% 22% 8% 1	4694
	21st to end	Day	47% 8% 13% 23% 9% 1	5173
June	1st to 10th	Day	41% 9% 19% 21% 10% 1	2850
	11th to 20th	Day	42% 10% 17% 21% 10% 1	2850
	21st to end	Day	39% 10% 20% 24% 5% 1	2850
July	1st to 10th	Day	33% 9% 26% 26% 5%	4676
	11th to 20th	Day	28% 8% 21% 36% 8%	4669
	21st to end	Day	27% 7% 25% 32% 9% 1	4781
August	1st to 10th	Day	35% 8% 18% 27% 12%	4314
	11th to 20th	Day	33% 6% 20% 33% 7%	4080
	21st to end	Day	33% 5% 22% 31% 9%	4531
September	1st to 10th	Day	32% 6% 19% 30% 12% 1	2329
	11th to 20th	Day	41% 8% 18% 24% 9% 1	2090
	21st to end	Day	38% 8% 16% 29% 9%	2090
October	1st to 10th	Day	35% 5% 12% 35% 11% 1	3295
	11th to 20th	Day	41% 6% 12% 27% 13%	2996
	21st to end	Day	48% 6% 13% 24% 9%	3091
November	1st to 10th	Day	54% 9% 11% 18% 7% 1	1667
	11th to 20th	Day	57% 6% 16% 14% 6%	1600
	21st to end	Day	57% 8% 14% 16% 5%	1435
December	1st to 10th	Day	63% 8% 14% 11% 4	2290
	11th to 20th	Day	54% 8% 14% 14% 9% 1	2640
	21st to end	Day	50% 6% 11% 21% 11%	3498
January	1st to 10th	Night	56% 8% 13% 17% 6%	6787
	11th to 20th	Night	56% 7% 12% 19% 6%	6595
	21st to end	Night	55% 7% 13% 19% 5%	6974
February	1st to 10th	Night	52% 7% 13% 17% 10% 1	2731
	11th to 20th	Night	42% 9% 15% 22% 12% 1	2534
	21st to end	Night	46% 8% 13% 21% 11% 1	1973
March	1st to 10th	Night	46% 9% 15% 21% 8%	3717
	11th to 20th	Night	38% 10% 16% 24% 12% 1	3480
	21st to end	Night	49% 10% 11% 20% 9% 1	3817
April	1st to 10th	Night	37% 8% 14% 24% 15% 2	1857
	11th to 20th	Night	50% 7% 11% 18% 12% 2	1689
	21st to end	Night	45% 8% 14% 21% 11% 2	1710
May	1st to 10th	Night	45% 7% 13% 25% 9% 1	2850
	11th to 20th	Night	41% 9% 14% 23% 11% 3	2211
	21st to end	Night	38% 8% 14% 28% 11% 1	2414
June	1st to 10th	Night	35% 10% 19% 25% 10% 2	1330
	11th to 20th	Night	36% 8% 17% 25% 12% 2	1330
	21st to end	Night	31% 12% 22% 28% 6% 1	1330
July	1st to 10th	Night	25% 8% 29% 30% 7% 1	2185
	11th to 20th	Night	21% 7% 20% 40% 11% 1	2178
	21st to end	Night	26% 6% 24% 33% 10% 1	2542
August	1st to 10th	Night	28% 6% 18% 32% 14% 1	2602
	11th to 20th	Night	29% 6% 23% 32% 9% 1	2825
	21st to end	Night	30% 5% 19% 34% 11% 1	3135
September	1st to 10th	Night	28% 7% 14% 35% 15% 2	1847
	11th to 20th	Night	32% 7% 20% 27% 13% 1	2090
	21st to end	Night	39% 7% 12% 29% 12% 1	2090
October	1st to 10th	Night	34% 6% 13% 30% 15% 1	3632
	11th to 20th	Night	37% 5% 13% 29% 15% 1	3927
	21st to end	Night	40% 6% 14% 31% 8%	4467
November	1st to 10th	Night	48% 10% 15% 17% 8% 2	2630
	11th to 20th	Night	55% 8% 14% 14% 7% 1	2800
	21st to end	Night	54% 8% 15% 16% 6%	2963
December	1st to 10th	Night	62% 8% 14% 12% 3	4900
	11th to 20th	Night	58% 7% 12% 15% 7%	5566
	21st to end	Night	51% 6% 13% 20% 10% 1	7480

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	8% 12% 35% 33% 11% 1	300
	11th to 20th	Day	12% 10% 42% 27% 9% 1	300
	21st to end	Day	14% 12% 41% 24% 9% 2	330
February	1st to 10th	Day	13% 14% 41% 25% 5% 2	300
	11th to 20th	Day	7% 18% 34% 33% 7% 1	300
	21st to end	Day	7% 8% 46% 30% 7% 1	237
March	1st to 10th	Day	14% 13% 31% 31% 10% 1	270
	11th to 20th	Day	16% 11% 31% 31% 10% 2	270
	21st to end	Day	11% 14% 31% 32% 8% 3	297
April	1st to 10th	Day	13% 16% 35% 26% 10% 1	501
	11th to 20th	Day	18% 13% 33% 25% 11% 1	640
	21st to end	Day	17% 12% 35% 24% 10% 2	650
May	1st to 10th	Day	16% 11% 31% 28% 11% 3	653
	11th to 20th	Day	19% 11% 29% 25% 13% 3	675
	21st to end	Day	19% 10% 24% 29% 15% 3	734
June	1st to 10th	Day	12% 12% 31% 25% 14% 5%	680
	11th to 20th	Day	15% 12% 35% 24% 12% 3	680
	21st to end	Day	13% 8% 28% 33% 15% 3	680
July	1st to 10th	Day	7% 6% 28% 32% 18% 8%	671
	11th to 20th	Day	10% 7% 31% 28% 19% 4	668
	21st to end	Day	4 5% 29% 35% 18% 8%	739
August	1st to 10th	Day	8% 6% 29% 30% 20% 6%	676
	11th to 20th	Day	10% 5% 25% 32% 18% 9%	665
	21st to end	Day	11% 7% 28% 33% 18% 4	748
September	1st to 10th	Day	10% 10% 35% 30% 12% 3	539
	11th to 20th	Day	18% 11% 32% 26% 12% 1	300
	21st to end	Day	22% 11% 30% 27% 9% 1	300
October	1st to 10th	Day	19% 17% 25% 26% 13% 1	300
	11th to 20th	Day	15% 11% 42% 25% 5% 2	300
	21st to end	Day	20% 13% 37% 20% 8% 2	330
November	1st to 10th	Day	22% 13% 29% 27% 9%	300
	11th to 20th	Day	14% 18% 36% 25% 6%	300
	21st to end	Day	15% 17% 40% 24% 5%	300
December	1st to 10th	Day	13% 12% 38% 26% 10% 2	300
	11th to 20th	Day	15% 16% 40% 25% 4 1	300
	21st to end	Day	12% 10% 38% 28% 8% 3	330
January	1st to 10th	Night	11% 13% 35% 30% 10% 1	1000
	11th to 20th	Night	14% 12% 39% 30% 6%	1000
	21st to end	Night	12% 13% 40% 28% 6% 1	1100
February	1st to 10th	Night	13% 12% 36% 31% 8% 1	1000
	11th to 20th	Night	9% 11% 37% 33% 9% 2	979
	21st to end	Night	11% 10% 38% 31% 9% 2	681
March	1st to 10th	Night	14% 11% 33% 28% 12% 2	756
	11th to 20th	Night	8% 11% 41% 27% 11% 2	570
	21st to end	Night	15% 9% 29% 32% 11% 4	627
April	1st to 10th	Night	10% 9% 38% 33% 9% 1	570
	11th to 20th	Night	18% 8% 35% 29% 10%	563
	21st to end	Night	16% 8% 28% 37% 9% 1	570
May	1st to 10th	Night	18% 7% 33% 33% 9% 1	570
	11th to 20th	Night	17% 8% 28% 33% 14%	561
	21st to end	Night	18% 8% 31% 31% 11%	617
June	1st to 10th	Night	11% 8% 29% 38% 12% 1	570
	11th to 20th	Night	15% 6% 33% 31% 15% 1	570
	21st to end	Night	10% 7% 27% 39% 16% 1	570
July	1st to 10th	Night	6% 3 25% 41% 22% 2	555
	11th to 20th	Night	7% 5% 28% 41% 18% 1	552
	21st to end	Night	5% 3 26% 44% 19% 2	624
August	1st to 10th	Night	8% 4 24% 44% 20% 1	567
	11th to 20th	Night	10% 4 24% 38% 20% 4	564
	21st to end	Night	9% 6% 28% 39% 18% 1	627
September	1st to 10th	Night	10% 5% 32% 35% 16% 2	570
	11th to 20th	Night	13% 8% 29% 38% 11% 1	570
	21st to end	Night	18% 7% 34% 29% 12%	570
October	1st to 10th	Night	19% 11% 32% 30% 8%	657
	11th to 20th	Night	19% 11% 34% 28% 8%	845
	21st to end	Night	16% 12% 37% 27% 8% 1	1045
November	1st to 10th	Night	16% 12% 37% 26% 8% 1	975
	11th to 20th	Night	15% 14% 39% 24% 7% 2	1000
	21st to end	Night	15% 16% 39% 23% 5% 1	1000
December	1st to 10th	Night	10% 13% 38% 29% 9% 1	1000
	11th to 20th	Night	15% 13% 38% 27% 7% 1	1000
	21st to end	Night	18% 7% 35% 30% 9% 1	1100

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